| dc.description.abstract | The Middle-Late Ordovician Eureka Quatzite in western Utah and eastern Nevada is a unique supermature quartz arenite composed of very fine-medium grain, well-rounded, well-sorted sands that were deposited along the Early Paleozoic passive margin of western Laurentia. The Eureka Quartzite and its equivalents are the only regionally widespread siliciclastic deposits within a thick Cambrian – Devonian carbonate sequence. The Eureka Quartzite thins from Lakeside, Utah to Ruby, Nevada where the Tooele Arch sub-divides the western Utah Middle Ordovician rocks into the Ibex basin of west-central Utah and the northern Utah basin. Facies interpretations and detrital zircon data were used to establish depositional environment and provenance of the Eureka Quartzite sands adjacent to the Tooele Arch. Depositional environments in this area record an offshore-to-onshore shelf transition with five facies. Offshore facies are more commonly recognized in the Crystal Peak and Wah Wah Mountain sections, the center of the Ibex basin. Facies B-E are recognized in additional locations more proximal to the Tooele Arch or the Laurentian shoreline. Three high frequency sequences (E1, E2, E3) are recorded in the Crystal Peak section with sequence E2 only occurring in locations more proximal to the shoreline and the Tooele Arch. A majority of well exposed outcrops are dominated by intense bioturbation (Bioturbation Index 5-6).
Detrital zircon signatures in all Eureka Quartzite samples in this study show a strong dual-peaked distribution of Paleoproterozoic-Archean and Trans-Hudson Orogenic (~2.6-2.8 Ga and ~1.8-2.0 Ga, respectively) age zircons. ~1.6-1.8 Ga grains correspond to the nearby Yavapai-Mazatzal provinces. Small, but persistent peaks at ~2.0-2.1 Ga, ~2.4-2.6 Ga, ~2.9- 3.0 Ga, give insight into additional provenance areas. Most of the sediment in the Middle-Late Ordovician Eureka Quartzite was shed off the Transcontinental Arch, Wyoming Craton and multiple smaller terranes east of the Laurentian margin. Underlying Late Proterozoic and Cambrian siliciclastic units commonly contain Grenville (0.8-1.2 Ga) and granite-rhyolite province derived zircons (1.4-1.5 Ga) that are essentially absent in the Eureka Quartzite, however, indicating its sands are primarily first cycle deposits and multi-cycled detritus was not a large contributor. It is unlikely that the west-east trending Tooele Arch provided siliciclastic sediment to the Eureka Quartzite. Detrital Zircon data suggests potential for influence by the arch on sediment distribution patterns, however additional data is required. The two locations most proximal to the Tooele Arch show a consistently weak Archean ~2.6-2.8 Ga peak, suggesting limited sediment input from Archean crust, such as the Wyoming province, Medicine Hat Block, or Sask province. Dual-peak zircon signatures vary temporally at locations and may reflect changes in provenance and the potential impact of relative sea level during deposition. | en |
