Thiophenic biomarkers for palaeoenvironmental assessment and molecular stratigraphy

Abstract

RECONSTRUCTION of ancient depositional environments is an important objective in the Earth sciences. The complex assemblages of organic molecules in sediments include compounds that can be related to known biochemicals produced by specific biota from well defined habitats1–3, and these 'chemical fossils' are applied frequently to reconstruct palaeoenvironments, especially in studies of organic and petroleum geochemistry and in chemical oceanography. Most of the compounds used in this way are hydro-carbons2–4, although oxygenated (for example, alcohols, acids and ketones) and nitrogen-containing (for example, porphyrins) compounds have also been applied successfully1,2. Here we report on the use of organic sulphur compounds as geochemical tools for palaeoenvironmental and stratigraphic assessment. Depth profiles of specific sulphur compounds related to certain organisms show significant variations reflecting changes both in sources of organic matter and in physical conditions (such as salinity) of the depositional environment. In a number of cases these variations are not otherwise revealed by changes in lithology, geochemical bulk data and/or absolute and relative amounts of hydrocarbon biological markers. Moreover, several organic sulphur compounds reveal the presence of unprecedented biochemicals in these palaeoenvironments.