DETRITAL ZIRCON PROVENANCE AND PALEOGEOGRAPHIC TRENDS FOR PENNSYLVANIAN AND TRIASSIC SEDIMENTARY ROCKS IN SOUTHWESTERN WYOMING AND NORTHERN UTAH-COLORADO

The Pennsylvanian and Triassic paleogeographic framework of southwestern Wyoming is not well constrained and based largely on extrapolation from extensive work completed on correlative units further to the south, west, and northeast. To begin the process of unraveling the paleogeographic history of this region during and after the formation of the Ancestral Rockies, five samples of Pennsylvanian and Lower Triassic sedimentary rocks were collected from locations across southern Wyoming and northern Utah-Colorado for detrital zircon age dating by LA-MC-ICPMS. Samples analyzed include Dinwoody Fm. and Tensleep Ss. from the Red Canyon/Sinks Canyon area near Lander, WY, Dinwoody Fm. and Weber Ss. from the north side of the Uinta Mountains near Sheep Creek, UT, and Weber Ss. from Irish Canyon, CO.

Age populations present in samples include 2420–3500 Ma (primary source: Wyoming province), 1810–2015 Ma (cratonic suture belts), 1535–1810 Ma (Yavapai-Mazatzal provinces), 1300–1535 Ma (mid-continent anorogenic granites), 900–1300 Ma (Grenville orogen), 510–725 Ma (accreted peri-Gondwonan terranes) and 285–510 Ma (Appalachian orogen). Overall age distributions in all samples are consistent with transcontinental drainage networks recycling Paleozoic meta-sedimentary rocks in the central Appalachian region. Spectra from the Pennsylvanian Weber Ss. from CO and UT are nearly identical, however, the inferred age-correlative Tensleep Ss. in WY has a more peaked Appalachian source at 434 Ma, as well as a significantly higher proportion of 900–1300 Ma detrital zircons. This suggests a slightly different source region for the fluvial system that supplied detritus to form the Tensleep Ss. aeolianites in WY, potentially including sourcing of Grenville-age plutons.

The Early Triassic Dinwoody Fm. in the Uinta Mountains is similar in provenance to the Tensleep and Weber sandstones, yet has a greater proportion of <700 Ma detrital zircon grains. The Dinwoody Fm. from Red Canyon, WY, contains a markedly higher proportion (~28%) of >2420 Ma detrital zircon grains derived from the Wyoming Province, suggesting that a local source for grains of this age may have been exposed during Dinwoody Fm. depositional time.