Organic-walled microfossils from the Chert–phosphorite Member, Tal Formation, Precambrian–Cambrian Boundary, India

Abstract

The Chert Member (also designated Chert–phosphorite Member) of the Tal Formation in the Lesser Himalaya, contains well preserved organic-walled microfossil assemblage. The assemblage includes small (<25 μm) acanthomorphic acritarchs, sphaeromorphic acritarchs, cyanobacterial filaments, sponge spicules and thallophytic remains identified as Micrhystridium lanceolatum, M. dissimilare, M. tornatum, M. lanatum, cf Lophosphaeridium sp., Paracymatiosphaera irregularis, Cymatiosphaera sp., Estiastra minima, Leiosphaeridia sp., Siphonophycus robustum, thalloidal fragments and hexactinellid sponge spicules. The present assemblage, rich in small acanthomorphs, appears to be best developed in upper Nemakit–Daldynian beds. Based on acritarch biostratigraphy, the present work suggests a Nemakit–Daldynian to Early Tommotian age for the Chert Member, which is in agreement with the formerly proposed age based mainly on small shelly fossils. The assemblage is correlatable to the Precambrian–Cambrian boundary microbiotic assemblage from China, Central Asia and East European Platform. The assemblage shows low diversity of species, the characteristic of inshore biota.