Biostratigraphic Zonation of the Stromatolite-Bearing Horizons in the Aravallis of Udaipur District, Rajasthan

Prolific development of algal stromatolites occurs in the carbonate sequence of the Precambrian Aravalli Supergroup in the Udaipur District of Rajasthan. Based on the assemblage of the algal stromatolites in the fossiliferous beds of the Aravallis, the authors propose three distinct biostratigraphic units. viz., (i) Collenia columnaris Assemblage Zone. (ii) Collenia baicalica Assemblage Zone, and (iii) Oncolite Assemblage Zone, in ascending order. Of these, Collenia baicalica and Oncolite Assemblage Zones are highly phosphatic and contain workable deposits of phosphorite (rock phosphate). The Collenia columnaris Assemblage Zone is, however, non-phosphatic. These assemblage zones have been recorded in all the phosphorite deposits of Udaipur area, viz., Jhamar Kotra, Maton, Kharbaria, Kanpur, Dakan Kotra, Neemuch Mata and Badgaon. It is, therefore, suggested that the proposed biostratigraphic zonation may be utilised for local as well as regional correlation and for locating new phosphorite-bearing horizons.