Biodegraded bitumens dispersed in Vendian (Neoproterozoic) rocks of the Khatyspyt Formation, Northeastern Siberia

Abstract

The organic matter of the Vendian (Neoproterozoic) Khatyspyt Formation was investigated. The new data obtained from the GS and GS-MS analyses include: high UCM humps andheightened peaks of steranes and terpanes against the backdrop of C27+ alkanes on chromatograms of saturated hydrocarbons fractions of five samples; predominance of С21-С26 in n-alkanes distribution; the presence of 12- and 13-monomethylalkanes on chromatograms and demethylatedterpanes on filtered chromatograms (m/z 191 and 177). Besides, dispersed bitumens with biodegraded hydrocarbons have been for the first time identified in carbonate and carbonate-siliceous rocks of the Khatyspyt Formation. Also 8,14-sekohopanes resistant to biodegradation and gammacerane were established. The revealed features of the composition and distribution of hydrocarbons showed that their source was the autochthonous (syngeneic) organic matter of the Khatyspyt Formation,one of the potential hydrocarbon source rock of Northeastern Siberia. The composition and content of bitumen are found to be controlled by the inputs of primary organisms (eukaryotes and prokaryotes)which lived in Vendian seas, by changing redox conditions of sediment deposition and transformation, as well as by relatively little effect of temperature and high degree of biological oxidation in hypergenesis. The patterns of bitumen distribution throughout the section show, that besides the overlying deposits,their accumulations canbe discoveredin the Khatyspyt Formation.