A model for the evolution of the elemental composition of kerogen of proterozoic deposits in the McArthur basin (Australia) under the effect of trap intrusions

In the last few decades a number of mathematical models for the transformat ion of dispersed organic matter (DOM) and formation of hydrocarbons (HC) ha ve been constructed. Most of them permit estimation of the total yield of d estruction products and do not describe changes in DOM composition during t ransformations. The models for the dynamics of these changes are usually in tricate and cumbersome; their application involves some difficulties associ ated with determination of kinetic parameters of reactions. In this paper w e present a simple model for the transformation of kerogen of type II, perm itting one to follow its compositional changes. The initial DOM tentatively involves six independent components; on destruction of the DOM they produc e H2O, CO2 (at the beginning and at the end of transformation), a hydrocarb on CnHm, methane, and a carbonized residue (kerogen). The process of transf ormation of each component is described by a series of independent parallel first-order reactions. To develop the model, we used data of elemental analysis of DOM from the We llcarry Formation in the McArthur basin, Australia. We reconstructed the te mperature history of the studied samples which had transformed under the ef fect of trap intrusion in the sedimentary cover of the basin. The proposed model describes, in a first approximation, the processes that run in kerogen of type II during its transformation but takes little accoun t of the effect of the temperature history of the kerogen on ifs elemental composition.