Microfossils from the Kheinjua Formation, Mesoproterozoic Semri Group, Newari area, central India

Abstract

A well preserved and diversified microfossil assemblage is reported from a new locality, Newari, Son Valley area, Uttar Pradesh from the black bedded chert belonging to the Fawn Limestone Member of the Kheinjua Formation (∼ 1200 Ma), Semri Group (Lower Vindhyans). In all, 28 species belonging to 18 genera representing both coccoid and filamentous forms are described. These are associated with microbial laminites. Excluding Archaeoellipsoides and Bactrophycus, and forms of acritarchean affinity, the diameter range among coccoids is between 2 and 24 μm, averaging 10.4 μm, and the width of the filamentous forms is from 1.5 to 28 μm, averaging 6.8 μm. Eoentophysalis and Siphonophycus are the two most dominating forms. In comparison to filamentous forms the coccoid forms show more morphological diversity. Well preserved cellular filaments are few in number. In both coccoid and filamentous forms there is a possibility that many forms represent degradational variants of a common biological entity. When the Newari assemblage is compared with other Proterozoic microbial assemblages, it shows maximum resemblance with the assemblage described from the Meso- to Neoproterozoic Deoban Limestone, Garhwal Lesser Himalaya, India, with 12 genera being present in both assemblages. It has 9 genera in common with the Tindir Creek Group, 8 genera with the Balbirini Dolomite, 8 genera with the Draken Conglomerates assemblage, 8 genera with the Bitter Springs Formation and 6 genera with the Belcher Islands assemblage. The following assemblage is reported: (1) the coccoid forms Eoentophysalis belcherensis, E. magna, Myxococcoides minor, M. grandis, Sphaerophycus parvum, S. medium, Huroniospora sp., Eosynechococcus moorei and E. isolatus, cf. Palaeopleurocapsa sp., Tetraphycus major, T. congregatus, Glenobotrydion aenigmatis, Coniunctiophycus gaoyuzhuangense, Archaeoellipsoides sp., Bactrophycus oblongum, cf. Kheinjuasphaera vulgaris, cf. Trachysphaeridium sp., Leiosphaeridia jacutica; (2) the filamentous forms Palaeolyngbya sp., Oscillatoriopsis breviconvexa, O. sp., O. grandis n. sp., O. constrictum n. sp., Siphonophycus kestron, S. robustum, S. septatum and cf. Eomicrocoleus crassus.