Gilbert et al.—Himalayan Cambrian microfossils
11
been reported sporadically ever since. Early works described several hyoliths from early Cambrian rocks in the Salt Range of Pakistan (Waagen, 1891; Redlich, 1899; Schindewolf, 1955), and middle Cambrian rocks of Kashmir (Reed, 1934) and the Parahio Valley of Spiti (Reed, 1910). Two hyolith specimens were previously described from the Parahio Formation of the Parahio Valley (Reed, 1910) from about 836.41m (Hayden’s [1904] level 9) in the measured section of Myrow et al. (2006a), along with the putative conodonts mentioned above (Bhatt and Kumar, 1980) (Fig. 4). One of these specimens remains acces- sible and is commented on below. In later years, lowermost Cambrian rocks from the Lesser
Figure 1. Location of the Parahio (Spiti region) and Zanskar (Ladakh region) valleys within the Tethyan Himalaya, the most northern of the four lithotectonic zones of the Himalaya.
Peng and colleagues’ (2009) reassessment of Parahio
Formation trilobites highlights the peculiarity of the report of conodont genera from the formation (Bhatt and Kumar, 1980). The anomaly has four potential causes: (1) the trilobite bios- tratigraphy of Jell and Hughes (1997) and Peng et al. (2009) is incorrect; (2) there is an unrecognized stratigraphic break between ~1050mand ~1250m(the inferred height of the Bhatt and Kumar horizon) in the Parahio Valley section and the uppermost part of the Parahio Formation there is Furongian or later in age; (3) Bhatt and Kumar’s collection is middle Cambrian but records the stratigraphically earliest occurrence yet known of a range of conodont genera, some of which are known elsewhere only from the upper Cambrian or lower Ordovician; or (4) the taxonomic identifications of Bhatt and Kumar (1980) were incorrect. A two-pronged approach has been used to assess this con-
undrum. First, the original material of Bhatt and Kumar (1980), housed in the paleontology repository in the Geological Survey of India in Kolkata, has been inspected microscopically. Unfortunately, as this material can neither be loaned nor are facilities available in the repository for microfossil imaging, it is not possible to re-illustrate this material here. However, most of the preserved illustrated specimens purported to be conodonts are, in fact, brachiopods (which is evident from the published photographs themselves) and will be discussed elsewhere (Popov et al., 2015). Specimens attributed by Bhatt and Kumar (1980) to Oneotodus are not brachiopods and are considered below. Second, carbonate samples collected from the Parahio Formation have been processed to discover what microfossils, if any, occur with the trilobite specimens used to establish the biozonation of Peng and colleagues (2009). These collections have included PO9, located in the Parahio Formation at 1242.40m above the base of the Parahio Valley section along the Sumna river section, Spiti region, (Figs. 2, 4). Hammer marks consistent with bulk sampling suggest that this is the level that Bhatt and Kumar (1980) collected.
Other small shelly fossils from the Indian subcontinent
Hyoliths were among the first Cambrian fossils described from the Indian subcontinent (Waagen, 1882–1885), and they have
Himalaya have yielded a modestly rich assemblage of small shelly fossils attributed to the Anabarites trisulcatus- Protohertzinia anabarica Assemblage Zone (Bhatt et al., 1985; Brasier and Singh, 1987), which appears to be a little older than a comparable assemblage known from Abbottabad in Pakistan (Mostler, 1980). A Protohertzinia-Olivooides–bearing assemblage has also been reported from low in the Tethyan Cambrian in the Lolab Formation of Kashmir (Tiwari, 1989). The Pakistani assemblage belongs to a second successive fauna of small shelly fossils (Hughes et al., 2005), and contains the chancelloriids Archiasterella and Allonnia, along with sachitids. The sachitids suggest a pre-trilobitic age and this is consistent with the local lithostratigraphic context. Chancelloriids have also been reported from the Indian Lesser Himalaya above the Anabarites trisulcatus-Protohertzinia anabarica Assemblage Zone (Kumar et al., 1987). These finds were interpreted to be pre-trilobitic correlatives of the Sinosachites flabelliformis- Tannuolina zhangwentangi Assemblage zone of South China, but the possibility of a younger age has been mooted (Hughes et al., 2005). An assemblage of coiled mollusks has also been described
from the Lesser Himalaya (Kumar et al., 1983; Kumar et al., 1987), slightly above the chancelloriid-bearing level, and belonging to the Drepanuroides trilobite Zone (Hughes et al., 2005). All these finds, along with additional poorly preserved hyoliths from the Tethyan Himalaya of Kashmir (Kumar and Verma, 1987) are early Cambrian in age (see review in Hughes et al., 2005). Recently, Singh and colleagues (2015) have also recovered microfossils from the Parahio Valley section, repor- ted to occur at a level approximately 20m above the Hayde- naspis parvatya horizon, and interpreted by those authors to belong to Stage 4. Accordingly, to date no small shelly fossils have been described as occurring within the middle Cambrian of the Indian subcontinent, with the exception of those hyoliths mentioned above in the Parahio Formation and from Kashmir (Reed, 1910; Reed, 1934; Kobayashi, 1934). The attributions of several Singh and colleagues’ (2015) finds are considered below.
Material and methods
New limestone and dolostone samples collected from the Parahio Formation in the Parahio and Zanskar valleys were placed into an 8% formic acid (HCO2H) solution for acid digestion. Digestion times depended on the degree of dolomitization in each sample, but ranged from one week to a month or more (see Abrantes et al., 2005).
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