17th Caribbean Geological Conference 2005, San Juan PR
Relocation Of Earthquakes Western Puerto Rico Region Using Waveform Cross
Correlation And Double Difference Techniques
Abreu Rafael, Eugenio Asencio and Jay Pulliam
Department of Geology, University of Puerto Rico at Mayagüez;
Stephanie Ross, Andrew Michael and Shirley Baher
USGS Menlo Park, California
The Puerto Rico Region has a significant seismic hazard due to large local,
although relatively infrequent, earthquakes. To properly quantify this hazard we need to
improve our understanding of this seismicity by identifying and understanding specific
fault structures in the region. It is important to determine the location of such faults
because the hypocentral distance affects the amount of on-land shaking, which is a factor
used for earthquake planning by government agencies. Determining fault structure is
important because it helps define fault segmentation, which controls the sizes and
expected repeat times of earthquakes.
In this study, we seek to improve earthquake locations recorded by the Puerto
Rico Seismic Network (PRSN) by using waveform cross-correlation and doubledifference relocation techniques. This project is a collaborative effort between the U.S.
Geological Survey, in Menlo Park, the Department of Geology of the University of
Puerto Rico at Mayagüez and the Puerto Rico Seismic Network. Standard PRSN
locations for the region show a diffuse cloud of seismicity distributed over a broad
region, preventing proper correlation of events to specific active seismogenic sources.
The methods mentioned above have the advantage of simultaneous analysis of large
seismic datasets, significantly improving the accuracy of earthquake locations and
allowing the identification of clusters of earthquakes belonging to specific faults. Our
preliminary results show improved definition of active seismogenic sources in the
western part of the island of Puerto Rico.
Receiver Functions And SKS Splitting Measurements At Three Tectonically
Distinct Locations Around The Caribbean Support The Continental Undertow
Hypothesis
Baez Sanchez Gisela, Rafael Abreu París, Antonio Cameron Gonzales,
Eugenio Asencio, and Jay Pulliam
Red Sísmica de Puerto Rico, Dept. de Geología, Universidad de Puerto Rico,
Mayagüez, PR
The degree to which plate tectonic processes are controlled and/or affected by the
Earth’s mantle is unclear, yet tectonic processes that deform the Earth’s crust and upper
mantle apparently leave seismically-observable signatures in the form of large-scale
anisotropy and some structural features of the crust appear to have analogs in the upper
mantle. To examine remanent deformation we can study shear waves that penetrate the
Earth’s core. These waves (called “SKS phases”) are converted to compressional waves
for their path through the outer core and, when they re-enter the mantle and are converted
back into shear waves, their energy is polarized in the SV plane. If, when recorded at
broadband seismographic stations at the Earth’s surface, rotated into the proper, great-
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circle frame of reference, and examined, these SKS phases have energy polarized in the
SH direction, it means that the waves have encountered an anisotropic material
somewhere along their path from the core to the surface.
We observed such “bi-refringence” or “SKS splitting” on the three broadband stations
around the Caribbean that have been operating the longest: SDV in Venezuela, FDF in
Martinique, and SJG in Puerto Rico. We measured the polarization direction and time
lag indicated by the bi-refringence. SDV completes a transition between station BOCO,
to the southwest, and stations MNVV,HSPV, and ECPV, to the northeast that suggests
bending of the upper mantle deformation around the continental root of South America.
This is similar to the pattern shown—more densely in their case—for SKS splitting
parameters around the continental root of North America by Fouch et al. (2000). The two
oceanic islands have very different signatures. Results for SJG indicate a generally eastwest polarization and are consistent with the results of Russ et al. (1996). The
polarization found for FDF differs dramatically, however—it is approximately northsouth in orientation. Potential interpretations—including possible sources of error—will
be discussed for this result.
“Receiver functions”, formed by deconvolving the vertical seismic trace from the
radial trace to isolate the shear wave reverberations in the crust and upper mantle, allow
us to build an image of sharp boundaries (“layers”) in the Earth. We applied this
technique to stations SDV, FDF, and SJG in order to study the deep structure beneath
these distinct Caribbean locations. A synthesis of the receiver function and SKS
interpretations will be presented in the context of Caribbean seismicity, plate motions,
and other geophysical observables.
Late Cretaceous and early Tertiary Radiolaria from the Pacific coast of Costa Rica
Bandini, A.N. & Baumgartner,
Institute of Geology and Palaeontology, BFSH2, University of Lausanne, 1015 Lausanne,
Switzerland. Alexandre.Bandini@unil.ch, Peter.Baumgartner@unil.ch
We are in the process of a systematic study of late Cretaceous and early Tertiary
radiolarian bearing siliceous mudstones and cherts from the Nicoya and Osa peninsulas.
In these areas a variety of oceanic and arc derived terranes include mafic volcanics and
associated pelagic and hemipelagic rocks rich in biogenic silica which has favoured the
preservation of common moderately to well preserved radiolarians. Late Cretaceous to
early Tertiary palaeoenvironments along the pacific margin were characterised by high
terrestrial nutrient input derived from volcanic sources and active up-welling. High
radiolarian productivity is mostly caused by high nutrients concentration in surface
waters (Yamashita et al., 2002). Radiolarian preservation in the sediment is often
enhanced by the presence of silica-saturated volcanic tuffs and debris.
Currently, we have dated the Berrugate Formation and rocks mapped as Sabana Grande
Formation in the Nicoya Peninsula. The Berrugate Formation is a thick hemipelagicturbiditic sequence containing arc-derived volcanoclastic deposits (Flores et al. 2003). On
the bases of published zonations we can state a Coniancian radiolarian age for the
Berrugate Formation. We have determined the co-occurrence of Dictyomitra koslovae,
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Pseudoaulophacus florensis, Pseudoaulophacus lenticulatus and Theocampe salillum
(species that have not been cited earlier than Coniacian) of with Stichomitra communis (a
species that has not been cited later than Coniacian). The Sabana Grande formation
consists of pelagic, hemipelagic and turbiditic siliceous and calcareous shales and
mudstones (Flores et al. 2003). This formation is currently assumed to be of
Cenomanian-Turonian age on the base of its stratigraphic position below the Nambi and
Piedra Blancas formations that only indicate a pre-Campanian age. However, the
formation itself has not been directly dated. In addition, many isolated outcrops of
Sabana Grande lithologies are not stratigraphically constrained and could therefore have
a different age. Such an outcrop, sampled east of Nicoya, has yielded an early Eocene age
by the occurrence of Phormocyrtis striata striata.
More data will be presented during the conference, since our laboratory work is currently
in progress.
Figure 1
SEM-illustrations of late Cretaceous and early Tertiary radiolarians from the Nicoya
Peninsula, Costa Rica : 1. Dictyomitra koslovae Foreman, 2. Theocampe salillum
Campbell & Clark, 3. Stichomitra communis Squinabol, 4a-b. Pseudoaulophacus
lenticulatus White, 5a-b. Pseudoaulophacus floresensis Pessagno, 6. Phormocyrtis striata
striata Brandt
References
Flores. K., Denyer, P. & Aguilar, T. (2003): Nueva propuesta estratigráfica: Geología de
las hojas Matambú y Talolinga, Guanacaste, Costa Rica.- Rev. Geol. América
Central, 28, 131-138.
Yamashita, H., Takahashi, K. & Fujitani, N. (2002): Zonal and vertical distribution of
radiolarians in the western and central Equatorial Pacific in January 1999. DeepSea Research, II, 49, 2823–2862.
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Water Resources Development In Barbados--- A Geological Perspective.
Barker Leslie H. 2005
Barbados is a small island developing statewhich is the most easterly of the Lessser
Antilles Island Arc. Stratigraphically it is composed of three main rock groups: The
Basals or Scotland formation , a group of deep water turbidites of mid. to upper Eocene
age ; The Oceanic formation, a group of deep water argillaceous deposits of
contemporaneous age with the Scotlands; and a thin cover of Pleistocene to Recent reefal
limestones which cover some six- sevenths of the island.
This stratigraphic sequence together with the Pleistocene to Recent tectonic history of
the island have formed the basis for the mode of occurrence of ground water on the
island. The general lack of surface water is due to the widespread occurrence of
permeable limestone on the island. The ground water occurs in a coastal phreatic aquifer
which stretches almost entirely around the island except in the east where the Scotland
formation outcrops.
With the increasing demand for potable water one of the major problems facing us
todayis the need for optimizing the exploitation of groundwater in the face of increasing
seawater intrusion.
Although engineering science has played a major role in our water resources
development thus far we need a clear understanding of the island’s hydrogeology in
order to achieve this optimization of groundwater exploitation.
Barremian (Lower Cretaceous) Ammonites From Cuba: An Assemblage Rich On
Representatives Of The Family Pulchelliidae
Ricardo Barragán-Manzo1 and Consuelo Díaz-Otero2
1, Departamento de Paleontología, Instituto de Geología, UNAM, México.
2, Instituto de Geología y Paleontología, Vía Blanca y Carretera Central, 11000 La
Habana, Cuba.
Barremian (Lower Cretaceous) ammonites from Cuba are studied for the first time for
systematic and biochronostratigraphic purposes. The fossils under study come from
previous and recent sampling from different Barremian stratigraphic exposures within the
Las Villas Province. A rich stratigraphic-controlled assemblage of taxa belonging to the
Family Pulchelliidae conforms the focus of the studied material, allowing new
discussions on the geographical distribution of this taxon within the Tethyan Realm.
Preliminary results suggest that the ammonite association is predominated by
representatives of the Subfamilies Pulchelliinae and Psilotissotiinae. The data herein
discussed represent the first detailed systematic reports of these taxa in the Caribbean,
widening their paleobiogeographic significance and allowing for precise long distance
correlations of standard Barremian ammonite zonations between Cuba and other areas of
the world.
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Remnants Of Pacific Ocean Foor : Jurassic-Lower Cretaceous Radiolarites In
Central America And The Caribbean
Baumgartner, P.O.(1), Bandini, A.N.(1) & Denyer, P.(2) (1)Institut de Géologie et
Paléontologie, BFSH2, Université de Lausanne, 1015 Lausanne Switzerland.
Peter.Baumgartner@igp.unil.ch; (2)Escuela Centroamericana de Geología, Universidad
de Costa Rica. P.O. Box 214-2060 UCR, San José Costa Rica.
Pdenyer@geologia.ucr.ac.cr
Mesozoic ribbon-bedded radiolarites are widespread in Tethyan and circumpacific
orogenic belts, but they are unknown from the Atlantic, Gulf of Mexico and the
Venezuelan Mesozoic passive margin. Mesozoic radiolarites formed in detritally starved,
oceanic areas beneath moderate to high surface productivity. The Jurassic-Early
Cretaceous Central Atlantic – Paleo-Caribbean ocean basins formed a mediterranean sea
of generally low surface productivity, resulting in clay-rich and/or calcareous pelagic
facies throughout. However, ribbon-bedded radiolarites occur in various
tectonostratigraphic within the Modern Caribbean Plate. In the Nicoya Complex (NWCosta Rica), the Siuna Oceanic Complex (NE-Nicaragua), Tambor Group (Montagua,
Guatemala), Duarte Complex (Hispaniola), Mariquita Chert (Puerto Rico) and in the
Phare Unit (Désirade). These radiolarites are associated with mafic/ultramafic igneous
rocks of diverse petrogenetic origin: Association with MORB is the exception, more
often radiolarites are incorporated as exotic blocks in: Cretaceous plateaus (Nicoya
Complex), or subduction-related mélanges (Santa Elena, N Costa Rica, Puerto Rico). On
La Désirade, radiolarites are interbedded with pillow basalts of a back-arc setting.
Occurrencs of Nicaragua, Honduras and Guatemala are currently under study.
Faunal characteristics of radiolarian assemblages have been interpreted in terms of
paleo-latitude of formation. However, paleobiogeography of Tertiary to Recent
radiolarians shows that higher latitude radiolarian assemblages are very similar to
upwelling assemblages that occur throughout the tropical ream along the American
Pacific Margin. Several Caribbean radiolarian assemblages studied from La Désirade
closely resemble coeval faunas from the Califonian Coast Range Ophiolite, formed along
this margin. We consequently interpret Mesozoic radiolarites associated with the
Caribbean Plate, as remnants of Pacific ocean floor, some of which formed in arc-related
settings. Radiolarian faunas do not allow for paleo-latitudinal interpretation, but suggest
paleo-longitudinal displacement from the Eastern Pacific/Western American Margin into
their present position in Central America and the Eastern Caribbean. This interpretation
supports an allochthonous, Pacific origin of the Modern Caribbean Plate.
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Late Oligocene Caribbean Assemblages Of Larger Foraminifera Calibrated By
87Sr/86Sr (Nicoya, Costa Rica And Carriacou, Lesser Antilles)
Claudia Baumgartner-Mora (1), Pascal Tschudin (1), and Peter O. Baumgartner (1)
(1) Instuitut de Géologie et Paléontologie, BFSH2, Université de Lausanne, 1015
Lausanne Switzerland. Claudia.Baumgartner@igp.unil.ch
Upper Oligocene shallow water formations unconformably overlie PaleoceneEocene deepwater sediments in outcrops between Punta Peladas and Nosara River
(Nicoya Peninsula, Costa Rica). The bioclastic limestones of these outcrops yielded rich
assemblages of Larger Foraminifera that we studied in oriented sections, SEM for split
material and polished rock thin sections for transmitted light and cathodoluminescence
(CL). CL observation was essential for taxonomic determination of miogypsinids. CL
observation also revealed planktonic Foraminifera associated with the shallow water
material confirming the open marine environment indicated by the sedimentology. We
determined: Heterostegina antillea Cushman, Miogypsina tani Drooger, Miogypsina
gunteri Cole, Miogypsina cf. (Miolepidocyclina) panamensis (Cushman), Miogypsina sp.,
Miogypsinoides bermudezi (Drooger),Miogypsinoides cf. bantamensis (Tan Sin Hok),
Lepidocyclina (Nephrolepidina) vaughani Cushman, Lepidocyclina yurnagurensis
Cushman, Lepidocyclina undosa Cushman.
At Windward, Carriacou (Lesser Antilles) scattered outcrops of the Belvedere
Formation contain calciturbidites rich in Larger Foraminifera associated with a lower
upper Oligocene (NP24) nannofossil assemblage. Planktonic Foraminifera recovered
south of Windward in rocks slightly downsection indicate an upper middle Oligocene
age. Larger Foraminifer species collected from a coastal outcrop just north of Windward
include Lepidocyclina undosa Cushman and Miogypsina gunteri Cole.
The 87Sr/86Sr ratio was measured in 11 specimens of megalosphaeric
Lepidocyclina spp. Mechanically extracted from 2 rock samples collected at Punta
Peladas (Costa Rica). 87Sr/86Sr ratios range from 0.709088 to 0.708196. which
corresponds to a model age of 27.4 to 24.94 Ma. Very similar 87Sr/86Sr ratios, ranging
from 0.708150 to 0.708167 were obtained from 2 specimens extracted from a sample
collected in a coastal outcrop just N of Windward Village (Carriacou, Lesser Antilles).
All measured 87Sr/86Sr ratios fall within a Chattian (Late Oligocene) age.
The biochronologic range of the larger foraminifera listed above is currently
controversial, and has to be considered as poorly known. French authors have restricted
the range Miogypsina gunteri to the lower Aquitanian and Miogypsina. tani to the upper
Aquitanian. Nannofossils, planktonic foraminifera and identical 87Sr/86Sr ratios form
Punta Peladas and Windward clearly indicate a Chattian (upper Oligocene) occurrence of
Miogypsina gunteri and Miogypsina tani and confirm this age range for the other Larger
Foraminifera cited above.
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Puerto Rico Digital Earth-Science Data and the
US Geological Survey Mineral Resource Assessment Methodology
By: Walter J. Bawiec
United States Geological Survey
954 National Center
Reston, Virginia 20192
A mineral resource assessment of the Commonwealth of Puerto Rico was conducted
by the U.S. Geological Survey, the Puerto Rico Department of Natural Resources, and
the University of Puerto Rico (Bawiec, 2001). The purpose of this mineral resource
assessment is to provide an inventory of the known mineral occurrences, to give an
estimate of the potential for undiscovered mineral resources, and to provide a multipurpose earth-science database. The earth-science data presented in this report will assist
in long-range planning for environmental, health, and mineral-resource concerns in the
Commonwealth of Puerto Rico and will provide a clearer understanding of the mineral
potential of the island.
The mineral resource assessment of Puerto Rico represents a compilation of several
decades of mineral investigations and studies. The data used in the assessment are in a
digital format and may be used in geographic information systems (GIS). The data includes
maps of geology (and derivative maps), geophysics (Bouguer gravity, aeromagnetics),
geochemistry (stream sediments), mines and mineral occurrences, and tracts permissive for
various mineral deposit types. Although much of this information existed and was
published prior to the assessment, this is the first time it has appeared in a single
comprehensive publication.
The compiled earth-science data served as input into the three-part assessment method for
estimating undiscovered non-fuel mineral deposits. This assessment includes the
following steps:
1. Delineating areas permissive for undiscovered mineral resources according to the
types of deposits permitted by the geology;
2. Estimating the number of undiscovered deposits of each type for each delineated
area;
3. Estimating the amount of resources contained in the undiscovered deposits by
using appropriate grade and tonnage models for each deposit type.
Reference:
Bawiec, Walter J., 2001, ed., Geology, Geochemistry, Geophysics, Mineral Occurrences,
and Mineral Resource Assessment for the Commonwealth of Puerto Rico, USGS OpenFile Report 98-38, 1 CD-ROM.
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Structural Development of the Columbus Basin, offshore S.E. Trinidad
bpTT Exploration, Port of Spain, Trinidad and Tobago
The Columbus Basin, offshore S.E. Trinidad, marks the eastern extent of the Eastern
Venezuelan foreland Basin, bounded to the north by the transpressional Darien Ridge,
and southwards by the progressive onlap of the palaeo-Orinoco derived Plio – Pleistocene
depositional fill onto the Cretaceous and Early Palaeogene age passive margin of the
Venezuelan Plataforma Deltana. On a regional scale the basin is located along the
transpressional plate margin between the South American and Caribbean plates, and lies
west of the southern extension of the Barbados accretionary prism.
Essentially the basin is a modified foreland basin superimposed over the frontal, partly
detached, structures of a Late Miocene to Early Pliocene transpressional foldbelt. The
basin was subsequently re-inverted in Pleistocene times with the southern buttress to the
contraction marked by the onlap edge of deepwater Palaeogene through Early Miocene
age mudstones onto the relict passive margin. The extent of these facies has played a
critical role in the evolution of the internal geometry of the basin with the major PlioPleistocene aged structures regionally detached from the north dipping Cretaceous
passive margin succession.
Internally, there are two obvious structural elements that characterise the Columbus Basin
in Trinidad waters: NNE dipping regional growth faults and NE-SW trending inversion
anticlines. The superimposition of these trends provides the majority of the structural
containers that provide the petroleum traps. However, the major extension in the
Columbus Basin has occurred along NW-SE trending counter regional faults that were
initiated by the rapid loading of the palaeo-Orinoco sediments and the consequent
seaward excavation of the underlying over-pressured and mobile deepwater mudstones.
The extension systematically shifted from counter regional faults, and was
accommodated progressively eastwards on regional listric ‘growth’ fault sets.
3D Visualisation of the Columbus Basin, Offshore S.E. Trinidad
bpTT Exploration, Port of Spain, Trinidad and Tobago
The Columbus Basin, offshore S.E. Trinidad is an areally rich petroleum province (12-15
bcf/km2), bounded to the north by the transpressional Darien Ridge, and southwards by
the progressive onlap of the Plio – Pleistocene depositional fill onto the Venezuelan
foreland. The structural geometry in Trinidad waters is dominated by WSW-dipping
counter-regional, and NNE-SSW oriented regional faults, and internally is characterised
by stacked deltaic and shelfal sandstone reservoirs in extensional fault roll-overs.
Historically, the interpretation of the basin had been on a piecemeal basis, with a local
stratigraphic scheme for each of the fault blocks, covered by small-area 3D seismic
volumes. Through the merging of fifteen 3D seismic surveys, bpTT has constructed a
“mega-merge” volume, which for the first time has allowed a confident stratigraphic
correlation throughout the basin, calibrated by an extensive well dataset collected over
the forty-year exploration history of the basin.
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17th Caribbean Geological Conference 2005, San Juan PR
More than sixty regional surfaces have been mapped from the seismic volume to date.
Using GeoProbe software, the interpretation of these surfaces can be actively viewed in
3D together with well paths, proven reservoir segments, fault surfaces, attribute
extractions and pressure surfaces, overlain on the regional seismic cube. The visualisation
permits the identification of structural traps, the distribution of potential reservoir facies
and locally direct hydrocarbon detection. Collectively, the integration of all these data
allows a 3-dimensional understanding of the basin and its development through time.
Plio-Pleistocene Depositional fill of the Columbus Basin – Gross Depositional
Environment mapping.
bpTT Exploration, Port of Spain, Trinidad and Tobago
During Late Pliocene through Pleistocene times, the palaeo-Orinoco River, confined
within the Venezuelan and Central Trinidadian foreland basin, incised into the
continental shelf, where it formed a braided-river complex that transported sediment to a
series of shelf-edge deltas. During the progradation phase, river systems dumped large
amounts of sand and silt onto the delta front to form a “delta platform”. From the shelf
edge there was an abrupt transition into the slope and basin environment. During episodes
of low accommodation space creation, sand was conveyed past the shelf edge onto the
slope by channels, chutes, slumps and debris flows. Where the delta was building at a
rapid rate the depositional geometries were modified by sediment collapse scars, growth
faulting, turbidite channels and shelf edge canyons.
This description is derived from high resolution regional seismic imaging below the
present day shelf margin of the Columbus Basin and Plataforma Deltana which provides
new understandings of the interaction of active tectonics, fluvial process, and the
accommodation space fluctuations that influence deltaic and shelfal architecture. 3D
seismic attributes remarkably portray the most recent (16,000 - 12,000yr) shelf edge
deltaic system which is seen as a prograding sigmoid oblique clinoform bundle that
represents the most significant period of sediment accumulation. The package highlights
the syn-depositional tectonic influence on the deltaic architecture in terms of local
accommodation space creation.
The depositional model has been used as an analogue for the deeper depositional
sequences of the basin, which contain the bulk of the gas resource. This stratigraphy has
been divided into a series of sequence sets that relate to regional accommodation space
development, and a detailed Gross Depositional Environment (GDE) interpretation has
been made for 39 of the 97 sequences within these sequence sets. Regional seismic
surface mapping, seismic attributes and seismic facies calibrated to well data show the
progressive infilling of the Columbus Basin by Palaeo-Orinoco shelf edge deltas. GDE
maps are drawn at the time of the maximum extent of each delta to show the greatest
extent of sand that would be encountered in the reservoir sections. The maps provide an
easily understandable view of the deltaic geologic setting, helping us to constrain the
distribution of different reservoir facies and provide the basis for defining prospective
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17th Caribbean Geological Conference 2005, San Juan PR
play fairways. GDE’s also show the geographic distribution of key deltaic facies belts
with time, which include the active delta plain, delta front, shelf, and slope.
Common Risk Segment Mapping - focusing the exploration effort in the Columbus
Basin, Offshore S.E. Trinidad.
bpTT Exploration, Port of Spain, Trinidad and Tobago
Common Risk Segment (CRS) mapping is the key tool that allows the mapping of
relative risk on the individual petroleum play elements across an entire sedimentary
basin. Combining these elements to form a Composite CRS allows the description of play
risk on a regional scale and focuses the exploration effort to areas of lowest common risk.
Play Fairway risk is simply depicted using a traffic light scheme, where green indicates
areas of low risk, yellow moderate risk and red high risk.
The Columbus Basin, offshore S.E. Trinidad, is a prolific petroleum province, with
multiple reservoir targets. The stratigraphic interpretation of the basin has divided the
Plio-Pleistocene basin fill into Sequence Sets, and for each of these a Composite CRS
analysis has been made. The primary inputs to the analyses, the Gross Depositional
Environment (GDE) maps, are used to identify low risk areas for both reservoir and seal
presence. Reservoir quality distribution is determined from depth versus porosity plots
and depth structure maps. Petroleum systems analysis provides information to generate
individual CRS maps that describe seal effectiveness, source presence and potential, and
petroleum charge access. Biogenic charge CRS maps are created using temperature
versus depth plots. The maps are produced using Arc Gis software, which makes them
easy to update and edit when new data are acquired.
The Composite CRS interpretation provides an objective, map-based understanding of
the distribution of petroleum in the Columbus Basin, and is a powerful tool for inventory
ranking, portfolio analysis and as a framework for yet to find analysis. Identifying areas
that have low play risk determines where exploration dollars should be spent to access
and test the most attractive opportunities in the basin.
From Regional to the Shotpoint. Chachalaca Discovery, Columbus Basin,
Offshore S.E. Trinidad
bpTT Exploration, Port of Spain, Trinidad and Tobago
After an intense eighteen month study of the Columbus Basin, offshore SE Trinidad, the
exploration unit of bpTT, resumed operations in an untested region within bpTT’s eastern
acreage. On 13th December, 2004, the Chachalaca well was drilled as a deviated hole to a
total depth of 15633ft below rotary table, at a location about 52 miles east south east off
Trinidad’s east coast, in 335 feet of water. The well was plugged and abandoned as a Gas
Discovery well which resulted in the booking of a total resource of about 2 trillion cubic
feet (tcf).
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The Chachalaca well was drilled to evaluate the exploration potential of three target
reservoirs of Pleistocene age within two depositional sequence sets. These reservoirs
were predicted from regional and detailed Gross Depositional Environment (GDE)
mapping, and Common Risk Segment interpretation that identified the areas of the basin
with the lowest geological risk.
The reservoir sequences at Chachalaca are supported by a NE-SW oriented inversion
geometry, orthogonal to the NE-SW regional faults, and on trend with another earlier
field discovery, Corallita/Lantana. The well successfully tested these reservoirs, which
were vertically stacked within five thousand feet, but laterally separated by different fault
blocks. The oldest and most significant reservoir lies in the rollover to an early counterregional fault, and confirmed the depositional model developed in the regional
interpretation.
The success in defining this prospect was based on a thorough regional understanding of
the basin focusing the effort and spend to areas of lowest risk. This understanding was
based on detailed work on all aspects of the petroleum system: structural setting,
stratigraphy, facies distributions and petroleum migration and timing. Integration has
been the backbone of Chachalaca’s success. Similar work for future exploration, can
provide similar results.
Stratigraphy of the Cretaceous Succession in the Benbow Inlier, Jamaica
Ian C. Brown and Simon F. Mitchell
Department of Geography and Geology, University of the West Indies, Mona Campus,
Kingston 7, Jamaica.
A minimum 9-km-thick succession of lavas, volcaniclastic sediments, shales and
limestones is developed in the Benbow Inlier of central east Jamaica. This Lower
Cretaceous succession is amongst the most complete within the Caribbean, with a
minimum of seven limestones (several newly recognised), interbedded with volcanics
and clastics) containing diagnostic rudist-foraminifer faunas indicating the following
ages: Hauterivian; Late Barremian, early Aptian?; early Albian; late Albian; and possibly
early Cenomanian. The uppermost part of the succession has yielded a Turonian
nannofloral assemblage. Tholeiitic lavas in the lower part of the section are regarded as
part of the tholeiitic island arc suite, whereas the overlying Albian to Turonian rocks have
a calc-alkaline island arc suite. A new geologic map and the lithostratigraphy of the rocks
exposed in this inlier will be presented and the age-diagnostic faunas reviewed.
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Earthquake Monitoring In Panama
Eduardo Camacho
Instituto de Geociencias
Universidad de Panama
Panama, Panama
ecamacho@cableonda.net
The first seismic instrument in the Western Hemisphere was installed in Panama City,
Panama by The French Canal Company in early 1882. This instrument recorded the
great tsunamigenic earthquake (M8.0) of September 7, 1882, with epicenter offshore the
northeast Caribbean coast of the Isthmus.
BALBOA HEIGHTS PANAMA (BHP). Since 1909 the Panama Canal Company
installed two sets of Bosch Omori seismographs at Balboa Heights Panama (BHP). In
1932 these instruments were replaced by two Wood Anderson seismographs and in 1934
the first accelerograph outside the continental USA was installed at BHP. All these
instruments were replaced in 1962 by short period and long period instruments of the
WWSSN. BHP operated uninterruptedly until 1977.
UNIVERSITY OF PANAMA NETWORK (UPA). In 1983 the University of Panama
received the WWSSN instruments that had operated at BHP before and installed them
with the help of the USGS at the Panama City Campus.
Nowadays the UPA has 5 one component short period telemetric analog stations.
Additionally, there are one digital accelerograph and 3 three component short period
digital stations linked via INTERNET. The analog records of the telemetric stations are
digitized at the UPA observatory, at Panama City and the records from the three digital
stations are digitized on site.
In cooperation with the Geophysical Institute of the University of Mexico (UNAM), a
STS-2 broad band sensor has been installed at the UPA observatory at Panama City
CHIRINIET.
In western Panama operates a private network which consists of 6 digital short period
three component stations, deployed in that part of the country. The data transmission of
this network is via INTERNET and the records are digitized on site..
PANAMA CANAL AUTHORITY NETWORK
The Panama Canal Authority (ACP) operates since the beginning of 2005 a network of 3
short period 3 component digital stations and 4 digital accelerographs. This network is
deployed around the Panama canal Basin.
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17th Caribbean Geological Conference 2005, San Juan PR
All seismic networks in Panama: UPA, CHIRINET and ACPN exchange data and
cooperate very closely, through institutional agreements, to improve the seismic
monitoring of the country.
Development Of Rapid Moment Tensor Seismic Inversion Procedures For
Incorporation Into The Emergent Puerto Rico-Virgin Islands Tsunami Warning
System
Antonio Cameron González1, Eugenio Asencio1, Víctor Huérfano1, Carlos Mendoza2
(1) Puerto Rico Seismic Network, Dept. of Geology, University of Puerto Rico
Mayaguez (2) Centro de Geociencias de la UNAM, Campus Juriquilla, Quéretaro,
Mexico
We present a preliminary result of moment tensor inversion procedures for regional
events within the Caribbean Region. Our ultimate goal is to incorporate these procedures
into the emergent Puerto Rico-Virgin Islands Tsunami Warning System (PRVITWS).
