East-central Utah Research Articles

The Goldilocks Zone for maize agriculture and the settlement and abandonment of the West Tavaputs Plateau

Between 2100 and 500 BP, maize farming spread throughout the American Southwest, driving changes in land use patterns and relative increases in the number of archaeological sites, which is commonly interpreted as increases in population. In the context of the Southwest, with its variable topography and limited water sources, the locations suitable for productive maize agriculture are limited. Higher elevation locations often have a greater abundance of water, both in the form of precipitation and perennial water sources but lack the growing season lengths required for maize farming. Lower elevation locations have the long growing seasons required for maize, but often have higher evaporation rates corresponding with higher temperatures, and thus decreased soil moisture retention. The relationship between elevation and maize agriculture is well recognized, and locations where both growing season length and moisture requirements can be met serve as a Goldilocks Zone in which maize farming is possible. Here, we use a regional approach to model the Goldilocks Zone for maize farming in Utah, and then contextualize patterns of settlement and abandonment on the West Tavaputs Plateau (WTP) in east-central Utah. We use archaeological sites with direct evidence of maize cultivation, modern growing degree days estimates, and modern estimates of moisture abundance to bracket the prehistoric maize farming niche in Utah. Then, we apply the model to archaeological data from the WTP to test hypotheses derived from the Ideal Free Distribution model about the effects population and precipitation changes had on prehistoric land use patterns of settlement and abandonment, and whether the patterns of settlement and abandonment differ from one another. We find that a) population drives land use patterns in the WTP, but not in the way we originally hypothesized, suggesting there is an important decision variable missing from our model, which may pertain to the specific topographic setting of the WTP and the distribution of its water sources, b) precipitation has no effect on land use patterns suggesting that maize agriculture on the WTP was dependent on irrigation, and c) that patterns of settlement and abandonment seem to mirror each other.

The effect of saturation and salts on the rigidity of fine-grained material

Repeated multi-channel analysis of surface waves (MASW) and horizontal to vertical spectral ratio (HVSR) experiments were conducted on a hummock within a large landslide in east-central Utah adjacent to a small wetland. Stakes were placed into the ground to ensure identical array geometries and geophone locations. The landslide is an admixture of fine-grained material (clay, quartz and Na-plagioclase) and intermediate-composition volcanic clasts. A prominent crust of Na-salts covered the hummock surface, produced by evapotranspiration of shallow groundwater associated with the adjacent fen.The experiments produced three primary observations. First, on any given day, the Rayleigh wave frequency spectra were highly reproducible between individual experiments. Second, from May to October the spectra exhibited high variability between experiments conducted weeks apart, especially at frequencies <20 Hz. Third, a persistent subsurface boundary exists across which Vs increases from ~175 to ~300 m/s. However, that boundary migrated over time from a depth of ~5 to ~4 m.The low velocity of the upper ~5 m subsurface layer represents poorly-compacted landslide material, perhaps weakened from high Na+ concentrations. However, the variability in frequency spectra and upward migration of the boundary must have arisen from changing moisture and salt content over time. The fen was instrumented with a piezometer that showed an overall ~1 m decline in water levels from May to October with small, superimposed recharge events resulting from summer monsoon rains.This study leads to two important conclusions. Specific to this site and perhaps others, variable moisture content can affect capillary forces and the proportion of evaporite cements in the shallow subsurface that are manifested in strikingly different frequency spectra and migrating stiffness (Vs) boundaries. More generally, moisture and salt content can affect estimates of subsurface stiffness, including the position of apparent boundaries within unconsolidated materials.

Spectacular crinkled crust—A detachment fold train in the Carmel Formation, western San Rafael Swell, Utah

