The organic geochemistry of Peru margin surface sediments: II. Paleoenvironmental implications of hydrocarbon and alcohol profiles

Abstract

We assess the utility of sedimentary hydrocarbons and alcohols as indicators of short-term changes in depositional conditions in the coastal Peruvian upwelling regime at 15°S. The distribution of 35 lipids ( n-alkanes, n-alkanols, hopanols, keto-ols, lycopane, phytol, stenols, stanols, sterenes, and tetrahymanol) in a l m dated core from 253 m water depth are interpreted by (1) a principal components analysis and (2) a consideration of individual source-specific biomarkers. Profiles of odd-carbon-number n-alkanes (C 25-C 33) and even-carbon-number n-alkanols (C 24-C 28) reflect changes in the contribution of terrigenous sediment relative to marine sediment during deposition, as indicated by the correlations between these lipids and inorganic indicators of terrigenous clastic debris. The n-alkane carbon preference index (CPI) provides a less-sensitive record of fluctuations in the terrestrial input than the concentration profiles of the individual n-alkanes and n-alkanols, and these lipids are not well-correlated with the historical El Niño record. The similarity of all the stenol profiles measured and the lack of concordance between these profiles and inorganic indicators of terrigenous input suggest that any fluctuations in the abundance of higher-plant stenols are obscured by the larger marine contribution of these compounds. Similarities between the profiles of total organic carbon (TOC) and cholestanol/cholesterol are consistent with stenol hydrogenation being influenced by the sediment redox conditions.