SE Utah Research Articles

Consequences of Piñon-Juniper Woodland Fuel Reduction: Prescribed Fire Increases Soil Erosion While Mastication Does Not

Fire suppression has increased fuel load and the risk of catastrophic wildfire in forest and woodland ecosystems across the Western United States. In an effort to reduce fuel load and restore historical structure and function, land managers have implemented fuel reduction treatments on millions of acres. Reducing fuel loads protects people, structures, and in some cases, improves ecosystem health. However, the ecological risks of soil surface disturbance related to fuel reduction strategies, and subsequent soil erosion, may be significant in some cases. Here, we examined the effects of common fuel reduction strategies (mechanical mastication and two techniques for prescribed burning) on wind and water erosion in two upland pinon-juniper woodlands in SE Utah over 2 years. We also tested the impact of broadcast seeding coupled with fuel reduction as a way to mitigate erosional soil loss. Finally, we analyzed biotic and abiotic predictor variables to evaluate important drivers of soil erosion following fuel treatments. We found that both techniques for prescribed burning—pile burning and broadcast burning—increased wind-related sediment fluxes by an average of 11-fold and 58-fold, respectively. Mastication did not increase wind-related losses over untreated controls. Erosional fluxes measured at silt fences, that captured both wind- and water-driven sediments, followed similar trends with moderate increases from pile burning (fivefold) but larger increases from broadcast burning (17-fold). Seeding did not affect erosion rates. Our results suggest that prescribed fire significantly increases soil erosion in fuel-treated pinon-juniper woodlands and may be a degradation pathway when implementing treatments.

Abutting faults: a case study of the evolution of strain at Courthouse branch point, Moab Fault, Utah

Abstract. Slip planes and slip directions of subsequent generations of faults were measured and analysed in the interaction damage zone of two abutting faults in porous sandstones in order to understand the palaeostress/palaeostrain evolution. The Courthouse branch point of the Moab Fault in SE Utah (USA) is a much-studied, spectacular outcrop of two abutting faults, located in the footwall block of the main fault and in the hanging wall block of the abutting fault. The abutting fault is synthetic to the main fault. The outcrop shows a wide range of deformation structures and fault-related diagenesis such as striated slip planes, deformation bands, veins, Liesegang bands and copper-rich mineralization. By combining our own measurements with published data on the relative age of these structures, we classified the data in four sets. Using a Numeric Dynamic Analysis (NDA) to calculate the orientation of the kinematic axes we found three different palaeo-extension directions in the four sets, recording the evolution of stress/strain axes during the abutting process. The first phase of deformation is regional extension in the NE–SW direction. As the second fault approached the main fault from its footwall side and the two faults started to become kinematically linked, the extension direction changed so that the overall extension became perpendicular to the approaching fault (NW–SE). Finally, the extension direction changed back to being perpendicular to the first segment (NE–SW) when the two faults became geometrically linked and regional extension became dominant again.

Characteristics of bleaching around major structures in a reservoir-cap rock system, SE Utah, USA

Bleached rocks are commonly formed from CO2-saturated water leakage to the surface. This provides an opportunity to understand the controlling factors of fluid flow in the subsurface. This study examined the relationships between bleaching patterns and geologic features or elements. We analyzed bleaching characteristics of multiple-layered sedimentary rocks around two major faults (Moab and Salt Wash faults) and fold axes (Green river anticline system) based on field observations and quantitative measurements (scanline survey and permeability) in the exhumed reservoir-cap rock systems in SE Utah, USA. The results showed that strongly bleached layers of sedimentary rock have a higher density of deformation bands compared with unbleached layers. This is consistent with the general property of deformation bands that frequently develop in layers with higher porosity and permeability. Although almost all fault zones act as conduits for fluid flow, some fault zones filled with clay-rich gouges could impede fluid flow. In addition, the internal sealing characteristics of the layer boundaries such as bedding planes could be important factors as they can act either as a pathway or a barrier for lateral fluid flow depending on the existence of filling materials such as calcite or kerogen. Our research may be useful for assessing fluid leakage in oil reservoirs or CO2 sequestration sites located in a reservoir-cap rock system of sedimentary basins.