Imagine slipping on a small rug overlying a hardwood floor. In the process of sliding along the floor the rug produces a series of small folds and the rug moves forward from its original position. The same could be said for the “crinkled crust,” or folded layers of rocks in a detachment fold train. A spectacular detachment fold train, consisting of over 100 small, regularly spaced convex-upward folds called anticlines in gypsum-rich rock layers of the Middle Jurassic (about 168 million years ago [Ma]) Carmel Formation, is exposed immediately north of Interstate 70 (I-70) in the San Rafael Swell of east-central Utah (figures 1 and 2). The SanRafael Swell, a large anticlinal uplift, is an icon for everything that makes the Colorado Plateau dramatically scenic and geologically classic. However, the fold train is located in drab-colored, relatively featureless rock layers of the Carmel Formation in an area called Reed Wash along the gently dipping west flank of the Swell. After passing magnificent canyons, buttes, and mesas both to the east and west along I-70, the fold train typically goes unnoticed by not only the average tourist but geologists as well. Once the fold train is pointed out, the geologic observer is immediately struck with awe at this large, well-exposed, complex structural feature.&#x0D; Literally hundreds of classic geologic sites are well displayed in the San Rafael Swell; many are easily accessed overlooks and viewpoints. The detachment fold train, by contrast, is chosen as a geosite for its geologic uniqueness, educational instruction, and research opportunities in structural geology.

Ancient delta deposits in the Ivie Creek area, Ferron Sandstone member of the Mancos Shale, western San Rafael Swell, east-central Utah

In contrast to the beautiful array of colorful layers and spectacular cliffs of the Triassic and Jurassic (251 to 148 million years ago [Ma]) sections in the San Rafael Swell of east-central Utah, most of the Upper Cretaceous (96 to 86 Ma) Mancos Shale produces a drab, barren landscape. However, lying within the Mancos, the Ferron Sandstone, is the most studied unit in the San Rafael Swell. The Ferron has world-class outcrops of rock layers deposited near the shorelines of a sinking, fluvial- (stream) dominated delta system. Along the west flank of the San Rafael Swell, the 80-mile-long (130 km) Ferron outcrop belt of cliffs and side canyons (e.g., the Coal Cliffs, Molen Reef, and Limestone Cliffs [not actually limestone, just misnamed]) provides a three-dimensional view of vertical and lateral changes in the Ferron’s rock layers (facies and sequence stratigraphy), and, as such, is an excellent model for fluvial-deltaic oil and gas reservoirs worldwide (e.g., Chidsey and others, 2004).

Composite and diachronous stratigraphic surfaces in low-gradient, transitional settings: The J-3 “unconformity” and the Curtis Formation, east-central Utah, U.S.A.

ABSTRACTUnconformities, by definition, correspond to erosional or nondepositional surfaces, which separate older strata below, from younger rocks above, encapsulating significant time gaps. However, recent studies have highlighted the composite nature of some unconformities, as well as their heterochronous and diachronous character, which challenge the use of such a definition in a four-dimensional dynamic environment. The J-3 Unconformity, separating the Middle Jurassic Entrada Sandstone from the Upper Jurassic Curtis Formation (and laterally equivalent units) in east-central Utah (USA), is laterally variable, generated by either erosion-related processes such as eolian deflation, and water-induced erosion, or by deformational processes. The J-3 Unconformity is a composite surface, formed by numerous processes that interacted and overlapped spatially and temporally. This study therefore demonstrates the heterochronous, diachronous, and non-unique nature of this surface interpreted as unconformity, where one process can be represented by varying expressions in the stratigraphic record, and conversely many processes may result in the same stratigraphic expression.

Characterization of effective permeability in heterolithic, distal lower-shoreface sandstone reservoirs: Rannoch Formation, Brent Group, UK North Sea

The reservoir properties of distal lower-shoreface and distal wave-dominated delta-front deposits, which consist of sandstone beds with locally scoured bases and mudstone interbeds, are poorly understood. The lower Rannoch Formation (Middle Jurassic Brent Group) forms an interval of such heterolithic sandstones in many North Sea reservoirs, and is used to illustrate a workflow for rapid estimation of reservoir properties and their sensitivity to key parameters. Mudstone-interbed thickness distributions in cored reservoir successions are compared to the thickness distribution of sandstone scour-fills in an outcrop analogue(s) in order to identify mudstones with the potential to form laterally extensive barriers to vertical flow. Effective k v / k h at the scale of several typical reservoir-model grid cells (200 × 100 × 20 m) is estimated in intervals bounded by these mudstone barriers via a simple analytical technique that is calibrated to previously documented reservoir-modelling experiments, using values of sandstone proportion measured in cored reservoir successions. Using data from the G2 parasequence (Grassy Member, Blackhawk Formation, east-central Utah, USA) outcrop analogue, mudstones bounding 3–8 m-thick, upwards-coarsening successions in the lower Rannoch Formation may define separate stratigraphic compartments in which grid-cell-scale effective k v / k h is estimated to be 0.0001–0.001 using a streamline-based analytical method.

