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SCAR Report No 16, April 1999

SCAR Antarctic Offshore Stratigraphy Project (ANTOSTRAT)

Report of a Workshop on
Antarctic Late Phanerozoic Earth System Science
Hobart, Australia, July 6-11, 1997

Compiled by

Peter-N. Webb, Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University,
Columbus, OH, 43210 USA, E-mail: webb.3@osu.edu
and
Alan K. Cooper, U.S. Geological Survey, MS 999, 345 Middlefield Road, Menlo Park,
CA 94025 USA, E-mail: acooper@usgs.gov

Note: The pagination for the electronic version of the report is based on the U.S. 8.5x11 inch paper format, not on the A4 paper format. The report will print on A4 paper, but page numbers will differ.

Contents

Executive Summary........................................................................................ 4
Introduction ...................................................................................................... 5
Consesus Statement Developed at Workshop Plenary Session........... 7
Summary Statements on Data Bases, Current and Planned Projects, Technology and Thematic and Regional Earth Science Issues .........9
Introduction ................................................................................................................ 9
Late Phanerozoic Global Change Challenges
Data bases, current and planned projects, and technology issues ............................. 9

ANTOSTRAT Seismic Data Library System (SDLS)

ANTOSTRAT Antarctic Margin Ocean Drilling Program Initiatives

Deep Stratigraphic Drilling Outside the ODP Organization

Shallow Drilling Technology and Sampling of Late Phanerozoic Targets

Thematic Issues ............................................................................................................ 12

Late Mesozoic and Cenozoic Plate Tectonic and Crustal History of Antarctica
Geological Time, and Relative and Absolute Dating Systems
Continental Shelf Sedimentary Basins
Paleoceanography and Circum-Antarctic Deep Sea Marine Biosphere History
Glaciomarine Sedimentary Processes, Events and Stratigraphy
Terrestrial Geology
Antarctic Seismic Stratigraphy
Seismic Characterization and Physical Properties
Paleoclimate Modeling of Glacial and Climatic History

Regional Earth Science Issues..................................................................................... 19

Antarctic Peninsula
Weddell Sea
Prydz Bay Region
Wilkes Land Margin
Ross Sea

ACKNOWLEDGEMENTS ......................................................................................... 25
FIGURES AND CAPTIONS ....................................................................................... 26-32
APPENDICES .............................................................................................................. 33

1. ANTOSTRAT Steering Committee ......................................................................... 33
2. Workshop Participants ............................................................................................. 33
3. Selected References ................................................................................................. 34
4. ANTOSTRAT Workshop Program: Agenda and Format ....................................... 36
5. Report on Hobart Workshop published in EOS ...................................................... 41
6. Three documents related to the evolution and implementation of
the ANTOSTRAT subcommittee - July 1997 to July 1998 ................................... 45
6A. Response to Consensus Statement on Hobart Workshop, by
SCAR Executive Committee - August, 1997 .................................................... 45

6B. Recommendations taken to SCAR XXV Meeting
(Concepcion, Chile; July, 1998) ........................................................................ 45

6C. Recommendation approved by SCAR Delegates
at SCAR XXV (Concepcion, Chile; July, 1998) .............................................. 47

7. Working Papers On Data Bases, Current And Planned Projects, Technologies,
Thematic And Regional Earth Science Issues Prepared For Hobart Workshop ...................... 50

7.1 Webb: Late Phanerozoic Antarctica: Global Change Challenges
At Macro-, Meso- And Micro-temporal Scales ................................. 51
7.2 Cooper and Brancolini: Antostrat Seismic Data Library
System For Cooperative Research (SDLS) ....................................... 55
7.3 Barker: ANTOSTRAT Ocean Drilling Program Initiative ............................ 59
7.4 Barrett: Deep Stratigraphic Drilling In The Antarctic Outside ODP........................ 63
7.5 Kristoffersen: Approaches To Marine Shallow Drilling On The Antarctic Shelf................... 65
7.6 Elliot: The Late Mesozoic And Cenozoic Plate Tectonic And Crustal
History Of Antarctica: Implications For Marine And Terrestrial Sequences............ 67
7.7 Barrett: Continental Shelf Sedimentary Basins ............................................. 74
7.8 Wise: Mesozoic-Paleogene Paleoceanography And Marine Biosphere: Key Events................... 76
7.9 Powell: Glacier-Sea Interactions And The Utililty Of Process Studies For
Interpreting The Antarctic Glacial And Climatic Record On Different Time Scales ............................... 83
7.10 Webb: The Late Phanerozoic Terrestrial Realm ............................................. 87
7.11 Cooper: Antarctic Seismic Stratigraphy: Status, Questions and Future Priorities............. 91
7.12 Solheim: Seismic Stratigraphy And Sedimentary Properties: A Need For Ground Truth......... 97
7.13 Oglesby: Paleoclimate Modeling of Antarctica: What It Has Done ?, What It Can Do? ....... 102
7.14 Barker: Antarctic Peninsula Region ............................................................... 105
7.15 Jokat: Weddell Sea, Lazarev Sea, Riiser-Larsen Sea Region ........................ 106
7.16 O'Brien and Leitchenkov: Prydz Bay And Mac.Robertson Shelf Region .......... 111
7.17 Escutia: Late Phanerozoic (100-0 Ma) Studies On The Wilkes Land Margin ..........................115
7.18 Davey: The Ross Sea Region: Geology Of The Last 100 Ma .......................... 121

