Steroidal ketones in the early diagenetic transformations of Δ5 sterols in different types of sediments

Abstract Incubation experiments of cholesterol labelled with various isotopes ( 2 H, 3 H and 14 C) were performed in two different types of sediment, one highly oxygenated and the other completely anoxic, to ascertain the presence and the role of steroidal ketones in the early diagenesis of unsaturated sterols. Two different pathways for the hydrogenation of cholesterol have been observed, depending on the oxygenation rate of the sediment. If the intermediacy of steroidal ketones is evident in the oxic sediments of Lake Leman (Switzerland), a direct reduction of the Δ 5 double bond also occurs in the anoxic sediments of Motte Lake (France).