Fossil Discoveries in India

Abstract

A. Seilacher, P. Bose, and F. Pfluger (Reports, 2 Oct., p. [80][1]) state that they have recorded more than 1-billion-year-old triploblastic animal trace fossils from the Lower Vindhyan (Chorhat Sandstone of the Semri Group) of central India. They suggest that the metazoa evolved much earlier (about 400 million years) than the previous records. For this claim, they have depended solely on the published radiometric ages from the Vindhyan succession. Although the age of the Vindhyan Supergroup remained an unsolved problem of Indian stratigraphy for more than a century because of inconsistent biostratigraphic evidence and radiometric dates, the age is generally accepted by most as Mesoproterozoic-Neoproterozoic (approximately 1400 to 550 million years old). I have just published a report ([1][2]) of the discovery of abundant, small, shelly fossils from the uppermost limestone and shale layers of the Rohtas Formation (Semri Group, Lower Vindhyan), the unit which conformably overlies (without apparent interruption of sedimentation) the track-bearing unit in the Son Valley. Because such small, shelly fossils represent a part of the “Cambrian explosion” (of approximately 545 million years ago), it was necessary that I propose a major chronostratigraphic revision for the Vindhyan succession. The revision suggests that the Lower Vindhyan Semri Group would range from Vendian (Vindhyan sedimentation begins with a “basal conglomerate”) to early Cambrian and that the unconformably overlying Upper Vindhyan (Kaimur, Rewa, and Bhander groups, in ascending order) is of early Paleozoic age. To me, therefore, the occurrence of the triploblastic animal traces in the Lower Vindhyan is not a surprise, as they fall within the period of Ediacara biota. In fact, the finding of Seilacher and his team enlarges the scope of a better search for the remains of the Ediacaran soft-bodied animals in the Lower Vindhyan immediately below the appearance of the Precambrian-Cambrian boundary of small, shelly fossils. 1. [↵][3]1. R. J. Azmi , J. Geol. Soc. India 52, 381 (1998). [OpenUrl][4][Web of Science][5] [1]: /lookup/doi/10.1126/science.282.5386.80 [2]: #ref-1 [3]: #xref-ref-1-1 View reference 1 in text [4]: {openurl}?query=rft.jtitle%253DJ.%2BGeol.%2BSoc.%2BIndia%26rft.volume%253D52%26rft.spage%253D381%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [5]: /lookup/external-ref?access_num=000076385800002&link_type=ISI