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IODP Expedition 318:
Wilkes Land Glacial History
Site U1358 Summary
PDF file is available for download.
2 March 2010
(WLSHE-08A) is located on the continental shelf off the Adélie Coast at 499 m
water depth. The main objective at Site U1358 was to core across the regional
unconformity WL-U8. This unconformity marks a distinct change in the geometry
of the progradational wedge from low-dipping strata below to steeply dipping
foresets above (Eittreim et al., 1995; Escutia et al., 1997; De Santis et al.,
2003). It is inferred to represent a significant
change from intermittent glaciers to persistent oscillating ice sheets, either
during the Late Miocene (Escutia et al., 2005; Cooper et al., 2008) or
during the late Pliocene (~3 Ma; Rebesco et al., 2006). The steep foresets
above WL-U8 are thought to likely consist of ice proximal (i.e. till,
diamictite and debris flows) and open-water sediments deposited as grounded ice
sheets extended intermittently onto the outer shelf – similar to
sediments recovered during ODP Site 1167 on the Prydz Bay Trough fan (O'Brien
et al., 2001).
lies at the westernmost edge of the Mertz Bank and receives drainage from the
East Antarctic Ice Sheet through the Wilkes Subglacial Basin. At Site U1358,
unconformity WL-U8 occurs at ~165 mbsf (0.84s TWTT). Multichannel seismic
reflection profiles crossing Site U1358 show gently dipping strata on the shelf
that are truncated near the seafloor. This
provided a unique opportunity to sample across the unconformity by drilling at
very shallow penetration. The record from Site
U1358 is also to complement the more distal (i.e., glacial-interglacial cycles)
record from Site U1359 located on the continental rise.
two short holes at Site U1358 in a water depth of 499 m. Unfortunately, we were
only able to penetrate to 35.6 mbsf before the drill collars failed and we had
to abandon the hole.
Hole U1358A was drilled to a total depth
of 2.0 meters below sea floor (mbsf) and Hole U1358B to a total depth of 35.6
mbsf, both using the Rotary Core Barrel (RCB) system. The upper 8.2 m are
unconsolidated and moderately to strongly disturbed by drilling. Below 8.2
mbsf, the sediments are consolidated and only slightly disturbed by drilling.
Holes U1358A and U1358B penetrated diamictons and diamictites and are placed
within a single lithostratigraphic unit. The diamictons in the upper 8.2 mbsf
were probably deposited from floating ice. The diamictites below 8.2 mbsf were
either deposited from floating ice, where crudely stratified and laminated, or
subglacially, with possible remobilization through glacigenic debris flow.
Sediments from Holes U1358A and U1358B
contain siliceous and organic microfossils. Diatom biostratigraphy provides
tentative stratigraphic control throughout the section. Pliocene strata (9.32
to 28.62 mbsf) are overlain by uppermost Pleistocene to Holocene strata.
Dinocysts and radiolarians were encountered in trace amounts only, and provide
no further age constraints. Foraminifers were not
encountered in holes drilled at Site U1358. Diatom assemblages suggest a
high-nutrient, open-water environmental setting, similar to that of the modern
day Southern Ocean north of the winter sea ice extent. Palynological
associations are a mix of reworked and in situ palynomorphs. The in situ
protoperidinioid dinocysts confirm a nutrient-rich environment. High abundances
of reworked Mesozoic-Paleozoic microfossils indicate a significant input of
Whole-core magnetic susceptibility was
measured at 2.5 cm intervals (2 s measurement time). The raw data
values range from 3 to 2834 instrument units (IU). However, the majority of
measurements vary between 200 and 400 IU, with some peaks in Core U1358B-4R
representing gravel clasts. Variations in GRA density reflect variations in the
composition of the Pliocene-Pleistocene diamictite that varies between
clast-rich muddy and clast-rich sandy lithologies.
Cooper, A.K., Brancolini, G.,
Escutia, C., Kristoffersen, Y., Larter, R., Leitchenkov, G., O'Brien P., and
Jokat, W., 2009. Cenozoic Climate History from Seismic Reflection and Drilling
Studies on the Antarctic Continental Margin. In: Fabio Florindo and Martin
Siegert, editors: Developments in Earth and Environmental Sciences, Vol 8,
Antarctic Climate Evolution, Fabio Florindo and Martin Siegert. The
Netherlands: Elsevier, pp. 115–228.
De Santis, L., Brancolini, G., Donda, F.,
2003. Seismic-stratigraphic analysis of the Wilkes Land continental margin
(East Antarctica). Influence of glacially-driven processes on the Cenozoic
deposition. Deep-Sea Research. Part 2. Topical Studies in Oceanography 50
Eittreim, S.L., Cooper, A.K., Wannesson,
J., 1995. Seismic strati- graphic evidence of ice-sheet advances on the Wilkes
Land margin of Antarctica. Sedimentary Geology 96, 131–156.
Escutia, C., Eittreim,
S.L., Cooper, A.K., 1997. Cenozoic glacio- marine sequences on the Wilkes Land
continental rise, Antarctica. Proceedings Volume-VII International Symposium on
Antarctic Earth Sciences, pp. 791–795.
Escutia, C., De Santis, L., Donda, F.,
Dunbar, R. B., Brancolini, G., Eittreim, S. L., & Cooper, A. K. (2005).
Cenozoic Ice Sheet history from east Antarctic Wilkes Land continental margin
sediments. Global Planet. Change, 45, 1–3.
O'Brien, P.E., Cooper, A.K., Richter, C.,
et al., 2001. Proceedings of the Ocean Drilling Program. Initial Reports, 188.
ODP, College Station, TX, CD-ROM.
Rebesco, M., Camerlenghi, A., Geletti,
R., & Canals, M. (2006). Margin architecture reveals the transition to the
modern Antarctic Ice Sheet ca. 3Ma. Geology, 34, 301–304.