Ediacaran microbiota from the Baliana and Krol groups, Lesser Himalaya, India
Keywords:Cyanobacteria, Acritarchs, Ediacaran biota, Baliana Group, Krol Group, Lesser Himalaya, India
The different lithofacies of Infra Krol Formation of Baliana Group, Chambaghat and Mahi formations of Krol Group exposed in eight synclines of the Krol Belt in Lesser Himalaya have yielded rich Ediacaran microfossil assemblage. It is the first comprehensive account of excellent preservation of microfossils from these synclines. The assemblage comprises forty-one (41) taxa; three groups of the organic-walled microfossils (OWM)- A. algae (cyanobacteria and rhodophytes), B. protists and C. unknown affinities of biological forms, viz. multicellular cylindrical tubular and vase shaped microfossils (VSM). Studied litho-units include the black carbonaceous shale of Infra-Krol Formation of the Baliana Group; the phosphatic black chert lenticles and shale partings associated with quartz arenite of Chambaghat (Krol Sandstone) and black chert nodules associated with argillaceous limestone and shale of Mahi formations of Krol Group. The microfossil yielding succession conformably overlies the Cap Carbonate - a global marker lithounit of Blaini Formation, the base of the Ediacaran Period. Infra Krol, Chambaghat and Mahi formations underlies the Jarashi and Kauriyala formations of Krol Group which have yielded diversified soft bodied Ediacaran metazoans.
In the reported OWM assemblage, fifteen taxa of prokaryotes are comparable with the extant cyanobacteria belonging to Chroococcales, Entophysidales, Oscillatoriales and Nostocales. The acritarchs belonging to sphaeromorphida and sphaerohystrichomorphida subgroups are represented by twenty-two taxa. The two taxa of multicellular algal thalli (primitive/juvenile stage) of phylum Rhodophyta represents Wengania and Thallophyca, and single taxon of the two forms represented by vase-shaped microfossils (Melanocyrillium hexodiadema) and multicellular cylindrical tubular (Sinocyclocyclicus guizhouensis) of unknown affinities.
The recovered assemblage has close affinities with those microfossils known from the Ediacaran sediments exposed in other parts of the world, viz. Australia, Brazil, Canada, China, Finland, Namibia, Norway, Spitsbergen, Svalbard, Sweden, and Russian platform. The Krol Belt assemblage is exclusively characterized by the dominance of distinctive large sized acanthomorphs acritarchs (Filisphaeridium, Echinosphaeridium, Tianzhushania, Ericiasphaera, Meghystrichosphaeridium and Papillomembrana) followed by medium sized Goniosphaeridium, Gorgonisphaeridium, Trachyhystrichosphaera, Cymatiosphaeroides, Vandalosphaeridium, etc.), small spinose acritarchs (Micrhystridium and Paracymatiosphaera) and a few breakable/characteristic cyanobacteria (Bavlinella, Salome, Obruchevella, Sinocyclocyclicus, etc.). With meagre radiometric data available for Krol Belt of Lesser Himalaya, the present microfossil assemblage is recognized in establishing the biostratigraphic and environment framework for the investigated successions. The present microbial assemblage corroborates the age of the above succession to Ediacaran Period (630-542 Ma) and also supports the view that these formations were laid down in a tidal flat environment.