High resolution linkage of channel-coastal plain and shallow marine facies belts, Desert Member to Lower Castlegate Sandstone stratigraphic interval, Book Cliffs, Utah-Colorado, USA

AbstractThe Campanian Desert Member and Lower Castlegate Sandstone in the Book Cliffs of east-central Utah to western Colorado, USA, has served as a foundational data set in the development of sequence stratigraphy. Contrary to previous work, no third-order sequence boundaries are recognized. These were originally thought to partition the neighboring coastal plain and shallow marine facies belts into separate systems tracts, unlinked in time or space. In contrast, adjoining channel-coastal plain and shallow marine facies belts are genetically-, temporally-, and spatially-related. Evidence includes the (i) synchronous, strongly progradational stacking patterns within each facies belt, (ii) gradational and conformable transitions between adjoining facies belts, accentuated by the ubiquity of flat-topped, rooted foreshore sandstones passing upwards into carbonaceous-rich-mudstone-dominated coastal plain, (iii) parasequence-scale interfingering of coastal plain-channel and foreshore-shoreface deposits, with channels, white caps and coals embedded within stacked shoreface parasequences, (iv) regional correlation of coals and flooding surfaces, and (v) near orthogonal paleocurrent relationship between channels and shorelines. Terminal channels incise into proximal foreshore-shoreface sandstones in most Desert-Castlegate parasequences. Incisions are generally confined to the parasequence in which the channels are nested, rarely cutting deeper. These shoreface-incised channels are cut and filled at a parasequence-scale, and are bounded above by the same flooding surface that caps each foreshore-shoreface package. The ubiquity of ascending regressive shoreface trajectories and near absence of descending regressive trajectories that intersect depositional slope argues against any significant sea level fall. Increased rates of sediment supply, driven by autogenic and/or allogenic processes, likely generated the strongly progradational Desert-Castlegate great tongue of sandstone.

New Insights on the Impact of Tidal Currents on a Low-gradient, Semi-enclosed, Epicontinental Basin—the Curtis Formation, East-central Utah, USA

Based on a methodic sedimentological analysis, the Late Jurassic (Oxfordian) Curtis Formation unravels the intricate facies variability which occurs in a tide-dominated, fluvially starved, low-gradient, semi-enclosed epicontinental basin. This unit crops out in east-central Utah, between the eolian deposits of the underlying Middle Jurassic (Callovian) Entrada Sandstone, from which it is separated by the J-3 unconformity, and the conformable overlying supratidal Summerville Formation of Oxfordian age. A high-resolution sedimentary analysis of the succession led to the recognition of eight facies associations (FA) with six sub-facies associations. Based on the specific three-dimensional arrangement of these eight facies associations, it is proposed to separate the Curtis Formation into three sub-units: the lower, middle and upper Curtis. The J-3 unconformity defines the base of the lower Curtis, which consists of upper shoreface to beach deposits (FA 2), mud-domi­nated (FA 3a) and sand-dominated heterolithic subtidal flat (FA 3b), sand-rich sub- to supratidal flat (FA 4a) and correlative tidal channel infill (FA 4c). It is capped by the middle Curtis, which coincides with the sub- to intertidal channel-dune-flat complex of FA 5, and its lower boundary corresponds to a transgressive surface of regional extent, identified as the Major Transgressive Surface (MTS). This surface suggests a potential correlation between the middle and the upper Curtis and the neighboring Todilto Member of the Wanakah Forma­tion or Todilto Formation. The upper Curtis consists of the heterolithic upper sub- to intertidal flat (FA 6) and coastal dry eolian dunes belonging to the Moab Member of the Curtis Formation (FA 7), and it conformably overlies the middle Curtis.&#x0D; The spatial distribution of these sub-units supports the distinction of three different sectors across the study area: sector 1 in the north, sector 2 in the south-southwest, and sector 3 in the east. In sector 1, the Curtis Formation is represented by its three sub-units, whereas sector 2 is dominated by the middle and upper Curtis, and sector 3 encompasses the extent of the Moab Member of the Curtis Formation.&#x0D; This study also highlights the composite nature of the J-3 unconformity, which was impacted by various processes occurring before the Curtis Formation was deposited, as well as during the development of the lower and middle Curtis. Local collapse features within the lower and middle Curtis are linked to sand fluid over­pressure within a remobilized sandy substratum, potentially triggered by seismic activity. Furthermore, the occurrence of a sub-regional angular relationship between the middle Curtis and substratum implies that the area of study was impacted by a regional deformational event during the Late Jurassic, before the deposition of the middle Curtis.&#x0D; The spatial distribution of these sub-units supports the distinction of three different sectors across the study area: sector 1 in the north, sector 2 in the south-southwest, and sector 3 in the east. In sector 1, the Curtis For­mation is represented by its three sub-units, whereas sector 2 is dominated by the middle and upper Curtis, and sector 3 encompasses the extent of the Moab Member of the Curtis Formation.&#x0D; This study also highlights the composite nature of the J-3 unconformity, which was impacted by various processes occurring before the Curtis Formation was deposited, as well as during the development of the lower and middle Curtis. Local collapse features within the lower and middle Curtis are linked to sand fluid over­pressure within a remobilized sandy substratum, potentially triggered by seismic activity. Furthermore, the occurrence of a sub-regional angular relationship between the middle Curtis and substratum implies that the area of study was impacted by a regional deformational event during the Late Jurassic, before the deposition of the middle Curtis.