 

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Executive Summary

In June 1996, the Antarctic Offshore Stratigraphy Programme (ANTOSTRAT) was tasked by the Scientific Committee on Antarctic Research (SCAR), to convene a workshop in Hobart, Australia. The purpose was to gather a representative group of interested Antarctic Earth scientists to outline critical themes for investigation of Antarctic paleoenvironments during Cretaceous and Cenozoic times (the last 130 million years), and to recommend objectives and priorities for the next decade. A group of 40 scientists from 11 countries met for this purpose in July 1997 along side a parallel workshop for the Antarctic Ice Margin Environment Group (ANTIME), which focuses on the last 200,000 years. This report details the background, discussions, findings and recommendations of the ANTOSTRAT workshop.

The workshop recognized the extensive seismic database already organized through ANTOSTRAT, and the value of the Seismic Data Library System (SDLS), in developing Ocean Drilling Program (ODP) proposals for circum-Antarctic drilling (Antarctic Peninsula, Ross Sea, Wilkes Land, Prydz Bay, Weddell Sea), as well as the fast-ice drilling of Cape Roberts (McMurdo Sound). Participants reviewd and confirmed the necessity for geologic sampling of continental shelf and rise deposits, acknowledging the direct but incomplete record of the shelf and the indirect but more complete record of the rise. They also supported the importance of shallow drilling and coring of different sectors of the Antarctic, recognizing the major differences in behavior and timing of glaciation between East and West Antarctic ice. With the new round of large-scale drilling programs about to begin (ODP Leg 178 (Antarctic Peninsula) and Cape Roberts drilling), it was considered important to maintain momentum toward future drilling. At the same time, the group saw the need to focus on the use of data from sediment cores (age, depositional environment, paleoclimate) in improving scenarios of past ice and climate behaviour through ice sheet and climate modeling.

The workshop concluded that the focus for the next decade (1998-2008) should be the onset and development of Antarctic glaciation, and that this was best pursued through the following activities:

The plan for the next 4 years (1998-2002) is to work principally on core and sample recovery and interpretations, with some involvement of modelers and sector by sector assessment, followed by a broad review of results at a dedicated symposium in 2002.

The workshop report also outlines the evolution of the project from the initial ANTOSTRAT initiative under the Group of Specialists (1989-1996) to the current ANTOSTRAT committee, under the joint Working Groups on Geology and Solid Earth Geophysics, that was approved by SCAR in July

Introduction

Since the early 1970's, offshore drilling by the Deep Sea Drilling Project and Ocean Drilling Program, and fast-ice drilling in McMurdo Sound, provided major advances in our understanding of Antarctic climatic and tectonic history through Cenozoic times - a period of geographic isolation for the Antarctic continent and one which witnessed the replacement of relatively diverse marine and terrestrial environments by ice sheets. Also during the 1970's and 1980's, seismic surveys of strata beneath the Antarctic continental shelf were conducted by many countries and raised concerns about the use of these data for oil exploration as well as investigation of Cenozoic history. In 1986, a Workshop on Cenozoic Palaeoenvironments was held at the SCAR meeting in San Diego, and from that meeting emerged a plan for a Group of Specialist to coordinate and promote research on this broad topic. This was approved by SCAR and the Group began work in 1988.

At an early stage, it was realized that there needed to be a focus on the growing body of seismic data being collected around the Antarctic margin, both because of its scientific value and also the political sensitivity to possible misuse. This led to the formation of ANTOSTRAT (Antarctic Offshore Stratigraphy Project), which, during a meeting at Asilomar (California) in 1990, set up a series of regional working groups to organize the seismic data in five regions of the Antarctic margin (Fig. 1), and to use these data as the basis for proposals for coring key strata in each region, under the aegis of the Ocean Drilling Program (ODP).

In August 1996, the Group of Specialists on Cenozoic Paleoenvironments of the Southern High Latitudes (GOSC) concluded its 10-year term, by reporting its activities to the Working Group on Geology, the Working Group On Solid-Earth Geophysics, and the SCAR delegates at XXIV SCAR, Cambridge. GOSC was able to point to an extremely active decade of workshops, conferences, and successful initiatives involving Ocean Drilling Program and non-ODP drilling programs. However, there was a general feeling within the SCAR Earth Science Working Groups that continuing coordination of seismic activities and strenuous promotion of drilling activities would be required well beyond 1996 in order to maintain the momentum achieved over the past decade.

