Paper No. 22
Presentation Time: 9:00 AM-6:00 PM
DETERMINING THE SEDIMENT SOURCE AREA THROUGH PETROGRAPHIC ANALYSIS OF THE HERMOSA FORMATION, SILVERTON, SOUTHWESTERN CO
POURTABIB, Kristina P. and BURNS, Diane M., Department of Geology/Geography, Eastern Illinois University, 600 Lincoln Avenue, Charleston, IL 61920, kppourtabib@eiu.edu
The Pennsylvanian/Permian Hermosa Formation in southwestern Colorado is composed of arkosic sandstone, marine limestone, and silty shale that formed at a time when the depositional environments consisted of open-marine carbonate shelf and coastal plains. During the time of deposition, there were many tectonically active topographic highlands in the region, including the Ancestral Rockies to the west, the Uncompahgre and Emery Uplifts to the northwest, the San Luis Highlands to the southeast, and the Zuni-Defiance-Kaibab Uplifts to the southwest. Previous studies have attributed the source of the main sediment supply of the Hermosa Formation to the Ancestral Rocky Mountains (e.g. Wengerd, et al., 1958; Baars, et. al., 1981; Atchley, et. al., 1993). Because the area around the Hermosa Formation consisted of many different dynamic regional uplifts, it is possible that there was more than one sediment source area. By analyzing the sediment from the Hermosa Formation and determining the provenance, it will provide a better understanding of the paleogeographic evolution of this region.
The goal for this study is to analyze multiple field samples taken from the Hermosa Formation using the Gazzi-Dickinson point counting technique. Rock samples will be cut into billets and made into thin sections. These will be used to determine what type of highland(s) contributed sediments. Additionally, after the samples have been analyzed, the results will be compared to a previous sediment source area study on the contemporaneous Casper Formation of southeastern Wyoming (Dye and Burns, 2010). The results from their study indicated sediments of the Casper Formation were derived from both the Ancestral Rockies as well as from a northeastern topographic highland. The results from the study of the Hermosa will further the overall investigation into the regional tectonism during the Pennsylvanian/Permian. Sedimentary provenance studies like this can reveal many clues about rock formations, including: sediment source area(s), how the sediment was transported, and how the composition of the sediment was influenced by the depositional environment.
