Application of the change of sterane isomer ratios to the reconstruction of geothermal histories: Implications of the results of hydrous pyrolysis experiments

Abstract

Kinetic data for the change of the C-20 isomer ratio of 5α(H),14α(H),17α(H)-steranes have been derived from a series of hydrous pyrolysis experiments on samples of the lower Toarcian Posidonia shale from northern Germany. The results are compared with other published kinetic data for the same apparent biological marker reaction. It is shown that the sensitivity of these different sets of kinetic data varies drastically in the application to model calculations using predefined geothermal conditions. The difference in sensitivity is hard to estimate from an inspection of the numerical values of activation energy and frequency factor alone. A procedure for the selection of analytical sterane isomer ratios for kinetic assessment using a TTI approach is demonstrated. Error calculations show what level of accuracy can be reached in the prediction of formation temperatures and burial depths when the kinetic data are applied to the reconstruction of geothermal histories of sedimentary basins.