Paleogeographic and tectonic evolution of the Pranhita-Godavari Valley, Central India: a Stratigraphic perspective

Abstract

The Pranhita-Godavari Valley of central India preserves records of repeated opening and closing of Proterozoic and Gondwana rifts along the zone of NW-SE trending Neoarchean suture between the Dharwar and Bastar cratonic nuclei. The Proterozoic succession in the Valley comprises several major unconformity-bound sequences, each with a distinctive set of litho-assemblage, deposited under diverse tectonic environments with highly variable modes and tempos of sedimentation. Analysis of sedimentary attributes of unconformity-bound sequences indicates that Purana sedimentation in the Valley started with the deposition of stable platformal assemblage of carbonate-quartzarenite in an extensional sag basin. The basin opened at c. 1700 Ma. The stability of the craton was disrupted when the first major cratonic rift nucleated at c. 1620 Ma, and shortly evolved into an oceanic basin along the northeastern margin of the Valley with consanguineous deposition of a thick wedge of conglomerates, tidal sandstones and shales in the Mulug shelf, and a succession of graywacke, carbonate, siltstone-mudstone-black shale and tuff turbidites of the Somanpalli flysch in two parallel adjoining belts. The Somanpalli flysch is bounded by two shallow marine successions, analogous to several geosynclinal deposits preserved in orogenic belts, and was deposited in a deep oceanic basin along a rifted continental margin. Paleocurrent analysis reveals that siliciclastics in the flysch succession were derived primarily from a continental provenance to the southwest of the Mulug shelf, and were transported to the flysch basin across the margin. Coarse sands were deposited in large submarine fan complexes of graywackes and mixed carbonate-siliciclastics at several points. The voluminous carbonate turbidites in the flysch were also derived from the adjoining Mulug shelf. High quartz content of graywackes, their close association with tidally deposited arenites, and ocean-ward transport of sediments from cratonic hinterlands collectively attest to the deposition of the flysch in a trailing margin basin. Opening of the oceanic basin and deposition of the flysch were accompanied by extensive granulite facies metamorphism at deep crustal level indicating a genetic linkage between them, and the litho-tectonic elements were deformed into an orogenic belt during re-assembly of Dharwar and Bastar blocks. The orogenic belt girdled the northeastern margin of the PG Valley, wrapped around its southeastern corner making a syntaxial bend, and continued into the Ongole-NKSB orogenic belt which also had its peak metamorphism at c. 1600 Ma. The age of the orogeny is not well constrained, but was followed by a Neoproterozoic episode of extension, and formation of cratonic rift basin with the deposition of several thousand meters of quartz-rich sandstones of the Sullavai, Albaka and Usur sequences.