DETRITAL ZIRCON PROVENANCE OF THE ORDOVICIAN LANDER SANDSTONE LOCATED IN EASTERN AND CENTRAL WYOMING

This study uses detrital zircon U-Pb geochronology from the Lander Sandstone to provide evidence for provenance for the texturally mature cross-bedded quartz arenite. The Lander Sandstone’s stratigraphic position is directly beneath the Bighorn Dolomite, deposited in mid-Ordovician, ranging 1-5 meters in thickness. The two sample source areas were Crazy Woman Canyon, located in Northeast WY, and a Highway 16 road cut at Steerhead Ranch, located in Central WY (n=231). The results showed that zircon ages are predominantly Proterozoic in age (~74.5%) while the minority ages were Archean (25.5%). Probability density plots of the two-source areas show that the peak ages for Crazy Woman Canyon (n=90) are 1839.5, 2079.5, and 2699 Ma and Steerhead peak ages (n=141) are 1825.6, 2068.8, and 2694.4 Ma. Textures and dominant ages of these zircons indicate high wind eolian transport from the paleo-northeast of Laurentia, west of the transcontinental arch during the Trans-Hudson orogeny in the Ordovician. This interpretation is consistent with the paleogeography of Laurentia as well as the prevailing wind directions from the east. The zircons dating >2500 Ma may have originated from the local Wyoming province or more likely eolian transport from the Archean Superior or Hearne provinces. This study further supports Ordovician strata being distinct from Cambrian strata everywhere in the Cordillera, as well as zircons originating east of the transcontinental arch, such as that of the Ordovician St. Peter Sandstone, located in present day midcontinent region.