New Insights on the Impact of Tidal Currents on a Low-gradient, Semi-enclosed, Epicontinental Basin—the Curtis Formation, East-central Utah, USA

Based on a methodic sedimentological analysis, the Late Jurassic (Oxfordian) Curtis Formation unravels the intricate facies variability which occurs in a tide-dominated, fluvially starved, low-gradient, semi-enclosed epicontinental basin. This unit crops out in east-central Utah, between the eolian deposits of the underlying Middle Jurassic (Callovian) Entrada Sandstone, from which it is separated by the J-3 unconformity, and the conformable overlying supratidal Summerville Formation of Oxfordian age. A high-resolution sedimentary analysis of the succession led to the recognition of eight facies associations (FA) with six sub-facies associa­tions. Based on the specific three-dimensional arrangement of these eight facies associations, it is proposed to separate the Curtis Formation into three sub-units: the lower, middle and upper Curtis. The J-3 unconformity defines the base of the lower Curtis, which consists of upper shoreface to beach deposits (FA 2), mud-domi­nated (FA 3a) and sand-dominated heterolithic subtidal flat (FA 3b), sand-rich sub- to supratidal flat (FA 4a) and correlative tidal channel infill (FA 4c). It is capped by the middle Curtis, which coincides with the sub- to intertidal channel-dune-flat complex of FA 5, and its lower boundary corresponds to a transgressive surface of regional extent, identified as the Major Transgressive Surface (MTS). This surface suggests a potential correla­tion between the middle and the upper Curtis and the neighboring Todilto Member of the Wanakah Forma­tion or Todilto Formation. The upper Curtis consists of the heterolithic upper sub- to intertidal flat (FA 6) and coastal dry eolian dunes belonging to the Moab Member of the Curtis Formation (FA 7), and it conformably overlies the middle Curtis.

Impacts of relative permeability formulation on forecasts of CO2 phase behavior, phase distribution, and trapping mechanisms in a geologic carbon storage reservoir

