Development of an Orbital Calcareous Nannofossil Biochronology
for the Paleocene to lower Oligocene
PI: Tim Bralower, Pennsylvania State University
Funded by: American Chemical Society – Petroleum Research
Fund
Grant type: AC
Abstract
Geologists increasingly focus on changes in Earth
History that took place over orbital to millennial time
scales. Neogene time scales are approaching the level of
resolution required to study such changes, but the time
scale for the Paleogene and earlier intervals is far too
coarse for this new order of problems. This project seeks
to improve the precision and accuracy of the Paleocene and
Eocene time scale by: (1) compiling nannofossil
stratigraphic schemes with higher resolution than
previously attainable and integrating them with other
fossil groups; (2) developing orbital stratigraphy and
correlating it with biostratigraphy; (3) refining the
calibration between biostratigraphy and orbital
stratigraphy with magnetostratigraphy and
chemostratigraphy, (4) scaling the time scale using
astrochronology and radiometric age estimates; and (5)
publishing the time scale and all data used in its
development in a user-friendly format on the CHRONOS
website so that they are readily available to the
community.
The time scale developed will be widely applicable in
investigations of high-resolution Paleocene and Eocene
stratigraphy. In particular, the level of synchroneity and
diachroneity of datums has great significance to
interpretations of relative changes of sea level in shelf
and slope sections. Moreover, the time scale will allow
more precise interpretations of changes in carbon cycling
and abrupt events during this transitional climate
interval.
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Development of an Orbital Calcareous Nannofossil Biochronology
for the Paleocene to lower Oligocene
Project Overview
Microfossil biostratigraphy is often crucial to solving
important problems related to ancient global change. For
example, our understanding of global carbon cycling and
relative sea level changes is commonly based on interpretation
of sections dated using biostratigraphies of planktonic
foraminifers and calcareous nannofossils (e.g., Haq et al.,
1987; Aubry et al., 1988; Bralower et al., 1993; Zachos et
al., 1993; Hardenbol et al., 1999; Kurtz et al., 2003).
Other
stratigraphic techniques such as magnetostratigraphy and
macrofossil biostratigraphy are also used to obtain time
control in studies of global change, but these techniques are
generally of more limited applicability.
Despite their common application, microfossil
biostratigraphy suffers from significant limitations in
resolution, typically several million years per zone (Figure
1). Lack of resolution limits interpretation of transient
events and rapid paleoenvironmental changes that occur over
periods less than zonal durations (e.g., Kennett and Stott,
1991; Thomas, 1998; Bains et al., 2000). Moreover,
biostratigraphers commonly interpret unconformities where the
sequences of datums in a section differs from that in
3
traditional biostratigraphic schemes; these gaps may simply
result from differing relative positions of datums as a result
of spatial (i.e. latitudinal and shelf-open ocean)
diachroneity (see discussion in Aubry et al., 1996).
To reach
their full potential in the investigation of a range of
important geologic problems, we need to increase significantly
the biostratigraphic resolution of microfossil schemes and
constrain the synchroneity/diachroneity of individual datums.
Orbital chronology or astrochronology offers a unique
opportunity to determine the age of biostratigraphic datums
approaching the resolution of Milankovitch periodicities, i.e.
20-100 kyr (Cramer, 2001; Röhl et al., 2001, 2003).
Such
orbital tuning of biostratigraphic datums has been carried out
in the Neogene (e.g., Hilgen, 1991; Shackleton et al., 1995;
Shackleton et al., 1999) but to a limited degree in the older
part of the timescale (e.g., Röhl et al., 2001, 2003; Cramer
et al., 2003).
Remarkably cyclic sedimentary sections have
been recovered during recent legs of the Ocean Drilling
Program (ODP); these sequences offer a unique opportunity to
establish orbital chronology for microfossil biostratigraphic
datums and to determine the synchroneity of datums across a
wide latitudinal range.
The proposed investigation is
designed to establish an orbital nannofossil chronology for
the Paleocene to lowermost Oligocene and to apply the results
4
to a set of important paleoenvironmental problems associated
with carbon cycling and sea level change.
