We SRS1 11 3D Visualization of Miocene Tectonic Subsidence in the Northern and Central Vienna Basin Using BasinVis 1.0

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1 We SRS1 11 3D Visualization of Miocene Tectonic Subsidence in the Northern and Central Vienna Basin Using BasinVis 1.0 E.Y. Lee* (University of Vienna), J. Novotny (Brown University) & M. Wagreich (University of Vienna) SUMMARY This study analyzed and visualized data from 219 wells using a MATLAB-based program BasinVis 1.0 for the tectonic subsidence evolution of the northern and central Vienna Basin. Subsidence of the study area resulted in 3D subsidence depth maps and rate maps of tectonic subsidence in seven successive stages. Due to the position, the Vienna Basin has a complex evolution history from the piggy-back basin phase (Early Miocene) to the pull-apart basin phase (Middle Late Miocene). The 2D/3D maps generated in this study provided insights into the evolution of the Vienna Basin, which is closely related to changes in the changing regional stress field and basin structural setting. In the piggy-back basin phase, the tectonic subsidence was shallow, E-W/NE-SW trending, and restricted to small depressions. In the late Early Miocene, the Vienna Basin changed to a pull-apart basin system with wider and deeper tectonic subsidence by sinistral strike-slip faults and related normal faults. After almost stopped tectonic subsidence of the early Middle Miocene, the development of the Vienna Basin was controlled and accelerated mainly by NE-SW trending synsedimentary normal faults, especially the Steinberg fault. The Late Miocene was characterized by the slowing down of tectonic subsidence.

2 Introduction The Vienna Basin is a Neogene basin of about 200 km length and 55 km width, situated between the Eastern Alps, the Western Carpathians, and the Pannonian basin system (Figure 1). Due to its special location, the basin has been influenced by the evolution of each of these structural systems. The basin is characterized by four distinct tectonic phases; 1) Early Miocene piggy-back basin, 2) Middle - Late Miocene pull-apart basin, 3) Late Miocene - Pliocene compression and basin inversion, and 4) Quaternary basin formation (Figure 2). This study analysed a detailed regional subsidence history of the northern and central parts of the Vienna Basin to understand the tectonic evolution. Furthermore, the results of this study are compared with previous studies either covered the basin only locally or focused more on surrounding areas with only sparse well data. Compared to other publications on this topic, our study covers an extensive region of the basin and provides a more accurate analysis through the high density of considered boreholes, more realistic porosity-depth relations, and the 3D visualization by using a MATLAB - based program BasinVis 1.0 (Lee, 2015). Figure 1 Tectonic and structural sketch map of the Vienna Basin (revised from Wessely et al. 1993). a) Study area. The base depth map of the Neogene fill visualized by BasinVis 1.0. Locations of wells (black dots: wells reaching the pre-neogene basement, gray dots: wells reaching the Miocene basin fill, and white dots: synthetic wells) and a cross-section are shown. AT: Austria, SK: Slovakia, CZ: Czech Republic, VBTF: Vienna Basin Transfer Fault system. b) Geologic cross-section (revised from Beidinger and Decker 2014). Data and Methods The visualized region covers an area of 40 x 60 km in the northern and central parts of the Vienna Basin. The sediments thickness of each stages were arranged from 219 wells, and 24 synthetic wells were used for missing well-data in some areas. These data were evaluated and visualized with BasinVis 1.0 for 3D subsidence depth maps and 2D subsidence rate maps. For the tectonic subsidence analysis, this study used new porosity-depth relations evaluated geophysically for the Vienna Basin. Regional water-depth variations were taken from Sauer et al. (1992).

3 Tectonic Subsidence of the Vienna Basin The tectonic subsidence was visualized in seven successive stages based on the regional Central Paratethys chronostratigraphy for the Miocene (Figure 2); 1) Eggenburgian-Ottnangian (c Ma), 2) early Karpatian (c Ma), 3) late Karpatian (c Ma), 4) early Badenian (c Ma), 5) late Badenian (c Ma), 6) Sarmatian (c Ma) and 7) Pannonian (c Ma). During the Eggenburgian Ottnangian, the tectonic subsidence was minor showing low rates (Figure 3A). Subsidence spread over the study area, however, was localized in EW trending small areas. The relatively high subsidence area, found regionally at the southwestern corner of the study area, is correlating with the location of the deltaic-brackish complex (Bockfliess formation). In the early Karpatian, the study area showed locally increasing tectonic subsidence (up to 0.5 km deep), and the subsidence took place in a more NE-SW trending structural confinement (Figure 3B). During the late Karpatian, the tectonic subsidence was considerably high in the study area, especially in the areas between the Steinberg fault and the Laksary fault and along the Leitha-Láb fault system (Figure 3C). Figure 2 Stratigraphy and evolution of the Vienna Basin in the Miocene (revised from Lee, 2015). Figure 3 3D visualization of tectonic subsidence during the Miocene. 3D tectonic subsidence depth models (above) and 2D tectonic subsidence rate maps (below). The Alpine-Carpathian nappe borders are shown with blue lines, and the location of faults with black lines.

