Integrated high-resolution stratigraphy: Relative contributions of tectonics, eustasy and climate on basin evolution (Vienna Basin, Austria)

Sedimentary basins form in a range of large-scale tectonic settings involving extensional, compressional or lateral movements. The dynamics of the basin infill are controlled by driving mechanisms such as tectonics, climate and eustatic control. The created accommodation space in the basin is filled by sediments that formed by erosion in the higher areas and subsequently was transported by rivers and deposited into the basin. The sedimentary layers that are subsequently formed, also known as the stratigraphy, possibly provide information about the factors that influenced the sedimentary infill of the basin such as tectonics, climate change and eustasy (sea level changes). The goal of this thesis is to obtain a continuous borehole record in order to study the basin evolution and infill, and the relative importance of eustatic forcing, tectonic control and possible other factors in a case study. In order to achieve this, a new methodology is applied that combines various stratigraphic methods to obtain a high-resolution temporal record of a downhole sedimentary sequence. This method is applied in a case study on a well located in the Central Paratethyan Vienna Basin in Austria. The method is based on downhole magnetostratigraphic measurements and biostratigraphical analysis that form the basis of a chronostratigraphic framework, with accurate major time gaps identified from seismic data, well correlations and high-resolution electrical borehole images. The method is unique because it uses continuous magnetostratigraphy in the borehole provided by a palaeomagnetic logging tool that measures the remanent magnetization downhole. The measurements result in a series of polarity reversals and accurate age dating can be obtained when the reversals can be linked to the so called Global Polarity Time Scale (GPTS). In the case study of the Vienna Basin the applied methodology allowed for the construction of a detailed chronostratigraphic framework for the sedimentary sequence from the well (between ~12.5 and ~9.1 million years ago). The entire sequence can be regarded as part of one large cycle with the pull-apart phase of the basin creating accommodation space. Superimposed on the large tectonic signal the sedimentary sequence exhibits influences from global eustasy fluctuations. The study sheds new light on the occurrence of Milankovitch and sub-Milankovitch periodicities in the Middle to Late Miocene of the Vienna Basin. The use of different geophysical data within a detailed chronostratigraphic framework, and the application of spectral analysis methods, established the occurrence of the Milankovitch periodicities precession, obliquity and eccentricity. For the sub-Milankovitch periodicities the electrical borehole images proved a powerful tool. The high resolution of ~1 cm of these images allowed analysing millennial- to centennial-scale periodicities, with a concentration of significant periodicities being observed between 1 to 2 kyr as well as 500 to 800 years. These periodicities relate closely to the millennial- (Dansgaard-Oeschger and Bond cycles) and centennial-scale climate cycles documented from the Quaternary, but understanding the driving mechanism that established these cyclicities still requires considerable research.GeotechnologyCivil Engineering and Geoscience