FORMATION OF C-13 C-12 ISOTOPE RATIOS IN SPELEOTHEMS - A SEMIDYNAMIC MODEL

A theoretical approach towards predicting the carbon isotope composition of carbonate cave deposits is presented. The proposed model simulates time variations of both the chemical and isotopic composition of the carbonate solution and deposited calcite in the course of CaCO3 precipitation. Two phases of the precipitation process are distinguished and treated separately: initial outgassing of the solution until a certain degree of supersaturation of CO32- ions is reached and subsequent precipitation of CaCO3 related to further outgassing. Precipitation rates of CaCO3 predicted by the model agree fairly well with literature data. The model predicts δ13C values of deposited calcite within a range of c-16 to +3‰ depending on temperature, chemical and isotope parameters of the initial solution and actual degree of the precipitation process. -Authors