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The Cape Roberts Project
Normally, strata from that long ago (Mid-Cretaceous to Paleogene) are deeply buried, but strata from the sea floor off Cape Roberts record old glacial and rifting events at or near the surface. Operations are designed to recover a complete core representing the target 1,500 m of strata; drilling for cores at three separate locations will accomplish this, with the depth of individual excavations up to 700 m below the sea floor. Curators cut the aggregate core into 1 m lengths, describe them in geological detail, and then photograph them. Samples are then distributed to researchers for a wide range of analyses – from extracting specific target fossils to determining more precise age and composition data for the sample.
The cores should help scientists answer two important questions:
• Before the glaciations of the last 36 million years, were there ice sheets on Antarctica that may have caused fluctuations in world-wide sea levels?
• How and when did the rifting of the Antarctic continent contribute to the formation of the Transantarctic Mountains and the Ross Sea?
Developing scientific models to answer these questions should provide more general insight into the etiology of changes in global sea level, as well as the origins of mountains and basins.
Cretaceous-Paleogene foraminifera of the Victoria Land Basin (Cape
Fossils recovered from Cape Roberts Project (CRP) cores contribute to scientists' ability to reconstruct the ancient prehistory of the region. Foraminifera are marine protozoa with calcareous shells, one of the basic species found in the region. The drill may provide cores that aggregate to about 1,500 meters in depth, which indicate ages from 30 to about 100 million years (Late Cretaceous/Paleogene). This interval of geological time has yet to be documented by in situ stratigraphic sections in either the Ross Sea or East Antarctica.
The final disintegration of Gondwanaland occurred during this time frame, as New Zealand and Australia moved north, away from Antarctica. Foraminifera from the CRP drill holes should contribute to an understanding of the paleogeography and paleoceanography of a number of significant structures: The highlands and Pacific margin of East Antarctica (the location of the proto-Transantarctic Mountains), the west antarctic rift system basins and the highlands of West Antarctica. This will help scientists reconstruct the history of the marine margin of East Antarctica (the region near the drill holes), and decide among current, contending hypotheses: Was it located in a Cretaceous cul-de-sac; or did it occupy (at times) a position on a major oceanic circulation pathway between the southwest Indian, southwest Pacific, and southwest Atlantic Oceans?
By developing a comprehensive accounting of foraminifera – presence, abundance, preservation, species dominance and diversity, stratigraphic distribution, levels of endemism or cosmopolitanism in faunas, and completeness or fragmentation of population structures – we hope to provide data that can be used to address a variety of geological problems:
• We will date disconformities and acoustic reflectors, which we expect to encounter in the drill hole, as they extend across the rift system basins.
• We will use benthic foraminiferal bathymetric indicators to deduce major basin subsidence/uplift trends resulting from compaction and/or rift margin faulting.
• We hope to document phases of transgression and regression, based on more subtle cyclicity in the stratigraphic distribution of benthic species. These, in turn, may indicate a relationship between sea level oscillation and terrestrial glacial events. (GL-049-A and GL-049-B)
Diatom biostratigraphy and paleoenvironmental history of Cape Roberts
Diatoms are unicellular algae well represented in the fossil record because of their silicified cell walls that persist as skeletons after death. Analyses of these and other siliceous microfossils in Cape Roberts Project (CRP) cores are fundamental to an integrated biostratigraphy for the late Cretaceous/Paleogene age (30 million to 100 million years ago), a time period not well documented in the southern high latitudes. Diatoms, for example, can provide evidence of environmental changes in water depth, primary productivity, and the presence or absence of sea ice.
CRP cores will provide an excellent opportunity to study diatom evolution, including adaptations made in response to strong polar seasonality. CRP studies also provide a useful point of contrast and comparison for similar studies based in the Arctic. Data on Paleogene siliceous microfossils found in Arctic strata (for example, Ocean Drilling Program Leg 151) can be assimilated with our results to develop a wider perspective on Paleogene high-latitude phytoplankton evolution.
This project begins with field-based paleontologic analysis of siliceous microfossils retrieved from Cape Roberts cores. Core sections are then ferried to the Crary Science and Engineering Center (CSEC) at McMurdo Station for further, immediate analysis. As drilling operations continue and siting decisions must be made, this age-and-paleoenvironmental data is quickly available and can be a valuable part of such decision-making.
Each season, a preliminary biostratigraphic/ paleoenvironmental report based on siliceous microfossils is produced, and becomes incorporated into the CRP Initial Reports volume, along with preliminary results from other microfossil groups, as well as lithostratigraphic, magnetostratigraphic, and other analyses. (GL-051-O)
Downhole logging for the Cape Roberts Project.
Through continuous-core and downhole logging at the Cape Roberts Project (CRP) scientific drill holes, this project produces geophysical well logs that reveal variations in mineralogy and porosity through time. Geophysical logging is essential to producing the basic stratigraphic framework on which all of the other scientific work depends. This is accomplished by integrating our detailed one-dimensional records for each hole with available high-resolution seismic data; the result is a fine-grained, two-dimensional interpretation of the core's stratigraphy. This spatial/temporal framework then becomes the context for scientists from several disciplines to locate their own data in space and time, facilitating studies of climate, tectonics, and sea-level change and helping to pinpoint the onset of antarctic glaciation. (GL-055-O)
Calcareous nanofossil biostratigraphy and paleoenvironmental history
of the Cape Roberts Project cores.
Calcareous nanofossils are an important element in the Cape Roberts Project (CRP), since their biostratigraphic record spans the entire time interval revealed in the CRP cores. Recent work from other ocean drilling sites around Antarctica on this species has allowed scientists to produce a refined zonation model for the Southern Ocean. Hemipelagic and pelagic sediments recovered by the CRP can immediately be placed within this high-resolution biostratigraphic framework. By combining these results with data from other fossil groups, with magnetostratigraphic data, and with other age-dating methods, geological investigators will have a powerful, built-in control for dating their results.
