Hugo Ortner

Easy handling of tectonic data: the programs TectonicVB for Mac and TectonicsFP for Windows

TectonicVB for Macintosh and TectonicsFP for Windows TM operating systems are two menu-driven computer programs which allow the shared use of data on these environments. The programs can produce stereographic plots of orientation data (great circles, poles, lineations). Frequently used statistical procedures like calculation of eigenvalues and eigenvectors, calculation of mean vector with concentration parameters and confidence cone can be easily performed. Fault data can be plotted in stereographic projection (Angelier and Hoeppener plots). Sorting of datasets into homogeneous subsets and rotation of tectonic data can be performed in interactive two-diagram windows. The paleostress tensor can be calculated from fault data sets using graphical (calculation of kinematic axes and right dihedra method) or mathematical methods (direct inversion or numerical dynamical analysis). The calculations can be checked in dimensionless Mohr diagrams and fluctuation histograms.

Geometry, amount, and sequence of thrusting in the Subalpine Molasse of western Austria and southern Germany, European Alps

In this paper we review the structure of the most external thrust belt of the Alps between the Rhein valley and Salzburg based on a new tectonic map and the (re)interpretation of seismic sections. Specifically we address the correlation between deformation in the Subalpine Molasse and the Alpine thrust belt in general and focus on the control of sedimentary facies on the structural style. A dramatic change in architecture from a ramp-flat structure to buckle folding is related to a change from coarse-grained fans to fine-grained deposits within the Subalpine Molasse. Additionally the interaction of escape tectonics with postcollisional shortening controls the decrease of late Early Miocene and younger shortening within the Subalpine Molasse from 50 km near the Rhine valley to almost zero near Salzburg. Transfer of shortening into the hinterland, which is the zone of lateral escape, ended foreland propagation of the Alpine thrusts and initiated a general break-back sequence of thrusting. Throughout this time the thrusts remained active. In such a scenario, tectonic units on top of the Subalpine Molasse are expected to undergo clockwise rotation around vertical axes. As thrusting in the Subalpine Molasse is closely related to contemporaneous transport and shortening within the tectonically higher Helvetic thrust sheets, amounts of Miocene differential shortening and related clockwise vertical axis rotation are minimum amounts. True clockwise vertical axis rotation is probably larger than the 12° deduced from the Subalpine Molasse thrust belt.

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 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 basin9s 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 basin9s 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.