Global and Planetary Change 24 Ž2000. 41–58
www.elsevier.comrlocatergloplacha
Elevated marine terraces from Eleuthera žBahamas/ and Bermuda:
sedimentological, petrographic and geochronological evidence for
important deglaciation events during the middle Pleistocene
Pascal Kindler a,) , Paul J. Hearty b
a
Section of Earth Sciences, UniÕersity of GeneÕa, Maraıchers
13, 1211 GeneÕa 4, Switzerland
ˆ
b
4208 Ai Road, P.O. Box 190, Kalaheo, Kauai, HI 96741, USA
Received 15 February 1999; accepted 15 March 1999
Abstract
Sedimentological, petrographic and geochronological Žuranium series and amino acid racemization dating. study of
middle Pleistocene deposits from the archipelagos of Bermuda and The Bahamas revealed the occurrence of marine terraces
of possible stage 11 age at q2, q7 and over 20 m above mean sea level. Considering the tectonic stability of the
investigated regions, these elevated deposits likely correspond to three discrete, higher than present sea levels during this
time period, which is regarded by many as the warmest interglacial of the late Quaternary. It follows that warmer than
present climatic conditions might profoundly modify water distribution between the cryosphere and the oceans. The
punctuated nature of our stratigraphy further suggests that future deglaciation might not be a smooth process, but could be
marked by rapid ice-sheet breakdown leading to abrupt, meter-scale sea-level rises. Given the long period of warm climate
and stable sea level of the past few thousands of years and CO 2 loading of the atmosphere, the probability of a rapid eustatic
rise must be seriously considered. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Bahamas; Bermuda; Middle Pleistocene; marine terraces; geochronology; sedimentology; sedimentary petrography; eustacy; Ice
caps
1. Introduction
Many uncertainties remain regarding the hydrosphere response to the recent anthropogenic rise in
global temperature because the controlling factors
and complex feedback mechanisms interconnecting
the external geospheres are not fully understood and
difficult to model. Wigley and Raper Ž1993. cau)
Corresponding author. Tel.: q41-22-702-6649; fax: q41-22320-5732.
E-mail address: kindler@sc2a.unige.ch ŽP. Kindler..
tiously predict that thermal expansion of the oceans
and the melting of land-based ice will raise sea level
by 0.03–1.24 m Žbest estimate 0.46 m. during the
next century. By contrast, Mercer Ž1978. proposed
that sudden disintegration of the West Antarctic ice
sheet ŽWAIS., which is mostly grounded on land
below sea level, could possibly add another 5–6 m
of waters into the oceans within the coming century.
Most recent theoretical studies and glaciological field
evidence do not seem to support the idea of WAIS
instability ŽBentley, 1997; Oppenheimer, 1998., but
geological data of higher than present sea levels
0921-8181r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 8 1 8 1 Ž 9 9 . 0 0 0 6 8 - 5
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
42
during the last interglacial are widespread ŽSelivanov,
1992. and Antarctic-ice collapse has been invoked to
account for the peak late Quaternary datum at ca.
6–7 m at the beginning of this time interval Žisotopic
substage 5e; Mercer, 1978; Neumann and Hearty,
1996..
In this paper, we present sedimentological, petrographic and geochronological data from Bermuda
and The Bahamas confirming that sea level was also
close to its 5e level during at least one middle
Pleistocene interglacial Žpossibly isotope stage 11;
Hearty and Kindler, 1995a. and briefly exceeded the
q20 m datum near the end of that period. Our data
further provide new insights about the validity of the
oxygen-isotope record from deep-sea sediments as a
sea-level indicator, the stability of large ice sheets,
and the possible modes of deglaciation.
2. Setting and methods
In the following sections, we present data from
three geological sites. Two of them are situated on
Eleuthera Island in the northwestern Bahamas; the
other one is located on the main island of Bermuda
in the middle of the North Atlantic Ocean ŽFig. 1..
The Bahamas islands represent the emerged portions of a series of isolated carbonate platforms
located to the E of Florida and to the N of Cuba, and
extending for more than 1200 km in a N–S direction, and 400 km in an E–W direction ŽFig. 1..
Fig. 1. Location map of study areas.
Fig. 2. Tectonic setting of the northwestern Bahamas. Note proximity of the banks to the North American–Caribbean plate boundary and ancient faults inherited from the late Jurassic rifting phase.
These platforms are standing on the passive North
American continental margin and appear to be affected by slow Ž1.6 cmr10 3 years, Lynts, 1970.
subsidence largely due to thermally induced sedimentary loading ŽPindell, 1985.. Nonetheless, the
archipelago lies in close proximity to the North
American–Caribbean plate boundary and is further
deeply underlain and dissected by a number of normal and wrench faults inherited from an upper Jurassic rifting phase ŽFig. 2.. These faults are presumed
to be inactive today ŽSheridan et al., 1988., but
recent sedimentological and seismic data suggest that
slow compressional deformation occurs in the western part of the archipelago ŽSantaren Anticline,
Masaferro et al., 1998.. Lying in an abyssal plain
setting about 1500 km northeast of The Bahamas, the
Bermuda platform supports approximately 150 islets
and consists of a thin Žca. 100 m. carbonate cap
overlying a volcanic pedestal ŽOfficer et al., 1952..
Despite the occurrence of two earthquakes of magnitude greater than 5.0 in 1988 ŽHartsock et al., 1995.,
the Bermuda region is considered to be tectonically
stable ŽLand et al., 1967; Stanley and Swift, 1968..
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
The stratigraphic record exposed in both areas consists of Ž1. peritidal limestone units formed during
interglacial periods when the platforms were flooded,
and Ž2. terra rossa paleosols which probably developed during glacial times when carbonate production
was shut off due to a lowered sea level. The Bahamian record extends from the middle Pleistocene
to the late Holocene Žfrom isotope stage ?13 to stage
1; Kindler and Hearty, 1997., whereas the longer
Bermudian record further includes one limestone
unit of early Pleistocene age ŽLand et al., 1967;
Hearty and Vacher, 1994.. Kindler and Hearty Ž1996.
proposed that climatic conditions controlled the petrographic composition of Bahamian limestone units.
Deposits accumulated during warmer than present
interglacials or interstadials Že.g., isotope substage
5e. predominantly include ooids and peloids; in contrast limestone units formed when climate was comparable or seemingly cooler than present Že.g., substage 5a. are characterized by skeletal particles.
Bermudian units exclusively consist of bioclastic
calcarenites ŽMackenzie, 1964. and reflect a climate
history generally cooler than The Bahamas.
The tectonic quiescence of both Bermuda and The
Bahamas makes them particularly suitable for extracting information about interglacial and interstadial sea levels from fossil coastal deposits Že.g.,
Land et al., 1967; Harmon et al., 1978; Kindler and
Bain, 1993; Hearty and Kindler, 1995a; Meischner et
al., 1995; Neumann and Hearty, 1996.. Lower than
present stands of sea level can be readily identified
by the occurrence of large-scale, landward-dipping
eolian foresets in the modern intertidal or subtidal
zones. By contrast, higher than present sea levels
may be recognized by emergent in situ coral reefs
and perched beaches. The latter are usually distinguished in the field by large-scale, planar cross-beds
with a low-angle seaward dip and, at a smaller scale,
by the occurrence of large intergranular pores Žkeystone vugs or fenestrae. which result from the trapping of air in beach sands by breaking wave action
ŽDunham, 1970.. The intertidal origin of such deposits can further be confirmed under a petrological
microscope by the occurrence of early circumgranular, isopachous, acicular cements Ž‘‘beachrock cements’’. which originally consist of aragonite or
high-Mg calcite and usually precipitate from marine
waters Že.g., Gischler and Lomando, 1997..
