Arjan de Leeuw

Paleomagnetic analyses on Badenian–Sarmatian drill cores from the North Carpathian foredeep (Middle Miocene, Poland)

Accurate dating of the Badenian–Sarmatian transition, a boundary between two regional Middle Miocene stages of the semi-isolated Paratethys Sea, is crucial to understand what event caused the corresponding major turnover in faunal assemblage at that point in time. The general opinion is that this event resulted from a sudden isolation of the Eastern Paratethys from ocean water, due to the closure of the Eastern Anatolian seaway to the Indian Ocean, but it remains debated if the final isolation had a tectonic or climatic cause. This pilot study presents paleomagnetic analyses of two drill cores from the North Carpathian Foredeep in Poland that straddle the Badenian–Sarmatian transition. Rock magnetic experiments, including thermomagnetic runs in air on a Curie balance, and hysteresis measurements on a MicroMag, indicate that the dominant magnetic carrier is the iron sulphide greigite. This is in agreement with the observed gyroremanence obtained during alternating field demagnetization above 40 mT. Alternating field and thermal demagnetization results are in good agreement and show a weak, mixed-polarity, signal for most of the Badenian, rapidly shifting to a much stronger and dominantly normal polarity signal in the Sarmatian part of the cores. First order reversal curves diagrams indicate that the greigite in the Sarmatian part is clearly of diagenetic origin, it thus most likely concerns a secondary overprint by the present-day field that cannot be used for magnetostratigraphic correlations. We conclude that the Paratethys-wide paleoenvironmental change that occurred at the Badenian–Sarmatian transition had probably also created different conditions for the formation and/or preservation of magnetic minerals

Micropaleontological response to the changing paleoenvironment across the Sarmatian-Pannonian boundary in the Transylvanian Basin (Miocene, Oarba de Mureş section, Romania)

Micropaleontological response to the changing paleoenvironment across the Sarmatian-Pannonian boundary in the Transylvanian Basin (Miocene, Oarba de Mureş section, Romania) The Sarmatian-Pannonian transition has been investigated in Section A of Oarba de Mureş in the central Transylvanian Basin. Micropaleontological assemblages are diagnostic for different environmental settings and demonstrate a clear zonation, which was used to reconstruct the genetic units. Five stratigraphic sequences were described and subdivided based on the microfossil assemblages. Transgressive intervals were documented by five-chambered and biserial planktonic foraminifera, normal regressions by assemblages with abundant mysid, dasyclads, diatoms, and benthic rotaliid foraminifera, while the forced regressions are characterized by reworking. The Sarmatian-Pannonian boundary (11.3 Ma) is clearly documented by microfossils and is calibrated with radiometric and magnetostratigraphic data. A new interpretation for the interbasinal correlation is proposed by synchronizing the top of the Central Paratethyan Sarmatian with the top of the Eastern Paratethyan Bessarabian.

Isotopic Events Preceding the Badenian Salinity Crisis in the Central Paratethys, Middle Miocene, Poland

Middle Miocene foraminifera from the Upper Silesian Basin (Poland) have been analysed. The stable oxygen and carbon isotope signatures in Uvigerina, Globigerina bulloides, and Globigerinoides quadrilobatus show a consistent tendency of directional changes. There is an abrupt, strong increase in the proportion of heavy isotopes of δ18O recorded about 10 m below the Badenian evaporites.