Using three-component digital broadband waveforms that were recorded by the Puerto
Rico Seismic Network (PRSN) for events between December 2004 and March 2005 we
estimate the source mechanism for 2 earthquakes with moment-magnitudes (Mw) higher
that 4.0 near the highly oblique oceanic subduction-strike-slip transition area along the
North America-Caribbean plate boundary.
Regional tectonic setting of the Caribbean showing
the epicenters of 2 regional events examined for this
study (red stars), and layout of seismic stations
operated by the PRSN.
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17th Caribbean Geological Conference 2005, San Juan PR
The procedures use the reflection-matrix method of Kennett (1983) to identify source
parameters that best reproduce the regional waveforms. The method used by Randall et
al. (1995) for regional event inversions was applied, with source depth fixed at 10 km.
The synthetic Green’s functions were estimate using a general Caribbean crustal velocity
model (Mann and Burke, 1984). A Butterworth passband filter with corners at 20 sec and
50 sec was applied to synthetic and observed data. The inversion scheme provides rapid
estimation of source parameters such as earthquake size (Mw) and fault geometry
(Mendoza and Huérfano, 2004), which are critical to the identification of possible
tsunamigenic events in the Caribbean region.
Geoprico-Do Project: A new marine geophysical study at northeastern Caribbean
Plate Boundary Zone (Dominican Republic-Puerto Rico-Islas Vírgenes).
A. Carbó and GEOPRICO-DO Working Group [ A. Carbó (1), D. Córdoba (2), J.M.
Dávila (3), P. Herranz (4), A. Muñoz (1), A. Pazos (2), M. Catalán (2), M. Gómez (4), C.
Von Hilldebrandt (6), U. Ten Brink (5), J. Payero (7), S. Dabreo (9), J.L. Granja (1) ,P.
Llanes (1), J. Álvarez (1), L.M. Agudo (1), M. Druet (1)
(1) Departamento de Geodinámica, Universidad Complutense de Madrid, Spain, (2)
Departamento de Geofísica, Universidad Complutense de Madrid, Spain, (3) Real
Observatorio de la Armada en San Fernando (Cádiz), Spain, (4) Instituto Español de
Oceanografía, Madrid, Spain, (5) U.S. Geological Survey, (6) Puerto Rico Seismic
Network, (7) Universidad Autónoma de Santo Domingo-Instituto Sismológico
Universitario, Dominican Republic, (8) Instituto Nacional de Recursos Hidráulicos,
Dominican Republic, (9) Department of Disaster Management,B.V.I.]
The Northeastern Caribbean Plate Boundary Zone presents an area of complex and very
active tectonics, where different processes interaction have been proposed: strain
partitioning (Calais et al, 2002), microplates (Mann et al, 1995), oblique subduction to
strike-slip transitions (Dolan & Mann, 1998; Dillon et al, 1994), opposing subducted
slabs (Deng and Sykes, 1995), crust arching (Van Gestel et al, 1998), tear fault (ten Brink
et al, in press), block rotation (Mason and Scanlon, 1991) among other. All these
processes produce a high seismic activity due tectonic deformation. The proof of this
activity is the constant record of events in the seismic networks and the historical seismic
record (Mona Passage, 1943, Ms = 7.6 offshore Northeastern Hispaniola, 1946 Ms = 8.1
Dolan et al, 1997). Moreover, these earthquakes can unleash submarine landslides, which
could be triggered by earthquakes, could be generated in the region because of the steep
slopes offshore (ten Brink, 2004). Recent GPS's studies have contributed to clarify the
kinematics of the zone (Calais et al, 2002).
The Northeastern Caribbean Boundary Zone (Hispaniola and Puerto Rico zone) has been
widely studied from 50's, but most studies have focused on northern Hispaniola and
Puerto Rico islands (e.g. Puerto Rico Trench, Bahamas Bank, Mona Rift, (Mann et al,
1995; Dolan et al, 1998; ten Brink et al, 2004)), very few studies have been carried out to
the south, resulting in a lack of information. During April, 2005 a marine geophysics
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17th Caribbean Geological Conference 2005, San Juan PR
cruise aboard the Spanish Oceanographic Research Vessel “Hespérides” was carried out
in this area of the Northeastern Caribbean Plate. In the project GEOPRICO-DO, which
are coordinated by Univesidad Complutense de Madrid (Geodynamics Department,
Geophysics Department, Spain) and Real Obsevatorio de la Armada de San Fernando
(Spain), also participate the Instituto Español de Oceanografía (Spain), Universidad de
Barcelona (Spain), U.S. Geological Service/Woods Hole Oceanographic Institution
(USGS/WHOI), Puerto Rico Seismic Network (University of Puerto Rico, Mayaguez),
Universidad Autónoma de Santo Domingo-Instituto Sismológico Universitario, Red
Sísmica del Instituto Dominicano de Recursos Hidráulicos and the Department of
Disaster Management (Virgin Islands). The data acquired in the cruise were; multibeam
bathymetry, potential fields (gravity and magnetism), multichanel reflection seismic,
deep seismic sounding with record on stations onland and streamer and OBS`s. The OBS
will remain at seabed recording seismicity for a continuous period of 6 months.
We present here the data acquired during the recently finished survey and some
preliminary results: geomagnetic anomaly maps, gravimetric (Bouguer) anomaly maps,
one brut stacked of seismic section and one section interpreted and acquired with a high
resolution topographic parametric seismic system (TOPAS), in the northeastern Puerto
Rico Trench and to the south of the Hispaniola and of Puerto Rico islands (Muertos
Trench). Besides, with the integration of all data we have elaborated a preliminary crustal
model for the plates boundaries in the Muertos Trench region.
Evaluation of Instability of Unsaturated Soil Slopes during Heavy Rainfall
By Migdalia Carrión1, Ana María Hagan2, Hebenly Celis3, and Miguel Pando4*
Rainfall-induced slope instabilities and landslides are common in Puerto Rico (PR). The
island has an area of 9103 square kilometers, about 70 to 80 percent of which is hilly or
mountainous. The presence of steep slopes in the mountainous terrain, coupled with
weathered soils and intense rainfall, lead to severe slope-stability problems throughout
the island. Natural hazards such as hurricanes further exacerbate these problems. All
physiographic provinces of the island have experienced landslides.
This poster presents an overview of the slope stability problem in PR with particular
emphasis on the problem of instability of unsaturated residual soil slopes during wet
periods. This type of slope failure is a recurring problem in PR. Infiltration during
rainfall decreases insitu soil suctions, resulting in decrease in shear strength due to the
loss of insitu suction, and ultimately slope failure. This triggering mechanism is
investigated with particular reference to recent slope failures in the Mayaguez area.
1
Undergraduate student, Department of Civil Engineering, University of Puerto Rico at
Mayaguez,
P.O. Box 9041, Mayaguez, PR, 00681-9041
2
Visiting undergraduate student, Department of Civil Engineering, University of Rhode
Island
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17th Caribbean Geological Conference 2005, San Juan PR
3
Graduate student, Department of Civil Engineering, University of Puerto Rico at
Mayaguez,
P.O. Box 9041, Mayaguez, PR, 00681-9041
4
Assistant Professor, Department of Civil Engineering, University of Puerto Rico at
Mayaguez,
P.O. Box 9041, Mayaguez, PR, 00681-9041. E-mail: mpando@uprm.edu
*: Corresponding author.
The Geometry Of The Basement In NW Colombia: Implications
In The Evolution Of The Colombia Basin.
John Ceron and R. Hernández
Empresa Colombiana de Petróleos, Bogotá, Colombia
Potential fields data, MBES and numerous seismic profiles, have contributed to the
mapping of the basement in the NW corner of South America. The type of crust
underlying the sedimentary accretionary prism has relevance on the exploration for
hydrocarbons in the region. The geometry of the prism is revealed by MBES which, in
turn, exposes new questions to the understanding of the evolution of the Colombia basin,
such like the meaning of the La Aguja submarine Canyon and the geometry of the
conjunction (?) of the Santa Marta and Oca faults Strain partitioning at the Caribbean –
NW South America collision zone have not been clearly explained, and the amount of
displacement required for present plate slip rates requires considerable movement along
strike-slip faults that has not been demonstrated by displacements of known faults. The
Romeral Fault Zone plays the role of a paleo-suture but it might also represent a zone of
strike slip displacement that will help explain present slip vectors in the SW Caribbean
plate. With this Poster we seek to create the scenario for discussion on the implications
of all these geometrical and geophysical considerations to the understanding of the
evolution of the Colombia basin, the postulation of Caribbean plate evolutionary models
and the clarification of the geological risk in the assessment of hydrocarbon plays.
BOLIVAR: A Cross-Section of the Caribbean-South American Plate Boundary at 64W
S.A. Clark, A. Levander, M.B. Magnani, D.S. Sawyer and the BOLIVAR Working Group
Department of Earth Science, Rice University, Houston, TX, USA
BOLIVAR, the Broadband Ocean-Land Investigation of Venezuela and the Antilles arc
Region, is an NSF and Venezuelan funded, collaborative seismic experiment in the
southeast Caribbean region. The purpose of the BOLIVAR project is to understand the
diffuse plate boundary formed by the oblique collision between the Caribbean and South
American plates (see Levander, this meeting). Profile 64W of the BOLIVAR experiment,
a 415 km-long, N-S transect onshore and offshore Venezuela approximately located at 64
deg W longitude, images the deep crustal structures formed by this process early in its
development, ~15 My after the Antilles arc collided with the continent at this longitude.
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17th Caribbean Geological Conference 2005, San Juan PR
The active source components of profile 64W include 275 km of MCS data, 33
coincident OBSs, and 344 land seismic stations which recorded 7500 offshore airgun
shots and 2 explosive land shots. A passive source experiment, consisting of 17
broadband seismometers in the vicinity of the profile, complements the active source
data.
We hypothesize that 64W transects a north-dipping, remnant subduction zone (VanDecar
et al., 2003) underlying the Serrania del Interior and Maturin Basin, formed at 16 Ma by
collision of the Caribbean forearc overriding South American crust. Backthrusting of this
subduction inverted and closed the Grenada Basin. This initial subduction gradually
choked on continental crust, causing a polarity reversal and jump to the north. Subduction
could not evolve in the Grenada Basin backthrust because it choked on the Aves
Ridge/La Blanquilla High. Instead, down-to-the-south subduction initiated further to the
north, where Caribbean oceanic crust of the Venezuela Basin began to subduct beneath
the Aves Ridge/La Blanquilla High in the Pliocene (~4 Ma) and appears to continue
today. Between the remnant subduction zone and the modern/nascent one, the El Pilar
and Coche strike-slip faults accommodate most of the transform motion of the plate
boundary. From the remnant subduction zone to the modern one, ~350 km of orogenic
float comprises the diffuse plate boundary.
Honduran seismic stations: Necessity of enhancing seismic monitoring in the
Caribbean Region of Central America
Gonzalo Cruz Calderón (gocruzc@yahoo.es)
(Universidad Nacional Autónoma de Honduras
Departamento de Física, Sección de Geofísica)
The Honduras status of the seismic observations is presented toward the future plans of
strengthens such a network. In this contest, we also review the limitations of regional
monitoring capabilities along some of the northern Central American coasts due to the
uneven distribution of several systems or the absence of stations in other areas which do
not allow the adequate observation of significant seismic events for hazard evaluation
purposes. Most of the Central American networks are concentrated along the pacific
coast, even though seismic events have also affected the northern and western regions.
This fact is especially crucial in the Gulf of Honduras (Honduras – Guatemala tectonic
environment), where some important seismic events have taken place in historical and
instrumental periods. For example, data from 1505 through 2000, show that about 60-70
seismic events grater than M = 4.5 have occurred in the Caribbean region shared by
Honduras and other countries, and some of them have generated tsunamis that have
affected cities and towns along the coast. Also, on July 11 of 1999 an earthquake (M=
6.4) occurred in the Honduras Gulf region and was felt strongly creating panic in Puerto
Cortes, San Pedro Sula (Honduras), Puerto Barrios in Guatemala and other regions of
northern and western Central America
In view of the worldwide awareness, we believe that it is of much importance for the
whole Caribbean Region to start building a broad regional and integral seismic hazard
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program for tsunami warning. Such an effort would require the enhancement of the
seismic monitoring of significant seismicity along the Caribbean region of Central
American counties. For Honduras, it would be crucially important to be part of such a
regional network. After reviewing the geological, seismological and strategic aspects for
our participation in such an effort, we suggest that the site of Puerto Cortes (the main port
facility of the country) would be the appropriate place for installing a seismic station.
Development of the Mid-Holocene Cañada Honda fossil reef, Dominican Republic:
Preliminary results and implications to modern trends of reef degradation in high
sedimentation environments
Cuevas-Miranda, David*, Ramírez, Wilson**, Sherman, Clark*, Hubbard, Dennis***
*Department of Marine Sciences, University of Puerto Rico at Mayagüez,
**Department of Geology, University of Puerto Rico at Mayaguez
*** Department of Geology, Oberlin College, Oberlin, OH 44074
Many modern coral reefs are in decline, in many areas related to high sedimentation rates
and sediment resuspension. However, there is evidence in the fossil record of reefs
developed in high sedimentation environments, such as the Cañada Honda outcrop in the
Dominican Republic, with a record of accretion spanning over a thousand years. The
Holocene coral reefs of the Enriquillo Valley, Dominican Republic provide a unique
record of coral development in an environment that seems to have been exposed to high
sediment input. They exhibit excellent preservation and offer an exceptional opportunity
to examine in detail the internal coral assemblage and sedimentary patterns of a Holocene
coral reef. In particular, the Cañada Honda outcrop reveals several sediment layers that
appear to represent single depositional events such as storms, probably with elevated
rainfall as is typical of the region today. These layers are rich in coral, bivalve and
gastropod fragments and can be traced several meters within the outcrop, where a
paleoreef surface can be followed. Coral and sediment samples were collected below and
above these sedimentary horizons for the purpose of dating and documenting any changes
in the coral-species assemblage, growth rate, siltation stress and carbon isotopes before
and after their deposition. Additional coral and sediment samples were collected
throughout the entire outcrop to observe similar changes through time. Quantitative
measurements of coral importance, diversity and sediment were obtained throughout the
whole stratigraphic section using quadrats along vertical transects. In addition, sediments
incorporated in coral skeleton and from the reef matrix are being examined to quantify
the input and variations in terrigenous sedimentation through the section. The information
obtained from this study will be instrumental to better understand modern reefs since
direct comparisons of this fossil reef with modern counterparts (with high sedimentation
in a restricted environment) will be possible.
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17th Caribbean Geological Conference 2005, San Juan PR
Nicoya Complex (Costa Rica) – a Cretaceous Plateau containing Middle Jurassic to
Cretaceous radiolarite blocks
Denyer, P.(2) & Baumgartner, P.O.(1) (1)Institut de Géologie et Paléontologie, BFSH2,
Université de Lausanne, 1015 Lausanne Switzerland. Peter.Baumgartner@igp.unil.ch;
(2)
Escuela Centroamericana de Geología, Universidad de Costa Rica. P.O. Box 214-2060
UCR, San José Costa Rica. Pdenyer@geologia.ucr.ac.cr
We re-examined igneous and sedimentary rocks and radiolarian biochronology in the
NW-Nicoya Peninsula, where the Nicoya Complex s.st. was originally defined. The
geologic data mapping, and the new Ar/Ar-dates and igneous isotope geochemistry done
by other authors, do not confirm either one of the current hypotheses on the
tectonostratigraphy of the area. Neither alpine-type nappe structures, nor a threefold
magmatostratigraphy, in which an oceanic basement and its Jurassic-Cretacecous
sediment cover would be overlain by Upper Cretaceous plateau basalts. Herein, we reassess field relationships between igneous rocks and radiolarites, and document refined.
We now interpret the Nicoya Complex s. str. as a fragment of a Cretaceous plateau
created by uplift and southward tilting during an early Campanian collisional event. The
deepest levels of the Plateau are exposed in NW-Nicoya, where over 50 % of the igneous
rocks are intrusives (gabbros and plagiogranites) that have a single mantle plume source,
common with the basalts. Ar/Ar-dates range from Valanginian to Campanian.
Radiolarian-dated, Bajocian (Middle Jurassic) to Albian (middle Cretaceous), Mn-rich
radiolarites, are set as stratigraphically incoherent blocks in a “matrix” of multiple basalt
flows, subsequent intrusions and cross-cutting dykes and sills. Chilled margins of
magmatites, and hydrothermal baking and leaching of the sediments confirm the Ar/Ardating of igneous rocks being consistently younger than most of the radiolarian cherts.
No Jurassic oceanic basement has been identified so far at the outcrop level in the Nicoya
Peninsula, but it could be buried beneath the surface. The Jurassic-Cretaceous chert
sediment pile became disrupted and detached from its original basement by multiple
intrusions during the formation of the Plateau. Radiolarian-dated, Coniacian - Santonian
(Late Cretaceous) thin, Fe-rich radiolarites are largely synchronous and associated with
late phases of the Plateau.
Tectonic control of the Barbados accretionary prism on the Orinoco turbidite
system (Southeastern Caribbean)
Deville Eric, Callec Yannick, Desaubliaux Guy, Mascle Alain,
Institut Français du Pétrole, 1-4, av. de Bois-Préau, 92 506 Rueil-Malmaison,
France
e-mail:eric.deville@ifp.fr
Huyghe-Mugnier Pascale,
Maison des Geosciences, BP 53, Université de Grenoble, 38041 Grenoble, France
Recent marine acquisitions (multibeam, seismic and 3.5 kHz profiles, piston cores)
provide a better understanding of the whole interference area between the Barbados
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17th Caribbean Geological Conference 2005, San Juan PR
accretionary prism and the Orinoco turbidite system. It appears that due to its location in
an active margin, the Orinoco turbidite system is not a passive deep delta. The
depositional system is morphologically and tectonically controlled by the compressional
structures of the Barbados prism, and as a consequence the system does not exhibit
classic fan geometry. The hinge between the slope of the front of the Barbados prism and
the slope of the Guyana margin induces the convergence of the turbidite channels in the
abyssal plain, at the front of the prism. Above the prism, upward the system is multisource with several distributaries, whereas downward the channel courses are more
complex with frequent convergences or divergences that are emphasized by the effects of
the undulating seafloor morphologies. Indeed, tectonics, shale diapirism, and mud
volcanism force the topography of the substratum generating local highs and confined
piggyback basins that control the courses of the channels. Erosion processes are mostly
absent in the upper part of the turbidite system. Erosion develops in the deep-water area
between 2000 and 4000 m above the compressional structures of the Barbados prism.
Incisions show irregular meandering and sinuous courses in the low relieve segments and
less sinuous courses where channels cut the structures. Larger canyons are 3 km wide and
300 m deep. The occurrence of different phases of successive incisions is responsible for
the development of similar terraces in both flanks of the canyons. This is probably the
consequence of two superimposed mechanisms: the tectonic activity of the deformation
front characterized by progressive uplift and thrusting of recent sediments, and the
superimposition of the fluctuations of Orinoco turbidite system activity.
Isotopic Correlation Between The Cotui Formation Exposures In The Cerro Buena
Vista Area And On Road Pr100,
Southwestern Puerto Rico
Viviana Díaz¹, Alvin Bonilla and Hernan Santos
Department of Geology, University of Puerto Rico, Mayagüez, PR
This work is based on the comparison of the isotopic signatures of two stratigraphic
sections: the Cotui Limestone in the Cerro Buena Vista area and from road PR100, Km
11.9, Cabo Rojo. The work is part of an investigation that aims to resolve recent debates
on whether the limestone exposed on PR100 is a depositional event between the older
Cotui Limestone and the younger Guaniquilla Formation; or part of the Cotui Limestone.
Samples were collected from both outcrops. After XRD analysis, the samples were
analyzed for C¹²/C¹³ ratios on a Stable Isotope Ratio Mass Spectrometer (GASI LabDepartment of Geology, UPRM). C¹²/C¹³ ratios were plotted against height in
stratigraphy. After comparison no match was found between the two graphs, however,
the PR 100 isotopic profile did match with a part of the Cotui Limestone profile. This
match suggests that the PR100 limestone correlates with part of the middle Cotui
Limestone.
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Cuaba Gneiss, Dominican Republic: An ultra high pressure metamorphic terrane
in the northern Caribbean
Grenville Draper, Department of Earth Sciences, Florida International University, Miami,
FL 33199, USA
Richard .N. Abbott, Department of Geology, Appalachian State Univ., Boone, NC 28608,
USA
Shantanu Keshav, Geophysical Laboratiry, Carnegie Institution of Washington,
Washington DC 20015, USA
The Cuaba Gneiss is narrow belt of mafic gneisses and minor schists that occurs as one
the of the units of the subduction- Rio San Juan Complex related in the northern
Dominican Republic. The gneisses consists of banded eclogite that have been
retrograded to amphibolite grade. The banding is near vertical and trends N-S, across the
major trend of the outcrop. kinematic indicators suggest that the gneisses underwent
consitent dextral shearing at eclogite conditions. Meter-scale bodies of garnet peridotite
and garnet pyroxenite occur as pods in the gneisses. Some blocks have been found that
contain coexisting garnet-clinopyroxene-spinel and corundum assemblages and magmatic
cumulate textures. Mineralogic phase relations indicate that such a magmatic assemblage
had to have formed at greater than 3.6Gpa and 15500C, that is to say at UHP (greater than
2.7 Gpa) conditions. We interpret these rocks as having formed in the hangingwall of the
Late Cretaceous, SW-dipping Greater Antillean (GA) subduction zone at depths of
greater than ~110km. They then became entrained in the downgoing, eclogitized
oceanic crust represented by the Cuaba Gneiss. This means that the Cuaba Gneiss itself
must have descended to these depths ans hould therefore be viewed as a UHP terrane.
The exhumation of the Cuaba terrane is problematic as it would not have had the
buoyancy of continental crust9the usual host for UHP rocks) and so buoancy cannot be
invoked as the exhumation mexchanism.
Revisión sobre los recursos minerales metálicos del Distrito de Bayaguana, al Este
de la República Dominicana
Por Julio E. Espaillat L.
Corporación Minera Dominicana, S.A.
El Distrito mineralizado de Bayaguana, se encuentra en la parte oriental de la isla de la
Hispaniola, aproximadamente 60 km. Al Noreste de la ciudad de Santo Domingo.
Las mineralizaciones descubiertas en la zona, consisten de diseminaciones y vetas
hidrotermales de pirita y sulfuros de cobre con enriquecimiento local de oro y plata. Estas
están contenidas en rocas volcánicas e intrusivas bi-modales basálticas y dacíticas con
pequeñas proporciones de sedimentos clásticos y carbonosos de la denominada
Formación Los Ranchos de edad Cretácica Inferior.
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17th Caribbean Geological Conference 2005, San Juan PR
Las mineralizaciones estudiadas están relacionadas con grandes zonas de alteración
hidrotermal que se extienden por mas de 50 kilómetros cuadrados de afloramientos
dentro de un edificio volcánico, claramente definido por mapeo geológico y visible en los
estudios de magnetometría aerotransportadas realizados en 1996 sobre la República
Dominicana.
Métodos convencionales de prospección minera fueron inicialmente usados para definir
las mineralizaciones del área incluyendo: mapeos geológicos, levantamientos
geoquímicos, geofísicos y excavación de trincheras.
Mediante sondeos diamantados, la Corporación Minera Dominicana, S.A., ha establecido
tres prospectos con inventarios minerales:
(1) El prospecto de Cerro Kiosko, consistente en una estructura tabular silicificada de
mas de 1.1 Km de longitud a lo largo de su rumbo, contenida en rocas máficas
alteradas. Esta mineralización se considera como una veta telescópica epitermal de
cuarzo con pequeñas cantidades de caolinita, rutilo y muscovita, conteniendo un
ensamblaje mineral de pirita, calcopirita, energita y bornita en formas diseminadas y
en vetillas (stockwork) enriquecidas con oro y plata. El inventario calculado es de
4,920,000 toneladas métricas de mineral con leyes de 2.0 gr./t Au, 5.06 gr./t Ag. y
1.0% Cu.
(2) Las mineralizaciones porfiríticas de cobre diseminado de Cerro Managuá,
consistentes en un manto o blanket de enriquecimiento supergénico de unos 100
metros de espesor y que se extiende dentro de una zona fuertemente silicificada de
rocas volcánicas máficas intruidas por dacitas porfiríticas consanguíneas. El
inventario mineral calculado en la zona de enriquecimiento secundario y donde
predomina la calcocita y la covelita es de unas 45 millones de toneladas métricas con
0.45% Cu y 0.22 gr./t Au. Esta zona apárece superpuesta a minealizaciones
hipogénicas de baja ley conteniendo pirita, calcopirita y trazas de molibdenita.
(3) Mineralizaciones de Ceja del Coco, consistente en una amplia zona de alteración
hidrotermal asociada a domos porfiríticos de cuarzo y feldespatos, fuertemente
silicificados y argilitizados, conteniendo diseminaciones y vetillas (stringers) de
pirita, calcopirita y bornita, parcialmente reemplazados por cantidades menores de
calcocita y covelita. El inventario mineral calculado preliminarmente mediante
sondeos es de 7.0 millones de toneladas métricas con 0.5% Cu.
Otros prospectos dentro del Distrito Bayaguana que han sido ensayados mediante
sondeos diamantados, han retornado valores anómalos y elevados de metales bases y
preciosos.
Para la ejecución de los programas de exploración se ha cumplido con todos los
requisitos ambientales establecidos en las normas y leyes ambientales de la República
Dominicana.
Review of the exploration for metallic mineral resources within the Bayaguana
District in the eastern Dominican Republic.
The mineralized district of Bayaguana is located in the eastern part of Hispaniola,
approximately 60 km. northeast of the city of Santo Domingo.
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17th Caribbean Geological Conference 2005, San Juan PR
Occurrences of mineralization discovered in the district consist of hydrothermal
disseminations and stringers of sulphides, dominated by pyrite, chalcopyrite and bornite,
and locally enriched with gold and silver. The mineralization is hosted by bi-modal
volcanic and intrusive rocks of basaltic and dacitic composition, with a minor proportion
of clastic and carbonaceous sediments of the Lower Cretaceous Los Ranchos Formation.
The known mineralization is related to a volcanic center that is clearly defined by
geological mapping and is visible on the 1996 magnetic airborne survey of the
Dominican Republic. Large hydrothermal alterations zone of over 50 square kilometers
envelopes the mineral occurrences.
Conventional exploration tools were used, including geological mapping, geochemical
and geophysical surveys and trenching initially to detect these prospects.
Throuh drilling, Corporación Minera Dominicana, S.A., has established three prospects
as follows:
(1) Cerro Kiosko prospect, in which a silicified, tabular mineralized structure has been
traced for 1.1 km, along strike, and is hosted by altered mafic volcanics. The mineral
assemblage observed in the epithermal telescopic quartz vein consists of
dissemination and stringers of pyrite, chalcopyrite, enargite and bornite, enriched
with gold and silver with an inventory of 4,920,000 metric tons @ 2.0 g/t Au, 5.06
g/t Ag and 1.0% Cu.
(2) Porphyritic disseminated copper mineralization of Cerro Managua. It consists of a
supergene blanket of approximately 100 meters thick that overlies a strongly silicified
zone of mafic volcanic rocks intruded by consanguineous porphyritic dacites. The
mineral inventory of the secondary enriched zone is 45.0 million metric tons @
0.45% Cu and 0.22 g/t Au.
(3) Ceja del Coco mineralization, consists of a broad zone of hydrothermal alteration
associated with porphyritic quartz and feldspar dacite and rhyolite domes, that are
strongly silicified and argillitized. The domes are mineralized with dissemination and
stringers (stockworks) of pyrite, chalcopyrite and minor amount of chalcocite and
covellite. The preliminary mineral inventory calculated by drilling is 7.0 million of
metric tons @ 0.5% Cu.
Other prospects within the District tested by drilling returned elevated and anomalous
base and precious metals values.
For the execution of the exploration programs, all environmental procedures and
requirements established in the Dominican environmental norms and laws were followed.
(English Version)
Review of the exploration for metallic mineral resources within the Bayaguana
District in the eastern Dominican Republic.
The mineralized district of Bayaguana is located in the eastern part of Hispaniola,
approximately 60 km. northeast of the city of Santo Domingo.
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Occurrences of mineralization discovered in the district consist of hydrothermal
disseminations and stringers of sulphides, dominated by pyrite, chalcopyrite and bornite,
and locally enriched with gold and silver. The mineralization is hosted by bi-modal
volcanic and intrusive rocks of basaltic and dacitic composition, with a minor proportion
of clastic and carbonaceous sediments of the Lower Cretaceous Los Ranchos Formation.
The known mineralization is related to a volcanic center that is clearly defined by
geological mapping and is visible on the 1996 magnetic airborne survey of the
Dominican Republic. Large hydrothermal alterations zone of over 50 square kilometers
envelopes the mineral occurrences.
Conventional exploration tools were used, including geological mapping, geochemical
and geophysical surveys and trenching initially to detect these prospects.
Throuh drilling, Corporación Minera Dominicana, S.A., has established three prospects
as follows:
(4) Cerro Kiosko prospect, in which a silicified, tabular mineralized structure has been
traced for 1.1 km, along strike, and is hosted by altered mafic volcanics. The mineral
assemblage observed in the epithermal telescopic quartz vein consists of
dissemination and stringers of pyrite, chalcopyrite, enargite and bornite, enriched
with gold and silver with an inventory of 4,920,000 metric tons @ 2.0 g/t Au, 5.06
g/t Ag and 1.0% Cu.
(5) Porphyritic disseminated copper mineralization of Cerro Managua. It consists of a
supergene blanket of approximately 100 meters thick that overlies a strongly silicified
zone of mafic volcanic rocks intruded by consanguineous porphyritic dacites. The
mineral inventory of the secondary enriched zone is 45.0 million metric tons @
0.45% Cu and 0.22 g/t Au.
