South-central Utah Research Articles

Factors affecting seasonal movements of juvenile Greater Sage-Grouse: A reconceptualized nest survival model

ABSTRACT Estimating the climatic and habitat factors that affect animal movement patterns (e.g., migration, dispersal, site fidelity) is informative for management and conservation. Juvenile Greater Sage-Grouse (Centrocercus urophasianus) have been identified as having a significant influence on population growth, but relatively little is known about factors that influence survival, movement, and the potential interrelation between the two. Movement out of fall habitat has been suggested to influence the survival of juvenile Greater Sage-Grouse. We reconceptualized the nest survival model (equating movement out of a focal area with failure of a nest) to extend its use to movement data on juveniles in south-central Utah. We found that juveniles' seasonal movements were affected by a linear trend in time (β = −0.655, 95% confidence interval [CI]: −1.049 to −0.26) and by precipitation (β = −3.718, 95% CI: −6.687 to −0.749), with an interaction between the parameters (β = 0.360, 95% CI: 0.002–0.718). In the a...

Copper King Mining Company: A Case Study In Using Loans And Equity To Finance A Start-Up

The proposed Copper King mine in south central Utah was expected to produce millions of dollars in copper, gold and silver. A nearby struggling town and thousands of speculators and large banks seized upon this promise. They all were willing to invest in developing the mine. Copper King tried a wide variety of financing approaches, one at a time, over a several year period during which a significant amount of funds were raised. The financing options employed allow a study of the technical financing requirements of each of the options (hard money loans, waterfall loans, private equity and public equity). Copper King Mining Company is a lesson in the difficulties of financing a start-up. Important theoretical concepts include the problem of banks dealing with asymmetric information and moral hazard, along with the tools they use to mitigate that risk. Asset valuation and the price of risk are also important lessons in this case.This case is most appropriate for classes in corporate finance, money and banking, investing and entrepreneurship.

A risk-based hydro-economic analysis for land and water management in water deficit and salinity affected farming regions

For on-farm decision-making in salinity affected water deficit regions, a hydro-economic analysis helps developing consistent resource management plans considering biophysical and economic constraints. However, variability of crop prices and yields is a practical difficulty when valuating resources. In this study, we proposed a novel hybrid framework that considers variable crop prices and yields to develop resource allocation strategies using a risk-based economic model. The FAO AquaCrop model and a linear regression model were used for yield simulation and price estimation, respectively. The predicted variability of crop prices and yields from these models are incorporated into the risk-based economic model. The hydro-economic analysis was conducted for making producers' pre-season decisions on land and water allocations in salinity-affected agricultural lands in south central Utah. The results showed alfalfa-dominant land and water allocation strategies are suitable options due to the high price and low production costs of alfalfa under high surface water availability. With limited surface water availability, the results opted to rent water rights to soils with high maize productivity for higher profits. The risk aversion behavior led to land and water allocation strategies with less variable profits. It was also found that the salinity stress severely degraded water productivity. The proposed approach provide a framework to manage resources for agricultural production in salnity affected and water deficits regions under variable price and climatic conditions.

Valleys, Estuaries, and Lagoons: Paleoenvironments and Regressive–Transgressive Architecture of the Upper Cretaceous Straight Cliffs Formation, Utah, U.S.A