43
Basic stratigraphic and morphostratigraphic ŽVacher, 1973; Garrett and Gould, 1984. principles were
used in the field as a measure of relative age of
Bahamian and Bermudian limestone units and thus
associated sea-level events. Additional age information was obtained from Hearty Ž1998. and Hearty et
al. Ž1999. who measured the amino acid content of
whole-rock samples collected from the studied deposits. This method, which relies on the slow conversion Žracemization. of L-amino acids to their Disomer form, is fully explained and discussed in
Hearty et al. Ž1992. for Bermuda and Hearty and
Kindler Ž1993, 1994. for The Bahamas. These authors measured the epimerization of D-alloisoleucine
and L-isoleucine, or ArI ratio, which is close to zero
in Holocene samples and increases with age up to an
equilibrium value of 1.30. Absolute ages were obtained from Hearty et al. Ž1999. who applied thermal
ionization mass spectrometric ŽTIMS. determination
of 230 Th and 231 Pa to travertine and coral fragments
following analytical procedures described by Edwards et al. Ž1987.. R.L. Edwards and H. Cheng
carried out TIMS dating at the University of Minnesota Isotope Laboratory in Minneapolis.
Fig. 3. Geologic map of the Glass Window area ŽNorth Eleuthera.
showing the location of the studied sections Žmodified from
Hearty and Kindler, 1995b..
44
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
3. Results
3.1. Bahamas data
Eleuthera Island lies in close proximity to the
northeastern margin of the Great Bahama Bank and
is fully exposed to the winds and swells of the open
ocean. For this reason, limestone units have built up
vertically rather than laterally as in lower energy
settings ŽKindler and Hearty, 1997.. Marine erosion
has cliffed these deposits forming remarkable exposures which are best accessible during fair weather
and at low tide. Previous stratigraphic studies in this
area include those of Kindler and Hearty Ž1995.,
Hearty Ž1998. and Hearty and Kindler Ž1995b.. In
the next paragraphs, we describe two geological
sections, EGC a3 and EGC a6 ŽEGC stands for
Eleuthera Goulding Cay. located along the Atlantic
shoreline of the island at, respectively, 2100 and
1350 m to the SE of the Glass Window bridge ŽFig.
3..
Fig. 4. Sedimentological log of EGC a3 and EGC a6. Beach
deposits characterized by low-angle cross-bedding and fenestrae
occur at q2, q7 and q17 m above MSL.
3.1.1. Section EGC a3
The lower part of this ca. 25 m-high section
displays two massive limestone units separated by a
Fig. 5. View of the basal part of EGC a3 showing the lower units Ž3a, 3b. and intervening erosion surface Ždashed line.. Cliff height is
about 15 m.
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
sloping erosional surface and capped by a prominent
karstic surface ŽFigs. 4 and 5.. The petrographic
composition of both units is very similar ŽTable 1..
They contain up to 80% of peloids and ooids and a
minor amount of bioclasts Žalgal, coral and echinoid
fragments, benthic foraminifers.. Although aragonite
may still be present in some samples, these rocks are
heavily cemented and recrystallized ŽFig. 6.. In situ
calcitized ooids ŽRichter, 1983. are common. The
45
lower unit Ž3a. shows low-angle, seaward-dipping
cross-beds and fenestrae near its base, and steep
landward-dipping foresets in its upper part. The former beds can be interpreted as beach deposits,
whereas the latter reflect deposition in an eolian
setting. The occurrence of pedogenic microfabrics
Ž Microcodia, micritic rinds, see Bain and Foos, 1993.
in the uppermost centimeters of the eolian facies
suggests that 3a was once overlain by a paleosol,
Table 1
Petrographic data from studied Bahamian sections. Statistics are based on 500-point counts per thin-section. S ratio is obtained by dividing
the percentage of bioclasts by the total percentages of ooids, peloids and bioclasts. For more details see Kindler and Hearty Ž1996.
Field a
Lab a
Setting
% Grains
Pores
Cement
Bioclasts
Ooids
Peloids
Misc.
S ratio
Aragonite
Goulding Cay a 3
Unit 3c
EGC 3f2
EL 116
EGC 3f
EL 91
EGC 3f2
EL 168
EGC 3e
EL 142
beach
beach
beach
beach
57.2
52.2
60.0
46.0
53.9
3.6
21.4
12.2
21.0
14.6
39.2
26.4
27.8
33.0
31.6
5.7
16.8
15.1
12.1
12.4
25.0
15.6
12.1
11.4
16.0
63.7
64.6
66.9
68.9
66.0
5.6
3.0
5.9
7.6
5.5
0.060
0.173
0.160
0.131
0.132
present
?
abundant
present
Unit 3b
EGC 3c3
EGC 3g2
EGC 3c2
EGC 3d
EL 141
EL 167
EL 140
EL 115
eolian
eolian
beach
beach
65.8
65.8
59.6
50.8
60.5
1.8
4.6
5.8
8.4
5.2
32.4
29.6
34.6
40.8
34.4
14.7
10.0
11.9
8.9
11.4
11.8
7.1
8.1
3.6
7.7
71.1
81.8
74.8
85.7
78.4
2.4
1.1
5.2
1.8
2.6
0.151
0.101
0.126
0.091
0.117
present
abundant
traces
?
Unit 3a
EGC 3a2
EGC 3c
EL 139
EL 114
eolian
beach
49.0
54.8
51.9
13.4
10.0
11.7
37.6
35.2
36.4
25.8
14.0
19.9
5.8
7.4
6.6
63.7
76.7
70.2
4.7
1.9
3.3
0.271
0.143
0.206
traces
present
Goulding Cay a 6
Unit 6f
EGC 6f3
EL 113
EGC 6f2
EL 112
EGC 6g
EL 138
EGC 6f1
EL 111
beach
beach
beach
beach
49.4
60.0
58.0
51.9
73.1
5.8
11.2
3.4
5.6
8.7
44.8
28.8
38.6
42.5
51.6
23.5
12.8
32.5
13.9
27.6
4.5
10.3
2.4
2.4
6.5
70.8
74.5
62.8
80.4
96.2
1.2
2.4
2.3
3.3
3.1
0.238
0.131
0.333
0.144
0.282
present
present
present
present
Unit 6e
EGC 6e4
EGC 6e3
EGC 6d2
EGC 6d1
EL 137
EL 136
EL 110
EL 109
eolian
eolian
eolian
eolian
54.2
49.2
56.6
58.4
54.6
11.8
7.0
7.2
3.6
7.4
34.0
43.8
36.2
38.0
38.0
9.3
11.7
20.8
9.4
12.8
8.2
8.3
10.0
8.0
8.6
79.6
74.0
66.9
80.4
75.2
2.9
6.2
2.3
2.2
3.4
0.096
0.124
0.213
0.096
0.132
Unit 6a r c
EGC 6c2
EGC 6c
EGC 6a
EL 135
EL 108
EL 107
? eolian
? eolian
? eolian
64.2
61.0
62.0
62.4
22.4
13.9
20.8
19.0
14.4
25.1
17.2
18.9
95.1
91.2
91.4
92.6
0.0
0.0
0.0
0.0
4.6
5.0
6.2
5.3
0.4
3.8
2.4
2.2
0.954
0.948
0.936
0.946
present
present
present
absent
absent
absent
46
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
Fig. 6. Sample EL 167, section EGC a3, unit 3b, eolian facies. Peloidal grainstone. Peloids have turned black when thin-section was
immersed in Feigl’s solution, indicating an aragonitic composition. Note high percentage of cement. Polygonal boundaries Žarrow. suggest
that early diagenesis occurred in a phreatic setting.
