A chemostratigraphic and geochemical facies analysis of strata deposited in an eocene australo-antarctic seaway: Is cyclicity evidence for glacioeustasy?

In this paper, geochemical facies correlations from Ocean Drilling Program Sites 1168, 1170, 1171 and 1172 are presented. These correlations, integrated with shipboard-determined lithologic and biostratigraphic information, define strati-graphic sequences. The sequences are typically characterized as coarsening upward: claystone and clayey siltstone overlain by siltstone, and in some cases sandy siltstone and sand. Sequence boundaries are marked by coarsening upward sequence tops, as well as geochemically-defmed flooding surfaces characterized primarily by peaks in total sulfur content, and secondarily by peaks in total organic carbon and carbonate content. The sequence stacking patterns can best be explained by sea-level cycles, indicating that early to middle Eocene glacioeustasy may have affected the Australo-Antarctic Seaway. This conclusion supports some conceptual models, but opposes the model in which Antarctic continental-scale glaciation, and hence glacioeustasy, did not develop until Eocene/Oligocene boundary initiation of the Antarctic Circumpolar Current. The chemostratigraphic correlations also provide stratigraphic refinement of critical chronostratigraphic boundaries including the Eocene/Oligocene boundary at Site 1171, the late/middle Eocene boundary at Site 1171 (and 1168?), the middle/early Eocene boundary at Site 1170, and the Paleocene/Eocene boundary at Sites 1171 and 1172.