Lithology and Conditions of Deposition of the Talchir Formation in North Karanpura Basin

Abstract

In North Karanpura basin, the Talchir Formation ranges in thickness from about a metre to 130m and consists of tillite, sandstone-conglomerate, rhythmite and sandstone/siltstone members. Synthesising surface and sub-surface data, these are interpreted mainly as glacial (drift) sediments. Field relationship suggests that the tillites were deposited mainly as 'ablation tillite' or 'basal tillite' on erosional embryonic basin. Restricted occurrences of 'lodgement tillite' are noted along the margins of the basin. Till fabric data indicates that several lobes of glaciers flowed towards the basin in response to local palaeoslope from the various cappings of ice occurring on the northern Hazaribagh as well as the southern Ranchi Plateaus. Present study reveals advancement of two separate systems of ice-lobes from NW or west and south or sw in the northern and southern parts of the basin respectively. A radiating ice-flow direction from the Lurunga-Indratoli high is noted in the southeastern part of the basin. Oscillations of ice front are documented in the southern part of the basin. Synthesis of data indicates that melting of these ice-lobes gave rise to the deposition of glaciofluvial and glaciolacustrine sediments in ice-contact or proglacial environment in various parts of the basin. Based on surface and subsurface data, several disconnected ice-bound lakes are delineated in different parts of the basin. During latter part of the Talchir sedimentation, the basin came under the domain of alluviation.