No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Vindhyan fossil controversy
Abstract
(In this issue we include a gist of reports by O.N. Bhargava and S.V. Srikantia, the comments of R.J. Azmi on their report and the peer-opinion by Prof. S.B. Bhatia. Several investigators were unable to confirm the presence of SSFs reported from the lower Vindhyan of central India. Kerr (1999, p.412), Brasier (1999, p.723) and Bhatt (1999, p.435) point to the possibility of sample contamination or misinterpretation of data).
... Views 1 and 3 are more or less the same except that in the latter case the older age limit of the VSG has been extended from ~1400 Ma tõ 1800 Ma, with an onus to demonstrate that the exceptionally older dates in the Lower Vindhyan are not due to the inherited components from the older provenance(s). For the acceptance of view 2, authenticity/reproducibility of Lower Cambrian SSF should be unequivocal (see reports in Editor JGSI 2000;Mahadevan 2002). ...
... The Lower Vindhyan fossils thus impart a plausible chronostratigraphic picture that suggests that the Gangau Tillite at the base of the VSG ( Fig. 2; see Bose et al. 2001 and references therein for the basal Vindhyan glacial event) is most likely a signature broadly correlatable with the global Marinoan glaciation event of ~635 Ma (Condon et al. 2005). The recent confirmation of occurrence of fossils resembling Edicaran-Cambrian forms in the Lower Vindhyan by Bengtson et al. (2007) is an independent validation of our view besides eroding the skepticism enumerated in the JGSI report (In Editor JGSI 2000). ...
We present a synoptic view on current discordant views on the age of the Vindhyan Supergroup (VSG), arising from the recent geo- and biochronological data sets. Against exceptionally long duration of ∼ 1200 million years (∼1800-600 Ma) from late Paleoproterozoic to late Neoproterozoic age based on geochronology, diverse paleontological evidences (metazoan traces, small shelly fossils, fossil embryos, calcareous skeletal algae, sponge spicules, acanthomorphic acritarchs, scolecodont-like structures and metaphytes) suggest a much shorter duration of Vendian - Early Cambrian (∼650-520 Ma) for deposition of the VSG. It is demonstrated that ∼1800 Ma (late Paleoproterozoic) initiation of the Vindhyan sedimentation is not in conformity with the regional geology, whereas the younger age for the VSG is consistent with the regional geology and is also supported by a basal Vindhyan glaciation of correlatable Marinoan (Vendian) age ("Snowball Earth"). We believe that the wide age disparity in the VSG stands sorted out by adhering to the regional geological perspective of the Vindhyan Basin.
... The PSI, realizing the significance of the discoveries, decided to organise an International Field Workshop on the Vindhyan Basin. It had a much larger participation from the active workers to discuss the findings of the subsequent reports on the work of Azmi (1998) (Bhatt et al., 1999;Bhargava et al., 2000;Chakrabarti, 2001). In this backdrop, an International Field Workshop was organised in 2002. ...
... The reported fossils in Rohtas Limestone or Khenjua Shale or their equivalents in the Semri Group (Lower Vindhyan) in Son valley include Anabarites, Hyolithelus, Rugatotheca, Protohertzina; Girvanella, Renalcis, Obruchevella, Spriggina; etc. Azmi and colleagues interpret the assemblage as Ediacaran and very early Cambrian in age. However, many identifications, occurrences, and even the locations of outcrops have been strongly disputed and declared unacceptable by Bagla (2000), Bhargava et al. (2000) and Bhatt et al. (1999). ...
Typically or arguably Ediacaran fossils (635 Ma to 543 Ma) are reported by several research groups from one unit of the Chhattisgarh
and two units of the Vindhyan Supergroups in peninsular India. Depositional ages of the host sediments, however, are inferred
to be ∼1000 Ma and ∼ 1630 Ma as determined by U-Pb dating of magmatic and detrital zircons in rhyolitic tuff (∼ porcellanite)
and sandstones, provenance considerations and paleopole positions. The contradiction of absolute ages results from inferring
the Ediacaran age strictly on the basis of fossils. I argue that the fossils reported from the Chhattisgarh and Vindhyan Supergroups
should be considered mostly Mesoproterozoic and late Proterozoic in age. I also argue that although the Ediacaran Period records
explosive diversity of preserved fossils, many forms very likely appeared much earlier with variable degrees of preservation
or none at all at times, and, that their age-ranges extend to the Paleoproterozoic. I hypothesize that the rate of increase
of biological diversity was lower than the rate of preservation in certain geological intervals, especially immediately after
extinction events.
The present guide book can be a good starting point for both students and research workers. It has all the details about the updated information on the Vindhyan Basin in general and for the Son Valley in particular. For each traverse it also summarizes
geology for the beginners.
Distortion of the paleontologic literature in most of the 450 papers bearing V. J. Gupta as author or co-author during the past 30 years has been documented by Agarwal and Singh (1981), Talent (1989a, 1989b, 1989c, 1990a, 1990b, 1990c, in press), Talent et al. (1988, 1989, 1990, 1991), Ahluwalia (1989), Bassi (1989, 1990), Brock et al. (1991), and Radhakrishna (1991). Replies to the charges of fabrication and distortion by Gupta (1989, 1990a, 1990b) were futile attempts to distract the reader, rather than to provide information to refute the charges.
The age of the Vindhyan sedimentary basin in central India is controversial, because geochronology indicating early Proterozoic ages clashes with reports of Cambrian fossils. We present here an integrated paleontologic-geochronologic investigation to resolve this conundrum. New sampling of Lower Vindhyan phosphoritic stromatolitic dolomites from the northern flank of the Vindhyans confirms the presence of fossils most closely resembling those found elsewhere in Cambrian deposits: annulated tubes, embryo-like globules with polygonal surface pattern, and filamentous and coccoidal microbial fabrics similar to Girvanella and Renalcis. None of the fossils, however, can be ascribed to uniquely Cambrian or Ediacaran taxa. Indeed, the embryo-like globules are not interpreted as fossils at all but as former gas bubbles trapped in mucus-rich cyanobacterial mats. Direct dating of the same fossiliferous phosphorite yielded a Pb-Pb isochron of 1,650 +/- 89 (2sigma) million years ago, confirming the Paleoproterozoic age of the fossils. New U-Pb geochronology of zircons from tuffaceous mudrocks in the Lower Vindhyan Porcellanite Formation on the southern flank of the Vindhyans give comparable ages. The Vindhyan phosphorites provide a window of 3-dimensionally preserved Paleoproterozoic fossils resembling filamentous and coccoidal cyanobacteria and filamentous eukaryotic algae, as well as problematic forms. Like Neoproterozoic phosphorites a billion years later, the Vindhyan deposits offer important new insights into the nature and diversity of life, and in particular, the early evolution of multicellular eukaryotes.
