Correlation of Phosphorite and Nonphosphorite Carbonate Sequences of the Lower Aravalli Group, Northwest India: Implications on the Paleoproterozoic Paleoenvironment

Abstract Nonphosphate and phosphate carbonates are prominent constituents of the Lower Aravalli Group metasediments of the Aravalli Supergroup in the northwestern India. The nonphosphatic carbonates are calcitic and dolomitic and exhibit bimodal, moderate, and high 13 C enrichments. These are globally coeval with the Lomagundi–Jatuli event of 2.06 Ga. The moderate 13 C enrichment (up to ∼5‰) is interpreted as an early premature oxygenation event preceding the high 13 C enrichment. The phosphatic carbonates, primarily dolomitic, show 13 C values close to 0‰ and show prolific growth of cyanobacterial stromatolitic colonies. basin-scale microenvironmental differences between phosphatic and nonphosphatic constituents within the Lower Aravalli Group are attributed to change in redox conditions. In this chapter, a review of correlations between phosphate basin (PB) and nonphosphate basin (NPB) is made on the basis of field relationship and chemostratigraphic study. The study suggests that the PBs evolved later to the NPBs. The Lower Aravalli Group carbonates preserve a unique record of stepwise rise in oxygen levels documented from the variations noticed in degree of oxygenation. This is displayed by disparity in 13 C enrichments. Peak levels of oxygen were witnessed with the bloom of cyanobacterial growths mediated by abundance of phosphorus. It is tempting to contemplate that the cyanobacterial colonies clogged enrichment of heavy carbon in the carbonates with reasons inexplicit. Chemostratigraphic sequencing of carbonate sections in the PBs and NPBs reveals paleoenvironmental evolution and simultaneously resolves the problem of correlation between the two.