Additional Terminal Proterozoic Organic-Walled Microfossils from the Infra-krol formation, Nainital Syncline, Lesser Himalaya, Uttaranchal

Black carbonaceous shale associated with black chert nodules of Infra Krol Formation, Baliana Group yielded diversified assemblage comprising 20 taxa of Organic-walled microfossils (OWM) represented by acritarchs and cyanobacterial remains. Out of these, 16 taxa are reported for the first time from this area which include five genera of acritarchs (sphaeromorphida subgroup) viz. Margominuscula simple, Granomarginata primiriva, Satka colonialica, Paracrassosphaera dedalea, Microconcentrica incrustata, and six genera (sphaerohystrichomorphida subgroup) viz. Baltisphaeridium perrarum, trachyhystrichosphaera vidalii, Gorgonisphaeridium maximum, Micrhystridium echintiatum, M. regulare, M. eatonensis, Archaeohystrichosphaeridium cellulare, A. semireliculatum,Germinosphaera unispinosa; four taxa of the cyanobacterial remains viz. Globophycus rugosum, Bavlinella faveolata, Eomicrocystis inalgica, Tetraphycus hebeiensis, Eophormidium orculiformis belong to Synaplomorphitae subgroup and single genus of VSM viz, Melanocyrillium hexodiadema.

The recovered microbiotic assemblage compares well with the assemblages known from the Terminal Proterozoic sediments. The large sized acanthomoph Trachyhystrichosphaera vidalii, recorded here for the first time, is known globally after. Varanger glaciation and before diversification of Ediacaran biota. An analysis of the recovered microbiotic assemblage in the Infra Krol Formation suggests its autochthonous nature. It was deposited in stable, shallow water, restricted pond or lake which had occasional contact with the open sea.