The Group of Specialists (GOSC) proposed, via a document circulated in advance of the SCAR meeting, that the joint working groups request that a new Group of Specialists on Late Phanerozoic Earth System Science be established. After extensive discussions, the joint working groups concluded that (SCAR Bulletin No. 126 , July 1997, page 20, item 8a through d)

"such prioritization and coordination (of future Late Phanerozoic science activities) require further thought that is probably best organized through the medium of an open Workshop, and that a new Group of Specialists is highly desirable, but could be much better formulated as an outcome of the Workshop deliberations, and then proposed to XXV SCAR. " (Item 8d)

SCAR Delegates then recommended that the successful ANTOSTRAT Project be extended for two years as the ANTOSTRAT Programme to accomplish two principal tasks:

ANTOSTRAT convened such a workshop at Hobart, at the same time as the ANTIME (Antarctic Ice Margin) group conducted a similar meeting. The two groups have many earth science thematic, climatic, and process-oriented interests in common but work on distinctly different time scales. Whereas ANTIME focuses on the last 200,000 years, the ANTOSTRAT group considers relationships and interactions within the Geosphere-Hydrosphere-Biosphere over the past 130 million years (Cretaceous-Cenozoic) of Earth history. The ANTOSTRAT Workshop at Hobart identified and discussed the most critical Cretaceous-Cenozoic earth science issues, priorities and goals for the next decade. Scientists from eleven SCAR nations contributed to this planning workshop. This report provides a record of the meeting and its recommendations.

Before the workshop, coordinators for each major thematic issue and geographic region were identified. These individuals compiled background information and lists of important unresolved research topics. Their contributions, mostly as submitted, form Appendix 7 of this report. The draft report was circulated to all participants prior to the workshop. In Hobart, the thematic issues and regional imperatives were discussed, priorities were assigned to research directions, and recommendations made. The body of this report lists the results of those discussions. The final task of the workshop was to attain a consensus statement from the research community, as to how SCAR could facilitate this research.

The consensus statement from the workshop (see next section) emphasized the need for acquiring geologic samples via coring and drilling in support of paleoenvironmental studies. The statement was subsequently reviewed by SCAR Executive and then rephrased by the ANTOSTRAT Steering Committee into a series of three recommendations to SCAR (Appendix 6A,B), to establish a special SCAR subgroup that, like its predecessor ANTOSTRAT would facilitate and coordinate implementation of the above field and laboratory studies.

A revised version of the draft workshop report, including the three recommendations, was circulated to all members of SCAR Executive and the Working Groups on Geology and Solid Earth Geophysics prior to the SCAR XXV meeting (Concepcion, Chile; July, 1998). In Concepcion, extensive discussions led to a formal recommendation from the Joint Working Groups (JWG) (Appendix 6C) that an ANTOSTRAT Subcommittee under the JWG be established to accomplish the above tasks. The JWG recommendation was subsequently approved by SCAR delegates during the SCAR XXV meeting.

The activities of the Hobart Workshop and the actions at SCAR XXIV and XXV described in the following report reflect the major efforts by a broad cross-section of Antarctic earth-science community to define important research directions for the coming decade, and how they can best be accomplished.

It is hoped that this report will be a useful tool for all National Antarctic Programs.

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Consesus Statement Developed at Workshop Plenary Session

The following statement was developed during the Hobart workshop and accepted by a consensus vote of all workshop participants, representing 11 countries.

"*Coordinating Committee on

Antarctic Glaciation - Onset and Development

The Antarctic continent has, on account of its polar position over the last 130 million years, had a profound and fundamental effect on the Earth's climate history and palaeoenvironments over this time. It is also a region most sensitive to future climate change. Therefore it is of extreme importance to document the variations in Antarctic ice sheet history since the transition from the warm Cretaceous period (130-65 million years) through the "dynamic" ice sheets of the early Cenozoic to the more or less persistent ice sheet of the present, as well as to understand the mechanisms behind ice volume fluctuations within this time frame. The long time perspective is necessary because temperature-forcing atmospheric gases, such as CO2, have already exceeded Quaternary interglacial values by around 30% and continue to rise. Climate scenarios for the next centuries should therefore take into account scenarios for pre-Quaternary Antarctica.

Past SCAR-sponsored activities (the Group of Specialists on Cenozoic Paleoenvironments and its ANTOSTRAT project) have set a solid basis for a qualitative documentation of the evolution of the Antarctic ice sheet, through syntheses of seismic stratigraphic studies around the Antarctic margin. These studies have led to an appreciation of the complexity of behavior of past ice sheets, with the possibility of substantial variations from one region to another. There is now a need to go beyond the reconnaissance level of understanding reached, by identifying new research approaches, both thematically and geographically. An essential requirement is obtaining "ground truth" by drilling in order to calibrate and extend our seismic interpretations, which have been largely responsible for present models of glacial processes.

We wish to propose through the Working Groups of Geology and Solid Earth Geophysics that SCAR establish a new *Coordinating Committee to promote and coordinate a range of programs to investigate the onset and development of Antarctic glaciation. These would include ground-truthing our seismic interpretations through the Ocean Drilling Program, through other existing coring and drilling systems, and through shallow drilling techniques currently under development.

The ultimate goal of the group is a series of scenarios illustrating Antarctic geography, climate, ice and sheets at selected intervals through Cretaceous and Cenozoic time. This will need to involve close interaction with climate and ice sheet modelers. In addition, the work proposed will lead to improvements in the range of models used for interpreting the sedimentary record, as well as to a much improved understanding of links between geography, climate, ice sheet and sea level responses, along with interactions with other parts of our planetary system.

