On the nature of the Blaini Boulder Bed

Abstract

From a closer study of the lithology and field relations of the 'Blaini Boulder Bed' in different areas in the Himalayas it seems clear that the evidences on which the stratigraphical importance of the bed as a glacial formation of Permo-Carboniferous age was based are liable to other and more convincing interpretation which divests it of that importance. The variety in size and form of the boulders as also their occasional surface markings which so far had been interpreted as denoting definite glacial action are all to be expected in rock fragments formed during Nappe movements along thrusts. Some of these features could also be attributed to valley detritus formed during folding movements. The lithological study of the included boulders indicates their derivation not only from the rocks below the boulder band but also from the rocks above it. The field position of the boulder 'bed' is also not definite; the 'bed' occurs variously at the junction of widely different rock formations the Jutoghs, Jaunsars, Simlas, Infra-Krols, Krols, etc., and more particularly at those junctions where an older rock formation occurs superposed over a younger one with an abnormal contact. These evidences are definitely against the glacial origin and lead one to conclude that the boulder formation is either a thrust breccia or a valley detritus formed during tectonic phases of Himalayan upheaval. In this continuation it may be pointed out that even the Salt Range Boulder Bed offers evidences of thrust movements 21 and of the derivation of some fossiliferous boulders from the overlying rocks.