Background
Paleogene Nannofossil biostratigraphy: Potential for
increased resolution
The Paleogene represents a key interval of time in the
evolution of nannoplankton. This period includes the adaptive
radiation of the few taxa that survived the Cretaceous/Tertiary
boundary extinction, continued diversification during the late
Paleocene and early Eocene climatic optimum, and a slight
decrease in diversity during cooiling coincident with the late
Eocene and early Oligocene (e.g., Bramlette and Sullivan 1964;
Perch-Nielsen 1977; Percival and Fischer 1977; Jiang and Gartner
1986; Pospichal and Wise 1990; Wei and Pospichal 1991; Aubry,
1992; Aubry, 1998).
A large amount of work has been carried out
on the taxonomy of Paleogene calcareous nannofossils (see review
in Perch-Nielsen, 1985; Aubry, 1984, 1988, 1989, 1990).
Despite significant attention, there are still numerous
uncertainties concerning Paleogene biostratigraphy.
Even though
original calcareous nannofossil zonations (Martini, 1971; Bukry,
1973, 1975; Okada and Bukry, 1980) have proven to be widely
applicable, there are individual datums that are difficult to
5
apply (e.g., Bralower in review). Also, the resolution of
Paleogene nannofossil biostratigraphy lags significantly behind
that of the Neogene and even that of parts of the Cretaceous
(Moore and Romine, 1981; Bralower et al., 1993).
Yet, the
Paleogene is an interval of high species diversity (Haq, 1973)
and, therefore, the potential for increased biostratigraphic
resolution exists (e.g., Bralower and Mutterlose, 1995).
Recent Ocean Drilling Program (ODP) cruises in high southern
latitude sites and the subtropical and tropical Pacific and South
Atlantic, have recovered expanded and largely continuous
Paleogene sequences that have been the targets of a host of
biostratigraphic investigations (Pospichal and Wise, 1990; Wei
and Wise, 1992; Bralower and Mutterlose, 1995; Bralower et al.,
2002a; Lyle et al., 2003; Erbacher et al., 2004; Zachos et al.,
2004). Thus there is great potential for improving the quality
and resolution of Paleogene nannofossil biostratigraphy.
For
example, the precise range of ~60 zonal and nonzonal events were
determined in the Paleogene section on Shatsky Rise, N.W. Pacific
(Bralower, in review) (Figure 1).
One of the most significant questions in Paleogene nannofossil
biostratigraphy is whether events are spatially diachronous
(e.g., Bralower and Mutterlose, 1995), or whether apparent
diachroneity results from errors in published ranges or extremely
rare species abundances near the geographic limits of a range.
6
With potentially large numbers of datums, we need to consider
ways to determine the synchroneity or diachroneity of events over
broad areas.
The most precise method is to utilize the sequence
of magnetostratigraphic polarity zones within sedimentary
sequences.
This technique is dependant on the ability to
identify clearly and correlate the sequence of polarity zones
regardless of their biostratigraphic correlations.
The
synchroneity/diachroneity of a number of Paleogene nannofossil
events has been addressed in this fashion by Wei and Wise (1989)
and Wei and Wise (1992).
7
Where magnetostratigraphy is unavailable other approaches have
to be used to assess the synchroneity/diachroneity of fossil
datums.
One such approach is an application of the technique of
Shaw (1964), in which x-y plots of various types of events in two
different sequences are used to analyze the sedimentation
histories of these two sections.
applied in biostratigraphy.
This technique has been widely
Differences in order of events among
sections may result from inaccuracy when determining an event,
differing taxonomic concepts among various workers, and
diachroneity of an event in different parts of the ocean.
Shaw
plots also have the potential to yield information about
unconformities.
For example plots of different sections from ODP
Leg 198 show numerous events that cluster at a narrow range of
depths at Site 1211 suggesting the presence of unconformities or
extremely slow sedimentation (Figure 1).
