The Cambrian palaeontological record of the Indian subcontinent

Abstract

The Indian subcontinent's biota and biostratigraphy is amongst the least well known internationally of any Cambrian succession worldwide. Recent revision of previously described type material and a substantial number of new finds reveal a typical Cambrian skeletonized fauna and an organic walled biota, as well as various trace fossils. This biota, reviewed here synoptically, currently contains 51 non-agnostoid trilobite genera belonging to 50 species; 15 genera and species of agnostoids; one species of bradoriid arthropod; 18 brachiopod genera containing 20 species; echinoderm thecal and columnal plates; a soft-bodied eldoniid; representatives of three hyolith genera; other small shelly fossils some of which are identified to species level; acritarchs; and a variety of ichnotaxa. Regional biostratigraphic zonations for trilobites, brachiopods, small shelly fossils, and trace fossils are herein combined into an integrated Cambrian biostratigraphical scheme that permits correlation along and across the lithotectonic zones of the Himalayan margin and southward onto cratonic India. These consist of 13 named

Zircon (U‐Th)/He Thermochronometric Constraints on Himalayan Thrust Belt Exhumation, Bedrock Weathering, and Cenozoic Seawater Chemistry

“…Foreland provenance shifts at 16 Ma are recorded by an overall upward coarsening of clastic deposits, a decreased contribution of metamorphic detritus, and a marked increase in depositional lag time-the temporal difference between the mineral cooling age during exhumation and the depositional age in the basin (Reiners & Brandon, 2006;Ruiz et al, 2004)-of detrital white mica 40 Ar/ 39 Ar ages that represent a shift from high-grade GH rocks to low-grade LH rocks that lack Cenozoic age white mica (Najman et al, 2009;White et al, 2002). While these data clearly demonstrate the likelihood of earlier exhumation of LH rocks than that generally presumed (Chesley et al, 2000), the initial timing of LH exhumation continues to be widely disputed within the community, likely stemming from conflicting models of the north Indian margin before the onset of Himalayan orogenesis (e.g., DeCelles et al, 2000DeCelles et al, , 2016Hughes, 2016;Myrow et al, 2003Myrow et al, , 2015. Despite its importance, the timing of onset of oLH exhumation has remained poorly constrained as these rocks have not, until now, been a focus for thermochronometric investigation.…”

“…South of the Tons thrust, these klippen are structurally emplaced above lower greenschist facies oLH rocks that record peak metamorphic temperatures not exceeding 3308C (Celerier et al, 2009a). Whereas iLH strata have correlative, age-equivalent strata along strike across the Himalaya, exposure and preservation of oLH strata is mostly limited to northwest India where these rocks are preserved within structural synforms (Auden, 1934;Celerier et al, 2009b;Hughes, 2016;Valdiya, 1980;Webb et al, 2011). While the precollisional origin of oLH rocks has been debated, it is certain that Cambrian Geochemistry, Geophysics, Geosystems 10.1002/2017GC007191 sedimentation extended far onto the Indian craton, and likely that oLH rocks were deposited along a continuous Indian margin as part of an extensive sedimentary belt that spanned from Pakistan to the eastern syntaxis, and south onto the craton (Hughes, 2016;McKenzie et al, 2011;Myrow et al, 2003Myrow et al, , 2015.…”

“…Whereas iLH strata have correlative, age-equivalent strata along strike across the Himalaya, exposure and preservation of oLH strata is mostly limited to northwest India where these rocks are preserved within structural synforms (Auden, 1934;Celerier et al, 2009b;Hughes, 2016;Valdiya, 1980;Webb et al, 2011). While the precollisional origin of oLH rocks has been debated, it is certain that Cambrian Geochemistry, Geophysics, Geosystems 10.1002/2017GC007191 sedimentation extended far onto the Indian craton, and likely that oLH rocks were deposited along a continuous Indian margin as part of an extensive sedimentary belt that spanned from Pakistan to the eastern syntaxis, and south onto the craton (Hughes, 2016;McKenzie et al, 2011;Myrow et al, 2003Myrow et al, , 2015. Alongstrike variations in the structural geometry of the Tons thrust have demonstrated how oLH strata, currently preserved in northwest India, have likely been eroded away in Nepal (Yu et al, 2015) where Paleoproterozoic LH rocks are widely exposed as structurally repeated units within the LH duplex (DeCelles et al, 2001;Robinson & Martin, 2014;Robinson et al, 2003).…”

Cambrian trilobite biostratigraphy and its role in developing an integrated history of the Earth system

“…Taylor 1976Speyer & Brett 1986;Speyer 1987Speyer , 1991Whiteley et al 2002;Robison & Babcock 2011) and their stratigraphical and geographical distributions (e.g. Harrington et al 1959;Palmer 1965a;Taylor & Forester 1979;Chang 1989;Whittington 1992;Shergold 1997;Whittington et al 1997;Whiteley et al 2002;Zhang et al 2003;Bruthansova et al 2007;Choi 2007;Zhou & Zhen 2008;Sundberg 2011;Webster 2011;Hughes 2016).…”

Late Mesoproterozoic – early Neoproterozoic organic‐walled microfossils from the Madhubani Group of the Ganga Valley, northern India

“…; McKenzie et al . ; Tripathy & Singh ; Hughes ) controversy remains concerning the age constraints of the Ganga Supergroup and its correlation with the Proterozoic successions in the Vindhyan Basin and Lesser Himalaya. It has been hypothesized that the Ganga Supergroup was deposited in a separate basin with distinct origins, age and tectonic history relative to the Vindhyan Basin and Lesser Himalaya (Fuloria ; Prasad & Asher ).…”