Caroline M. Burberry
Date of this Version
Palu, J.M., 2017, A Case Study in Basement and Surface Structure Relationships and Their Implications for Fault Reactivation, Sawtooth Range, MT [M.S. thesis]: Lincoln, University of Nebraska, 78 p.
The reactivation of pre-existing basement structures affects the geometry of subsequent deformation structures. A case study analyzing the results of these interactions can be used to examine multiple fold-thrust systems and lead to valuable deformation predictions. These predictions include the potential for hydrocarbon traps or seismic risk in an actively deforming area. This case study examined the development of structures close to the Augusta Syncline in the Sawtooth Range, Montana (USA), using: 1) an ArcGIS map of basement structures, based on analysis of gravimetric and aeromagnetic data, seismic data, and well logs; 2) an ArcGIS map of the surface deformation structures of the belt, based on interpretation of remote sensing images and verification through the collection of surface field data indicating stress directions and age relationships; 3) analog sandbox experiments established and completed under controlled circumstances; and 4) a comparison of the remote sensing and field data with respect to results from the sandbox models. This comparison was then applied to the Sawtooth Range to better understand its development. Thrust faults in the Sawtooth Range change orientation from NNW-SSE in the north near the Gibson Reservoir to a WNW-ESE orientation near Haystack Butte. The change in orientation of these thrust faults correlates with pre-existing deformation structures within the Great Falls Tectonic Zone; the Scapegoat-Bannatyne trend within this Zone coincides with the change in orientation. Locally the Scapegoat-Bannatyne trend may be composed of up to 4 NE-SW oriented en echelon basement faults. These faults are most likely reactivated sinistral strike-slip faults; the observed up-dip transport direction is W to E. This indicates that the pre-existing basement features have a profound effect on the geometry of the later deformation. The case study’s main potential lies in developing a better understanding of the seismic hazard and hydrocarbon pool locations in the study area and it’s vicinity and how they were influenced by pre-existing basement faults.
Advisor: Caroline M. Burberry