Neoproterozoic sedimentation and depositional environment: an example from Narji Formation, Cuddapah Basin, India

Abstract

In the west-central part of Kurnool sub-basin of Cuddapah Basin, around Betamcherla–Bagannapali area, the Neoproterozoic Narji Formation rocks (Kurnool Group) of Cuddapah Supergroup are deposited. Sedimentary facies analysis including sedimentary structures and petrographic analysis of the studied samples have been carried out for understanding the depositional environment of the studied formation during Neoproterozoic time period. Sedimentological investigation of the studied formation rocks reveals intertidal-to-subtidal facies associations consisting of six lithofacies such as quartzite bearing massive purple limestone, laminated limestone, calcareous shale, heterolithic, massive whitish grey limestone and intra-formational conglomerate. Sedimentary deformation structures such as load structures and slump structures (micro-faults and folds) indicate perturbation and basin subsidence. Presence of pyrite (reducing condition) and glauconite also indicates shallow marine sediments (at depths of 50–300 m). Overall, the entire basin-fills are inferred to be deposited in shallow marine tidal flat area with occasional deep burial condition in an isolated basin with little clastic influx. Comparing with other coeval successions of Narji Formation lithology, it can be concluded that similar type of depositional milieu prevailed over the globe at early Neo-Proterozoic time during the formation of Rodinia.