Distribution of a New Invasive Species, Sipha maydis (Heteroptera: Aphididae), on Cereals and Wild Grasses in the Southern Plains and Rocky Mountain States.

Sipha maydis Passerini (Heteroptera: Aphididae) is a cereal pest with an extensive geographical range that includes countries in Europe, Asia, Africa, and South America. Reports of S. maydis in the United States have been infrequent since it was first detected in California, 2007. Two studies, focused (NW CO) and multistate (OK, TX, NM, CO, UT, WY), were conducted to determine the distribution and host range of S. maydis in the Rocky Mountain and Southern Plains states over a 3-yr period, 2015-2017. In 2015, focused sampling in NW Colorado found S. maydis at 59% of the 37 sites, primarily on wheat. Sipha maydis did not survive extreme winter temperatures from late December 2015 to early January 2016 that ranged from -9.0 to -20.9°C over a 9-d period, which resulted in no aphids detected in 2016. In the multistate study, S. maydis occurred in 14.6% of 96 sites sampled in 2015, 8% of 123 sites in 2016, and 9% of 85 sites in 2017 at wide range of altitudes from 1,359 to 2,645 m. Sipha maydis occurred mainly in NW and SW Colorado and NE New Mexico along with a few sites in NE Colorado, SE Utah, and SE Wyoming. This aphid mainly infested wheat followed by a variety of eight wild grass species. No parasites, predators, sexual morphs, or significant plant damage occurred at the sites. Sipha maydis utilized 14 hosts in the United States including 8 new host records, which expands its host range to 52 plant species worldwide. Sipha maydis may be of concern to wheat, barley, and sorghum production in the United States if its populations continue to increase.

Smoothing of Fault Slip Surfaces by Scale‐Invariant Wear

AbstractPrevious field observations suggest that fault slip surface roughness may decrease with slip. However, measurements have yet to confidently isolate the effect of slip from other possible controls, such as lithology or tectonic setting. We describe the evolution of slip surfaces in normal faults in SE Utah that cut well‐sorted, high‐porosity sandstones and accommodated regional extension at 1‐ to 4‐km depth. Tight controls on fault offset and uniform tectonic history allowed us to isolate the effect of slip during early stages of faulting (0‐ to 55‐m slip). Slip surfaces progress from rough joints and deformation bands toward smooth, continuous, and mirror‐like surfaces with increasing slip. We collected 123 scans of pristine slip surfaces, which measure surface geometry from micrometers to meters in length scale. Results indicate that slip surface roughness is systematically smoother than joint surfaces and deformation band edges. Over the best resolved length scales (0.1–10 mm), we observe roughness decreases with slip according to a power law with exponent −1 in the slip direction. Slip‐perpendicular profiles, though rougher, exhibit the same smoothing trend. The Hurst scaling exponent does not change with slip. These observations require wear to be multiscale. Boundary element method models suggest that mechanical wear of completely mated surfaces occurs by asperity failure and that the wear rate depends on the aspect ratio of asperities. These results indicate that at large slip, asperity failure at all length scales can cause slip surfaces to smooth while maintaining the fractal geometry characteristic of faults.

Climatic Sensitivity of Dryland Soil CO2 Fluxes Differs Dramatically with Biological Soil Crust Successional State

