| Orca Basin is an anoxic, highly reducing basin of the continental slope of the northwestern Gulf of Mexico. Stable isotope ratios and total organic carbon percentages were determined for subsamples taken from two cores from within the basin and one control core from the perimeter. Results show that the organic carbon content of the basin is consistently 2 to 3 times that of the control core. The Pleistocene-Holocene boundary, indicated by a break in the (delta)('13)C vs. depth profiles, occurs at a greater sediment depth and extends over a greater range in the basin cores than in the control core. A close core subsampling interval has made it possible to detect a fine structure in the (delta)('13)C profiles which may be a record of the effects of a small climatic changes of geologically short duration.; The total lipid was extracted from subsamples from the control core and one basin core. Results of the compositional analyses show that there are no unusual sources of organic material to this sediment. Lipid concentration, relative to total organic carbon, is 3 to 5 times greater in the surface sediment of the basin than in the control core, indicating increased preservation of this material in the anoxic environment of the basin.; The range of stable carbon isotope ratios (isotopic identity) for the total organic carbon, total lipid extract, and lipid fractions was determined for both cores and for representative biogenic source material. Results of these analyses show that the lipid at the surface of the basin core has a greater retention of isotopic identity than at the surface of the control core. This difference is interpreted to show that the lipid material deposited under anoxic conditions is preserved to a greater degree in the sediment than that deposited under normal aerobic conditions.; Sediments from two shallower environments, the continental shelf of the Gulf of Mexico and Baffin, Bay, Texas, were also analyzed to determine the effects of water column length on degradation of lipid carbon. Results show that a substantial amount of the isotopic identity of lipid carbon, present in the source material, is lost in the upper water column. |
