Carbon, oxygen and strontium isotope geochemistry of Proterozoic carbonate rocks of the Vindhyan Basin, central India

Carbon, oxygen and strontium isotope compositions of carbonate rocks of the Proterozoic Vindhyan Supergroup, central India suggest that they can be correlated with the isotope evolution curves of marine carbonates during the latter Proterozoic. The carbonate rocks of the Lower Vindhyan Supergroup from eastern Son Valley and central Vindhyan sections show delta C-13 values of similar to 0 parts per thousand (V-PDB) and those from Rajasthan section are enriched up to + 2.8 parts per thousand. In contrast, the carbonate rocks of the Upper Vindhyan succession record both positive and negative shifts in delta C-13 compositions. In the central Vindhyan section, the carbonates exhibit positive delta C-13 values up to + 5.7 parts per thousand and those from Rajasthan show negative values down to -5.2 parts per thousand. The delta O-18 values of most of the carbonate rocks from the Vindhyan Supergroup show a narrow range between -10 and -5 parts per thousand (V-PDB) and are similar to the 'best preserved' O-18 compositions of the Proterozoic carbonate rocks. In the central Vindhyan and eastern Son Valley sections, carbonates from the Lower Vindhyan exhibit best-preserved Sr-87/Sr-86 compositions of 0.7059 +/- 6, which are lower compared to those from Rajasthan (0.7068 +/- 4). The carbonates with positive delta C-13 values from Upper Vindhyan are characterized by lower Sr-87/Sr-86 values (0.7068 +/- 2) than those with negative delta C-13 values (0.7082 +/- 6). A comparison of C and Sr isotope data of carbonate rocks of the Vindhyan Supergroup with isotope evolution curves of the latter Proterozoic along with available geochronological data suggest that the Lower Vindhyan sediments were deposited during the Mesoproterozoic Eon and those from the Upper Vindhyan represent a Neoproterozoic interval of deposition. (C) 2002 Elsevier Science B.V. All rights reserved.