ORGANIC MATTER AND STRATAL HIERARCHY IN MIOCENE AND OLIGOCENE ROCKS FROM THE VICTORIA LAND BASIN, ANTARCTICA

Following a preliminary organic geochemical analysis of the CRP-2/2A core from the Victoria Land Basin, Antarctica, a higher-resolution study was completed to investigate the relationship between organic matter content and position within a sequence stratigraphic framework that was established previously. A Miocene (Sequence 9) and an Oligocene (Sequence 19) sequence, each 50 m thick, were selected for this higher-resolution investigation and were sampled at 1.7 m intervals. Elemental analyses and characterization of solvent-soluble organic matter were combined with micropaleontological observations and published grain size analyses. Although TOC values are low -averaging 0.3% for both sequences- values as high as 0.6% and 1.5% were measured in Sequences 9 and 19, respectively. Increases in TOC values generally correspond to intervals identified as condensed sections based on the abundance and diversity of microflora and the clay content of these rocks. The correlation of higher TOC values with condensed sections has been observed in a number of other settings: the combination of maximum water depth and minimal clastic dilution is considered to promote greater concentrations of marine-derived organic matter. TOC:N ratios can be used to discern two populations of organic matter in these rocks. 1)Organic matter with very high TOC:N ratios (average 166) is interpreted to be coal detritus derived from the Beacon Supergroup, whereas 2)organic matter with much lower TOC:N ratios (average 8.9) is considered to be derived from aquatic organic sources with much less input from coal detritus. The samples that have the highest TOC values in each sequence have TOC:N ratios (15 and 32) that are too high to have been derived largely from aquatic sources. Moreover, the high TOC values correspond well with increases in the silt content of the rocks. The highest TOC values observed in these two sequences are not the products of facilitated deposition of marine organic matter in a sediment-starved environment. Rather the highest TOC values reflect the transport of fine-grained and buoyant terrigenous sedimentary particles to the distal portion of a prograding glacio-marine depositional system.