4 Piggy-back basin phase: A. Eggenburgian Ottnangian (c Ma) B. Early Karpatian (c Ma) Pull-aparting phase: C. Late Karpatian (c Ma) Pull-apart basin phase: D. Early Badenian (c Ma) E. Late Badenian (c Ma) F. Sarmatian (c Ma) G. Pannonian (c Ma) After the large scale subsidence phase, the early Badenian tectonic subsidence almost stopped with low rate (0 0.1 km/ma) (Figure 3D). From the late Badenian, the high tectonic subsidence commenced along the Steinberg Fault (Figure 3E), and the Spannberg ridge uplifted during the late Karpatian also subsided from this time onwards. However, the high rate (more than 0.5 km/ma) of the tectonic subsidence is more restricted to the Zistersdorf depression. During the Sarmatian, the basin subsided mainly in the hanging wall region of the Steinberg fault (Figure 3F). Compared to the late Badenian subsidence, the Sarmatian subsidence area shifted slightly to the south. Tectonic subsidence during the Pannonian time show similarities to the Sarmatian ones (Figure 3G), with subsidence mainly in the hanging wall of the Steinberg fault, however, the Pannonian subsidence rate was much lower. Discussion and Conclusions This study presents the Early to Late Miocene basin evolution of the Vienna basin with visualizing the tectonic subsidence. The results demonstrate that the tectonic subsidence evolution in the Vienna Basin is closely coupled with changes of the basin structural setting and the regional stress field. In the Early Miocene, the minor and locally confined tectonic subsidence trend is indicating the complex piggy-back basin structural features of the Vienna Basin, formed on top of the nappes of the moving Alpine-Carpathian thrustbelt. The Eggenburgian Ottnangian piggy-back basin system was shallow and slowly subsiding in E-W trending depressions, while the early Karpatian setting was deeper and NE-SW trending. The NE-SW trending strike, however, is not genetically related to the Leitha-Láb strike-slip fault system. This can be related to an apparent counterclockwise rotation of the

5 Alpine thrust front between the Eggenburgian and the Karpatian (Beidinger and Decker, 2014), resulted from the eastward increase of the cumulative in-sequence thrust distance. In the late Early Miocene, the tectonic subsidence pattern changed abruptly as a result of the principal change in the basin type to a pull-apart basin system due to the transtensional tectonic regime. Therefore the deep subsiding areas were activated mainly by the Leitha-Láb fault system and between the Steinberg fault and Laksary fault, while the northern part was relatively stationary regarding subsidence. In the study area, the early Badenian tectonic subsidence was abruptly slow and confined in a narrow area. In contrast, high tectonic subsidence rate of the early Badenian (the Upper Ladenid Zone) is observed in the southern part (Hölzel et al., 2008). There are two suggestions trying to explain this regional difference of the early Badenian subsidence. Hölzel et al. (2008) explained the different subsidence pattern mainly with a paleoenvironmental effect caused by the Spannberg ridge. The ridge largely restricted sedimentation to the southern part during the early Badenian. Lee (2015) suggested that the regional difference of the Badenian tectonic subsidence might be influenced by a Badenian paleostress change, considering a change of the major tensional regime shifting from transtension to E-W directed extension toward the late Middle Miocene. From the late Badenian to the Pannonian, the NE-SW trending normal faults, especially the Steinberg fault in the central Vienna Basin, seem to govern the basin subsidence in the Vienna Basin. These faults induced subsidence mainly in the Zisterdorf depression and the Moravian-Central depression along the Steinberg fault, while the sinistral strike-slip faults along the southeastern border zone played a minor role. The subsidence is corresponding to the E-W trending extension found in the western parts (e.g. Styrian Basin and Danube Basin) of the Pannonian Basin system for the late Sarmatian early Pannonian (Huismans et al. 2001). References Beidinger, A. and Decker, K. [2014] Quantifying Early Miocene in-sequence and out-of-sequence thrusting at the Alpine-Carpathian junction, Tectonics 33, , doi: /2012tc Hölzel, M., Faber, R. and Wagreich, M. [2008] Regional subsidence analysis in the Vienna Basin. Austrian Journal of Earth Sciences 101, Huismans, R.S., Podladchikov, Y.Y., Cloetingh, S. [2001] Dynamic modelling of the transition from passive to active rifting, application to the Pannonian Basin. Tectonics 20, Lee, E.Y. [2015] Integrated Basin Analysis of the Vienna Basin, central Europe. Doctoral Thesis, University of Vienna, Vienna, Austria, 127 pp. Sauer, R., Seifert, P., and Wessely, G. [1992] Part I: Outline of Sedimentation, Tectonic Framework and Hydrocarbon Occurrence in Eastern Lower Austria. Austrian Journal of Earth Sciences 85, Wessely, G., Kröll, A., Jiříček, R., and Nemec, F. [1993] Wiener Becken und angrenzende Gebiete- Geologische Einheiten des präneogenen Beckenuntergrundes. Geologische Themenkarte der Republik Österreich 1: , Geologische Bundesanstalt, Vienna.