Arid and semiarid ecosystems make up approximately 41% of Earth’s terrestrial surface and are suggested to regulate the trend and interannual variability of the global terrestrial carbon (C) sink. Biological soil crusts (biocrusts) are common dryland soil surface communities of bryophytes, lichens, and/or cyanobacteria that bind the soil surface together and that may play an important role in regulating the climatic sensitivity of the dryland C cycle. Major uncertainties exist in our understanding of the interacting effects of changing temperature and moisture on CO2 uptake (photosynthesis) and loss (respiration) from biocrust and sub-crust soil, particularly as related to biocrust successional state. Here, we used a mesocosm approach to assess how biocrust successional states related to climate treatments. We subjected bare soil (Bare), early successional lightly pigmented cyanobacterial biocrust (Early), and late successional darkly pigmented moss-lichen biocrust (Late) to either ambient or + 5°C above ambient soil temperature for 84 days. Under ambient temperatures, Late biocrust mesocosms showed frequent net uptake of CO2, whereas Bare soil, Early biocrust, and warmed Late biocrust mesocosms mostly lost CO2 to the atmosphere. The inhibiting effect of warming on CO2 exchange was a result of accelerated drying of biocrust and soil. We used these data to parameterize, via Bayesian methods, a model of ecosystem CO2 fluxes, and evaluated the model with data from an autochamber CO2 system at our field site on the Colorado Plateau in SE Utah. In the context of the field experiment, the data underscore the negative effect of warming on fluxes both biocrust CO2 uptake and loss—which, because biocrusts are a dominant land cover type in this ecosystem, may extend to ecosystem-scale C cycling.

Cultural and Genetic Contexts for Early Turkey Domestication in the Northern Southwest

AbstractThe turkey (Meleagris gallopavo) was independently domesticated in Mesoamerica and the Southwest, the latter as the only case of Native American animal domestication north of Mexico. In the upland (non-desert) portion of the American Southwest, distinctive closely related mtDNA lineages belonging to haplogroup H1 (thought to indicate domestication) occur from ca. 1 A.D. (Basketmaker II period) through early historic times. At many sites, low frequencies of lineages belonging to haplogroup H2 also occur, apparently derived from the local Merriam’s subspecies. We report genetic, stable isotope, and coprolite data from turkey remains recovered at three early sites in SE Utah and SW Colorado dating to the Basketmaker II, III, and early Pueblo II periods. Evidence from these and other early sites indicates that both the H1 and H2 turkeys had a predominantly maize-based diet similar to that of humans; prior to late Pueblo II times, the birds were kept primarily to provide feathers for blankets and ritual uses; and ritualized burials indicate turkeys’ symbolic value. We argue that viewing individuals from the H1 and H2 haplogroups as “domestic” versus “wild” is an oversimplification.

Salt-dissolution faults versus tectonic faults from the case study of salt collapse in Spanish Valley, SE Utah (USA)

A paleoseismological investigation in Spanish Valley, SE Utah, reveals that faults related to interstratal karstification of salt may show episodic displacement and significantly different parameters than tectonic faults. Spanish Valley is a 25-km-long, 3-km-wide, NW-SE–trending graben formed by the collapse of the crest of a salt anticline. This collapse is related to the karstification of Paleozoic salts, which are several kilometers thick and form the core of the anticline. Differential passive bending of the supra-evaporitic Mesozoic strata produced smaller-scale, NW-SE–trending anticlines and synclines parallel to the axis of the graben on both margins of the collapse valley. Mapping reveals that swarms of synthetic and antithetic normal faults associated with these folds accommodate most of the vertical displacement. A 27-m-long, 4.5-m-deep, trench-like artificial excavation was dug into the hanging wall of the master normal fault of the NE flank with 30–40 m of throw. The excavation exposed a complex structure consisting of a half graben and an asymmetric upper graben separated by a horst. Nine displacement events have been inferred and constrained by consistent AMS (Accelerator mass spectrometry) radiocarbon dates, indicating an anomalously high mean vertical slip rate of 3.07 mm/yr and a very low average recurrence of ∼316 yr. The most recent recorded faulting event took place after 2330 cal. yr B.P. Data derived from detailed maps indicate that the faults have aspect ratios (maximum displacement to fault length) comparable to those reported for tectonic faults. However, they show greater aperiodicity, with coefficient of variation values greater than 1, long-term slip rates between 2 and 25 times greater, and displacement per event values up to 30 times higher than those expected for tectonic faults of the same length.

