Provenance of sediments in the Marwar Supergroup, Rajasthan, India: Implications for basin evolution and Neoproterozoic global events

摘要

The Marwar Supergroup of NW India is one of the largest Neoproterozoic sedimentary successions of India. Deposited in an intracratonic sag basin, the Supergroup contains largely unmetamorphosed and undeformed fluvial and marginal marine siliciclastics, marine carbonates, and minor volcaniclastics which hold clues to the geotectonic evolution of India subsequent to the disintegration of the Rodinia and during the formation of the Gondwanaland. Here, we present age constraints for the initiation of sedimentation and evolution of the basin. The Rb-Sr whole rock isochron of a felsic tuff from the lower part of the Supergroup, yields an age of 703 +/- 40 Ma, which suggests that the sedimentation in the Marwar basin started in the Cryogenian period. The result of Sr isotope stratigraphy suggests a depositional age of similar to 570 Ma (Late Ediacaran) for the carbonate sequences in the middle part of the Supergroup, indicating a depositional hiatus of similar to 100 Ma between the lower and middle Marwars. We speculate that this relapse in the sedimentation could be related to the widespread Pan-African event (Malagasy Orogeny). Provenance analysis using Neodymium (Nd) isotopes and trace elements shows that sediments in the lower Marwars were contributed by the Delhi Supergroup (similar to 1.6 Ga), Banded Gneissic Complex-2 (> 1.8 Ga) and possibly the Erinpura Granites (similar to 850 Ma), whereas the siliciclastics deposited in the middle and upper Marwars were predominantly sourced from the Delhi Supergroup. Interestingly, the contribution from the Malani Igneous Suite (MIS) to the sedimentation is limited only to the basal formation near the basin margin.