Neogene subsidence rates of the southern Peri Pannonian realm (1D basin modeling): Constraints on the extensional geodynamic drivers of the asymmetric Toplica basin (central-southern Serbia)

Abstract

With the objective to quantify the Neogene extensional geodynamic drivers of the Peri Pannonian Realm s.l., a series of 1D basin models were carried out by integrating the available geological and geochemical data extracted from the landlocked Toplica Basin (central-southern Serbia; Serbo-Macedonian Unit). The modeling was conducted on four wells located immediately south of Jastrebac Mt., in the area of the Toplica Basin. The investigated southernmost point of the Peri Pannonian Ream s.l. (areas surrounding the basin, to the south of rivers Danube and Sava) underwent intense tectonically-driven subsidence episodes, which lasted from the Lower Miocene up to the Pliocene. The restored Neogene burial history (subsidence rates), paleotemperature, and calibrated paleo-heat fluxes (or changes in the ancient crustal or basal heat flow) indicated a two-staged crustal stretching of the wider Toplica area. The combined tectonic, i.e., thermal subsidence, resulted in a very high sedimentation rate, having an average ca. 300–400 m/Ma (Čučale unit). The intense tectonically-driven subsidence is consistent with the involvement of extensional processes, affecting the crustal and lithospheric layers of the retreating Adria/Dinarides, amplified by a distant Carpathian rollback stage. The regional extension led to the asymmetric opening and the formation of the Toplica Lower Miocene mesosaline to the freshwater lacustrine system. Higher participation of mixed microbiologically reworked/terrestrial organic matter incorporated in oil-prone Type II kerogen mainly characterized the investigated lacustrine sedimentary sequence. The latest Oligocene–earliest Neogene subsidence onset was characterized by elevated temperatures, affecting the early development of the oil window (ca. at 16 Ma). The 1D models also showed that the Lower Čučale unit achieved ca. 50% transformation ratio for the Type II organic matter. The two intra-Neogene extensional episodes suggested the existence of the Early Neogene “syn-rift” stage, followed by a thermal sagging. The Neogene continuous thinning of the overriding Serbo-Macedonian continental crust contributed to the “negative inversion” of the former pre-Neogene nappes. Therefore, Neogene tectonic reactivation induced contemporaneous subsidence, further allowing the extensional rise of the Jastrebac core complex.