Fracture corridors as seal-bypass systems in siliciclastic reservoir-cap rock successions: Field-based insights from the Jurassic Entrada Formation (SE Utah, USA)

Closely spaced, sub-parallel fracture networks contained within localized tabular zones that are fracture corridors may compromise top seal integrity and form pathways for vertical fluid flow between reservoirs at different stratigraphic levels. This geometry is exemplified by fracture corridors found in outcrops of the Jurassic Entrada Formation in Utah (USA). These fracture corridors exhibit discolored (bleached) zones, interpreted as evidence of ancient fracture-enhanced circulation of reducing fluids within an exhumed siliciclastic reservoir-cap rock succession. Extensive structural and stratigraphic mapping and logging provided fracture data for analysis with respect to their occurrence and relationships to larger faults and folds. Three types of fracture corridors, representing end-members of a continuum of possibly interrelated structures were identified: 1) fault damage zone including segment relays; 2) fault-tip process zone; and 3) fold-related crestal-zone fracture corridors. The three types exhibit intrinsic orientations and patterns, which in sum define a local- to regional network of inferred vertical and lateral, high-permeability conduits. The results from our analysis may provide improved basis for the evaluation of trap integrity and flow paths across the reservoir-cap rock interface, applicable to both CO2 storage operations and the hydrocarbon industry.

Syn-sedimentary salt diapirism as a control on fluvial-system evolution: an example from the proximal Permian Cutler Group, SE Utah, USA

Loading of subsurface salt during accumulation of fluvial strata can result in halokinesis and the growth of salt pillows, walls and diapirs. Such movement may eventually result in the formation of salt-walled mini-basins, whose style of architectural infill may be used to infer both the relative rates of salt-wall growth and sedimentation and the nature of the fluvial-system response to salt movement. The Salt Anticline Region of the Paradox Basin of SE Utah comprises a series of elongate salt-walled mini-basins, arranged in a NW-trending array. The bulk of salt movement occurred during deposition of the Permian Cutler Group, a wedge of predominantly quartzo-feldspathic clastic strata comprising sediment derived from the Uncompahgre Uplift to the NE. The sedimentary architecture of selected mini-basin fills has been determined at high resolution through outcrop study. Mini-basin centres are characterized by multi-storey fluvial channel elements arranged into stacked channel complexes, with only limited preservation of overbank elements. At mini-basin margins, thick successions of fluvial overbank and sheet-like elements dominate in rim-syncline depocentres adjacent to salt walls; many such accumulations are unconformably overlain by single-storey fluvial channel elements that accumulated during episodes of salt-wall breaching. The absence of gypsum clasts suggests that sediment influx was high, preventing syn-sedimentary surface exposure of salt. Instead, fluvial breaching of salt-generated topography reworked previously deposited sediments of the Cutler Group atop growing salt walls. Palaeocurrent data indicate that fluvial palaeoflow to the SW early in the history of basin infill was subsequently diverted to the W and ultimately to the NW as the salt walls grew to form topographic barriers. Late-stage retreat of the Cutler fluvial system coincided with construction and accumulation of an aeolian system, recording a period of heightened climatic aridity. Aeolian sediments are preserved in the lees of some salt walls, demonstrating that halokinesis played a complex role in the differential trapping of sediment.

Twentieth century carbon stock changes related to Piñon-Juniper expansion into a black sagebrush community

