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 carbonatesiliciclastics 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.

Evolving provenance in the Proterozoic Pranhita-Godavari Basin, India

“…1). Although previous workers had suggested that the Proterozoic sedimentary rocks in the basin were likely to be the preserved relics of a much larger basin (Ramakrishnan and Vaidyanathan, 2008), sedimentological studies by Chaudhuri et al (2012) demonstrated that the rocks were deposited largely within the present rift boundaries. The rift developed along the NWeSE trending Karimnagar Orogenic Belt, which delineates a Neoarchaean granulite belt between the Dharwar and Bastar cratonic nuclei.…”

“…2). Both Pur ana and Gondwana outcrop belts maintain similar depositional and structural trends (Chaudhuri et al, 2012), and Pur ana formations can be lithostratigraphically correlated across the valley into several unconformity-bound sequences (Chaudhuri, 2003;Chaudhuri et al, 2012). The sequences, by turn, can be classified into at least three 1st or 2nd order depositional cycles (Fig.…”

“…The Mulug and Somanpalli Groups have been interpreted, on the basis of regional stratigraphic considerations, to have developed as two parallel belts within a protracted rift system. The former developed as a shallow tidal shelf deposit and the latter was deposited in a genetically related deep water slope and continental rise environment (Chaudhuri et al, 2012). Sedimentation in the shallow wateredeep water couplet was terminated by contractional deformation (Ghosh and Saha, 2003), termed the Somanpalli orogenic belt by Chaudhuri et al (2012).…”

“…The former developed as a shallow tidal shelf deposit and the latter was deposited in a genetically related deep water slope and continental rise environment (Chaudhuri et al, 2012). Sedimentation in the shallow wateredeep water couplet was terminated by contractional deformation (Ghosh and Saha, 2003), termed the Somanpalli orogenic belt by Chaudhuri et al (2012). The age of basin inversion is not well constrained, but we consider that it coincides with the closure of MulugeSomanpalli basin, and pre-dates deposition of the Penganga Group that overlies the Mulug Group above a major erosional unconformity.…”

Chapter 12 Conflicts in stratigraphic classification of the Puranas of the Pranhita–Godavari Valley: review, recommendations and status of the ‘Penganga’ sequence

“…Sustained field mapping together with facies analysis over the last few decades by many workers has confirmed that King's three-fold classification was not adequate from the point of view of basin evolution (Nageswara Rao 1964;Basumallick 1967;Chaudhuri 1970Chaudhuri , 1985Chaudhuri , 2003Subba Raju et al 1978;Srinivasa Rao et al 1979a, b;Sreenivasa Rao 1985, 2001Chaudhuri et al 2012). In fact, because of episodic uplift, differential erosion and the consequent development of several tectonically mediated unconformities (Chaudhuri et al 2012), dramatic facies variations across the basin, post-Purana development of the Gondwana rift system and fragmentation of Purana outcrops, correlation of different outcrops across the valley and classification of the said successions in relation to the Proterozoic evolutionary events in the PG Valley remain difficult. As a result, a number of contradictions remain among the schemes of classification currently in vogue, and all hinge primarily on the consideration of the unconformity-bound successions as lithostratigraphic units of 'Subgroup', 'Group' and 'Supergroup' ranks (Tables 12.1 & 12.2).…”