Sedimentological study of Khalsi Formation of Ladakh "Implications for Paleogeographic reconstruction"

Abstract

Carbonates of the Tethys Himalaya in the Ladakh region present a complex relation with rocks of the Indus group and subduction-related volcanics. The present study involves field recognition of the limestone units, collection of mega fossils, petrographic analysis, elemental and mineral composition of Khalsi Formation of Indus group. We present the results on depositional environment, field relation, paleogeographic conditions, and regional significance of Khalsi Formation. The field relation of Khalsi Formation suggests a complex interaction with the igneous intrusion, foredeep turbidite association, metamorphism, and tectonic deformation. The structural disturbance is evidenced by the folding in shale, imprints of sinistral movement, and localized compaction of limestone. The fossil assemblage collected during this study includes Auroradiolites biconvexus, rudists, crinoids, forams (Orbitolinid) corals, colonial bryozoans, belemnite, and some unidentified marine organisms. The faunal assemblage reflects a shallow-water depositional environment. The petrographic analysis of the samples of Khalsi Formation suggests bioclasts as a major component mainly enriched with the fragments of forams, micrite as cementing material, and pyrite and zircon crystals as noncarbonate constituents. The SEM-EDX data suggest significant calcite content in the samples. The SEM-EDX data suggest significant calcite content in the samples. We suggest the rudists, corals, forams (Orbitulina), crinoids, and bryozoans colonies were widely distributed as a reefal framework along tropical and subtropical tethyan ocean margin having a close affinity with the south Asian-Pacific faunal province. These fossils represent a shallow warm water environment of deposition for Khalsi Formation due to the uplifting of the ocean floor in this region after completion of subduction of the Indian plate beneath Eurasian.