Genesis of Early Cambrian Phosphorite of Krol Belt, Lesser Himalaya

Early Cambrian phosphogenesis in the lesser Himalaya is represented by a well-developed sequence of phosphorite, black shale and black chert with interbedded phosphatic dolomite in the Krol Belt. Prevalence of shallow marine depositional structures support shallow subtidal to intertidal depositional environment. Similar shallow marine character for Late Vendian and Early Cambrian phosphorites have been recorded from Yangtze Basin (South China), Khubshugul Basin (Mongolia), Karatau Basin (Kazakhstan), Soltaniah Basin (Iran), Tal Basin (Lesser Himalaya, India), Hazara Basin (Pakistan) and Georgia Basin (Australia). We have characterized the Tal Phosphorites of Krol Belt, Lesser Himalaya in terms of mineralogy and petrography. The phosphogenic model for the modern Peru-Chile shelf-slope phosphorite is inadequate to explain the genesis of Cambrian phosphorite. Physicochemical characters of the Cambrian phosphorites demand a shallow marine phosphorous source. Based on the available early Cambrian oceanographic models, we envisage a repeated influx of P and ¹²C rich water on to the shallow platform. Amorphous calcium phosphate (ACP) precipitated from the shallow water column overlying the sediment water interface and subsequently modified to microsphorite (micritic phosphorite). Influx of P resulted in proliferation of algal mat and stromatolites, which are found in abundance in Tal phosphorites. The algal and mudstone phosphorites were the parent material for granular phosphorites.