3RD-ORDER MIDDLE MIOCENE EARLY PLIOCENE DEPOSITIONAL SEQUENCES IN THEPROGRADING DELTA-COMPLEX OF THE PANNONIAN BASIN

Few studies exist in the geologic literature that show the distributio n of seismic facies and depositional sequences within a lacustrine bas in. The Pannonian Basin of Central Europe offers a unique opportunity to evaluate the influence of the eustatic signal on lacustrine deposit ion. Seismic stratigraphic and sedimentological studies indicate that the Middle Miocene-Early Pliocene infill of the transtensional Pannoni an Basin was formed by large delta systems. Systematic sequence strati graphic analysis of 6000 km of reflection seismic data and more than 1 00 hydrocarbon exploration wells in Hungary allowed the identification of twelve third-order sequence boundaries in the late Neogene sedimen tary fill. This number of depositional sequences corresponds to that o f the published global eustatic curve for this time period. Furthermor e, based on magnetostratigraphic and radiometric data, the ages of the se depositional sequences can be tentatively correlated with the globa l eustatic curve. The Pannonian Basin became isolated from the world s ea at the Sarmatian/Pannonian (11.5 Ma) boundary and formed a large la ke. The stratal patterns and sedimentary facies of individual systems tracts within the lacustrine sequences display the same characteristic s as marine depositional sequences. The relatively low rate of thermal subsidence and the high rate of sediment supply resulted in a good se quence resolution. Within the third-order sequences higher-order seque nces can be recognized with an average duration of about 0.1-0.5 Ma.