Articles written in Journal of Earth System Science

    • Palaeoenvironmental and sequence stratigraphic analyses of the Jurassic Datta Formation, Salt Range, Pakistan

      Shahid Iqbal Irfan U Jan M Gulraiz Akhter Mehwish Bibi

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      The Lower Jurassic Datta Formation, western Salt Range, Pakistan, comprises three facies associations:

      channel belt facies association (CBFA),

      channel margin, and overbank facies association (CMOFA), and

      lagoonal facies association (LFA).

      A cyclic fining-upward trend in the succession is represented by basal quartzose conglomerate/pebbly sandstone, through coarse to fine quartzose sandstone to silt-stone and shales/claystone, which contains some carbonate accumulation. Two prominent depositional sequences are recognized in the Datta Formation with the lower high and upper low magnitude cycles. The Datta Formation thus represents a thick sedimentary succession and in the study area, i.e., western Salt Range, mainly channel belt, flood plain and/or delta top facies are exposed. The palaeocurrent analysis shows that the source area with acidic plutonic rocks laid to S–SE in the Indian shield, aravalies or older sedimentary rocks of the Indus Basin (i.e., Khewra, Tobra and Warchha formations). A tentative stratigraphic correlation of the Datta Formation with the lower Jurassic Lathi Formation, India invites further work in parts of India, which will elaborate the extent of the Datta Formation in the Greater Indian peninsula and develop palaeogeographic setting for this Lower Jurassic deltaic rock unit.

    • 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)


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      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.


      $\bullet$ Organic matter within the Datta Formation is dominated by Type III and Type II kerogens.

      $\bullet$ The Lower Jurassic Datta Formation is enriched in inertinite, vitrinite and amorphinite with minor liptinite.

      $\bullet$ The Datta Formation was deposited in a fluvio-deltaic setting influenced by both terrigenous and marine organic influx.

      $\bullet$ The suboxic to anoxic conditions during shales deposition promoted organic matter preservation.

      $\bullet$ Datta Formation correlates with the Lathi Formation of Jaisalmer Basin of India.

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