BackgroundIncreases in the spatial extent and density of woody plants relative to herbaceous species have been observed across many ecosystems. These changes can have large effects on ecosystem carbon stocks and therefore are of interest for regional and national carbon inventories and for potential carbon sequestration or management activities. However, it is challenging to estimate the effect of woody plant encroachment on carbon because aboveground carbon stocks are very heterogeneous spatially and belowground carbon stocks exhibit complex and variable responses to changing plant cover. As a result, estimates of carbon stock changes with woody plant cover remain highly uncertain. In this study, we use a combination of plot- and remote sensing-based techniques to estimate the carbon impacts of piñon and juniper (PJ) encroachment in SE Utah across a variety of spatial scales with a specific focus on the role of spatial heterogeneity in carbon estimates.ResultsAt a plot scale (300 m2) areas piñon juniper (PJ) encroached areas had 0.26 kg C m-2 less understory vegetation carbon compared to un-encroached sites. This lower amount of carbon was offset by an average of 1.82 kg C m-2 higher carbon in PJ vegetation and 0.50 kg m-2 of C in PJ surface-litter carbon. Soil mineral carbon stocks were unaffected by woody plant cover and density. Aboveground carbon stocks were highly dependent on PJ vegetation density. At a 300 m2 plot-scale, plots with low and high density of PJ forest had 1.40 kg C m-2 and 3.69 kg m-2 more carbon than the un-encroached plot. To examine how these 300 m2 variations influence landscape scale C estimates, historical and contemporary aerial photos were analyzed to develop forest density maps in order to estimate above ground PJ associated C stock changes in a 25 ha area. This technique yielded an average estimate of 1.43 kg m-2 of C accumulation with PJ encroachment. Combining this estimate with analysis of tree growth increments from dendrochronologies, we estimate that these PJ stands are accumulating aboveground C at an annual rate of 0.02 kg C m-2 with no slowing of this rate in healthy PJ. This result is in contrast to what has been observed in large areas of drought related PJ mortality, where C accumulation has ceased.ConclusionsThese results illustrate that the encroachment of PJ forests in SE Utah over the last century has resulted in a large (and ongoing) accumulation of carbon in PJ trees and surface litter. However, the magnitude of the increase depends to on the density of vegetation across the landscape and the health of forest stands. Both management activities that remove forest carbon and forest mortality due to drought or wildfire have the potential to quickly reverse the multi-decadal accumulation of carbon in these stands.

Controls on fluvial sedimentary architecture and sediment‐fill state in salt‐walled mini‐basins: Triassic Moenkopi Formation, Salt Anticline Region, SE Utah, USA

AbstractThe Triassic Moenkopi Formation in the Salt Anticline Region, SE Utah, represents the preserved record of a low‐relief ephemeral fluvial system that accumulated in a series of actively subsiding salt‐walled mini‐basins. Development and evolution of the fluvial system and its resultant preserved architecture was controlled by the following: (1) the inherited state of the basin geometry at the time of commencement of sedimentation; (2) the rate of sediment delivery to the developing basins; (3) the orientation of fluvial pathways relative to the salt walls that bounded the basins; (4) spatially and temporally variable rates and styles of mini‐basin subsidence and associated salt‐wall uplift; and (5) temporal changes in regional climate. Detailed outcrop‐based tectono‐stratigraphic analyses demonstrate how three coevally developing mini‐basins and their intervening salt walls evolved in response to progressive sediment loading of a succession of Pennsylvanian salt (the Paradox Formation) by the younger Moenkopi Formation, deposits of which record a dryland fluvial system in which flow was primarily directed parallel to a series of elongate salt walls. In some mini‐basins, fluvial channel elements are stacked vertically within and along the central basin axes, in response to preferential salt withdrawal and resulting subsidence. In other basins, rim synclines have developed adjacent to bounding salt walls and these served as loci for accumulation of stacked fluvial channel complexes. Neighbouring mini‐basins exhibit different styles of infill at equivalent stratigraphic levels: sand‐poor basins dominated by fine‐grained, sheet‐like sandstone fluvial elements, which are representative of nonchannelised flow processes, apparently developed synchronously with neighbouring sand‐prone basins dominated by major fluvial channel‐belts, demonstrating effective partitioning of sediment route‐ways by surface topography generated by uplifting salt walls. Reworked gypsum clasts present in parts of the stratigraphy demonstrate the subaerial exposure of some salt walls, and their partial erosion and reworking into the fill of adjoining mini‐basins during accumulation of the Moenkopi Formation. Complex spatial changes in preserved stratigraphic thickness of four members in the Moenkopi Formation, both within and between mini‐basins, demonstrates a complex relationship between the location and timing of subsidence and the infill of the generated accommodation by fluvial processes.

