Burial History and Hydrocarbon Potential of the Harudi and Fulra Limestone of Kachchh, Western India Constrained using Carbonate Clumped Isotope Thermometry

Abstract

Abstract The clumped isotope paleothermometry is used to estimate minimum burial depth of the mid Eocene Harudi and Fulra Limestone Formations of Kachchh, western India. The Nummulites and other fossil foraminiferal genera were separated for conventional (δ18O, δ13C) and clumped isotopic (Δ47) measurements. The measurements were also made on whole rock (WR) to visualize the different phases of diagenetic alteration, expected depth of burial and capacity to generate hydrocarbon. The measured δ18O and δ13C values of WR samples vary between -3.09 and -2.21‰ and -0.78 and 0.96‰ respectively, with average values of -2.88‰ and 0.16‰. The δ18O and δ13C values of benthic foraminifera vary between -3.52 and -3.20‰ (Average: -3.35±0.013) and -1.04 and 0.81‰ (Average: 0.26±0.76) respectively. The measured Δ47 for the foraminifera translates to temperature of 35 and 49°C and between 26 and 48°C for WR indicating minor diagenetic alteration. The minimum estimates for the burial depth of the studied formations are up to 2 km which is based on the temperature difference between the ecological preference temperature of benthic foraminifera and the diagenetically altered foraminifera and δ13C of WR and foraminifera, indicating that rocks have potential to generate methane.