1998. It is hoped that this document will be a useful tool for all National Antarctic Programs.
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Task for the new group

To investigate the onset and development of Antarctic glaciation by:

* the statement from the Hobart Workshop called for either a Group of Specialists or a Coordinating Committee. Subsequent discussion has persuaded the ANTOSTRAT Steering Committee that a Coordinating Committee would be the appropriate body to set up to achieve the goals of the community. As a postscript, at SCAR XXV (July 1998), the name approved was the ANTOSTRAT Subcommittee.

 
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Summary Statements on Data Bases, Current and Planned Projects, Technology and Thematic and Regional Earth Science Issues

Introduction

Late Phanerozoic Global Change Challenges: The last 130 million years of the Phanerozoic Eon (Cretaceous, Tertiary, and Quaternary Periods) were marked by major latitudinal and longitudinal transport of continents, significant interaction between plates, very active sea floor spreading and evolution toward modern ocean configurations (Fig. 2). Further, these global events were also associated with ever-evolving ocean current circulation systems, eustatic oscillations, major biotic adjustments, at time rapid organic evolution, significant shifts in the demarcation of biogeographic province boundaries, and the transition from a "warm" hothouse Earth to a "cold" bipolar icehouse Earth. It is generally accepted that these and other geological phenomena are linked in an over-arching Earth System that involves an interrelation between the paleo-geosphere, atmosphere, hydrosphere and biosphere.

What has been the role of continental Antarctica and the south polar oceans in global late Phanerozoic earth system science? The earth science community in general, and the south polar research community in particular accept, that the Antarctic region has affected geological history in other regions of the globe, particularly during the last ~50 million years. Geologic and climatic events in the lower latitudes also impacted the southern high latitude record intervals of the Late Phanerozoic.

The Hobart Workshop provided an opportunity for a cross-section of the earth science community to review the vast progress made in the southern high latitudes in the past four decades since the International Geophysical Year (1957-58), and to identify and discuss the most important unresolved earth science research issues. Earth scientists have advanced from the initial reconnaissance phases to now, when we have diverse and comprehensive data bases, and advanced land- and sea-based technologies. Most importantly, the south-polar earth-science sub disciplines have recently moved to promote investigation of thematic and process issues, generate hypotheses, test hypotheses, and consider linkages between related and disparate data bases within and beyond the south polar realm.

The central concept behind the 1997 Hobart Workshop was a comprehensive preview of the next decade (1998-2008), with special emphasis on where and how to promote the further development of thematic and geographic data bases in all sub disciplines; and integration of these with major global programs that share the same basic objectives (Webb, Appendix 7.1, this report).

Data Bases, Current And Planned Projects, And Technology Issues

ANTOSTRAT Seismic Data Library System (SDLS): The Antarctic Seismic Data Library System provides open access to multichannel seismic reflection data collected by all countries (Fig. 3) that have been involved in Antarctic geophysical research, to facilitate large-scale cooperative research programs. In 1991 the SDLS was formally implemented under Antarctic Treaty Consultative Meeting (ATCM) Recommendation XVI-12. The SDLS has established library branches in 10 countries and provides three principal functions, i.e. education, data protection, and data storage. The SDLS operates under the general auspices of the Scientific Committee on Antarctic Research, and is currently overseen by the ANTOSTRAT Project. Management costs are underwritten by the U.S. National Science Foundation, U.S. Geological Survey, and the Osservatorio Geofisico Sperimentale (Trieste, Italy). Until the end of 1998 SDLS will be overseen by the SCAR ANTOSTRAT Project; thereafter the SDLS will be associated with either the Working Group On Solid-Earth Geophysics or a new SCAR-appointed Group of Specialists or Coordinating Committee (Cooper and Brancolini, Appendix 7.2, this report).

Priorities and goals:

ANTOSTRAT Antarctic Margin Ocean Drilling Program Initiatives: During the early 1990's it was apparent that the ANTOSTRAT seismic data base was mature enough to be used in planning a comprehensive stratigraphic drilling strategy for several regions of the Antarctic margin. Prime objectives of the coordinated effort were broadly defined to include deciphering the glacial history of the Antarctic continent, to link this history to global records of sea-level oscillations, paleoclimates, paleoceanography, organic (evolution, and atmospheric circulation. Another critical objective was to correlate Antarctic seismic stratigraphy with well-documented and dated sedimentary successions. The ambitious undertaking and acquisition of sedimentary records to depths of 1000m below the sea floor in abyssal water depths demanded involvement with the Ocean Drilling Program (ODP). Direct interactions between ANTOSTRAT and ODP resulted in the preparation and submission of five region drilling proposals. These proposals called for drilling legs on the Pacific margin of the Antarctic Peninsula, in the Weddell Sea, Prydz Bay, the Wilkes Land margin, and the Ross Sea. At the present time (July, 1998), the Antarctic Peninsula program has been completed as ODP Leg 178 (Fig. 4), a drilling leg (Leg 188) in Prydz Bay has tentatively been scheduled for 2000, and the proposals for the three remaining regions are in advanced stages of review and consideration by panels of the Ocean Drilling Program (Barker, Appendix 7.3, this report).

