δ13C stratigraphy of the Birmania Basin, Rajasthan, India: implications for the Vendian–Cambrian transition

Abstract

AbstractThe Birmania Basin is an oval-shaped, isolated remnant of the Marwar Basin (Neoproterozoic–Early Palaeozoic), located in the heart of the Thar Desert of western Rajasthan, India. The Birmania Basin comprises a 900 metre-thick sedimentary sequence of siliciclastic, carbonate and phosphorite facies. δ13C and δ18O-values are presented in this paper, based on samples of phosphorite and carbonate collected at close intervals along two sample lines near Birmania and Kohra in the Birmania Basin, Rajasthan, India. The carbonates of the Birmania Basin sampled have suffered neither deep burial nor alteration and may provide pristine samples of the C-cycle at the time of their deposition. These values can be useful in inter-regional correlation, particularly for unfossiliferous successions. The carbon isotopic pattern observed in the Birmania succession appears to be similar to that observed in well-established Precambrian–Cambrian boundary sections globally. A worldwide phase of phosphogenesis, at or near the Precambrian–Cambrian boundary, supports the inference that biological controls driven by ocean fertility changes influenced the marine carbon reservoir.