Permian occurrence of Crowded Rosselia Ichnofabric (CRI) from the Spiti Himalaya, India

A dense population of Rosselia socialis referable to as the Crowded Rosselia Ichnofabric (CRI) was found in a 1.67 m thick amalgamated coarse hybrid sandstone of the Gechang Formation (Permian) at Guling locality in the Spiti region, Himalaya. CRI is confined to 6-7 cm of the uppermost part of the hybrid sandstone of the Gechang Formation and indicates penetration of the trace maker from the upper surface. The bioturbation index of the R. socialis bearing bed is 4 (60-90%) and the density varies from 27 to 34 per m(2). Sedimentological evidence shows that the Gechang Formation was deposited in fluvio-marine nearshore to upper shoreface-lower shoreface setting under high-energetic and fluctuating substrate conditions. The CRI-bearing bed is particularly interpreted as a tempestite bed deposited in storm conditions in the upper shoreface environment.