Priorities and goals:

Deep Stratigraphic Drilling In Antarctica Outside The ODP Organization: Knowledge of geology of the Antarctic continental shelf and surrounding deep ocean basins has benefited from past DSDP and ODP drilling campaigns (Legs 28, 35, 113, 114, 119, 120, and 178) between 1972 and 1998. Terrestrial programs such as the land-based Dry Valley Drilling Project, and littoral sea ice-based MSSTS, CIROS and Cape Roberts Project have also contributed a wealth of additional stratigraphic, chronostratigraphic, basin history and paleoclimate data to the Ross Sea sector of Antarctica, and strengthened linkages with the above-mentioned DSDP and ODP activities. (Barrett, Appendix 7.4, this report).

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Priorities and goals:

Shallow Drilling Technology And Sampling Of Late Phanerozoic Targets: A variety of conventional bottom sampling devices, such as grabs and corers, have encountered pre-Holocene or pre-Quaternary sediments at or close to the sea floor on Antarctic continental shelves. Seismic stratigraphic data indicate that Neogene, Paleogene and Cretaceous sediments are very widely distributed and may be sampled by devices capable of up to 50 meters penetration. A variety of ship-mounted shallow drilling rigs are used in industry and might be suitable for use in Antarctic waters. The Norwegian Terra Bor System (A/S Terra Bor-Namsos, Norway), now called Geo Drilling, is under development for use in polar environments, with prototypes having undergone one Arctic and two Antarctic seasons of testing. Shallow drilling procedures will allow transect drilling and sampling along dip and strike lines, and allow the construction of composite successions. It will also allow much broader areal coverage of targets than is possible with conventional single site deep drilling techniques (Kristoffersen, Appendix 7.5, this report).

Priorities and goals:

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Thematic Issues

Late Mesozoic And Cenozoic Plate Tectonic And Crustal History Of Antarctica: Much of the Late Mesozoic and Cenozoic geologic history of Antarctica is contained in the sedimentary sequences on the continental shelves. That history, however, in a large measure reflects the evolution of the Antarctic Plate, including both its plate tectonic and its crustal development. The Antarctic Plate was created by the break-up of Gondwanaland and today, except for the Scotia region, is bounded by spreading ridges. The Antarctic continental shelves rimming the East Antarctic craton are passive margins resulting from the separation of southeastern Africa, India, and Australia. The remaining part of the continent has a complex history, which includes fragmentation into microcontinents or blocks, rotations and displacements of those blocks, and subduction and passive margin evolution. In general, the post-break-up history can be divided into: the mid Jurassic to mid Cretaceous, by which time the Antarctic continent had attained its present configuration and essentially polar position; and the mid Cretaceous (130 Ma) to Recent. During the latter time interval break-up between Antarctica and Australia/New Zealand occurred, the link between South America and the Antarctic Peninsula was severed, and events leading up to the present day rift system through West Antarctic ensued (Elliot, Appendix 7.6, this report).

Priorities and goals:

Geological Time, And Relative And Absolute Dating Systems: The primary objective of "ground-truthing" seismic stratigraphy, through coupling these data with well documented drillhole data, must involve consideration of geological time at several resolution scales. The ANTOSTRAT mandate cannot be attained without the existence and application of a robust chronostratigraphic framework in the five Antarctica regions of principal interest. As a minimum standard, the chronostratgraphic framework should be capable of resolving problems of correlation, recognition of time spans, establishing rates of processes, etc, to at least a resolution of 2 million years. Such a capability would allow solution of major earth science problems and issues within Antarctica; and the accurate relating of Antarctic marine and terrestrial events with coeval events elsewhere on Earth. Regrettably, Antarctic Cretaceous and Cenozoic chronostratigraphy still lags far behind that available to workers in other regions of the globe (Webb, Appendix 7.1, this report).

Priorities and goals:

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Continental Shelf Sedimentary Basins: The most direct record of Antarctic climatic history over the past 130 million years is to be found in the blanket of sediment that covers the Antarctic continental shelf. The sediment pile ranges in thickness from zero up to approximately 14 km. The location of greatest thickness, the sedimentary basins, are typically tens to hundreds of kilometers across and vary in shape from subcircular depressions to half grabens to linear troughs. From limited knowledge obtained thus far on the age of the sediments in the basins, there appear to have been two main periods of basin development; the first a consequence of Gondwanide fragmentation during the Cretaceous resulted in the syn-rift episode of basin filling; and the second, post-rift phase, occurred during the Paleogene and or Neogene. Understanding the differential subsidence history of the numerous continental shelf basins around the Antarctic margins is important for two reasons. First, basin subsidence was active in the different basins at different times and a combining of stratigraphic records is necessary for the reconstruction of complete histories in any single region. Second, rapid subsidence has the potential for providing complete and high resolution records. However, success in piecing together records from different basins requires unambiguous correlation and an accurate chronology, for which data from both seismic surveys and drillhole must be combined (Barrett, Appendix 7.7, this report).

