Alpine-scale 3D geospatial modeling: Applying new techniques to old problems

The investigation of geologically complex settings in Alpine or mountainous terrains is still dominated by traditional data collection and analytical techniques. The application of computer-aided geometric design and three-dimensional (3D) visualization and interpretation is rarely applied to such settings, despite its significant benefits. This contribution uses the Gosau Muttekopf Basin (Eastern Alps, Austria) to demonstrate that the application of 3D geospatial models can both provide new insights into our understanding of such settings and result in a more robust and reproducible synthesis of a complex region. The objective of studying the Muttekopf Basin is to investigate the 3D structural control on the deposition of the deepwater sedimentary basin fill. Data for the investigation only consist of that which would be collected in a traditional field study (e.g., structural mapping, stratigraphic logging, and data localities derived from hand-held GPS [global positioning system]). The 3D basin configuration is initially derived using traditional analysis techniques (e.g., cross-section construction, photo-panel mapping, block diagrams, etc.). Using these analysis techniques, significant thickness variations are observed in the basin fill and are related to temporal and spatial variations in displacement of the controlling structure on the southern basin margin. However, there are significant limitations to this approach. In particular, because of the uncertainty in projection and spatial positioning, these techniques can only be used in an illustrative or qualitative fashion. To overcome these limitations, a 3D geospatial model is constructed from the same input data and illustrates that 3D geospatial modeling is a powerful technique for understanding complex geological settings. Integration of map data, stratigraphic section data, photographic images, structural data, and rock property data (gamma ray) into a single geospatial model maximizes the constraints of the limited data set. It also facilitates a deeper data analysis by significantly decreasing the time involved in generating multiple surfaces required for isopach generation. The use of the isopach maps in the Muttekopf Basin provides significant insights into the basin's evolution. In the Schlenkerkar section, the isopach maps reveal: (1) there was very little sediment thickness variation across the basin during the early basin fill; (2) the intermediate episode was characterized by a very thick accumulation in the basin's axis with significant thinning onto the southern uplifted margin; and (3) a northward migration of accumulation occurred during the late stage of the basin fill. Overall, the isopach maps suggest that the structure on the southern margin was the primary control on accommodation space creation and that it was most active during the intermediate basin-fill episode. Using similar observations from isopach maps for the entire basin reveals that the change in structural style of the southern margin from a fold- to a fault-dominated system plays a significant role both on internal deformation of the basin as well as the sedimentology of the syngrowth basin fill. Geospatial models, therefore, provide a more robust technique for analyzing and interpreting data within a 3D environment. In addition, they enable analysis that would be impossible with traditional techniques, such as probabilistic geocellular model construction and input models for 3D structural restorations.