NSF Award
0948692
First-order outstanding questions regarding foreland deformation center on geodynamic processes that form diverse orientations of basement arches, mechanisms of basement deformation and its transfer to the sedimentary cover, and relationships to plate margin stresses. This project will integrate structural, anisotropy of magnetic susceptibility (AMS), and paleomagnetic studies of Laramide structures in Wyoming to test various tectonic models of foreland deformation. Testable models include, temporal changes in stress directions (possibly associated with flat-slab subduction), spatial variations in stress and fault orientations (potentially associated with basement anisotropy), and varying components of shear along differently oriented structures. Results of this project will further provide data on structural traps, fracture systems, and fault patterns within the Wyoming foreland, which will improve understanding of hydrocarbon reservoirs and potential sites for carbon dioxide sequestration. Finally, this collaborative investigation will be merged with ongoing paleomagnetic and structural studies of other orogens to compare processes of mountain building in different settings, and will generate large data sets for statistical comparisons of various strain and paleostress methods used in kinematic and mechanical analysis.<br/><br/>The focus of this investigation will be on key structures that display a range of trends and deformation styles in the Wyoming foreland, and on two stratigraphic levels (Triassic redbeds and Jurassic limestone) that are well exposed, carry primary remanent magnetizations, and contain multiple strain markers. Characteristics of minor fault systems will be measured and analyzed to estimate paleostress patterns, strain orientations will be estimated from AMS fabrics and calcite twin analysis, and oriented cores will be drilled for paleomagnetic analysis to quantify timing and magnitudes of vertical-axis rotations. Characteristics of fracture patterns will be quantified for selected well-exposed surfaces to test relationships to fold and fault mechanics. By integrating multiple data sets, limitations of each set will be reduced. Critically, paleomagnetic data will be combined with deformation fabrics (minor faults, AMS, calcite twins, and fractures) and cross sections/3-D restorations to quantify both vertical-axis rotations and spatial-temporal changes in paleostress/strain. This project will provide an expansive data base, building on previous studies, in order to critically test kinematic models and mechanical processes of Laramide foreland deformation.