Priorities and goals

Paleoceanography And Circum-Antarctic Deep-Sea Marine Biosphere History: Significant Mesozoic-Paleogene global and regional paleoenvironmental events that help delineate the evolution of the Southern Ocean are discussed in detail by Harwood and Wise (1995, in P.-N. Webb and G.S. Wilson, editors, Byrd Polar Research Center, Report No. 10, pp. 47-53). A selection of primary objectives is provided here. See also

Wise, Appendix 7.8, this report)

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Priorities and goals:

Glaciomarine Sedimentary Processes, Events And Stratigraphy: Glacial and climatic records are best inferred by using quantitative, predictive models based on well documented processes that are active today. In the high latitude marine there is potential for major variability on environments and processes in both time and space. This translates as rapid vertical and lateral changes in stratigraphy and lithofacies (Powell, Appendix 7.9, this report)

Priorities and goals:

Terrestrial Geology: The Late Phanerozoic terrestrial record is the most poorly understood of all major continental landmasses. Perhaps as little as 15 percent of the last 130 m.y. is documented, even to a reconnaissance level. Prior to the Pliocene, terrestrial environmental and climatic scenario's depend almost enirely on analyses of proxy data recovered from the continental shelves and deep sea by the Deep Sea Drilling Project and Ocean Drilling Program. Because of the probability of recycling and other problems, such data cannot usually be used to make high time resolution interpretations of events in specific regions of Antarctica. Much of the existing Cretaceous and Cenozoic terrestrial data is derived from locations along the margins of West and East Antarctica, e.g. Antarctic Peninsula, Amery Graben-Prince Charles Mountains, and the Transantarctic Mountains. Central themes of the ANTOSTRAT initiative involve consideration of past climates (glaciation and deglaciation), sediment budgets, tectonic histories, and sea level oscillation, etc, all interpreted primarily from the continental shelf data but strongly influenced by the terrestrial record. It follows then, that investigation of Antarctica's terrrestrial realm must be accorded renewed urgency

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(Webb, Appendix 7.10, this report).

Priorities and goals:

on the assumption that the terrestrial record in different parts of Antarctica is not identical and involved histories that evolved within discrete mega-drainage systems. It is recommended that regional Southern Ocean ODP drilling and on-land drilling programs in the same region or sector be closely coordinated and perhaps treated as linked longitudinal transects.

Antarctic Seismic Stratigraphy: Seismic stratigraphic surveys have been completed across nearly all accessible regions of the Antarctic margin, resulting in the collection of more than 300,000 km of small-airgun single-channel data (SCS) and nearly 200,000 km of large-airgun multichannel seismic reflection data (MCS). A very detailed discussion is provided in (Cooper, Appendix 7.11, this report,).

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Priorities and goals:

Seismic Characterization And Physical Properties: Physical property measurements are particularly well suited for down-hole logging. It provides advantages in that records are continuous stratigraphically and results will be much closer to real in situ conditions. A number of different sensors, combined in a variety of ways are available. For studies of Cenozoic sediments the most essential parameters to measure are, P-wave velocity, bulk density, lithology and magnetic properties (susceptibility and polarity). These are all standard parameters measured in ODP logging operations. Acoustic velocity can be measured with a vertical resolution of 20 cm and magnetic susceptibility with a resolution of 25 mm. Lithology and porosity information can be obtained from natural gamma tools combined with neutron tools (Solheim, Appendix 7.12, this report).

Priorities and goals:

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Paleoclimate Modeling Of Glacial And Climatic History: The major deficiencies that remain outstanding in paleoclimate modeling of Antarctica center on model inadequacies and insufficient or poorly understood data by which to establish model boundary conditions and evaluation. A coordinated plan is required for meshing improved geological data and improved models. The central goal of the exercise is to use global and regional climate models to help understand glacial and other climatic events important in the history of Antarctica, and to relate these to past and possible future global climate. Climate models play a key role in helping to synthesize and integrate our understanding of major glacial and climatic events and can also be used to suggest correspondences and inconsistencies in the interpretation of these events from the geologic record. Model results can also be used as a guide to where future geologic data needs are greatest (Ogelsby, Appendix 7.13, this report).

As a result of deliberations at the Hobart Workshop, a series of time slice or time interval window modeling targets were identified. These were selected because reasonably well documented global, hemispheric and or regional events, phases or trends can be associated with each. These significant "moments" in past time provide logical starting points for a large scale modeling experiment.

Priorities and goals:

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In all these experiments, global and regional paleogeographic, paleotopographic and paleobathymetric data are needed to establish boundary conditions as accurately as possible. Information on external forcings, such as broad estimates of atmospheric carbon dioxide and changes in solar luminosity, etc. are also needed. Detailed site reconstructions will be essential for subsequent evaluation and interpretation of model simulations.

