Burial history and hydrocarbon generation model of the Lower–Middle Jurassic sediments in the Tarnovo depression

Abstract

This study deals with the geodynamic evolution in the Tarnovo depression, contributes to a better understanding of the burial and thermal history, and gives a model of the generation of hydrocarbons from the Lower–Middle Jurassic rocks. The implications of the complex heat flow scenario for the timing of hydrocarbon generation from the Stefanets Member of the Etropole Formation in selected sections were also analyzed. The Tarnovo depression is defined as a small tectonic unit in the central part of the South Moesian Platform margin developed mainly during the Early–Middle Jurassic. Therefore, the sediment subsidence during the Early–Middle Jurassic is largely a consequence of the tectonic processes in an extensional basin with tilted, fault-bounded, and eventually rotated blocks. There is a trend of increasing tectonic and basin subsidence in southern direction, observed in modeled well sections. The Lower–Middle Jurassic rocks enter the “oil window” in the late Barremian, Hauterivian, or even the late Valanginian towards the south, starting active generation in the middle Aptian. The model shows that gas generation is possible only in the southern and marginal zones of the Tarnovo depression. Among the sequence, the Stefanets Member of the Etropole Formation (Aalenian–early Bajocian in age), composed of shales and siltstones, possesses source rock qualities and good hydrocarbon generation potential. The research model argues for peak of the oil generation from the Stefanets Member at the end of the Barremian up to the Albian to the north and gas generation starting in the Barremian and continuing during the Cenozoic only in the southern part.