Record of Permian Tethyan transgression in eastern India: A reappraisal of the Barren Measures Formation, West Bokaro Coalfield

Abstract

The Barren Measures Formation (middle Permian, ∼271–260 Ma), the non-coaliferous lithounit sandwitched between two major coal-bearing formations in the Indian Lower Gondwana succession, was earlier interpreted as continental fluvio-lacustrine deposits. The present contribution documents sedimentary attributes of marginal marine tide–wave interference from the Barren Measures Formation of eastern peninsular India, exposed along the Bokaro River section, West Bokaro Coalfield, Jharkhand. Tidalites, including various tidal bundle sequences with frequent reactivation surfaces (velocity asymmetry) and single/double mud drapes (pause planes), systematic arrangement of tidal beddings (flaser, wavy, lenticular) and tidal rhythmites with alternate sand-dominated and mud-dominated plane-laminated units, manifest sedimentation by open marine spring–neap–spring tidal cycles under diurnal inequalities in a semi-diurnal tidal system. The architecture of tidalites attests to sedimentation in shallow subtidal to intertidal flat facies, affected by intermittent strong to week reworking by open marine waves/storms. Wave reworking is manifested by wave ripples, combined-flow ripples and wave-generated tidal bundles. Their coexistence and gradation with tidalites indicate low-energy wave/storm interference with tidal currents in a sheltered, tide-dominated estuary, especially on tidal flats along estuary channel banks. Overall fining-up facies sequence, upward increase of prodeltaic mud over tide–wave led sediments, signify a sustained transgressive phase onlaping the estuary system in eastern peninsular India during middle Permian (Guadalupian).