DELTA-C-13 EXCURSION IN THE END PROTEROZOIC STRATA OF THE VINDHYAN BASIN (CENTRAL INDIA) - ITS CHRONOSTRATIGRAPHIC SIGNIFICANCE

The Vindhyan basin of central peninsular India contains strata ranging in age from 1400 m.y. to 550 m.y. It is thus likely that the Precambr ian-Cambrian boundary interval may be present in the upper part of the Vindhyan succession. In order to locate the boundary interval in the Vindhyan basin, carbon isotopic analyses of the carbonate horizons of the succession have been performed. The samples chosen for isotopic an alysis were carefully selected after petrographic, cathodoluminesence and microelement studies to get the original isotopic signal. The anal yses reveal that the carbonates of the lower part of the succession (m iddle Proterozoic) have delta(13)C(PDB) values close to zero (-1.1 to +0.9 permil). However, the carbon isotope profile of the uppermost par t of the succession (Bhander and Sirbu Limestones) shows a positive sh ift of around 5 permil followed by a sharp drop in value to 2.7 permil . The isotope profile of this part of the Vindhyan succession is remar kably similar to those of well-established Precambrian-Cambrian bounda ry sections of the world. It thus seems that the Bhander and Sirbu Lim estones may represent the Precambrian-Cambrian boundary interval in th e Vindhyan basin. The carbon isotope chronostratigraphic marker for th e Precambrian-Cambrian boundary interval has been identified in the Kr ol strata of the Himalayas, which were deposited in the late Precambri an-early Cambrian Tethys seaway. Of special significance to the presen t study is the fact that during this period the Vindhyan basin was als o connected with the Tethys seaway.