This project supports the drilling program by providing rapid age-and-paleoenvironmental information; as with other allied work, sedimentary cores will be studied at the Crary Science and Engineering Center (CSEC) at McMurdo Station for the target species – in this case calcareous nanofossils – and a biostratigraphic record of the core published in the Initial Reports volume.
These nanofossils also provide an excellent paleoenvironmental gauge of surface-water temperature and productivity. Through statistical analysis, a census of their population in an area can tell scientists a lot about the general climate. When combined with data from other fossil groups and sedimentological studies, they provide a lens to assess climatic change in the distant past. (GL-057-O)
Initial sedimentological characterization of the Late Cretaceous-Early
Cenozoic drill cores from Cape Roberts, Antarctica.
The Cape Roberts Project (CRP) aims to provide new data about the development of the west antarctic rift system, the subsidence history of the Ross Sea, and ice-sheet fluctuations on Antarctica through a critical time interval for which not enough is known. Previous work has, however, successfully documented the development of the region and its environmental history. But CPR can now draw upon newly compiled geophysical databases, and hopes to produce a sharper and more fine-grained spatial and temporal record.
While other researchers examine the sedimentary cores for fossilized fauna and other elements, this project is solid geology – initial description and sedimentological characterization of the successive layers, defining and constructing facies sequences, and interpreting environments through time when specific depositions were made. The sediments are also subjected to petrologic, petrogenetic, and initial clay mineralogical analysis.
The stratigraphic sections so described then become points of reference for modeling observed marine and geophysical events. The results also go into the Ocean Drilling Program-style Initial Report for each drilling season. Combined with information provided by other specialists (such as biostratigraphy, magnetostratigraphy, geophysical logs, and geochemical interpretations), these yield an initial interpretation of the region's history, and provide a foundation for any regional or global ramifications that may flow from that history. (GL-070-O)
Paleomagnetic and mineral magnetic characterization of drill cores
from the Cape Roberts Project.
Over time, the magnetic polarity of the Earth is dynamic, and periodically reverses altogether. This change in turn affects magnetized and other particles in the earth; over long, ancient time frames (paleo) the study of these changes – paleomagnetic stratigraphy – combined with the appropriate mineral magnetic studies, can produce an age record of the region.
The integrated science plan for the Cape Roberts Project (CRP) entails delivering the cores to McMurdo Station, where all of the initial scientific characterization of the cores will be done, including magnetostratigraphy, biostratigraphy, petrography, mineralogy, and sedimentology. A primary output of this initial work is the age of the strata in the cores, because a temporal framework is fundamental to the history of climatic and tectonic events. The on-site magnetic studies of this project will:
• undertake logging of the whole-core magnetic susceptibility, which will help correlate the several overlapping cores to be recovered during the CRP;
• determine a magnetostratigraphic framework for dating the cores;
• undertake mineral-magnetic and environmental-magnetic studies to assess the reliability of the paleomagnetic signal;
• determine if environmental magnetic properties yield information concerning changes in the tectonic, sedimentologic, diagenetic, or climatic influences on the sedimentary record at Cape Roberts; and
• undertake detailed environmental and mineral magnetic studies to evaluate how well the sediments actually record the geomagnetic field.
Ultimately, the CRP records provide the potential to obtain rare, high southern latitude constraints on geomagnetic field behavior. Paleomagnetic studies should also provide important data concerning crustal movements and rift development in the Ross Sea sector. (GL-075-O)
Stress field history, Cape Roberts, Antarctica.
The Cape Roberts Project (CRP) is providing the opportunity to develop the first age-calibrated stress-field history within the west antarctic rift system of Antarctica. The drill site, (not coincidentally) located along the margin between the uplifted Transantarctic Mountains and the rifted crust of the Victoria Land basin, is expected to yield information on the paleostress history of the Mesozoic and Cenozoic rift-basin fill material through analysis of the core, and from downhole logging of natural fractures and faults.
To establish the stress state contemporaneous with any particular stratigraphic level, researchers in this project will examine the cores for coring-induced stress fractures; and also the borehole (with a downhole televiewer and dipmeter) for any wellbore breakouts and fractures that may have been reactivated by contemporaneous geologic and tectonic events.
The stress data should produce answers to a number of questions relevant to the paleo- and neo-tectonic evolution of the Antarctic Plate. A number of seminal, outstanding issues may be resolved; such as:
• the cause of the anomalous aseismicity of the continent,
• the geometry of stresses along the lithospheric boundary between the Transantarctic Mountains and the west antarctic rift system, and
• the evolution of the antarctic intraplate stress field and its relation to rifting episodes associated with the breakup of Gondwanaland.
Current stress data obtained from this research will be added to the global stress database, helping to fill out the sketchy global stress evaluations associated with the Antarctic Plate. (GL-079-O)
Initial palynological characterization of Cape Roberts drill cores.
Palynomorphs – both marine (dinocysts) and nonmarine (spores, pollen) types – have proven invaluable for constructing the biostratigraphic and paleoenvironmental record in Antarctica. They record extensive and diverse geologic information, and are preserved in a wide variety of lithofacies formed in various paleoenvironments.
This collaborative project with New Zealand palynologists will provide initial palynological characterization of the Cape Roberts Project (CRP) drill cores. Our analyses provide constraining data for an integrated biostratigraphic and paleoenvironmental framework, based on all microfossil groups present. Such a framework should be of use to all future geologic, geophysical, and paleontologic studies conducted on the cores and in the drilling area. (GL-080-O)
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