probably stripped prior to deposition of the second
unit Ž3b.. The latter displays a vertical succession of
sedimentary structures from subtidal Žsmall-scale
trough cross-beds., intertidal Žlow-angle planar
cross-beds. to eolian Žsteeply landward-dipping
cross-beds, Figs. 4 and 5.. The occurrence of an
early generation of isopachous fibrous cement
Ž‘‘beachrock cement’’. within the low-angle planar
cross-beds confirms their intertidal origin. Relative
sea-level elevation during deposition can be estimated at about q2 m for 3a and q7 m for 3b.
Samples collected from these units yielded ArI ratios between 0.678 " 0.024 and 0.632 " 0.013 ŽFig.
4; Hearty, 1998. indicating a middle Pleistocene age.
Such an age is further supported by stratigraphic
relationships Ž3b is laterally overlain by early Sangamonian deposits; Kindler and Hearty, 1995. and by a
high degree of diagenetic transformation within the
rocks ŽLand et al., 1967; Kindler and Hearty, 1997..
The eolian facies of 3b is further carved by an
erosional bench from about 13 to 22 m above mean
sea level ŽMSL, Figs. 4 and 7.. One sample collected
from unit 3b just below the platform surface revealed
an early generation of fibrous cement typical of the
marine diagenetic realm ŽLongman, 1980., indicating
that the erosional bench was cut by marine processes. This platform is overlain by a thin limestone
unit Ž3c. characterized by low-angle, seaward-dipping planar cross-beds ŽFig. 7. and the presence of
numerous fenestrae ŽFig. 8.. The petrographic composition of these rocks is similar to that of underlying units although it contains a higher proportion of
ooids ŽTable 1.. Particularly interesting is the presence of a well-preserved early generation of fibrous
cement rimming constituent grains ŽFig. 9. and locally showing a pendant fabric. Such a cement likely
precipitated from marine waters ŽLongman, 1980..
Its presence within fenestrae-rich, low-angle, planar
cross-beds identify 3c as a former beach deposit.
Relative sea-level datum during formation of this
unit can be estimated at about q17 m based on the
occurrence of pendant fibrous cement typical of the
upper intertidal zone. Samples collected from 3c
gave ArI ratios of 0.709 " 0.181 ŽFig. 4; Hearty,
1998.. This value, probably slightly elevated as a
result of surface heating in the thin deposits, is
statistically consistent with those measured from the
underlying units ŽHearty, 1998..
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
47
Fig. 7. Upper part of EGC a3. The upper unit Ž3c. displays low-angle cross-bedding that usually characterize a beach setting. Dashed line
emphasizes the sloping erosional surface between 3c and underlying and adjacent unit Ž3b.. Seawards is to the left. Bag is 50 cm in length.
3.1.2. Section EGC a6
The basal part of this 20 m-high section ŽFig. 4.
consists of two well-lithified, coarse-grained, bioclastic limestone units Ž6arc., separated by an orange, Cerion-rich, sandy protosol Ž6b., and capped
by a red paleosol showing calcrete and breccia horizons Ž6d.. No aragonite has been observed in these
calcarenites which include numerous fragments of
benthic foraminifers as well as recrystallized Halimeda debris ŽFig. 10.. Sedimentary structures have
Fig. 8. Section EGC a3, unit 3c. Fenestral porosity visible both on bed surface and broken slab. Such porosity results from the trapping of
air in sands by breaking waves and is typical of the upper intertidal zone.
48
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
Fig. 9. Sample EL 168, section EGC a3, unit 3c. Cement stratigraphy within 3c limestones. Note early isopachous rims indicating a
phreatic, probably marine, early diagenetic setting Žfibrous crystals are locally preserved.. Younger cement consists of equant calcite crystals
showing a meniscus fabric typical of a fresh-water vadose environment.
been largely erased, but the occurrence a few landward-dipping foresets, intervening protosol, and
widespread fresh-water vadose cements ŽFig. 10.
suggest an eolian depositional setting for these units.
Relative sea level was thus below modern datum
during the formation of 6arc. No reliable ArI ratio
Fig. 10. Sample EL 135, section EGC a6, unit 6arc. Microscopic view of stage ?13 bioclastic calcarenite. Thin, non-isopachous rims of
small calcite crystals Ž‘‘grain-skin’’ cement; Land et al., 1967; arrow. characterize a fresh-water vadose environment.
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
could be obtained at this site, probably because of
the intensity of diagenetic transformations that lowered the concentration of amino acids within the
rocks. However, one sample collected from the same
unit on an adjacent section yielded a ratio of 0.789 "
0.036, suggesting a middle Pleistocene age, possibly
stage 13 or 15 ŽHearty, 1998.. The upper part of the
EGG a6 section consists of a deeply karstified,
massive peloidal–oolitic unit Ž6e, Fig. 4.. These
limestones are strongly cemented and recrystallized,
but still contain traces of aragonite. Fine grain-size,
good sorting and the presence of steep, landward-dipping cross-bedding testify to an eolian origin for
this unit which can be correlated with the 3b eolianite at EGC a3. The absence of subtidal and intertidal
facies within 6e is presumably related to the high
elevation Žq7 m. of the underlying bioclastic calcarenites at EGC a6 andror to erosional processes.
A narrow Žca. 30 m. bench at the elevation of
q16 m ŽFigs. 4 and 11. truncates the 6e unit. One
sample collected just below the platform surface
shows a well-preserved early generation of isopachous fibrous cement, suggesting that the platform
was carved by marine erosion. Superimposed on the
platform is a thin limestone unit Ž6f. showing lowangle cross-beds dipping seaward and numerous fenestrae. Petrographic composition of 6f is similar to
49
that of the underlying unit, although bioclasts may be
abundant in some samples ŽTable 1.. Thin-section
analysis further revealed the presence of an early
generation of isopachous acicular cement typical of
the phreatic marine diagenetic environment ŽLongman, 1980.. Unit 6f can thus be interpreted as a
fossil beach. Relative sea-level datum during deposition of this unit can be estimated at ca. q17 m. ArI
ratios measured from 6f samples average at 0.716 "
0.023 ŽFig. 4; Hearty, 1998., a value nearly identical
to that measured on unit 3c at EGC a3. Both units
can thus be correlated and represent the remnants of
a marine terrace of middle Pleistocene age.
