Report on glaciogenic Talchir deposits from Koradi area, Nagpur district, Central India: Lithofacies and petrography

The four lithofacies namely, i) basal massive diamictite, ii) stratified diamictite and sandstones, iii) mediumto fine-grained sandstones and iv) siltstones-shale, are noted from Talchir Formation of the Koradi area, Maharashtra, Central India. The basal massive diamictites that are laterally discontinuous, unstratified and matrix- to clast-supported represent the continental tills. These deposits are inferred to be deposited under subglacial conditions by grounded ice during ice retreat. The stratified diamictite and sandstones unit shows the decrease in the boulder and cobble clasts and increase in pebble clasts. These are deposited by melting of glaciers at outwash plains. Medium- to fine-grained sandstones are associated with the very thin, fine-grained sand and clay layering (varves). These deposits represent glaciolacustrine depositional conditions in the glacial regions, caused by the development of still water bodies and even ice-dammed lakes. The petrographic characteristics of stratified diamictite and sandstones (Sds) and medium- to fine-grained sandstones bring out textural immaturity also suggesting the deposition close to the source in cold- arid climatic conditions under interior type of continental block provenance. The wide range of grain size values from medium to very fine sands with polymodal grain size distribution, poor sorting, positive to very positive skewness, and very leptokurtic to leptokurtic nature of sediments divulge the glacial environment for the deposition. The palaeocurrent analysis shows unimodal palaeocurrent bearing vector mean of 323° and the consistency ratio of 67%. The critical value of vector strength/ magnitude (r) for Rayleigh’s test is 0.367 at the 0.05 significance level. The computed value of χ 2 (42.37) is greater than critical value (24.73) for 11 degree of freedom at the 0.01 significance level, which indicate significant paleocurrent direction.