Limits of application of the reaction kinetic method in paleogeothermics

Abstract

The applicability of organic geochemical reactions in thermal history reconstruction of basins is investigated. The requirements of kinetic parameters of the reactions suitable to study the basins of temporally increasing temperature, are discussed in detail. Two basin types with extreme heating rates, i.e. a rapid and a slow heating rate, are discussed. The thermal history of the basins is studied on the basis of a simplified model, in which the heating rate proved to be a constant value before τ₀ moment. At that moment, the heating rate was suddenly increased to the recent value.

The mathematical description of the model is given. Applying this to reactions of different ΔH* activation energy and of different A pre-exponential factor it is demonstrated that to study the basins of increasing temperature the reactions of low activation energy and of low pre-exponential factors are more suitable to follow the thermal history. In the case of a slow heating rate, these reactions are suitable to trace the thermal history up to several 10 million years while in the case of a high heating rate this is possible only to several million years if the reaction parameters are exactly known.

The uncertainties deriving from the inaccuracies of measurement data are also studied, i.e. how these affect the time interval to be determined.

Finally, it is stated that in order to carry out a reliable thermal history reconstruction, the investigation should include the exact determination of parameters of the reactions of vitrinite-type, i.e. of low activation energy and of small pre-exponential factor. Reliable reconstruction free of contradictions can be carried out only in possession of a suitable number of data and by also taking into account the error calculations.