Paleostrain stratigraphic analysis of calcite twins across the Cambrian–Ordovician unconformity in the Tethyan Himalaya, Spiti and Zanskar valley regions, India

Extraordinary transport and mixing of sediment across Himalayan central Gondwana during the Cambrian-Ordovician

“…In northern India , this event resulted in deposition of a coarse red-bed succession, from which our Thango, MS-5, and MBQ samples were taken (Myrow et al, 2006b). There are minor structural effects in the Tethyan of India for this event (Fuchs, 1982;Wiesmayr and Grasemann, 2002;Draganits et al, 2004;Myrow et al, 2006b;Paulsen et al, 2007), and there are little or no documented structural effects of this orogeny in the Indian Lesser Himalaya. Along strike in Nepal , there is evidence for regional deformation, melting of crust, and the emplacement of granite bodies at this time (ca.…”

“…To the north, Tethyan Himalayan strata also record passive-margin deposition prior to the Cambrian-Ordovician boundary. At that time, there was an enigmatic tectonic event Myrow et al, 2006a;Paulsen et al, 2007) that Srikantia (1981) referred to as the Kurgiakh orogeny, but that named the Bhimphedian orogeny. The cause of this event is unknown, and workers have attributed the event to terrane accretion (DeCelles et al, 2000), fold-and-thrust belt tectonism (Gaetani and Garzanti, 1991;Shankar et al, 1999;DeCelles et al, 2000;Gehrels et al, 2003Gehrels et al, , 2006, and rifting (Murphy and Nance, 1991;Hughes and Jell, 1999;Wyss, 1999;Miller et al, 2001;Wiesmayr and Grasemann, 2002) along the Tethyan continental margin of northern Indian.…”

“…Sample Thango was collected from the Thango Formation of the Spiti Valley in rocks known to be of Ordovician age Suttner, 2007). This particular unit is a syntectonic molasse that records an enigmatic and controversial uplift event of Late Cambrian to Early Ordovician age (Srikantia, 1981;Miller et al, 2001;Gehrels et al, 2003;Myrow et al, 2006aMyrow et al, , 2006bPaulsen et al, 2007). Finally, sample MS-5 comes from the Ralam Conglomerate, a correlative Ordovician red bed unit that unconformably overlies the Cambrian Martoli Formation in the Kumaon area of northern India (Bhargava, 1995;Hughes, 2002).…”

Late Cambrian deformation in the Lesser Himalaya

“…It is rather an extraordinary coincidence that not only the Cambrian folds are co-axial with the Tertiary folds (Wiesmayr and Grasemann, 2002;Paulsen et al, 2007) but also even the direction of propagation of the Late Cambrian DTS from the NE direction is similar to that of the thrust sheets pertaining to the Himalayan Orogeny. Not only this, the granite bearing part, like the present Central Crystalline Axis formed during the Himalayan Orogeny, was also raised between the Tethyan and Lesser Himalayan basins during the Late Cambrian to provide 525 Ma zircons to both basins.…”

“…In the Spiti Valley (Tethyan part, Himachal) the pre-Ordovician folds observed in the Cambrian rocks are of gentle nature and co-axial with the Himalayan folds (Wiesmayr and Grasemann, 2002). Paulsen et al (2007) based on paleostrain analysis of calcite twins also concluded a co-axial relationship of the Cambrian folds with the Himalayan folds. In the Lesser Himalaya a thin strip of the Permian overlaps the Ediacaran sequence and various units of the Cambrian sequence signifying a pre-Permian erosion and discordant nature of contact.…”