3.2. Bermuda data
Geologic research in Bermuda began in the early
19th century and current understanding of the island
stratigraphy is much refined in comparison with that
of The Bahamas Žsee for example Vacher et al.,
1995.. In a landmark paper, Land et al. Ž1967.
documented a ‘‘marine conglomerate’’ deposited
against a sea cliff carved in the oldest Bermudian
unit ŽWalsingham Formation, early Pleistocene;
Hearty and Vacher, 1994; Hearty et al., 1992. at the
elevation of 28 m above MSL in Government Quarry
ŽFig. 12.. The outcrop was unfortunately destroyed
Fig. 11. View of the upper part of EGC a6 showing units 6e Žeolianite. and 6f Žbeach.. Dashed line emphasizes the contours of unit 6f.
50
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
Fig. 12. Location map of UGQ a4 site on Bermuda.
by quarry expansion a few years later and its relevance to Quaternary sea-level history was never
exploited. A single archive sample from this outcrop,
stored in the Bermuda Aquarium Museum, yielded a
whole-rock ArI ratio of about 0.92, suggesting an
apparent age of ) 700 ka ŽHearty and Vacher, 1994;
Hearty et al., 1992.. The ratio obtained from this
isolated sample is of doubtful significance because
of unknown provenance and depth of burial, and
hence, uncertain thermal history. In early 1997, one
of us ŽPJH., upon the suggestion of David Wingate,
found a lateral equivalent of these deposits in a
well-protected small cave Žsite UGQ a4. in the
quarry wall, located a few tens of meters from the
original marine terrace described by Land et al.
Ž1967..
3.2.1. Site UGQ a4
Located near the western entrance of Government
Quarry, the cave is about 3 m in diameter and is only
accessible by ropes and harness. It is cut in the
eolianites of the Walsingham Formation Ž4a. and,
because of its mainly horizontal dimensions, is interpreted as a former phreatic passage. The cave floor
has been precisely surveyed at q21.6 m. The cavity
is partly filled by a succession of sediments and
flowstone layers ŽFig. 13., including a basal silty
horizon with mm-sized concretions Ž4b., a dark
brown laminated travertine Ž4c., crudely stratified
pebbly calcarenites described in more detail hereafter
Ž4d., a cone-shaped body of fine-grained sand Ž4e.,
and an upper layer of clear laminated travertine Ž4f.,
which partly covers the underlying deposits. The
limit between the pebbly calcarenites Ž4d. and the
underlying travertine Ž4c. is erosional. The former
deposits consist of a basal conglomeratic layer and
an upper interval where pebbles and cobbles are less
abundant. Gravel-sized constituents include limestone clasts from the Walsingham Formation, volcanic-rock fragments, bird bones, whole and fragmented marine shells, and coral debris. Thin-section
analysis of the calcarenite matrix bounding the conglomerate revealed the predominance of bioclasts
Žred alga, coral, echinoid, mollusk and foraminifer
fragments., some of which are still aragonitic, and
lithoclasts Žcalcitized volcanic rocks, skeletal grainstone.. Cement pattern ŽFig. 14. includes an early
generation of isopachous rims Žca. 50 mm in thickness. composed of bladed or fibrous crystals, and a
later generation of equant to bladed crystals forming
menisci at grain contacts, whole or partial rims
around grains and locally filling in pore spaces. Both
cements now consist of low-Mg calcite, but the
fabrics of the earlier one suggest an aragonite or
high-Mg calcite precursor. Sedimentological and petrographic data of the UGQ a4 site will be discussed
in the following section. Three calcarenite samples
Fig. 13. Stratigraphic units at UGQ a4. See text for more
explanations.
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
51
Fig. 14. Sample BER 1, site UGQ a4, base of unit 4d. Grains are bound by two generations of isopachous cement typical of a phreatic
diagenetic environment. Fibrous crystal habit of the inner rim further indicate precipitation from marine waters. Dashed line emphasizes the
limit with the underlying travertine Ž4c..
collected from Unit 4d gave a mean ArI ratio of
0.67 " 0.05 ŽHearty et al., 1999., indicating a middle
Pleistocene age and allowing correlation with the
Lower Town Hill Formation ŽArI s 0.69 " 0.01,
Hearty et al., 1992.. Uranium series TIMS analyses
ŽHearty et al., 1999. gave an infinite age for the
lower flowstone Ž4c. and an average maximal age of
525 " 45 ka for the interior portion of a coral pebble
Ž Montastrea sp.. gathered from the pebbly calcarenites Ž4d.. A chemically reliable age of 420 " 30 ka
52
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
was obtained from the basal 5 mm of the upper
flowstone Ž4f.. The age of the 4d unit can thus be
bracketed with some certainty between 390 and 570
ka.
4. Discussion
4.1. Sedimentological and petrographic data
Deposits exposed at ca. 20 m in both Eleuthera
sites can surely be identified as fossil beaches because: Ž1. the morphology of the underlying platforms clearly results from marine erosion; Ž2. largescale Žlow-angle planar cross-beds. and small-scale
Žfenestrae. sedimentary structures are characteristic
of the intertidal zone; and Ž3. early isopachous cements of likely marine origin occur within both the
perched deposits and the upper interval of the underlying units. In contrast, the Bermuda occurrence is
subject to alternative explanations. The pebbly calcarenites at UGQ a4 could conceivably be interpreted as: Ž1. cave collapse deposits; Ž2. storm sediments forced through a vadose shaft and reworked
by groundwater; and Ž3. marine deposits accumulated in a previously breached phreatic passage. Only
the latter hypothesis implies a relative stand of sea
level higher than the present one during deposition.
Although some collapsed material can be observed at the studied site ŽFig. 13., the first hypothesis can easily be dismissed because of the lithological contrast between unit 4d Žcoarse-grained, pebbly
calcarenites. and the encasing Walsingham Formation Žfine-grained eolianite.. The second hypothesis
has some validity. Unit 4d essentially consists of
marine material, but undoubtedly rests in a karstic
cavity and shows textural similarities with cave sediments described elsewhere Že.g., Engel et al., 1997..
Furthermore, aragonite and high-Mg calcite, which
probably are the precursors of unit 4d early cements,
can also precipitate in a cave environment from
Mg-rich meteoric waters ŽMurray, 1954; Frisia et al.,
1997.. Marine sands and pebbles could thus have
been brought to a high elevation during a storm and
forced into a sinkhole connected with the studied
cave. However, the lack of insoluble material Žsilts
and clays from terra rossa soils. within the studied
sediments does not support the idea of surface wash-
ing by storm waves. In addition, reworking of this
material by vadose water is unlikely because UGQ
a4 is located near the top of a hill and there is a
minimal topography above it. It is thus improbable
that groundwater recharge could have been strong
enough at that location to transport and sort dm-sized
cobbles and deposit clean sands in the cave. More
convincingly, Land et al. Ž1967. and Mackenzie
Žunpublished data. clearly described an erosional
bench below their marine conglomerate that cannot
result from storm processes. Therefore, we conclude
that unit 4d represents a marine deposit accumulated
in an older cave passage that had been breached by
the rising sea. A modern equivalent has been observed by one of us ŽPK. along the southeastern
shoreline of Cat Island ŽBahamas, Fig. 15.. In Watch
Hill Park ŽBermuda., similar small sea caves containing marine rubble of substage 5e age and flowstone
occur at about q2 m ŽMeischner et al., 1995.. The
presence of an early-fibrous cement similar to those
found in modern beachrock could further indicate a
intertidal depositional environment for the elevated
deposits at UGQ a4.
