34. TERRIGENOUS AND MARINE LIPIDS IN AMAZON FAN SEDIMENTS: IMPLICATIONS FOR SEDIMENTOLOGICAL RECONSTRUCTIONS1Kai-Uwe Hinrichs2 and Jürgen Rullkötter2 |
ABSTRACTPreliminary lipid analyses of Amazon Fan sediments focused on the general characteristics of bitumen composition. Of particular interest was the identification of distinct sedimentary facies on a molecular level. We investigated sediments from different fan environments (pelagic and hemipelagic sediments as well as active channel-levee sediments). On a qualitative molecular level (i.e., types of compounds detected), bitumen compositions of different fan environments are very similar to each other. Relative differences in bitumen distribution in terms of marine vs. terrigenous origin appear to be significantly correlated with the dilution of the autochthonous signal by terrigenous detritus. These differences distinguish normal hemipelagic sediment (Site 942) from active channel-levee sediment (Site 940) of the Amazon Channel, where marine compounds represent a background signal. The range of the ratio of two distinct groups of lipids (i.e., terrigenous wax alcohols over plankton-derived fatty acids) corresponds very well to rough sedimentological estimates of sediment accumulation rates, which vary, depending on location and sea level, by more than 2 orders of magnitude. We suggest that this approach can be utilized for a rough estimate of the dilution of the autochthonous signal by terrigenous detritus in environments such as the Amazon Fan. |
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