Cambrian microfossils from the Tethyan Himalaya

Abstract

Cambrian biostratigraphy of the Indian subcontinent is best documented from the Parahio Formation of the Tethyan Himalaya. Recently established trilobite biostratigraphy shows that the formation encompasses the latest part of unnamed Stage 4 and much of unnamed Stage 5. A variety of small shelly fossils have been recovered via acid digestion of carbonate beds and include tetract and pentact hexactinellid sponge spicules, chancelloriid spicules belonging to Chancelloria sp. and a new species, Archiasterella dhiraji, shells of an helcionelloid comparable to Igorella maidipingensis, a meraspid ptychopariid trilobite, the tubular Cupitheca sp., a poorly preserved hyolith, and an assortment of spinose microfossils of uncertain affinity. These newly recovered microfossils are consistent with the trilobite-based lower and middle Cambrian age determination and do not support a late Cambrian age for the top of the Parahio Formation advocated in some recent literature. The microfossils reported herein significantly expand the known diversity of such fossils from Cambrian strata in the Himalayan region, and allow for comparison of this fauna with others from Gondwanaland and elsewhere. Integration with trilobite data indicate that the stratigraphic ranges of many small shelly fossils described in this study are greater than previously recognized.

Himalayan Cambrian hyoliths

“…Recently recovered internal moulds from the Parahio Valley section identified by Gilbert et al . (in press) as ‘hyolith indet.’ span a broader interval covering much of Stage 5, but are indeterminate even to ordinal level. The co‐occurring Cupitheca sp.…”

Chancelloriid sclerites from the Dyeran–Delamaran (‘Lower–Middle’ Cambrian) boundary interval of the Pioche–Caliente region, Nevada, USA

“…2014 (see also Bengtson & Collins 2015; Gilbert et al . 2016). The set of sclerites from a single individual is termed a scleritome (Bengtson 1985).…”

“…hirundo small sclerites with a tall principal ray and the same topology as A. cometensis and A. uncinata ; we agree with Gilbert et al . (2016) that these cannot be accommodated within A. hirundo . Similarly, reported occurrences of A. hirundo or A .…”

“…nov., A. charma Moore et al ., 2014, A. cometensis Moore sp. nov., A. coriacea Bengtson & Collins, 2015, A. dhiraji Gilbert et al ., 2016, A. elegans Demidenko in Gravestock et al ., 2001, A. fletchergryllus Randell et al ., 2005, A. hirundo Bengtson in Bengtson et al ., 1990, A. palmiformis Vasil'eva in Vasil'eva & Sayutina, 1988, A .? quadratina Lee, 1987, A. quadriradiata Vasil'eva, 1998, A. robusta Vasil'eva, 1985, A .?…”

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

“…have contributed to a better understanding of the Cambrian biostratigraphy and biozonation of the Tethyan Himalaya Zone Singh et al, 2015Singh et al, , 2016Singh et al, , 2017aSingh et al, , 2017bSingh et al, , 2019aPopov et al, 2015;Gilbert et al, 2016;Hughes, 2016;Yin et al, 2018;Kaur et al, 2019).…”