CYCLO-BIOSTRATIGRAPHY IN ANTARCTIC OLIGOCENE-LOWER MIOCENE STRATIGRAPHIC SEQUENCES

Fifty-five unconformity-bounded glacimarine stratigraphic sequences occur in the upper 1082m of a 1525m Oligocene-Miocene succession on the western margin of the Victoria Land Basin. The thickest sequence is 64m. Complete sequences comprise basal diamictite, sandstone, mudstone & sandstone, & uppermost sandstone units. Basal diamictites are interpreted as lowstand, ice-proximal; mid-sequence fine-grained facies as transgressional, highstand, ice-distal; & upper sequence facies as regressional, ice-proximal. The non-depositional erosion phase at basal unconformities represents extreme eustatic lowstand & maximum glacial advance. Chronostratigraphy for the three thickest sequences indicate durations of <~100,000 years for each. More than 20 fossil groups were recovered from sampling of all lithofacies within sequences. Biotal patterns & environmental interpretations parallel lithofacies & stratigraphic subdivisions. Highest benthic-planktic abundances & species diversities occur in sandstone & mudstone facies of middle sequence intervals, suggesting, dynamic trophic structures during ice retreat, maximum transgression, normal marine hydrological conditions, and optimum marine connections to the Southern Ocean. Assemblages are depleted or absent in basal diamictites due to high levels of meltwater & sediment input during glacier margin retreat. Fossil assemblages exhibit minor overturn across sequence boundaries with unconformity durations of 103 to 105 yrs, with overturn more pronounced at unconformities of longer duration (106 yrs). Closely coupled biofacies-lithofacies associations within each sequence result in intermittent biostratigraphic range patterns in multiple sequence stacks. Formal biostratigraphic zonal nomenclature is established for planktic diatoms, & along with calcareous nannoplankton, allow correlation with Southern Ocean biostratigraphy. High frequency glacial oscillations, complex basin margin lithostratigraphy, and hiatuses, allow for the possibility within all fossil groups, of partial and/or diachronous ranges when compared with outer continental shelf and Southern Ocean biostratigraphy. Given the short duration of individual VLB sequences, these potential range and datum discrepencies are of relatively minor significance.