Should dates trump context? Evaluation of the Cave 7 skeletal assemblage radiocarbon dates

“Massacre” was the accepted interpretation for a prehistoric skeletal assemblage of around 90 individuals from Cave 7 in the SE Utah of the North American Southwest since the 1890s. Coltrain and others (Journal of Archaeological Science 39, 2220–2230) rejected this account based on a dispersed suite of AMS radiocarbon dates on purified bone collagen from the interred individuals. Since dates from skeletons exhibiting perimortem damage were scattered across some 400 radiocarbon years, Coltrain et al. argued for multiple interments of victims of violence and related kin spread across several centuries. The temporal placement of interment events in Cave 7 clearly cannot be known independent of radiocarbon assays but such assays should not be privileged above contextual information about which individuals were interred together unless verified by an independent dating laboratory. Only by ignoring important information about burial context in the 1893 field record can the dates of Coltrain et al. be accepted as accurate estimates of time of death. We redated residual collagen from 11 of the Cave 7 individuals because of significant contextual anomalies with some of the prior results. The new assays combined with contextual evidence demonstrate that some of Coltrain et al.’s dates are either too old or too young; the dates are neither sufficiently accurate (true estimates of sample age) nor sufficiently precise (small confidence intervals) to refute a single-event massacre or to confirm multiple interment events in Cave 7. Nonetheless, dates that meet these criteria disclose at least two interment events, a large one of mostly adult males, many exhibiting perimortem damage (a massacre assemblage), and a small one consisting of an adult female with three children. A third interment event of a few adult females and child is possible based primarily on context since the date distribution in this case overlaps substantially with that of the massacre victims; context also hints at other interment events. Aside from chronology we clarify the number of Basketmaker individuals interred at the site and the incidence of perimortem violence. A single-event mass killing continues to be the most likely interpretation for around 58 individuals, mostly adult males (at least 35) but also adult females and children. This incident occurred between cal. AD 20–80 and doubtless had a significant social impact at the time because of its scale, reverberating throughout the early farming communities of the Southwest.

Stone-boiling maize with limestone: experimental results and implications for nutrition among SE Utah preceramic groups

Groups living on Cedar Mesa, SE Utah in the late Basketmaker II period (Grand Gulch phase, AD 200–400) were heavily maize-dependent, but lacked beans as a supplemental plant protein, and pottery vessels for cooking. Common occurrence of limestone fragments in their household middens suggests 1) limestone may have been used as the heating element for stone-boiling maize and 2) this practice might have made some maize proteins more available for human nutrition. Experiments examined these possibilities; results indicate that stone-boiling with Cedar Mesa limestone creates an alkaline cooking environment suitable for nixtamalization of maize kernels, and that maize cooked in this fashion shows significant increases in availability of lysine, tryptophan, and methionine. Archaeological limestone fragments from a Grand Gulch phase site show amounts of fragmentation and changes in density consistent with repeated heating. While not conclusive, these data indicate that further research (e.g., examination of archaeological limestone fragments for maize starch grains or phytoliths) is warranted. It is suggested that greater attention be paid to archaeological indications of stone-boiling with limestone among maize-dependent but pre-pottery societies.

Deformation bands formed during soft-sediment deformation: Observations from SE Utah

Several types of syndepositional deformation structures contain strain localization structures known as disaggregation bands. Abundant field examples from Utah show that such bands can be related to vertical movements linked to loading and fluid expulsion, forming a pre-tectonic set of strain localization structures in deformed sandstones that can easily be overlooked or misinterpreted as tectonic structures in petroleum reservoirs. Plug measurements and thin-section investigations show that they have little or no influence on fluid flow. In contrast, disaggregation bands formed as a response to tectonic stress at higher confining pressures (depths) in the same lithology show up to 3–4 orders of magnitude reduction in permeability. This makes it important to distinguish between synsedimentary and tectonic deformation bands. They should also be separated because only bands formed in relation to tectonic stress can be used to predict nearness to important faults and to assess the extent of faulting in a reservoir.