Cyclostratigraphy: Elapsed time between datum horizons
Because magnetostratigraphy does not generally provide
resolution less than about 500 kyr and Shaw plots do not
provide absolute time control, the most precise way to
determine true synchroneity/diachroneity of datums in
complete sections is using orbital cyclicity.
Fluctuations
in carbonate and clay content expressed in deep sea
sections have been shown to reflect precessional, obliquity
8
and eccentricity cycles in the Earth’s orbit with
frequencies ranging from 20 kyr to 400 kyr.
Such cycles
have provided the framework for tuning of Neogene
timescales (e.g., Hilgen, 1991) and for identification of
the level of synchroneity of datums (e.g., Chepstow-Lusty
et al., 1989; Raffi et al., 1993; Flores et al., 1995;
Backman and Raffi, 1997; Raffi, 1999; Gibbs et al., 2004).
Orbital cycles imprinted in sediments provide accurate and
precise chronometers to measure events to perhaps 5-10 kyr
resolution.
Cyclic patterns of oxygen isotopes, carbonate
content, and other measures are the workhorses of PlioPleistocene stratigraphy (Hays et al., 1976; Raymo et al., 1989;
Hilgen, 1991; Imbrie et al., 1984; Shackleton et al., 1990;
Shackleton and Crowhurst, 1997).
Moving farther back in
geologic time, astronomical cycles no longer can be used as a
time template, because the details of the planetary orbits are
not known precisely (Laskar, 1999).
However, orbital cycles
still provide a very useful measure of elapsed time between
datum horizons given by biostratigraphic, paleomagnetic, or
chemostratigraphic studies. Herbert et al. (1995) showed that it
is possible to obtain very good estimates of elapsed time in
sediments simply by knowing the mean orbital repeat times.
For
example, individual precessional cycles (modern mean repeat time
9
one assumes that each cycle has a constant repeat time, and to
-7%) if one averages over 10
or more cycles.
The relative errors using obliquity (period 41
kyr) and eccentricity (periods at 95 and 404 kyr) cycles are
significantly less.
Recent high-resolution work across the
Paleocene/Eocene boundary (Norris and Röhl, 1999; Röhl et al.,
2000; Cramer et al., 2003) shows that the paleoceanographic
community now accepts the use of orbital tuning to help solve
pre-Neogene problems.
Spectacular, cyclic Paleogene sections have been recovered on
a number of recent ODP legs. For example, drilling during Leg
198 at four sites on Shatsky Rise recovered a series of nearly
complete Paleogene sections dominated by eccentricity cycles
(Figure 2).
These cycles can be correlated precisely between
sites and likely reflect regional fluctuations of a combination
of productivity and dissolution of calcareous microplankton.
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PROPOSED RESEARCH: DEVELOPMENT OF AN ORBITAL TIMESCALE FOR THE
PALEOCENE TO EARLY OLIGOCENE
Stages of time scale construction: The proposed orbital
Paleogene time scale will be constructed in a logical fashion in
five steps (Figure 3).
11
The foundation of the new scheme
will be a high-resolution
nannofossil biostratigraphy
(Step 1).
Step 2 involves the
refinement and development of
orbital stratigraphy.
Higher
resolution biostratigraphy will
improve the correlation of all
of the different time scale
components, including other
fossil biostratigraphies,
magnetostratigraphy,
chemostratigraphy, orbital
stratigraphy, epoch boundaries, and especially radiometric dates
(Step 3).
Precise ties between biostratigraphy,
magnetostratigraphy, and radiometric dates will be the
foundation of scaling of the time scale (Step 4).
Orbital
“tuning” of events will be done within the constraints of
magnetostratigraphy and radiometric dating.
The time scale will be made available to the geologic community
on the NSF- and community supported CHRONOS web site (Step 5).
The web site will also archive the time scale, allowing
accessibility to detailed documentation, and maintenance and
future improvement to be readily accomplished.
12
In the following,
we discuss the sequence of steps involved in building the new
time scale.
Step 1.
