Abstract
The seismic sediment record of the Amundsen Sea continental rise provides insight into the sedimentation processes from pre-glacial to glacial times, variations in ocean-bottom circulation, early ice sheet growth, and intensification towards the present icehouse regime. Seismic reflection data acquired during the 2010 RV Polarstern and the 2006 RV Tangaroa expeditions, created a >2000km long continuous Amundsen Sea to Ross Sea seismic transect. Pre-existing lines linked to this transect, connect key seismic stratigraphy horizons from the Ross Sea shelf to the rise and farther along the West Antarctic margin, up to the Amundsen Sea Embayment. Seismic units AS-1 to AS-3 constitute the Cretaceous to Eocene pre-glacial (PG) sequence (79–34Ma), units AS-4 to AS-6 the Eocene to mid-Miocene transitional (T) sequence (34–15.5Ma), and units AS-7 to AS-11 the mid-Miocene to Quaternary full glacial (FG) climate sequence (15.5–0Ma). The top PG sequence boundary horizon AS-u3/uPG-T, links to unconformity RSU6 of the Ross Sea shelf and to the base of Unit II of the eastern Amundsen Sea, and is interpreted as the first arrival of grounded ice on the shelf. The top T sequence boundary AS-u6/uT-FG, links to RSU4 and the base of Unit III, and is interpreted as the onset of the FG regime with intensified ice sheet advances onto the outer shelves. The Amundsen Sea basin accumulated up to 3.9km thick sediments in its centre. Seismic facies geometry analysis suggests Paleocene–Eocene bottom-current activity, late Eocene shelf grounding of the West Antarctic Ice Sheet, and no apparent difference in the deep-sea sediment transport processes or temporal shift in deposition between the Amundsen Sea and Ross Sea. Implications for a Marie Byrd Land uplift starting at ~30Ma are observed by a progressive change in horizon dip in the central Amundsen Sea seismic sequences.
Highlights
West Antarctica has played a vital role in palaeoenvironmental and palaeoclimate processes due to its low-lying topography sculpted by West Antarctic Rift System Cenozoic tectonics and crustal thinning
It hosts an ice sheet of 3–5 m sea-level equivalent (Bamber et al, 2009; Fretwell et al, 2013) that is potentially vulnerable to global warming and likely to be affected by changes in global ocean circulation (e.g. Pritchard et al, 2012)
The acoustic basement can generally be divided into four regions based on their distinct structural characteristics. (i) The transect segment from the eastern Ross Sea up to the Kohiko Fracture Zone (FZ) shows a rugged and irregular topography, possibly associated with a decrease in spreading rates from 74 to 22 mm/yr, between chrons 27 and 22 (63–50 Ma) (Wobbe et al, 2012; Fig. 2)
Summary
West Antarctica has played a vital role in palaeoenvironmental and palaeoclimate processes due to its low-lying topography sculpted by West Antarctic Rift System Cenozoic tectonics and crustal thinning It hosts an ice sheet of 3–5 m sea-level equivalent (Bamber et al, 2009; Fretwell et al, 2013) that is potentially vulnerable to global warming and likely to be affected by changes in global ocean circulation At the stages where continental-scale ice sheets began to expand and grounded on the continental shelf, erosion and rapid transport moved large amounts of sediments from inland to the coast, shelf, slope, and deep-sea Such increased sediment supply and changes in transport/depositional processes combine to form sedimentary features that can be identified in seismic reflection images. The characteristics of these features, such as the geometry and reflectivity, can be related back to a general depositional environment or process (e.g. Shanmugam, 2006)
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