Ancient Denudational Surfaces in the Gondwana Sequences of Peninsular India

Gondwana basins of Peninsular India contain a thick pile of clastic sediments of predominantly fluvial origin. As expected in such a depositional milieu, the sedimentary pile is punctuated by numerous episodes of contemporaneous uplift, non-deposition and erosion. Most of these events are localised in nature and hence not correlatable from one basin to another. However, a few events of regional nature can be recognized. They comprise (a) basement surface with glaciated features like polishing, striations and frost wedging below the basal Talchir strata; (b) surface of angular and erosional unconformity between Permian/Triassic and Early Triassic/infra - Late Norian and (c) a major diastrophic episode resulting in reversal of palaeoslope between Late Jurassic and Early Cretaceous. Besides these, localized events represented by surfaces of contemporaneous subaerial exposure and oxidation showing characters of pedogenic (palaeosol) and lateritic (latosol) profiles have been recorded. These include Lower Barakar (Early Permian) of Hutar basin of Koel valley, Barren Measures (Late Permian) and Triassic/Jurassic contact of Rewa and Satpura basins, and Late Cretaceous Lometa Beds in Rewa Basin. Breaks represented by conglomerate beds occur in Early Permian Barakar strata of Talchir coalfield and Late Mesozoic Bagra Formation of Satpura basin. The palaeosols vary in thickness from 4 m to 25 m and are characterised by red brown clay with mottles, ischolar_mainlets, slickensides, ferruginous concretions and calcareous veinlets. The palaeosols are hydromorphic and are developed under poorly drained to well drained groundwater conditions. Even where the palaeosols are not present, the bedrock displays evidences of deep weathering. These probably represent the earlier topographic positive areas affected by physical weathering and intense groundwater activity.