RESEARCHING BASIN AND RANGE EXTENSION: DISCOVERING GROWTH FAULTS IN AN ADVANCED UNDERGRADUATE FIELD COURSE IN THE LAKE MEAD AREA, SOUTHERN NEVADA

Geology and Environmental Science majors of the University of St. Thomas Geology department embarked on a journey to the Lake Mead area of the Mojave Desert to continue research we did for the 200-level field methods course as freshman and sophomores. Now juniors and seniors, we came out to this area again for the 400-level advanced field methods course to gain more experience in undergraduate research and improve our field method skills. Our research is taking place in the White Basin near Lake Mead, to find out the structure of faulting within the basin, determine depositional environments within the basin, and learn more about Basin and Range extension. As a part of a larger overarching project in the Lake Mead area, our professors carve out smaller projects that complement one another. The White Basin has hosted many field courses, and this year we were able to fill in a large gap in the middle of the mapping area, thereby connecting all the data that has been obtained from past years.

We are currently working in the Horse Spring Formation, ~24-13 Ma, and focusing on the youngest member, the Lovell Wash Member, ~14-13 Ma. The Lovell Wash Member contains a mix of siliciclastic and carbonate units that vary laterally and vertically. This is a change from the fairly homogenous Bitter Ridge Limestone Member below and suggests a change in the style of faulting. More closely spaced faults broke up the large lake into a series of smaller basins, creating variations of thicknesses in the stratigraphy. This complex stratigraphy of the White Basin records the faulting history during Basin and Range extension.

To determine the faulting history, we mapped out marker beds. We focused on tuffs and limestone beds because they form continuously well-exposed outcrops. Specifically we had two tuffs of the upper Lovell Wash Member that were the most laterally continuous and well exposed. Other rocks of the member were not as easy to correlate because of lateral variations within individual facies, but these are proving useful in recognizing growth faults. Inputting marker bed data into ArcGIS, we are able to see a more complex system of faults. Using the map pattern along with detailed measured sections from the White Basin, we document multiple growth faults.