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SCAR Report No 16,

Appendix 7

LATE PHANEROZOIC (100-0 MA) STUDIES ON THE
WILKES LAND MARGIN OF EAST ANTARCTICA
Carlota Escutia U.S. Geological Survey Menlo Park, CA 94025

The Wilkes Land is a key area to reconstruct the evolution of the Wilkes Land continental margin and Indian Ocean region during the past 100 Ma. The existing data base (i.e. mainly the ANTOSTRAT MCS data base and numerous sediment cores) give a regional knowledge of the area, which will be very useful for planning future surveys into selected areas. At present, interpretation on the nature and age of the seismic sequences and events in the Wilkes Land margin are mainly based on the seismic character and indirect correlations with DSDP 268 and 269. Thus, many of the questions outlined below are focussed on obtaining the ground truth (coring/drilling) information of the sedimentary sequences to establish stratal ages and environments of deposition. Three main future thematic areas of study are envisioned, in order of priority: 1) glacial history and paleoenvironments, 2) sedimentary basin evolution, and 3) patterns and events in the tectonic and structural history. Studies in the patterns and events in the tectonic and structural history of the Wilkes Land may not be attainable whithin the next 10 years, but they represent the present and future research interests of international working teams in this margin, and they provide the scientific community with a full view of the achievements that can be expected from this margin.

l. Glacial History And Paleoenvironments

Problem
The Wilkes Land region is a key area to:

  • reconstruct the Cenozoic and late Quaternary depositional and glacial history of the East Antarctic Ice Sheet. The growth history of the Antarctic Ice Sheet is of great importance because its link with global climate changes and sea level fluctuations. At present, the growth history of the Antarctic Ice Sheet is not well known, being inferred principally from deep-ocean oxygen isotopic measurements, and from the non-polar continental-shelf seismic-stratigraphic records. The inferences are equivocal and in some cases disagree.
  • study the depositional processes related to grounded ice sheets and glaciers in polar regions, for example, what are the linkages among the shelf, slope and rise settings in terms of glacial/interglacial processes?

The short-and-long term depositional and glacial history of the Wilkes Land Antarctic margin region, which is sensitive to East Antarctic ice sheet fluctuations, can be obtained from the study of the sedimentary sections in three depositional environments: a) nearshore shelf basins, b) shelf troughs, and c) rise drifts.

  • Nearshore shelf basins (e.g. Mertz, Ninnis) sediment records, will provide a high-resolution Holocene record of coastal productivity, climate and/or glacial dynamics. These records will help answer questions such us: what is the climatic variability along the coastal setting of the Wilkes Land and what is the response of the marine ecosystem and sedimentation to these changes?
  • Continental shelf troughs and banks. Study of sedimentary record on shelf troughs and banks will help resolve questions such as:
    • What is the role of shallow banks and deep troughs on sediment supply and sedimentary processes?
    • What is the history of glaciation in the shelf?
    • When was ice at its maximum extent?
    • Where was the ice edge?
    • What are the regional differences in ice maxima (timing and extent)?
    • How is the retreat of the last glacial maximum characterized in the sediment record?
    • What is the rate of retreat?
    • How does ice reatreat correlate with external factors such as sea level?
    • Are there rapid or episodic events (e.g. Dansgaar-Oeshger, Heinrich) in the late Quaternary record as we see in the Northern Hemisphere?
    • What are the differences if any between sedimentary processes in convergent and divergent ice drainage systems?
    • What are the differences if any between convergent and divergent ice drainage systems (i.e. Wilkes Land margin vs. Prydz Bay stratigraphic records)?
    • Are divergent ice margins such as the Wilkes Land and Queen Maud Land acting as line sources?
    • Do ice streams shift with time?
    • What is happening on the banks during the glaciations?, No ice? Slow ice?
    • How has climate impacted the sratigraphic record on the shelf, slope and rise?
    • How the sedimentary record vary across the shelf?
    • What processes are influencing sedimentation on the shelf and how are they linked?
    • Can the stratigraphy of the shelf be correlated with the slope and rise?
  • Continental-rise drift deposits. Drift deposits, which appear to have high-sedimentation rates and depositional continuity on the rise, can provide us with a high-resolution continuous and datable record of Pliocene-Pleistocene glacial/interglacials, that are depositionally linked to the glacial sedimentation processes of the adjacent shelf.

