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Precambrian Research 121 (2003) 103–140 C, O, Sr and Pb isotope systematics of carbonate sequences of the Vindhyan Supergroup, India: age, diagenesis, correlations and implications for global events Jyotiranjan S. Ray a,∗ , J. Veizer a,b , W.J. Davis c a Ottawa-Carleton Geoscience Center, University of Ottawa, Ottawa, Ont., Canada K1N 6N5 b Institut für Geologie, Mineralogie und Geophysik, Ruhr Universität, Bochum 44780, Germany c Geological Survey of Canada, Ottawa, Ont., Canada K1A 0E8 Received 7 March 2002; accepted 21 November 2002 Abstract The Vindhyan Supergroup of central India records a substantial portion of Proterozoic time and contains some of the most disputed Precambrian/Cambrian fossil discoveries. Despite the significance of these “fossil” finds, many issues, including reliable geochronology, remained unresolved. Similarly, the geochemical aspects of the sedimentary sequences and their implications to the evolution of Proterozoic oceans, have been studied only at a reconnaissance level. Here we report the results of the Pb–Pb dating for the Rohtasgarh Limestone from the Lower Vindhyan Supergroup giving an age of 1601 ± 130 Ma, an estimate that is in accord with the recent U–Pb zircon dating of the Lower Vindhyan Supergroup by Rasmussen et al. [Geology 30 (2002) 103] and Ray et al. [Geology 30 (2002) 131]. Sr isotope stratigraphy of carbonates from the Upper Vindhyan Supergroup suggests a Mid-Neoproterozoic (750–650 Ma) age for these formations. This, in turn, argues for a long hiatus between the deposition of the Lower and Upper Vindhyan Supergroups. Our results conflict with the reports of Cambrian age small shelly fossils and Ediacaran fossils from the Upper Vindhyan rocks. At the same time, they suggest that the alleged trace fossils in the Lower Vindhyan rocks must be of Paleoproterozoic age. The most common δ 18 O values for calcitic components from limestone formations of the Supergroup range from −10 to −7‰, similar to Paleo-Neoproterozoic carbonates worldwide. The modes of δ 13 C in the Lower and Upper Vindhyan Supergroups are 0 ± 2 and 3 ± 2‰, respectively, again consistent with the worldwide dataset. The secular patterns of carbon isotope trends do not support the earlier assumptions that the carbonate sequences at the southern margin correlate with those at the western or northern margins of the Vindhyan Basin. C and Sr isotope data provide new calibration points for the seawater evolutionary curves, particularly for the Paleoproterozoic. For strontium isotopes, the data from the Lower Vindhyan Supergroup suggest that seawater departed probably less rapidly from mantle values than was previously believed. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Vindhyan Supergroup; India; Proterozoic; Isotope stratigraphy; Pb–Pb dating; Carbonates ∗ Corresponding author. Present address: Planetary and Geo- sciences Division, Physical Research Laboratory, Navarangpura, Ahmedabad 380 009, India. Fax: +91-79-630-1502. E-mail address: jyotiranjan [email protected] (J.S. Ray). 1. Introduction Secular variations in isotopic composition of (bio)chemical sediments and in carbonaceous mat- ter are among the best proxies available for studies 0301-9268/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0301-9268(02)00223-1
