Study of Oxygen and Carbon Isotopic Equilibrium in Coexisting Limestone and Crystallised Calcite

Department of Chemistry, Patna University, Patna-5

Department of Chemistry, L. S. College, Muzaffarpur

(Manuscript received 3 June 1972; revised 11 September 1972; accepted 14 November 1972)

Limestone samples associated with crystallised calcite have been studied for O¹⁸/O¹⁶ and C¹³/C¹² variations. The isotopic data are indicative of exchanged marine nature of the samples. The fractionation between the crystallised calcites and the limestones are in the range —1.41 to +1.49 for 0" and —0.80 to +2.95 for C¹³. The ∆O¹⁸_{LS_C} values have been found to be scattered and the scattering in data are indicative of slow processes involved in dissolution and crystallisa­tion under non-isotopic equilibrium. The more positive ∆C¹⁸_{LS_C} values are the consequences of the negative 6 value of the calcite which may arise due to exchange of the HCO^-₃ (from which calcite crystallised) with biogenic carbon dioxide.