3D modelling is a highly efficient way to understand the stratigraphic context, structure, and subsidence of sedimentary basins by showing how geological data are distributed over the area. However, several obstacles usually emerge during the process of 3D modelling of sedimentary basins. The main problem is to combine geologic data and 3D modelling methods. Because the geologic data are scattered and sparse in a huge time and dimensional space, the data have to be interpolated by modelling techniques. This is visually done with 3D modelling software which is expensive, complicated or both. Therefore, in order to allow geologists to map and analyse data easily, this study uses MATLAB to visualize and model geologic data. MATLAB is an extensive and widely used numerical computing environment. We focus on the 3D modelling of stratigraphic (sediments distribution and isopach) and basement subsidence evolution.
For the stratigraphic subsidence mapping we arranged sample data to a set of 3D points based on their map location (x, y coordinates) and the depths (z1, z2, z3, ...) of stratigraphic boundaries and the subsided basement. Subsidence was analysed by the backstripping technique and resulted in the total basement subsidence.
The reconstruction of depth maps from the arranged data used the Thin-Plate Spline (TPS) which can be employed to reconstruct a smooth surface from a set of 3D points. The basic physical model of the TPS is based on the bending behavior of a thin metal sheet that is constrained only by a sparse set of fixed points. MATLAB was used to calculate the TPS interpolation function. This modelling program is still under development and other interpolation methods will be tested, in order to increase its usability and accuracy.
The major functions of this program are illustrated by a case study from a 35x62 km area located in the Neogene Vienna Basin. The studied data were mainly derived from about 200 boreholes drilled in the area. The stratigraphic column and age range were divided into six stages based on the Central Paratethys Stages in the Miocene. At each stage, three different kinds (sediments distribution, isopach, and subsided basement) of mapping were performed in this study. Within the case study, our software tool allowed us to gain better insight into the data and helped to improve theoretical models for the tectonic evolution of the Vienna Basin.
Our MATLAB program evaluates the interpolation function at intersection points of a grid on the xy-plane. An adjustable resolution of the grid ensures that all details of the surface are captured. The final visualization is obtained by linear interpolation between the grid points. The reconstructed surface can be viewed as surface or contour plot. A colormap is used to encode the depth of the surface in order to emphasize its shape. However, the modelling approach currently cannot integrate the displacement and timing of faults completely. It therefore gives partly fuzzy, non-complete pictures contouring over faults. In addition, different faulting (timing of fault movement) may have caused differences in sedimentation and its rates in different areas through time.
Keywords: MATLAB, modelling, surface reconstruction, stratigraphy, subsidence, Vienna Basin
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