(6) Ceja del Coco mineralization, consists of a broad zone of hydrothermal alteration
associated with porphyritic quartz and feldspar dacite and rhyolite domes, that are
strongly silicified and argillitized. The domes are mineralized with dissemination and
stringers (stockworks) of pyrite, chalcopyrite and minor amount of chalcocite and
covellite. The preliminary mineral inventory calculated by drilling is 7.0 million of
metric tons @ 0.5% Cu.
Other prospects within the District tested by drilling returned elevated and anomalous
base and precious metals values.
For the execution of the exploration programs, all environmental procedures and
requirements established in the Dominican environmental norms and laws were followed.
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17th Caribbean Geological Conference 2005, San Juan PR
Pre-Campanian Terranes in Nicoya area (Costa Rica, Middle America)
Kennet Flores (1), Peter O. Baumgartner (1), Percy Denyer (2), Alexandre Bandini (1),
and Claudia Baumgartner-Mora (1)
(1) Instuitut de Géologie et Paléontologie, BFSH2, Université de Lausanne, 1015
Lausanne Switzerland. Kennet.FloresReyes@igp.unil.ch
(2) Escuela Centroamericana de Geología, Universidad de Costa Rica. P.O. Box 2142060 UCR, San José Costa Rica. Pdenyer@geologia.ucr.ac.cr
Field mapping, isotopic and palaeontologic dating in Nicoya reveals coeval preCampanian, middle to late Cretaceous magmatic/sedimentary sequences of different
geodynamic paleoenvironments.
1- The Nicoya Complex is a pile of plateau basalts and intrusives of Berriasian to
Campanian igneous ages, including Middle Jurassic to Santonian radiolarites.
2- The Matambu Terrane comprises a basaltic basement of unknown origin and age,
overlain by late Albian bituminous, siliceous shales (Loma Chumico Formation). This
formation is thermally affected by younger basaltic flows and intrusives of the Nicoya
(plateau) Complex. The Loma Chumico Formation is overlain by pelagic,
hemipelagic/turbiditic siliceous and calcareous shales and mudstones of the Sabana
Grande Formation (estimated as Cenomanian to Coniancian in age). Upsection, the
Nambi Formation is characterized by volcaniclastic turbidities derived from the Nicoya
Complex. 87Sr/86Sr isotopic analysis of Inoceramus gave a value of 0.70738, interpreted
as a Coniacian age. The top of Nambi is marked by the presence of reworked Campanian
shallow water bioclasts, announcing the transition to the overlap sediments.
3- The Manzanillo Terrane is floored by a basaltic basement intruded by the
Tortugual Komatiitic suite of Turonian (89 ma) age. Upsection, a thick hemipelagicturbiditic sequence containing arc-derived volcaniclastic deposits is defined as Berrugate
Formation, dated by radiolarian biochronology as Coniancian/Campanian.
The Manzanillo Terrane documents pre-Campanian evolved arc volcanism that
resulted from active subduction of ocean floor once located between the exotic Nicoya
Complex (1) /Matambu Terrane (2), and the Manzanillo Terrane (3). The Manzanillo
Terrane could represent a fore-arc area at the foot of the western edge of the future
Caribbean Plate. Subduction stopped when (1) and (2) reached the trench and collided
with the Caribbean Plate during the Campanian.
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Subduction events in Cuba
Antonio García-Casco(1), Rafael Torres-Roldán(1), Guillermo Millán(2), Manuel IturraldeVinent(4), Kenya Nuñez Cambra(2), Concepción Lázaro Calisalvo(1), Antonio Rodríguez
Vega(4)
(1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva
s/n, 18002 Granada, Spain.
(2) Instituto de Geología y Paleontología, Via Blanca y Carretera Central, La Habana,
Cuba.
(3) Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas, La Habana
10100, Cuba.
(4) Instituto Superior Minero-Metalúrgico, Departamento de Geología, Las Coloradas de
Moa, Holguín, Cuba.
The diversity of P-T paths, ages, and tectonic settings of formation of high-pressure
complexes of oceanic material in Cuba documents a protracted history of subduction at
the northern margin of the Caribbean Plate during the Mesozoic that is analyzed within
the framework of available geological data and plate-tectonic models. In Western and
Central Cuba, HP blocks within serpentinite-mélanges separated ca. 800 km along strike
of the belt document cold (i.e., mature) subduction of oceanic lithosphere at pre-Aptian
times and mélange formation and uplift at the Aptian-Albian. The P-T evolutions are
clockwise, with subtle changes in P-T during the prograde sections of the paths and
relatively hot geothermal gradient during exhumation (i.e., “Alpine-type”) incompatible
with steady-state subduction. Petrological arguments favor an intra-oceanic collision
setting at the Aptian-Albian that caused arrest of subduction. Either a Pacific or a ProtoCaribbean subduction system can explain the formation of these rocks at the midCretaceous. In Eastern Cuba, HP blocks within serpentinite mélanges document hot
subduction of oceanic lithosphere, with partial melting of amphibolites and formation of
trondhjemitic melts at ca. 750 ºC 15-18 kbar followed by cooling at high pressure (i.e.,
counterclockwise P-T paths). This petrologic evolution makes the correlation of Eastern
and West-Central Cuban mélanges doubtful. Indeed, available data support formation of
hot-subduction complexes at the Aptian-Albian upon the onset of a new subduction
system that evolved to normal (cold) subduction during the Upper Cretaceous. A SWdipping Proto-Caribbean subduction system can be proposed, though geological and
structural data indicate a complex arrangement of subduction systems in Eastern Cuba
during the Upper Cretaceous. Finally, HP ophiolitic material tectonically juxtaposed
within subducted platform metasediments of the Escambray complex (Central Cuba)
decompressed at relatively cold geothermal gradients (“Franciscan-type” P-T paths),
suggesting syn-subduction exhumation at the uppermost Cretaceous (ca. 70 Ma).
Geological, petrological and structural data suggests subduction of the Proto-Caribbean.
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17th Caribbean Geological Conference 2005, San Juan PR
Upper Cretaceous Stratigraphy Of The Oriental Cordillera (Dominican Republic)
Jesús García Senz1, Jacques Monthel2, Alberto Díaz de Neira3, Pedro Pablo HernáizHuerta4, Andrés Pérez Estaún5
1
Dept. de Geodinàmica i Geofísica, Universitat de Barcelona (formerly Inypsa Group)
2
Bureau de Rechereches Geologiques et Minières, BRGM, France
3
Geoprin, Spain (formerly Inypsa Group)
4
Iniciativas y Proyectos S.A, Inypsa, Spain
5
Consejo Superior de Investigaciones Científicas, CSIC, Spain
Extensive mapping in the Oriental Cordillera allows to define the stratigraphy of a 6 kmthick upper Cretaceous sequence, deposited in a fore-arc basin at the northern margin of
the Caribbean plate.
Las Guayabas Fm (Cenomanian-upper Coniacian) consists of well stratified lithicfeldespatolithic sandstones with volcanic grains and lesser amounts of metamorphic and
sedimentary grains, radiolaria and planktonic foraminifera, interpreted as deep-water
epiclastites and tuffs derived from a volcanic arc source. The lower part of the formation
includes debris-flow conglomerates of ultrabasic rocks (El Cujano Mb, Lower Coniacian)
possibly eroded from the accretionary prism located to the north, and a basaltic-andesitic
lava horizon (Loma La Vega Mb) with geochemical affinities to magmas generated above
the subduction zone. The upper part of Las Guayabas Fm intercalates gravely sandstones
(Hato Mayor Mb), interpreted as concentrated turbidites. Capping the succession, the
Arroyo La Yabana Mb (upper Coniacian-Santonian), is a key level made of centimetric
beds of radiolarites interbedded with silt, indicative of the temporal cease of volcanism.
The overlying Las Auyamas Mb (Campanian-Maastrichtian) consists of thin beds of
volcanic lithic sandstones and silt, interbedded with biomicrites. They grade in lateral and
in vertical to calcareous turbidites (Río Chavón Fm) with sporadic volcanic gravel and
clasts of shallow-water biota derived from the destruction of a southern carbonate
platform. These resedimented deposits are gradually replaced by hemipelagic biomicrites
and marls, ending the cretaceous sequence by red calcarenites with ondulated
stratification and cross-bedding (Loma de Anglada Fm, Maastrichtian), volcanic-lithic
sandstones and rudist biostromes, deposited on a serpentinite seamount. The correlative
deposits to the north are calcareous turbidites.
The overall sedimentary trend is a reduction of the volume of detritics of volcanic origin
and the increase of detritics from a sedimentary source, coeval with the filling of the forearc basin.
This contribution is a result of the SYSMIN Program (2002-2004) financed by the
European Union.
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The Structure Of The Oriental Cordillera Of The Dominican Republic
Jesús García Senz1, Jacques Monthel2, Alberto Díaz de Neira3, Pedro Pablo HernáizHuerta4 & Andrés Pérez Estaún5
1
Dept. de Geodinàmica i Geofísica, Universitat de Barcelona (formerly Inypsa Group)
2
Bureau de Rechereches Geologiques et Minières, BRGM, France
3
Geoprin, Spain (formerly Inypsa Group)
4
Iniciativas y Proyectos S.A, Inypsa, Spain
5
Consejo Superior de Investigaciones Científicas, CSIC, Spain
The Oriental Cordillera extends 135 km adjacent to the south coast of the Samaná
peninsula, exposing little-metamorphosed rocks of the Lower Cretaceous island-arc and
the Late Cretaceous fore-arc basin. Regional maps clearly shows a big domal structure
plunging to the east, with their north limb cut by the Samaná strike-slip fault. Map-scale
folds with upright axial surfaces outcrop along the southern limb of the dome, eroded by
the Paleocene conglomerates. They are refolded by NW-SE folds, giving a Type 1
interference pattern, which is best developed on the east-plunging end of the dome.
The most important structure in this area is the NW_SE Yabón fault, pierced by
serpentinite intrusions. Other prominent features are pop-up structures that made up the
highs of the sierra, right-stepping conical folds with the apex pointing to the NW, and
WNW-ESE Riedel shears cutting previous and contemporaneous folds as half-anticlines
and half-synclines. The region of maximum shortening is located between the villages of
Miches and Las Lisas, as deduced by extensive cleavage development. The cleavage
disappears following the fold axis to the SE, a fact previously interpreted as the evidence
of two terranes, El Seibo and El Oro, with different deformational grade. The
arrangement of structures described in the Oriental Cordillera indicate contraction and
uplift simultaneous with wrench along sinistral E-W and NW-SE strike-slip faults,
characteristic of transpressional tectonics. Transpression is an active process today
forcing the retreat of the sea and the doming of the Plio-pleistocene reef 400 m above sea
level.
This contribution is a result of the SYSMIN Program (2002-2004) financed by the
European Union.
Preliminary Description Of A Bed Containing Glass Spherules In The Bejucalito
Section (Oriental Cordillera, Dominican Republic). A New Possible K/T Boundary
Layer
Jesús García Senz1 & José Pedro Calvo2
1
Dept. de Geodinàmica i Geofísica, Universitat de Barcelona
2
Instituto Geológico y Minero de España, IGME
A spherule layer in the Bejucalito section, 20 km southeast of the El Seibo village
(Oriental Cordillera, UTM: 051220, 206535) possibly represents impact glass from the
Chicxulub crater and a new K/T boundary site. The Bejucalito section contains shallowwater deposits spanning the Maastrichtian to Eocene, deposited non-conformable on a
serpentinite seamount in the upper Cretaceous fore-arc basin.
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The Maastrichtian Loma de Anglada Fm on top of the serpentinite, consists of about 100
m of red sandstones with nodular stratification enhanced by iron oxides, quartz grains,
volcanic minerals, coral fragments, bivalves, echinoids, gastropoda and Sulcoperculina
sp. A Maastrichtian age has recently been stablished in the close río Mana section based
on rudist bivalves (Pons, García Senz and Bernárdez, this Conference). The top of Loma
de Anglada Fm is an erosional surface filled by an up to 2 m-thick breccia with reworked
centimetric clasts of serpentinite and sandstone in a red matrix. The absence of age
diagnostic fossils in this breccia has prevented age determination of the erosional event
capping the maastrichtian platform. Above lies the Paleocene-Eocene Bejucal reefal
limestone, starting with a 2 m-thick polymict microbreccia with reworked rock inclusions
of glass spherules, serpentinite, corallinae algae, bivalves and echinoids. Glass spherules,
ranging 0.2 – 6.8 mm in size, are loosely distributed in limestone showing a packstonegrainstone fabric.
At the time of redaction of this abstract, the microprobe analysis of the glass is in
progress, but based on the age of the section and their position close to the Chicxulub
crater, we tentatively interpret the spherules level as a K/T boundary ejecta deposit.
This contribution is a result of the SYSMIN Program (2002-2004) financed by the
European Union.
Validation Of Remote Sensors For Benthic Habitat Studies
In Southwestern Puerto Rico
Fernando Gilbes and Jeanette Arce
Geological and Environmental Remote Sensing Laboratory
Department of Geology
University of Puerto Rico at Mayaguez
Different remote sensing techniques were employed to study benthic habitats in La
Parguera, Puerto Rico. These include the comparison of two sensors with different spatial
and spectral resolution, IKONOS (1 m, 4 bands) and Hyperion (30 m, 220 bands). Image
processing of IKONOS included atmospheric, sun glint, water column corrections, and
supervised classifications for the characterization of sea grass, sand and coral. Hyperion
data analyses included destriping, atmospheric correction, sun glint correction and
classifications. Field data collection was performed by the establishment of three
transects with ten quadrants for each habitat class. The benthic composition from
transects were compared with those generated by the image classifications. Field
validation shows the potential of the techniques used, but demonstrates that these
processing methods require improvement. Preliminary analyses show that the most
appropriate remote sensing technique for benthic habitat classification is merging the data
of these two sensors.
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Spectral Characterization Of Sandy Beaches In Western Puerto Rico
Fernando Gilbes and Gretchen Chiqués
Geological and Environmental Remote Sensing Laboratory
Department of Geology
University of Puerto Rico at Mayaguez
Remote sensing applications to beach system in Puerto Rico have been limited by low
spatial resolution of the available images and lack of appropriate equipment for field
validation. A GER-1500 spectroradiometer was used to collect reflectance measurements
with a spectral range from 350 to 1050 nanometers in 15 sandy beaches in western Puerto
Rico. Samples of the beaches were analyzed in the laboratory to determine the
composition. Results indicate a change in magnitude in the reflectance curve compared
with the composition. Higher magnitude correlated with more carbonate material
concentration in the sand and lower magnitude correlated with higher concentration of
dark mineral. The reflectance shows a change in the curve between 450 to 550 nanometer
that is present in all 15 beaches. The spectral slope in that range was calculated and
related to the composition. The results of the field reflectance measurements were
compared to a high resolution (1m) of IKONOS satellite image. Using band math these
images show a correlation between the field measurement and the satellite image. A
methodology to obtain information about composition in sand beaches using remote
sensing was developed. For the first time a spectral library of beach sand sediment for
western Puerto Rico was created.
Carbonate Diagenesis from Evaporated Seawater
Goldstein1, Robert H. and Csoma1,2, Anita, E., 1University of Kansas, Department of
Geology, 1475 Jayhawk Blvd., Lawrence, Kansas 66045; 2Current Address,
ConocoPhillips Company, Upstream Technology, Integrated Geological Analyses, 600
N. Dairy Ashford, PR 3064, Houston, TX 77079-1175.
Many of the Plio-Pleistocene diagenetic phases, that previously have been
interpreted as forming from low-temperature seawater, precipitate, at least in part, from
evaporated seawater. These phases include Mg-calcite, calcite, and dolomite from the
Clino core of the western Bahamas, Hope Gate Formation of Jamaica, and Eocene
section of Enewetak Atoll. Each of these examples contains diagenetic phases which
have been interpreted as forming in water of normal marine salinity on the basis of
petrographic relationships and stable isotopic compositions. Fluid inclusion data,
however, provide strong evidence for evaporated seawater.
Dolomites from Enewetak Atoll are found below 1200 meters and lie at the base of a
permeable slope deposit. The Sr isotopic composition is more radiogenic than the
depositional carbonate, indicating that dolomitizing fluids were young. Fluid inclusion
data (Tm ice = -2.4 to -4.4C) indicate dolomitization from fluids of 44 to 85 ppt
salinity. Thus, dolomitization was at least in part from deeply refluxing evaporated
seawater.
Samples from the drill core Clino, western Bahamas, show significant calcite
cementation after compaction in grainy carbonates of Pliocene age. Fluid inclusion data
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from calcite cements (Tm ice = -2.2 to -10.8C) indicate elevated salinity, ranging from
37 ppt to highly saline brines of 148 ppt.
Clear Mg-rich calcite from the Plio-Pleistocene Hope Gate Formation of Jamaica
contains fluid inclusions with Tm ice values ranging from -1.9 to -2.4ºC, indicating
precipitation from normal to slightly evaporated seawater (35 to 45 ppt).
These data provide a climatically significant record of ancient seawater evaporation
that has been previously unrecognized. Generation of such high density fluids at the
surface could lead to deep reflux of fluids, resulting in the precipitation of either calcite,
Mg-rich calcite, or dolomite, strong evidence that mineralogy and process are controlled
more by microbial processes than fluid origin and salinity.
Petrography And Stable Isotope Geochemistry Of Upper Cretaceous Carbonate
Concretions And Veins In The Cariblanco Formation Of Southcentral Puerto Rico:
Implications For Hydrocarbon Generation And Migration
Luis A. González , Department of Geology, University of Kansas,
Lawrence Kansas 66049
Rubén Uribe, ExxonMobil Exploration Company, Houston Texas 77210
Calcite cements in concretions and veins of the Upper Cretaceous Cariblanco Formation
of south-central Puerto Rico contain the only documented occurrence of live
hydrocarbons in Puerto Rico. Concretions preserve the complex diagenetic history of the
Upper Cariblanco Formation and provide important clues about the generation and
migration of hydrocarbons. Paragenetic sequence preserved by concretions consist of 1)
Synsedimentary pyrite formation; 2) three distinct events of vein/fracture formation
accompanied by sediment infilling; 3) pyrite formation throughout the concretion matrix
and sediment vein fills; 4) four events of larger vein and fracture formation and infilling
by distinct calcite cements; 5) late barite and quartz void filling cements; and 6) very late
formation of calcite-filled veinlets. Stable isotopic values of concretion components and
vein calcite define two distinct diagenetic trends of progressive δ18O depletion and δ13C
enrichment. δ18O depletion in both cases resulted from progressive warming of
circulating seawater as magma emplacement proceeded and/or from the fluid interaction
with the volcaniclastic materials during burial diagenesis. The 13C-depleted CO2
involved in calcite cementation in both concretion matrix and vein calcite is most likely
sourced from the oxidation of methane. Marked differences are observed between the
oxygen isotopic composition of early diagenetic concretion components and the oxygen
isotopic compositions of concretion late diagenetic cement phases as well as vein
calcite precipitation. Early diagenetic fluids were most likely marine in origin and
presumably circulated through the sediments as a result of thermally driven advection.
The fluids precipitating vein calcite and late concretion cements were sourced deeper in
the basin and were certainly warmer than earlier fluids.
The presence of hydrocarbon fluid inclusions, the common fluorescence of vein
calcites, and the exclusive association of the live hydrocarbon with calcite veins and late
cements in concretions clearly indicate that this later fluid mobilized the hydrocarbons. A
better knowledge of the source rock potential of the Cariblanco Formation will provide a
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better foundation for assessing the paradigm that no appreciable quantities of
hydrocarbons exist in the Cretaceous rocks in and around Puerto Rico.
A New Seismotectonic Model For The Chortis Block
Marco Guzmán-Speziale
Centro de Geociencias, UNAM, México
+52 442 238 1119 ext 125
+52 442 238 1101 (fax)
marco@geociencias.unam.mx
Using centroid moment-tensor solutions (CMTs) published by Harvard University, we
study the state of stress in the northwestern corner of the Caribbean plate. Plate
boundaries are located in the vicinity of this region: the convergent margin between the
Cocos and the Caribbean plate along the Middle America trench, and the transform plate
boundary between the North America (NOAM) and Caribbean (CARB) plates along the
Motagua-Polochic fault system, both of them seismically very active. There are also
tectonic earthquakes (right-lateral, strike-slip mechanisms) along the Central America
Volcanic Arc (CAVO), parallel to the trench.
P axes of events along the CAVO show horizontal, N-NW compression whereas strikeslip events along the NOAM-CARB margin show P axes oriented S-SW. Compression,
then, is directed towards the corner of the Caribbean plate.
T axes show SE orientation for the NOAM-CARB boundary, and a NE general azimuth
for events along the CAVO, both of which add to a general eastern tensional regime.
Eigenvalues associated to P and T axes are similar in magnitude for both groups of
events, along the NOAM-CARB plate boundary and along the CAVO, which together
with orientations of P and T axes, suggest that the northwestern corner of the Caribbean
plate is under NNW horizontal compression, probably due to subduction of the Cocos
plate, and SSW horizontal tension because of the relative motion of the North America
plate. Superposition of bot stress regimes suggest that this parto f the Caribbean plate is
being extruded to the East.
The Coniacian Santonian Boundary in the Oil Fields of Northern Iraq
Rund A. Hammoudi
Dept. of Geology ,College of Science, Mosul University
Mosul , Iraq
Phone 00964 60 812609
Mobile 00964 770 160 1990
e-mail rundhammoudi@yahoo.com
rundhammoudi@gmail.com
Biostratigraphic data from the subsurface sections in the oil fields of northern Iraq
provides evidence for defining the Coniacian - Santonian boundary . Depending on the
distribution of foraminifera in Kirkuk and Balad oil wells , the Coniacian - Santonian
boundary is located within the upper part of the Concavata Zone . The last appearance of
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the Marginotruncana renzi and the first appearance of the Globotruncana linneana marks
this boundary .Other foraminiferal assemblages have been recognized for determining the
end of Coniacian.
Use of Seismic Techniques to Locate and Define Sinkholes
James C. Hasbrouck, B.S., R.Gp., Suelos Inc., Hato Rey, Puerto Rico
Carlos Rodriguez Molina*, M.S., P.E., C.E., Suelos Inc., Hato Rey, Puerto Rico
*Speaker
Within many parts of the Caribbean the presence of sinkholes create financial and
logistical problems in the development of public and private infrastructure. Surface
seismic surveys are used for regional mapping of limestone depth and topography to
identify subsurface depressions within the buried limestone that are typically associated
with the existence of sinkholes or sinkhole related phenomena. Once anomalous areas
have been identified, surface to borehole seismic surveys aid in the detailed geometry
mapping of possible sinkholes with only a small amount of drilling. Thus the application
of these geophysical techniques to locate and define sinkholes makes it possible to
prepare, at minimal costs, development plans that provide usage of good land.
Examples are shown of the combined use of surface and surface to borehole seismic
techniques to locate and define sinkholes along the axis of a planned highway in Puerto
Rico. Using surface refraction seismic and the delay-time processing method several
anomalous topographic depressions within the subsurface limestone are identified to
depths greater than 100 feet. Seismic techniques are well suited for use in most urban
areas because of the limited influence of electrical utilities and metal fences (both of
which can adversely affect electrical resistivity and electromagnetic data) and noise from
nearby traffic can be minimized through careful data acquisition procedures.
Anomalous areas identified along the proposed highway axis from surface refraction
seismic data, aerial photography and field reconnaissance are surveyed with the surface
to borehole seismic technique to detail the geometry of suspected sinkholes. To
adequately map the sinkholes and enable three dimensional representations, data are
acquired along four overlapping lines centered on each of three boreholes at an
anomalous area. Thus two seismic survey types and a minimal amount of boreholes at
selected anomalous areas enable the cost-effective and safe design of highways and other
infrastructure.
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The tectonic evolution of the Caribbean Plate: Insights from volcanic rocks in
Jamaica and the Virgin Islands.
Alan R. Hastie1, Andrew C. Kerr1, Simon F. Mitchell2 and Trevor A. Jackson2.
School of Earth Ocean and Planetary Sciences, Cardiff University, Main Building,
Park Place, Cardiff, CF10 3YE, U.K.
Department of Geography and Geology, University of the West Indies, Mona,
Kingston 7, Jamaica, W.I.
The complex question of Caribbean plate tectonic evolution requires a multidisciplinary
approach involving volcanology, igneous petrology, structural geology and
palaeontology. Plate tectonic models of Caribbean plate evolution are widely debated,
and this study on the Cretaceous-Tertiary igneous rocks of Jamaica and the Virgin Islands
will aim to clarify the existing models.
Information relating to volcanic rocks in Jamaica and the Virgin Islands is sparse with
Information relating to volcanic rocks in Jamaica and the Virgin Islands is sparse with
few geochemical and geochronological studies having been carried out. Some of the
volcanics have been identified stratigraphically, but their petrogenesis is still unknown
i.e. did they originate in a subduction-related setting, a mid-ocean ridge or an oceanic
plateau? The temporal and spatial identification of the volcanic rocks in these islands
will be valuable in determining plate evolution by identifying when, where and how the
different volcanic rocks formed.
Fieldwork has demonstrated the variety of volcanic and plutonic rocks on Jamaica.
During the summer of 2004 samples were collected from the Blue Mountains, Central,
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17th Caribbean Geological Conference 2005, San Juan PR
Above Rocks and Benbow Cretaceous Inliers throughout the island. Recent major and
trace element data has been obtained by state of the art ICP-OES and ICP-MS facilities at
Cardiff University, U.K. The data has confirmed the presence of a plateau section and a
number of primitive and evolved Cretaceous island arc sequences. Due to intense tropical
weathering many elements have been mobilised, and it is for this reason that most of the
samples analysed were interpretated using immobile trace elements. These new findings
are presented here, and it is hoped that together with the stratigraphical and temporal
location of the igneous rocks that the “Pacific” model of Caribbean plate evolution can be
supported and/or refined.]
Holocene Coral-Reef Development In Canada Honda, SW Dominican Republic
HUBBARD, Dennis K. 1, RAMIREZ, Wilson2, DAVIS, Allicia1, LAWSON, Gregory R.
1
, ORAM, Jessica1, PARSONS-HUBBARD, Karla1, CUEVAS, David2, and DEL
CORO, Monica2, (1) Dept. of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH
44074, (2) Dept. of Geology, University of Puerto Rico, PO Box 9017, Mayaguez, PR
00681 contact: dennis.hubbard@oberlin.edu
Facies preserved in a 400-m long outcrop at Cañada Honda in the western Dominican
Republic span a depth range of over 40 m, and mimic the zonation pattern seen on
modern Caribbean reefs. Twenty-seven scleractinean species have been recorded in the
outcrop, along with 56 species of mollusks. Coral abundance in 53 quadrats from 21
vertical transects averaged over 60%, and ranged from 35% in the platy coral zone to
76% in the mixed-coral facies. Taphonomic data from corals buried by a prominent
storm-debris layer (mostly Madracis mirabilis) that crosses the outcrop indicate that
roughly half the buried colonies were already dead. This infers that the 60% coral
abundance in quadrats probably reflects live-coral cover near 30%. This value is similar
to that seen on modern Caribbean reefs, and closely matches the coral recovery from
Holocene reef cores throughout the region. Facies geometry reflects early transgression
starting ca. 10,000 years ago, followed by the outbuilding of shallow facies by 6,000
years CALbp, as sea-level rise slowed.
Despite the high diversity within the outcrop, the reefs were probably exposed to high
levels of sedimentation. The dominant corals were Siderastrea siderea and Montastraea
faveolata, both sediment-tolerant species. Elevated sedimentation is further supported by
the absence of Acropora palmata, a coral without a biological strategy for sediment
removal. Massive corals vary from hemispheres to conical to columnar forms as
sedimentation presumably increased. Siderastrea spp. are dominantly conical, while
Montastraea spp. tend to form columns. Many corals show interrupted growth that is
manifested in flared colony margins, giving an appearance likened to a stack of pancakes.
Thus, colony shape provides a useful proxy for both the magnitude and constancy of
sedimentation.
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17th Caribbean Geological Conference 2005, San Juan PR
Where’s The Reef? – Clues To Gaps In The Caribbean Record Of Acropora Palmata
At 5,800 And 3,000 Calpb
HUBBARD, Dennis K., LAWSON, Gregory R., and TOMLINSON, M., Dept. of
Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074 contact:
dennis.hubbard@oberlin.edu
It has been proposed that the recent decline of coral reefs is an event unprecedented over
Holocene time or perhaps longer. In apparent contrast, two Caribbean-wide gaps in the
Holocene record of Acropora palmata appear to have occurred approximately 5,800 and
3,000 years ago. Oceanographic and meteorological patterns vary significantly across the
sites where these gaps have been seen, and a regional or global mechanism is required to
explain the pattern. Existing sea-level data seem to preclude a sudden rise as a factor. Of
the possible causes that we can envision, only bleaching and disease have not been ruled
out. However, the lack of proof for other mechanisms is not a priori proof that either of
these was responsible for the two millennial-scale gaps described above. It is nevertheless
interesting that the two remaining possibilities are important elements of the recent
decline.
In 2002, we collected over 200 branch segments from still-standing colonies of A.
palmata killed in the early 1980s by White Band Disease. Each was cut in cross section
and made into a thin section. Preliminary analyses indicate that the standing-dead
branches are dominantly encrusted by coralline algae, vermetid gastropods and the
foraminifer Gypsina spp. The total thickness and diversity within the crust vary between
the branch top and bottom. In contrast, samples of A. palmata recovered from two 2-m
deep excavations in the adjacent substrate are generally less encrusted and have
significant quantities of the foraminifer Carpenteria spp. Homotrema rubrum is common
in both sample sets, but exhibits a markedly different morphology between standing-dead
and buried branches. The presence of an encrusting “signature” that is unique to standingdead colonies may be useful in understanding the origins of the gaps in the Caribbean A.
palmata record.
Telemetred multichannel system for geophysical cable
Mr. Florin Ionica
Earthquake Unit, University of the West Indies
Kingston – Jamaica
E-mail: florin.ionica@uwimona.edu.jm
A new telemetred multichannel system for geophysical cable is presented.The
investigation of the boreholes is very important to be done using as many measuring
channels as possible in order to have fast and effective results.
Multiwire cables which are now used in multichannel systems are very problematic due
the connectors, durability and wear. Water tightness must be very high because of the
high pressure which exists in boreholes over 1000 meters. Also noises and disturbances
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17th Caribbean Geological Conference 2005, San Juan PR
generated by external electromagnetic fields are big problems especially in VSP or HSP
measuring where all the signals, including the weakest reflections must be recorded at
sufficient resolution.