Objectives

  • To determine the timing of glacial onset (middle Eocene or older), in this part of the East Antarctic margin;
  • To determine changes in the glacial regime and sea-level recorded in prominent change in sedimentary wedge geometry (middle Miocene?);
  • To determine in detail Pliocene-Pleistocene glacial history, and a high-resolution record of paleoenvironmental and paleoceanographic changes during glacial/interglacial cycles; and
  • To obtain high-resolution Holocene through sedimentologic and micropaleontologic analyses of long (9m piston cores) and high-resolution seismic profiles (Huntec/CHIRP) collected from deep (>1000m) inner shelf basins.

Logistics

Late Quaternary (including Holocene) studies will require long/jumbo piston cores, multibeam bathymetry, and high-resolution Chirp/Huntec and 3.5 kHz seismic profiles. These technologies can easily be deployed from most research vessel. However, to recover the Holocene record from deep (>1000 m) inner-shelf basins such as the Mertz and the Ninnis located close to glacier outlets an ice breaker may be required to work in areas covered by sea ice.

On the Wilkes Land margin longer-term Cenozoic depositional and glacial objectives can be achieved by using shallow drilling techniques and by ODP drilling. Shallow drilling devices are currently being developed and tested (e.g. the shallow penetration Terrabore, has been tested by the Norwegians in Antarctica over the last field season). Because key stratigraphic horizons are exposed at shallow depths the shelf a transect of 50-100 m cores would sample a long and potentially continuous stratigraphic section.

Target areas

  • Inner- basins: Mertz, Ninnis and Vincennes Bay
  • Shelf troughs located west of the Adelie Bank on the Adelie Coast of the Wilkes Land, and west of the Dibble ice tongue.
  • Drift deposits developed on the continental rise in front of the Mertz Trough, and the shelf trough west of the Dibble ice tongue.

II. Origin Of Sedimentary Sequences

Problem
At present the nature and age of the seismic sequences and events recorded on the Wilkes Land margin are mainly based on the seismic character, relative stratigraphic position and indirect correlation of these sequences to DSDP 269 (Eittreim and Smith, 1987; Wannesson et al., 1985; Tanahashi et al., 1994). Unfortunately this site is separated from the margin by a topographic high, and all but the uppermost strata are truncated. Two key unconformities (unconformities WL4 and WL3 of Tanahashi et al., 1994) occur in the seismic records which relate the stratigraphic sequences to times before, during or after rifting. A third unconformity, WL2, occurs at shallower levels of the postrift section (Eittreim and Smith, 1987). WL2 marks the beginning of a new style of deposition characterized by progradation on the continental shelf (Eittreim et al., 1995), and increased turbidite deposition on the rise with development of large channel-levee complexes and drift deposits (Escutia et al., 1995; Escutia et al., in press). The WL2 unconformity has been interpreted to represent the onset of glacial conditions in this segment of the East Antarctic margin.

Objectives
To constrain the age, nature and paleoenvironment of the main sedimentary sequences. For example,

  • What is the nature and age of the deepest stratified sequence (i.e. sequence D of Eittreim and Smith, 1987)? Eittreim and Smith (1987) interpret this sequence to represent prerift continental strata based on the erosionally-truncated edges of fault blocks of this sequence. Veevers (1987) however interpret sequence D as synrift, because the amount of extension experienced by this sequence is anomalously small to be explained by extensional faulting associated with significant crustal thinning. An interpretation of how far north the Antarctic continental crust extends depends on the interpretation of this sequence.
  • What is the nature and age of sequences C, B and A of Eittreim and Smith (1987)?
  • What is the paleoenvironment of the Wilkes Land margin building?

Logistics
Recovery of the sequences targeted in this theme can only be achieved by means of ODP drilling, in areas of the continental rise where buried oceanic basement highs reach to within 1000 m below seafloor.

