The application of illite crystallinity(IC) to reconstruct thermal history of the marine carbonates: a case study from northeast Sichuan basin, southwest China

Abstract

Paleogeothermometer is one of the uppermost parameters of the reconstruction of thermal history in sedimentary basins. Because there is no suitable paleogeothermometer in the Lower Palaeozoic sequences which are composed of highly and excessively mature carbonates, the reconstruction of thermal history and hydrocarbon generation history is a problem impeding the pace of petroleum exploration of the marine carbonates in China all the time. This paper aims at researching the possibility of illite crystallinity(IC) as the paleogeothermometer of marine carbonates. By thermal simulation experiments, the quantitative relationship between illite crystallinity(IC) and vitrinite reflectance (Ro) has been established and applied to the reconstruction of thermal history in Northeast Sichuan Basin. The result of simulation experiments shows that in Northeast Sichuan Basin, the value of paleoheat flow was 53.5mW/m2 at Middle Silurian which increased gradually from Middle Silurian to Late Permian, and from the beginning of Late Permian it went up to the maximum abruptly (65.3mW/m2). After that it dramatically decreased, reaching 50.3mW/m2 at Early Triassic. The value of paleoheat flow decreased gradually up to 44mW/m2.