GEOCHRONOLOGIC AND GEOCHEMICAL CONSTRAINTS ON THE AGE OF THE JHAMARKOTRA CARBONATES FROM THE ARAVALLI SUPERGROUP, NORTHWESTERN INDIA

Studied Palaeoproterozoic carbonates are impure dolomites from the Jhamarkotra Formation of the Lower Aravalli Group, the Aravalli Supergroup of northwestern Indian shield. The Jhamarkotra carbonates are bounded by the underlying White Mica palaeosol and the overlying Red Ochre palaeosol. The geochronological constraints for the Aravalli Supergroup suggest the 2.1 to 1.9 Ga age. In addition, carbon isotope systematics of carbonates from the Jhamarkotra Formation, Aravalli Supergroup is comparable with that of ca. 2.22-2.10 Ga carbonates. The Jhamarkotra carbonates can be divided into phosphatic and non-phosphatic dolomites. Non-phosphatic dolomites (NPD) have higher carbonate content; contain more Mg, Fe, Sr, Zn, and V and less Ba as compared to phosphatic dolomites (PD).

NPD also show moderate to highly enriched d¹³C values ranging between +1.4 ‰ V-PDB and +11.9 ‰ V-PDB that are localized in few areas (e.g. Ghasiar: N 73°38’; E 24° 42’ and Umra: N 73°46’; 24°30’). d¹³C enrichment in the NPD was prior to deposition of the PD of the Jhamarkotra Formation. The end of the carbon isotope excursion was followed by the deposition of Mn-carbonates, phosphorites, and organic-rich shale worldwide (Bekker et al., 2003). Based on the available geochronological data and new chemostratigraphic data, the Jhamarkotra carbonates are correlative with the ca. 2.22-2.10 Ga sedimentary carbonates worldwide that carry similar carbon isotope signal. The proposed correlation allows narrowing down the age brackets for deposition of the Jhamarkotra carbonates to those corresponding with the end of the ca. 2.22-2.10 Ga carbon isotope excursion on the Fennoscandian Shield between 2.11 Ga and 2.06 Ga (Karhu, 1993).