Cambrian of the Himalaya and the Peninsular India-Biozonation, Depositional Environments and Biogeographic Provinces

Abstract

In the Indian Himalaya, the Cambrian sequences are exposed in the Lesser and Tethyan Himalayan zones (LHZ and THZ). In the LHZ, the Cambrian biozonation is available at four stratigraphic intervals, i.e., at ~542-535 Ma, ~524-513 Ma, ~516 Ma, and ~512 Ma. In the THZ, the Cambrian biozonation exists broadly at two stratigraphic intervals, i.e., ~514-505 Ma (in the Spiti region and partially in the Kashmir region) and ~505-498 Ma (in the Zanskar region and partially in the Kashmir region). The Indian Cambrian faunal elements share Gondwanan and peri-gondwanan affinities. The depositional environments of the Cambrian sediments of THZ and LHZ show a wide array of settings. Cambrian of the Himalaya and the Peninsular India In the Paleozoic succession of the Indian Himalaya, the Cambrian sequences, volumetrically form the most abundant rocks (Wadia, 1975; Brookfield, 1993). The Cambrian sequences occurs in two broad lithotectonic zones (i) the LHZ framed by the Main Boundary Thrust (MBT) in the south and the Main Central Thrust (MCT) in the north and, (ii) the THZ bounded by the Vaikrita Group rocks with tectonic / non-conformable contact with the Greater Himalayan Zone (GHZ) in the south and the Indus-Tsangpo Suture Zone (ITSZ) in the north. The Cambrian sequences within each zone are classified according to the structural/topographic basin in which they occur. Myrow et al. (2009) suggested that the Greater Himalayan Zone (GHZ) also includes deformed Cambrian sedimentary rocks in its central part-a contention yet to be proved. Rocks of the Cambrian age are also known from the craton of the peninsular part of the Indian plate i.e., the Bikaner-Nagaur region of the Rajasthan basin (

Revised lithostratigraphic classification of the Cambrian Kunzam La Formation and its biostratigraphic correlations from Zanskar to Spiti, Tethyan Himalaya

“…The low-grade Neoproterozoic to Cretaceous/Eocene marine sedimentary successions of the Tethyan Himalayan Fold-thrust belt (Bhargava & Bassi, 1998; Corfield & Searle, 2000; Searle, 1986; Singh & Bhargava, 2020; Steck et al, 1993; Wiesmayr & Grasemann, 2002), exposed within the Spiti–Zanskar regions, are bounded to the south by the high-grade gneisses of the Greater Himalaya across the ‘South Tibetan Detachment System’, a NE-dipping normal fault system (Figure 1a; Burg et al, 1984; Searle, 1986; Vannay & Grasemann, 1998; Vannay et al, 2004; Wyss et al, 1999). The northern boundary of this belt is the south-dipping Cenozoic Greater Counter Thrust, which marks the Indus–Tsangpo Suture Zone (ITSZ), separating rocks of the Indian and Eurasian plates to the south and north, respectively (Figure 1a; Srikantia, 1981; Thakur, 1980; Webb et al, 2011; Yin & Harrison, 2000; Yin & Yang, 1999).…”

“…The Kunzam La Formation is the only Cambrian formational unit well-developed and preserved from Zanskar to the Spiti regions, including the Baralacha La sector (Lahaul). However, detailed palaeontological and sedimentological inputs on this formation are only available in the Parahio Valley (Myrow et al, 2006a; Peng et al, 2009; Singh et al, 2016a; Singh & Bhargava, 2020), and the biostratigraphic correlation from Zanskar to the Spiti regions is poorly understood (Peng et al, 2009; Singh & Bhargava, 2020).…”

“…The Cambrian deposits in the northern margin of the Indian plate are considered to belong to a passive margin (Brookfield, 1987) or passive to active tectonic margin setting (Garzanti et al, 1986) related to the Cambro–Ordovician Kurgiakh orogeny (Myrow et al, 2016; Srikantia et al, 1976). The northern margin of the Indian plate during the Cambrian period constituted a part of the Gondwanan realm (Hughes, 2016; Singh et al, 2020). In recent years, the revision of previously known Cambrian trilobite fauna of the Himalayas and its assignment to a broad biostratigraphic and geochronological framework have revived global interest in the Cambrian sediments of the Himalayas (Hughes, 2016; Jell & Hughes, 1997; Peng et al, 2009; Singh & Bhargava, 2020).…”

“…The northern margin of the Indian plate during the Cambrian period constituted a part of the Gondwanan realm (Hughes, 2016; Singh et al, 2020). In recent years, the revision of previously known Cambrian trilobite fauna of the Himalayas and its assignment to a broad biostratigraphic and geochronological framework have revived global interest in the Cambrian sediments of the Himalayas (Hughes, 2016; Jell & Hughes, 1997; Peng et al, 2009; Singh & Bhargava, 2020).…”

“…The Cambrian in the Parahio Valley (Spiti) and along the Purni–Phuktal section (Zanskar) measures ~1,300–1,400 m; these are the only well-studied sections in the Tethyan Himalaya, yet there is a glaring disparity in the biostratigraphic records (Peng et al, 2009; Singh & Bhargava, 2020). In the Parahio Valley, out of the ~1,360 m thick Kunzam La Formation, nearly 900 m of the strata (~78 m from the base of the section to ~1,010 m up in the section) contains nine trilobite biozones and levels spanning late Cambrian Series 2 (Stage 4) to the middle part of Wuliuan (Miaolingian), that is, (a) Haydenaspis parvartya level, (b) Pagetia – Kunmingaspis level, (c) Oryctocephalus indicus biozone, (d) Peronopsis – Gaotanaspis level (e) Kaotaia prachina biozone, (f) Parmecephalus defossus biozone, (g) Oryctocephalus salteri biozone, (h) Pagetia – Xingrenaspis level and (i) Iranoleesia butes level (Peng et al, 2009; Singh et al, 2016a, 2016b, 2017a, 2017b, 2021, Singh & Bhargava, 2020). On the other hand, the ~1,320 m thick Kunzam La Formation in the Purni–Phuktal section (Zanskar region) contains only Sudanomocarina sinindica biozone (uppermost Wuliuan, Miaolingian) in the uppermost part of the Kunzam La Formation.…”