Timing and facies analysis of the Middle Miocene Badenian flood deposits in southern Central Paratethys—insights from KC-4 borehole, western Serbia

We provide new insights into the Badenian transgression (Langhian to early Serravallian) in western Serbia, focusing on the marginal part of the Central Paratethys. Nano- and microfossils (calcareous nannofossils, foraminifers, and ostracods) are used along with U–Pb radioisotope dating of a tuff layer near the Badenian lower boundary to reconstruct the timing of the middle Badenian marine flooding. Our findings reveal the occurrence of a second (main) Badenian transgression (TB2.4 third-order cycle) around 14.2–13.8 million years ago. The Badenian marine waters flooded the continental formation of the poorly defined early-middle Miocene sequences. The sedimentary succession (KC-4 core, 490–205 m) is grouped into five units (I–V). The lower two units (I–II) are non-marine alluvials that are characterized by coarse-grained siliciclastics. Unit III represents the basal coarse-grained clastites and sandy limestones of the initial shallow-marine environment and unit IV consists of marls and high-calcitic fine-grained clastites of neritic facies. Unit V contains carbonaceous marlstone and limestone deposited in a restricted marine shallow-water environment. Biostratigraphically, over 154 m of dominantly fine-grained clastites (units III–IV) confirm the presence of the marine middle and upper Badenian. Its lower part (366–325 m) corresponds to the nannofossil NN5 Zone and the youngest Upper Lagenidae Zone (local Zone Ammonia viennensis–Trilobatus trilobus ), as well as a part of the Spirorutilus carinatus Zone. The upper part (325–212 m) corresponds to the nannofossil NN6 Zone as well as the foraminifer Bulimina-Bolivina Zone. The U–Pb age for zircon grains is 14.58 ± 0.08 Ma. Petrographic data from the tuff sample show a strong correlation with volcanic records along the S-SW margin of Central Paratethys (N Croatia, NE Bosnia, and central Serbia). The U–Pb age as well as tuff glass composition and mineralogy suggest the possible source of the tuff as from the Subotica area (N Serbia) or the Bükkalja Volcanic Field in NE Hungary. Graphic abstract