EFFECT OF CENOZOIC ICE-SHEET FLUCTUATIONS IN ANTARCTICA ON THE STRATIGRAPHIC SIGNATURE OF THE NEOGENE

Stratigraphic successions from the Gulf of Mexico-offshore Alabama, northeast Java-Indonesia, Ross Sea-Antarctica, and several other continental margins have been examined. All are characterized by very similar Neogene stratal geometries. In seismic profiles and well log cross sections from these areas, a large, mid-Oligocene (i.e., latest Early Oligocene-earliest Late Oligocene), basinward shift in coastal onlap is followed by a major early Miocene transgression and aggradation, which is in turn followed by early middle Miocene transgressions and late middle and late Miocene progradational episodes. The succession culminates in Plio-Pleistocene high-frequency progradations and transgressions. The interregional character of the Neogene stratal signature and its similarity to the stratal geometry found in seismic data from the Ross Sea continental shelf (Antarctica) suggest that the Neogene stratal signature is a manifestation of glacioeustatic fluctuations. A review of the literature and an analysis of recently acquired and published data indicate that the first major ice sheet grounding event in the Ross Sea occurred during middle to late Oligocene time. The Ross Sea is the repository for ice flowing from a major portion of the continental interior. Thus the glacial record of the Ross Sea should serve as a gage of ice volume changes on the continent that were large enough to influence global eustasy. The ice advance onto the Ross Sea continental shelf during middle to late Oligocene time may have been the result of a decrease in the rate of shelf subsidence as rifting in the Ross Sea slowed or ceased. Advance of the ice sheet resulted in widespread erosion of the continental shelf and shelf overdeepening. It is hypothesized that metastable, marine-based ice sheets have waxed and waned on the Antarctic continental shelf since at least the Oligocene and that the these waxing and waning events were responsible for the development of a global Neogene stratigraphic signature.