AGE AND PROVENANCE OF QUARTZITE CLASTS IN TERTIARY CONGLOMERATES, WESTERN BIG HORN BASIN, WY USING DETRITAL ZIRCON U/PB GEOCHRONOLOGY

Quartzite cobble conglomerates occur within the Tertiary strata of the western Big Horn Basin. Our goal in this research is to characterize the age and provenance of these clasts using detrital zircon U/Pb Geochronology. As part of this study, we sampled three different formations (#332 zircon analysis total). The Paleocene Fort Union Formation was sampled along Grass Creek (#83). The lower Eocene Willwood Formation was sampled at two localities: along Gooseberry Creek (#84) and near Meeteetse (#96). The middle Eocene Wapiti Formation was sampled at Jim Mountain (#70). Meso- and Paleoproterozic (1300-2000 Ma) dominated each of the samples, ranging from 79-87%. Each locality also contained smaller amounts of Archean (>2500 Ma 7-17%) and Grenville (950-1200 Ma; 6-10%). The most abundant age for each sample is 1650-1700 Ma. The similarity of detrital zircon signatures indicates that these rocks were most likely derived from the same source area, which is the Sevier highlands to the west. The sandstone protolith of these quartzites were eroded from Yavapai-Mazatzal rocks and then transported north to the Neoproterozoic continental margin of Idaho and Montana. These quartzites were then uplifted during the Sevier orogeny, were weathered, and shed as clasts east into the Western Interior Basin during early Tertiary time. These quartzite clasts have similar deterital zircon spectra to the time equivalent Harebelle and Pinyon Formations to the west.