Eolian Topography as a Control on Deposition Incorporating Lessons from Modern Dune Seas: Permian Cedar Mesa Sandstone, SE Utah, U.S.A.

Abstract The dominant current model for the accumulation of eolian strata in the rock record emphasizes translation and climb of bedforms and the preservation of continuous beds. Studies of modern dune fields, however, show that, when large dunes form, they create a topographically irregular surface; later episodes of eolian activity commonly fill the low-lying areas between the older dunes, resulting in beds that are laterally discontinuous. Strata in part of the Permian Cedar Mesa Sandstone in southeastern Utah require this model. In this new model, inherited eolian topography influences subsequent deposition. Detailed GPS mapping of an 8 km2 area was used to trace eolian strata through a 20–25-m-thick unit in the Cedar Mesa Sandstone. The unit is bounded above and below by subparallel erosion surfaces that have up to 5 m of relief. Within the unit, large transverse draa (or megadune) deposits, are spaced 1 km apart. Locally (over 0.5 km wide areas), the draa deposits fill the entire 25 m thickness of the unit, only to be completely replaced by interdraa deposits a few hundred meters away. The draa surfaces were eroded and exposed prior to the filling of the intervening lows with alternations of barchanoid dune deposits, sand sheets, and ponds, which formed in the topographic lows. The Cedar Mesa Sandstone illustrates aggradation wherein the important factor is the preserved eolian topography. The draas formed an undulating stable surface, from which subsequent deposition filled the interdraa low. Large eolian dunes that influenced subsequent deposition are also observed in several Pleistocene to Recent dune seas. This mechanism offers an alternative to the existing models that require continuous migration of large dunes.

Upheaval Dome, Utah, USA: Impact origin confirmed

Research Article| March 01, 2008 Upheaval Dome, Utah, USA: Impact origin confirmed Elmar Buchner; Elmar Buchner 1Institut für Planetologie, Universität Stuttgart, 70174 Stuttgart, Germany Search for other works by this author on: GSW Google Scholar Thomas Kenkmann Thomas Kenkmann 2Museum für Naturkunde-Mineralogie, Humboldt-Universität zu Berlin, 10115 Berlin, Germany Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (3): 227–230. https://doi.org/10.1130/G24287A.1 Article history received: 27 Jul 2007 rev-recd: 02 Nov 2007 accepted: 06 Nov 2007 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Elmar Buchner, Thomas Kenkmann; Upheaval Dome, Utah, USA: Impact origin confirmed. Geology 2008;; 36 (3): 227–230. doi: https://doi.org/10.1130/G24287A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Upheaval Dome is a unique circular structure on the Colorado Plateau in SE Utah, the origin of which has been controversially discussed for decades. It has been interpreted as a crypto volcanic feature, a salt diapir, a pinched-off salt diapir, and an eroded impact crater. While recent structural mapping, modeling, and analyses of deformation mechanisms strongly support an impact origin, ultimate proof, namely the documentation of unambiguous shock features, has yet to be successfully provided. In this study, we document, for the first time, shocked quartz grains from this crater in sandstones of the Jurassic Kayenta Formation. The investigated grains contain multiple sets of decorated planar deformation features. Transmission electron microscopy (TEM) reveals that the amorphous lamellae are annealed and exhibit dense tangles of dislocations as well as trails of fluid inclusions. The shocked quartz grains were found in the periphery of the central uplift in the northeastern sector of the crater, which most likely represents the cross range crater sector. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Dynamics of cover, UV-protective pigments, and quantum yield in biological soil crust communities of an undisturbed Mojave Desert shrubland

