Δ13 C ISOTOPE AS PRECURSOR TO RECONSTRUCT PALEO-VEGETATION TYPE AND DEPOSITIONAL ENVIRONMENTS OF MID-SIWALIK SEDIMENTS OF NW HIMALAYAN FORELAND BASIN, PAKISTAN

Abstract

Using an elemental analyzer-isotope ratio mass spectrometer (EA-IRMS), the organic matter extracted from sandstone samples of the mid-Siwalik Dhok Pathan Formation exposed on the western limb of the Makerwal anticline in the Surghar-Shingar Range of the NW-Himalayan foreland Fold-and-Thrust-Belt was examined for δ13C isotope. These molasse sediments have revealed significant information about the paleo-vegetation type and their depositional environments in the sandstone facies. Their average δ13C isotope value calculated through EA-IRMS is -26.56‰, which corresponds to cold growing environment C3 type vegetation. The δ13C isotope findings range from -24.50 to -28.43‰. The δ13C isotope data showed that C3 biomass dominated in the ecosystem throughout the Miocene particularly in the studies part of foreland basin. The coaly-to-semi coaly phytoclasts are classified as vitrinite-huminite based on their morphology obtained through back scattered imaging on scanning electron microscope (SEM). These phytoclasts had been contributed by terrestrial vegetation and designated as Type-III kerogen. The SEM study confirms the development & replacement of diagenetic frambiodal pyrite, which advocate the deposition under reducing conditions