Facies Analysis of the Late Proterozoic Nagthat Formation, Nainital Hills, Kumaun Lesser Himalaya

The Proterozoic Nagthat Fonnation of Nainital area is composed mainly of fine- to coarse-grained quartzarenite with subordinate amount of pebbly sandstone, conglomerate, siltstone and silty shales. On the basis of such parameters as grain size, primary structures, palaeocurrent and morphology of lithounits, seven major lithofacies have been distinguished in the Nagthat sequence. These are, medium to coarse-grained gravelly quartzarenite (Lithofacies A), bar cross-bedded medium-grained quartzarentite (Lithofacies B), horizontally laminated fine-grained quartzarenite (Lithofacies C), fine to medium-grained channelised quartzarenite (Lithofacies D), fine-grained quartzitic sandstone (Lithofacies E), silty sandstone-shale (Lithofacies F) and matrix supported conglomerate (Lithofacies G).

Lateral and vertical distribution of constituent lithofacies demonstrate deposition of Nagthat sediments in a progradational (regressive) barrier island system, in subtidal upper shoreface and channels, subtidal longshore bars, foreshore beachface, tidal channels (inlets), intertidal sandflat-channel and mixed flat environments, and occasionally as gravity flows in subtidal gravelly channels.