A critical aspect in the risk assessment of geologic carbon storage, a carbon-emissions reduction method under extensive review and testing, is effective multiphase CO2 flow and transport simulation. Relative permeability is a flow parameter particularly critical for accurate forecasting of the multiphase behavior of CO2 in the subsurface. The relative permeability relationship assumed and especially the residual saturation of the gas phase greatly impacts predicted CO2 trapping mechanisms and long-term plume migration behavior. A primary goal of this study was to evaluate the impact of the selection of relative permeability formulations on the efficacy of regional-scale CO2 sequestration models. To accomplish this, we selected the San Rafael Swell area of East-central Utah as a case study to evaluate the impact of relative permeability formulations on CO2 plume movement and behavior. A 2D vertical cross section model was built to simulate injection of CO2 into a brine aquifer for 30 years followed by 970 years of post-injection monitoring. We evaluated five different relative permeability relationships to quantify their relative impacts on forecasted flow results of the model, with all other parameters maintained uniform and constant. Because of the interdependence between phase saturation and relative permeability in numerical simulations we expected to see some variation in phase behavior, phase distribution, and CO2 trapping mechanisms. An almost 60% difference in residually trapped gas was observed across the different relative permeability relationships. Large variations of up to 40% in the saturation of both dissolved phase and mobile supercritical phase CO2 were also observed. The pressure buildup and decay observed was not significantly affected by the relative permeability formulation until after injection pressures have dissipated. Results of this analysis suggest that CO2 plume movement and behavior are significantly dependent on the specific relative permeability formulation assigned, including the assumed residual saturation values of CO2 and brine. More specifically, different relative permeability relationships translate to significant differences in CO2 plume behavior and corresponding trapping mechanisms. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd

Review: Building Zion: The Material World of Mormon Settlement, by Thomas Carter

Thomas Carter. Building Zion: The Material World of Mormon Settlement Minneapolis: University of Minnesota Press, 2015, 358 pp., 2 tables, 215 b/w illus. $112.50 (cloth), ISBN 9780816689569; $37.50 (paper), ISBN 9780816689576 The academic study of vernacular landscapes has matured over the past two generations in parallel with the increasingly sophisticated study of Mormonism. This confluence of subject and method reach peak scholarly expression with the publication of Thomas Carter's Building Zion . The summation of a career's worth of work on Utah's built environment, the book exemplifies what happens when the right author with the right project reaches the right publisher at the right time. Carter, a longtime faculty member in the College of Architecture and Planning at the University of Utah, has provided a definitive treatment of the character of the Latter-day Saints’ western settlements. Production by the University of Minnesota Press has enabled him to interweave his analysis with more than two hundred useful photographs, maps, and original measured drawings of individual buildings and towns, allowing his architectural evidence full expression. This evidence is further bolstered by impressive archival research. The result points to some surprising conclusions. Despite the many controversies accompanying the foundational decades of the Church of Jesus Christ of Latter-day Saints, Carter concludes that much about early Mormon material life could be rather ordinary. His study spans the years from the founding of the church in 1830 to its newfound stability by the end of the nineteenth century. He takes as his particular field of focus the settlements of east-central Utah's Sanpete Valley, with the city of Manti (founded in 1849) serving as the study's center of gravity. But Carter's study frequently …

Sedimentologic and sequence-stratigraphic characteristics of wave-dominated deltas

Wave-dominated deltaic strata form prolific hydrocarbon plays in many mature basins across the world. Examples include the Jurassic Brent Group play in the North Sea, offshore United Kingdom and Norway (e.g., Husmo et al., 2003); Eocene Jackson Group and Oligocene Frio Formation plays, Texas, onshore United States (e.g., Fisher et al., 1970; Galloway and Morton, 1989); and Tertiary plays in the Niger Delta province, offshore Nigeria (e.g., Evamy et al., 1978), the Baram Delta province, offshore Brunei (e.g., Rijks, 1981), and the Columbus Basin, offshore Trinidad and Tobago (e.g., Sydow et al., 2003). Wave-dominated deltas also form key exploration targets in frontier basins (e.g., Triassic Snadd Formation, Barents Sea, offshore Norway; Klausen et al., 2014, 2016). The overall architecture of many wave-dominated deltaic reservoirs is determined by their sequence-stratigraphic framework together with their structural configuration. Sequence-stratigraphic frameworks contain elements such as shoreface–shelf parasequences bounded by flooding surfaces and fluvio-estuarine complexes that fill incised coastal valleys developed at sequence boundaries. The internal facies distributions and stacking patterns of such elements are ordered, which aids prediction of reservoir character and behavior. Outcrop analogs of wave-dominated deltaic reservoirs display aspects of ordered stratigraphic architecture across a range of spatial scales that are equivalent to those observed in core, well-log, and seismic data and can therefore be used to support interpretation of their subsurface counterparts. The Cretaceous Blackhawk Formation contains wave-dominated deltaic strata that are superbly exposed in the Book Cliffs of eastcentral Utah (Figure 1A). The extensive, continuous exposures of the Book Cliffs outcrop belt have allowed the wave-dominated deltas and related deposits to be mapped for tens of kilometers (e.g., Young, 1955; Balsley, 1980), and, consequently, these strata were the “birthplace” of high-resolution sequence stratigraphy using outcrop data (Van Wagoner et al., 1990). The Blackhawk Formation and related …

