Cambrian Depositional History of the Zanskar Valley Region of the Indian Himalaya: Tectonic Implications

Abstract

A well-preserved Cambrian section in the Zanskar Valley of northern India has previously been interpreted to record the transition from a passive to an active tectonic margin related to Cambrian-Ordovician orogenesis. This interpretation has been used to support the tectonostratigraphic interpretation of other successions across the Tethyan Himalaya. Our detailed paleoenvironmental analysis significantly revises the tectonic and depositional history of these Cambrian deposits: no definitive record of impending Cambrian-Ordovician orogenesis is recorded in these late Middle Cambrian rocks.A critical transition from an , 125-m-thick, stromatolite-bearing carbonate deposit, the Karsha Formation, into shale and sandstone of the Kurgiakh Formation, was interpreted to represent tectonically induced drowning of a carbonate platform. Siliciclastic strata of the Kurgiakh Formation were thought to record deep-water flysch deposition in a tectonically active foreland basin next to an arc-trench system. This interpretation was based on sandstone beds with classic Bouma sequences. We show that these event beds in the Kurgiakh instead contain hummocky cross-stratification, quasi-planar lamination, and combined-flow ripple stratification, all of which reflect deposition in shallow-marine, storm-influenced environments. Thus, although the Karsha carbonate platform may have been drowned, it did not culminate in deep-sea flysch deposition, and this in turn eliminates a major line of evidence linking Kurgiakh deposition to the onset of Cambrian-Ordovician orogenesis. Other aspects of Cambrian-Ordovician deposits of northern India also shed doubt on the proposed link between Kurgiakh sedimentation and the Cambrian-Ordovician orogenic event. First, our improved biostratigraphic database suggests that the transition from the Karsha carbonate to the Kurgiakh Formation may have predated the main phase of Cambrian-Ordovician orogenesis, as recorded by overlying Ordovician molasse, by as much as 20-30 My. Second, published data from the Ordovician molasse indicate northward paleocurrents, which are parallel to those recorded by siliciclastic deposits of the Parahio Formation below the Karsha, and thus are at odds with standard models of foreland basin development for the Cambrian-Ordovician event.Our sedimentological analysis of depositional cycles of the Parahio Formation indicates that these strata record storminfluenced environments from offshore marine to shoreface to fluvial settings. This is at odds with previous paleoenvironmental interpretations that ranged from deep-sea flysch to intertidal deposits. Paleocurrent data for marine and fluvial facies of the Parahio Formation in both Zanskar and the Spiti Valley to the south indicate northeast sediment transport. This supports the view that the Parahio and overlying carbonate of the Karsha Formation record the ancient northern passive margin of India during the Cambrian and that these strata may be distal equivalents of the younger Cambrian deposits of the Lesser Himalaya.

Kwangsian crustal anatexis within the eastern South China Block: Geochemical, zircon U–Pb geochronological and Hf isotopic fingerprints from the gneissoid granites of Wugong and Wuyi–Yunkai Domains

“…Wang et al (2010) and Yu et al (2007b) considered that the eastern SCB might be located at the northern margin of Gondwana linking Terra Australis orogen and Bhimphedian orogen during late early Paleozoic time. This link is also supported by (1) the similarity of detrital provenance and sedimentary sequences among the Northern India, Greater Himalaya, Lesser Himalaya and Cathaysia Blocks during late Neoproterozoic and early Paleozoic time (DeCelles et al, 2000;Gehrels et al, 2003;Myrow et al, 2006Myrow et al, , 2009Myrow et al, , 2010Metcalfe, 2011;Yu et al, 2007aYu et al, , 2007bWang et al, 2010), and (2) the unconformity between the Ordovician and Cambrian successions in northern India (e.g., Hughes, 2002;Myrow et al, 2009Myrow et al, , 2010, Hainan and Yunkai Domains of the eastern Cathaysia (e.g., Guangdong BGMR, 1988;Wang et al, 2010;Zhang AM et al, 2011). Thus we propose that the Kwangsian intracontinental orogeny of the Yangtze and Cathaysia Blocks might have geodynamically resulted from the far-field response for the amalgamation of the Australian-Indian plate and the Cathaysia (also Indochina) Block along the northern margin of east Gondwana.…”

Geochronological, geochemical and Nd–Hf–Os isotopic fingerprinting of an early Neoproterozoic arc–back-arc system in South China and its accretionary assembly along the margin of Rodinia

“…The final amalgamation along the Wuyi-Yunkai domain is roughly synchronous with the deformation of the East Ghats of India (∼960 Ma) and the northern Prince Charles Mountains of East Antarctica (∼990-960 Ma; e.g., Boger et al, 2000;Jayananda et al, 2000). These relationships, combined with the biogeographic consistency of the eastern SCB with Australia and the late Neoproterozoic tectonic relationship with India (e.g., Wang and Li, 2003;Yang et al, 2004;Myrow et al, 2006Myrow et al, , 2009Wang et al, 2010b), suggest to us that the SCB was situated along the margin of Rodinia between Australia and East Antarctica (e.g., Hoffman, 1991;Yang et al, 2004), as shown in Fig. 17.…”

“…At ∼0.98-0.90 Ga (Fig. 18a), Eastern Cathaysia of the eastern SCB received orogenic detritus from the latest Mesoproterozoic mountain belt that lay in the Prince Charles mountains region of Antarctica (e.g., Myrow et al, 2006Myrow et al, , 2009Boger et al, 2000;Jayananda et al, 2000). At the same time, the Wuyi-Yunkai arc-back-arc system was developed and the Shuangxiwu system continued until ∼880 Ma.…”

Integrated ichnological and sedimentological studies of the Parahio Formation (Cambrian) of the Zanskar region (Zanskar-Spiti Basin), Northwest Himalaya

“…The proven Cambrian rocks in the Zanskar region are well exposed along a NW-SE trending outcrop belt, extending from Karsha village in the Padam Valley to the Niri-Tsarap Chu and Kurgiakh valleys (Fig.1). Stratigraphically, the Cambrian rocks of the Zanskar region are grouped under the Haimanta Group and are subdivided into the Phe, Parahio, Karsha and Kurgiakh formations (Nanda and Singh, 1977;Garzanti et al 1986;Gaetani et al 1986, Myrow et al 2006a). However, Srikantia et al (1978) (Myrow et al 2006a, b).…”

“…However, in the Zanskar region the lower boundary of the Parahio Formation is defined at the first appearance of trace fossils (Hughes and Droser, 1992) and the upper boundary is a conformable contact with the carbonates of the Thidsi Member of the Karsha Formation. Lithologically, the Parahio Formation consists of thin-to thickly-bedded shale, siltstone, sandstone and dolomite with episodically storm-influenced shoaling cycles deposited under offshore marine-shoreface to fluvial environments (Myrow et al 2006a). In the Zanskar region, body fossils have not been recorded from the lower part of the Parahio Formation, while the trace fossils are common in the sandy and muddy facies (Singh, 2008).…”