Taking in account these requirements it was designed one modular system which is
constructed to function on one coaxial cable where all the channels are located in parallel
in frequency domain. This kind of system is called telemetry system and it is used mostly
in airplane and space equipment.
This telemetry system consist of transducer units (each one with three geophones),
preamplifiers, circuits to transfer signals to cable, electronic controls and power supply
components. All units are connected on a strong main coaxial cable as many as needed.
Physically they are in series with cable but electrically are in parallel as on a bus line.
The power supply is delivered via the same cable as single DC-supply voltage where
units take their power from switching regulators.
Transmission of seismic data using High Voltage Electrical Lines –Power Line
Carrier Systems
Mr. Florin Ionica
Earthquake Unit, University of the West Indies
Kingston – Jamaica
E-mail: florin.ionica@uwimona.edu.jm
Section: Seismology-Poster
Among the different kind of communication systems to be used like bearer, the Power
Line Carrier (PLC) Systems represent in many countries a main part of utility-owned
transmission system.
The PLC technology remains in fact always cost attractive because, by using as
transmission bearer the same power network, is able to:
- connect exactly all the main points involved with the required exchange of
information reducing the number of the communication equipment and
maintenance work
- guarantee good communication also on High Voltage (H.V.) power lines of some
hundred kilometers, without any need of repeaters, in any climatic conditions and
independently of natural barriers (hills, mountains, etc.)
- guarantee highly reliable communications for the high mechanical safety of the
H.V. power lines which are designed to withstand the worst Nature can do.
Some aspects regarding the using of the PLC Systems for seismic data transmission are
presented.
A PLC System is generally composed of a few main elements such as:
- line traps
- coupling devices
- PLC equipment
- teleprotection equipment
Transmission of the signals in PLC Systems is using high frequency carriers (generally in
the 40 to 500 KHz band) between two or more locations.
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17th Caribbean Geological Conference 2005, San Juan PR
The PLC equipment converts the low frequency signals (e.g. VCO’s) or serial outputs
from seismic data-loggers into high frequency signals to be transmitted on the High
Voltage lines: the opposite conversions are performed for the received high frequency
signals.
Biogeographic implications of Caribbean Paleogeography: The origin and evolution
of an inter-oceanic seaway
Manuel A. Iturralde-Vinent
Museo Nacional de Historia Natural, Obispo no. 61, Plaza de Armas,
La Habana 10100, Cuba;
iturralde@mnhnc.inf.cu
Since latest Triassic the Caribbean started to be formed as a system of Jurassic rift valleys
within west-central Pangaea, later evolving into a mediterranean sea where distinct
volcanic and non volcanic island evolved. Since its very early formation this sea has been
playing an important roll controlling the historical patterns of ocean water circulation,
moderating the world climate, and determining the possibilities of biotic exchange of the
surrounding terrestrial and marine ecosystems. The formation of a Mesozoic marine
seaway between the western Tethys and the eastern Pacific, across west-central Pangaea,
has been postulated for the Early Jurassic (Hettangian-Pliensbachian) according to
biogeographic thesis, but supporting stratigraphic data is lacking. Probably since the
Bathonian but certainly since the Oxfordian, the stratigraphic record indicate that this
connection was fully functional and the Circum Tropical marine current was active.
Overland dispersal between western Laurasia (North America) and western Gondwana
(South America) has been interrupted since the Callovian when the continents were
separated by a marine gap. Later, a connecting landbridge may have been present during
the latest Campanian/Maastrichtian (~75-65 Ma), and since the Plio-Pleistocene (2.5-2.3
Ma). Evidence for a precursor bridge late in the Middle Miocene is ambiguous at this
time. Since the formation of the first volcanic archipelago within the Caribbean realm, at
about the Jurassic-Cretaceous transition, volcanic islands, shallow banks, and ridges have
been present in the paleogeographic scenario of the area. But these lands were generally
ephemeral, as they lasted just a few million years. Only after the Middle Eocene (<40 Ma
ago) permanent lands were present within the Caribbean geographic scenario, providing
the substrates for the formation and development of the present terrestrial biota.
Keywords: Paleogeography, paleoceanography, biogeography, Caribbean, Mesozoic,
Cenozoic.
This paper is a contribution to IUGS/UNESCO International Geological Correlation
Programe Project 433: Caribbean Plate Tectonics
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17th Caribbean Geological Conference 2005, San Juan PR
Paleoproductivity in the Caribbean Sea
During Closure of the Central American Seaway
Sreepat Jain and Laurel S. Collins, Department of Earth Sciences, Florida International
University, Miami, Florida 33199, USA
Increased Caribbean oligotrophy is a predicted effect of the closure of the
Caribbean – Eastern Pacific seaway about 4 Ma. We examine nutrient proxies at sites
ODP 999 and DSDP 502, Colombian Basin, from before (8 Ma) to after (2.5 Ma) this
event. PpP (paleoproductivity) is based on a transfer function converting carbonate mass
accumulation rates, and BFAR is the rate of accumulation of benthic foraminifers (>63
μm), a proxy for organic matter accumulation on the seafloor.
Between 7.3–6 Ma, paleoproductivity and Site 502 BFAR decreased from
moderately high values, although Site 999 values were low. The trend agrees with high
global paleoproductivity associated with the Late Miocene Carbon Isotope Shift (7.6–6.8
Ma). From 6–5.3 Ma, paleoproductivity and seafloor accumulation of organic matter
increased, and PpP increased to its highest values. This interval corresponds to the onset
of the Messinian Salinity Crisis around 6 Ma and higher productivity. From 5.3–4.75
Ma, PpP and BFAR decreased, reflecting decreased global productivity associated with
the Terminal Messinian Flood and eustatic rise at 5.3 Ma. During the last stages of
seaway closure 4.75–4.0 Ma, paleoproductivity and seafloor accumulation of organic
matter increased again. Enhanced ventilation of the deep Caribbean Basin and better
carbonate preservation has been documented starting at 4.6 Ma. From 4–2.5 Ma, PpP
values declined slightly. BFAR values generally agree with PpP estimates until 4 Ma,
after which the proxies diverge. Site 999 BFAR peaked at 3.5 Ma, but Site 502 BFAR
has its highest values at 4 and 3 Ma.
Conclusions: 1) Paleoproductivity and accumulation of organic matter on the
seafloor varied within the Colombian Basin. 2) Paleoproductivity reached a high around
the Miocene/Pliocene boundary and, after a drop and recovery 5–4 Ma, gradually
declined. 3) Both proxies effectively track global and regional signals.
Comparison of the Stratigraphy of the Tertiary Limestone Across Central
Jamaica
Ennika James and Simon F. Mitchell
University of the West indies, Mona, Kingston 7
This
study
is
concerned
with
understanding
the
distribution
of
carbonate-microfacies on a Middle Eocene, carbonate platform (Chapelton
Formation) in Jamaica. Three sections across central Jamaica (Watermont, St.
Catherine in the east, Coleyville, Clarendon in central Jamaica and Litchfield,
Manchester, in the west) were investigated. Representative samples were collected and
thin sections for microfacies analysis prepared. In the eastern part, the
Chapelton Formation is represented by poorly developed limestones with pellatisperelladominanted sparse biomicrites interbedded with fossiliferous mudstones and clastic
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17th Caribbean Geological Conference 2005, San Juan PR
sandstones. In the western sections the carbonates consist of fossiliferous
(foraminiferan and molluscan) packstones and grainstones. Sporadically
dolomitization of the facies has occurred with either mimick replacement or
the development of cross-cutting dolomite rhombs. The succession forms a
part of a back stepping depositional system with the progressive
restriction of clastic components to the south-east and the development of
thick foraminiferan and molluscan dominated microfacies in an extensive
shallow marine carbonate sea to the north-west. The distribution of
microfacies has importance to ongoing hydrocarbon exploration in Jamaica.
Geochemistry And Formation Of Horizontal Elongate Concretions In A Mixed
Sand-Gravel Shoreface
1
Sherene A. James , Simon F. Mitchell1, Jim D. Marshall2 and Steve F. Crowley2
1
Department of Geography and Geology University of the West Indies, Mona Kingston 7,
Jamaica
2
Department of Earth and Ocean Sciences, University of Liverpool, United Kingdom.
Horizontal, highly elongate concretions occur in Late Pleistocene, marine shoreface
sandstones at the base of a 4 m high Pleistocene sea cliff at Roselle, St. Thomas, Jamaica.
These concretions have width:length ratios of 3-5, are orientated perpendicular to the
modern shoreline, and cut by vadose-zone rhizocretion columns. This study examined the
method of formation of these concretions using geochemistry and petrography. The
cements in the concretions consist of large (up to 1 cm) polikotopic plates, which are
confirmed as calcite by X-ray diffraction. In cathodoluminescence and backscatter
scanning electron microscopy, these cements show strong luminescence. Trace element
analysis demonstrates relatively high concentrations of Mn and low concentrations of Fe,
with the Mn likely the cause of the luminescence. The high Mn would suggest a marine
environment; and the lack of pyrite, coupled with the high Mn, indicates crystallization
occurred within the sub-oxic zone, before Fe reduction. Oxygen isotopes (-4.9-5.8‰
PDB) indicate near-surface temperatures consistent with a marine or meteoric water
source. The relatively negative δ13C (-10.3 to -13.9‰ PDB) values suggest the
incorporation of bicarbonate from bacterial reduction of organic matter. The lack of
pyrite, the near surface temperatures for oxygen isotope data, the high Mn values, and the
presence of poikilotopic plates indicate growth in the suboxic zone in a phreatic
environment created by stagnant mixed marine and meteoric water. The source of
calcium ions could be either internal (dissolution of marine bioclasts and Ca-rich
minerals) or external. Cementation is envisaged to have occurred as the system was
flushed by mixed marine-meteoric waters as sea level fell following the Sangomonian
high stand, prior to the establishment of a vadose diagenetic environment. These results
indicate that cementation of sandstones beneath sequence boundaries occur during sealevel fall.
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17th Caribbean Geological Conference 2005, San Juan PR
Remote sensing evaluation of regional chemistry and element dispersion of
porphyry copper deposits in the Silver Bell Mountains, Arizona
Jaramillo-Nieves, Lorna G. (Ph.D., Geology) [Department of Physical Sciences, UPR,
Río Piedras]
Porphyry copper deposits in southeastern Arizona belong to a cluster of 38 mineralized
centers covering a region extending from northern Mexico to western New Mexico and
southern Arizona. Presently, some of these deposits are being actively mined and the rest
are prospects or abandoned mining sites. As a result of the large number of porphyry
copper deposits in this region, research on the interaction between mineralized centers
and the environment is important; in particular, the dispersion characteristics of acidgenerating metal-enriched materials at the shallow alluvial margins of these centers. The
present research uses remote sensing techniques, groundwater chemistry, trace element,
and mineralogical analysis to characterize dispersion chemistry surrounding porphyry
copper deposits in the Silver Bell Mountains. Hyperspectral imagery obtained by the
Airborne Visible/Infrared Spectrometer and HyMap are used to map supergene minerals
by analyzing their spectral profiles in the visible and short wave infrared regions of the
electromagnetic spectrum. Reflectance profiles are characteristic of each mineral and
shifts in absorption features within one mineral are a result of differences in cation
content. Image reflectance profiles are compared with stream sediment mineralogy and
reflectance spectral profiles to better outline concentrations of Fe, S, K, Na, Ca, Mg, Cu,
and Al. In addition, groundwater modeling in the Silver Bell Mountains is considered for
various flow paths within shallow aquifers in the region and compared to actual
groundwater chemistry and surface lithology. The Silver Bell Mountains serve as a case
study for element mobility and concentration distribution in other areas where
undisturbed deposits, historic and present-day excavation activity occurs, where semiarid climate and a deep vadose zone are variables that influence element mobility and
concentration. Results obtained from hyperspectral image processing indicate the
possible enrichment of stream sediment samples in iron and/or magnesium, based on
absorption shifts observed for phyllosilicates in the region. The extent of alteration
patterns in porphyry copper deposits located in the Silver Bell Mountains supports the
concept of narrow dispersion haloes in semi-arid environments.
Role of crustal melting in petrogenesis of the Cretaceous Water Island Formation,
Virgin Islands Northeast Antilles Island Arc
Wayne T. Jolly, Department of Earth Sciences, Brock University, St. Catharines, Ontario,
Canada L2S 3A1
Edward G. Lidiak, Department of Earth and Planetary Sciences, University of Pittsburgh,
Pittsburgh, Penna., USA 15260
The Late Aptian to Early Albian (~115 Ma) Water Island Formation in the Virgin Islands
is comprised of approximately 20% degraded island arc basalt (spilite; 46-56% SiO2) and
80% dacite and rhyolite (keratophyre; 65-85% SiO2). Trace element patterns of both endmembers, characterized by pronounced negative normalized high field-strength element
(HFSE) anomalies, relatively flat rare earth element (REE) patterns, and highly depleted
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17th Caribbean Geological Conference 2005, San Juan PR
Sr/Y, have analogues in plagiorhyolite suites from bimodal Cenozoic arcs, including the
western Aleutians, Izu-Bonin, and the Kermedacs. Incompatible element patterns are
consistent with melting models involving partial fusion of amphibole-bearing oceanic
crust at low pressures within the stability range of plagioclase. Predominance of
plagiorhyolite relative to basalt, and simultaneous extrusion of basalt and plagiorhyolite
throughout volcanism, indicate basaltic melts were underplated along the crust-mantle
boundary from earliest stages of volcanism. Moreover, truncation of the erupted
fractional crystallization series at SiO2 = 56% indicates evolved basaltic fractionates were
gradually displaced from crustal magma conduits as the volume of more buoyant
plagiorhyolite melt increased and eventually became trapped in sub-crustal magma
chambers by density contrasts. Volcanism occurred in two successive eruptive cycles.
First cycle basalts have borderline boninitic compositions, characterized by flat to slightly
depleted normalized REE patterns, and depleted light rare earth element concentrations.
Interlayered first cycle plagiorhyolites contain a significant basalt component (~25%),
indicating intermingling between basaltic melt and crustal source material. Second cycle
basalts have flat to slightly enriched REE patterns with elevated LREE abundances,
analogous to modern intra-oceanic island arc basalts. Associated plagiorhyolites are free
of basalt contamination, reflecting greater physical isolation of second cycle
plagiorhyolite melts compared with the previous cycle, probably due to migration of the
melting zone to higher crustal levels, out of a restate zone produced during the first cycle.
Late Cretaceous to Mid-Eocene Pelagic Sediment Budget in Puerto Rico and the
Virgin Islands, Northeast Antilles Island Arc
Wayne T. Jolly, Department of Earth Sciences, Brock University, St. Catharines,
Ontario, Canada L2S 3A1 wayne@craton.geol.brocku.ca
Edward G. Lidiak, Department of Earth and Planetary Sciences, University of
Pittsburgh, Pittsburgh, PA., USA 15260 egl+@pitt.edu
Alan P. Dickin, Department of Geology and Geography, McMaster University,
Hamilton, Ontario Canada L8S 4M1 dickin@mcmaster.ca
Island arc basalts (IAB) in the extinct Greater Antilles, dating between Albian
and mid-Eocene time (~125 to 45 Ma), consist of an early low-K, primitive island arc
(PIA) basalt series and a later, predominantly intermediate calcalkaline (CA) series. The
rocks resemble modern sediment-poor, low-light rare earth element (LREE)/heavy rare
earth element (HREE) arc basalts from intra-oceanic tectonic settings and sediment-rich,
high-LREE/HREE types from continental margin arcs, respectively. Isotope and
incompatible trace element distribution along a 450 km segment of the arc in the
northeast Antilles demonstrates that low-LREE/HREE basalts predominate in Albian to
mid-Santonian (~85 Ma) stratigraphic sequences in the Virgin Islands (VI) and northeast
Puerto Rico (NEPR), while there is a gradual but spectacular increase in both
LREE/HREE and absolute abundances of incompatible elements in central Puerto Rico
(CPR). Northeastern Antilles basalts have consistently elevated La/Nb and relatively
low Nb/Zr, both inconsistent with the presence of a significant ocean island basalt (OIB)
component. Hence, observed differences are interpreted to reflect variation in
proportions of pelagic sediment subducted by the south-dipping Antilles arc system as it
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17th Caribbean Geological Conference 2005, San Juan PR
swept northeastward across the Caribbean region and eventually approached the Bahama
Banks along the southeastern fringes of the North American Plate. Trace element mixing
models indicate sediment proportions in VI and NEPR were limited, averaging
considerably below 1.0%. In comparison, sediment content in CPR increased from an
average slightly above 1.0% in Albian (~125-95 Ma) basalts to as high as 8% in
Cenomanian (90-95 Ma) types. Following collision of neighboring Hispaniola with the
Bahamas, and a shift from predominantly northeast to east-northeast convergence,
sediment budgets in the northeast Antilles stabilized at moderate levels from 2 to 3%,
reflecting widespread subduction of North Atlantic Cretaceous pelagic sediment
(AKPS).
Impact of the November 2003 Rains on Hillslopes, Embankments, Rock Cuts and
Ghuts in the British Virgin Islands.
Joyce J. and Santos H., Dept. of Geology, University of Puerto Rico Mayagüez PR
Heavy rains fell over the northeastern Caribbean during the week of November 917, 2003 . Rainfalls recorded at the Tortola airport exceeded 7 inches on 12th and 13th and
6 inches on 14th. The rainfall data clearly show that the distribution of rain was irregular
and did not appear to have a geographic control. The greatest rainfall accumulation of 34
inches occurred at Beef Island airport, a relatively low area at the eastern end of Tortola
whereas only about 13 inches accumulated at the highest elevation recording station
located in Chalwell, in the west central portion of the island. The two primary causes of
the extent of the impact were uncontrolled roadway drainage and inadequate drainage
capabilities in the ghuts. The problem was worsened where ghut culverts were clogged by
debris flows and overflowed on to the roadway. The slope failures not related to roadway
runoff largely occurred on over steepened rock cuts along roads and behind homes.
Natural slope failures were limited to debris flows in the ghuts and sea cliffs. Most of the
debris flows on natural and man-made slopes occurred along joint intersections. The cut
slope failures were generally superficial and largely controlled by rock type. The stronger
massive rock layers failed by sliding along joints and joint intersection wedges creating
rock falls and avalanches. The thin bedded weaker units failed by superficial debris
avalanches. The intrusive batholithic rocks of eastern Tortola and Virgin Gorda exhibited
joint controlled rock sliding and a granodiorite tor topple. The common occurrence of
thick colluvial deposits in many road cuts indicates that rainfall events of this magnitude
have occurred in the past and are likely to occur again.
November 2004 Mogote Topple Manati Puerto Rico
Joyce, J. and Velez, R., University of Puerto Rico, Mayagüez, Puerto Rico
An enormous portion of a hilltop mogote toppled off of a 50 meter high limestone hill
and crushed houses in the urbanization that lay below. As the mogote section fell it broke
up into blocks and pieces, the largest of which was 2-3 times the size of the impacted
homes. Although damage was severe there were no personal injuries due largely to the
fact that the home dwellers were not present at the time. The cause of the event was
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17th Caribbean Geological Conference 2005, San Juan PR
natural, a combination of paleo-karst dissolution features, the orientation of the mogote
bounding joints and the thin bedded limestone that lay below the mogote. The mogote
formed part of a northeast trending mogote karst ridge in the Aymamon Limestone. The
mogote top was composed of recrystallized massive limestone and underlain by thin
bedded recrystallized grainstone. The remainder of the hill slope below the mogote was
composed of thick to very thick bedded recrystallized limestone. The base of the
remaining section of the mogote ridge was marked by a prominent notch. Smaller notches
and weathering at the base of the largest fallen block indicates the notch was continuous
along the mogote ridge. The notch tracked into a small cave suggesting it represents a
paleo-phreatic level. The mass of the remaining mogote ridge was clearly inclined over
the notch and towards the urbanization. This tilt and the undercut notch caused a section
of the mogote ridge to peel off the underlying thin beds and topple on to the urbanization
below. The remaining thin beds of limestone were heaved up and tilted the topple
direction. Although the topple required the combination of several geologic features it
may not represent a unique event. Similar conditions may be found elsewhere in the
mogote karst and present a hazard to other urbanizations.
The Amorphous Mystery
Shakira Khan and Simon F. Mitchell
Department of Geography and Geology, University of the West Indies, Mona, Kingston,
Jamaica
Jamaica’s carbonate sand beaches consist of skeletal and non-skeletal sand-sized grains.
The skeletal grains can be identified in thin section and consist of fragments of marine
organisms, including foraminifers, red algae, green algae, echinoids, molluscs and corals.
The non-skeletal fraction consists of crystalline, amorphous and clastic grains.
Compositional analysis, of sediment collected around the island of Jamaica, shows that
amorphous grains contribute up to 50% of the total beach in many areas. Previously,
several ways have been suggested for the formation of amorphous grains (for instance,
alteration of skeletal grains, fecal pellets, mud balls, etc.). Because of their importance as
a major constituent of beach sand, an understanding of the origin of these non-skeletal
grains is critical in modeling the production of beach sediment.
This study focuses on identifying the origin of amorphous grains; two techniques were
used: petrography and scanning electron microscopy (SEM). For petrographic analysis,
sand samples were resin impregnated, and thin sections prepared from the blocks.
Individual amorphous grains were studied for traces of internal structure that might
indicate their origin. For SEM analysis, individual grains were fractured and mounted on
a stub. They were coated with gold-palladium and viewed under the SEM, with attention
being drawn to internal features. The results indicate the origin for the amorphous grains
in Jamaican beaches – but like any good who-done-it you don’t want to know the answer
yet!
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17th Caribbean Geological Conference 2005, San Juan PR
Pressure-temperature-time paths critically constrain Cretaceous subduction-zone
dynamics in the Rio San Juan Complex (Northern Dominican Republic)
Krebs, M.*, Maresch, W.V.*, Schertl, H.-P.*, Draper, G.**, Idleman, B.***
*
Institute of Geology, Mineralogy and Geophysics, Ruhr-University of Bochum, 44780
Bochum, Germany
**
Dep't of Geology, Florida International University, University Park,
Miami FL 33199, USA
***
Dept. of Earth and Environmental Sciences,
Lehigh University, Bethlehem, PA 18015, USA
Serpentinite melanges associated with Cretaceous subduction at the leading edge of
the eastward-drifting Caribbean plate now decorate the trace of the Caribbean / NorthAmerican suture zone exposed in Cuba and northern Dominican Republic. Blocks of
various types of metamorphic rocks (e.g., eclogites, blueschists, metagranitoids) in the
melanges exhibit a series of different but interrelated P-T-paths. Comparison with
numerical models yields critical information on the dynamics of a young and maturing
subduction-zone / island-arc complex. The P-T paths can be summarized into three
categories: 1) oldest, "nascent" stage: Typically shallow ("hot") P/T gradients and peak
conditions of 700°C/22 kbar. Unusual anticlockwise P-T paths with isobaric cooling and
later isothermal exhumation are common in eclogites. U-Pb-zircon protolith ages of
139.9 ± 4.1 Ma constrain the beginning of subduction. Lu-Hf-data on Grt-Ep-Amp-OmpWR yield an age of 103.9 ± 2.2 Ma for peak metamorphic conditions. Rb-Sr-ages of 74.7
± 0.5 Ma (Phe-Grt-WR) and Ar-Ar (Phe) of 73.18 ± 0.99 Ma constrain the exhumation
path. 2) maturing stage: Continuous cooling and steepening of the subduction-zone P-T
gradient is recorded. Omphacite blueschists yield an age of 80.3 ± 1.1 Ma (Rb-Sr on PheAmp-WR) for peak metamorphic conditions (550°C/18 kbar) and an age of 72.97 ± 1.01
Ma for cooling below 400°C (Ar-Ar on Phe) during exhumation. 3) mature stage:
Typified by jadeite-lawsonite blueschists (380°C/>16 kbar) recording very steep, "cold"
P/T-gradients. Rb-Sr-ages (Phe-Amp-WR) of 62.1 ± 1.4 Ma date peak metamorphic
conditions. This distinctive array of P-T paths in space and time is in accord with
subduction-zone models calling for progressive serpentinization, weakening and
incorporation into channel-flow circulation of the hanging-wall lithospheric mantle,
induced by fluids emanating from the downgoing slab.
Preliminary Study of Serpentinite Deformation in Southwest Puerto Rico
Laó-Dávila, D.A.1, Campbell, P.2, and Anderson, T.H.1
1
Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA,
USA 15260
2
Department of Geography, Geology, and the Environment, Slippery Rock University,
Slippery Rock, PA, USA 16057
In southwest Puerto Rico, three belts of ultramafic rocks crop out: Monte del
Estado peridotite belt (MEPB), Guanajibo serpentinite belt (GSB), and the Bermeja
Complex. Preliminary field studies in the GSB and the MEPB reveal common brittle
(kernel joints, serpentinite veins, and cataclasites) and ductile structures (S-C fabrics and
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17th Caribbean Geological Conference 2005, San Juan PR
folded foliations) in the serpentinite. Within the GSB, foliated serpentinite is
characterized by steeply dipping E-W striking S-C fabric that distinguishes a left-lateral
shear zone. The steep S-C fabric overprints an earlier fabric. The easterly strike and
steep dip of the youngest fabric suggest its development along a Tertiary strike-slip fault.
Serpentinite at the southern contact of the MEPB is topographically high and
locally structurally overlies Late Cretaceous rocks along contacts with gentle apparent
dips. Quarry exposures reveal moderately dipping NW-SE striking faults and shear
zones. Some of which contain foliated serpentinite that records folds with hinges
trending NW-SE. Drag and offset of distinctive features suggest southwest-directed
transport.
Previous interpretations of the geologic history of these ultramafic rocks include:
1) northward-directed obduction during Early Cretaceous subduction followed by
weathering, and formation of conglomerate and breccia containing clasts of serpentinite
that constitute the base of the overlying Late Cretaceous rocks; 2) diapirism of the
serpentinite through the overlying Late Cretaceous rocks; and 3) serpentinite deformation
in response to early Tertiary contraction.
None of the above interpretations is supported by the results of our preliminary
structural studies in the GSB and MPB. The presence of nearby ductile and cataclastic
structures indicates a more complex tectonic history than previously recognized. Our
results from three locations suggest: 1) emplacement of cold, somewhat deformed,
serpentinite above Late Cretaceous units, and 2) development of left-lateral steep shear
zones that may be related to regional late Eocene strike-slip faults. Older, yet
unrecognized events are not precluded.
BOLIVAR: Continental Growth and Deformation along the South AmericanCaribbean Plate Boundary
A. Levander* and the BOLIVAR Working Group
*Department of Earth Science, Rice University, Houston, TX, USA 77005 alan@rice.edu
BOLIVAR (Broadband Ocean-Land Investigation of Venezuela and the Antilles arc
Region) is a 5 year seismic, geological, and geochemical study funded by the NSF
Continental Dynamics Program to investigate continental growth and deformation along
the South American-Caribbean (SA-Car) plate boundary. The study area extends from
western Venezuela to the Atlantic Ocean. Since the SA-Car collision at 55 Ma, the
Americas have migrated westward with respect to the Caribbean plate, with SA passing
the leading edge of the Antilles subduction zone across the entire northern SA margin.
This oblique continent-arc collision has simultaneously formed a foreland fold and thrust
belt on the SA mainland, a strike slip system separating SA from the Caribbean Leeward
Antilles arc, and incorporated elements of the volcanic arc into the continental margin.
Offshore a new west striking, southward-dipping subduction zone has formed beneath SA
due to SA-Car convergence.
Our investigations of this region have included an active seismic program acquiring 6000
km of marine reflection profiles, 4 onshore-offshore and 5 OBS profiles as well as
seismic recordings on the islands of the Leeward Antilles and Venezuelan arcs. Five
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17th Caribbean Geological Conference 2005, San Juan PR
major reflection/wide-angle transects are designed to give cross-sections of the arc and
margin showing the evolution of the plate boundary from 55 Ma to the present.
To investigate the upper mantle of this complex region we are currently operating a 35
element PASSCAL broadband array in Venezuela and a 14 element longterm OBS array
in the southeastern Caribbean to complement the 35 element permanently installed
Venezuelan broadband seismic network operated by FUNVISIS.
Geological studies include age dating of rocks along the Leeward Antilles arc, field
mapping, exhumation rate, and fault studies on the ABC islands and in northern
Venezuela, and basin analysis of a number of the Venezuelan and offshore sedimentary
basins.
New Petrological And Geochemical Constraints On The Origin Of Loma Caribe
Peridotite (Dominican Republic)
J.F. Lewis(1), J.A. Proenza(2), F. Longo(3),
(1) Dept. of Earth and Environmental Sciences, George Washington University,
Washington, D.C. 20052. jlewis@gwu.edu
(2) Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de
Barcelona, Martí i
Franquès, s/n, 08028 Barcelona, Spain. joaquin@natura.geo.ub.es
(3) Falconbridge Dominicana, Bonao, Dominican Republic
Loma Caribe peridotite is exposed along the Median Belt in the northeastern
part of the Cordillera Central, Dominican Republic. The peridotite body is about 4-5 km
wide and extends for 95 km from La Vega to Cerro Prieta north of Santo Domingo.
These mantle rocks are considered to have been exposed because of the collision of an
oceanic plateau (Duarte plateau terrane) with the primitive Caribbean island–arc
(Maimon-Amina terrane) at Aptian time. The Loma Caribe peridotite is composed of
mainly harzburgite with Cpx-rich harzburgite, lherzolite and dunite. The peridotites
typically show porphyroclastic and coarse-grained granoblastic textures. These
metamorphic textures together with the presence of strongly deformed orthopyroxene
phenocrysts are consistent with the view that the peridotites represent remnants of
depleted upper mantle.
The Cr/(Cr+Al# in accessory Cr-spinel from Loma Caribe peridotites vary from
0.30 to 0.88. These large compositional variations indicate the occurrence of peridotites
with very different melting histories. In addition, the olivine Mg# of dunite (91-92) is
slightly higher than that of harzburgite (90-91), and higher than lherzolite (89.5-90.5).
