Paper No. 28
Presentation Time: 8:00 AM-6:00 PM
HEAVY MINERAL PROVENANCE ANALYSIS OF THE WILLWOOD FM., ABSAROKA RANGE, NORTHWESTERN WYOMING
CALHOUN, Justin J., Geosciences, University of Wisconsin-Milwaukee, 3209 North Maryland Avenue, Milwaukee, WI 53211, GEARY, Jesse D., Geology, Macalester College, 1600 Grand Avenue, St. Paul, MN 55105, SCHROEDER, Kat E., Geology-Geography, Illinois State University, Campus Box 4400, Normal, IL 61790, MALONE, David H., Illinois State University, Normal, IL 61761 and CRADDOCK, John P., Geology Department, Macalester College, 1600 Grand Avenue, St. Paul, MN 55105, jcalhoun@uwm.edu
The provenance of Cretaceous-Eocene synorogenic quartzite cobble conglomerates in the Sevier-Laramide deformation zones of NW Wyoming is poorly understood. There is also no known source for any of these quartzite bearing conglomerates although previous work suggests a source from the now-eroded ancestral Targhee uplift to the northwest. Eocene quartzite cobble conglomerates are present within the syn-Laramide Willwood Formation at numerous localities in the Absaroka Basin. Our goal is to characterize the heavy mineral provenance and detrital zircon ages of the Willwood Formation. Detrital zircon analysis are in progress. The heavy mineral data is presented herein.
The Willwood Formation crops out extensively in the Absaroka and Big Horn Basins. It is as much as 1200 m thick in the Absaroka basin, and consists of interbedded variegated mudstone, yellow-brown quartz and lithic sandstones, and quartzite cobble conglomerates. Three samples of the Willwood conglomeratic sandstone were collected in the Absaroka Basin: One from the Ishawooa Hills area, the second from the base of Fourbear Mountain near the basal contact of the Formation, and the third at the base of Jim Mountain near the top of the Formation. The Ishawooa sample, which is furthest south, has a heavy mineral suite that includes zircon, magnetite, ilmenite, and rutile. The Fourbear and Jim Mountain samples were rich in garnet, magnetite and ilmenite. The Fourbear and Jim Mountain heavy mineral assemblages are consistent with a metasedimentary provenance such as the Targhee uplift. The Ishawooa sample heavy mineral assemblage has a felsic igneous provenance, most likely associated with a Laramide basement-cored uplift.
