Ordovician Ichnofossils and Microbially induced Sedimentary Structures from the Takche Formation, Tethyan Himalaya: Implications for Shallow Marine Palaeoecology and Palaeoenvironments

This study presents the first report of ichnofossils and MISS from the Ordovician Takche Formation exposed at its type section in the Spiti region of the Tethyan Himalaya, India. The ichnoassemblage comprises eleven ichnospecies belonging to nine ichnogenera, namely Arthrophycus, Bergaueria, Chondrites, Lockeia, Palaeophycus, Planolites, Rosselia, Rugalichnus and Treptichnus. The assemblage is dominated by horizontal and shallow-tier burrows and exhibits low to moderate bioturbation intensity, indicating deposition under low-energy distal shelf conditions below the intertidal 
zone. Ichnofabric attributes, tiering relationships and cross-cutting patterns further suggest fluctuating benthic oxygenation. The Deep-tier Chondrites reflects early colonisation under dysoxic substrate conditions, followed by improved oxygenation that allowed the expansion of shallow- and intermediate-tier burrowing activity. The occurrence of microbially induced sedimentary structures, represented by (Rugalichnus), within fine-grained siliciclastic intervals suggests episodic suppression of benthic metazoan activity and temporary microbial stabilisation of the substrate. Notably, despite siliciclastic deposition in a shelf setting, the absence of diagnostic arthropod traces such as Cruziana and Rusophycus supports interpretation of a low-energy, distal expression of the Cruziana ichnofacies rather than a proximal shoreface environment. These findings refine the palaeoenvironmental interpretation of the Takche Formation at its type section and contribute to a better understanding of Ordovician benthic ecosystem organisation along the Tethyan Himalayan margin.