DEPOSITIONAL CONSTRAINTS ON THE LOWER CRETACEOUS STIKES QUARRY DINOSAUR SITE: UPPER YELLOW CAT MEMBER, CEDAR MOUNTAIN FORMATION, UTAH

A new mass death assemblage in Lower Cretaceous strata of east-central Utah contains well-preserved skeletons representing an ontogenetic series of individuals of Utahraptor , and at minimum two iguanodont grade ornithischian skeletons. The dinosaurs were entombed in ovoid-lensoidal, fine-grained sandstone sills linked by sandstone pipes and/or dikes and another basal lensoidal mass with scattered and broken iguanodont and sauropod bones and to an underlying gravelly sandstone bed. Exposed in the excavation high-walls are syndepositional normal-faults bounding graded ripple strata. Multiphased fluid over-pressurization in an artesian setting creating the structures. Trapping, killing, and subsequent burial mechanism was generated by variations of pressure in a localized artesian spring system that breached the surface and is the first such mechanism documented with numerous dinosaur victims.

The Lower Cretaceous in east-central Utah—The Cedar Mountain Formation and its bounding strata

Although only recognized as a discrete stratigraphic unit since 1944, the Cedar Mountain Formation represents tens of millions of years of geological and biological history on the central Colorado Plateau. This field guide represents an attempt to pull together the results of recent research on the lithostratigraphy, chronostratigraphy, sequence stratigraphy, chemostratigraphy, and biostratigraphy of these medial Mesozoic strata that document the dynamic and complex geological history of this region. Additionally, these data provide a framework by which to examine the history of terrestrial faunas during the final breakup of Pangaea. In fact, the medial Mesozoic faunal record of eastern Utah should be considered a keystone in understanding the history of life across the northern hemisphere. Following a period of erosion and sediment bypass spanning the Jurassic–Cretaceous boundary, sedimentation across the quiescent Colorado Plateau began during the Early Cretaceous. Thickening of these basal Cretaceous strata across the northern Paradox Basin indicate that salt tectonics may have been the predominant control on deposition in this region leading to the local preservation of fossiliferous strata, while sediment bypass continued elsewhere. Thickening of overlying Aptian strata west across the San Rafael Swell provides direct evidence of the earliest development of a foreland basin with Sevier thrusting that postdates geochemical evidence for the initial development of a rain shadow.

Towards a sequence stratigraphic solution set for autogenic processes and allogenic controls: Upper Cretaceous strata, Book Cliffs, Utah, USA

Upper Cretaceous strata exposed in the Book Cliffs of east–central Utah are widely used as an archetype for the sequence stratigraphy of marginal-marine and shallow-marine deposits. Their stratal architectures are classically interpreted in terms of accommodation controls that were external to the sediment routing system (allogenic), and that forced the formation of flooding surfaces, sequence boundaries, and parasequence and parasequence-set stacking patterns. Processes internal to the sediment routing system (autogenic) and allogenic sediment supply controls provide alternatives that can plausibly explain aspects of the stratal architecture, including the following: (1) switching of wave-dominated delta lobes, expressed by the internal architecture of parasequences; (2) river avulsion, expressed by the internal architecture of multistorey fluvial sandbodies and related deposits; (3) avulsion-generated clustering of fluvial sandbodies in delta plain strata; (4) ‘autoretreat’ owing to increasing sediment storage on the delta plain as it lengthened during progradation, expressed by progradational-to-aggradational stacking of parasequences; (5) sediment supply control on the stacking of, and sediment grain-size fractionation within, parasequence sets. The various potential allogenic controls and autogenic processes are combined to form a sequence stratigraphic solution set. This approach avoids anchoring of sequence stratigraphic interpretations on a specific control and acknowledges the non-unique origin of stratal architectures.

