Ross Sea G Brancolini and G Leitchenkov

The Ross Sea has four large sedimentary basins with thick Cenozoic sequences that record the proximal paleoenvironmental histories of the East and West Antarctic Ice Sheets (Cooper and Davey, 1985; Cooper et al., 1991b, c). Here, ice-sheet evolution is linked to the Cenozoic uplift histories of the Transantarctic Mountains and Marie Byrd Land. Offshore, the West Antarctic Ice Sheet (WAIS) flows across the Eastern basin, and the East Antarctic Ice Sheet (EAIS) passes over the Transantarctic Mountains and flows across the Victoria Land basin, the Northern basin and the Central trough (Fig. RS-1).

170°E 180" 170°W

Figure RS-1: Map showing the structural framework of the ross sea. The limits of the basins are based on the depositional limits of the seismic Sequence RSS-1. VL, Victoria Land; VLB, Victoria Land basin; NB, Northern basin; CoH, Coulman high; CH, Central high; CT, Central trough; EB, Eastern basin; WAIS, West Antarctic Ice Sheet; EAIS, East Antarctic Ice Sheet. The heavy dashed line marks the postulated boundary between East Antarctic Ice Sheet and West Antarctic Ice Sheet drainage.

Numerous seismic studies have been done in the Ross Sea region since the 1960s, with more than 45,000 km of MCS reflection data collected since 1980 (Hinz and Block, 1984; Sato et al., 1984; Cooper and Davey, 1987; Hinz and Kristoffersen, 1987; Zayatz et al., 1990; Brancolini et al., 1991) (Fig. RS-2a), to provide tectonic and deep stratigraphic control. A large number of singlechannel seismic (SCS) surveys have also been conducted for greater resolution of the shallow subsurface (Fig. RS-2b). Drilling at several sites by DSDP (Deep Sea Drilling Project, Hayes and Frakes, 1975), DVDP (Dry Valley Drilling Project, McGinnis, 1981), MSSTS (McMurdo Sound Sediment and Tectonic Study, Barrett, 1986), CIROS (Cenozoic Investigation in the Western Ross Sea, Barrett, 1989) and CRP (Cape Roberts Project,

Figure RS-2: (A): Multichannel seismic-reflection surveys in the Ross Sea (modified from Brancolini et al., 1995). Some of these data are available in digital format from Cooper et al. (1995) and others from the Antarctic Seismic Data Library (Childs et al., 1994; Wardell et al., 2007). (B) Singlechannel seismic surveys in the Ross Sea (modified from Barrett et al., 1999).

Figure RS-3: Correlation of Ross Sea area drilling and seismic stratigraphy with global oxygen isotope (Miller et al., 1987) and eustacy (Haq et al., 1987) curves (modified from Brancolini et al., 1995; Cooper et al., 1995). Regional erosional unconformities in Oligocene and younger sections are interpreted to be due in part to sub-ice erosion, especially in late Neogene time.

Cape Roberts Science Team, 1998, 1999, 2000, 2001) ANDRILL (Antarctic geological Drilling, Naish et al., 2007; Florindo et al., 2008; Harwood et al.. 2008) provides geologic ground truth data (Fig. RS-3). A regional seismic stratigraphy has been derived by the ANTOSTRAT project with seismic sequences and unconformities tied to drilling data (Fig. RS-3; Cooper et al., 1995).

Ross Sea seismic data are used by many to infer glacial sedimentary processes (e.g. Cooper et al., 1991b; Alonso et al., 1992; Anderson and

Bartek, 1992; Shipp et al., 1994; Brancolini et al., 1995; Cochrane et al., 1995; De Santis et al., 1995; Bartek et al., 1996; De Santis et al., 1999; Bart et al., 2000; Bart, 2003; Chow and Bart, 2003; Accaino et al., 2005). Characteristic features and inferred processes in Oligocene and younger strata include:

1. Landward-deepening seafloor of the continental shelf with broad (up to 100 km wide) cross-shelf troughs and banks formed by ice-stream erosion and deposition, respectively.

2. Numerous regional seismic unconformities believed to result from erosion of the continental shelf by grounded ice sheets.

3. Steep prograding sedimentary sequences (i.e. foreseest dips more than 5° and eroded topset strata) interpreted as ice-proximal till deltas from grounded ice.

4. Wedge-shape, non-reflective units interpreted as 'till tongues' deposited by grounded ice.

5. Shallow sediment with high velocities, considered due to overcompaction by grounded ice.

The seismic stratigraphy and drilling help establish ice-sheet evolution in the Ross Sea region, and are discussed below for four key intervals.

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