The post-Kurgiakh orogeny Sanugba Group (Ordovician–Silurian) Zanskar–Spiti–Kinnaur: Reclassification, depositional architecture, basin evolution and the embryonic South Tibetan Detachment System (STDS)

The recognition of an additional component in the Thango Formation and new fossil evidence from the Takche Formation necessitate reclassification of the Sanugba Group. The Thango Formation is subdivided into the Yamrang La, Chango and Shian members, representing transgressive–paralic, beach and high-energy shallow-marine settings. The Takche Formation is divided into the Farrakha, Pin and Thanam Members, corresponding to mid- and outer-ramp, reefal and fore slope environments. Post-Kurgiakh Orogeny, marine transgression was diachronous, initiating in Kinnaur and advancing westward into Spiti and Zanskar, with the Takche Basin remaining shallowest in the east. Variations in sedimentary architecture reflect basement structures, notably the Chandra–Sarchu and Kaurik–Chango faults. During the Himalayan Orogeny, fault systems bounding the Tethyan Rift Basin were tilted, uplifted and displaced, transporting the overlying Tethyan sediments. This tectonic boundary fault is now recognised as the South Tibetan Detachment System (STDS).