Regional Earth Science Issues

Antarctic Peninsula: The Antarctic Peninsula is a narrow upland region, comparatively well exposed, with broad flanking continental shelves. Study of the onshore geology is actively pursued by many SCAR countries, and a considerable marine data base exists for the readily accessible Pacific continental margin. Geoscience research is, in many fields, well beyond the reconnaissance stage, and ready for more focused attention. The original ANTOSTRAT Antarctic Peninsula Working group concerned itself with subduction neotectonics, and both past and present back-arc extension as well as investigations of the glacial margin. The Antarctic Peninsula region contains an excellent onshore Late Cretaceous and Paleogene shallow-water section with few breaks, in the James Ross Island region, which has already been investigated but has further potential. The Paleogene and Neogene onshore record is less continuous but compares well with other regions of Antarctica. The record of "full" glaciation offshore is extremely well-ordered and well-preserved, and was recently investigated during ODP Leg 178 operations (Fig. 4). It is estimated that the onset of grounded ice sheet extension to the continental shelf edge dates from late Miocene (7-10 Ma), significantly later than in East Antarctica. Barker, Appendix 7.14, this report).

Priorities and goals:

Weddell Sea: The Weddell Sea region was involved in the earliest rifting events associated with the break-up of the Gondwana supercontinent. After South America and Africa had separated from Antarctica, the rifting process continued into the recent Lazarev and Riiser Larsen seas to split off India. The break-up of these continental masses resulted in the creation of new restricted basins. At approximately 130 Myr a major reorganization of the seafloor spreading occurred and Maud Rise, a large volcanic feature developed. A hiatus lasting from 110-120 to 40 Myr was documented in ODP holes 692 and 693. During the same time span oceanic crust formed along the South Atlantic/Indian ocean sector of East Antarctica. Although Cenozoic glacial conditions are thought to have occurred in the region during the late Paleogene and Neogene this is not well documented. For example, it is not known with precision when and how often phases of the Filchner-Ronne Ice Shelf extended to the shelf break in the late Neogene. (Jokat, Appendix 7.15, this report).

Priorities and goals:

Prydz Bay Region: The Prydz Bay region is key to understanding the early history of break-up between Antarctica and Greater India and the development of the Indian Ocean. The major crustal and tectonic feature of this region is the prominent north-east south-west trending rift system, the Lambert Graben, which crosses the continental margin obliquely and extends into the continent toward the south. Two parallel rift grabens, divided by a crystalline basin high occur within the shelf, continental slope and Prydz Bay, representing a typical "Double Rift" system, with intracontinental and pericontinental branches The pericontinental rift branch exhibits transfer faults with an offset of up to 100 km. Prydz Bay was probably one of the first Antarctic basins to receive Cenozoic sediments and these are known to crop out on the sea floor. At the present time about 20% of the East Antarctic ice Sheet drains through the Lambert Graben into Prydz Bay and it was likely to have acted as a major trunk drainage system throughout the Cenozoic. Included in this catchment are the Gamburtsev Subglacial Mountains, a possible initial ice accumulation region within East Antarctica.

The Mac.Robertson Shelf west of Prydz Bay also contains a record of the rifting history of this margin. It is a scalped shelf with Precambrian basement, Mesozoic and pre-glacial Cenozoic sediments cropping out at the seafloor. The inner shelf half graben is filled with Cretaceous sediments. Gently dipping Jurassic, Paleocene and Eocene sediments underlie the outer shelf. The Paleocene and Eocene sediments are clearly post-rift but the it is not clear how the Jurassic sediments fit into the tectonic history of the margin. The Cretaceous age of the syn-rift sediments is at odds with the interpretations of rifting of India from Gondwana based on evidence from the Jurassic age of oceanic crust off Western Australia. (O'Obrien and Leitchenkov, Appendix 7.16, this report).

Priorities and goals:

Wilkes Land Margin: The Wilkes Land margin is a key area by which to reconstruct the evolution of the Wilkes Land continental margin and Indian Ocean region during the last 130 m.y. This area provides one of the few locations along the margin of East Antarctica where Mesozoic rocks are exposed at the seafloor. The area lies at the northern limit of the Wilkes Subglacial Basin, a major intracontinental depression that extends ~1500 km towards the South Pole inland of the Transantarctic Mountains, and is ~500 km wide in places. This basin may be the repository of a Paleogene-Neogene marine and terrestrial record, one that preserves pre-glacial, transitional and glacial sediments. Basins on the Wilkes Land margin have probably retained the northernmost portion of this record. During Paleogene-Neogene glacial phases the Polar Front probably came close to this margin of Antarctica and so there is the potential of strong deep sea paloceanographic influences in basins along the margin. Deep inner shelf basins contain an ultra high resolution Quaternary-Holocene record that has the potential of recording ice margin fluctuations (Escutia, Appendix 7.17, this report).

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Priorities and goals:

Ross Sea: The Ross Sea lies along the Pacific margin of the Jurassic rift that is delineated by the extensive dolerite sills of the Ferrar Group of the Transantarctic Mountains, and coincides in part with the active Cenozoic West Antarctic Rift System. The Transantarctic Mountains, one of the world's great mountain chains, forms, for a large part of its length, the rift shoulder of the West Antarctic Rift System. It is over 4,000 km long, reaches elevations of over 4,000 m, and is block-faulted and back-tilted towards the East Antarctic craton. The complementary rift shoulder in the Edward VII Peninsula and western Marie Byrd Land is far more subdued and has more of a horst and graben (basin and range) style of morphology that is mostly ice covered and extends about 1000 m above and below sea level.

