Molecular Indicators of the Supply of Marine and Terrigenous Organic Matter to a Pleistocene Organic-Matter–Rich Layer in the Alboran Basin (Western Mediterranean Sea)

Abstract

The organic matter in sediment series across two organic-matter–rich layers from Ocean Drilling Program Hole 977A drilled in the Alboran Basin of the Western Mediterranean Sea has been characterized by organic geochemical methods. Organic carbon contents reached more than 2% in the organic-matter–rich layer and was ~1% in the background sediment under and overlying it. Molecular compositions of the extractable bitumens in the organic-matter–rich layer for a wide range of compound groups are broadly similar to those of the background sediments. The organic matter in the organic-matter–rich layer is enriched in marine biomarkers, especially long-chain diols and keto-ols and particularly sterols. A higher supply of landderived material to the sediment during formation of the organic-matter–rich layer is indicated by concentrations of long-chain alkanes and n-alcohols largely following the organic carbon profile. The elevated terrigenous runoff during times of more humid land climate may have fertilized marine bioproductivity.