The Lower Cretaceous in east-central Utah—The Cedar Mountain Formation and its bounding strata

Although only recognized as a discrete stratigraphic unit since 1944, the Cedar Mountain Formation represents tens of millions of years of geological and biological history on the central Colorado Plateau. This field guide represents an attempt to pull together the results of recent research on the lithostratigraphy, chronostratigraphy, sequence stratigraphy, chemostratigraphy, and biostratigraphy of these medial Mesozoic strata that document the dynamic and complex geological history of this region. Additionally, these data provide a framework by which to examine the history of terrestrial faunas during the final breakup of Pangaea. In fact, the medial Mesozoic faunal record of eastern Utah should be considered a keystone in understanding the history of life across the northern hemisphere. Following a period of erosion and sediment bypass spanning the Jurassic–Cretaceous boundary, sedimentation across the quiescent Colorado Plateau began during the Early Cretaceous. Thickening of these basal Cretaceous strata across the northern Paradox Basin indicate that salt tectonics may have been the predominant control on deposition in this region leading to the local preservation of fossiliferous strata, while sediment bypass continued elsewhere. Thickening of overlying Aptian strata west across the San Rafael Swell provides direct evidence of the earliest development of a foreland basin with Sevier thrusting that postdates geochemical evidence for the initial development of a rain shadow.

Investigation of late and post-Fremont alluvial stratigraphy of Range Creek, east-central Utah: Use of OSL when radiocarbon fails

Range Creek in east-central Utah hosts a unique abundance of Fremont-aged archaeological sites. Although good age control is available for cultural artifacts and sites, radiocarbon ages from alluvial sequences along the valley floor have generally produced age overestimates. In order to provide an alternative dating technique and test the reliability of the radiocarbon results, samples for single-grain quartz optically stimulated luminescence (OSL) dating were collected from three alluvial profiles where 18 radiocarbon samples of charcoal and aggregated pollen had been analyzed. While AMS radiocarbon age results were more precise, the single-grain OSL ages were stratigraphically consistent and suggest radiocarbon age overestimation of up to 2–6 ka, with the greatest divergence observed in the results from aggregated pollen samples. OSL results and geochemical analyses suggest that hydrocarbon contamination may have affected the accuracy of the radiocarbon results; age overestimates are likely due to contribution from oil-shale deposits within the catchment.OSL and stratigraphic results suggest fluvial deposition began prior to 0.88 ka (AD 1130) at the site. Floodplain aggradation continued by conformable deposition of tabular flood packages, commonly capped with charcoal and ash-rich sediments, until interrupted by channel (arroyo?) entrenchment prior to 0.34 ka (AD 1670). Sandy flood packages filled this channel and re-aggradation continued until historic arroyo entrenchment of Range Creek in the late AD 1800's. OSL age constraints indicate that the alluvial sediments at the study sites were deposited during and immediately following Fremont occupation of Range Creek at AD 1000–1200 and may contain valuable archives of environmental conditions leading up to and following the abandonment of Fremont peoples from the region. Moreover, OSL results point to the importance of the use of multiple chronometers to date alluvial deposits, as the radiocarbon chronology alone would suggest that the study sites contained pre-Fremont-aged deposits and may lead to the misinterpretation of associated cultural and environmental records.

Fault-controlled CO2 leakage from natural reservoirs in the Colorado Plateau, East-Central Utah

