Abstract

NAGARAJAN, Ramasamy et al. Carbon and oxygen isotope geochemistry of Neoproterozoic limestones of the Shahabad Formation, Bhima basin, Karnataka, southern India. Rev. mex. cienc. geol [online]. 2008, vol.25, n.2, pp. 225-235. ISSN 1026-8774.

Petrography, major (including four trace elements), stable isotopes (carbon and oxygen), and ⁸⁷Sr/86Sr geochemistry of limestones of the Shahabad Formation, Bhima basin, Karnataka, southern India are reported. These limestones show a narrow range of δ¹³C (1.34-1.96) and δ¹⁸O ( -6.04 to - 7.61 ) values. The petrographic study reveals the presence of microsparite and micro- and macrostylolites. The δ¹³C and 87Sr/86Sr values indicate that these limestones were deposited during the late Neoproterozoic age and the δ¹⁸ O values also are very similar to the average Proterozoic carbonate values. Mn and Sr concentrations and low Mn/Sr ratio (<1) together with the stable and radiogenic isotope data suggest that the studied samples are well-preserved or scarcely altered limestones and probably have retained their primary isotopic signatures.

Keywords : geochemistry; stable isotopes; delta oxygen; delta carbon; strontium isotopes; carbonate rocks; diagenesis; Bhima basin; India.