Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Sanghamitra Ray ¹

Affiliations
1 Geological Studies Unit, Indian Statistical Institute, 203, B.T. Road, Calcutta - 35, IN

Abstract

The "Infra-Kamthi" Formation is described from the central part of Pranhita-Godavari valley as an essentially sandstone rich horizon with subordinate amount of red mudstone in the lower part and highly ferruginous shale (ironstones) in the upper part of the rock succession. This formation is renamed here as Kundaram Formation, after the village Kundaram in its type area. The northwestern part of the valley has yielded the only known Late Permian reptilian fauna so far found in India.

The lithologs reveal a distinct lateral variation of the formation from the sand-dominant central Pranhita-Godavari to red mudstone rich horizon of the northwest. Ironstones are absent. Sheet sand bodies form composite complexes in the lower part of the rock succession followed upward by thick red mudstone units with small lenses of channel-fill sandstone. This package of sediments were probably deposited by anastomosing river channels.

Keywords

Stratigraphy, Gondwana, Pranhita-Godavari Valley, Infra-Kamthi, Kundaram, Formation.

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Debarati Mukherjee ¹, Sanghamitra Ray ¹, Saurav Chandra ¹, Shrabani Pal ¹, Saswati Bandyopadhyay ²

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur - 721 302, IN
2 Geological Studies Unit, Indian Statistical Institute, 203 B. T. Road, Kolkata - 700 108, IN

Abstract

The current work attempts to address a century old problem regarding the stratigraphic disposition of the Upper Gondwana succession of the Rewa basin based on geological mapping and litholog preparation along well exposed transects. The proposed Upper Gondwana stratigraphy of the Rewa basin comprises a continuous and thick package of Triassic sediments unconformably overlain by the Jurassic Parsora Formation. The Triassic succession consists of a basal Pali Formation, an intermediate and newly designated Karki Formation and the overlying mud-dominant Tiki Formation. These formations are well defined based on physical attributes such as lithology, textures and sedimentary structures, and are easily distinguishable in the field. Based on stratigraphic correlation and fossil content, a Lower-Middle Triassic age has been assigned for the Pali and Karki formations, while the Tiki Formation is Upper Triassic (Carnian) in age. Preliminary observations based on lithological characteristics, sand body geometry and sand: mud ratios suggest that within a fluvial setting there were considerable changes in environments of deposition through time, especially during Triassic to Jurassic transition.

Keywords

Gondwana, Lithostratigraphy, Parsora Formation, Triassic, Rewa Basin.

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