Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set

Abstract

In 2001 and 2002, Australia acquired an integrated geophysical data set over the deep-water continental margin of East Antarctica from west of Enderby Land to offshore from Prydz Bay. The data include approximately 7700 km of high-quality, deep-seismic data with coincident gravity, magnetic and bathymetry data, and 37 non-reversed refraction stations using expendable sonobuoys. Integration of these data with similar quality data recorded by Japan in 1999 allows a new regional interpretation of this sector of the Antarctic margin. This part of the Antarctic continental margin formed during the breakup of the eastern margin of India and East Antarctica, which culminated with the onset of seafloor spreading in the Valanginian. The geology of the Antarctic margin and the adjacent oceanic crust can be divided into distinct east and west sectors by an interpreted crustal boundary at approximately 58°E. Across this boundary, the continent-ocean boundary (COB), defined as the inboard edge of unequivocal oceanic crust, steps outboard from west to east by about 100 km. Structure in the sector west of 58°E is largely controlled by the mixed rift-transform setting. The edge of the onshore ArchaeanProterozoic Napier Complex is downfaulted oceanwards near the shelf edge by at least 6 km and these rocks are interpreted to underlie a rift basin beneath the continental slope. The thickness of rift and pre-rift rocks cannot be accurately determined with the available data, but they appear to be relatively thin. The margin is overlain by a blanket of post-rift sedimentary rocks that are up to 6 km thick beneath the lower continental slope. The COB in this sector is interpreted from the seismic reflection data and potential field modelling to coincide with the base of a basement depression at 8.0-8.5 s two-way time, approximately 170 km oceanwards of the shelf-edge bounding fault system. Oceanic crust in this sector is highly variable in character, from rugged with a relief of more than 1 km over distances of 10-20 km, to rugose with low-amplitude relief set on a long-wavelength undulating basement. The crustal velocity profile appears unusual, with velocities of 7.6-7.95 km s )1 being recorded at several stations at a depth that gives a thickness of crust of only 4 km. If these velocities are from mantle, then the thin crust may be due to the presence of fracture zones. Alternatively, the velocities may be coming from a lower crust that has been heavily altered by the intrusion of mantle rocks. The sector east of 58°E has formed in a normal rifted margin setting, with complexities in the east from the underlying structure of the N-S trending Palaeozoic Lambert Graben. The Napier Complex is downfaulted to depths of 8-10 km beneath the upper continental slope, and the margin rift basin is more than 300 km wide. As in the western sector, the riftstage rocks are probably relatively thin. This part of the margin is blanketed by post-rift sediments that are up to about 8 km thick. The interpreted COB in the eastern sector is the...

Chapter 5 Cenozoic Climate History from Seismic Reflection and Drilling Studies on the Antarctic Continental Margin

“…WL-1) formed during the Cretaceous separation of Australia and Antarctica (Cande and Mutter, 1982;Veevers, 1987;Sayers et al, 2001;Colwell et al, 2006;Leitchenkov et al, 2007;O'Brien and Stagg, 2007). The stratigraphy of the margin is known mainly from the seismic stratigraphic interpretation of numerous MCS surveys (Sato et al, 1984;Wanneson et al, 1985;Tsumuraya et al, 1985;Eittreim and Hampton, 1987;Ishihara et al, 1996;Tanahashi et al, 1997;Brancolini and Harris, 2000;Stagg et al, 2004a, b); complemented by surface sediment cores (Domack et al, 1980;Domack, 1982;Tsumuraya et al, 1985;Hampton et al, 1987;Ishihara et al, 1996;Tanahashi et al, 1997;Brancolini and Harris, 2000;Leventer et al, 2001;Escutia et al, 2003;Michel et al, 2006); and limited deep geological sampling recovery at DSDP Sites 268 and 269 . The best-surveyed area is the eastern Wilkes Land margin (EWL) from the Ade´lie Coast to George V Land.…”

“…The best-surveyed area is the eastern Wilkes Land margin (EWL) from the Ade´lie Coast to George V Land. West of this area (the western Wilkes Land margin-WWL), Japan and Russia collected widely spaced seismic lines that were then augmented during the 2001-2002 Australian Antarctic and Southern Ocean Profiling (ASSOPP) Project (Stagg et al, 2004a, b;Leitchenkov et al, 2007).…”

“…Pre-Eocene syn-rift strata are about 3 km thick and are highly variable in seismic character, with discontinuous, faulted, and tilted strata onlapping the flanks of the acoustic basement (Eittreim and Smith, 1987;Eittreim, 1994;De Santis et al, 2003;Stagg et al, 2004a, b;Leitchenkov et al, 2007).…”

“…The continental rise seaward of Prydz Bay contains up to 5 km of post-rift sediments (Figs. PB-2, Foldouts PB-1 and PB-2; Mizukoshi et al, 1986, Stagg et al, 2004a. The lowermost seismic stratigraphic unit has parallel, mostly continuous reflectors typical of deep-ocean deposition that probably occurred during pre-ice-sheet times (Mizukoshi et al, 1986;Kuvaas and Leitchenkov, 1992;Kuvaas et al, 2005).…”

“…These regions include similar geomorphic and stratigraphic features. Although we do not include them in the discussion below due to space considerations, we include here representative citations to some of the studies published for the Bellingshausen and Amundsen seas Tucholke and Houtz, 1976;Tucholke, 1977;Kimura, 1982;Yamaguchi et al, 1988;Cunningham et al, 1994Cunningham et al, , 2002Gohl et al, 1997Gohl et al, , 2007Nitsche et al, 1997Nitsche et al, , 2000Wellner et al, 2001Wellner et al, , 2006Lowe and Anderson, 2002;Ó Cofaigh et al, 2005;Dowdeswell et al, 2006;Evans et al, 2006;Scheuer et al, 2006a, b;Larter et al, 2007;Uenzelmann-Neben et al, 2007) and for offshore areas of Queen Maud Land and Enderby Land (Kuvaas et al, 2004a(Kuvaas et al, , b, 2005Hinz et al, 2005;Stagg et al, 2004a, b;Leitchenkov et al, 2007;Solli et al, 2007a, b, c).…”