Abstract: The John Henry Member of the Upper Cretaceous Straight Cliffs Formation preserves deposition of four regressive–transgressive (R-T) cycles in 350 m of strata of the Sevier foredeep in south-central Utah, USA. Each cycle is discussed in detail, with emphasis on the transgressive phases of deposition. Regressive intervals comprise wave-dominated shorefaces and coastal-plain strata, whereas transgressive intervals record tide-influenced coastal-margin and low-energy-bay and lagoonal deposits. One R-T cycle in the lower John Henry Member preserves a compound incised-valley system filled with a complex assemblage of tidal and estuarine facies. In contrast, overlying R-T cycles are not associated with valley formation, but instead preserve sandstone-rich back-barrier platform deposits that transition landward into tidal-creek, tidal-flat, and marsh depositional settings. Excellent outcrop expression permits detailed examination of the complex internal architecture of the compound incised-valley, and demonstrates that: 1) tidal ravinement significantly modified the initial valley shape during transgression, a process not fully recognized in most conceptual models of valley formation and fill; 2) the valley system incised in a basin-axial position (NNE–SSW), subparallel to the thrust front and oblique to the orientation of pre-valley-formation shorefaces, which prograded from west to east. Axial systems are well-known transporters of large volumes of sediment in foreland basins, and yet most incised-valley models imply a direct and oversimplified relationship between up-dip (source area and tectonics) and down-dip (base level) controls; 3) the major subaerial unconformity and bypass surface occurred at a higher (younger) stratigraphic position than previously interpreted, and is herein renamed the lower John Henry Member sequence boundary. The changes in regional correlations necessitated by this discovery have several broader implications for sequence stratigraphic models; 4) finally, correlations down dip along the axial valley system indicate a steep topographic gradient of 0.011, with 47% vertical, compacted expansion of the whole John Henry Member over 14 km from south to the north. This suggests structural control on sediment transport and deposition, with significant lateral variability in accommodation parallel to the fold-thrust belt. This study adds to the growing body of literature documenting the complex nature of transgressive deposits, which will aid in the interpretation, prediction, and management of analogous subsurface reservoirs.

Palynology of the Upper Cretaceous (Turonian) Ferron Sandstone Member, Utah, USA: identification of marine flooding surfaces and Milankovitch cycles in subtropical, ever-wet, paralic to non-marine palaeoenvironments

The Upper Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah includes coal and gas deposits and is an important outcrop analogue to study reservoir characterisation of fluvial–deltaic petroleum systems. Numerous sedimentological and sequence stratigraphic studies of the Notom fluvial–deltaic wedge have been conducted recently; however, palynological analyses had not previously been undertaken. Here, we present palynological data from 128 samples collected in the Notom wedge of the Ferron Sandstone Member outcropping in south-central Utah. The purpose of this study is to use palynological analysis to refine the broader depositional environments, evaluate the climatic setting, and to build a biostratigraphic palynological framework. The dominance of terrestrial palynomorphs, especially the high yield of moisture-loving cryptogam spores, indicates a primarily ever-wet depositional environment characteristic of hydromorphic floodplain palaeosols formed in subtropical to tropical climates. Although dinoflagellates are rare, four intervals with occurrences of marine cysts indicate periods of increased marine/tidal influence associated with previously identified flooding surfaces within Milankovitch-scale parasequences of the largely non-marine stratal succession. These flooding surfaces confirm correlations from regional high-resolution sequence stratigraphic studies and allow correlative marine parasequences and systems tracts to be extended within floodplain-dominated stratal successions. The presence of Nyssapollenites albertensis pollen places the interval studied within the Nyssapollenites albertensis Interval Zone (Nichols 1994), constraining the age of the Ferron Sandstone Member to the latter part of the Cenomanian and the early Coniacian. This largely agrees with the bentonite- and ammonite-derived Turonian age proposed in previous studies.

The Slothful Claw: Osteology and Taphonomy of Nothronychus mckinleyi and N. graffami (Dinosauria: Theropoda) and Anatomical Considerations for Derived Therizinosaurids.

Nothronychus was the first definitive therizinosaurian discovered in North America and currently represents the most specialized North American therizinosaurian genus. It is known from two species, No. mckinleyi from the Moreno Hill Formation (middle Turonian) in west-central New Mexico, and No. graffami from the Tropic Shale (early Turonian) in south-central Utah. Both species are represented by partial to nearly complete skeletons that have helped elucidate evolutionary trends in Therizinosauria. In spite of the biogeographical and evolutionary importance of these two taxa, neither has received a detailed description. Here, we present comprehensive descriptions of No. mckinleyi and No. graffami, the latter of which represents the most complete therizinosaurid skeleton known to date. We amend previous preliminary descriptions of No. mckinleyi and No. graffami based on these new data and modify previous character states based on an in-depth morphological analysis. Additionally, we review the depositional history of both specimens of Nothronychus and compare their taphonomic modes. We demonstrate that the species were not only separated geographically, but also temporally. Based on ammonoid biozones, the species appear to have been separated by at least 1.5 million years and up to 3 million years. We then discuss the impacts of diagenetic deformation on morphology and reevaluate potentially diagnostic characters in light of these new data. For example, the ulna of No. mckinleyi is curved whereas the ulna of No. graffami was considered straight, a character originally separating the two species. However, here we present the difference as much more likely related to diagenetic compression in No. graffami rather than as a true biologic difference. Finally, we include copies of three-dimensional surface scans of all major bones for both taxa for reference.

