Petrography and stable isotopic variations in Dalmiapuram Formation of Cauvery Basin, South India: implication on OAE1d

Abstract

Petrography, carbon and oxygen isotopic study was carried out to interpret isotopic variations on the predominant carbonate sequence of the Dalmiapuram Formation of the Cauvery Basin, South India. The common petrographic types identified in the Dalmiapuram Formation range from wackestone to boundstone. The gray shale and limestone members show large variations in d<sup>13</sup>C and d<sup>18</sup>O values (Gray shale member: +1.44 to +2.40 ‰ VPDB, -3.05 to -5.92 ‰ VPDB, respectively; Limestone member: -6.07 to +2.93 ‰ VPDB; -7.08 to -0.39 ‰ VPDB; respectively). In the present study, the carbon and oxygen values are not correlated, which supports the fact that these limestones retain their primary isotopic signatures. In carbon isotope curve, one negative shift is identified in the gray shale member and a positive isotopic excursion is detected in the coral algal limestone (CAL). The observed positive isotopic excursion in the lower part of the CAL correlates with OAE1d and suggests the global nature of the late Albian OAE1d in the Cauvery Basin.