Opx composition in harburgite shows higher Mg# (90.6-91.4), and Al2O3 contents
ranging from 2.8 to 3.1 wt.%. Opx from lherzolite in Loma Caribe exhibits lower Mg# (<
90.5) and higher Al2O3 (up to 3.3 wt.%). The equilibration temperature estimates
(according to three thermometric formulations using pyroxenes) give large ranges of
equilibration temperature between 980º and 1260º C.
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17th Caribbean Geological Conference 2005, San Juan PR
REE analyses of harzburgite and dunite show homogeneous HREE contents and
are characterized by relatively flat LREE patterns and a steep HREE fractionated
segment. These patterns are similar to those of depleted peridotites from the eastern
Cuban ophiolite, and to peridotites from the Izu-Bonin-Mariana forearc. The REE
compositions can be interpreted as the result of partial melting and mantle interaction
with ascending melt at a suprasubduction zone. In contrast, lherzolites from the Loma
Caribe peridotite are enriched in MREE and HREE compared to harzburgite and dunite.
REE pattern show low LREE/MREE and MREE/HREE ratios consistent with partial
melting in the garnet peridotite facies. In addition, Loma Caribe peridotites are relatively
enriched in Cs, Rb and U, and depleted in Th. It therefore appears that the upper mantle
rocks present in Loma Caribe peridotite are probably from several suboceanic mantle
sources, including mantle slices from beneath an ceanic ridge, oceanic plateau and island
arc.
Composition And Mineralogy Of PGE-Rich Loma Peguera Chromitites, Dominican
Republic
J.F. Lewis(1), F. Zaccarini(2), J.A. Proenza(3), F. Longo(4), G. Garuti(5)
(1)
George Washington University, USA, jlewis@gwu.edu
(2)
University of Leoben, Austria, fedezac@tsc4.com
(3)
Universitat de Barcelona, Spain, joaquin@geo.ub.es
(4)
Falconbridge Dominicana, Bonao, Dominican Republic,
LongoF@bonao.falconbridge.com
(5)
University of Modena and Reggio Emilia, Italy, garutig@unimo.it
Loma Peguera chromitites are located in the central part of the Loma Caribe
peridotite in the Cordillera Central, Dominican Republic. The chromitite forms small
podiform bodies enclosed in dunite, and shows mainly massive textures, with
intergranular silicates such as olivine, serpentine and chlorite accompanied by minor
pentlandite and Fe-Ni alloys. Primary chromite composition from the Loma Peguera
chromitite is Cr-rich. The Cr# varies from 0.75 to 0.78, the Mg# from 0.47 to 0.50.
These values are typical of ophiolitic chromitites elsewhere. However, Loma Peguera
chromite exhibits systematically high TiO2 (0.79-0.93 wt%) and Fe2O3 (7.23-8.46
wt%) contents.
Total PGE concentrations in the Loma Peguera chromitites are high, ranging from
1.82 to 2.04 ppm. Chondrite-normalized PGE patterns show an enrichment in
Os+Ir+Ru relative to Rh+Pd+Pt, causing a negative slope between IPGE and PPGE.
Consistent with the high PGE concentrations, PGM are very abundant in Loma
Peguera chromitites. Platinum-group minerals (PGM) were discovered in 14 polished
sections of chromitite with an average frequency of about 2 grains per square
centimeter. Generally, they are less than 10 µm in size. The mineralogy of PGM is
made up of Ru, Os, Ir and Pt phases, including laurite, irarsite, ferronickelplatinum,
Ru-Os-Ir-Fe oxides, unknown Ru-Os-Ir-Pt-Fe-Ni-Cu compounds, native Ru and Rurich Ni-Fe alloy.
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17th Caribbean Geological Conference 2005, San Juan PR
Loma Peguera chromitites are hosted in typical mantle peridotites in terms of
mineralogy, composition and texture, and seem to be derived from a magma
characterized by high Cr, Fe and PGE contents. The composition of chromitite from
Loma Peguera is similar to that reported for Cr-spinel from oceanic plateau basalts
(e.g. Nauru Basin Oceanic Plateau, SW Pacific; Tokuyama and Batiza, 1981). It is
therefore likely that Loma Peguera chromitite represents an example of chromitite
formed in a suboceanic upper mantle affected by a mantle plume (Duarte plume).
Anomalous Granitoid Compositions From The Northwestern Cayman Trench:
Implications For The Composition And Evolution Of The Cayman Ridge.
John F. Lewis, Michael R. Perfit, Giuseppina Kysar Mattietti, Ricardo Aravalo, James
Mortensen. Thomas Ullrich, Richard Friedman and George Kamenov
Perfit and Heezen (1979) showed that granitoid rocks crop out along the steep walls of
the Cayman Ridge. Six of the granitoid rock samples, dredged from the western Cayman
Trench, immediately south of the Rosario Bank area, between 83W and 8454’W, have
been radiometrically dated and analyzed for major and trace element geochemistry, and
Pb isotope compositions. The granitoid rocks range from 55% to 72% SiO2 and are
characterized by high concentrations of Th (up to 41ppm in acid rocks), Zr (112-261
ppm), Nb (5-18ppm), and LREE (La=16-65ppm). Yitrium and HREE concentrations are
very low (Yb < 0.22 ppm in 5 samples with sample 2172F at 0.56ppm). Ce/Yb ratios **
John might be better to quote this as the chondrite normalized ratio*** range from 116 to
1150. These values are more typical of continental arc granitoids (eg Sierra Nevada
batholith) and contrast with the oceanic island arc compositions of granitoids from the
Greater Antilles islands including the Sierra Maestra of Cuba. Three of the western
Cayman Trench granitoids have Pb isotope compositions that are decidedly more
radiogenic than other granitoids from the Greater Antilles and are consistent with the
incorporation of an isotopically more evolved component such as continental crust or sea
floor sediment.
West Cayman granitoids yield satisfactory U/Pb ages on titanite and Ar/Ar ages on
hornblende and biotite from 62 to 64 Ma with one biotite plateau age at 66.35 ± 0.34 Ma,
slightly older than previous K/Ar determinations (Perfit and Heezen,1979). These ages
and compositions contrast with those of the Sierra Maestra of Cuba, considered to be an
uplifted extension of the Cayman Ridge. Sierra Maestra granitoids yield U/Pb ages on
zircon that range from 46.8 ± 0.2 to 60.5 ± 2.2Ma (Mattietti et al. 1998; Rojas et al.
2004). Trace element plots of Sierra Maestra granitoids show geochemical signatures
intermediate between oceanic arc granitoids and MOR plutonic rocks **Is this what you
mean?). Pb isotope compositions lie along the MORB array and indicate a minimal
subduction component
There have been no reliable dates of greater than 60.5 Ma for granitoid rocks in the
Sierra Maestra although Paleogene volcanism, which lasted for about 20 Ma, might have
begun in early Danian time. ??? confusing sentence?? On the other hand there have been
no reliable dates younger than 62 Ma recorded for granitoid rocks from the western
Cayman Ridge.
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17th Caribbean Geological Conference 2005, San Juan PR
Although volcaniclastic turbidites, of early Eocene age, similar to those in the Sierra
Maestra, have been drilled (DSDP Hole XXX) on the western Cayman Rise at 83W, the
crust underlying the western Cayman Ridge appears to include granitoid rocks with a
distinct continental affinity, very different from the Sierra Maestra. The deeper crustal
rocks of the western Cayman Ridge are likely to be a rifted eastern extension of the
northern marginal basement complex of the Chortis block of Honduras, as has been
suggested previously (who?). It is concluded that the composition and Cretaceous-early
Paleocene history of the western Cayman Ridge probably differed significantly from that
of the Sierra Maestra.
Cretaceous (115-75 Ma) Geochemical Stratigraphy In The Northern Virgin
Islands, Northeast Antilles Island Arc
Edward G. Lidiak, Department of Geology and Planetary Science, University of
Pittsburgh, Pittsburgh, PA., USA 15260. e-mail: egl@pitt.edu
Wayne T. Jolly, Department of Earth Sciences, Brock University, St. Catharines, Ontario,
Canada L2S 3A1. e-mail: wayne@craton.geol.brocku.ca
Island arc volcanism in the northern Virgin Islands consists of a conformable sequence of
flows, breccias, tuffs, and their volcaniclastic equivalents that range in age from AptianAlbian (125-110 Ma) to Campanian-Maastrichtian (75 Ma). The earliest strata are rocks
of the Water Island Formation, a bimodal basalt-plagiorhyolite suite, dominated by a
mixture of mantle-derived basalt (20%) and crust-derived felsic lava (80%). The mafic
end-member contains transitional intermediate-Ti boninites and high-Ti island arc basalts
that are highly depleted in incompatible elements. In contrast, rocks from the overlying
Louisenhoj Formation are tri-modal (basalts, 65%; andesite, 20%; plagiorhyolite, 5%)
and contain slightly higher incompatible element concentrations. A low LREE content
places both the Water Island and the Louisenhoj in the Antillean primitive island arc
(PIA) suite. The sequence in the US Virgin Islands is capped by a series of basaltic
andesite-to-andesite lavas (Tutu Formation) with distinctly elevated LREE, indicating
that they belong in the Antillean calcalkaline (CA) suite. The compositional shift from
PIA to CA is consistent with a gradual increase in the proportion of pelagic sediment
derived from source regions. Compositional similarities and structural relations in the
British Virgin Islands, where strata are dominated by a basalt-to-dacite fractional
crystallization series (Tortola Fm), indicate correlation with Louisenhoj strata.
Plagiorhyolite lavas in the Virgin Islands, characterized by low Na, Al2O3, and Sr/Y,
represent melts generated by low-pressure fusion of oceanic crust. The proportion of
plagiorhyolite decreases significantly from 80% in Water Island strata, to 15% in the
Louisenhoj, to 0% in the Tutu Formation, reflecting decreasing temperatures and
decreasing proportion of crustal melt generated in the system. Andesitic lavas in the
Louisenhoj Formation represent products of fusion within under plated arc gabbros
produced during initial Water Island volcanism. A significant proportion of Tutu volcanic
rocks were contaminated by similar remelted arc-related material.
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17th Caribbean Geological Conference 2005, San Juan PR
Seizing the opportunity to build more resilient hazard monitoring networks in the
Eastern Caribbean
Lloyd L. Lynch
Seismic Research Unit
University of the West Indies
St. Augustine, TRINIDAD and TOBAGO
A major initiative is currently underway to establish a program for reducing the risk to
various coastal hazards in the Inter Americas Seas. This initiative is lead by the
Caribbean Charter of the International Oceanic Commission (IOCARIBE). It involves
most regional institutions and agencies that are already engaged in the monitoring and
study of coastal and other hazards as well as several disaster management organizations.
Initially, priority is being given to the development of a Tsunami Warning System (TWS)
and support programs to empower threatened communities to respond correctly to alerts
and warnings.
Although the consequences of future tsunamis are likely to be more severe than past
events, it is a fact that the recurrence rate of these events is quite low. Decision-makers
usually devote limited resources to current and the most salient problems rather than to
problems that may not occur during their term of office. To do otherwise, a decisionmaker must have a cost-effective justification. Not only are Tsunami Warning Systems
expensive to establish, they are also difficult to sustain and require high levels of
coordination and commitment to function effectively. Close collaboration among
institutions and organizations of several countries is a needed for rapid exchange of data
and warnings and to maintain the seismic and ocean observing system. An initial goal in
establishing the TWS is to pool and use resources from existing regional monitoring and
disaster management systems in a synergistic manner so as to attain cost-efficiency at all
levels of design and operation. The same principle will also be applied to new
overlapping networks being established by adjacent jurisdictions.
The Seismic Research Unit (SRU), University of the West Indies currently operates a 60station seismic volcano and earthquake monitoring network in the Eastern Caribbean.
The Unit is well positioned to provide meaningful contributions to the TWS and the
broader hazard mitigation initiative. It brings to the pool, several dedicated staff
members with a wealth of experience, a substantial amount of resources and a network of
support that has played a key role in its operation that has been sustained for over fifty
years.
Some level of upgrade is needed to transform strategically located SRU
installations to the status required to contribute to the TWS network and for the Unit
headquarters to function as a TWS sub-focal center. It is however anticipated that the
cost/benefit advantage of the target multi-hazard system will attract the support needed
and spawn the development of techniques to overcome technical and other obstacles.
Through collaboration with other institutions SRU will secure improved data
communication links and other resources that will facilitate real-time transfer of data on
current Volcano Surveillance, Seismic and Sea observing networks and support
complementary programs such as real-time geo-dynamic monitoring .
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17th Caribbean Geological Conference 2005, San Juan PR
BOLIVAR: A Snapshot of the Caribbean-South American plate Boundary at
67.5W
M.B. Magnani, C.A. Zelt, A. Levander, S.A. Clark and the BOLIVAR Working Group
Department of Earth Science, Rice University, Houston, TX, USA
The active seismic component of the BOLIVAR experiment (Broadband Ocean Land
Investigation of Venezuela and the Antilles arc Region), funded by NSF Continental
Dynamics involved the acquisition of ~6000 km of marine reflection profiles, four
onshore/offshore/OBS profiles across the Venezuelan margin and seismic recording on
six of the Leeward Antilles arc and Venezuelan islands (see Levander et al., this session).
The five main transects were designed to image the upper mantle and crustal structure of
the South American-Caribbean (SA-Car) plate boundary at different stages of its
evolution as the Americas moved west and the Caribbean collided obliquely with SA.
The multi-channel marine reflection data and the onshore/offshore wide-angle data along
one of these transects approximately along the 67.5W meridian and adjacent reflection
profiles provide a snapshot of the plate boundary processes since the Antilles subduction
zone passed this point of the margin at ~30 My.
The seismic data document the complex evolution of the plate boundary starting from the
development of the Caribbean Mountain system and the accretion of the volcanic arc on
the SA continental margin, and the opening of the Falcon-Bonaire-Grenada basins (~55
Ma). The south-dipping subduction of the Caribbean plate started at 28 Ma and the
Moron-El Pilar dextral strike-slip system developed at about 12 Ma, inverting several
Paleogene extensional features on the southern edge of the Bonaire-Grenada basin.
The wide-angle data show a complex crustal velocity structure underneath the volcanic
arc, where the Moho is at about 27 km depth, under the Bonaire basin, where the Moho
rises to about 25km depth, and across the Moron-El Pilar strike-slip system, where the
Moho drops abruptly to about 40 km underneath the South American continent. The
Moron - El Pilar fault is associated with high velocities (~6.5-7.0 km/s) visible to about
15 km depth. A similar high velocity structure characterizes the northern edge of the Los
Aves and Los Roques block, where the reflection data image the backstop of the
Caribbean Deformed Belt.
For more information: http://earthscience.rice.edu/BOLIVAR.html
Subduction Zone Dynamics And Interpretation Of Caribbean Fossil Suture Zones
*
Maresch, W.V.* and Gerya, T.V.**
Institute of Geology, Mineralogy and Geophysics, Ruhr-University of Bochum, 44780
Bochum, Germany
**
Geological Institute, ETH - Zürich, CH-8092 Zürich, Switzerland,
The Caribbean area is characterized by well-preserved fossil collision zones to the
north and south, in which oceanic subduction-zone/island-arc complexes have been
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17th Caribbean Geological Conference 2005, San Juan PR
sutured to and preserved along the adjoining continents. The dynamics of these extinct
subduction-zone/island-arc systems and the processes accompanying the actual collision
are of both general interest in understanding "subduction-zone factories" world-wide, and
of particular interest in reconstructing the tectonic history of the Caribbean area. The
study of exposed metamorphic rocks in suture zones allows the "depth dimension" to be
incorporated into terrane analysis. The study of exposed magmatic rocks yields
information on input, output, conveyor belts and plant facilities of the subduction-zone
factory. It has become possible in recent years not only to formulate realistic models of
the subduction-zone factory in general and of oceanic subduction-zone/island-arc
complexes in particular, but also to allow visualization of these multi-parameter
numerical models, so that interactive optimization on the basis of field and laboratory
data becomes possible. This presentation will focus on the following specific topics and
relate them to Caribbean examples: 1) Why can arrays of pressure-temperature-time
paths determined for high-pressure metamorphic rocks provide critical constraints on the
history and development of a particular subduction zone rather than providing evidence
for different subduction zone types? The San Juan Complex of the Dominican Republic
provides a text-book example. 2) Can subduction-unrelated simple overthrusting/stacking
of rock series produce blueschists? Are blueschist belts without an accompanying
volcanic arc possible? What, for instance, is the significance of blueschist pods in the
Cangre belt of western Cuba? 3) Arc volcanics are one end-product of the subductionzone factory. How variable can geochemistry be for a given geometry and constant type
of input? 4) Can a subduction-zone "flip" really be a true flip? Can high-pressure rocks be
"keel-hauled" from one side to the other of a "flipped" volcanic arc?
Late Cretaceous Charophytes From Puerto Rico
Michael Martínez(1), Adriana García(2), Shirley Mercado(1), Simon Mitchel(3), and
Eduardo A. Musacchio(4).
(1) GeoScience Education Program, Universidad del Este, PR; (2) School of Earth and
Environmental Sciences, University of Wollongong-Australia; (3) Department of
Geology, University of West Indies-Jamaica; (4) Universidad Nacional de la PatagoniaArgentina
Late Cretaceous (Uppermost Maestrichtian) sediments and sedimentary rocks from the
Upper El Rayo Formation, southwest Puerto Rico, has yielded the first occurence of
fossil charophytes (Charales).
The fauna consists of Feistiella gildemesteri
(Maestrichtian-Paleocene), Platychara grambastii (Maestrichtian), Platychara cf.
cruciana, Feistiella cf. anluensis and Amblyochara sp. Fossil charophytes have been
described elsewhere in the Caribbean-Greater Antilles but this assemblage reassembles
those found in Peru and Argentina during the Late Cretaceous (Maestrichtian). In the
Central Inlier in Jamaica, the Thomas River Formation, formerly known as Slippery Rock
Formation, fossil charophytes have been described as: Platychara grambastii, Porochara
cf. anulensis, Porochara oblonga. This formation was assigned an age of 68mya based
on 87Sr/86Sr analysis on the rudistid Chiapasella radiolitiformis. The charophyte faunal
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assemblages, although sparse, never have been studied in detail in terms of distributional
patterns, biogeographical interrelationship between islands, and as a possible
Cretaceous/Tertiary boundary indicator in the Caribbean.
Cretaceous rocks of the Upper El Rayo Formation, are composed of basaltic to andesitic
volcanic flows interbedded with volcaniclastic conglomerates, sandstones, and
limestones. The charophyte bearing sediments are altered and weathered pyroclastic
materials overlying rudistid-bearing limestones. These altered materials marked the last
Cretaceous volcanic episode of the southwest Igneous Province of Puerto Rico.
Sedimentary analysis shows the development of deltaic environments
contemporaneous with the appearance of the charophytes. The discovered charophyte
assemblage provides supporting evidence, for the first time, of the presence of nonmarine (fresh water/brackish water) environments by the end of the Maestrichtian in
Puerto Rico.
Paleoecological Distribution (Benthic Foraminifera) along the
Oligocene/Miocene Boundary in Southern Puerto Rico: Local or Global
Implication?
Michael Martínez1, Carmen Urbina1, Wilfredo Morales1, Rosángela Pérez1, James
Galluzzo2, and Wilson Ramírez3
(1) GeoScience Education Program, Universidad del Este, PR; (2) Department of
Geology, Tulane University, New Orleans; (3) Department of Geology, University of
Puerto Rico-Mayaguez Campus
Benthic foraminifera distribution patterns, in the Santa Helena and Playa Jaboncillos
sections, of the Juana Díaz Formation are strongly related to relative sea level changes
with a global influence. These patterns not only show changes on species dominance
along the stratigraphic sequence but also show extinction events of larger foraminifera
(i.e. Lepidocyclina undosa, Lepidocyclina canelli) prior to the Oligocene/Miocene
boundary (planktic biozone: P21-M1; benthic biozone: Miogypsinoides sp., ~23.8 Ma).
This extinction event was not abrupt indicative of a non-catastrophic climatic change
allowing the slow demise of these larger foraminifera. Distribution patterns showed a
relative shallow water environment that prevailed during the Late Oligocene. An abrupt
decrease in sea level, during and after the Oligocene/Miocene boundary, evidenced a
stress to the Oligocene fauna and environment and is attributed to tectonic uplift. This
event favored an increase in species richness (opportunistic foraminifera) and a more
diverse fauna in the Early Miocene. This is indicative of a more stable tectonic setting,
hence, a more suitable environment for the foraminifera to flourish on the southern coast
of Puerto Rico.
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Holocene Ostracods/Foraminifera assemblages on reef/deltaic environments on
Lake Enriquillo-Dominican Republic:
Preliminary survey
(1)
Michael Martínez , Rebecca Abréu(2), Wilson Ramírez(3),and Carlos J. Santos(4)
(1) GeoScience Education Program, Universidad del Este, PR; (2) Department of
Microbiology, Universidad del Este, PR; (3) Department of Geology, University
of Puerto Rico-Mayagüez; (4) Department of Biology, University of Puerto RicoMayagüez
Lake Enriquillo, once a small seaway, is a hyper-saline lake in western Dominican
Republic formed by the enclosure of the area due to tectonic uplift. It is surrounded by
well developed fossil reef facies overlain by deltaic sequences containing very diverse
ostracod assemblages. The main purpose of this work is to document, for the first time,
the distribution patterns of fossil ostracods and foraminifera through the transition
between these environments (reef vs. deltaic). Scarce benthic and planktic foraminifera
were found in the reef facies (carbonate rich sediments). Ostracods were also scarce and
had the morphological characteristics of those found in fresh/brackish waters, indicative
of transport. This trend is persistent throughout the studied reef facies sequence.
On the other hand, rich epiclastic sediments of the deltaic facies showed a dominance
and high diversity of non-marine ostracods. Morphological differences between
ostracods are a result of different wave energy regimes or environments. Highly
ornamented morphologies (i.e. primary reticulation, tubercle, and dense tests) are
associated with sand rich sediments, indicative of a proximity to a shoreline. Less
ornamented morphologies (i.e. non-reticulated, punctae, smooth and delicate tests, etc.)
are characteristic of lower energy regimes or environments, associated with silty rich
sediments. Distribution cycles of ornamented and non-ornamented ostracods are the
result of changes in the sedimentation regimes due to changes in climate (i.e.
precipitation) and possible tectonics (uplift) of the studied area.
Upper Cretaceous (Maestrichtian) microfauna of the Thomas River and Guinea
Corn Formation in Jamaica (Central Inlier)
Michael Martinez(1), Shirley Mercado(1), Simon Mitchel(2), Adriana Gracia(3) and
Eduardo A. Mussacio(4)
(1) GeoScience Education Program, Universidad del Este; (2) Department of Geology,
University of West Indies-Jamaica; (3) School of Earth and Environmental Sciences,
University of Wollongong-Australia; (4) Universidad Nacional de la PatagoniaArgentina
Sedimentary sequences on Late Cretaceous (Maestrichtian) Central Inlier Jamaica,
represents different paleoenvironmental settings. These are represented by the Thomas
River and Guinea Corn Formations part of the Kellits Synthem. The studied section of
the Thomas River Formation consists of tidal influenced environment based on
sedimentary structures (sandstones/mudstone interbedding, laminated heterolithics,
flaser-wavyy-lenticular bedding, and rythmites), lack of marine fossils, and abundance of
fossil charophytes (fresh/brackish waters). Marine environments, on the other hand, are
represented by Guinea Corn Formation (late Maestrichtian) consisting of a diverse coral
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and rudist bivalve assemblages (i.e. Titanosarcolites giganteus and Chiapasella
radiolitiformis), abundant echinoid assemblages, and micrite matrix dominated
limestones. Preliminary fossil microfaunal analyses on both formations show a
relationship between sediment grain size and type of microfossil. Siltstones and
mudstones are characterized by being barren and occasionally ostracods (poorly
ornamented indicative of low energy environments) are in abundance with some benthic
foraminifera (Kathina jamaicensis).
Abundant smaller benthic foraminifera are
associated with fine grained silty sandstones.
The Thomas River Formation represent a two stage Highstand System Tract (HST):
stage 1- marine tidal flat deposits; and stage 2- fresh/brackish water charophyte bearing
tidal flat.
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Geochemical interpretation of Jamaican rocks displaying pozzolanic properties to be used
in the manufacture of cement
Mr. N. Mckenzie, Research Student/Mining Engineer
Department of Geography and Geology
University of the West Indies, Mona Kingston, 7 Jamaica.
Caribbean Cement Company LTD.
Rockfort, Kingston, Jamaica
nmckenzie@caribcement.com
The effect of pozzolan replacement for clinker in the cement industry is well known and
has developed over the years among major cement producers. The Caribbean Cement
Company Ltd (CCCL) a subsidiary of Trinidad Cement Company (TCL) has being using
pozzolanic material purchased from Martinique since 2002 as a replacement for clinker in
their blended cement product.
This study looks at two alternative sources locally for pozzolanic material as a means to
reduce cost and to optimise cement late days strength (28 days).
The high correlation (r value) between pozzolan from Martinique and local material
(volcanic tuff and andesite) is noted for the geochemistry and mineralogy. It is expected
that over similar geologic environment such as volcanics and ignimbrite that the
concentrated values would be similar and within the range of pozzolanic material used in
cement production.
Experimental data indicates that rocks of the study area show similarity in weight
percentage of SiO2, FeO3 and Al2O3 and that the pozzolan reactivity index is similar to
natural pozzolan. The material can be used as a percentage substitute for clinker in
cement production.
The results show that rocks of both study area when used as a mineral admixture show
progressive increases in strength with increasing percentages of replacement, up to the
15% level.
Capability Analysis of a Proposed Nine Station Seismic Network in the Caribbean
D. McNamara, H. Benz, P. Earle, J. Odum, J. McCarthy, B. Presgrave, J. Weaver, B.
Leith, C. Hutt, D. Oppenheimer
The USGS will deploy nine seismic stations to monitor earthquake activity in the Caribbean region as
a part of the Global Seismograph Network (GSN) by September of 2006. The new seismic network is part
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of a larger effort to monitor and mitigate tsunami hazard in the region. Destructive earthquakes and
tsunamis are known to be a threat in various parts of the Caribbean. These natural hazards cause damage,
not only from strong ground shaking and surface rupture, but also from liquefaction, extensive land sliding
and tsunami waves. A critical component for the accurate assessment of earthquake hazards in the region is
local and regional monitoring of seismic activity and deformation. Long-term monitoring of active faults
provides critical information needed for response activities, local and regional planning and, ultimately,
building resilient communities throughout the Caribbean. Installation of the new seismic network is a
collaborative effort that will involve contributions from several participants from the United States
Geological Survey (USGS), the Puerto Rico Seismic Network (PRSN), Seismic Research Unit of the
University of the West Indies, and several additional institutions in the Caribbean region. In this
presentation we assess the capabilities of the proposed seismic network using three different measures of
capability. The three measures of network capability are: 1) minimum Mw detection threshold; 2) response
time of the automatic processing system and; 3) theoretical earthquake location errors. For the proposed
upgrade scenario we demonstrate that considerable improvement in network magnitude threshold, response
time and earthquake location error can be achieved. We also demonstrate that the technique used in this
analysis is valuable for quantifying seismic network capability improvements and a useful tool for network
design planning.
A Preliminary Evaluation of Tsunami Hazard and Risk in Jamaica Using A
Geographical Information System (GIS)
Mr. S. Miller, Research Student
Dr. Martin Degg, Senior Lecturer
Department of Geography,
University College Chester,
Parkgate Road, Chester,
Cheshire,
CH1 4BJ, UK.
s.miller@chester.ac.uk , m.degg@chester.ac.uk
The December 26, 2004, tsunami in the Indian Ocean served to highlight the dramatic
escalation of tsunami risk that has occurred in low-lying regions with significant tourist
development. Island economies of the Caribbean region are strongly dependent on
tourism for their economic survival, and low-lying coastal areas of the region have
witnessed phenomenal rates of development during the last three decades. This paper
shows that many of these areas are exposed to significant tsunami hazard, and that this
hazard has been largely overlooked compared to the attention and resources devoted to
mitigating the seemingly more immediate threats posed by hurricane activity.
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The paper presents a regional review of tsunami hazard that sets the context for a specific
assessment of tsunami hazard and risk on the island of Jamaica. This country experienced
damaging tsunamis in 1688, 1692, 1780, 1812, 1881 and 1907, but the coastal zone was
far less intensively developed then than is now the case. A Geographical Information
System (GIS) is used to create a preliminary tsunami hazard map for Jamaica. This
highlights that the severity of the tsunami hazard varies quite considerably around the
coastal zone, and that some of the most highly urbanised and most economically
important parts of the country are potentially at risk. The paper concludes by considering
risk reduction strategies that might be employed in these areas to reduce the potential for
catastrophic human and economic impact from future tsunami occurences.
GIS and Landslide hazard mapping in St. Thomas Jamaica
Mr, S. Miller, Research Student
Department of Geography,
University College Chester,
Parkgate Road, Chester,
Cheshire CH1 4BJ.
s.miller@chester.ac.uk
Landslides are a major natural hazard in Jamaica, and have resulted in loss of life, major
economic losses, social disruption and damage to public and private properties. The
parish of St. Thomas has the highest incident of slope instability on the island and is
extremely prone to catastrophic landslides. The Judgement Cliff landslide in the parish is
arguably the most infamous landslide on the island, and in 1692, killed 19 people and
moved a settlement half a mile from its original location. St Thomas is particularly prone
to slope instability due to its geology, steep and partially bare slopes, deeply weathered
soils, improper land-use and high rainfall intensity. There is a need to delineate the areas
that are prone to landslippage in order to mitigate their effects. One way of achieving
this is to create landslide susceptibility maps in a Geographical Information System
(GIS).
There are a number of GIS methodologies that may be employed to create susceptibility
maps but care must be taken to choose the best method that is suitable for the terrain and
the contributing factors to slope instability unique to Jamaica. Five methods were
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examined, these were; Simple overlay, Index overlay, Fuzzy logics, Multiple logistic
regression and Bayesian conditional probability. Of these five methodologies, the
Bayesian, Fuzzy Logics and Multiple logistic regression methods has the highest rate of
success in classifying the existing and ‘future’ landslides into the high and very high
susceptibility zones and may be useful in creating models for other areas of Jamaica.
