Basinal autoclastic mass flow regime in the Precambrian Chanda Limestone Formation, Adilabad, India

Abstract

The Precambrian Chanda Limestone Formation in Adilabad District, Andhra Pradesh, India transcribes carbonate mass flow deposition in an extensional basin within the Godavari rift valley system. In the lower part of the formation, conglomerate beds which commonly interrupt the sequence of thin-bedded lime-mud turbidites, register pulsatory reinvigoration of mass flow processes. These gravelly mass flow products are significant because they indicate (i) deposition far below the wave base, (ii) intrabasinal origin, (iii) disassociation with any depositional slope like reef margins, (iv) occurrence in discrete vertical packages, (v) clear signals for sediment gravity flows, and (vi) invariable facies successions. The conglomerate bodies are extensive, parallel to the depositional strike, but restricted across the latter. The main mode of accretion is dominantly vertical aggradation, only the muddy turbidites spreading far and wide into the basin. The course of temporal evolution of the mass flows are also interpreted from vertical facies transitions. Although every flow eventually gave rise to turbidity currents, their initial states differred in three distinct ways which are correlated with gradient of the translational slope. Gradual decrease in declivity of the depositional substrate through time is interpreted.