Integrated sedimentological and ichnological studies of the Cambrian of the Tidong Valley, Kinnaur, its correlation with Zanskar-Spiti regions, and reconstruction of the northern margin of Indian Plate

A low diversity trace fossil assemblage that includes Bergaueria perata, Bergaueria hemilaris, Psammichnites gigas gigas along with arthropod scratch marks, are for the first time, recorded from the Cambrian Kunzam La Formation exposed between the Charang and Alingdhar localities in the Tidong Valley, Kinnaur. These traces are from the uppermost part of the Kunzam La Formation and confirm the presence of Psammichnites gigas gigas sub-ichnozone in the Kunzam La Formation (latest part of Cambrian Series 2, Stage 4) immediately below the rocks of the Ordovician Thango Formation. The bioturbation (ii = 1-2) is only confined to the uppermost part of the section. Body fossils have not been recovered. Sedimentological analysis shows five lithofacies i.e., (i) dominant trough cross-bedded facies with rip-up mud clasts (fluvial to nearshore), (ii) wavy (tabular) bedded sandstone facies (proximal to the shoreline), (iii) conglomerate facies (fluvial), (iv) sandstonesiltstone-shale facies (shoreface) and (v) bedded siltstone facies (transition zone). These lithofacies although do not show sedimentary cycles but overall they record upward shoaling. Hummocky crossstratification (HCS), dark shale facies (offshore), and carbonate facies, which are well known from the Zanskar-Spiti regions, as well as contains trilobite and brachiopod fossils, are absent in the Tidong Valley (Kinnaur). Integrated sedimentological and ichnological data suggest that the Kunzam La Formation in the Tidong Valley was deposited in a shallow-marine, nearshore to upper shoreface environment, where the main river fed the northern margin of the Indian Plate during the Cambrian period.