Biomarker geochemistry of black shales from Cretaceous oceans — An overview

Abstract

Cretaceous black shales have an extensive distribution in the Atlantic and other areas of the world oceans. They are sediments rich in organic matter which were deposited in anoxic environments under various paleoenvironmental conditions of sedimentation. The literature is reviewed briefly and some type areas are examined using biomarker geochemistry to assess the sources and maturity of the organic matter and the paleoenvironmental conditions of sedimentation. These areas are the eastern Angola Basin, the Cape Verde Basin and eastern North Atlantic, the western North and South Atlantic, and the Pacific Oceans. Molecular marker indicators were identified in bitumens and in kerogen pyrolysates. In addition, bitumens were characterized by other geochemical techniques, thus delineating the terrigenous versus autochthonous sources and the paleoenvironmental preservation of this organic fraction. The kerogens were characterized by their elemental composition, stable carbon isotope composition, and by pyrolysis GC or pyrolysis GC—MS, including Rock-Eval, data. These parameters confirmed that the organic matter in sediments of the Cretaceous oceans was derived from several different sources, is relatively immature, and was preserved under various paleoenvironmental conditions.