Molecular parameters of maturation in the Toarcian shales, Paris Basin, France—I. Changes in the configurations of acyclic isoprenoid alkanes, steranes and triterpanes

Steroids are used to illustrate some of the significant advances that have been made in recent years in understanding the biological origin and geological fate of the organic compounds in sediments. The precursor sterols are transformed, initially by microbial activity and later by physicochemical constraints, into thermodynamically more stable saturated and aromatic hydrocarbons in mature sediments and petroleums. The steps in this transformation result in a complex web linking biogenesis, diagenesis, and catagenesis. Indeed, the complexity and variety of biological lipids such as the steroids are evidently matched in the corresponding geolipids. The extent of preservation of the biochemical imprint in the structures and stereochemistry of these geolipids, even over hundreds of millions of years, is startling, as is the systematic and sequential nature of the geochemical changes they evidently undergo. This new understanding of molecular organic geochemistry has applications in petroleum geochemistry, where biological marker compounds are valuable in the assessment of sediment maturity and in correlation work.

https://science.sciencemag.org/content/sci/217/4559/491.full.pdf

Chemical fossils: the geological fate of steroids.

Organic geochemical studies of a Messinian evaporitic basin, northern Apennines (Italy) I: Hydrocarbon biological markers for a hypersaline environment

THE steroid carbon skeleton has been widely used as an indicator of biological origin of the organic material in ancient sediments1–3 and petroleum4. Sterols, presumed precursors of the geolipid steranes, and stanols, their saturated analogues, have been identified in Recent5–7 and ancient8,9 sediments. In view of their generally low abundance in living organisms, the presence of stanols in Recent sediments suggests the operation of a sterol hydrogenation process early in the geological time scale. We have sought to confirm this hypothesis by examination of the contemporary sediments of Rostherne Mere, Cheshire, England. The sterol composition of the sediment, and its variation with depth, provide circumstantial evidence for the hydrogenation of Δ5-sterols10. Here we describe the application of radiochemical techniques11,12 to the study of the early diagenesis of cholesterol (cholest-5-en-3β-ol) in Rostherne sediment and report the first direct evidence of rapid sterol hydrogenation in a geological environment. The sediment chosen for study is that of a highly productive lake. Significant allochthonous (land-derived) organic input to Rosterne Mere has been exceeded in recent years by an increasing autochthonous production of blue-green algae13,14. The sediments in the deepest part of the lake (from where samples were taken) remain severely depleted in oxygen throughout the year15. As a National Nature Reserve, Rostherne Mere is protected from gross pollution, though there is some chemical evidence to suggest a recent input of petroleum-derived material14.

Rapid hydrogenation of sterols in a contemporary lacustrine sediment

Tri- and tetraterpenoid hydrocarbons in the Messel oil shale

Steranes and triterpanes identification from Green River shale by capillary gas liquid chromatography and mass spectrometry

Vojtech Wollrab

Papers

Identification of steranes and triterpanes from a geological source by capillary gas liquid chromatography and mass spectrometry