Hydrocarbon Biomarkers in Elucidating Source Organic Matter and Palaeodepositional Environment: A Case Study from Cambay Basin, India

A detailed biomarker characterisation has been carried out from the Early Palaeogene samples from the Cambay Basin. The present study examines the biomarker applications in interpreting organic matter sources and palaeodepositional environment from the Palaeogene shales of the Cambay Basin, India. The detailed saturated and aromatic biomarkers identified from the mass chromatograms of GC-MS and GC × GC-TOF-MS, such as sesquiterpanes, tricyclic, tetracyclic, and pentacyclic triterpanes including hopanoids and methylhopanes, oleananes, bicadinanes, secobicadinanes, C30 tetrapolyprenoid, C29 28-nor-spergulane, aromatic sesquiterpanes, diaromatic tricyclic terpane, aromatic non-hopanoid triterpenoids, aromatic diterpenoids, diaryl isoprenoids, and acyclic isoprenoids efficiently discriminate between the organic matter sources, compositions, and palaeodepositional environment in north and south blocks of the Cambay Basin. Low values of pristane/phytane, along with the extended series of tricyclic terpanes, 3β-methylated hopanes, diaryl isoprenoids, C30 tetrapolyprenoid and C29 28-norspergulane in the northern block samples, indicate that the organic matter was deposited in the photic zone under sub-oxic to anoxic settings, most likely in a restricted marine/lacustrine environment. Similarly, the occurrence of oleanane, bicadinanes, secobicadinanes and higher plant aromatic triterpenoids in the southern block samples suggests dominant angiospermous organic matter input deposited in an oxic fluvio-deltaic environment. Moreover, the presence of bicadinanes and secobicadinanes clearly indicates the advent of evergreen tropical rainforests in the Early Eocene.