Improving the Resolution of Nannofossil Zonations and
Integrated Biozonations
A great deal of work on Paleogene nannofossil biostratigraphy
has been carried out since currently-applied zonations (e.g.,
Martini, 1971; Bukry, 1973; Okada and Bukry, 1980) were
developed.
This work has revised the taxonomic and
biostratigraphic basis of a number of the events used in these
zonation schemes to the point where some of the zonal units are
now impossible to apply (see discussions in Perch-Nielsen, 1985;
Pospichal and Wise, 1990; Wei and Wise, 1992; Aubry et al.,
1996).
Bralower and Mutterlose (1995) determined the level of 72
Paleogene nannofossil datums at Site 865 in the equatorial
Pacific and correlated them to 15 other sections at sites from
low and high latitudes and from the deep sea and continental
margins.
Consistency in the order of numerous events between
many of the sites suggests that many datums have the potential
for correlation between different settings and that higherresolution biostratigraphy is feasible; however, the order of
events needs to be tested further, especially in expanded and
continuous sections with excellent nannofossil preservation.
13
The proposed refinement of high-resolution nannofossil
biostratigraphy will include:
Development of revised zonation schemes that will be
applicable on a global basis. We plan to alter current
zonations only where markers have been shown not to be widely
applicable. Markers included in this zonation will be
restricted to those that are non-controversial taxonomically
and recognized by all specialists.
These zonation schemes
will include zonal and subzonal units.
Zones will be
recognizable in all sections regardless of preservation;
subzones are units that can be defined in sections with
moderate to good preservation.
In general, the plan is to
make as few changes in current biostratigraphies as possible.
For example, new subzones can be inserted within current zonal
units without modifying existing zonal biostratigraphies.
Further development of a scheme of subzonal biohorizons,
events that can be determined in well-preserved material.
The
PI has been actively involved in reconstructing a
representative sequence of biohorizons in well-preserved
material from different locations (Bralower and Mutterlose,
1995; Bralower, in review).
In most intervals the number of
potential events has increased dramatically through time as
taxonomies have been revised and stratigraphic ranges refined.
Figure 4 shows examples of working schemes; we stress that
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these schemes are far from finalized and need more
substantiation in a wide range of sections.
Thus we plan to
collaborate with other workers who are currently involved in
establishing nannofossil biostratigraphy of newly-recovered
high-quality Paleogene sections (Figure 5).
The proposed
investigation will be carried out using a sampling resolution
higher than normal for the Paleogene; near the ends of
species’ ranges, we will work on four to five samples per
orbital cycle, typically ~5 kyr for precessional cycles and
~20 kyr for 100 kyr eccentricity cycles. To determine the
order of events that vary in order between different sections,
we will apply graphic correlation (e.g., Shaw, 1964).
15
Step 2. Providing Orbital Chronometry for Paleocene to early
Oligocene
Orbital chronometry will be constructed for the Paleocene to
early Oligocene.
We will focus on sequences with well-developed
cycles including Sites 1209 and 1210 on Shatsky Rise (N.W.
Pacific; Bralower et al., 2002a), Site 690 (Maud Rise, S.
16
Atlantic sector of Southern Ocean; Barker et al., 1988), and
Sites 1262 and 1267 (Walvis Ridge, South Atlantic; Zachos et
al., 2004) (Figure 5).
We will produce orbitally-tuned chronologies for key sections
by following circa 20, 100 and 400 kyr modulations of the
precessional cycle, which seems the dominant high frequency
orbital beat of the Paleogene climate system.
Our tuning will
therefore rely on the most stable elements of the celestial
mechanical system (Berger et al., 1992; Laskar, 1999).
Furthermore, the 100 kyr and 400 kyr wavelengths are
commensurate with the biostratigraphic and magnetostratigraphic
resolution we seek to achieve in our timescale, and can be
recognized where small gaps interrupt core recovery, or
ambiguities in individual 20 kyr cycle identification exist.
17
For cyclostratigraphy to work we need: (1) a signal that can
be measured objectively; (2) sections that are as complete as
possible; and (3) the ability to correlate between key sections
to document the reliability of orbital dating.