Stratigraphy of the Sunning Hill Inlier, SE Jamaica: rudist faunas upside down
Simon F. Mitchell
Department of Geography and Geology University of the West Indies, Mona Kingston 7,
Jamaica
The geological succession in the Sunning Hill Inlier has been determined by geological
mapping at a scale of 1:12,500 and the collection of rudist assemblages. The oldest rocks
are a thick pile of andesitic lavas. These are succeeded by a thin red-bed sequence of
locally derived conglomerates and sandstones with occasional calcrete palaeosols. The
red beds are succeeded by a thin sequence of limestones and shales with abundant in situ
fossils. The fauanl assemblage includes abundant actaeonellid gastropods, the echinoid
Hemiaster, and rare rudists. Rudists from loose blocks include ‘Barrettia’ sp. nov. aff.
“B.” gigas and Torreites chubbi. This assemblage is of Early Middle Campanian age. The
limestones are succeeded by a sequence of mudstones and conglomerates. The
conglomerates contain a diverse assemblage of individual transported rudists including:
Barrettia coatesi (Chubb), Durania lopeztrigoi (Palmer); Durania curasavica (Martin),
Bournonia sp. and Biradiolites sp. This assemblage is clearly of Middle Santonian age.
The conglomerates are replaced up section by interbedded sandstones and shales
(?turbidites). The succession is interpreted in terms of pre-rift and syn-rift deposits. The
andesites and red beds at the base of the succession are interpreted as pre-rift deposits.
Rifting began in the Early Campanian and the rift was flooded by marine waters
producing a marine limestone. Further subsidence saw the appearance of extensive
reworked material from the rift margins including abundant Santonian rudists. The results
of this study indicate that care must be taken when reworked rudist assemblages are used
to date succession, as such assemblages may be reworked into younger stratigraphic
intervals.
Tidal deposits in the Kellits Synthem (Maastrichtian) of the Central Inlier, Jamaica
Simon F. Mitchell
Department of Geography and Geology University of the West Indies, Mona Kingston 7,
Jamaica
The Thomas River, Guinea Corn and Green River formations form part of the major (3rd
Order) transgressive-regressive, Maastrichtian-Paleocene Kellits Synthem. The synthem
is extensively exposed across the Central Inlier of central Jamaica and all available
stratigraphic sections have been logged. Using a sequence of faunal event beds and
biostratigraphic markers (mainly rudists and corals) it is now possible to correlate smallscale cycles (circa 40 kyrs) across the inlier. The sedimentology of these cycles has been
investigated and a strong tidal signature has been recognised. The following major tidedominated facies associations are recognised. 1, Supratidal red mudstones with paleosols.
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2, Intertidal mud-flat deposits with mm-scale interlaminated mudstones and organic-rich
(plant debris) layers with a restricted marine/brackish water fauna/flora. 2, Laminated
mudstones and sandstones with symmetrical and asymmetrical ripple form sets. 4, Tidal
channel heterolithics (interlaminated mudstones and sandstones) with flaser, wavy and
lenticular bedding, and basal erosion surfaces/shell beds. 5, Tidal channel sandstones and
granule conglomerates with erosional bases. 6, Tidal sandwave complexes with low angle
cross bedded sets up to several meters thick consisting of carbonate or mixed clasticcarbonate sands in 20-40 cm thick beds. The tidal deposits characterise the transgressive
systems tracts of the high frequency cycles in the Kellits Synthem, and there is a
significant spatial separation of diverse rudist-coral assemblages and the tidal deposits
(although some rudists occur as reworked elements in some tidal deposits, they are
invariably interpreted as reworked from older limestones). This suggests a tidally
dominated inshore zone with clastic and mixed clastic-carbonate deposits and an offshore
carbonate or mixed clastic-carbonate zone with diverse rudist and coral assemblages.
Cretaceous and Cainozoic evolution of Jamaica.
How does it test the current models?
Simon F. Mitchell
Department of Geography and Geology, University of the West Indies, Mona Campus,
Kingston 7, Jamaica.
Throughout the Cretaceous and Cenozoic Jamaica has been situated close to the northern
boundary of Caribbean Plate and contains a record of the changing geological
development of this plate boundary. Extensive studies on this succession have resulted in
the development of a well-constrained chronology, and can be used to compare the
various models suggested for the evolution of this part of the Caribbean.
Jamaica is divided into two terrains with different geological histories: the
Cornwall-Middlesex Block, and the Blue Mountains Block. The Cornwall-Middlesex
Block has a three-fold stratigraphy: a pre-Santonian sequence of volcanics and rudistbearing limestones; the Crofts Synthem (Santonian to Campanian rudist-bearing
limestones and deep water clastics); and the transgressive-regressive Kellits Synthem
(Upper Maastrichtian-Paleocene). The Blue Mountain Block has a Turonian-Conician
ophiolite suite, and a Santonian to Early? Maastrichtian island arc suite (limestones
indicating the Santonian, Early Middle Campanian and Early? Maastrichtian).
Rifting progressed across the island from late Maastrichtian time onwards: Latest
Maastrichtian to Early Paleocene in the John Crowe Trough; Late Paleocene to Early
Eocene in the Wagwater Trough and North Coast Belt, and Middle Eocene in the
Montpelier–Newmarket Trough, Negril–Sav-la-Mar Trough and Walton Basin. The
resultant Block and Trough topography/bathymetry controlled Neogene sedimentation
patterns, with mixed deltaics (Middle Eocene) and shallow-water platform limestones
(Middle Eocene to Miocene) on the blocks, and deep-water pelagic and mass-flow
deposits in the troughs.
In the Miocene, tanspression affected Jamaica with differential uplift and
subsidence. The Tertiary limestone cover of the uplifted regions was stripped off and the
volcano-sedimentary successions beneath exposed to erosion. This provided extensive
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clastic detritus that were shed into the adjacent basins to form thick mixed clasticcarbonate sequences.
Cretaceous (Campanian and Aptian) Radiolarians of the Washikemba Formation,
Bonaire, Netherlands Antilles
Homer Montgomery, Emile Pessagno, Mohsen Kariminia
University of Texas at Dallas
The Cretaceous Washikemba Formation of western Bonaire is composed of a 3-km-thick
package of pillow lavas, volcaniclastic sediments, and rhyodacite flows in the Southern
Complex and a 5-km-thick accumulation of volcanics, pelagic sediments, and
volcaniclastic sandstones in the Northern Complex. The formation is reported to contain
upper Albian ammonite imprints in the Southern Complex and Coniacian inoceramids
and Turonian and Coniacian planktonic foraminifera in the Northern. Ar-Ar dating
suggests a minimum age of 95 + 2 Ma for a rhyodacite flow. This age is not completely
reliable due to the degree of alteration. Recently, 18 outcrops of chert in the Washikemba
were sampled with only two, both dark blue-gray to black chert in the Southern Complex
located near Punt’l Wekua, yielding radiolarian microfossils in HF residue. One sample
contains a well-preserved radiolarian assemblage of low diversity. The occurrence of
Archaeospongoprunum hueyi, a taxon presently known only from the upper Campanian,
suggests that at least part of the Washikemba may be younger than previously reported.
Campanian radiolarians are common in the Caribbean being reported in Puerto Rico,
Hispaniola, Cuba, Panama, and DSDP Site 146 drilled between Hispaniola and
Venezuela. The second sample contains a diverse fauna of well-preserved radiolarians
that are likely Aptian based on the presence of Thanarla conica, Pseudodictyomitra
carpatica and Sethocapsa sp. among many other forms. The discovery of radiolarians in
the Southern Complex of the Washikemba that are both older (by 10-20 Ma) and younger
(by 10 Ma) than any previously reported fossils will necessitate rethinking the
stratigraphy of the formation as well as perhaps reevaluating the significance of the
reported geochemistry characteristics.
USGS Seismic Hazard Maps for Puerto Rico and the U.S. Virgin Islands
Charles S. Mueller, Arthur D. Frankel, Mark D. Petersen, and E. V. Leyendecker
U.S. Geological Survey, Golden, CO
New seismic hazard maps for Puerto Rico and the U. S. Virgin Islands were developed
by the U.S. Geological Survey in 2003. Modeled seismic sources include: 1) subductioninterface and crustal faults with known rates, 2) gridded seismicity to account for
subduction-intraslab activity and crustal activity not associated with specific faults, and
3) zones of crustal extension in the Mona Passage and Anegada Passage regions with
activity rates determined by GPS geodesy. Attenuation relations are derived from
worldwide data for subduction sources and from western North America data for crustal
sources; alternative relations are combined using logic trees. A new Caribbean-specific
relation gives large high-frequency ground motions, and is used with low weight; it has
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since been revised, and we will show the sensitivity of the computed hazard to the
revision.
We map mean, time-independent, probabilistic peak ground acceleration and 1.0-, 0.3-,
and 0.2-s spectral acceleration for a Vs30= 760-m/s site condition. Example pga values
for 10% probability of exceedance in 50 years are 0.23 g at San Juan, 0.25 g at
Mayaguez, 0.21 g at Ponce, and 0.28 g at Charlotte Amalie. At San Juan contributions
from shallow and deep gridded seismicity and Puerto Rico Trench subduction dominate
the hazard about equally for pga greater than about 0.10 g, with shallow seismicity
increasingly dominant above 0.40 g. At Mayaguez and Ponce shallow and deep gridded
seismicity dominate over the Mona Passage extensional source and Puerto Rico Trench
subduction for pga equal to about 0.10 g, but the Mona Passage source dominates above
0.25 g. At Charlotte Amalie shallow and deep gridded seismicity dominate for all pga.
Deaggregations indicate that the South Lajas Fault can be a major contributor to local
hazard in southwestern Puerto Rico for some exceedance probabilities, showing the
importance of identifying other active onshore faults.
Timing And Duration Of The Last Interglacial Period From U-Series Ages Of
Unaltered Reef Corals, Northern And Western Puerto Rico
MUHS, D.R., U.S. Geol Survey, MS 980, Box 25046, Federal Center, Denver, CO
80225, dmuhs@usgs.gov, SIMMONS, K.R., U.S. Geological Survey, MS 980, Box
25046 Federal Center, Denver, CO 80225, TAGGART, B.E., U.S. Geol Survey, 10
Bearfoot Road, Northborough, MA 01532, PRENTICE, C.S., U.S. Geol Survey, 345
Middlefield Rd., MS 977, Menlo Park, CA 94025, JOYCE, J., Dept. of Geology, Univ of
Puerto Rico, Mayagüez, PR 00681, and TROESTER, J.W., U.S. Geol Survey, 651
Federal Drive, Suite 400-15, Guaynabo, PR 00965-5703
Although there have been many studies of last-interglacial (LIG) shorelines (emergent
reefs and terraces), there are still uncertainties about the timing and duration of LIG sea
level elevations near or above the present sea level. The island of Puerto Rico has
probably experienced slow, long-term uplift in the late Quaternary (on the order of 0.030.05 m/ka) and therefore sea level records need to be interpreted with caution.
Nevertheless, LIG reef tract deposits are common along much of the northern and
western coasts of Puerto Rico and contain well preserved corals (95-100% aragonite). We
analyzed corals from localities near Palmas Altas, El Vigia, Punta Agujereada and Punta
Higüero for U-series dating. Corals in growth position are common in most reef tracts
and are found at elevations between about 0.5 and 1.5 m above high tide level. Of 19 LIG
corals analyzed, all have U contents similar to their modern counterparts and low
common Th contents. Fifteen of the corals have back-calculated initial 234-U/238-U
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activity ratios of 1.140 to 1.154, overlapping the range of values found in modern
seawater. These 15 samples indicate probable closed-system histories with respect to Useries nuclides and yield ages with a high degree of confidence. Ages range from 127.7 ±
0.7 ka to 114 ± 2 ka (two-sigma errors); one sample gave an age of 105.0 ± 0.5 ka. In the
Holocene, sea level rose to present levels several thousand years after the high-latitude,
Northern Hemisphere summer insolation peak at ~11 ka. The Puerto Rico coral data
presented here indicate that sea level was near or above present at the time of the
previous summer insolation peak at ~127 ka. Further, the Puerto Rico data indicate that
the LIG high sea level probably lasted a minimum of 12 ka. This contrasts with the deepsea oxygen isotope record, wherein the LIG high sea stand is thought to have had a
duration of only about 7 ka at most.
Aquifer Recharge thru Sinkholes
Presented by: Omar Negrón, P.G.
President
GEOWORKS, INC
20 of the most beautiful sinkholes in the north of the island aretested to obtain their
aquifer recharge potentials. Sinkholes varying in diameter from 10 to 160 feet wide and
varying in depths from 10 to 70 feet. Field tests were developed by GEOWORKS, INC.
to obtain detailed modeling of their natural potentials. Results were used to define their
collapse potentials, water management capabilities and engineering mitigation to its
surroundings. Previous methods used pumping water at high gpm’s, but a different
approach was developed to emphasize on testing the sinkholes via rapid
massive water discharges in excess of 75 CFS using aluminum containers that served as
water reservoirs. Over 20 sinkholes tested in various projects presented convincing
results of how the sinkholes managed the massive water outputs. 7,000 to 20,000 gallons
of water were observed to be managed thru this natural systems within seconds of
receiving the massive water output almost Hollywood style. Obtained data was followed
by comprehensive drilling, geophysical and geothecnical analysis. The presentation is a
combination of the methodologies used, comparison with other modeling techniques and
data extrapolation. Various types of sinkholes are seen trhu video at the moment
of the modeling and others are presented trhu photographs and aerial views. A great
display of the awesome power of water and limestone geology.
Seismic Study Of The Subduction To Strike-Slip Transition Of The
North American-Caribbean Plate Boundary In The Dominican Republic
Denisse Ocasio Campos1, Jay Pulliam1, Victor Huérfano1, Christa von HillebrandtAndrade1,
Ivelisse Camacho1, Luis Odonel Gomez2, Juan Payero3
(1) Red Sísmica de Puerto Rico, Dept. de Geología, Universidad de Puerto Rico,
Mayagüez, PR
(2) Instituto Nacional de Recursos Hidráulicos, República Dominicana
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(3) Instituto Sismológico Universitario de la Universidad Autónoma Santo
Domingo, Ciudad Universitario, Apto. Postal 1335, Santo Domingo,
República Dominicana
The Northern Caribbean Plate Boundary Zone is a complex region that has been modified extensively
by the relative eastward movement of the Caribbean Plate and the plate’s impact with the buoyant Bahama
carbonate platform (see Figure). The results include extensive subduction of oceanic crust belonging to the
North American Plate, a broad zone of deformation to accommodate strain, the development of several new
transform and normal faults to relieve stress after collisions, the formation and rotation of microplates, and
the rearrangement and aggregation of crustal fragments into new islands.
On 22 September 2003, a large (mW=6.5) earthquake struck the Dominican Republic, causing
widespread damage that included partially collapsed buildings and bridges in the cities of Santiago and
Puerto Plata and landslides in the mountainous outlying areas. Aftershocks reaching mW =5.1 followed for
weeks afterward. This earthquake sequence is the strongest to affect the Dominican Republic since a series
of powerful thrust events, including five earthquakes ranging in magnitude from 7.1 to 8.1, occurred
between 1943 and 1953. Prior to 1943, significant earthquakes occurred in 1564 (in which the city of
Santiago was destroyed), 1783, 1842, 1887, and 1897.
Following the 2003 Puerto Plata main shock we deployed 10 broadband seismographs borrowed from
IRIS’ PASSCAL Instrument Center around the aftershock zone for a period of two months and analyzed
the data jointly with data from two permanent seismic networks in the DR. Analyses included estimating a
new 1D model of earth structure, re-locating more than 300 aftershocks, producing a 3D tomographic
model of the fault zone from phase arrivals, and computing focal mechanisms. We will report the results of
these analyses and their implications for regional structure, processes and seismic hazard.
Schematic of the Northern Caribbean Plate Boundary Zone with
the location of the 22 September 2003 main shock (red star).
(inset) Map of currently and recently operating seismic stations in the Dominican Republic. The
symbol indicates the station’s network affiliation: ISU stations are S1-10 and ISU01-10; INDRHI
stations are DR01-16; PRSN/UT temporary stations are YB01-10. The star is a broadband
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station at PUCMM in Santiago. Symbol color indicates the sensor’s passband: red = shortperiod, green = intermediate-period, black = broadband. Black outlines indicate three-component
sensors.
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Near-Surface S- And P-Wave Velocities, Vs30, And
NEHRP Site Classification At Selected Urban And
Seismograph Sites Within The Commonwealth Of Puerto
Rico
Jack K. Odum1, Robert A. Williams1, William J. Stephenson1, Christa von
Hillebrandt-Andrade2, Eugenio Asencio3, and Antonio Cameron2
1
2
U.S. Geological Survey, Geologic Hazards Team, Golden, CO
Puerto Rico Seismic Network, University of Puerto Rico- Mayagüez, PR
3
Department of Geology, University of Puerto Rico-Mayagüez, PR
Studies over the last few decades have established that shear-wave seismic velocity (Vs) in
the upper 30 to 60 m can greatly influence the amplification and duration of earthquake ground
motions observed at the surface. The determination of near-surface seismic velocities is motivated
by their use in the National Earthquake Hazards Reduction Program (NEHRP) model code
provisions (Building Seismic Safety Council, 1997).
In 2004 and 2005, the Puerto Rico Seismic Network (PRSN), the Puerto Rico Strong
Motion Program (PRSMP) and the Geology Department, all of the University of Puerto-RicoMayagüez (UPRM), collaborated with personnel from the U.S. Geological Survey to study Vs and
compressional-wave velocities (Vp) in and around major urban areas of Puerto Rico and at some
seismic stations of the PRSN and PRSN (see arrows on figure). Using noninvasive seismic
refraction-reflection profiling techniques, we acquired velocities at 27 locations. Sites within the
urbanized areas were selected to sample near-surface materials associated with the primary
geologic units within the urbanized areas. Geologic units surveyed included Cretaceous intrusive
and volcanic bedrock, Tertiary sedimentary units, and Quaternary and Holocene fluvial, beach,
and lagoon unconsolidated deposits.
From the acquired data we constructed Vp and Vs depth columns, calculated average V S
to 30-m depth (VS30), and derived NEHRP site classifications for the 14 sites from the 2004
campaign. The distribution of determined NEHRP classes is as follows: two class “E” (Vs30
below180 m/s), six class ”D” (Vs30 between 180 and 360 m/s), five class “C” (Vs30 between 360
and 760 m/s), and one class “B” (Vs30 greater than 760 m/s). Results will be used to calibrate site
response at seismograph stations and in the development of regional and local Shake Map models
for the Commonwealth of Puerto Rico. The data from the 13 additional sites surveyed in 2005 are
currently being processed.
Relief map of Puerto Rico showing (white arrows) location of Vs and Vp sites.
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Sedimentation And Coral-Reef Development: Enriquillo Valley, Sw Dominican
Republic
ORAM, Jessica1, HUBBARD, Dennis K. 1, BREWER, Joshua1, STEIN, Alexandra1,
TOMLINSON, Michael1, TIMMONS, Erikson1, RAMIREZ, Wilson3, and DAVIS,
Allicia1, (1) Dept. of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074,
(2) Dept. of Geology, University of Puerto Rico, PO Box 9017, Mayaguez, PR 00681
contact: dennis.hubbard@oberlin.edu
A well-developed Holocene reef exposed at Cañada Honda in the western Dominican
Republic provides an ideal opportunity to map coral-reef facies, and to relate both species
distribution and colony shape to location on the reef, paleo-water depth and presumed
rates of sedimentation. Where sedimentation was slower, hemispherical colonies similar
to those seen in the massive-coral zone of most Caribbean reefs dominate. Where
sedimentation was higher, colonies progressively take on conical and then columnar
morphologies as lateral growth is increasingly discouraged. Regardless of average
sedimentation rate, ragged colony margins accurately record periodic increases in
sedimentation, followed by lateral overgrowth of the substrate by the remaining live
colony. The result is a fluted colony that resembles a “Christmas tree” or a “stack of
pancakes”. Detailed measurements of density banding seen in X-radiographs reveal that
average growth rate in the Dominican corals (1-4 mm/yr) is lower than that for similar
species in less stressed settings (5-10 mm/yr) throughout the Caribbean. Sedimentation
pulses responsible for the “pancake” morphology described above recur with a roughly
decadal periodicity.
Data from 1-m2 quadrats along vertical transects throughout the outcrop provide
quantitative information on overall coral abundance (>60%) and species diversity (27) in
the reef. Storm layers provide “time lines” along which species patterns can be measured
and compared to similar data from modern Caribbean reefs. Together, these data provide
a detailed picture of a diverse but slower-growing coral community that was well-adapted
to elevated sedimentation. The surprising diversity in this reef is to some degree contrary
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of our perceptions of reef-community structure in sediment-stressed areas, and may
provide a valuable tool for separating reefs exposed to chronic natural stress from those
under the increasing influence of anthropogenic sedimentation.
Micro-Boudinage In Blueschists Of Eastern Jamaica
Pallov Pal and Grenville Draper
Department of Earth Sciences
Florida International University
Miami, FL 33199, USA
The ?lower Cretaceous blueshist-greenschist grade Mt. Hibernia Schists in eastern
Jamaica show well-developed examples of micro-boudinage in relict, originally igneous,
augite grains. The rocks have been examined using conventional quantitative microscopy
and a new, promising technique that successfully combines digital, microscopic images
and GIS to make measurements easier and more accurately. Comparison of bulk strain
estimated from elongated sphene aggregates, that appear as white streaks in the XZ and
XY sections in hand specimens of the rock, with that of the boudinaged augites indicate
that the boudin trains underestimate elongation by ~50% using Ramsay’s classic method.
The more recently devised Strain Reversal (SR) method, which takes into account farfield matrix strain, also produces similar underestimates. Relict igneous augites are
boudinaged with the inter-boudin gaps being successively filled by secondary grains of
quartz, crossite and actinolite sometimes in a quasi-symmetrical, other times in an
asymmetric manner. The infilling minerals in the boudin gaps indicate a crack and fill
mechanism, taking place syn-metamorphically. It is suggested that the gaps opened as
metamorphic fluid composition changed. Thus, the textures may provide a test of the
mid-point fracture model of Ramberg’s classical study, and SR method.. This analysis
may further lead to methods of assessing strain rate and relative differential stress
conditions during deformation of these rocks. .
Field Development in a Challenging Geological Environment
The Angostura Story
The Greater Angostura Structure, comprising the Kairi, Canteen, Aripo and Angostura
structurally defined areas, lies offshore Trinidad and Tobago in Block 2(C). Development
drilling on the structure began in September of 2003 and First Oil was achieved in
January of 2005.
The Angostura Development is centered on the production of oil and gas reservoired
within the Angostura Sandstone, a thick Early to Middle Oligocene sequence of sediment
gravity flows that are interpreted to have been deposited in a slope type setting.
Hydrocarbons were first discovered on the structure with the drilling of Angostura-1 in
the second quarter of 1999, but it was not until the discovery of a moderately thick oil
column underlying an extensive gas cap in Kairi-1, drilled in August of 2001, that the
pace of field appraisal and subsequent development quickened.
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With data from a limited number of exploration and appraisal wells and a seismic data set
of moderate to poor quality covering a fairly large structure with a varied and complex
history, the field development plan needed to have a strong focus on technical risk
mitigation.
Since development drilling began, a combination of nineteen appraisal and development
wells have been drilled on the structure with data from each successive well assisting in
modifying and refining the forward drilling plan. Technical challenges encountered
during the development programme have been reduced and overcome by maintaining
flexibility within the plan and by maintaining and developing contingencies on both a
well-by-well and whole programme basis.
Proto-Caribbean slab-window origin for the Caribbean Large Igneous Province
James Pindell, Dept. of Earth Science, Rice University, 6100 Main Street, Houston,
Texas, 77005 USA jim@tectonicanalysis.com
A common belief is that the Caribbean large igneous province (CLIP) was
extruded as Caribbean lithosphere passed over Galapagos hot spot (GHS) before entering
the inter-American gap from the Pacific. However, (1) Guatemalan and Andean
stratigraphies indicate Caribbean-American tectonic interactions by Turonian during
CLIP extrusion, such that the Caribbean was east of paleo-GHS [if fixed mantle
reference] by then; (2) GHS can be dated to Oligocene only, leaving doubt about is
Cretaceous existence; (3) it is unclear how GHS might have affected an area as large as
CLIP; (4) Costa Rica arc began in Albian according to sandstone mineralogy, thus the
Galapagos model requires the Costa Rica Benioff Zone to have passed over GHS after
CLIP extrusion (unlikely). I propose instead that a slab window formed as the ProtoCaribbean spreading ridge was subducted beneath Caribbean Plate during entry into the
widening inter-American gap, through which Proto-Caribbean mantle convection reached
the base of Caribbean lithosphere. Caribbean migration between the Americas from the
Pacific began ~120 Ma, as shown by (1) Hi-P suites along the Caribbean’s eastern edge
dating back to Aptian, (2) “Antillean-Cycle” Caribbean arcs dating back to Albian.
Atlantic magnetics show that Proto-Caribbean spreading continued to Santonian. Thus
the Proto-Caribbean Ridge was subducted from Aptian to Santonian, exactly matching
the period of CLIP extrusion. Paleotectonic maps integrate Caribbean-American
interactions and the formation of Hi-P suites, Antillean arcs, and the slab window whose
size approached that of the CLIP by 90Ma (most common age of CLIP). Observed midCretaceous Caribbean crustal extension and CLIP volcanism is reminiscent of Basin and
Range geology, but in oceanic crust. Field examples of the CLIP (Aruba, Hispaniola)
indicate partial subaerial exposure during extrusion, carrying thermal implications for
Caribbean sedimentary basins. The slab window model may explain why certain
batholiths (e.g., Aruba Batholith) are not necessarily arc related.
This work forms part of the regional framework of the BOLIVAR NSF-funded
research program assessing crustal structure and continental growth along northern South
America.
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The Paleogene Proto-Caribbean Subduction Zone and the arc-arc collision between
South America and the Caribbean Plate
James Pindell, Dept. of Earth Science, Rice University, 6100 Main Street, Houston,
Texas, 77005 USA jim@tectonicanalysis.com
Plate kinematic, seismic tomographic (Hilst, 1990), stratigraphic, and heavy
mineral data are synthesised to show that the long-held model of E-wardly diachronous
arc-continent collision between the Caribbean Plate (CA) and northern South America
(SA) is overly simple. The SA passive margin was converted into an active, S-dipping
subduction margin in the Maastrichtian, at which several hundred km of Proto-Caribbean
(P-CA) lithosphere was subducted beneath SA prior to the progressive arrival of CA from
its Pacific origin. Thus, CA-SA interaction has been an E-wardly progressive “arc-arc”
collision of sorts, although SA did not develop arc magmatism because the magnitude
and rate of P-CA subduction was too small. The P-CA trench can be seen in gravity and
basement structure maps emerging E-ward from beneath from Barbados Ridge ahead of
Barbados to Atlantic magnetic anomaly 31 (Late Maastichtian). Thus the P-CA trench
probably formed a simple triple junction with a ridge-transform corner of the Atlantic
Spreading Ridge at that time. Subsequent kinematics can be described by a simple
rotation of SA toward North America since that time. Field studies and heavy-mineral
patterns constrain a dynamic model for “hanging wall” uplift just prior to arc-arc
collision. This uplift is E-wardly diachronous but culminates in the Serranía Oriental at
end-Eocene. The new tectono-stratigraphic model for the evolution of northern South
America explains long-standing controversies such as Paleogene flysch-like deposition in
Eastern Venezuela-Trinidad (northern Vidoño, Chaudiere, Scotland fms) earlier than the
Late Oligocene arrival of CA along the Serranía Oriental, the apparent depth of incision
in the SA hanging wall (N and E fringes of the Serranía), and the magnitude of normal
fault throws that cannot be explained by a forebulge model in arc-continent collision. The
model also provides a framework in which to understand the Early Oligocene clastic play
along the Central Range of Trinidad.
This work forms part of the regional framework and onshore basin analysis
components of the BOLIVAR NSF-funded research program assessing crustal structure
and continental growth along northern South America.
Natural Rock Drainage Associated With Unmined Porphyry Copper Deposits In
The Rio Grande De Arecibo Watershed, Puerto Rico
M. Plaza Toledo1, J.H. Schellekens1, R.R. Seal II2, F. Gilbes Santaella1
1University of Puerto Rico Department of Geology, P.O. Box 9017, Mayagüez P.R.
00681
2 U.S. Geological Survey 954 National Center, Reston V.A. 20192
The Río Grande de Arecibo is located at the north-central part of the island of Puerto
Rico; its watershed is unique because it contains most of the discovered porphyry copper
deposits of Puerto Rico. Several of them were extensively explored but were never
mined. The premining geochemical signature for areas around mineral deposits, known
as geochemical background in pristine areas, or a geochemical baseline in areas that have
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experienced anthropogenic activity, is essential for realistic reclamation goals for after
mining at proposed mines and at abandoned mines (Runnels et al. 1998). This study
represents a geochemical background characterization that can be used as a remote
analogue for porphyry copper deposits in tropical climates. This will be performed on
the basis of water geochemical analysis of the Río Viví in Utuado, which passes through
the deposits, and Río Pellejas in Adjuntas which drains the deposits. In addition to these
analyses, processed images from the IKONOS satellite will be used to better characterize
vegetation on the vicinity of the deposits. A comparison will be made using the
information obtained by these images and the water quality data obtained in this study.
A Maastrichtian Rudist Bivalves Association Found In The Oriental Cordillera
(Dominican Republic)
Jose Maria Pons1, Jesús García Senz2 & Enrique Bernárdez3
1
Dept. de Geologia, Facultat de Ciències, Universitat Autònoma de Barcelona
2
Dept. Geodinàmica i Geofisica, Facultat de Geologia, Universitat de Barcelona
3
Dept. de Paleontología, Facultad de Geología, Universidad Complutense, Madrid
A rudist bivalves association has been found in the Río Mana section (UTM: 052125,
206408), 28 km southeast of the village of El Seibo, in the Oriental Cordillera of
Dominican Republic. The discovery expands the record of this bivalve group in the
Greater Antilles and has importance to study their decline and extinction pattern close to
the K/T boundary.
