The Mesozoic and Cenozoic fault inventory of the Molasse Basin and its Mesozoic basement was studied using the example of the Trattnach area (~40 km WSW Linz). To achieve these objectives, 3D seismic data, acquired in 2007 and kindly provided by Rohöl-Aufsuchungs AG to the University of Leoben within the frame of the “Trattnach project”, was interpreted. As a first step a number of key horizons were mapped in the Mesozoic and Cenozoic succession. Thereafter, stratigraphic intervals ranging from the Jurassic to the Upper Puchkirchen Formation were identified and their seismic facies was described. The interpreted faults and horizons were used to analyze the Mesozoic and Cenozoic tectonic evolution recorded in the area of interest. A series of seismic attributes were derived from pre-stack time migrated data (PrSTM) and semblance cubes. Especially semblance data was important for this study because maps created from it helped in identifying discontinuities and structural features. The area of investigation is part of the Alpine Foreland Basin. The most obvious deformation patterns are those related to Cenozoic normal faulting. Normal faulting in the Molasse Basin is the response of the European foreland to the advancing Alpine nappe system. In addition there is a deformation record older than that dating back to Mesozoic times. To some extent these older fault systems predefined the orientation of Cenozoic normal faulting. Within the study area three deformational events can be distinguish: (1) During a Late Cretaceous deformation phase horizontal stresses were approximately E-W directed. In response a N-S trending bulge formed during the Turonian to Coniacian. This structural element is about 3 km long and 500 m wide and its steeper western flank it is bordered by a reverse fault. Along with this bulge NNW-SSE trending reverse faults were formed. These deformational structures have not yet been described for the area of investigation. The deformation is caused by E-W directed horizontal stresses originating from sea floor spreading in the N-Atlantic realm. Besides that it is suggested that contemporaneous NE-SW directed horizontal stresses were induced on the European foreland by the convergence of Africa towards Iberia-Europe. (2) During the Paleocene, triggered by the collision of the Austro-Alpine unit with the European foreland, a pulse of NE-SW directed intraplate compression affected Europe. In the area of investigation the Paleocene stress pattern caused the formation of the NNW-SSE trending Trattnach reverse fault which borders a broad anticline on the W-side. As the structurally highest points of this anticline the Trattnach Anticline and the Altenhof Anticline were formed. The Trattnach Anticline hosts an oil deposit (“Trattnach Oil Field”) which is in production since the 1970's. (3) The Cenozoic fault pattern in the Upper Austrian Molasse Basin originates from flexural down-bending of the foreland crust due to the load exerted by the advancing Alpine nappe system. Down-bending was accommodated by E-W trending, N- and S-dipping normal faults. Faulting commenced during latest Eocene and Early Oligocene times. The S-dipping normal faults remained active until the end of the Egerian. This is indicated by the increasing throw from top to bottom. During the deposition of the Lower Puchkirchen Formation (Egerian) a local block-rotation took place. This block-rotation is documented by an angular unconformity within the deposits of the Lower Puchkirchen Formation.
|Translated title of the contribution
|Mesozoische und känozoische Störungssystem in der Molassezone: Am Beispiel des Trattnach Ölfeldes (Oberösterreich)
|17 Dec 2010
|Published - 2010
Bibliographical noteembargoed until 23-09-2015
- Alpine Foreland Basin