Bulk organic geochemical and palynofacies analyses of the Hettangian Datta Formation (Potwar Basin, Pakistan): Regional comparison with the time equivalent Lathi Formation (Jaisalmer Basin, India)

A detailed lithostratigraphic, bulk organic geochemical and palynofacies analyses were performed on organic-rich shale and coal samples from the Hettangian Datta Formation in the western Salt Range, southern Potwar Basin, Pakistan, to evaluate its hydrocarbon generation potential. Organic matter (OM) in the formation is mainly dominated by gas-prone Type III kerogen and oil- and gas-prone Type II kerogen. The coal and OM-rich shale intervals are thermally mature, while grey shale intervals are thermally immature. Palynofacies studies showed that the Datta Formation is rich in inertinite, vitrinite and amorphinite with minor liptinite. The OM is mainly of terrigenous origin with minor marine contribution and is interpreted to have been deposited under suboxic to anoxic conditions in a fluvio-deltaic depositional setting. The thermal maturity estimated from Spore Colour Index (SCI) and Thermal Alteration Index (TAI) was entirely consistent with estimates based on bulk organic geochemical data. Variations in thermal maturity are interpreted to be due to change in kerogen types as well as burial depth. Overall, the organic geochemical and palynofacies studies showed that the coal and OM-rich shale intervals in the Datta Formation have good-to-excellent source rock potential in the study area, whereas the grey shale intervals have poor potential as source rocks. The Datta Formation has tentatively been correlated with the stratigraphically equivalent Lathi Formation in the Jaisalmer Basin, India, which was deposited in a similar palaeo-depositional setting on the NW margin of the Indian Plate affected by Neo-Tethys realms. Research Highlights Organic matter within the Datta Formation is dominated by Type III and Type II kerogens. The Lower Jurassic Datta Formation is enriched in inertinite, vitrinite and amorphinite with minor liptinite. The Datta Formation was deposited in a fluvio-deltaic setting influenced by both terrigenous and marine organic influx. The suboxic to anoxic conditions during shales deposition promoted organic matter preservation. Datta Formation correlates with the Lathi Formation of Jaisalmer Basin of India.