4.2. Age of the perched deposits
Well-preserved in situ coral reefs from the last
interglacial period can and have been accurately
dated using U-series disequilibrium methods Že.g.,
Chen et al., 1991.. Unfortunately, the precision
of the results decreases with increasing age, commonly because of sample diagenesis and ages in ; 500
ka range require confirmation by other lines of
evidence. In this study, age estimates are derived
from stratigraphic and morphostratigraphic analyses,
amino acid racemization ŽAAR. measurements and
ThrU TIMS dating, all of which suggest a middle
Pleistocene age for the elevated marine deposits in
Eleuthera and Bermuda. The perched beaches at
EGC a3 and a6 certainly predate the last interglacial period because they are capped by a karstic
surface that can be followed beneath a well-exposed
Sangamonian sequence ŽKindler and Hearty, 1995;
Hearty, 1998.. The age of the perched marine conglomerate in Bermuda can be stratigraphically constrained between the early Pleistocene Žage of the
Walsingham Formation; Hearty et al., 1992. and the
present, but the outcrop position in ‘‘Older Bermuda’’
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
53
Fig. 15. Breached sea cave partly filled with conglomeratic deposit Žcontours emphasized by dashed line.. This view was taken near
Columbus Point on Cat Island ŽBahamas. at low tide and could correspond to a modern equivalent of UGQ a4 site on Bermuda. Hammer is
36 cm long.
also supports a pre-Sangamonian age. AAR data
show a good correlation between the ca. 20 m deposits from both Eleuthera ŽArI s 0.71. and
Bermuda ŽArI s 0.67., the former values reflecting
the warmer temperature history in The Bahamas.
ArI values measured from the UGQ a4 deposits are
considerably higher than the oldest U-series calibrated aminozone in Bermuda Ž0.44 " 0.03, 204 " 11
ka, Hearty et al., 1992.. ArI ratios from the Eleuthera
sites are also significantly larger than those measured
from well-identified deposits of stage 7 age on that
island Ž0.58 " 0.01, Hearty, 1998. and on neighboring New Providence Ž0.56 " 0.02, Hearty and
Kindler, 1997.. Finally, radiometric dating puts an
upper age limit for the UGQ a4 calcarenites at
420 " 30 ka. The stratigraphic, radiometric and AAR
data thus show that Ž1. the elevated deposits are
probably coeval, and Ž2. they predate the penultimate
interglacial period Žisotope stage 7. by a considerable amount of time. The age of these deposits can
probably be constrained between stages 9, 11 and 13.
Among these, we favor stage 11 Ž427–364 ka,
Bassinot et al., 1994. because several lines of evidence from the marine record ŽBurckle, 1993;
Howard, 1997. indicate that it was an interglacial of
exceptional warmth and duration.
4.3. Origin of perched deposits
The studied deposits record three ancient relative
sea-level stands at ca. q2 m, q7 m and q20 m,
respectively ŽFigs. 4 and 13.. Among the various
factors controlling relative sea level, only the following can induce changes similar in amplitude Ž10–20
m. and time-scale Žprobably 10 ka. to those associated with the perched marine deposits described in
this paper: Ž1. glacio-isostatic subsidence; Ž2. eustatic effect of changes in liquid water on land; Ž3.
regional tectonic motions; and Ž4. glacio-eustatic
variations.
According to Peltier Ž1988, 1998., the postglacial
sea-level history in both The Bahamas and Bermuda
is characterized by monotonic submergence strongly
influenced by the collapse of the northern hemisphere ice-sheet forebulge. Lambeck and Nakada
Ž1992. further claim that, in these regions, the elevated coral reefs and marine shorelines of the last
interglacial actually record a relatiÕe sea-level rise
54
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
linked to increased isostatic subsidence. The same
phenomenon, possibly amplified by the protracted
duration of the corresponding interglacial episode,
could account for the high elevation of the marine
deposits presented in this study. However, we would
like to point out that geophysical models are based
on a series of assumptions Že.g., the timing of onset
and termination of the last interglacial. that are not
fully verified. In addition, the studied terraces in
Eleuthera clearly record an episodic rather than a
continuous trend of sea-level rise. Finally, the most
likely time for terrace formation is isotopic stage 11
which, based on independent geochemical ŽBurckle,
1993; Howard, 1997. and paleontological ŽScherer et
al., 1998. evidence, was an interglacial of exceptional warmth when ocean volume may have been
considerably larger than today. Therefore, we believe
that isostatic subsidence was only a subordinate factor in the building up of the described deposits.
Climate-induced changes in groundwater levels
ŽHay and Leslie, 1990. can theoretically result in
sea-level variations of suitable amplitude and frequency to account for our stratigraphy. However,
according to this model, sea-level rises are expected
to occur during cold and dry periods when the water
table is lowered by decreased precipitation which is
probably not the case during interglacial stages. Thus,
the high relative sea levels recorded by the marine
terraces in Bermuda and The Bahamas cannot be
explained by an input of groundwater from the continents.
The occurrence of recent earthquakes in Bermuda
ŽHartsock et al., 1995. shows that the area is subject
to some tectonic stress probably engendered by
movements of the North American plate from the
Mid-Atlantic Ridge. Thus, although unlikely, vertical
tectonic displacement of the Bermuda platform cannot be totally excluded. This is also true for the
Eleuthera area that could have been uplifted by
transpressive movements along the regional fault
system ŽFig. 2; Sheridan et al., 1988. reactivated by
tectonic activity at the North American–Caribbean
plate boundary. This would adequately explain the
old age of the north-Eleuthera sea cliffs and the
absence of marine or beach deposits at ca. q20 m
elsewhere in The Bahamas. However, except for
vertical fractures formed in response to undercutting
of the bank margin during glacial lowstands ŽAby,
1994., no evidence of faulting Ži.e., displaced beds.
has ever been observed in The Bahamas islands. In
Bermuda, fracture systems appear to be related to
limestone collapse into pre-existing deep caverns
rimming a buried volcanic caldera ŽHartsock et al.,
1995.. Moreover, in both areas, the sedimentary
facies within limestone units predating and postdating the studied deposits occur at the expected elevation for stable or slightly subsident tectonic settings.
In particular, the bioclastic limestones underlying the
studied deposits at EGC a6 ŽFig. 4. only display
eolian bedding, whereas beach or subtidal facies
should be visible if the area had been uplifted by 20
m. Finally, a synchronous tectonic uplift of similar
amplitude in such distant regions as The Bahamas
and Bermuda is not realistic.
The foregoing discussion shows that the elevated
marine deposits described in this study mainly record
episodes of continental ice wastage. If a combination
of steric change, isostatic rebound and melting of
alpine glaciers could possibly explain the first rise to
ca. q2 m, the latter two clearly imply a major
contribution from polar ice. More specifically, a rise
of sea level up to a q20 m datum requires total
disintegration of the Greenland and West Antarctic
ice sheets, which could, respectively, add ca. 5 and 7
m of water to the world oceans ŽDuplessy and Morel,
1990., and a significant input ŽG 6 m. from the East
Antarctic ice sheet. The implications of the glacioeustatic origin of the marine terraces described in
this study are discussed in the following section.