Magnetic
susceptibility measurements are now made routinely on ODP legs
(e.g., Bralower et al., 2002a; Erbacher et al., 2004; Zachos et
al., 2004) but not on older legs such as at Site 690 on Leg 113
in the Weddell Sea (Barker, Kennett, et al., 1988).
Susceptibililty and other nearly continuous measurements of
these cores will be made as a part of this investigation.
Orbital chronologies will be determined in sections with
excellent potential for high-resolution nannofossil
biochronology, and, wherever possible, with
magnetostratigraphies. Sites 1209 and 1210 are characterized by
100 kyr and 400 kyr eccentricity cycles (Figure 3); Sites 690,
1262, and 1267 by precessional (20 kyr) cycles.
We are
confident that by following 20, 100, and 400 kyr signals in
sedimentation, we can move between core locations to generate a
consistent timescale for the entire early Paleocene-early
Oligocene interval.
Timescales developed with orbital control have the potential
to determine whether biostratigraphic events are diachronous
across latitudes and between basins. Such diachrony will be
easier to identify in the low-latitude sections where orbital
18
cycles are examined in magnetic susceptibility records.
Moreover, diachrony will be consistent with gradually offset
ranges across latitudes and between basins.
If an event is only
diachronous at one site and this diachrony cannot be explained
by geographic range (i.e. the one site is the high latitude
location), then it is likely that there is a mistake with the
timescale as a result of missing section or an error in the
event position.
High-latitude Site 690 is critical in this
assessment and fortunately has a well-developed
magnetostratigraphy that will augment cyclostratigraphy in
evaluating the diachroneity of datums. However, extreme caution
must be taken in avoiding circular reasoning.
Thus, individual
cycles at different sites must either be correlated using
distinctive patterns. Alternatively, magnetic polarity chron
boundaries must be used to correlate cycles. If the numbers of
cycles in individual polarity chrons match between sites, then
cycles might be correlated directly.
Precessional cycles (Sites
690, 1262, 1267) can be correlated to eccentricity cycles (Sites
1209, 1210) in similar ways especially since several of the
latter cycles show evidence for finer-scale alternations (Fig.
2).
Step 3.
Improving Correlation of Different Chronostratigraphic
Elements
19
Considerable effort has been devoted recently to the
correlation between different time scale components:
biostratigraphy, magnetostratigraphy, chemostratigraphy, stage
boundaries, and radiometric age estimates (see detailed
discussions in Aubry et al., 1988; Berggren et al., 1995; Cande
and Kent, 1995; Berggren et al., 2000). The orbital nannofossil
chronology developed as a part of this investigation will
provide significant improvements in the correlation of the
different time scale components.
Detailed studies of planktic
foraminiferal biostratigraphy, magnetostratigraphy, and
chemostratigraphy at the sites to be investigated are in
progress by shipboard scientists on ODP Legs 198 and 208. Such
detailed stratigraphic datasets are available for Site 690
(Stott et al., 1990; Stott and Kennett, 1990).
Some of the
correlations between nannofossil events and other stratigraphic
elements may be achieved via the CHRONOS database (see Step 5).
Step 4. Improving Time Scale Construction and Scaling
Time scale construction will be based only on the highest
precision radiometric ages (e.g., Cande and Kent., 1995); mostly
40
Ar/39Ar dates.
We will use the Cande and Kent (1995) GPTS as
the basis of our investigation.
This time scale uses recently
revised block models scaled assuming constant spreading rates
between high-quality 40Ar/39Ar date tie-points.
20
We will compare
this approach with fits that maximize the match of radiometric
("absolute" ages) and orbital ("elapsed" time) data.
High-
quality magnetostratigraphy is available at Sites 690, 1262 and
1267 and in parts of the section at Sites 1209 and 1210 (Spieb,
1990; Zachos et al., 2004; Evans and Channell, in review).
Step 5. Making the Time Scale User-Friendly
Publication of a more precise time scale does not ensure that
it will be applied correctly by all researchers.
