Paleogeographic evolution of the Southern Pannonian Basin: 40Ar/39Ar age constraints on the Miocene continental series of notthern Croatia

The Pannonian Basin, originating during the Early Miocene, is a large extensional basin incorporated between Alpine, Carpathian and Dinaride fold-thrust belts. Back-arc extensional tectonics triggered deposition of up to 500-m-thick continental fluvio-lacustrine deposits distributed in numerous sub-basins of the Southern Pannonian Basin. Extensive andesitic and dacitic volcanism accompanied the syn-rift deposition and caused a number of pyroclastic intercalations. Here, we analyze two volcanic ash layers located at the base and top of the continental series. The lowermost ash from Mt. Kalnik yielded an 40Ar/39Ar age of 18.07 ± 0.07 Ma. This indicates that the marine-continental transition in the Slovenia-Zagorje Basin, coinciding with the onset of rifting tectonics in the Southern Pannonian Basin, occurs roughly at the Eggenburgian/ Ottnangian boundary of the regional Paratethys time scale. This age proves the synchronicity of initial rifting in the Southern Pannonian Basin with the beginning of sedimentation in the Dinaride Lake System. Beside geodynamic evolution, the two regions also share a biotic evolutionary history: both belong to the same ecoregion, which we designate here as the Illyrian Bioprovince. The youngest volcanic ash level is sampled at the Glina and Karlovac sub-depressions, and both sites yield the same 40Ar/39Ar age of 15.91 ± 0.06 and 16.03 ± 0.06 Ma, respectively. This indicates that lacustrine sedimentation in the Southern Pannonian Basin continued at least until the earliest Badenian. The present results provide not only important bench marks on duration of initial synrift in the Pannonian Basin System, but also deliver substantial backbone data for paleogeographic reconstructions in Central and Southeastern Europe around the Early–Middle Miocene transition

A revision of the genus Europicardium

The cardiid genus Europicardium Popov, 1977 was introduced for a small group of Cenozoic species from Europe, but remained almost unknown in the western literature until about 15 years ago, and its type species, Cardium multicostatum Brocchi, 1814, continued to be cited mainly as Trachycardium multicostatum. Many records are available for this species from the Miocene of Europe, but most are based on several distinct, often misidentified species. In the present revision, based on museum material, the taxonomy of Europicardium is discussed and the identity of its type species is fixed. Seven species are assigned to Europicardium: E. multicostatum (Brocchi, 1814), E. miorotundatum (Sacco, 1899) (lectotype designated), E. miocaudatum (Sacco, 1899), E. polycolpatum (Cossmann & Peyrot, 1912), E. pseudomulticostatum (Zhizhchenko, 1934), E. badeniense (Kokay, 1996) and E. hoernesi sp. nov. from the middle Miocene of Austria. However, literature records and museum material suggest the occurrence of additional species and the need for further investigation. The oldest record of Europicardium is from the early Miocene of the Aquitaine Basin, from where the genus likely spread into the Mediterranean and throughout the Paratethys. Europicardium reached a maximum diversity in the early middle Miocene (Badenian) of the Paratethys, probably in relation to the Miocene Climatic Optimum, and also with the complex and variable palaeogeography of the Paratethys, which promoted differentiation and diversity. Europicardium disappeared from the Paratethys when it became a freshwater basin in the late Miocene, and from the Mediterranean due to the Messinian Salinity Crisis. The last European species was E. multicostatum, which arrived in the Mediterranean from the adjacent Atlantic with the post-Messinian recolonization, and became extinct in the Pleistocene due to climatic deterioration. At the present day, Europicardium occurs in the tropical waters of West Africa, with three specie