| Popis: |
A reconnaissance isotope survey has been carried out on sedimentary carbonate formations from the middle and late Proterozoic ( ∼ 1.0 to ∼ 2.0 Ga ) Kaladgi, Badami and Bhima Groups of Karnataka, southern India. While the δ 13 C values of the Kaladgi dolomites and limestones ( 0.3 ± 1.2%o [PDB]) are consistent with an interpretation of this sequence as a ‘normal’ marine carbonate facies as previously inferred from geological and sedimentological evidence, the markedly increased average of 3.4 ± 0.5%o [PDB] for the dolomite members of the overlying Badami and Bhima Groups suggests genetic relationships to a primary hypersaline (evaporitic) environment. The δ 18 O values of the two carbonate provinces are very similar ( 21.7 ± 1.3%o and 21.1 ± 1.2%o [SMOW], respectively), displaying the 18 O-deficiency typical of Precambrian carbonates. |
