Alluvial architecture, paleohydrology and provenance tracking from the Neoproterozoic Banganapalle formation, Kurnool Group, India: An example of continental sedimentation before land plants

Abstract

An integrated study involving facies association analysis, architectural element analysis, paleohydrology and detrital zircon geochronology allowed detail insight of sedimentology and paleogeography of Neoproterozoic Banganapalle Formation (BF), Kurnool Group. Detailed process-based facies and paleoenvironmental analysis have led to the identification of fourteen facies types, grouped under four different facies associations, which record paleoenvironmental settings ranging between mid-alluvial fan to distal fluvial plain. Whereas mass flows, hyperconcentrated flows, streamlets and sheet floods dominate the depositional process on the BF fan (middle to distal) surface, streams of varied geometry viz. braided and ephemeral meandering occupied the proximal and distal BF alluvial plain. Our study supports the emerging view that even without the buffering effect of land plants channels developed sinuous planform in pre-vegetation time subject to low-gradient and discharge of alluvial plain and adequate supply of fine detritus. From occurrence of boulder/gravelly mass flows, boundary/pebbly streamlet thalweg and pebbly/granular sheet flood deposits in the alluvial fan, thick silty-muddy stable flood plain deposits in the distal alluvial plain and unequivocal southward paleocurrent irrespective of facies association, it is inferred that the BF alluvial basin received mixed sediment from long-term beveled source in the north and northwest. From two U-Pb detrital zircon geochronology age clusters viz. Paleo- to Mesoarchean (3410 Ma – 3075 Ma) and Neoarchean to late Paleoproterozoic (2750 Ma – 2500 Ma), provenance for the BF is tracked in the north and northwest of the Kurnool basin i.e. the TTG suite of the Peninsular Gneiss and volcanics-hosted greenstone belts in the central and western Dharwar craton. A mixing of sediments from two different provenances is inferred. A consistent low water discharge with marginal downstream increase is suggested for the BF alluvial system from paleohydraulic analysis, except for some occasional spurts of high discharge in mid fan at times of intense rainfall in the hinterland.