Date of Award
Master of Science (MS)
Department of Geography-Geology: Hydrogeology
David H. Malone
The purpose of this study is to deconstruct the relationship between the Leaf River anticline and the preglacial bedrock paleo topography at the eastern terminus of the Plum River Fault Zone in Ogle County, Illinois. A geostatistical approach was used to model the subsurface elevation of the bedrock paleo topography and the Leaf River anticline. The contour maps derived from the elevation models provided detailed depictions of the ancient bedrock landscape and subsurface structure in the study area. The Leaf River anticline is interpreted to be a component of hanging wall anticline at the terminus of the Plum River Fault Zone. The topographic high created by the anticline controlled local drainage and led to the development of the Leaf River paleovalley prior to the Pleistocene. The catastrophic failure of an ice damn during the Illinois Glacial Episode carved a glacial spillway into the north flank of the Leaf River anticline that interfaced with a tributary of the Leaf River paleovalley. This rerouted the preglacial drainage network and permanently diverted the ancient Rock River to its modern day position. Ultimately, the subsurface geometry of the Leaf River anticline and its relationship to the local bedrock paleo topography was revealed by the elevation models. The position and development of the Leaf River paleovalley and glacial spillway interpreted in this study aligned with the regional interpretations for the evolution of the ancient bedrock landscape established in prior works. However, this study revealed that the Leaf River anticline, and by association, the terminus of the Plum River Fault Zone extends farther east into the region than indicated by prior works.
Rhoads, Matthew, "Exploration of the Northern Illinois Bedrock Surface" (2017). Theses and Dissertations. 704.