Target areas
Hakurei seamount or any of the other seamounts in the same region.

lll. Patterns And Events In The Tectonic And Structural History

Problem
Earliest oceanic crust separating Australia from Antarctica is estimated at about 96Ma, according to the oldest identified magnetic anomalies in this area (i.e. anomaly 34, 85 Ma), and an interpretation of the edge effect magnetic anomaly at the oceanic crust edge during the Cretaceous Magnetic Quiet Zone (MQZ) (Cande and Mutter, 1982; Veevers, 1987). The transition zone from continental to oceanic crust (COB) in the western Wilkes Land margin runs parallel to the continental margin (Eittreim, 1994). In the eastern Wilkes Land margin, there are two interpretations of where the COB is located: 1) based on magnetic and seismic profiles Veevers (1990) locates the COB south of the Hakurei (former Homachi seamount); 2) based on gravimetric Geosat vertical profiles, Royer and Sandwell (1989) locates the COB north of the Hakurei/Homachi seamount. NE of the Hakurei seamount recently recovered peridotite derived from sub-continental mantle, has been interpreted as being emplaced in connection with the early stages of ocean basin development (Yuasa et al., in press). The origin of the magnetic quiet zone may be explained by the presence of underlying remnant continental crust. The existence of thick manganese crusts is also consistent with the seamount having been exposed for a period of several tens of millions of years.

Objectives

  • To determine the timing of the breakup between Australia and Antarctica which is believed to have occurred in early-Late Cretaceous times (96 Ma) (Cande and Mutter, 1982).
  • To determine the thickness and nature of the continental-oceanic crust boundary (COB) and the transition between the two types of crust.
  • To determine nature and age of subbottom highs (e.g. Hakurei Seamount) located in an area of crustal anomalies.

Logistics
MCS, gravity and magnetic profiles, ocean bottom seismometers, and large volume (70 litre) airgun arrays are needed.

Two approaches have been proposed to solve these problems:

  • to sample the crustal and mantle rocks from seafloor around the seamount by ODP drilling,
  • to get many kind of rocks consisting the seamount by short core drilling and dredging.

Target areas
Hakurei seamount and the seamount NE of Hakurei where the peridotite was recovered.

IV. Current And Planned Projects

Approved research
A 25-day cruise with the Research Vessel from the Osservatorio Geofisico Sperimentale, Trieste (Italy), is scheduled for 1999 under the WEGA (Wilkes Land Glacial History) Project. This cruise will acquire multichannel and high-resolution seismic profiles, gradiometric and gravity profiles, subbottom and side scan sonar profiles and gravity cores, across the Wilkes Land continental margin from about 200 to 4000 m. The aim of this project is to reconstruct the late Cenozoic history of the East Antarctic Ice Sheet and its link with global climate changes and sea level fluctuations, by providing statements of the continental shelf, slope and rise paleoenvironment particularly over the Holocene, the last Glacial cycle, and the Pliocene.

Pending research

  • A drilling proposal (#482 and 482-rev), has been submitted to ODP as one of five ANTOSTRAT drilling proposals. The Wilkes Land drilling will sample glacial and interglacial Cenozoic sedimentary sections, to acquire ground-truth proximal data for the glacial and sea-level histories of this segment of the East Antarctic continental margin. It has been proposed to drill the prograding-shelf sequences and continental rise drift deposits. Wilkes Land drilling, when combined with other Antarctic margin drilling, should provide a proximal record for the Cenozoic history of continent-wide fluctuations of the Antarctic Ice Sheet. By drilling the Wilkes Land margin, we anticipate recovering cores that will
    • establish the times for initiation of glaciation and major inferred middle Miocene and Plio-Pleistocene fluctuations of the Antarctic Ice Sheet in this part of East Antarctica;
    • establish times of expanded ice sheets grounded to the continental shelf edge (i.e. glacial maxima) and open waters on the shelf (i.e, interglacial), to link oxygen isotope ratios and sea-levels directly to ice volumes for this part of the Antarctic margin.
    • provide paleoenvironmental data for sedimentary sequences, to help derive regional Neogene climate and depositional variabilities from high-resolution seismic data.
  • A marine geological study has been proposed to the U.S. Antarctic to obtain very high-resolution (Huntec and CHIRP), high-resolution (3.5kHz) seismic data, and long piston cores (10m) from a transect across the Wilkes Land margin (i.e. inner-shelf basins, shelf troughs and rise drift deposits). It is proposed to conduct a detailed (laminae by laminae) study of the sediment cores to determine late Quaternary including Holocene, depositional and glacial histories. Additionally, it has been proposed to collect new MCS data, and to use the recovered sediment cores to augment existing data for site surveys for the ODP drilling proposal.

