Pb-Pb age of the Gotan Limestone, Marwar Supergroup: Implications for Ediacaran-Cambrian transition events in the peninsular India

Abstract

The rocks of the Marwar Supergroup of western India are known to contain important clues for the evolution of complex multicellular life, changes in chemistry of ocean water, and changes in global climate during the Proterozoic-Cambrian transition. However, the timings of these event markers remain tentative due to insufficient radiometric ages. Here, we present dating results of the only limestone formation of the supergroup, the Gotan Limestone of the Bilara Group, by Pb-Pb method and use the existing chemo/chrono stratigraphic information to provide constraints on the age of deposition of the supergroup. The 207Pb/204Pb-206Pb/204Pb isochron yielded an age of 537 ± 19 (2σ) Ma, which is in agreement with the age estimate suggested by 87Sr/86Sr stratigraphy. Therefore, the negative excursions observed in the δ13C record of the Bilara Group should now be assigned terminal Ediacaran and early Cambrian ages, respectively. This new Pb-Pb age considered together with δ13C and 87Sr/86Sr stratigraphic records suggests that the Ediacaran-Cambrian transition in the Marwar Supergroup is likely contained within the Bilara Group, and it is the first such report from the peninsular India.