There are
numerous cases where zones have been correlated incorrectly in
sections, where old boundary definitions have been used, or
where workers have relied on a fossil group that provides
conflicting age information from other groups.
Problems will be
compounded once a new zonal scheme is defined as the ranges of
zonal markers will need to be recognized in published range
charts and because the ranges of many of the new zonal markers
have not been identified in sections that were studied a long
time ago or even rather recently.
We will make the time scale available to the geologic
community via the CHRONOS web site (www.chonos.org) as
downloadable Excel files.
CHRONOS and affiliated database
programs (SEDDB and Paleostrat) will provide correlation of
datums with geochemical data, chemostratigraphic data, and
magnetostratigraphy. These programs are funded by NSF and
21
provide stable, long-term, user-friendly archives for storing
data and making them available to the geologic community.
We stress that time scales are constantly in need of revision
as new data are acquired.
Thus all of the basic data collected
as a part of this investigation will be archived on the web
site.
This will allow other workers to obtain access to our
data, simplifying future modifications.
We will also publish
our results in the open literature.
APPLICATIONS OF ORBITAL CHRONOLOGY
The developed orbital timescale has numerous potential
applications in interpreting Paleogene paleooceanography,
geochemical cycling and depositional systems.
Here, I
highlight two of these.
Constraining the controls of the carbon cycle
The Paleogene included major modifications in the nature of
carbon cycling as a result of changes in climate and oceanic
circulation as well as of tectonic forces (e.g., Corfield and
Norris, 1996; Zachos et al., 2001; Kurtz et al., 2003).
One of
the most diagnostic proxies for carbon cycle changes is the
benthic and planktic foraminiferal carbon isotope record. Penn
State MS student Anna Hilting has been compiling carbon isotope
data from different DSDP and ODP sites and has produced smoothed
curves that will serve as inputs for biogeochemical models
22
designed to constrain the controls of carbon cycles including
burial of organic matter, ocean circulation, and continental
weathering. However, such compilation is inhibited by
difficulties in correlation between different sites (Anna
Hilting, pers. comm.). Moreover, estimating precise accumulation
rates of carbon and carbonate is also difficult as a result of
poor chronology.
Much attention has been paid to short-term changes such as the
Paleocene-Eocene thermal maximum (PETM) at 55 Ma (e.g., Kennett
and Stott, 1991) where input of large quantities of greenhouse
gas is thought to have driven profound changes in climate, biotas
and geochemical cycling (e.g., Dickens et al., 1995; Koch et al.,
1995; Thomas and Shackleton, 1996; Crouch et al., 2001; Thomas et
al., 2002). There is a possibility that other “mini-PETM” events
also occur in the Paleogene (Thomas et al., 2000; Bralower et
al., 2002b; Bohaty and Zachos, 2003).
The PETM has detailed
orbital chronology (Röhl et al., 2000) and He-3 chronology
(Farley and Eltgroth, 2003), but other events have yet to be
constrained by high-resolution chronology.
By improving the resolution and precision of chronology, this
investigation will help detailed study of the Paleogene carbon
cycle. We will input these data into compilations of carbon
isotope data (A. Hilting, MS thesis, in prep) and update modeling
studies.
The chronology of the PETM is stable, however, the
23
orbital timescale will allow detailed investigation of other
mini-PETM events such events in the early Paleocene, the early
late Paleocene and the early Eocene (Thomas et al., 2000;
Bralower et al., 2002b; Bohaty et el., 2003).
High-resolution
chronology will allow: (1) detailed chronology of these events at
different sites, and (2) precise estimates of accumulation rates
of C and CaCO3 which will help us understand changes in carbon
cycling.
Unconformities and sea level
Considerable debate has occurred over the topic of whether
differences in relative order of microfossil datums reflects
diachroneity or the presence of unconformities in shelf, slope,
and deep-sea sections (e.g., Aubry et al., 1986; Aubry, 1995;
Aubry et al., 1996; Miller et
al., 1996).
