δ13C Stratigraphy of the Birmania Basin, Rajasthan, India: Implications for the Vendian- Cambrian Transition

Overview The paleogeographic reconstruction of the late Neoproterozoic assumes a marked significance due to the fact that the interactions between the biosphere, atmosphere, hydrosphere, and geosphere during this time strongly influenced the evolution of life and initiated a remarkable phase of organic evolution, well documented in the rocks of this age. Time-related changes in these carbon reservoirs and processes during the late Proterozoic have played an important role in the evolution of the environment and of life (Des Marais, 1997). Brasier (1992) discussed, at length, various factors which pushed the shallow marine ecosystem of the late Neoproterozoic-Cambrian towards P-limitation and suggested that nitrate fixation, density stratification and massive removal of P in the sediments were responsible for the formation of phosphatic deposits within this time interval. The East Gondwana assembly of continents provides fine examples of stratigraphic successions in which the ideas related to oceanic stratification, phosphate deposition, enhanced organic production and carbon isotope fluctuations can be verified and correlated from continent to continent (Banerjee and Majumdar, 1999).