Distributions and stable carbon isotopic compositions of biomarkers in torbanites from different palaeogeographical locations

The relative distributions and stable carbon isotopic compositions of certa in aliphatic and aromatic biomarkers from I I Botryococcus braunii rich tor banites from Scotland, South Africa and Australia covering the Late Carboni ferous to Late Permian were investigated. The data was scrutinised for any evidence of molecular features which may be characteristic of palaeogeograp hy. The torbanites studied were selected to cover a range of age and palaeo climatic conditions (e.g. Permian and Late Carboniferous when Gondwana was covered by an extensive ice sheet, the Late Permian when the climate warmed from glacial to cool to temperate and the Carboniferous when Laurasia was located within the equatorial zone), All torbanites are composed of abundan t n-alkanes and novel macrocyclic alkanes which, based on similar delta C-1 3 values, are ascribed a common origin. All samples are also characterised by a high cyanobacterial input as indicated by abundant hopanoids. Other bi omarker distributions and stable carbon isotopic compositional differences separated the torbanites into three groups, which also correlate to three d ifferent palaeogeographical/palaeoclimatic precincts: (i) Group A-southern Africa and eastern Australia (Temi) torbanites which are characterised by a high relative abundance of cyanobacterial and methylotrophic hopanoids, ab undant branched hydrocarbons and C-13 enriched homologous series of monomet hylakanes; (ii) Group B-eastern Australia (Newnes and Glen Davis) torbanite s contain relatively high amounts of drimanes and abundant C-13 enriched ho mologous series of monomethylakanes; and (iii) Group C-Scottish torbanites (Torbane Hill and Westfield) contain high relative amounts of cyanobacteria l hopanoids, methylotrophic hopanoids and abundant branched aliphatics (but no C-13 enriched homologous series of monomethylakanes). (C) 2001 Elsevier Science Ltd. All rights reserved.