High-resolution orbital chronology will allow us to rigorously
determine which nannofossil events are synchronous over great
distances and which are diachronous. This will shed light on
whether differences between the sequence of events in different
sections result from diachrony or from unconformities.
Unconformities in shelf and upper slope sections are likely to be
related to landward-shifting depocenters during late
transgressive and highstand phases of sea level (e.g., Loutit et
al., 1988). Deep-sea unconformities are more likely a result of
24
erosion by strong currents (e.g., Miller et al., 1987).
Biostratigraphy of most of the relevant sections exists and will
not be acquired during the current investigation; rather by
determining the true order and level of diachrony of the datums
we will be able to evaluate the validity of previous
unconformities and their interpretation in terms of sea level
change.
SYNTHESIS OF PROJECT OUTCOMES
The Paleogene orbital time scale will provide both higher
stratigraphic resolution and precision.
In addition, the time
scale will be made available to the community so that workers
can accurately estimate the ages of their samples.
The benefits
of the new time scale include:
Fewer errors in age estimates of samples will result in
more accurate interpretations.
Greater time scale precision will enable more realistic
estimates of timing and rates of geochemical cycling, sea
level change, and evolution.
Higher chronostratigraphic resolution will allow more
detailed investigations of rapid paleoenvironmental
changes.
25
Refined biostratigraphy and, in intervals, orbital stratigraphy
will allow precise correlation between sites enabling more
accurate global reconstructions in environmental change.
LOGISTICAL CONSIDERATIONS
Research Team: We have assembled an experienced team of
scientists to collaborate in the proposed effort to rebuild the
Paleocene to early Oligocene time scale. The investigation will
be directed by P.I. Timothy Bralower at Pennsylvania State
University (PSU).
Bralower will oversee integration of the
various time scale elements.
Nannofossil biostratigraphy will
be carried out by a graduate student research assistant at PSU.
An undergraduate technician at PSU will be responsible for
preparation of smear slides.
We will also collaborate with
Isabella Raffi who is working on the Paleogene nannofossil
biostratigraphy of ODP sections from ODP Leg 208 (Walvis Ridge,
South Atlantic).
The orbital stratigraphy which will be an integral part of the
development of the Paleocene to early Oligocene time scale will
be carried out by Ursula Röhl at Bremen University.
The
investigation will be closely liaised with continuing studies of
the biostratigraphy of other fossil groups including planktic
26
foraminifera by Isabella Premoli Silva and Maria Rose Petrizzo
(University of Milan), and D. Clay Kelly (U. Wisconsin).
METHODS
Biostratigraphic analysis: Nannofossil biostratigraphy will be
carried out on high-resolution sample collections from the
relevant ODP sections.
In general sample spacing will be
approximately four to five samples per orbital cycle.
Standard
smear slides will be observed in polarizing light microscopes at
PSU.
The microscopes are hooked up with digital cameras so
images can be stored.
We already have biostratigraphies on
samples at a resolution of 1.5 m. We estimate that an additional
1000 samples will be studied from Sites 690, 1209, and 1210.
Astrochronology:
Detailed astrochronology is available for
Sites 1209, 1210, 1262, and 1267 (Röhl et al., in review). We
will send cores from Site 690 to Bremen University for detailed
XRF core scanning and magnetic susceptibility measurements.
These techniques are documented in Röhl and Abrams (2000).
Project Schedule: We propose a three-year program.
Years 1 and
2 will be focused on acquiring data, developing
biostratigraphies, acquiring orbital stratigraphic data and
refining correlations. Year 3 will be devoted to correlation,
time scale construction, publication of all information on the
CHRONOS web site, and manuscript preparation.
27
28
References Cited
Aubry, M.-P., 1986. Paleogene calcareous nannoplankton
biochronology of Northwestern Europe. Paleogeog.
Paleoclimatol., Paleoecol., 55: 267-334.
Aubry, M.-P., 1984. Handbook of Cenozoic calcareous
nannoplankton. Book 1: Ortholthae (Discoasters).
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