Aspidella: the Ediacaran body fossil from the Jodhpur Sandstone of the Marwar Supergroup, Sursagar area, Jodhpur, western Rajasthan, India
Aspidella: un fósil de cuerpo blando ediacárico de la Arenisca de Jodhpur (Supergrupo de Marwar), área de Sursagar, Jodhpur, Rajasthan occidental, India

V.S. Parihar¹, H. Ram¹, S.L. Nama¹, S.C. Mathur¹

¹Department of Geology, Jai Narain Vyas University, Jodhpur -342005, Rajasthan, India. Email: geoparihar@gmail.com; ORCID ID: https://orcid.org/0000-0002-6055-8378, https://orcid.org/0000-0003-1582-6334, https://orcid.org/0000-0002-0745-377X, https://orcid.org/0000-0002-6269-4656

IntroductionTOP

The present paper describes well-preserved Aspidella remains, the Ediacaran body fossils from the Jodhpur Sandstone of the Marwar Supergroup in Sursagar area, Jodhpur, western Rajasthan, India. The Jodhpur Sandstone is the basal and significant group of the Marwar Supergroup (MSG).

ResultsTOP

The Marwar Supergroup was earlier described as Trans-Aravalli Vindhyans as it is occurring on the western side of the NE-SW trending Aravalli Mountains, and occupies a large area in the northwestern Rajasthan (Pareek, 1984; Chauhan et al., 2004). It is up to 1000 m thick, unmetamorphosed and undeformed, highly diversified sedimentary sequences comprising sandstone, conglomerate, siltstone, dolostone, limestone and shale indicates various marine, shallow marine to sub-tidal and non-marine environments (Pareek, 1984; Pandey & Bahadur, 2009). The Marwar Supergroup (MSG) is uncomformably overlying an uneven and ragged basement of the rocks of Malani Igneous Suite of 780 to 680 Ma of age (Rathore et al., 1999; Gregory et al., 2009). Lithostratigraphically, the Marwar Supergroup is divided into the basal Jodhpur Group followed by the Bilara Group, the Hanseran Group and the Nagaur Group at the top (Pareek 1984; Chauhan et al., 2001). The Jodhpur and Nagaur groups are argillaceous-arenaceous while the Bilara Group is calcareous in nature, and the Hanseran Group is dominated by evaporite deposits. The Jodhpur Group has been further subdivided into the Pokaran Boulder Bed, the Sonia Sandstone and the Girbhakar Sandstone (Pareek, 1981). Later on both the Sonia Sandstone and Girbhakar Sandstone have merged into the Jodhpur Sandstone by Chauhan et al. (2004). The present Aspidella disc assemblages are recorded in a section, about 16 m thick, of the middle part of the Jodhpur Sandstone in Sursagar mines area. In Sursagar area, the Jodhpur Sandstone known as Sonia Sandstone of Jodhpur Group, which is located about 8 km NNE of Jodhpur city. It is represented by yellowish brown, purple and pinkish brown medium- to fine-grained sandstone, siltstone and brown shale and few conglomeratic beds are also present. These beds are more or less horizontal, having laminations, ripple-marks, cross-bedding, graded bedding and rain-prints sedimentary structures (Chauhan et al., 2001). Here the Aspidella disc remains are found in yellowish brown to pinkish brown medium- to fine-grained sandstone bedding surfaces in discoidal forms with mostly positive relief and sometime in negative relief (Fig. 1). Morphologically, these are flat, circular to sub-circular or oval -shaped discs with very sharp inner circular body. The relief of Aspidella discs is slightly flat and raised rim is clearly seen with positive relief. The maximum relief of the ridges is up to 4–10 mm. They occur as individuals or in a near one to another in few cases (Fig. 1d). No radial ribs were found in our Aspidella specimens extending from centre to margin of the discs. The diameter of Aspidella assemblages is in range from 3cm-14cm, with an inner circular body from 1 to 2cm. These dimensions are common to the total range of Aspidella morphs compare to global compilation of Aspidella, but its reaches up to diameter about 50cm (Gehling et al., 2000; Fedonkin et al., 2007; Menon et al., 2013; Tarhan et al., 2015). Earlier, the Aspidella is interpreted as remains of mollusk, lichen, fungi, medusoid, gas-escaping circle or structure and or a concretion. According to Gehling et al. (2000), the Aspidella is most common discs as casts of the basal impression which comprises a great variety of flat morphs, and its type species is Aspidella terranovica, (Billings, 1872) and considered as a buried holdfast of frond-like organisms (Gehling et al., 2000). Alternatively, it’s represent vagile, epifaunal animals of the cnidarian or jellyfish affinity (Menon et al., 2013), or may be non-metazoan, microbial organisms (Grazhdankin et al., 2014; Liu et al., 2015). The present specimens of Aspidella discs assemblages’ are showing good preservations of discoidal forms (Fig. 1) and very closely similar to Aspidella discs from the South Australia and Fermuse Formation, Newfoundland (Gehling et al., 2007). The Hiemalora sp., large Ediacaran discs (diameter from 22 to 4 cm), Tirasiana disciformis, Medusinites asteroides, Anfesta-like Ediacaran body fossils and microbial mat structures are also occurred in same Aspidella discs bearing horizon.

Concluding remarksTOP

The benthic habitat interpolated from the palaeontological record yielded by the Jodhpur Sandstone of the Marwar Supergroup in Sursagar area, Jodhpur, western Rajasthan, India suggests shallow-marine environments under moderate energy conditions for yellowish brown to pinkish brown medium to fine grained sandstone of Jodhpur Sandstone of Marwar Supergroup of Sursagar area as characterizes the worldwide famous Ediacaran fossil sites including Fermuse Formation of Newfoundland, South Australia and White Sea of Russia (Gehling et al., 2000, 2002, 2007; Narbonne & Gehling, 2003; Fedonkin et al., 2007; Narbonne et al., 2014). Detailed study of this Aspidella disc assemblages bearing horizon of Jodhpur Sandstone is much needed for more specific palaeoenvironment, palaeoecology and palaeobiological interpretations.

ReferencesTOP