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Sedimentary Basin Fill of Lake Pannon in the Eastern Part of Drava basin

Lake Pannon was filled by rapid sedimentation during the Late Miocene to Pliocene. The initially vast and deep lake was finally infilled by large sediment input, sig- nificantly exceeding the creation of accommodation space. Despite various sedimentological, paleontological and seis-mic stratigraphy-related research, there is still little know-ledge about different factors that were shaping the geome-try of this basin infill. These uncertainties can be resolved by an integrated study of the clinoforms system. More precisely, it can help in better understanding of the inter-play between shelf- edge trajectory, direction of sedimentary transport, spatial distribution of paleoenvironments, and basin morphology (paleobatimetry) combined with local tectonic events (TOMLJENOVIĆ & CSONTOS, 2001).The study is situated in the Eastern part of the Drava basin, in the area between Slatina and Valpovo. Numerous seismic horizons, mapped on 3D seismic data, were used for the construction of structural and thickness maps in the time domain. Seismic attributes, like RMS amplitude and spectral decomposition, were applied on the data as well. For the purpose of well to seismic ties, VSP and checkshots data were used. Geological age estimation of seismically defined and mapped horizons is based on existing stratigraphic logs from deep wells in the area. Some of these data are old. Based on seismic facies, two generations of clinoforms can be distinguished, a thicker older, and a thinner younger set. The first set is composed of 255 ms high sigmoidal cli- noforms in the western area, indicating a water depth of ca. 610 m. During their deposition, the shelf- margin trajectory was flat, until maximum regression was reached. Then, the second generation of clinoforms appears, showing oblique shape in the west, with downlap features to the east. Their height is increasing in the same direction, where clinoforms start to develop sigmoidal architecture, like in the older thicker set, with an interpreted depth of water column of ca. 190 m to 270 m.Seismic sections, structural, thickness and seismic at-tributes maps, show that delta progradation happened be- fore or during the initiation of basin inversion in this area (BALÁZS et al., 2016 ; SAFTIĆ et al., 2003). Prograding slope reached this area between 6.8 Ma and 5.3. Ma ago, and then, during the inversion, the whole studied sequence was tilted to the southwest. Observations confirmed that delta progradation occurred from the present day northwest and continued to the southeast. Distributary channels and basin floor lobes orientation are indicating that sedimentary input patterns may be gently influenced by inherited structures. Furthermore, different stratal stacking patterns are revealing lacustrine base level fluctuations. The flat trajectory of first clinoform progradation suggests steady base level, which continued to maximum regression, when the slope related canyons also developed (SZTANÓ et al., 2013). This event was followed by base level rise of more than 200 m. As a re- sult, the second generation of smaller clinoforms prograded on the new shelf and over the old slope. Similar events of base-level rise are common in Lake Pannon, nearby in the northern part of the Drava basin (UHRIN & SZTANÓ, 2012), yet far less than 100 m (SZTANÓ et al., 2013 ; BALÁZS et al., 2018), while much larger in the Eastern part of the Great Plain. Moreover, infilling patterns were probably influenced by local structures and basin topogra-phy, possibly connected to the large- scale tectonic events in this marginal part of Pannonian basin system.Despite many similar studies were done inside the in-dustry (IVKOVIĆ, 2000), this is the first published seis-mic study with focus on timing and factors controlling the morphological shelf-slope progradation, in the south-western part of the Pannonian basin system. Results are showing complex infilling patterns and changing base level throughout the time of progradation. Therefore, dating and palynological studies on well and outcrop data, will play a crucial role in solving the distribution of different paleoen-vironments through space and time, thus confirming the interpretation of depositional system that is in such a way manifested on seismic data.

Lake Pannon, Drava basin, morphological shelf-slope progradation, infilling patterns

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