Abstract

Ripple-drift cross-laminations are described from tidal deposits of the Precambrian Bhander Formation, which belongs to the Vindhyan Supergroup of central India. Considering the transport processes operative in modern midflats, ripple-drift cross-laminations should be common in ancient counterparts. The generation of ripple-drift cross-laminations is, however, usually hindered by the absence of persistent, unidirectional current flow. These structures can only develop in areas of the midflat where there is persistent, unidirectional current. Because of periodic velocity changes of tidal currents, rhythmically size-differentiated foreset laminae appear to be a diagnostic feature of tidal ripple-drift cross-laminations. Size differentiation is normally absent in the ripple-drift cross-laminations of turbidites and fluvial sequences, for in the environments responsible, there exists no cyclic pattern of water movement (that is, currents that alternate with periods of slack water) as is found in the tidal-flat environment.

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