4.4. Implications for sea-leÕel and climate history
The sea-level data gathered from this study bring
new or complementary information regarding the
validity of the oxygen-isotope record from deep-sea
sediments as a proxy indicator of sea level, the
stability of large ice sheets, and the nature of
deglaciations.
4.4.1. Oxygen isotope curÕe as a proxy for sea leÕel
Ever since the work of Shackleton and Opdyke
Ž1973., the d18 O record from deep-sea sediments has
been used as an indicator of continental-ice volume
back through time, and often considered as the best
record of glacio-eustatic sea-level fluctuations during
the Quaternary ŽMatthews, 1990.. Nevertheless, in
addition to indistinguishable elements of ocean tem-
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
perature and salinity, there are some discrepancies
between the d18 O curve and the record obtained
from the study of reefal terraces and fossil shoreline
deposits, from both stable and tectonically active
regions, that justify a critical attitude towards the
limitations inherent in the isotopic record. Particular
points of disagreement concern sea-level elevation
during substage 5a Že.g., Vacher and Hearty, 1989.
and the numbers of highstands during substage 5e
Že.g., Aharon et al., 1980.. The high sea levels
documented in this study correlate well with several
low-latitude benthic records for isotopic stage 11
which indicate a 18 O depletion of approximately 0.2
‰ with respect to stage 1 ŽBurckle, 1993; Raymo,
1997.. These lighter values suggest that the volume
of ocean waters was larger during this period than it
is today. However, in most records, the d18 O curve
for stage 11 shows one single ŽImbrie et al., 1984;
Hodell, 1993. or a double peak ŽPrell et al., 1986.,
whereas our stratigraphy suggests the occurrence of
three fluctuations during this time period. Caution is
thus required when directly translating d18 O curve
wiggles in terms of sea-level changes.
4.4.2. Stability of large ice sheets
There is much controversy about how large ice
sheets, particularly in Antarctica, will respond to
CO 2-induced global warming Žsee for example Meier,
1990; Bentley, 1997; Oppenheimer, 1998.. They
might disintegrate by accelerated discharge and melting Že.g., Rignot, 1998., or, alternatively, build up
because of increased precipitation, as documented
from the Greenland ice sheet ŽZwally, 1989.. In
other words, it is unclear whether the present
cryosphere has reached some kind of interglacial
equilibrium where wastage is compensated by accumulation, or if this apparent stability is only a lure
linked to a lack of both observations and knowledge
of ice-sheet dynamics. Our study suggests that the
present balance between continental ice and ocean
waters is fragile. Warmer climatic conditions, such
as those probably prevailing during stage 11 ŽBurckle,
1993; Hodell, 1993; Howard, 1997; Scherer et al.,
1998., might induce wastage of polar ice sheets,
including parts of East Antarctica, and consequently
elevate sea level to heights comparable to those
recorded from the marine terraces in Eleuthera and
Bermuda.
55
4.4.3. Nature of deglaciations
If ice sheets were to melt further, some knowledge about modes of deglaciation and melting rates
will be of prime importance to evaluate coastal
response and impact on human communities. Several
models have been proposed for ice-sheet demise at
the end of the last glacial period Žsee review in
Ruddiman, 1987., including a ‘‘smooth deglaciation
model’’, a ‘‘two-step model’’, a ‘‘younger Dryas
model’’ Žwith a reversal.. Judging from the elevation
and ages of drowned reefs from the Caribbean region, Blanchon and Shaw Ž1995. more recently proposed that the last deglaciation was punctuated by
sudden ice-sheet collapses and subsequent meterscale sea-level rise events ŽCREs or Catastrophic
Rise Events; Blanchon and Shaw, 1995.. Similarly,
geological data from both the terrestrial and marine
record support a two-step deglaciation at the isotopic
stage 6r5e transition Žtermination II, Seidenkrantz et
al., 1996.. The stratigraphic record at EGC a3 shows
three shallowing-upward sequences of facies separated by marine erosional surfaces. The latter probably represent short periods of accelerated sea-level
rise, shifting coastal depocenters landward. In contrast, the intervening sedimentary sequences may
reflect times of stable or slowly rising sea level
characterized by a seaward progradation of coastal
sediments. Our data suggest that the deglaciation
associated with the studied deposits occurred in
pulses. Had polar ice slowly melted, sediment production would have kept pace with sea-level rise and
the geologic record at EGC a3 would be represented
by one thick sequence of coastal sediments. Our data
further agree with the scenario first envisaged by
Hollin Ž1965., and recently reactualized by Neumann
and Hearty Ž1996., that the end of the last interglacial period was marked by a rapid sea-level rise
triggered by the surging of Antarctic ice sheets.
5. Conclusions
The occurrence of marine terraces of middle
Pleistocene age at ca. q2, q7 and more than 20 m
in the tectonically stable, or slightly subsident
archipelagos of Bermuda and The Bahamas documents major deglaciation events during this time
interval. Stratigraphic, geochemical ŽAAR. and ra-
56
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
diometric data constrain the age of these terraces
between isotopic stages 13 Ž528–474 ka, Bassinot et
al., 1994. and 9 Ž334–301 ka, idem.. We tend to
correlate these deposits with isotopic stage 11 Ž427–
364 ka, idem. because the high sea levels recorded
by our data are essentially coherent with the d18 O
record and other lines of evidence from both the
deep sea and continental realms ŽBurckle, 1993;
Howard, 1997; Scherer et al., 1998. which indicate
this was the warmest interglacial in the past half
million years. In addition, our best constraining radiometric date Ž420 " 30 ka. agrees with a stage 11
age for these deposits. Considering the tectonic setting of the studied areas, the values of q2, q7 and
q20 m are minimum elevations that sea level may
have reached during this time interval. It follows that
the present-day equilibrium of the cryosphere–ocean
system may be fragile, and that warmer climatic
conditions could modify the water balance between
these two reservoirs. Finally, our data support punctuated deglaciation models proposed for this and the
previous interglacial, whereby the demise of ice
sheets is marked by sudden collapses triggering extremely rapid Žca. 100–300 yr.. meter-scale sea-level
rises. Considering the warm climate and slowly rising sea level of the past few millennia, one is
compelled to examine a scenario that includes a
potentially disastrous rise in sea level.
Acknowledgements
This work was partly supported by a grant from
the National Science Fund of Switzerland Ža2040638.94.. We are very thankful to Andre´ Droxler
and John Farrell for inviting us to present our data at
the 1997 AGU Spring Meeting special session on
‘‘The Carbonate Marine System during Stage 11’’.
We thank Paul Aharon, Andre´ Droxler and an
anonymous reviewer for constructive comments on
an earlier draft of this paper. Contribution a24 from
the Bermuda Biodiversity Project, Bermuda Aquarium, Natural History Museum and Zoo.
References
Aby, S.B., 1994. Relation of bank-margin fractures to sea-level
change, Exuma Islands, Bahamas. Geology 22, 1063–1066.
Aharon, P., Chappell, J., Compston, W., 1980. Stable isotope and
sea-level data from New Guinea supports Antarctic ice-surge
theory of ice ages. Nature 283, 649–651.
