DETRITAL ZIRCON PROVINCE OF THE JURASSIC SUNDANCE FORMATION LOCATED IN BUFFALO, WYOMING

The Jurassic Sundance formation of Wyoming was deposited during the transition from cratonic to synorogenic sedimentation in the Sevier-Laramide foreland. The Sundance in the western Powder river basin consists of an oolitic limestone and green glauconitic sandstone at the base, green shales in the middle, and a yellow quartz arenite with coquina “oyster” beds at the top. U-Pb analyses of detrital zircons using LA-ICP-MS were conducted on two samples collected in the Bud Love wildlife habitat management area, 10 km northwest of Buffalo, WY. The two samples were taken from the upper and lower sandstone members of the Sundance formation (n=288 total zircons). The samples show a distinct difference in detrital zircon age spectra. The lower sandstone age spectrum ranges from 260-3172 ma with 22.6% of the ages being Paleozoic, 71.4% being Proterozoic, and 6% being Archean. this lower stratum has detrital zircon age peaks at 343, 432, 686, 1039, 1431, 1662, 1748, 1941, 2433, and 3179 Ma. In comparison to the upper strata, with ages ranging from 157-2949 Ma and age peaks at 170, 243, 440, 545, 1082, 1467, 1681, and 1985 Ma. The maximum deposition age for the upper member is 157 Ma. Mesozoic aged grains make up 15.6% of the zircons, 14.7% were Paleozoic, 65.7% were Proterozoic, and 4% were Archean in age. The appearance of Mesozoic zircons in the upper sandstone marks the first significant appearance of westerly sourced zircons, and perhaps reflects the earliest uplift of the Sevier fold and thrust belt. The lower sandstone shows an easterly Appalachian-Ouachita provenance, which persisted in the region since the beginning of the Carboniferous. Mesozoic aged grains appear in the upper stratum which are interpreted to being derived from arc terranes being exposed due to Cordilleran orogeny to the west.