11 Detrital Zircons Studies in the Western Interior U.S. and Their Implications for Ancient Landscape Evolution (Posters)

Wednesday, 9 May 2012
8:00 AM - 5:30 PM
Alvarado D&E

DETRITAL ZIRCON AGES INDICATE HIGH SEDIMENTATION RATES IN PERMIAN EOLIAN STRATA ADJACENT TO THE CASTLE VALLEY SALT WALL, PARADOX BASIN, UTAH

Paper number: 11-4
Program: Theme Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

Detrital zircon ages, composition and geometry of eolian strata near the Castle Valley salt wall in the Paradox Basin document the influence of salt on local wind patterns and sedimentation rates in the Permian White Rim Sandstone (WRS). Samples of arkosic fluvial facies of the Cutler Group directly beneath the WRS have bimodal age-probability peaks at 1725 and 1443 Ma that represent local basement ages in the nearby Uncompahgre uplift. Samples from the base of the eolian section contain these age-probability peaks and a broader spectrum of Proterozoic and early Paleozoic ages. The WRS from the greater White Rim erg in Canyonlands National Park (CNP) and near Hite, Ut, contains a broad array of ages, including Archean (3.5-2.5 Ga), Paleoproterozoic (2.2-1.8 Ga), Neoproterozoic (0.74-0.52Ga), and early Paleozoic (542-280 Ma) age groups. Upsection through the 100 m thick eolian interval at Castle Valley, the restricted Paleoproterozoic peaks are increasingly diluted by grain ages similar to those of the greater White Rim erg, indicating that detrital input from the underlying fluvial strata became increasingly diluted upsection by erg detritus.

Sandstone composition of the Castle Valley eolianites also indicates significant contribution of detritus from the underlying feldspathic fluvial facies. Basal eolianites grade from arkose to subarkose upsection, and all samples contain abundant biotite grains, in contrast with biotite-free quartzarenite of the WRS in CNP. We infer that high rates of eolian influx from the main erg overwhelmed local arkosic composition and detrital zircon character of the fluvial Cutler facies.

Stratigraphic geometry of the Castle Valley eolianites corroborates high eolian sedimentation rates adjacent to the Castle Valley salt wall. Abrupt termination of thick eolian strata against the diapir and lack of halokinetic upturn and thinning indicate that sedimentation rates at the salt wall margin far exceeded diapiric rise rates. Subsurface data indicate that the WRS connects with eolianites deposited against the Salt Valley and Castle Valley salt walls by prevailing NW winds influenced by salt wall orientation and topography and, combined with detrital zircon geochronology and sandstone composition, record migration of the greater White Rim erg into the proximal part of the Paradox Basin.