Organic matter thermal maturity analysis and its modelling in the Paleozoic–Mesozoic section of the Miechów Trough (southern Poland) – implications for thermal evolution and petroleum exploration.

Abstract

In this work, vitrinite reflectance analyses and 1-D thermal maturity modeling of the Paleozoic–Mesozoic section of the Miechów Trough allowed to explain the thermal history that influenced hydrocarbon generation. The thermal maturity of organic matter dispersed in the Lower Paleozoic to Mesozoic sedimentary successions is in the range of 0.49 to 3.06% of mean random vitrinite reflectance. The estimated maximum palaeotemperatures of analyzed rocks are in range from ~70 to ~290°C. The Variscan thermal regime was different than Mesozoic one. At least two fluid flow events might be identified. Maximum palaeotemperature (~120-290 ºC) in the Silurian to Lower Carboniferous sedimentary succession was achieved in the late Carboniferous to early Permian. The Late Variscan tectonics activity may have been triggered by increased heat flow that was, at least partly, connected with fluid circulation. Maximum palaeotemperature (~70-150 ºC) of the Zechstein to Jurassic sedimentary succession was achieved during Mid-Late Jurassic. It was likely caused by a hot fluid flow event. The hydrocarbon potential of Paleozoic source rocks was exhausted before the Upper Jurassic and Cenomanian reservoir rocks and traps were formed. Consequently, the majority of hydrocarbons generated during the pre-Late Jurassic stages were lost. Thus, the hydrocarbons contained in Mesozoic reservoirs were charged by younger source rocks, such as the Oligocene Menilite Shales from the Outer Carpathians.