A comparison of two vitrinite reflectance methods for estimating paleotemperature gradients

Abstract

Two methods of determining the paleogeothermal gradient from vitrinite reflectance versus depth data are compared by application to 8 boreholes. One method, developed by BUNTEBARTH proposes that vitrinite reflectance is essentially proportional to depth (for constant burial rate and thermal gradient), whereas the second method, developed by MIDDLETON, proposes that vitrinite reflectance increases exponentially with depth. The two methods give similar paleothermal gradients for 2 boreholes from 8, where the subsidence rate is about 0.08 km/Ma. The difference in another 3 boreholes is less than 15 K/km. A poor fit is found for 3 boreholes in German basins which subsided or began to subside during the Upper Carboniferous. The difference in the methods probably results from the simplification and from differences in the principles used in the two methods.