The Cedar Mountain Formation contains the most diverse record of Early Cretaceous dinosaurs in the western hemisphere. However, analyses of its faunas have been hindered because 1) most taxa are based on incomplete/fragmentary materials or incomplete descriptions, 2) most sites and some horizons preserve few taxa, and 3) the stratigraphy and geochronology are poorly understood. To help resolve these stratigraphic and correlation problems U-Pb LA-ICP-MS detrital zircon ages were obtained at significant sites and horizons. These dates indicate all sites at or near the base of the formation are no older than 122 to 124 Ma, thus all basal stratigraphic packages are time equivalent. Detrital zircons coarsely bracket the temporal span of the Ruby Ranch Member between about 115 Ma to 111 Ma while the base of the Mussentuchit Member is dated between 108 to 104 Ma and the top of the member is Cenomanian in age. Multivariate analyses utilizing Simpson and Raup-Crick similarity index and pair-group moving algorithms reveal that formationfs faunas fall into two groups. These groups are compared statistically with European, Asian, and Morrison faunas. Results indicate (1) that there is no close relationship between the Yellow Cat fauna and the Morrison Formation fauna and (2) corroborate long-standing hypotheses that the Yellow Cat fauna has European ties and the Mussentuchit fauna has Asian ties. Detrital zircon LA-ICP-MS U-Pb ages were used in this study to approximate the time of deposition of strata because volcanic ashes are rarely preserved in the formation. The ability to select the youngest crystals in a sample prior to applying analytical methods could substantially reduce the number of crystals and cost required to obtain these dates. To this end, the hypothesis that the most pristine, unabraded crystals should be younger than abraded crystals was tested by imaging detrital zircons via SEM, ranking the crystals by the degree of abrasion, and determining their ages. Results of this study partly corroborate the hypothesis in that there is a correlation between the degree of abrasion and ages – obviously abraded crystals are most likely the oldest while pristine to slightly abraded crystals are usually the youngest in a given sample.

No description available.

The Cedar Mountain and Dakota Formations are significant gas producers in the southern Uinta Basin of Utah. To date, however, predicting the stratigraphic distribution and lateral extent of potential gas-bearing channel sandstone reservoirs in these fluvial units has proven difficult due to their complex architecture, and the limited spacing of wells in the region. A new strategy to correlate the Cedar Mountain and Dakota Formations has been developed using core, well-log, and 3D seismic data. The detailed stratigraphy and sedimentology of the interval were interpreted using descriptions of a near continuous core of the Dakota Formation from the study area. The gamma-ray and density-porosity log signatures of interpreted mud-dominated overbank, coal-bearing overbank, and channel sandstone intervals from the cored well were used to identify the same lithologies in nearby wells and correlate similar stratal packages across the study area. Data from three 3D seismic surveys covering approximately 140 mi2 (225 km2) of the study area were utilized to generate spectral decomposition, waveform classification, and percent less-than-threshold attributes of the Dakota-Cedar Mountain interval. These individual attributes were combined to create a composite attribute that was merged with interpreted lithological data from the well-log correlations. The overall process resulted in a high-resolution correlation of the Dakota-Cedar Mountain interval that permitted the identification and mapping of fluvial-channel reservoir fairways and channel belts throughout the study area. In the future, the strategy employed in this study may result in improved well-success rates in the southern Uinta Basin and assist in more detailed reconstructions of the Cedar Mountain and Dakota Formation depositional systems.

Numerous well-preserved, exhumed paleochannels in the Morrison, Cedar Mountain and Dakota Sandstone formations are exposed east of Castle Dale, Utah. These channels consist primarily of point bar complexes and scattered, low sinuosity channels. To determine the vertical and lateral relationships of these channels within the Cedar Mountain and Dakota Sandstone formations, a 1:24,000 scale geologic map covering ~140 km2 was created showing the fluvial sandstones. In the study area the Cedar Mountain Formation consists, from bottom to top, of 2.5-10 m of Buckhorn Conglomerate Member equivalent units, ~80 m of the Ruby Ranch Member, and ~30 m of the Mussentuchit Member. The Dakota Sandstone consists of conglomeratic to sandy, meandering channel fills within the Mussentuchit Member. The Ruby Ranch-Mussentuchit member contact is diagnosed as the top of a laterally extensive, ~10 meter thick, maroon paleosol with calcrete horizons and root traces. When deeply weathered the contact is discernable as a shift from maroon mudstone to a pale green-white, silty mudstone. Like the balance of the Mussentuchit Member overbank deposits, the white-green mudstone is rich in smectitic clays. In the southern one-third of the mapped area, Ruby Ranch Member sandstones are thin, discontinuous channel segments surrounded by floodplain deposits. In the middle to northern area, point bar complexes dominate, some of which are laterally amalgamated. Flow direction data from four meander complexes and a low sinuosity channel indicate an average northeast flow. Dakota Sandstone channels all of which are within the Mussentuchit Member also flowed to the northeast but point bar complexes are both more numerous and more laterally continuous than in the Ruby Ranch Member, indicating deposition in an area with less accommodation space than during Ruby Ranch Member time. The data indicate the Dakota Sandstone consists exclusively of fluvial sandstones encased within the Mussentuchit Member of the Cedar Mountain Formation. Therefore, these units are coeval and simply different facies of the same depositional system. Consequently the Mussentuchit Member is considered a member facies of the Dakota Formation.

No description available.

The Lower Cretaceous Cedar Mountain Formation preserves several vertebrate faunas and has the potential of providing critical timing information pertaining to Early Cretaceous dinosaurs and the Sierran magmatic arc. Historically, the Morrison/Cedar Mountain contact and the duration of the unconformity between them have been difficult or impossible to determine because 1) the formations were deposited in similar environments, 2) the basal Cedar Mountain Formation is composed of reworked Morrison Formation, and 3) there are no radiometric ages for the lower Cedar Mountain Formation. A stratigraphic study through central Utah reveals a diagnostic suite of pedogenic and sedimentologic characters across the previously enigmatic boundary. The uppermost Morrison Formation is characterized by redoximorphic paleosol features, including iron concentrations, manganese-coated grains, and intense red-purple-green mottling. Upsection increases in chert-pebble lags and channelized conglomerates within the paleosol section indicate a period of reduced accommodation space in the Tithonian. The paleosols are usually capped by a groundwater or pedogenic carbonate. This unit is consistently present from Green River, Utah to the Utah-Colorado border. The lower Cedar Mountain Formation above this package is a poorly sorted mixture of fine-grained material and sand-gravel sized chert grains. Within a sequence stratigraphic framework, these characters record a terrestrial sequence boundary in the uppermost Morrison Formation and degradational-aggradational systems tracts in the Cedar Mountain Formation. To resolve the lack of age control for the basal Cedar Mountain Formation, a geochronologic zircon study was conducted near the Dalton Wells dinosaur quarry, Moab, Utah. The Dalton Wells quarry, along with numerous other fossil assemblages occurs in the basal Yellowcat Member. Zircons from the Dalton Wells quarry and a correlative eggshell site place the age of this horizon near the Barremian/Aptian boundary at ~124 Ma. Thus, the Yellowcat fauna is time equivalent with the feathered dinosaurs of the Yixian Formation, of Liaoning, China. This age constrains the Morrison/Cedar Mountain unconformity to a period of magmatic quiescence in western North America from 148 Ma-124 Ma. The basal Cedar Mountain age coincides with renewed magmatic activity at ~125 Ma. The Cedar Mountain Formation covers a period of 27 Myr and likely contains numerous small unconformities.