Abstract
This PhD thesis presents new chronostratigraphic results from the Dacian Basin and adjacent regions as part of the Paratethys paleoprovince. In the first three chapters, a new chronology for the Upper Miocene to Pliocene deposits (approximately 8 to 3 Ma) of the Dacian Basin is presented based on high resolution
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magneto-biostratigraphic data from the Romanian Carpathians foredeep. The new age control permits the calculation of accumulation rates for each polarity zone, which shows a significant increase at approximately 5.8-6.0 Ma in the eastern Carpathians. The calculated values for the average duration of the observed sedimentary cycles are very close to that of precession (21.7 kyr), indicating that the sedimentary cycles from the eastern Carpathian foredeep are astronomically forced. Consequently, the main Mio-Pliocene stage boundaries are now accurately dated, resulting in new ages for the Meotian/Pontian boundary at 5.8 Ma, the Pontian/Dacian boundary at 4.8 Ma, and the Dacian/Romanian boundary at 4.1 Ma. This allows a chronostratigraphic correlation to the Mediterranean event stratigraphy, which shows that the Messinian Salinity Crisis is represented by the lower part of the Pontian Stage, but that the main palaeoenvironmental and biostratigraphic changes in our sections do not indicate a relation with the dramatic desiccation and reflooding events of the Mediterranean. The following two chapters deal with the tectonic and geodynamic implications for the Carpathian arc. Paleomagnetic rotation results indicate that: (1) systematic ~30 clockwise rotations occurred in the southern Carpathians after ~13 Ma; (2) tectonic rotation had ceased in the eastern and southern Carpathians regions after ~9, Ma except in the Bend Area where recent clockwise rotations took place after ~5 Ma. The anisotropy of the magnetic susceptibility (AMS) data from the Romanian Carpathian foredeep reveal compression directions perpendicular (radial) to the Carpathian orogenic arc. AMS analyses along the contact between the orogenic nappe pile, the lower plate and the overlying sediments, indicate that two factors are critical for the distribution of the stress field during and after collision: the inherited highly bended plate geometry and Quaternary deformation. Chapters 6 and 7 deal with the paleoenvironment aspects of the study region. Detailed rock magnetic investigations and scanning electron microscope (SEM) analyses indicate that the major magnetic iron sulphide mineral is greigite. It is argued that (most of) the greigite was formed under early diagenetic conditions, i.e. within 1000 years of deposition of the sediment, and that it thus can be considered as a reliable recorder of the palaeomagnetic signal. Trace-element contents and Sr isotopes of Cyprideis torosa valves and molluscs shells were analysed to depict changes in seawater geochemistry and paleoenvironment of the Eastern Paratethys. The recorded values decrease with decreasing age of the samples, which is contrary to the increasing trend for the Sr curve for marine waters. The cause of the deceasing 87Sr/86Sr values suggest change in the water input into the basin. Finally, the last two chapters deal with the Sarmatian/Pannonian boundary in Transylvania and Croatia, located in the central Paratethys.
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