The age of the Sarmatian–Pannonian transition in the Transylvanian Basin (Central Paratethys)

A marked paleoenvironmental change took place at the beginning of the late Miocene in the Central Paratethys, with dominantly marine Sarmatian successions grading rapidly into mainly brackish Pannonian deposits. A long and excellently exposed section comprising the Sarmatian–Pannonian transition has been investigated at Oarba de Mureş in the Transylvanian basin (Romania). In this paper, we focus on both radiometric and magnetostratigraphic dating to provide a chronology for the Sarmatian–Pannonian transition in Transylvania. Two volcaniclastic layers, located approximately 40 m below the Sarmatian–Pannonian transition, yield excellent 40Ar/ 39Ar ages. The weighted mean plateau age for biotite and sanidine separates provided isotopic ages of 11.62 ± 0.12 Ma and 11.65 ± 0.13 Ma. This implies deposition during the magnetic chron C5r.2r, which is in agreement with the magnetostratigraphic results of the Oarba de Mureş composite section. Rock magnetic analyses indicate greigite as the main magnetic carrier, with characteristics very similar to the magnetosomal greigite found in the Carpathian foredeep. The newly obtained chronology at Oarba de Mureş constrains the age of the Sarmatian–Pannonian transition in the Transylvanian basin to 11.3 ± 0.1 Ma, slightly younger than the 11.61 Ma postulated in the Styrian and Vienna Basins.