Seismic stratigraphy of McMurdo Sound, Antarctica: implications for glacially influenced early Cenozoic eustatic change?

Abstract

Analyses by Barrett et al. (1989) of the stratigraphic sequences of the CIROS-1 drill core provided evidence of late Paleogene and early Neogene glacial advances and retreats that appear to correlate with the global eustatic curve of Haq et al. (1987). During Leg 2 of the Polar Duke 90 (PD90) cruise in the Ross Sea approximately 650 km of highresolution seismic data were collected in McMurdo Sound with the main objective of facilitating regional correlation of stratigraphic events observed in the cores of the CIROS-1, DVDP-15, and MSSTS-1 drilling programs, and therefore providing an opportunity to test hypotheses on linkages between Cenozoic eustatic and Antarctic ice volume fluctuations. Twenty unconformity-bound, seismic-stratigraphic sequences (labeled from top A to T) were identified in the McMurdo Sound PD90 data base. However, seismic data from the shallow shelf on which CIROS-1 was drilled show erosional surfaces at many levels, indicating a condensed section in this area. It is difficult to distinguish individual lithological units identified by Barrett et al. (1989) in the seismic data, but seismic units O, P and Q correspond to the upper Oligocene interval where they recognized 3 glacioeustatic events. These three sequences, totaling around 300 m in thickness, can be traced over a distance of almost 100 km. However, they lack the seismic characteristics of glacial facies identified by Anderson and Bartek (1992) and thus the significance of waxing and waning events suggested for upper Oligocene strata in CIROS-1 remains equivocal. The younger sequences in the McMurdo Sound data base are largely Miocene (E-N), the oldest of these forming the upper 70 m in CIROS-1. These sequences can be traced 300 km north into the center of the Victoria Land basin, where they have seismic features characteristic of glacial facies. This suggests that ice sheets of continental scale (and hence large enough to affect eustasy) waxed and waned across the Ross Sea continental shelf at least 10 times during the Miocene. The data presented here for the Oligocene do not preclude similar ice sheet behavior, but are insufficient to test the hypothesis properly.