Pyritized Chuaria-Tawuia from the Pre-Ediacaran Samria Shale, Upper Vindhyans, Rajasthan: An Indication of Anaerobic Environmental Conditions

Abstract

The paper records carbonaceous megafossils assignable to pre-Ediacaran age from a new horizon, Samria Shale, Bhander Group, Upper Vindhyans, Bundi district, Rajasthan. The assemblage is represented by Pyritized Chuaria and Tawuia with equally good morphological details like excystment structures, suggesting their resistant vesicles and eukaryotic affinity. In addition, the assemblage also comprises multicellular metaphytes. Pyritized fossils indicate almost anaerobic environmental condition, rapid burial of organisms under ocean sediment and small amount of decaying bacteria. Pyritization also indicate the presence of sulphur reducing bacteria and dissolved iron at the time of fossilization. Present assemblage is represented by Chuaria circularis, Tawuia dalensis, Ellipsophysa sp., Eopalmaria prinstina, Tuanshanzia lanceolata or Changchengia stipitata,Longfengshania sp. and Proterotainia montana. Two unidentified fossils forms informally described as Form ‘A’ and ‘B’. An unusual and rarely reported process of fossil pyritization has been observed in present assemblage.