C-Sr-Pb isotope systematics of the carbonate sequences of Kaladgi Supergroup, India: Implications for basin evolution and correlation with Proterozoic global events

Abstract

The Kaladgi Basin is one of the several Proterozoic sedimentary basins of India. This basin has a binary evolutionary history with an angular unconformity separating the older deformed and younger undeformed rock sequences of the Kaladgi Supergroup, named the Bagalkot and Badami Groups, respectively. The Bagalkot Group is known to be of late Paleoproterozoic-Mesoproterozoic age. However, the timings of deposition of the Badami Group sediments and the closure of the basin have been speculative. We carried out C-O-Sr isotope studies of the marine carbonate successions of this basin namely Chitrabhanukot, Chikshellikeri, Lakshanhatti (Bagalkot Group), and Konkankoppa (Badami Group). Our results indicate that δ13C of all the carbonate formations have preserved the primary marine signature. Restricted variation of δ13C in the carbonates of the Bagalkot Group (0 ± 2 ‰) suggests a steady state organic carbon burial; whereas, much wider range of variation of δ13C in the Konkankoppa Limestone of Badami Group (-2.2 to + 3.5 ‰) hints at a dynamic organic carbon burial scenario. These signatures are consistent with the C-isotope stratigraphy of the Meso-Neoproterozoic times. The 206Pb-207Pb dating of the youngest unit of the Kaladgi Supergroup, the Konkankoppa Limestone yielded a depositional age of 604 ± 25 Ma. This age, considered together with the primary 87Sr/86Sr ratio of 0.70781, extends the active sedimentation of the Badami Group well into the Ediacaran Period. These data confirm the existence of a long duration depositional hiatus, of >500 million years, between the Bagalkot and the Badami Groups. Results of this study also refutes the claim that the sedimentation in most of the Proterozoic basins of peninsular India ended by 1000 Ma.