The Loma de Anglada Fm, within which the rudists are found, was deposited in a
sedimentary high in a fore-arc basin adjacent to the northern boundary of the Caribbean
plate. It is made of 450 m of shallow-water calcarenites with ondulated bedding and
cross-stratification, followed by limestones with volcanic rock gravel and volcanic lithic
sandstones. The rudist beds form biostromal bodies at the upper part of metric-thick
parasequences starting with lithic sandstones, and bearing broken and slightly rounded
shells belonging to the rudist families Antillocaprinidae, Radiolitidae and Hippuritidae,
together with gastropods and orbitoidal foraminifers.
The following species have been identified in 23 m of section: Titanosarcolites giganteus
(Whit.), Antillocaprina sp., Thyrastylon cf. adhaerens (Whit.) and Praebarrettia
sparcilirata (Whit.). All of them are well known from the lower part of the
Titanosarcolites Limestones of Jamaica, dated as Maastrichtian.
This contribution is a result of the SYSMIN Program (2002-2004) financed by the European Union .
Paleoseismology in the Caribbean: A review of studies in Hispaniola, Puerto Rico
and Trinidad
Carol S. Prentice, U.S. Geological Survey, 345 Middlefield Rd, MS 977, Menlo Park, CA
94025, cprentice@usgs.gov, 1-650-329-5690, Paul Mann, Institute for Geophysics,
University of Texas, Austin, TX, 78713, John Weber, Department of Geology, Grand
Valley State University, Allendale, MI 49401, PEÑA, L.R., Avenue Cuesta Colorada,
#2, Santiago, Dominican Republic, and Christopher Crosby, U.S. Geological Survey, 345
Middlefield Rd, MS 977, Menlo Park, CA 94025
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We have applied paleoseismic techniques to the study of faults on three of the islands in
the Caribbean region: Hispaniola, Puerto Rico, and Trinidad. The Septentrional fault zone
(SFZ) is the major North American-Caribbean plate-boundary fault in Hispaniola, where it
traverses the densely populated and rapidly developing Cibao Valley in northern Dominican
Republic. Our studies show that the most recent ground rupture on the SFZ east of Santiago,
in the central part of the valley, occurred about 800 years ago, and was associated with a
minimum of about 4 m of left-lateral strike-slip displacement. The penultimate event
occurred after AD30, suggesting a recurrence interval of 800 to 1200 years. Studies of
offset Holocene stream terraces suggest a SFZ slip rate of 6-12 mm/yr, indicating that
this structure accommodates about half of the geodetically determined total plateboundary motion of approximately 19 mm/yr. These paleoseismic data suggest that the
seismic hazard associated with the SFZ is high.
The major structures of the North American-Caribbean plate boundary are offshore north
of Puerto Rico. However, the location of the island within the plate-boundary zone
suggests the possibility of onshore Holocene faults, though no faults with Holocene
displacement have previously been documented on the island, and current seismic hazard
assessments only consider the impact of distant, offshore seismic sources. Our mapping
and paleoseismic studies demonstrate that repeated Holocene surface rupture has
occurred on a previously unrecognized fault in the Lajas Valley of southwestern Puerto
Rico. We identified an approximately east-west trending scarp crossing an alluvial fan on
the southern side of the Lajas Valley, and several excavations across this scarp exposed
faulted alluvium. In one of our excavations, we see evidence for two, and possibly three
earthquakes. In addition, relations exposed in both fault-perpendicular and fault-parallel
trenches suggest a right-lateral component of slip in addition to a normal component.
Very little material suitable for radiocarbon analysis was present in the sediments
exposed in the trenches. We collected five samples, which we hope will yield age
constraints on the timing of these earthquakes. Based on the ages of samples collected
and analyzed in 2000, we conclude that there have been at least two earthquakes in the
last 5000 years on this fault. We anticipate that additional radiocarbon analyses will
provide additional age constraints.
Trinidad is located along the transform plate boundary between the South American and Caribbean
plates. Analysis and comparison of historic triangulation and GPS data suggest that a significant fraction
(14+/-3 mm/yr) of the total plate-boundary motion (about 20 mm/yr) is being accommodated across the
Central Range Fault in central Trinidad. Geomorphic evidence of Quaternary faulting along the Central
Range Fault includes linear drainages, aligned topographic saddles and troughs, offset ridges, right-laterally
deflected streams, and linear scarps, supporting the geodetic evidence for youthful fault slip. We exposed a
6-m-wide shear zone within Pliocene(?) material in a trench cut into a fluvial terrace across the Central
Range Fault. The overlying Holocene fluvial gravel is faulted and folded across the shear zone, and
Holocene fluvial deposits are faulted against the shear zone on the north side. Our paleoseismic studies
demonstrate that surface rupture has occurred within the past 4500 years on this previously unrecognized,
active fault.
Holocene marine terraces in Puerto Rico: Evidence for tectonic uplift?
Prentice, C.S. McGeehin, J., Simmons, K.R., Muhs, D.R., Roig, C., Joyce, J., Taggart, B.
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We identified paleo-shorelines and associated marine deposits at elevations of
approximately 3-5 m above modern sea level on the island of Puerto Rico in four widely
separated locations: Patillas, Salinas, Rincón, and Ramey. Near Patillas (southeastern
Puerto Rico), a paleo-seacliff extends up to 200 m inland and has a shore-parallel extent
of ~5 km. Pits excavated into the terrace surfaces seaward of these paleo-shorelines
exposed fossiliferous marine sand beneath soils. Seven radiocarbon analyses of samples
from the Patillas terrace range in age from 400-520 yr BP to 730-900 yr BP (two-sigma
ages). Near Salinas (southern Puerto Rico), well-developed paleo-sea cliffs extend up to
800 m inland and at least 8 km parallel to the modern shore. Eleven radiocarbon ages
and two U-series ages of samples collected from the Salinas terrace range from 670-860
yr BP to 2740-2870 yr BP. Near Rincón, in northwestern Puerto Rico, ongoing
commercial sand extraction activities on a terrace approximately 1 km inland exposed
fossiliferous marine sand approximately 3 m above sea level that underlie fluvial and
marsh deposits. Radiocarbon analyses of two coral samples yield ages of 1350-1550 yr
BP and 1680-1870 yr BP. At the Ramey locality, a well-developed paleo-seacliff extends
up to 20 km parallel to the coastline and up to 500 m inland. Sand extraction activities
have removed deposits associated with this terrace, but fossil corals left behind on the
bedrock platform approximately 3-5 m above sea level yield eight U-series ages ranging
from 4000 yr BP to 7000 yr BP. Studies in the Caribbean suggest that sea level has been
steadily rising in this region for the last 10 ka and has not been higher than it is today
during the Holocene. Glacio-hydro-isostatic models do not predict a relative high sea
level for the Caribbean during the Holocene. In addition, the preliminary ages suggest
that the marine terraces are not all of the same age. These data suggest Holocene tectonic
uplift as a possible mechanism of formation for the terraces.
PAST, PRESENT AND FUTURE OF SEISMIC MONITORING IN
THE DOMINICAN REPUBLIC
Rafael Pujols, Juan Payero and Félix Martínez
Instituto Sismológico Universitario, Universidad Autónomo de Santo Domingo
The “Instituto Sismológico Universitario (ISU)” was founded following a major
earthquake that occurred on August 4, 1946 in the Scottish Bay. This earthquake, which
registered a magnitude 8.1 on the Richter scale, caused damage in San Francisco de
Macorís, Moca, La Vega, Santiago, Samaná, and Nagua, among others localities and the
total destruction of the municipality of Matancitas, located in the Province María
Trinidad Sánchez (Nagua), due to a tsunami. Approximately 300 human casualties were
reported.
ISU began its operations on February 26, 1948, under the direction of Father Joseph
Lynch, with two three-component seismic stations: one Sprengnether Series H shortperiod instrument and one Sprengnether broadband. These stations operated until 1987.
Following the construction of the Tavera-Bao dam in 1979, seven additional short period
stations that utilized, for the first time, digital recording were installed. These stations
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were a contribution from the University of Texas at Austin. In 1984, under an agreement
with several national and international institutions, six short period stations that operated
via telemetry and a central, three-component station in Santo Domingo were installed.
This network consisted of Geotech Model S-13 seismometers. This network operated
with its maximum capacity from 1985 to 1988. Eight digital short-period stations were
also added to the Tavera-Bao project in 1984, for a total of fifteen. In 1996 the
Dominican government contributed three single-component, short-period telemetered
stations, consisting of Kinemetrics Ranger SS1 seismometers.
In 1998, with the SYSMIN project, a network was constructed in the northeast that
consisted of ten digital short period stations. Equipment included a Kinemetrics Altus K2
digitizer, SS1 seismometer, and a spread spectrum digital radio at each station and a
central acquisition and data analysis center near the town of San Francisco de Macorís.
In addition, five accelerometers were installed with Kinemetrics Altus K2 digitizers and
FBA23 sensors.
In 2002, six new short period analog telemetered stations were installed broadly around
the Dominican Republic. Each station consists of a Geotech Instruments S-13J sensor
with Geotech DSPA64 and DSP32C digital data acquisition systems located at the ISU
laboratory in Santo Domingo. A broadband, three-component station, consisting of a
KS-2000 sensor plus a DL-24 digitizer, is also located in a basement vault beneath ISU’s
laboratory. In 2004, following a cooperative agreement with the Puerto Rico Seismic
Network, a VISEIS digital acquisition system and EARTHWORM real time data transfer
were introduced. Earthworm permits data exchange between both networks in real time
through the Internet.
In the near future, also with the collaboration of the Puerto Rico Seismic Network, two
broadband stations will be installed in Punta Cana and Samaná, respectively. In addition,
with financial support from the Dominican government, additional short period and
broadband stations may be installed, data processing capabilities expanded, computer
capacity upgraded, and a new, modern building constructed to house the improved
monitoring network.
The University Of Trinidad And Tobago
Dr. Sally Radford
The University of Trinidad and Tobago is a new entrepreneurial university established as
a partnership between government and
industry.
It aims to commercialise research and development in the fields of energy and
environment in the Caribbean Basin and is pleased
to announce a new Master of Science degree in Oil and Gas Exploration and Production.
Further details may be obtained from
UTT
Point Lisas Campus
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Esperanza Road, Brechin Castle, Couva, Trinidad, WI. www.utt.edu.tt
Conservation Of Reefs Around Tobago
Several projects have been established with the aim of conserving the coastal resources
around Tobago. The University of the West Indies in Trinidad is currently conducting a
survey of foraminifera in habitats of Buccoo Reef.
These have recently been mapped by GIS.
The Buccoo Reef Marine and Coastal GIS database may be obtained from
Buccoo Reef Trust
Cowie's Building
Auchenskeoch Road
Carnbee, Tobago, WI.
www.buccooreeftrust.org
Evaluating the Effects of Land Development on Sediment Production and
Sediment Yields in Dry Tropical Areas of the Eastern Caribbean
Author: Ramos-Scharrón, Carlos E.
Island Resources Foundation
3605 Steck Ave. #1132
Austin, TX 78759
Tel. 787/587-0416
Email: cramos@irf.org
Anecdotal evidence suggests that an observed long-term decline in coral reef cover
within the Caribbean Region may be associated with localized increases in anthropogenic
stresses. Of particular concern is the rise in sediment loading rates that typically
accompanies land development. This study describes the impacts that land development
has had on sediment production and delivery rates on dry tropical areas of the Eastern
Caribbean. The objectives of this study were to: (1) measure erosion rates from a variety
of anthropogenic and natural sources; and (2) develop a GIS-based model to estimate
basin-scale sediment delivery.
Sediment production rates were measured from unsurfaced roads, road cutslopes, undisturbed
hillslopes, streambanks, and treethrow on St. John-USVI and La Parguera-Puerto Rico. Unsurfaced roads
had the highest erosion rates with values up to 23 kg m-2 yr-1, while road cutslopes generated only about 0.8
kg m-2 yr-1. Since undisturbed areas produced only 0.001 kg m-2 yr-1, unsurfaced roads can increase
hillslope-scale sediment production rates by up to four orders of magnitude. Sediment production rates
from erodible streambanks were estimated to be nearly 13 kg m-2 yr-1, while uprooting of trees along stream
margins was estimated to deliver 0.17 kg yr-1 of sediment per meter of stream length.
The St. John Erosion model (STJ-EROS) uses a series of empirical sediment production
models and sediment delivery ratios to estimate watershed-scale sediment yields in a
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GIS-based system. The model has been applied to four watersheds in St. John
representing a disturbance gradient and the results suggest that current sediment yields
are four to forty times higher than undisturbed conditions. Predicted sediment yields are
consistent with measured sediment yields and bay sedimentation rates. Actively-used
unsurfaced roads were identified as the dominant source of sediment in each of the four
watersheds. Cutslopes and streambanks played a secondary role in total sediment yields,
while undisturbed hillslopes and treethrow contributed only minimal amounts.
Sedimentology and tectonic evolution of the Campanian to Paleocene succession in
northern Blue Mountains, eastern Jamaica
Ryan Ramsook and Simon F. Mitchell
Department of Geography and Geology, University of the West Indies, Mona, Kingston
7, Jamaica
Detailed mapping and logging of the Campanian-Paleocene succession in the northern
Blue Mountains, eastern Jamaica, has produced a revised geological map and tectonic
evolution for the area. The region underwent NW-SE directed extension and rifting
related to a change from north-eastward to eastwards motion of the Caribbean Plate
following collision between the Nicaragua Rise and the Yucatàn Block in the late
Campanian/early Maastrichtian. The geologic history is divided into pre-rift, syn-rift and
post-rift stages. The Campanian to Early? Maastrichtian pre-rift sequence consists of
andesitic volcanics and associated marine limestones and clastics. In the northern part of
the study area, the succession consists of the Bonnie View Andesite (Campanian?
porphyritic pyroxene and plagioclase andesite) with pillow structures and the fault
bounded Providence Formation (calcareous poorly sorted conglomerates and graded
sandstones, siltstones, shales and mudstones with Campanian ammonites). In the central
study area the succession was deposited closer to an active island arc volcano and
consists of a thick andesitic pile (including the Bellevue Formation) with a thin early
Middle Campanian marine incursion (Back Rio Grande Formation) and is overlain by
?Early Maastrichtian rudist-bearing limestones and associated proximal volcaniclastics
(Rio Grande Formation). The Bowden Pen Formation (? latest Maastrichtian) represents
the base of the syn-rift sequence and is represented by poorly sorted conglomerates and
sandstones deposited in alluvial fans and proximal submarine fans as the rift system
developed. This is succeeded by a coarsening upwards (rift-filling) sequence of abyssal
turbiditc sandstones and shales passing up into thick sandstones. Post-rift deposition is
marked by a change to carbonate deposition in the late Paleocene, and marks the
cessation of uplift on the rift’s margins and westward migration of rifting to the
Wagwater Trough.
Identifying Submarine Slides on Jamaica’s Southern Island Slopes.
by Edward Robinson1, Deborah-Ann. C. Rowe1 and Rafi Ahmad2
Submarine slides have occurred in Jamaica during storms or earthquakes, as for example
following the Port Royal earthquake of 1692, and as suggested by telephone cable breaks
related to earthquakes in1907 and 1993.
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The vulnerability of Jamaica’s coastline to storm surge from hurricanes has been amply
demonstrated. Although tsunami have occurred in historical times, their sources and
extent in the Jamaican coastal environment and damage potential is not known. Tsunami
may arise locally from submarine slides on the island shelf or slope, generated by storms
or earthquakes, as well as from seismic events themselves. Warning times for such local
events will usually be very short, as was the case following the 1907 earthquake.
Signatures from past tsunami events are probably preserved as tsunamigenic sediments
on the island,s shelf/slope..
Direct investigation of the incidence of slides on the island’s south slope has been
initiated by the Marine Geology Unit at the University of the West Indies, through
analysis of high-density bathymetric data. Of slide deposits so far identified, one exceeds
20 million cubic metres in volume. However, bathymetry for most of the north coast shelf
and slope is lacking, although such data are crucial in determining the likely parameters
of future tsunami and surge events.
1
Marine Geology Unit, 2Unit for Disaster Studies,
Department of Geography & Geology, University of the West Indies, Mona, Kingston 7,
Jamaica. mgu@uwimona.edu.jm
SO2 conversion rates at Soufrière Hills volcano, Montserrat, B.W.I.
LA Rodríguez1; IM Watson1,2; V Hards3, 4; G Ryan3; M Edmonds5; C Oppenheimer6; WI
Rose1; GJS Bluth1
1. Geological and Mining Engineering & Sciences, Michigan Technological University,
Houghton, MI 49931
2. Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
3. Montserrat Volcano Observatory, Flemings, Montserrat, BWI
4. British Geological Survey, Keyworth, Nottingham, UK
5. USGS-Hawaiian Volcano Observatory, Hawaii National Park, HI 96718
6. Department of Geography, Cambridge University, Cambridge, UK
Volcanic SO2 emission rates are commonly measured on plume cross sections some distance
downwind from the active vent; after interacting with other volcanogenic gases, particles and droplets of
volcanogenic and/or meteoric origin, and atmospheric gases. The emission rates therefore do not
necessarily represent the real fluxes, due to the conversion of SO 2 to SO4-2. It is important to quantify
volcanic SO2 conversion rates as a function of meteorological environment and plume age as near source
plume chemistry can have significant effects on climatologically active species. We used two mini-UV
spectrometers to measure SO2 emission rates at Soufrière Hills volcano, Montserrat, which is a low altitude
volcano (summit altitude <1100 m above sea level) in a wet atmosphere. Helicopter and boat traverses
where conducted in March and April 2004. Here we present our results from measurements taken at a
variety of distances from the vent downwind (maximum of ~16 km), which represent different plume ages.
Weather data will help clarify the effects of Montserrat’s low, moist, and absorptive atmosphere upon
conversion rates. Preliminary results indicate that the average loss rates are in the order of 10 -4 s-1; however
they are not constant throughout the plume. The variations could be caused by plume puffing, plume
interactions at the coast, turbulence, and aerosol evolution. This research is complemented by
measurements at Lascar and Etna volcanoes, which represent dry and intermediate atmospheric conditions.
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Bioturbation by the sea urchin Diadema antillarum:
Effects on sediment and diversity
Rodriguez-Iglesias, Esther M.
Graduate Student
University of Puerto Rico, Mayaguez Campus
Department of Marine Sciences
P.O. Box 3342, Mayaguez, P.R. 00681-3342
e_rodrigem@yahoo.com
Yoshioka, Paul
Professor
University of Puerto Rico, Mayaguez Campus
Department of Marine Sciences
P.O. Box 9013, Mayaguez, P.R. 00681-9013
p_yoshioka@cima.uprm.edu
The sea urchin Diadema antillarum is a keystone species of the Caribbean reefs. Its
grazing activity both cleans and produces sediments by bioerosion. Diadema suffered a
mass mortality across the Caribbean in 1983-84 (95-99% eliminated). Effects of this
event included macroalgal blooms, drops in coral cover and transition from coral to algal
dominance. Although recruitment of corals increased in “hard ground” habitats, coral
cover remained low because of higher recruit mortality. We believe that the latter effects
result from changes in the bedload regime arising from Diadema’s effect on sediments
and its interaction with water motion, topographic relief, and the slope of the terrain. We
are studying these effects of Diadema with caging experiments at Media Luna reef in La
Parguera, Lajas. Areas inside and outside of 8 (0.5x0.5x0.25m) cages will be monitored
before, during and after transplants of Diadema for periods of 1, 1 and 2 months
respectively. Four of the cages will serve as controls. Photographs, sediment collection,
estimates of bedload transport (measured with nylon-mesh sediment traps), and
macrofauna and flora identifications will be made on a weekly basis in the field during
this period. Laboratory analyses include characterization of sediment, granulometry,
angularity and composition. Sediment consolidation will be estimated by extracted
chlorophyll a concentrations in sediments. We expect a change in sediment composition,
especially in terms of organic material, as well as in grain characteristics during the
study. We also anticipate that bedload transport will increase in the presence of Diadema
due to its bioerosional and sediment cleaning effects. We then expect that it will be
difficult for coral recruits to become established because of this bedload regime.
Post-Jurassic Evolution of the Chortis Block and its role in the evolution of the
Caribbean
Robert Rogers, Department of Geology, University of Puerto Rico- Mayagüez,
P.O. Box 9017 Mayaguez, PR 00681
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17th Caribbean Geological Conference 2005, San Juan PR
Four post-Jurassic tectonic events are recorded in the geology of the Chortis block
of northern Central America within the context of the regional evolution of the Caribbean
plate and the southernmost North American Cordillera. The earliest event is Aptian-early
Cenomanian, intra-arc rifting followed by late Cretaceous inversion of the rift basin in the
Frey Pedro range of east-central Honduras. A 3.5-km-thick stratigraphic section of
clastic, carbonate, volcaniclastic and volcanic rocks were deposited in the intra-arc rift
and on its rift shoulders. The geochemistry of rift-related volcanic rocks shows magmatic
arc affinity.
The northwest-directed Colon fold-thrust belt of eastern Honduras and the
Nicaragua Rise and adjacent island arc Siuna belt of northern Nicaragua, record the late
Cretaceous collision between the south-facing margin of the Chortis block and the
northeastward-moving Caribbean arc system. This previously unrecognized arccontinent collision can be traced for a distance of 350 km across Honduras and the
Nicaragua Rise.
North trending rifting of the western Chortis block and NNW-SSE transtensional
extension of northern Honduras and the offshore Honduran borderlands reveal Miocene
to Recent divergence between the Caribbean and North America plates. Observed
boundary-normal extension occurs where the angle between the plate boundary fault and
the Caribbean motion vector is greater than 10º and boundary-parallel transtension where
the angle is between 5 and 10º.
P-wave tomographic images of the mantle beneath northern Central America
reveal a detached slab of the subducted Cocos plate. Landscape features of the region
above the detached slab are consistent with epeirogenic uplift produced by mantle
upwelling following slab breakoff between 10 and 4 Ma.
Correlation of regional aeromagnetic data with outcrop exposures allows
subdivision of the Chortis block into five terranes: 1) Central Chortis with continental
Paleozoic basement; 2) Eastern Chortis with Jurassic metasedimentary basement; 3)
Southern Chortis of low magnetic intensity and covered by Miocene volcanic strata; 4)
Siuna with oceanic island arc basement; and 5) Northern Chortis where early Tertiary
magmatism overprints the Central and Eastern Chortis terranes. Common geologic and
geophysical characteristics of the Chortis terranes and Mexico terranes allow improved
reconstructions of the region prior to its Tertiary fragmentation.
LATE GLACIAL STAGE-HOLOCENE TRANSITION RECORDED IN A NORTHERN
VENEZUELA STALAGMITE
S.M. Rosner1, L.A. Gonzlalez1, H. Cheng2, L. Edwards2, and F. Urbani3, R. Gomez4
1
University of Kansas, Department of Geology, Lawrence KS USA 66045; 2University of
Minnesota, Department of Geology and Geophysics, Minneapolis MN USA 55455;
3
Universidad Central de Venezuela, Escuela de Geologia, Minas y Geophisica, Departamento
de Geologia, Caracas Venezuela; 4MFG Inc., Austin TX USA, 78703
Northern South America and the southern Caribbean have undergone major
climatic and environmental changes during the Late Glacial through the Holocene.
Foraminifera isotope data from the Cariaco Basin off the coast of Venezuela indicate a
major temperature change (~ 4°C) from Late Glacial to Holocene (Lin et al., 1997).
Lacustrine records from Lake Miragoane, Haiti and Lake Valencia, northern Venezuela
indicate a change from dry to wet climate in the early Holocene (Hodell et. al., 1991,
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Curtis et al., 1999). This climatic/environmental change in the region has been attributed
to migration of the mean position of the Inter Tropical Convergence Zone (ITCZ) in
response to insolation changes (Seltzer et al., 2000; Haug et al., 2001). Presently the
average northern most position of the ITCZ over South America lies over northern
Venezuela. Thus, paleoclimate proxies from northern Venezuela record critical
information needed to understand climatic changes from Late Glacial to Present. Data
has/is been generated from a stalagmite from Cueva Zarraga located in northern
Venezuela. Isotope records span the last 20,000 years, during which time decreases in
both 13C and 18O indicate a change to warmer and wetter conditions from the Late
Glacial to the early Holocene. Presently the chronology of the stalagmite is not well
constrained before about 10,500 years BP. Further isotope work, stable and radiogenic,
is in progress to better determine the timing of the environmental change preserved in the
stalagmite.
Geologic uncertainty in the assessment of undiscovered oil and gas resources of the JurassicCretaceous Composite Total Petroleum System, Northwestern Cuba
Christopher J. Schenk, U.S. Geological Survey
The U.S. Geological Survey (USGS) recently assessed the undiscovered oil and gas potential of the
Jurassic-Cretaceous Composite Total Petroleum System (TPS) in northwestern Cuba (mostly offshore).
The USGS assessed three assessment units (AU) within the TPS: 1) North Cuba Fold and Thrust Belt AU,
2) North Cuba Foreland Basin AU, and 3) North Cuba Platform Margin Carbonate AU. The proposed
geologic model for the composite TPS has oil and gas generated from Jurassic and Cretaceous organic-rich
shales within the Paleogene thrust belt. Petroleum migrated updip during the Paleogene into structurally
controlled reservoirs in the fold and thrust belt and below and within the foreland basin, and into reservoirs
along the margins of the carbonate platform. For the North Cuba Fold and Thrust Belt AU, the USGS
estimated a mean of 0.49 billion barrels of undiscovered oil (BBO) (with 0.6 trillion cubic feet [TCF] of
associated gas); a mean of 3.2 BBO (with 6.4 TCF of associated gas and 1.2 TCF non-associate gas) in the
North Cuba Foreland Basin AU, and a mean of 0.9 BBO (and 1.6 TCF associated gas) in the Platform
Margin Carbonate AU, for a total mean undiscovered resource of about 4.6 BBO and 9.8 TCFG. Geologic
uncertainties in the assessment involved the efficacy of petroleum fluid migration from sources in the thrust
belt into reservoirs of the foreland basin and platform margins, reservoir quality in all assessment units, and
the preservation of reservoired petroleum since possible trapping during the Paleogene.
Age and facies of submerged Late Pleistocene reefs, Oahu, Hawaii: Implications for
stage 7 and late stage 5 sea levels
C.E. Sherman*, C.H. Fletcher, K.H. Rubin, K.R. Simmonsb, W.H. Adey
Department of Geology and Geophysics, School of Ocean and Earth Science and
Technology, University of Hawaii at Manoa, 1680 East-West Road, Honolulu, Hawaii
96822, USA, bU.S. Geological Survey, MS980, Federal Center, Denver, Colorado
80225,
USA, cDepartment of Botany, National Museum of Natural History, Smithsonian
Institution, Washington, D.C. 20560, USA
* Corresponding author. Address: Department of Marine Sciences, University of Puerto
Rico, Mayagüez
Campus, Isla Magueyes, Laboratories, PO Box 908, Lajas, PR 00667. PH: 787/ 899-2048
E-mail: c_sherman@cima.uprm.edu
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In situ Pleistocene reefs form a gently sloping nearshore terrace around the island of
Oahu. The windward margin of the terrace is dominated by coralline algal bindstones
(algal ridge) that formed in a shallow, high-energy environment within 1-2 m of paleosea
level. The leeward margin of the terrace is dominated by coral framestones, bindstones,
and rudstones. TIMS Th-U ages of in situ corals indicate that most of the terrace on both
the windward and leeward sides of Oahu is composed of reefal limestones correlating to
marine oxygen isotope stage 7 (186-242 ka). This in situ stage 7 reef complex is
informally referred to as the Waianae Reef. The position of the Waianae Reef indicates
that it formed during periods when sea level was ~ 9 to 20 m below present sea level. Its
extensiveness and geomorphic prominence as well as a paucity of emergent stage 7
deposits on Oahu suggest that much of isotope stage 7 was characterized by sea levels
below present. Later accretion along the seaward front of the terrace occurred during the
latter part of isotope stage 5 (i.e., <120 ka, post-5e). The position of the late stage 5 reefal
limestones is consistent with formation during a period when sea level may have been
below present. The general trend of decreasing Th-U age of stage 5 corals with distance
offshore may suggest that accretion along the seaward front of the terrace occurred
during a period of general sea-level fall during the latter part of stage 5. The dearth of
Holocene accretion over the submerged Pleistocene reefs of Oahu is a result of
insufficient time and accommodation space for reefs to develop during the Holocene.
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Tectonic Evolution of the Caribbean Mountain System, Northern Venezuela:
Evidence for an Atypical Origin for a Fold and Thrust Belt
Virginia B. Sisson and Hans G. Avé Lallemant, Dept. of Earth Science, MS-126, Rice
University, Houston TX 77251-1892
Superficially, the Caribbean Mountain system resembles a fold and thrust belt with a foreland and
an igneous-metamorphic hinterland. However, the foreland formed in the Tertiary whereas the
metamorphism is generally Mesozoic, and igneous rocks are Mesozoic to Lower Paleozoic. The Cordillera
de la Costa belt is a subduction mélange with eclogite, granite, and granitic gneiss knockers in a mica schist
and serpentinite matrix. The eclogite formed at ~75 km in mid-Cretaceous, and retrograded following a
path typical of collisional terranes. Geochemistry of the eclogites and matrix indicate MORB and active
margin sedimentary protoliths. Deformation structures formed during retrograde metamorphism, indicate
NS shortening, EW dextral simple shear, and EW plate boundary parallel extension as an important
mechanism of exhumation. Near Puerto Cabello, exhumation did not occur until after 35 Ma. The
Caucagua-El Tinaco belt consists of gneisses, amphibolites, peridotites, and volcanic and sedimentary
rocks. A new amphibole 40Ar/39Ar determination of the Tinaco complex yielded 146 Ma. The Tinaquillo
peridotites are mylonites formed during Jurassic rifting at 190 Ma. The mid-Cretaceous Villa de Cura belt
is a sequence of blueschist facies volcanic arc basalts and volcaniclastic rocks. There is little retrograde
overprint, typical of Franciscan-type terranes. The Serranía del Interior fold and thrust belt is older in the
west (Eocene) and younger in eastern Venezuela (Miocene). Apatite fission-track ages indicate a
deformation event related to the passage of the Antilles volcanic arc. In north-central and eastern
Venezuela, there are two populations of apatite fission-track ages: one Eocene age and the other Miocene.
