Sedimentary Lipids as Indicators of Depositional Conditions in the CoastalPeruvian Upwelling Regime

摘要

Sedimentary lipids were examined as indicators of depositional conditions andsedimentary organic matter sources in the Peru margin upwelling regime. The sedimentary C37 alkenone-Uk37 signals of individual El Nino/Southern Oscillation events were substantially attenuated, and periods of frequent El Nino activity were more readily identified than isolated El Nino events. Profiles of odd-carbon number n-alkanes (C25-C33) and even-carbon number n-alkanols (C24-C28) reflect changes in the input of terrigenous sediment relative to marine sediment, as indicated by the correlations between these lipids and inorganic indicators of terrigenous clastic debris; these lipids are not correlated with the El Nino record. The similarity of all the stenol profiles measured suggests that fluctuations in input of higher-plant stenols are obscured by the marine contribution of these compounds. Similarities between total organic carbon and cholestanol/cholesterol profiles are consistent with stenol hydrogenation being influenced by the sediment redox conditions. Fatty acids account for most of the lipid content of Thioploca, a genus of sulfur-oxidizing bacteria. Thioploca does not contain significant hydroxy fatty acids, hopanoids or hydrocarbons, but does contain cyclolaudenol, an unusual C31 sterol. Alteration products of this sterol may serve as sedimentary markers for Thioplaca input and hence for paleo-upwelling environments.