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The Ross Sea and its southern continuation under the Ross Ice Shelf forms the Ross Embayment, which is about 500 m deep and generally has a gentle ridge and valley morphology with a maximum depth (1200 m) along the western margin, adjacent to the Transantarctic Mountains. The sedimentary basins in the Ross Sea were probably formed largely by rifting processes during and since break-up of this part of Gondwanaland in the Late Cretaceous. There were two phases of basin formation. An initial regional extension phase related to the Gondwana break-up episode, and a possibly mid-Cenozoic phase, which was localized to the western Ross Sea. Uplift of the Transantarctic Mountains appears to have occurred in several phases commencing at about 115 Ma. The structural and deposition framework of the Ross Sea is formed by four principal depocenters, the Victoria Land basin, the Northern basin, the Central Trough and the Eastern basin. Seismic data linked to drillhole information has shown that some thousands of meters of sediments are present in the deepest part of the Ross depocenters. The oldest sediments probably range back into the Paleocene, Cretaceous, and possibly the early Mesozoic. The presence of Eocene and Oligocene sediments have been confirmed in drillholes and appear to be widespread in the western and central Ross Sea. Neogene sediments also appear to be very widespread, having been documented in drillholes in the Ross Sea, at its western margins, and within the trunk valley fjordal systems that traverse the Transantarctic Mountains.

Late Neogene terrestrial glacial successions in the Transantarctic Mountain highlands provide potential for future linking of cratonic and rift basin stratigraphy, investigation of sediment transport budgets between terrestrial and marine regions, tectonic history, paleotopography and glacial history.

The Ross Sea region has several other unique attributes for Antarctica. It is the largest and most accessible southern high latitude continental shelf. In terms of global comparisons it is one of the largest rift mountain-basin structures, with extensive linear volcanic provinces (<40 Ma) along the western Ross Sea and Marie Byrd Land rift margins. Shelf basins have been long-lived catchments for ice and sediment for parts of both the East and West Antarctic ice sheets. The ice sheet, ice shelf, and open marine interfaces have interacted and fluctuated over at least 40 m.y., resulting in a variety of proximal and distal glacigene facies. Paleocoastlines are known with reasonable certainty. The proximity of volcanic provinces provides an opportunity to develop a sound chronostratigraphy via dating of rock and tephra-based techniques. Given the wealth of information on craton margin and rift basin multi-unit stratigraphy, widespread unconformities, lithofacies trends and relationships, biostratigraphy, and environmental interpretations, future research in the Ross Sea region is likely to evolve toward detailed interpretations of the respective roles of tectonic, paleoclimate and eustatic factors in the determining the histories of the extensive continental shelf basins in this part of Antarctica (Davey, Appendix 7.18, this report).

Priorities and goals:

 

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Acknowledgements

We acknowledge travel assistance grants from the Scientific Committee On Antarctic Research and the national Antarctic programs of the workshop participant's countries.

Dr Ian Goodwin of the SCAR Global Change Program office at Hobart arranged the amenities used during the meeting and offered many forms of assistance during the pre-workshop planning phase. We thank the Cooperative Research Centre, University of Hobart for providing the workshop meeting facilities. The compilers also extend thanks to all authors for their extensive contributions to the workshop and report, and to the many reviewers within the SCAR Geology and Solid Earth Working Groups and earth science community who provided comments.

Peter-Noel Webb and Alan K. Cooper

Workshop Conveners

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Note: The electronic version of the report, distributed by e-mail attachment, does not contain the six figures. If desired, the 6 TIF files for the figures can be obtained from the report compilers via e-mail request. The figures are the same as those distributed with the last draft of the report (7/98).

Figure Captions

  1. Map of Antarctica showing locations of major Cenozoic prograding sedimentary sequences, for the five areas around Antarctica that have been studied by the ANTOSTRAT project. These sequences lie at the seaward end of inferred former ice streams (Cooper and Webb, 1994).
  2. Fragmentation of parts of Gondwana super-continent and evolution of Antarctic Plate, during the Cretaceous and Cenozoic (Modified after Lawver, Gahagan and Coffin, 1992).
  3. Map showing location of multichannel seismic reflection profiles from the Antarctic continental margin (Cooper and Webb, 1992; modified from Behrendt, 1990)
  4. Deep Sea Drilling Project and Ocean Drilling Program sites completed in the southern Atlantic, Indian and Pacific oceans since 1972. ODP drillsites around the Antarctic Peninsula (in small type) were completed in early 1998 as part of Leg 178. These sites were proposed by the ANTOSTRAT Antarctic Peninsula regional working group.
  5. Proposed locations of Ocean Drilling Program drillsites, as proposed by the Weddell Sea, Prydz Bay, Wilkes Land margin and Ross Sea ANTOSTRAT regional working groups. Proposals for these sites are currently in review.
  6. Generalized cross section of the Antarctic continental margin showing the geometry and distribution of preglacial and glacial sedimentary sections for areas where the continental shelf has been extensively prograded and aggraded (Cooper and Webb, 1994, modified from Cooper et al., 1993).

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Appendices