The older dates suggest NS contraction occurred long before the Antilles reached the area. Significant new
findings indicate a range in tectonic processes from orogenic events correlated with the Appalachians,
Jurassic rifting, Cretaceous subduction, Cretaceous-to-Tertiary exhumation and contraction, as well as
formation of the Tertiary fold and thrust belt.
Pre-historic volcanism of the Soufrière Hills-South Soufrière Hills volcanic complex, Southern
Montserrat, West Indies
A. L. Smith1, M. J. Roobol2, J. H. Schellekens, and G. Mattioli3
Department of Geology, University of Puerto Rico, Mayaguez, Puerto Rico
The Soufrière Hills-South Soufrière Hills volcanoes although morphologically
distinct, on the basis of stratigraphy and petrology appear to belong to a single
volcanic complex. Although considerable attention has been focused on the current
eruption of the Soufrière Hills volcano, the pre-historic record of the complex is less
well known. Stratigraphic studies indicate that the Soufrière Hills volcano is
dominated by the extrusion of Pelean domes and their associated block and ash flow
deposits. In contrast, the South Soufrière Hills center is composed mainly of deposits
from scoria and ash flows and scoriaceous falls characteristic of St. Vincent-style
activity. Their combined stratigraphies record over 400,000 years of history. The
recent history of the complex, based on age dating and stratigraphy, has been
subdivided into 7 episodes (Soufrière Hills subunit I, South Soufrière Hills, Soufrière
Hills subunits II-VI). Subunit I (< 175 ka) is essentially composed of deposits from
Pelean-style eruptions, however near its top ignimbrites characteristic of Plinian-style
activity are abundant. The South Soufrière Hills (~130 ka) is characterized by
deposits from open crater St. Vincent-style eruptions. Subunits II to V (~112,000 to
~400 years B.P.) represent a return to the characteristic Pelean activity, although the
period between 22,000 and 20,000 years B.P. is dominated by deposits of semi83
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vesicular andesite. Similar deposits have been described from the present eruption,
thus providing a mechanism for their formation. Age dating suggests that the
Soufrière Hills was active just prior to European settlement in 1632 AD. Since then
there have been four volcano-seismic crises, the last of which was a precursor for the
present eruption (subunit VI). This eruption, dominated by dome growth and the
generation of associated pyroclastic flows appears to be typical of the eruptive style
characteristic of this volcano.
(1) Department of Geological Sciences, California State University, San Bernardino,
California; (2) Saudi Geological Survey, PO Box 54141, Jeddah, 21514, Saudi
Arabia; (3) Department of Geology, University of Arkansas, Fayetteville,
Arkansas
Biostratigraphic Study Of The Rio Maton Limestone Member Of The Robles
Formation And The Torrecilla Breccia, Along The Pr # 1 In Cayey, Puerto Rico
Ailec D. Soto Feliciano and Hernán Santos
Department of Geology, University of Puerto Rico, Mayagüez Campus
A detailed stratigraphic section along the PR #1 in Cayey, Puerto Rico, between the Río
Matón Limestone Member of the Robles Formation and the Torrecilla Breccia was
developed. This stratigraphic section will allow for the reconstruction of the paleofacies,
depositional environments, and relative sea level changes in the area. A stratigraphic
section was measured, and fossils were collected to determine the age of the Formations.
Gastropods, bivalves, echinoderms, corals and plant fragments were found. The presence
of the rudist bivalve fossil Coalcomana ramosa, an index fossil of Lower Albian age,
established the age of the formation. On the basis of the composition of carbonate rocks
mixed with volcaniclastic sediments, as well as the presence of the shallow water fossil
fauna, the paleofacies reconstruction made suggests the area was located in an inner
platform environment. The Río Matón Limestone Member ended with a transgressive
event that resulted in the deposition of the Cayey Siltstone Member.
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Contrasting high-pressure and low-pressure P-T-t-d paths in a single nappe pile: a
case study from the Cuban collisional suture
Stanek, K.P., Institut für Geologie, Technische Universität Bergakademie Freiberg, D-09596 Freiberg, Germany
Maresch, W.V., Institut für Geologie, Mineralogie und Geophysik; Ruhr-Universität Bochum, D-44780 Bochum,
Germany
Grafe, F., IBeWa Consulting, Lessingstraße 46, D-09599 Freiberg, Germany
Grevel, Ch. ERFTCARBON GmbH & Co KG, Aluminiumstraße 4, D-41515 Grevenbroich, Germany
Baumann, A., Institut für Mineralogie, Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany
Millán Trujillo, G., Instituto de Geología y Paleontología, Via Blanca y Linea del Ferrocarril, Ciudad de La
Habana CP 11000, Cuba
Brix, M.R., Institut für Geologie, Mineralogie und Geophysik; Ruhr-Universität Bochum, D-44780 Bochum,
Germany
Hames, W.E., Department of Geology and Geography, Auburn University, Auburn, AL, 36830, USA
Idleman, B., Department of Earth & Environmental Sciences, Lehigh University, Bethlehem, PA 18015-3188,
USA
Thomson, N.S., Department of Geology & Geophysics, Yale University, P.O. Box 208109, New Haven, CT,
06520-8109, USA
The eastern part of the Escambray Massif in Central Cuba comprises four nappe units, of
which at least two indicate high-pressure (HP/LT) metamorphism and represent a former
subduction-accretion complex. Tectonic features and fabric analyses argue for a
northward thrusting and stacking of the metamorphic rocks. Boudins of eclogite and
blueschist-facies rocks corroborate maximum conditions of 16-25 kbar and 580-630C.
An island-arc unit with LP/HT metamorphism of ~7 kbar at 620-700C was thrust over
the HP-nappes. Late Cretaceous (88-81 Ma) pegmatoids cross-cutting the shear zone
between island-arc and HP-metamorphic rocks give a minimum age for the juxtaposition
and metamorphism of these distinctly different nappes. SHRIMP zircon ages of ~170 Ma
likely date the eclogite protolith and U/Pb, Rb/Sr and Ar/Ar data suggest a Middle to Late
Cretaceous (106 to 88 Ma) age for the HP-metamorphism of the metasediments and
eclogites, which originated off southeast Yucatán. The origin of the subducted rocks, the
arc polarity, the timing of metamorphism, and preliminary paleomagnetic data support a
Pacific origin of the Cretaceous Great Antillean island arc and its final exhumation
together with the subduction-accretion complex in the Caribbean along the southwestern
edge of the Bahamas platform.
Early Cenozoic Recovery Of Caribbean Reef Coral Communities
Stemann, Thomas A. Department of Geography and Geology, The University of the West
Indies, Mona, Kingston 7 Jamaica
Recent collections from latest Maastrichtian successions in Jamaica reveal that diverse
reef coral communities persisted up until the very end of the Cretaceous. Faunas at this
time include 60 species from 40 genera of scleractinians and octocorals. This level of
species richness is comparable to that typically found on modern Jamaican reefs or in
diverse mid to late Cenozoic faunas. Paleocene and early Eocene Caribbean corals,
however, are scarce and poorly known.
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New collections of early Cenozoic corals from Jamaica are providing new insight into
Caribbean reef communities immediately following the K-T boundary event. Systematic
studies are on-going but presently < 5% of the Jamaican Cretaceous corals are found to
range into the Cenozoic. Collections from the Paleocene of eastern Jamaica contain less
than 5 coral species from each sample site and total sampled richness is lower than at any
time in the Cenozoic or Cretaceous. Endemism is high in early Cenozoic faunas but
ecologic diversity is significantly lower with communities composed only of thin
branching colonies or small solitary corals. Richness rises slightly in the early through
middle Eocene but remains low compared to typical levels found in Oligocene and
younger units. Dense accumulations of reef corals including large massive, branched and
plate shaped colonies do not become common until the late middle Eocene.
Part of this pattern may result from the paucity of ‘reefal’ environments preserved in the
Paleocene-Eocene rocks of Jamaica. Still, known reef coral associations from throughout
the Caribbean contrast markedly with the rich faunas recorded from Europe, Africa and
Asia. After significant extinctions at the end of the Cretaceous, coral community
recovery is slow in the Caribbean and faunas here remain species poor and ecologically
simple considerably longer than elsewhere in the world.
Connectivity Within a Field: How Production Startup Data Can Answer Some of
the Questions.
Greater Angostura Development, Trinidad and Tobago
Chris Taylor
Trinidad and Tobago Asset Team
BHPBilliton
1360 Post Oak Bvld., Suite 150
Houston, Texas, 77056
The Greater Angostura Structure, comprising the Kairi, Canteen, Aripo and Angostura
structurally defined areas, lies offshore Trinidad and Tobago in Block 2(C). Development
drilling on the structure began in September of 2003 and First Oil was achieved in
January of 2005.
The Angostura Development is centered on the production of oil and gas reservoired
within the Angostura Sandstone, a thick Early to Middle Oligocene sequence of sediment
gravity flows that are interpreted to have been deposited in a slope type setting.
The first Phase of the development targets the two oil bearing fault blocks of Kairi and
Canteen. To date, 10 oil production, 3 gas injection, and a single dual-duty (oil
production followed by gas injection) well have been drilled and completed. A total of 10
bottom hole gauges have been installed for reservoir performance monitoring.
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This presentation reviews the pre-production expectation and post-production
interpretation of the inter-well connectivity within the Kairi fault block based upon the
bottom hole pressure data. The actual data will be shown and the justification for the
interpretations given. The impact of the interpreted results on the next phase of the
Greater Angostura development will also be presented.
Volcanic Activity in all Caribbean Plate Margins: Forecast and Risk Assessment
R. B. TROMBLEY, Ph.D.
Southwest Volcano Research Centre
3405 S. Tomahawk Rd., Suite # 31
Apache Junction, Arizona USA 85219-9169
(480) 671-1601
e-mail: swvrc@usa.net
website: http://www.swvrc.org
The following presents the current eruption status and forecast for all volcanoes
within the Caribbean Plate boundaries.
appropriate and as necessary.
It is upgraded from time to time as
The forecasting and risk assessment has been
compiled, using presently loaded data, from the SWVRC software programme,
ERUPTION Pro 10.5, the only known long-range and reasonably accurate
forecasting programme of it kind in the world.
The Caribbean area primarily consists of the countries of Mexico, Guatemala, Honduras,
Nicaragua, Costa Rica, Panama, Columbia and Venezuela and the island nations
represented in the Lesser Antilles. Some countries such as Cuba, Dominican Republic,
Puerto Rico, Jamaica and Venezuela, do not have any active volcanoes within.
Pattern of saltwater contamination resulting from tsunami
inundation of small islands
Dr. Lensyl Urbano
Department of Earth Sciences
University of Memphis
Memphis, TN 38152
Email: lurbano@memphis.edu
Phone: (901) 678-4543
The inundation of coastal regions and small islands by the Indian Ocean tsunami on
December 2004 resulted in extensive salinization of shallow groundwater resources. In
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order to investigate the spatial and temporal consequences of tsunami inundation, I
employ an idealized numerical model that simulates the effects of inundation on natural
and anthropogenically impacted freshwater lenses of small islands. On unimpacted
islands the primary determinant of saline contamination of the aquifer is local
topography. Saline water is collected in local depressions that serve as focus points for
infiltration into the aquifer. A second major parameter affecting saline infiltration is the
heterogeneity of the aquifer permeability; infiltration is focused through high
permeability regions. On islands with significant anthropogenic groundwater
withdrawals, however, the location and size shallow wells are extremely important.
Unprotected wells can serve as direct paths for salt water into the aquifer, while the cones
of depression surrounding wells focus saline recharge water toward the wells. Once the
saline recharge is focused, density effects drive the saline water deeper into the aquifer
and continues to focus flow even without further withdrawals. The results of these
numerical experiments suggest that wellhead protection and a strategic water extraction
scheme may help ameliorate the adverse effects of tsunami inundation.
Puerto Rico Seismic Network, Geology Dept. , UPRM
José Vélez González, Victor Huerfano and Christa von Hillebrandt-Andrade
The Puerto Rico Seismic Network (PRSN) has generated hypocentral information for
earthquakes in the Puerto Rico and Virgin Islands region (PR-VI) since 1974 when the
network was installed by the USGS for the Puerto Rico Electrical Power Authority.
Although there are data for the last 30 years, the PRSN has reliable instrumental
information as of 1987 when the Network was transferred to the Geology Dept. of the
University of Puerto Rico at Mayag|ez.
The PRSN has been significantly upgraded since 1999 when the first broadband station
was installed. At present the network operates 14 broadband and 11 short period stations
installed throughout Puerto Rico and the US and British Virgin Islands. Along with the
improvements in seismic instrumentation, new computer tools, as well as numerical
algorithms have been implemented to analyze the data. These improvements include new
magnitude computations, extended format in the parametric data, community accepted
waveform formats, the inclusion of instrumental responses and the use of a new locator.
Independent of the method, the assessment of seismic hazard and seismic research relies
on published catalogues. The PRSN catalogue of both parametrical and associated
waveforms is available as of late 1991 when the digital recording systems were
implemented. Nevertheless, this earthquake catalogue has not been significantly revised
since 1994 when it was recompiled with the magnitude equations of von Hillebrandt and
Bataille and the crustal model of Huirfano. To proceed with the evaluation of seismic
hazard and related research for the Puerto Rico and Virgin Island region, a substantial
revision of the earthquake database is required. The main goal of this project is to
produce a unified earthquake catalogue for Puerto Rico and the Virgi n Islands and to
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build a comprehensive and homogeneous database based on current cross platform
MySQL tools. This is being achieved by collecting and re-analyzing automatically
primary sources of data, merging all available information using the new algorithms and
saving the outputs in the new MySQL tables.
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Tertiary Crocodylians From Puerto Rico
JorgeVélez-Juarbe , Christopher A. Brochu 2, Hernán Santos1, Ángel M. Nieves-Rivera 3
and Juan D. Daza-Vaca4
1
Department of Geology, P.O. Box 9017, University of Puerto Rico, Mayagüez, PR
00681-9017
2
Department of Geoscience, University of Iowa, Iowa City, IA 52242
3
Department of Marine Sciences, P.O. Box 9013, University of Puerto Rico, Mayagüez,
PR 00681-9013
4
Department of Biology, University of Puerto Rico, PO Box 23360, San Juan, PR 00931
1
During the Tertiary, the groups of islands known today as the Greater Antilles were host
to a fauna different to the one found in modern times. The complex geological history of
these islands makes difficult the study of the origin of these organisms. One of the
organisms present (now extinct) during part of the Tertiary in Puerto Rico was the
crocodylians. These have been poorly studied, mostly due to the incompleteness of their
remains. Even though the remains are not enough for species-level diagnosis, they are
sufficient to rule out any crocodylian currently found in the Americas and any of the
Tertiary longirostrine species known from the region. Morphological aspects suggest the
possibility of an endemic group of crocodylians from the Greater Antilles during the
middle Tertiary of the region, this in congruence with the dispersal models for the
biography of Crocodylus and of similar Neogene endemic radiations in other regions of
the world. The purpose of this work is to briefly describe the evidence found in Puerto
Rico.
Cretaceous To Tertiary Echinoderms From Puerto Rico
Jorge Vélez-Juarbe and Hernán Santos
Department of Geology, University of Puerto Rico, Mayaguez Campus, Mayaguez PR
Fossil Echinodermata, from six Cretaceous age formations, eight Tertiary age
formations and one Quaternary age formation were collected and identified to the lowest
taxonomic level possible. These were collected from a total of 35 localities, around the
island of Puerto Rico, but mostly along the northwest and southwest parts of the island.
This is the first attempt to include most of the groups within the Echinodermata,
including the starfishes, brittle stars, crinoids, sand dollars and sea urchins that can be
found the fossil record of Puerto Rico. Distribution and occurrence of several of the
species herein identified can be used in the determination of paleoenvironment, age, and
formation where they are found.
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Seismic Monitoring of the Northeastern Caribbean Region
Christa G. von Hillebrandt-Andrade, Víctor Huérfano and Juan Lugo
Puerto Rico Seismic Network, Dept. Geology, UPR-Mayagüez
christa@midas.uprm.edu
José Martínez Cruzado, John Clinton and Georgia Cua
Puerto Rico Strong Motion Program, Dept. of Civil and Surveying Engineering,
UPR-Mayagüez
martinez@uprm.edu
The seismicity of the northeastern Caribbean region is monitored jointly by the Puerto
Rico Seismic Network (PRSN) and the Puerto Rico Strong Motion Program (PRSMP) of
the University of Puerto Rico at Mayagüez. The objectives of the two networks are to
record, process, analyze, and research local, regional and teleseismic earthquakes. The
ultimate goals are to produce high quality data and information in order to be able to
respond to the needs of emergency management and the industrial, academic and
research communities, as well as the general public.
The PRSN was established in 1974 to monitor the seismicity and identify earthquake
sources in the Puerto Rico Region (latitudes 17.00N-20.00N and longitudes 63.5W69.00W). In 1987 it was transferred to the Geology Department, University of Puerto
Rico at Mayagüez. It presently operates 10 short period stations and 12 broadband
stations throughout Puerto Rico and the US and British Virgin Islands. The analogue
short period seismic stations consist of Teledyne S-13 and Mark L-4 seismometers and
the data is continuously digitized at 100 sps at the offices of the PRSN. The broadband
stations (BB) consist of Guralp CMG 40T, CMG 3 ESP and CMG 3T seismometers and
24 bit Refraction Technology, DAQ and Quanterra digitizers sampling at 40 sps. The
BB’s are linked in real time to the central data collection center via Monitron UHF digital
radios, DDS 56K telephone lines, spread-spectrum radios and Internet service. The
Earthworm system is used to store and distribute the data. PR-DANIS software
developed at the PRSN is used for locating and processing earthquakes. The data is
saved in GSE2.1 format. As part of the emergent Puerto Rico and Virgin Islands
Tsunami Warning System, the Early Bird system developed by the Alaska Tsunami
Warning Center was installed in 2003 to automatically locate, calculate magnitudes and
distribute earthquake information. This system monitors the PRSN stations as well as
some 15 other stations operating in the America’s and Atlantic. A system to
automatically determine Regional Moment Tensors is currently being developed.
The Puerto Rico Strong Motion Program (PRSMP) has also been in operation since the
1970’s. Currently the Program maintains a network of 75 3-component ETNA stations,
which are primarily located in the urban areas – in fire stations and church grounds. In
addition there are 7 densely instrumented structures (2 bridges, 3 concrete dams and 2
high-rise buildings) with 9-12 channel K-2 systems. Recent initiatives have concentrated
on introducing real-time communications and recording systems with higher dynamic
range to the network. At the moment, 47 ETNA stations have dial-in capability, and 8
ETNA’s have been installed at free field sites with continuous ethernet telemetry to
Mayagüez. The PRSMP has 8 strong motion sensors co-located with PRSN broadband
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sensors, ensuring the entire seismic frequency and amplitude bandwidth is covered at
these stations. Communication with the stations (as well as PRSN) is supported by
ANTELOPE software which also allows location and magnitude determinations (in
backup to PRSN operations). Research initiatives that are currently being pursued at the
PRSMP include ShakeMap production, regional Mw magnitude calculations, real-time
structural health monitoring, and the installation of 2 more joint stations in the Dominican
Republic.
Sinking of obducted oceanic forearc-arc terrane in Caribbean-South American
plate boundary zone
John Weber1, Shimon Wdowinski2, and Edmundo Norabuena2
1Geology Department; Grand Valley State University, Allendale, MI 49403 USA;
weberj@gvsu.edu
2University of Miami, RSMAS-MGG, 4600 Rickenbacker Causeway, Miami, FL 33149
USA
On April 22, 1997 the largest (M 6.6) recorded earthquake in Trinidad-Tobago occurred
near the boundary between the obducted oceanic arc-forearc of the Tobago terrane and
continental South America. A WSW striking (250° azimuth), shallowly dipping, dextralnormal fault ruptured a shallow (≤ 5-15 km deep) fault patch ~10 km south of Tobago.
This event is anomalous given the current ~E-W dextral shearing in the plate boundary.
We use GPS data before and after the earthquake at two sites in Tobago to determine
coseismic offsets. The north-directed GPS-derived offsets are largest in southern
Tobago, closest to the epicenter, and taper off to the north. We used an elastic
dislocation model, with fault dimensions (30 km along strike x 25 km down dip) fixed by
aftershocks, and fault strike fixed to the 250° CMT value. We obtained a best-fit model
with a fault dip of 28° NW, a slip rake of –142°, and a 100 cm average fault slip. We get
a close model match to our GPS-derived and empirically calculated displacements. The
250° strike of the fault patch ruptured matches that of the mapped terrane boundary; the
fault plane is brought into coincidence with the subsurface projection of the mapped
boundary using a ~5 km epicentral depth.
We conclude that this event simply reactivated and inverted the Tobago terrane
boundary, which initially had a low dip angle and opposite (thrust) dip-slip sense of
motion. During the event, the southern, oceanic edge of the Tobago terrane largely
“sunk” into a gravitationally more stable position. Similar earthquakes acting over the
past few m.y. can explain the peculiar sunken geomorphic expression of the entire
accreted oceanic arc-forearc terrane (i.e., the Aruba-Bonaire-Curacao island chain) in the
plate boundary zone.
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Trinidad’s mega-geomorphology records neotectonic ups and downs on edge of the
Gulf of Paria pull-apart basin
John Weber1, John Ritter2, Carol Prentice3 and Laurent de Verteuil4
1Geology
Department, Grand Valley State University, Allendale, MI 49403 USA;
weberj@gvsu.edu
2Geology Department, Whittenberg University, PO Box 720, Springfield, OH 45501
USA
3U.S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025
4Latinum Ltd Saddle Road, Maraval, Trinidad
GPS (Global Positioning System) and GPS-to-triangulation geodesy has provided a
precise short-term snapshot of Trinidad’s horizontal neotectonics; it is now clear that the
Caribbean plate moves ~20 mm/yr eastward relative to South America, and that such
dextral wrenching is concentrated on the El Pilar Fault in Venezuela, and on the Central
Range Fault in Trinidad. This motion must thus step across the intervening Gulf of Paria
(pull-apart basin). Geodesy, however, does a poor job resolving Trinidad’s vertical
motions.
We are studying a suite of geomorphic features that record Trinidad’s Quaternary vertical
neotectonics. Young (Pleistocene ?) alluvial fans near the southern foot of the Northern
Range are elevated and dissected in the east (near Valencia), and buried in the subsurface
beneath Caroni swamp deposits in the west (near Port-of-Spain). Northern Range stream
valley bottoms and peaks both show a systematic and correlative east-to-west decrease in
elevation. Drainage basins in the range tend to widen toward the west. The northern
Trinidad coastline is sharp and straight in the east (i.e., emergent), and scalloped and
highly embayed in the west (i.e., submergent), with a sharp ~N-S-trending transition
(hinge) near Chupara Bay. Uplifted wave-cut marine terraces are present in the high
northeastern Northern Range, and the western islands like Monos and Chachachacare are
drowned Northern Range peaks.
We interpret that a quasi-rigid block encompassing all of the Northern Range, Northern
Basin, and Central Range (and perhaps all of Trinidad) is tilting westward into the Gulf
of Paria pull-apart basin. A good semi-quantitative match is obtained in a comparison
made between the observed east-to-west elevation changes, the magnitude of crustal
stretching in the Gulf (~5 km), and a simple 1-D crustal stretching model. Additional
mapping and dating of Trinidad’s geomorphic features are needed to better quantify
Quaternary uplift and subsidence rates and to better flesh out the titling model.
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Jamaican Seismicity & The Jamaica Seismograph Network
Margaret D. Wiggins-Grandison (margaret.wigginsgrandison@uwimona.edu.jm)
The Earthquake Unit, University of the West Indies, Mona, Kingston 7, Jamaica
Jamaica’s seismicity is associated with the proximity of the island to the North AmericaCaribbean plate boundary on which the sense of faulting is left-lateral. The fault regime
on the island itself is predominantly strike-slip, with some reverse faulting in central
Jamaica. At least one magnitude 4 event is expected per year and as many as three have
occurred in some years. The largest event in recent times occurred in January 1993. The
magnitude was 5.4 and the epicentre was located in the Blue Mountains of eastern
Jamaica. Intensities of VII were experienced in the epicentral region falling off to IV in
western Jamaica. This year a magnitude 5.1 earthquake in central Jamaica triggered
intensities of VII in the epicentral area.
However, earthquakes are not new to Jamaica. The history dates back to the 17th century,
when in 1692 the city of Port Royal was destroyed. And to date, fourteen earthquakes of
intensity VII and higher are documented, along with numerous smaller events. In 1957 a
magnitude 6.8 earthquake with epicentre near Montego Bay caused intensities of VIII in
western Jamaica. Following this event the Jamaica Seismograph Network (JSN) was
started. Annually, about 200 earthquakes on and near to Jamaica are recorded.
The JSN consists of twelve analogue, short-period stations. These are linked in real-time
by radio telemetry to the Central Recording Station (CRS) which is located at the Mona
campus of University of the West Indies in Kingston. Four stations have threecomponents while the remaining eight have vertical seismometers only. Mark L-4C 1Hertz seismometers are used along with Geotech amplifiers, modulators and
demodulators. One Guralp CMG 40-T broadband seismograph and DM24 digitiser is
located at Mona and there are seven Kinemetrics digital accelerographs installed across
the island.
At the CRS the signals are digitized at 50 Hertz using a National Instruments AMUX64T 16-bit AD board and a PC-based DOS-driven seismic data acquisition (SDA)
system. A Trimble SVee8 GPS is used for timing. The signals are demultiplexed and
processed on a PC-based windows-driven seismic data processing (SDP) system. Both
the SDA and SDP are products of the Geophysical Institute of Israel. That particular
digitizer board and on-board GPS are no longer being manufactured therefore the EQU is
embarking on changing from the SDA to SEISLOG data logging software from the
University of Bergen (UiB). SEISLOG is more versatile and can be configured to
operate with a number of standard digitisers, including Earth Data, SARA and others.
SEISAN, also from UiB, running on a UNIX platform is already being used for more
advanced data processing and analyses.
In the last five years a number of studies have been conducted using local earthquake
data. These include determining a new Jamaican crustal model from inversion of travel
times; measuring crustal attenuation using coda and S-wave decay envelopes; and
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modelling the stress regime of the island’s crust by analysing fault plane solutions of
local earthquakes.
Reservoir Characterization and Hydrocarbon Implications of the Early
Pliocene Deltaic Sedimentary Succession of the Columbus Channel, Trinidad
René Winter – MS Candidate, University of Texas, Austin.
Ron Steel - Supervisor, University of Texas, Austin
Ian Stewar - Advisor, Exploration Advisor, BPTT, Trinidad.
The Pliocene–Pleistocene succession of the Columbus Basin off SE Trinidad has been a
prolific hydrocarbon province. A recent stratigraphic initiative achieved basinwide
correlation of the stacked, 4th/5th-order sequences of the Plio-Pleistocene shelf succession
that record the regional cyclic shelf transits of the Plio-Pleistocene Orinoco Delta. This
new stratigraphy has the potential to drive new play concepts that can sustain reserve
growth as the current reservoirs mature. Integration of well, outcrop and seismic data
between the onshore Southern Basin and offshore Columbus Channel is allowing
reconstruction of the evolution of the Early Pliocene shelf margin as it accreted
eastwards. The earliest Pliocene growth of the paleo-Orinoco shelf margin in the inner
Columbus Channel and back into Venezuela shows a spectacular development of shelfedge collapse and canyons, suggesting sediment by-pass into the deepwater basin at this
time. This rapid regressive growth of the shelf margin reflects a shift and re-organization
of the Orinoco Delta into this region. This was followed by a time of significant
transgression and eastward backstepping of the delta. Subsequent early Pliocene
regression brought the delta back to the shelf edge and initiated a new period of vigorous
shelf-margin growth. In contrast to the preceding regressive period, there was now
abundant growth-fault development but apparently little canyon generation
accompanying shelf-margin accretion. Detailing the role of the paleo-Orinoco and this
early history of development of the Orinoco Shelf Margin will involve an integration of
seismic and well data with outcrop studies along the south coast of Trinidad.
Origin Of The Caribbean Plate: A View From Aruba And Curacao
J. E. Wright and S.J. Wyld, Department of Geology, University of Georgia, Athens GA
30602; jwright@gly.uga.edu
Geochemical studies of widely dispersed basaltic igneous rocks believed to be
accreted fragments of the Caribbean plate are interpreted to indicate an oceanic plateau
origin. Some recent models suggest that the plateau formed in the Pacific and that arrival
of the plateau at the subducting boundary of a west-facing arc led to subduction reversal
trapping the overthickened plateau crust behind the newly formed east-facing arc.
Basaltic lavas and diabasic intrusions on the Leeward Antilles islands of Aruba and
Curacao are believed to represent fragments of the Caribbean plate. Detailed mapping
coupled with ongoing geochronological investigations of these islands, leads us to an
alternative model for the development of the Caribbean plate. Field relations on Aruba
and Curacao indicate that both islands became emergent in the Late Cretaceous. Basalt
and diabase on both islands exhibit abundant evidence for Late Cretaceous weathering .
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In addition, on Aruba a distinctive unit of Late Cretaceous basaltic accretionary tuff
overlies weathered basalt and diabase, further indicating subaerial conditions. Following
emergence , the geologic evolution of the two islands significantly diverged. Aruba
underwent regional deformation and metamorphism prior to emplacement of a tonalite
batholith at 89 ± 1Ma, whereas Curacao records subsidence and deep marine
sedimentation. We suggest that the basaltic rocks on Aruba and Curacao formed at the
intersection of a spreading ridge and mantle plume. While both islands were above the
plume thermal anomaly they ultimately became emergent and underwent subaerial
erosion. Following this Aruba was partially subducted beneath an east-facing arc along
with the mantle plume. Curacao moved off the axis of the thermal anomaly due to seafloor spreading, subsided and continued to receive hemipelagic sedimentation while
Aruba was still at depth. Subduction of the mantle plume led to crustal thickening in the
backarc region producing the overthickened crust of the Caribbean plate.
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