The study investigated a natural analogue for soil CO2 fluxes where CO2 has naturally leaked on the Colorado Plateau, East-Central Utah in order to identify various factors that control CO2 leakage and to understand regional-scale CO2 leakage processes in fault systems. The total 332 and 140 measurements of soil CO2 flux were made at 287 and 129 sites in the Little Grand Wash (LGW) and Salt Wash (SW) fault zones, respectively. Measurement sites for CO2 flux involved not only conspicuous CO2 degassing features (e.g., CO2-driven springs/geysers) but also linear features (e.g., joints/fractures and areas of diffusive leakage around a fault damage zone). CO2 flux anomalies were mostly observed along the fault traces. Specifically, CO2 flux anomalies were focused in the northern footwall of the both LGW and SW faults, supporting the existence of north-plunging anticlinal CO2 trap against south-dipping faults as well as higher probability of the north major fault traces as conduits. Anomalous CO2 fluxes also appeared in active travertines adjacent to CO2-driven cold springs and geysers (e.g., 36,259 g m−2 d−1 at Crystal Geyser), ancient travertines (e.g., 5,917 g m−2 d−1), joint zones in sandstone (e.g., 120 g m−2 d−1), and brine discharge zones (e.g., 5,515 g m−2 d−1). These observations indicate that CO2 has escaped through those pathways and that CO2 leakage from these fault zones does not correspond to point source leakage. The magnitude of CO2 flux is progressively reduced from north (i.e. the LGW fault zone, ∼36,259 g m−2 d−1) to south (i.e. the SW fault zone, ∼1,428 g m−2 d−1) despite new inputs of CO2 and CO2-saturated brine to the northerly SW fault from depth. This discrepancy in CO2 flux is most likely resulting from the differences in fault zone architecture and associated permeability structure. CO2-rich fluids from the LGW fault zone may become depleted with respect to CO2 during lateral transport, resulting in an additional decrease in CO2 fluxes within the SW fault zone. In other words, CO2 and CO2-charged brine originating from the LGW fault zone could migrate southward over 10–20 km through a series of high-permeable aquifers (e.g., Entrada, Navajo, Kayenta, Wingate, and White Rim Sandstones). These CO2-rich fluids could finally reach the southernmost Tumbleweed and Chaffin Ranch Geysers across the SW fault zone. The potential lateral transport of both CO2 and CO2-laden brine can be further supported by similar CO2/3He and 3He/4He ratios of gas and a systematic chemical evolution of water emitted from the regional springs and geysers, which suggest the same crustal origins of CO2 and CO2-rich brine for the region.

Analysis Of Fluvial Architecture In the Blackhawk Formation, Wasatch Plateau, Utah, U.S.A., Using Large 3D Photorealistic Models

Abstract There are numerous allocyclic and autocyclic factors which influence fluvial sandbody geometry. Unraveling the relative importance of such factors is challenging because fluvial systems can migrate and avulse across significant distances on the floodplain, so that collecting datasets that cover a large enough area with sufficient detail is difficult. This problem has been addressed by acquiring an oblique helicopter-mounted lidar survey over 16 km of exposed sections from Cretaceous coastal-plain deposits cropping out in the Wasatch Plateau of east-central Utah. The exposures of the Blackhawk Formation occur in steep cliffs, which are continuous for several tens of kilometers, and have been previously inaccessible for study. The recorded lidar data were used to build detailed photorealistic models (virtual outcrops) from which quantitative dimensional data on fluvial architectural elements (mostly sandstone channel bodies) were collected. Those channelized bodies show significant variation in width and thickness. 26% of the sandbodies were identified as being multistory channel bodies, with a thickness of 9.1 m (± 4.67 m; 1 σ) and a width of 142.6 m (± 180.7 m), which are significantly larger than the measured single-story sandbodies (5.9 m and 96.9 m, respectively). 50% of all sandbodies have aspect ratios smaller 13∶1 and the highest values reach 78∶1. The spatial constraint of the 397 fluvial sandbodies enabled the recognition of a series of vertical trends within the dataset. These trends include a subtle upward increase in width and thickness of both the mean and maximum values. This is coupled with a general upward decrease in the number of sandbodies and results in a broadly constant channel-to-overbank ratio. A clear correlation between wider channels with increased distance to the shoreline could also be documented. These observations can be explained by considering the entire Blackhawk Formation as the deposits of a large distributive fluvial system. In this model the key control on channel architecture is the distance to the shoreline, contrasting with previous interpretations of the Blackhawk depositional system in which the rate of accommodation creation in the coastal plain was thought to be the key control on channel geometry and stacking patterns.

Gopher Snake Searching Cliff Swallow Nests in East Central Utah

We report details of a serendipitous encounter in July 2010 with a gopher snake (Pituophis catenifer) hunting in the mud nests of Cliff Swallows (Petrochelidon pyrrhonota). The swallow nests occurred beneath a deeply overhung sandstone cliff ledge in a box canyon of Ferron Creek in the shale deserts near Ferren, Emery County, Utah. The inaccessibility of the nests and the movement of the snake to and through them attest to both the extraordinary climbing ability of the gopher snake and the nest site selection and nest construction ability of the swallows.