Bain, R.J., Foos, A.M., 1993. Carbonate microfabrics related to
subaerial exposure and paleosol formation. In: Rezak, R.,
Lavoie, D.L. ŽEds.., Carbonate Microfabrics. Springer, New
York, pp. 19–27.
Bassinot, F.C., Labeyrie, L.D., Vincent, E., Quidelleur, X., Shackleton, N.J., Lancelot, Y., 1994. The astronomical theory of
climate and the age of the Brunhes–Matuyama magnetic
reversal. Earth Planet. Sci. Lett. 126, 91–108.
Bentley, C.R., 1997. Rapid sea-level rise soon from West Antarctic ice sheet collapse? Science 275, 1077–1078.
Blanchon, P., Shaw, J., 1995. Reef drowning during the last
deglaciation: evidence for catastrophic sea-level rise and icesheet collapse. Geology 23, 4–8.
Burckle, L.H., 1993. Late Quaternary interglacial stages warmer
than present. Quat. Sci. Rev. 12, 825–831.
Chen, J.H., Curran, H.A., White, B., Wasserburg, G.J., 1991.
Precise chronology of the last interglacial period: 234 U– 230 Th
data from fossil coral reefs in The Bahamas. Geol. Soc. Am.
Bull. 103, 82–97.
Dunham, R.J., 1970. Keystone vugs in carbonate beach deposits.
Am. Assoc. Pet. Geol. Bull. 54, 845, Abstr.
Duplessy, J.-C., Morel, P., 1990. In: Jacob, O. ŽEd.., Gros temps
sur la planete.
` Paris, 296 pp.
Edwards, R.L., Chen, J.H., Wasserburg, G.J., 1987. 238 U– 234 U–
230
Th– 232 Th systematics and the precise measurement of
time over the past 500,000 years. Earth Planet. Sci. Lett. 81,
175–192.
Engel, A.S., Lascu, C., Badescu, A., Sarbu, S., Sasowsky, I.,
Huff, W., 1997. A study of cave sediment from Movile Cave,
Southern Dobrogea, Romania. In: Jeannin, P.-Y. ŽEd.., Proc.
12th Int. Congress of Speleol., La Chaux de Fonds, Switzerland. pp. 247–250.
Frisia, S., Borsato, A., Fairchild, I.J., Longinelli, A., 1997. Aragonite precipitation at Grotte de Clamouse ŽHerault,
France.: role
´
of magnesium and drip rate. In: Jeannin, P.-Y. ŽEd.., Proc.
12th Int. Congress of Speleol., La Chaux de Fonds, Switzerland. pp. 247–250.
Garrett, P., Gould, S.J., 1984. Geology of New Providence Island,
Bahamas. Geol. Soc. Am. Bull. 95, 209–220.
Gischler, E., Lomando, A.J., 1997. Holocene cemented beach
deposits in Belize. Sediment. Geol. 110, 277–297.
Harmon, R.S., Schwarcz, H.P., Ford, D.C., 1978. Late Pleistocene
sea level history of Bermuda. Quat. Res. 9, 205–218.
Hartsock, J.K., Woodrow, D.L., McKinney, D.B., 1995. Fracture
systems in northeastern Bermuda. In: Curran, H.A., White, B.
ŽEds.., Terrestrial and Shallow Marine Geology of the Bahamas and Bermuda. Geol. Soc. Am., Spec. Pap. 300, 325–
334, Boulder.
Hay, W.W., Leslie, M.A., 1990. Could possible changes in global
groundwater reservoir cause eustatic sea-level fluctuations? In:
Natl. Res. Counc. ŽEd.., Sea Level Change. Natl. Acad. Press,
Washington, pp. 161–170.
Hearty, P.J., 1998. The geology of Eleuthera Island, Bahamas: a
rosetta stone of Quaternary stratigraphy and sea-level history.
Quat. Sci. Rev. 17, 333–355.
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
Hearty, P.J., Kindler, P., 1993. New perspectives on Bahamian
geology: San Salvador Island, Bahamas. J. Coastal Res. 9,
577–594.
Hearty, P.J., Kindler, P., 1994. Straw men, glass houses, apples
and oranges: a response to Carew and Mylroie’s comment on
Hearty and Kindler Ž1993.. J. Coastal Res. 10, 1095–1104.
Hearty, P.J., Kindler, P., 1995a. Sea-level highstand chronology
from stable carbonate platforms ŽBermuda and The Bahamas..
J. Coastal Res. 11, 675–689.
Hearty, P.J., Kindler, P.,1995. The geology of North Eleuthera,
Bahamas: a ‘‘rosetta stone’’ of Quaternary stratigraphy and
sea levels. Field trip a3 guideb, First SEPM Congr. on
Sedimentary Geology, St. Pete Beach, Fla., 23 pp.
Hearty, P.J., Kindler, P., 1997. The stratigraphy and surficial
geology of New Providence and surrounding islands, Bahamas. J. Coastal Res. 13, 798–812.
Hearty, P.J., Kindler, P., Cheng, H., Edwards, R.L., 1999. A q20
m middle Pleistocene sea-level highstand ŽBermuda and The
Bahamas. due to partial collapse of Antarctic ice. Geology 27,
375–378.
Hearty, P.J., Vacher, H.L., 1994. Quaternary stratigraphy of
Bermuda: a high-resolution pre-Sangamonian rock record.
Quat. Sci. Rev. 13, 685–697.
Hearty, P.J., Vacher, H.L., Mitterer, R.M., 1992. Aminostratigraphy and ages of Pleistocene limestones of Bermuda. Geol.
Soc. Am. Bull. 104, 471–480.
Hodell, D.A., 1993. Late Pleistocene paleoceanography of the
South Atlantic sector of the Southern Ocean: Ocean Drilling
Program Hole 704 A. Paleoceanography 8, 47–67.
Hollin, J.T., 1965. Wilson’s theory of ice ages. Nature 206,
12–16.
Howard, W.R., 1997. A warm future in the past. Nature 388,
418–419.
Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C.,
Morley, J.J., Pisias, N.G., Prell, W.L., Shackleton, N.J., 1984.
The orbital theory of Pleistocene climate: support from a
revised chronology of the marine d18 O record. In: Berger,
A.L. et al., ŽEd.., Milankovitch and Climate, Part I. Reidel,
Dordrecht, The Netherlands, pp. 269–305.
Kindler, P., Bain, R.J., 1993. Submerged upper Holocene
beachrock on San Salvador Island, Bahamas: implications for
recent sea-level history. Geol. Rundsch. 82, 241–247.
Kindler, P., Hearty, P.J., 1995. Pre-Sangamonian eolianites in the
Bahamas? New evidence from Eleuthera Island. Mar. Geol.
127, 73–86.
Kindler, P., Hearty, P.J., 1996. Carbonate petrography as an
indicator of climate and sea-level changes: new data from
Bahamian Quaternary units. Sedimentology 43, 381–399.
Kindler, P., Hearty, P.J., 1997. Geology of The Bahamas: architecture of Bahamian Islands. In: Vacher, H.L., Quinn, T.M.
ŽEds.., Geology and Hydrogeology of Carbonate Islands. Dev.
Sedimentol. 54, 141–160, Elsevier, Amsterdam.