Biological soil crusts are an integral part of dryland ecosystems. We monitored the cover of lichens and mosses, cyanobacterial biomass, concentrations of UV-protective pigments in both free-living and lichenized cyanobacteria, and quantum yield in the soil lichen species Collema in an undisturbed Mojave Desert shrubland. During our sampling time, the site received historically high and low levels of precipitation, whereas temperatures were close to normal. Lichen cover, dominated by Collema tenax and C. coccophorum, and moss cover, dominated by Syntrichia caninervis, responded to both increases and decreases in precipitation. This finding for Collema spp. at a hot Mojave Desert site is in contrast to a similar study conducted at a cool desert site on the Colorado Plateau in SE Utah, USA, where Collema spp. cover dropped in response to elevated temperatures, but did not respond to changes in rainfall. The concentrations of UV-protective pigments in free-living cyanobacteria at the Mojave Desert site were also strongly and positively related to rainfall received between sampling times ( R 2 values ranged from 0.78 to 0.99). However, pigment levels in the lichenized cyanobacteria showed little correlation with rainfall. Quantum yield in Collema spp. was closely correlated with rainfall. Climate models in this region predict a 3.5–4.0 °C rise in temperature and a 15–20% decline in winter precipitation by 2099. Based on our data, this rise in temperature is unlikely to have a strong effect on the dominant species of the soil crusts. However, the predicted drop in precipitation will likely lead to a decrease in soil lichen and moss cover, and high stress or mortality in soil cyanobacteria as levels of UV-protective pigments decline. In addition, surface-disturbing activities (e.g., recreation, military activities, fire) are rapidly increasing in the Mojave Desert, and these disturbances quickly remove soil lichens and mosses. These stresses combined are likely to lead to shifts in species composition and the local extirpation of some lichen or moss species. As these organisms are critical components of nutrient cycling, soil fertility, and soil stability, such changes are likely to reverberate throughout these ecosystems.

Earthen Architecture at the Bluff Great House Site in SE Utah

An earthen terrace has been identified at Bluff Great House, a Chacoan site located in SE Utah. The Bluff site was part of the Chacoan regional system that operated in the northern part of the American Southwest between about A.D. 900 and 1150 and was focused on Chaco Canyon in NW New Mexico. Several types of earthen structures have been identified at great houses in Chaco Canyon and throughout its region, usually associated with the construction of ritual landscapes. The Bluff terrace is part of this tradition of earthen construction, but is unlike most other reported examples. It seems to express the same concern with creating an appropriate setting, however, and may be interpreted as part of the ritual landscape that surrounded and defined the Bluff great house, although other interpretations are considered. It dates not only to the Chaco era, but also to the first part of the post-Chaco era (A.D. 1150–1225).

Direct Effects of Soil Amendments on Field Emergence and Growth of the Invasive Annual Grass Bromus tectorum L. and the Native Perennial Grass Hilaria jamesii (Torr.) Benth

Bromus tectorum L. is a non-native, annual grass that has invaded western North America. In SE Utah, B. tectorum generally occurs in grasslands dominated by the native perennial grass, Hilaria jamesii (Torr.) Benth. and rarely where the natives Stipa hymenoides Roem. and Schult. and S. comata Trin. & Rupr. are dominant. This patchy invasion is likely due to differences in soil chemistry. Previous laboratory experiments investigated using soil amendments that would allow B. tectorum to germinate but would reduce B. tectorum emergence without affecting H. jamesii. For this study we selected the most successful treatments (CaCl2, MgCl2, NaCl and zeolite) from a previous laboratory study and applied them in the field in two different years at B. tectorum-dominated field sites. All amendments except the lowest level of CaCl2 and zeolite negatively affected B. tectorum emergence and/or biomass. No amendments negatively affected the biomass of H. jamesii but NaCl reduced emergence. Amendment effectiveness depended on year of application and the length of time since application. The medium concentration of zeolite had the strongest negative effect on B. tectorum with little effect on H. jamesii. We conducted a laboratory experiment to determine why zeolite was effective and found it released large amounts of Na+, adsorbed Ca2+, and increased Zn2+, Fe2+, Mn2+, Cu2+, exchangeable Mg2+, exchangeable K, and NH4+ in the soil. Our results suggest several possible amendments to control B. tectorum. However, variability in effectiveness due to abiotic factors such as precipitation and soil type must be accounted for when establishing management plans.