Phosphate-bearing stromatolites of the Precambrian Aravalli phosphorite deposits of the Udaipur region, their environmental significance and genesis of phosphorite

1.1 Tectonic Evolution and Major Global Earth-Surface Palaeoenvironmental Events in the Palaeoproterozoic

“…The most remarkable c. 2.0 Ga occurrence is the Jhamarkotra stromatolitic phosphorites (Fig. 1.2y) containing up to 35 wt.% P 2 O 5 and reaching 25 m in thickness in the Lower Aravalli Group in Rajasthan, India (Banerjee 1971;Chauhan 1979). Similar age phosphorites, though in redeposited, clastic form ( Fig.…”

Structural geometry of uraniferous rocks in the Umra area, Aravalli Supergroup, India

“…This unit directly overlies the basement surface in areas not completely covered by the Debari Formation. The presence of varieties of stromatolites in the carbonates indicates deposition in a subtidal, tidal and supratidal flat environment (Chauhan, 1979). Frequent lithofacies changes of carbonates and quartzites, and the presence of ripple marks and cross bedding in the calcareous arenites (Roy and Paliwal, 1981) also indicate a shallow-water deposition environment.…”

The influence of magnesium ions during the formation of stromatolitic phosphorites of Udaipur, Rajasthan, India

“…Some small euhedral crystals of dolomite up to 100 lam size occur in the cement. The petrography of the deposits is presented in more detail elsewhere (Chauhan, 1979;Chauhan & Sisodia 1984, in press;Sisodia 1986). …”

“…1) are unusual in being strictly confined to stromatolites. They were deposited in marine epicontinental subtidal to supratidal environments and now occur as a series of isolated deposits around the city (Chauhan 1979;Banerjee et al 1980;Roy & Paliwal 1981;Sisodia 1986). The stromatolites are composed of carbonate and phosphate with both components in quite variable proportions, such that they can be classified as stromatolites with dominantly phosphate or dominantly carbonate compositions, or as stromatolites having alternate phosphate and carbonate laminae.…”