Integrated sedimentological,ichnological and sequence stratigraphical studies of the Koti Dhaman Formation (Tal Group), Nigali Dhar Syncline,Lesser Himalaya,India: paleoenvironmental,paleoecological, paleogeographic significance

Abstract

Integrated ichnology, sedimentology and sequence stratigraphy of the Lower Quartzite Member to the Arkosic Sandstone Member of the Koti Dhaman Formation (Cambrian Series 2, Stage 4), Tal Group, Nigali Dhar Syncline, Lesser Himalayan lithotectonic zone are presented. Trilobite traces of Gondwanan affinity i.e., Cruziana salomonis, Cruziana fasciculata, Rusophycus dispar and Rusophycus burjensis are recorded along with Arenicolites isp. and Skolithos isp. from the Lower Quartzite Member. A rich and diverse ichnoassemblage attributed to the Cruziana ichnofacies is described for the first time from the Arkosic Sandstone Member of the same formation. Seven ichnofossil assemblages, i.e., Cruziana-Rusophycus, Planolites-Palaeophycus, Cruziana problematica, Diplichnites, Cochlichnus anguineus, Bergaueria perata and Psammichnites gigas have been recognized in the Lower Quartzite to Arkosic Sandstone members of the Koti Dhaman Formation. Seven sedimentary facies i.e., sandstone–shale facies (FT1), cross-bedded (trough and planar) sandstone (FT2), bedded sandstone facies (FT3), shale facies (FT4), shale–sandstone facies (FT5), shale-rippled sandstone facies (FT6) and planar and trough cross-laminated sandstone (FT7) and four facies associations FA1-FA4 are identified in the Koti Dhaman Formation. The formation contains shallowing upward parasequences of a tidal flat complex. Overall, two major events are recognized: i) the break in sedimentation between the Lower Quartzite Member and the overlying Shale Member probably related to forced-regressive event and ii) the facies shift from FT6 to FT7 of the Arkosic Sandstone Member represents an erosive transgressive event; the surface is interpreted as wave ravinement surface, which also serves as a sequence boundary. Integrated ichnology, sedimentology and sequence stratigraphic studies indicate that the Lower Quartzite Member was deposited in a shallow subtidal sand sheet complex and tidal flat complex; the Shale Member was deposited in a mud flat setting of a tidal flat complex, and the Arkosic Sandstone Member in a mixed-flat (tidal flat complex) to sand sheet complex front and margin (subtidal sand sheet complex). Overall, the lower to middle part of the Koti Dhaman Formation represents a tide-dominated shallow subtidal–intertidal to mud-flat subenvironments of the tidal flat complex. A palaeogeographic reconstruction of lower Cambrian (516–514?Ma) is presented based on the distribution of trilobite traces from the Lesser Himalaya and the Bikaner–Nagaur area of Peninsular India (eastern Gondwana), Egypt, Jordan, Turkey (western Gondwana) and Canada (Avalonia).