Variability in Cenozoic sedimentation along the continental rise of the Bellingshausen Sea, West Antarctica

Abstract

Seismic reflection profiles, bathymetric and magnetic data collected along and across the continental margin of the Bellingshausen Sea provide new constraints and interpretations of the oceanic basement structure and Cenozoic glacial history of West Antarctica. Evidence for tectonic boundaries that lie perpendicular to the margin has been identified on the basis of one previously unpublished along-slope multichannel seismic reflection profile. By combining several magnetic data sets, we determined basement ages and verified the positions of possible fracture zones, enabling us to improve previous tectonic and stratigraphic models. We establish three main sediment units on the basis of one seismic along-slope profile and by correlation to the continental shelf via one cross-slope profile. We interpret a lowermost unit, Be3 (older then 9.6 Ma), as representing a long period of slow accumulation of mainly turbiditic sediments. Unit Be2 (from about 9.6 to 5.3 Ma) may represent a period of shortlived ice advances on the continental shelf. The uppermost unit, Be1 (from about 5.3 Ma to present), apparently consists of rapidly deposited terrigenous sediment that we interpret as having been transported to the shelf edge by frequent advances of grounded ice. Listric faults are observed in Be1 and indicate sediment instability due to interactions between different depositional processes. Correlation of the sediment classification scheme with the continental rise of the western Antarctic Peninsula shows obvious differences in sediment depositional patterns. We estimate a very high sedimentation rate for Unit Be1 (up to 295 m/my) which points to an increase in glacial sediment supply due to major glacial outlets that flowed to nearby parts of the shelf edge in Pliocene and Quaternary times. This is in contrast to the situation at the adjacent Antarctic Peninsular margin and many other parts of the continental rise around Antarctica.

The sedimentary legacy of a palaeo-ice stream on the shelf of the southern Bellingshausen Sea: Clues to West Antarctic glacial history during the Late Quaternary

“…The seismic profiles revealed unconformities on the outer shelf and evidence for debris flows and slumps on the slope. These depositional patterns were interpreted as results of repeated WAIS advances and retreats across the shelf during the Pliocene and Quaternary (Nitsche et al, 1997(Nitsche et al, , 2000Cunningham et al, 2002;Scheuer et al, 2006). Nitsche et al (1997Nitsche et al ( , 2000 noted that the slope in the study area is gentler (1e2 ) but that the shelf break prograded further (w32 km) than in other areas of the Bellingshausen and Amundsen seas.…”

“…The first marine geoscientific data published from the southern Bellingshausen Sea were multi-channel seismic profiles crossing the outer shelf, continental slope and rise (Nitsche et al, 1997(Nitsche et al, , 2000Cunningham et al, 2002;Scheuer et al, 2006). The seismic stratigraphy on the outer shelf and slope shows a general transition from aggradational to progradational and then back to aggradational geometries.…”

Bottom-current control on sedimentation in the western Bellingshausen Sea, West Antarctica

“…3) is located closest to the continental margin. It crosses one of the largest sediment mounds (about 130 km wide and 700 m high) of the West Antarctic continental margin, referred to as Depocentre C by Scheuer et al (2006). This mound developed on the elevated basement at the eastern side of the tectonic boundary defined by the BGA.…”

“…Channel-related contourite drifts and individual sediment mounds have been observed along the Antarctic Peninsula margin (e.g. Rebesco et al 1997) whereas a wide trough-mouth fan has been identified along the continental margin in the central Bellingshausen Sea (Scheuer et al 2006).…”

Untitled

“…The age for the oldest ridge-trench collision in the western Bellingshausen Sea can be roughly estimated to be about 50 Ma, using a few identified spreading anomalies (Eagles et al, 2004;Scheuer et al, 2006). Oceanic crustal age along the margin becomes progressively younger toward the northeast (Larter and Barker, 1991).…”