Lambeck, K., Nakada, M., 1992. Constraints on the age and
duration of the last interglacial period and on sea-level variations. Nature 357, 125–128.
Land, L.S., MacKenzie, F.T., Gould, S.J., 1967. Pleistocene history of Bermuda. Geol. Soc. Am. Bull. 78, 993–1006.
57
Longman, M.W., 1980. Carbonate diagenetic textures from nearsurface diagenetic environments. Am. Assoc. Pet. Geol. Bull.
64, 461–487.
Lynts, G.W., 1970. Conceptual model of the Bahamian platform
for the last 135 million years. Nature 225, 1226–1228.
Mackenzie, F.T., 1964. Bermuda Pleistocene eolianites and paleowinds. Sedimentology 3, 52–64.
Masaferro, J.L., Poblet, J., Bulnes, M., Eberli, G.P., Dixon, T.H.,
McClay, K., 1998. Interplay of carbonate sedimentation and
detachment folding in the Bahamas foreland basin: implications for the timing of the Cuban orogen. In: Abstr. 15th Int.
Sedimentol. Congr., Alicante, Spain. p. 541.
Matthews, R.K., 1990. Quaternary sea-level change. In: Natl. Res.
Counc. ŽEd.., Sea Level Change. Natl. Acad. Press, Washington, pp. 88–103.
Meier, M.F., 1990. Role of land ice in present and future sea-level
change. In: Natl. Res. Counc. ŽEd.., Sea Level Change. Natl.
Acad. Press, Washington, pp. 171–184.
Meischner, D., Vollbrecht, R., Wehmeyer, D., 1995. Pleistocene
sea-level yo-yo recorded in stacked beaches, Bermuda south
shore. In: Curran, H.A., White, B. ŽEds.., Terrestrial and
Shallow Marine Geology of the Bahamas and Bermuda. Geol.
Soc. Am., Spec. Pap. 300, 295–309, Boulder.
Mercer, J.H., 1978. West Antarctic ice sheet and CO 2 greenhouse
effect: a threat of disaster. Nature 271, 321–325.
Murray, J.W., 1954. The deposition of calcite and aragonite in
caves. J. Geol. 62, 481–492.
Neumann, A.C., Hearty, P.J., 1996. Rapid sea-level changes at the
close of the last interglacial Žsubstage 5e. recorded in Bahamian island geology. Geology 24, 775–778.
Officer, C.B., Ewing, M., Wuenschel, P.C., 1952. Seismic refraction measurements in the Atlantic Ocean: Part IV. Bermuda,
Bermuda Rise, and Nares Basin. Geol. Soc. Am. Bull. 63,
777–808.
Oppenheimer, M., 1998. Global warming and the stability of the
West Antarctic Ice Sheet. Nature 393, 325–332.
Peltier, W.R., 1988. Lithospheric thickness, Antarctic deglaciation
history, and ocean basin discretization effects in a global
model of postglacial sea level change: a summary of some
sources of nonuniqueness. Quat. Res. 29, 93–112.
Peltier, W.R., 1998. Postglacial variations in the level of the sea:
implications for climate dynamics and solid-earth geophysics.
Rev. Geophys. 36, 603–689.
Pindell, J.L., 1985. Alleghenian reconstruction and subsequent
evolution of the Gulf of Mexico, Bahamas, and proto-Caribbean. Tectonics 4, 1–39.
Prell, W.L., Imbrie, J., Martinson, D.G., Morley, J.J., Pisias, N.G.,
Shackleton, N.J., Streeter, H.F., 1986. Graphic correlation of
oxygen isotope stratigraphy applications to the Late Quaternary. Paleoceanography 1, 137–162.
Raymo, M.E., 1997. The timing of major climate terminations.
Paleoceanography 12, 577–585.
Richter, D.K., 1983. Calcareous ooids: a synopsis. In: Peryt, T.M.
ŽEd.., Coated Grains. Springer Verlag, Berlin, pp. 71–99.
Rignot, E.J., 1998. Fast recession of a West Antarctic glacier.
Science 281, 549–551.
Ruddiman, W.F., 1987. Synthesis; the ocean icersheet record. In:
58
P. Kindler, P.J. Heartyr Global and Planetary Change 24 (2000) 41–58
Ruddiman, W.F., Wright, H.E. Jr. ŽEds.., The geology of
North America, Vol. K-3, North America and adjacent oceans
during the last deglaciation. Geol. Soc. Am., 463–478, Boulder.
Scherer, R.P., Aldahan, A., Tulaczyk, S., Possnert, G., Engelhardt, H., Kamb, B., 1998. Pleistocene collapse of the West
Antarctic ice sheet. Science 281, 82–85.
Seidenkrantz, M.-S., Bornmalm, L., Johnsen, S.J., Knudsen, K.L.,
Kuijpers, A., Lauritzen, S.-E., Leroy, S.A.G., Mergeai, I.,
Schweger, C., Van Vliet-Lanoe,
¨ B., 1996. Two-step deglaciation at the oxygen isotope stage 6r5e transition: the Zeifen–
Kattegat climate oscillation. Quat. Sci. Rev. 15, 63–75.
Selivanov, A.O., 1992. Spatial-temporal analysis of large Pleistocene sea-level fluctuations. J. Coastal Res. 8, 408–418.
Shackleton, N.J., Opdyke, N.D., 1973. Oxygen isotope and
palaeomagnetic stratigraphy of Equatorial Pacific core V28–
238: oxygen isotope temperatures and ice volume on a 10 5
year and 10 6 year scale. Quat. Res. 3, 39–55.
Sheridan, R.E., Mullins, H.T., Austin, J.A. Jr., Ball, M.M., Ladd,
J.W., 1988. Geology and geophysics of the Bahamas. In:
Sheridan, R.E., Grow, J.A. ŽEds.., The Geology of North
America, vol. 1–2, The Atlantic Continental Margin. U.S.
Geol. Soc. Am. Boulder, pp. 329–364.
Stanley, D.J., Swift, D.J.P., 1968. Bermuda’s reef-front platform:
bathymetry and significance. Mar. Geol. 6, 479–500.
Vacher, L., 1973. Coastal dunes of Younger Bermuda. In: Coates,
D.R. ŽEd.., Coastal Geomorphology. Publications in Geomorphology, State Univ. of New York, pp. 355–391.
Vacher, H.L., Hearty, P.J., 1989. History of stage 5 sea level in
Bermuda: review with new evidence of a rise to present sea
level during substage 5a. Quat. Sci. Rev. 8, 159–168.
Vacher, H.L., Hearty, P.J., Rowe, M.P., 1995. Stratigraphy of
Bermuda: nomenclature, concepts and status of multiple systems of classification. In: Curran, H.A., White, B. ŽEds..,
Terrestrial and Shallow Marine Geology of the Bahamas and
Bermuda. Geol. Soc. Am., Spec. Pap. 300, 271–294, Boulder.
Wigley, T.M.L., Raper, S.C.B., 1993. Future changes in global
mean temperature and sea level. In: Warrick, R.A., Barrow,
E.M., Wigley, T.M.L. ŽEds.., Climate and Sea Level Change:
Observations, Projections and Implications. Cambridge University Press, Cambridge, pp. 111–133.
Zwally, H.J., 1989. Growth of Greenland ice sheet: interpretation.
Science 246, 1589–1591.