Tectonic versus climatic control on the evolution of fluvio-deltaic systems in a lake basin, Eastern Pannonian Basin

Abstract

The Pannonian Basin is a back-arc lake basin, situated inside the Central European Carpathian loop, surrounded by the orogenic belts of the Eastern Alps, Carpathians and Dinarides. Integrated stratigraphical and sedimentological research reported here focuses on palaeogeographical evolution, and particularly the response of the fluvio-deltaic systems to climatic and tectonic controls in the Late-Neogene sedimentary succession, in the eastern part of the Pannonian Basin. This work has been carried out using subsurface data including regional composite seismic profiles and well-logs. Dip sections were studied to define the stratigraphical architecture, depositional environments and sequence stratigraphy, and to interpret the sedimentary evolution of the area. The eastern Pannonian Basin is characterized by sediment input from the north–east which was one of the main routes of the fluvial-deltaic systems entering and progressively filling Lake Pannon from 11.6–2.6 Ma. The formations studied were deposited in environments that ranged from the deep-water basin plain, slope, delta front, and coastal plain to alluvial plain, causing the deposition of characteristic lithofacies associations, and characteristic biofacies. These form laterally continuous lithofacies units that can be correlated through the basin. All depositional facies units have considerable thicknesses (300–1000 m) in the deepest parts of the sub-basins. Sequence stratigraphical interpretation was carried out correlating 3rd and 4th-order sequences (Ma to ky in range) through a regional composite seismic profile network in the dip direction. Stratigraphical architecture and sedimentary facies indicate that the 3rd-order cycles were controlled by tectonic driving forces, while 4th-order cycles were probably driven by large-scale climatic changes within the Milankovitch band. In the 3rd-order time interval Pa-3 between 9.1 and 6.8 Ma, a major tectonostratigraphic event occurred, highlighting the role of strike-slip faulting-related transtensional subsidence in the Derecske sub-basin, superimposed on the regional post-rift thermal subsidence of the Eastern Pannonian region. The substantial base level fall at SB Pa-4 at 6.8 Ma (over 200 m, perhaps amplified by subsequent tectonic movements) can be related to the onset of a new compressional phase of structural evolution in the basin.