Abstract

Three mappable diamictite units occur in the Lower Gondwana Talchir Formation (Permian-Carboniferous) of the Pench Valley coalfield of Satpura basin, central India. These diamictite units (each about 28 to 45 m thick) are predominantly green, polymictic, and poorly sorted. Portions of the units that are massive diamictite include a variety of twisted and deformed to tabular and wedge-shaped sandstone bodies, as well as thin tenses of conglomerate and sandstone that locally exhibit parallel groove markings on the upper surface. Portions of the units that are stratified diamictite are characterized by “grouped” clasts and thin interbeds of siltstone and sandstone showing fine, parallel grooves (striae) and linguoid ripples where the interbeds occur beneath diamictite. Each diamictite unit is overlain by an assemblage of interbedded green siltstone, shale, and sandstone. Such an assemblage contains a variety of primary depositional structures plus local striated “lonestones.” The upper part of the Talchir Formation, the transitional assemblage, is characterized by horizontally bedded to cross-bedded conglomeratic sandstone in which embedded clasts are more rounded than those of the diamictite.

A synthesis of the above features discounts the possibility that turbidity currents or mass flows were the sole formative mechanisms. Alternatively, lithologic and sedimentary characteristics of the lower Talchir strata and their over-all stratigraphic and tectonic setting strongly favor a glacial origin for the diamictite; this corroborates previously published views. We postulate a glaciomarine model, however, to explain the Talchir sedimentation in the study area. The ice sheets may have advanced into central India from the south several times. The overlying transitional assemblage may be glaciofluvial in origin.

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