Geochemistry of cretaceous rocks, Pakistan: I. Biomarker approach to assess thermal maturity of OM.

The sediment samples from cretaceous sequences, Lower Indus basin, were analyzed using diagnostic biomarkers to predict the thermal maturity of organic matter. The sediments were tested for aliphatic biomarkers ratios, i.e. homohopanes and steranes isomerization ratios and carbon preference indices. These biomarker maturity parameters reveal that the Lower Goru (including its members Upper shale, Lower shale, and Talhar shale) and Sembar Formations in the Lower Indus Basin of Cretaceous age have reached the maturity level equivalent to the main zone of hydrocarbons generation, whereas Parh and Upper Goru Formations are immature and far from oil window. Geochemical analyses carried out stresses that hydrocarbons derived from the Sembar and Lower Goru Formations (particularly deeper Members) are within the zone of peak oil generation. [ABSTRACT FROM AUTHOR]