THE RISE AND DECLINE OF THE EDIACARAN BIOTA: PALAEOBIOLOGICAL AND STABLE ISOTOPIC EVIDENCE FROM THE NW AND NE LESSER HIMALAYA, INDIA

Abstract

Sediments of Ediacaran age have recently been recognized in the Krol Belt (NW Lesser Himalaya, India) with the discovery of pre-Ediacaran and Ediacaran biotas, carbon isotopic excursions matching the global curve and evidence for one Neoproterozoic glacial event. Other data include evidence for termination of the Krol algal-stromatolitic carbonate cycle in Late Proterozoic and deposition of phosphorite, phosphatic stromatolites similar to Tommotian taxa, and diversification of Small Shelly Fossils (SSF) of Tommotian/Meischucunian Zone 1 in Lower Tal Formation. Recently, Riphean-Ediacaran organic-walled microfossils, stromatolites and sponge spicules (monaxon) have been recovered. The link between the decrease in microbial-induced carbonate sedimentation and the decline of large Riphean stromatolites is recorded in the inner sedimentary belt (Deoban-Gangolihat). The first appearance of complex organic-walled microfossils and acanthomorphic acritarchs is recorded in the Blaini-Infrakrol sediments along with possible Ediacaran soft-bodied metazoans and metaphytes in the Krol Formation. In India, the Late Proterozoic base occurs at the bottom of a pink, microbial limestone in the Blaini Formation, and the Precambrian-Cambrian boundary occurs somewhere in the Lower Tal Formation. Ediacaran metazoans occur above glacial deposits assigned to the Varangian/Marinoan/Blainian and below the first occurrence of SSF (Meischucunian zone I), in the lowermost Cambrian.