V. Future Projects And Cooperative Considerations

Other than the above mentioned projects that concentrate mainly in the eastern Wilkes Land margin, there is a need to for reconnaissance studies in the western Wilkes Land margin. At present, the western Wilkes Land margin is poorly surveyed, and most of the existing data has been collected by JNOC. Although JNOC's research in the following years will not focus on surveying the Wilkes Land, the existing data set could be an important resource and the base for planning future surveys and for future collaboration.

Potential cooperative studies can be established between the Australia, France (Ice breaker Astrolabe supplies yearly the Dumont D'Urville base which can do some geophysical work in the way back and the Marion D'Ufre, not an icebreaker has multibeam, side scan sonar and a long-45 m- piston coring system), Italy and the US.

References

Cande, S.C., and Mutter, J.C., 1982. A revised identification of the oldest sea-floor spreading anomalies between Australia and Antarctica: Earth and Planetary Science Letters, 58, 151-160.Eittreim, S.L., 1994. Transition from continental to oceanic crust on the Wilkes-Adelie margin of Antarctica. Journal of Geophysical Research, 99, 24189-24205.
Eittreim, S.L., Cooper, A.K., and Wannesson, J., 1995. Seismic stratigraphic evidence of ice-sheet advances on the Wilkes Land margin of Antarctica. Sedimentary Geology, 96, 131-156.
Eittreim S.L. and Smith G.L., 1987. Seismic sequences and their distribution on the Wilkes Land margin. In: S.L. Eittreim and M.A. Hampton (eds.), The Antarctic Continental Margin: Geology and Geophysics of Offshore Wilkes Land. (Circum-Pacific Council for Energy and Mineral Resources Earth Sciences Ser., 5A) Houston, 15-43.
Escutia, C., Eittreim, S., and Cooper, A.K., 1995, Cenozoic glaciomarine sequences on Wilkes Land continental rise, Antarctica. VII International Symposium on Antarctic Earth Sciences, Siena, Italy, Abstracts Volume, p. 121.
Escutia, C., Eittreim, S.L., and Cooper, A.K., in press, Cenozoic glaciomarine sequences on the Wilkes Land continental rise, Antarctica: Proceedings Volume-VII International Sysposium on Antarctic Earth Sciences: p.791-795.
Rebesco, M., Larter, R., Barker, P.F., Camerlenghi, A., and Vanneste, L.E., in press, The history of sedimentation on the continental rise west of the Antarctic Peninsula, IN Barker, P.F. and A.K. Cooper eds., Geology and Seismic Stratigraphy of the Antarctic Margin - Part 2, AGU Antarctic Research Series.
Tanahashi, M., Eittreim, S., and Wannesson, J., 1994. Seismic stratigraphic sequences of the Wilkes Land margin. Terra Antartica, 1 (2), 391-393.
Veevers, J.J., 1987. The conjugate continental margin of Antarctica and Australia. In: S.L. Eittreim and M.A. Hampton (eds.), The Antarctic Continental Margin: Geology and Geophysics of Offshore Wilkes Land. (Circum-Pacific Council for Energy and Mineral Resources Earth Science Ser., 5A) Houston, 45-74.
Wannesson J., Pelras M., Pettitperrin B., Perret M., and Segoufin J., 1985. A geophysical survey of the Adelie margin, East Antarctica, Mar. Petrol. Geol., 2, 192-201.