Origin of the early Ediacaran chert from Infrakrol Formation in Krol Belt, Lesser Himalaya, India

Neoproterozoic-Cambrian deposits of the Krol belt of Lesser Himalaya provide a window to understand the early evolution of life. Here, investigation of geochemical characters and fossil assemblage of chert promises to unveil the palaeoenvironmental conditions favourable for the metazoan evolution. The present study involves petrological, geochemical and palaeobiological investigations of the chert from Ediacaran Infrakrol Formation to understand its origin, palaeoenvironmental conditions and tectonic setting. The petrographic analyses indicates replacement of carbonate during early diagenesis and fast precipitation of silica. The geochemical signatures indicate diagenetic replacement of carbonate, in addition to its contamination by the detrital components and deposition in anoxic to suboxic microenvironment within continental margin. The delta O-18 values reflect diagenetic environment's temperature and possibility of post-depositional intervention of hydrothermal solution. This study suggests that fossiliferous Ediacaran Infrakrol cherts were formed by early diagenetic replacement of precursor calcite nodules. They silicified due to change in pH-redox conditions facilitated by the presence of non-silica-secreting organic walled microfossils as well as detrital and hydrothermal input. Within shallow marine conditions, the organic-rich anoxic bottom water upwelled towards upper oxic water causing deposition of chert in marginal sea within continental slope.