Characterization of marine interval within neoproterozoic cave temple arenite, badami group

Abstract

Meso- to Neoproterozoic Kaladgi Basin, located on the north-western fringe of the western Dharwar craton, is comprised of deformed, older Bagalkot Group and the overlying undeformed, younger Badami Group, exposed mainly in the western and central portion of the Basin. The terrestrial sedimentary units overlying the Chitradurga Schist Belt and/or Peninsular Gneiss in the southeastern margin of the western portion of the Kaladgi Basin, is characterised by multistoried conglomerate and sandstone with some occasional finer shale to siltstone bodies, belonging to the basal Kendur Conglomerate Member and Cave Temple Arenite Member of the Badami Group. The entire succession comprises of three cycles within which lower and upper part is considered to be fluvial in origin but the middle one comprised of fluvial to marine interval, with a transitional unit, in between Amply preserved primary structures, enable one to apply state-of-the-art facies analysis scheme for the entire succession, which revealed major seven genetic facies, combined in to two distinct facies associations. The first of which represents fluvio-marine transitional association, characterized by intercalating occurrences of both unidirectional traction current and bidirectional wave induced current generated facies. The other association is entirely marine, with its thoroughly wave induced texturally matured sedimentary bodies. It covers a wide paleogreographic range within marine realm, ranging from beach foreshore to offshore. Deposition apparently took place in an open wave-influenced shelf, frequently experiencing storm activities. Sequence architectural studies delineate broadly about the sea-level changes during the deposition of this marine interval. The stacking pattern actually give a sense about, the overall transgression and regression of this western sector of Badami group. The overall marine encroachment towards land from the west side is depicted by correlating of synthetic section found at different locations. The whole succession documents several coarsening upward parasequences, distributed ina fashion to depict an initial deepening upward trend followed by a shallowing upward trend with an intervening shale-rich maximum flooding zone. Resting over the lowstand fluvial wedge, the marine transgression is initially slower, leading to the development of a thick transitional interval. Following transgressive systems tract (TST) culminates into a MFZ, and in turn is followed by the normal regressive highstand systems tract (HST). Unconformably overlying fluvial sediments of the topmost cycle, marks the termination of the sequence of middle cycle. Presence of mat-induced primary structures within the studied interval, not only attest the marine origin of that particular studied area, also gives a clear picture about the upper shoreface to middle shoreface paleogeography of the basin.