Stable isotopic insights into paleoclimatic conditions and alluvial depositional processes in the Kaiparowits Formation (Campanian, south-central Utah, U.S.A.)

The Kaiparowits Formation contains an exceptionally rich history of tectonic, climatic, and biologic conditions within the Western Interior of North America during the Campanian. Here we reconstruct aspects of the southern Cordilleran foreland basin's paleohydrology using δ18O and δ13C values determined from unionoid bivalve shells and pedogenic carbonate nodules derived from a suite of lithofacies associations. Unionoid shells derived from fluvial deposits display average water δ18O estimates of −13.7‰ ± 2.1 (1σ) (VSMOW) and shell δ13C values of −4.0‰ ± 1.5 (VPDB), whereas pedogenic carbonate nodules display average values of −6.0‰ ± 0.5 and −8.7‰ ± 0.8, respectively. Unionoid shells derived from pond deposits fall in between the two other environments with average values of −9.5‰ ± 1.8 and −5.7‰ ± 2.1, in δ18O and δ13C values respectively. Water δ18O estimates are interpreted to represent high altitude runoff within river systems, low elevation precipitation within the basin onto floodplain soils, and varying degrees of mixing between these two components within floodplain ponds. δ13C values track the isotopic composition of dissolved inorganic carbon within river, soil, and pond waters with high values likely reflecting greater contribution from chemically weathered marine carbonates exposed in the hinterland and lower values reflecting greater contributions from the in situ degradation of plant matter. Up-section there is a shift to lower δ18O values and higher δ13C values in fluvially-derived unionoid shells that post-dates an incursion of the Western Interior Seaway, but coincides with a shift in sediment provenance, an increase in basin sedimentation rates, and a change to a more anastomosed-style channel morphology within the basin foredeep depocentre. By combining the isotopic patterns with previously published sedimentologic, climate model, and paleofloral records we find: 1) additional evidence for humid, wet, and potentially monsoonal conditions within the region, 2) support for a tectonic uplift event, potentially related to Laramide deformation, and 3) greater aggradation and overbank flooding within the alluvial system in response to the uplift event.

Paleohydrology and 3D Facies Architecture of Ancient Point Bars, Ferron Sandstone, Notom Delta, South-Central Utah, U.S.A

Abstract Most outcrops of fluvial deposits consist of a series of cliff exposures, either natural or manmade (e.g., roadcuts). Predictions, and especially observation of plan-form geometry, such as might be made with numerical experiments or from studies of modern rivers, are challenging to test in most ancient outcrops. This study examines ancient exhumed channel belts from the Cretaceous Notom Delta of the Ferron Sandstone Member in south-central Utah. Extensive plan-view exposures with local vertical cliff exposures allowed documentation of channel plan-form, channel-belt dimension, bar migration patterns (translation versus expansion), and cross-sectional facies architecture. Channel-fill thickness and bedding structure, documented from the cliff exposures, were used in paleohydraulic reconstructions. Approximately 270 paleocurrent directions were integrated with grain-size measurements to reconstruct the 3D facies architecture. Paleocurrent measurements are consistent within specific facies architectural units (such as unit bars) and show systematic variation at the channel-belt scale that can be used to infer channel and bar migration patterns. In this example, the migration pattern of the single-thread channel bend was interpreted to change from expansion to translation with a corresponding bend sinuosity that increased from 1.01 to 1.44. Inclined large-scale foresets are interpreted to be indicative of unit bars. Empirical equations result in estimated average channel depths from 1.7 m to 3.6 m with corresponding widths of 23 m to 89 m respectively. These empirical estimates match the dimensions measured in the field. For example, channel widths of around 50 m were measured from abandoned channel fills. Bar thickness, measured from vertical outcrops, ranges from 5.4 m to 6.3 m, which yields a narrower estimate of channel width ranging from 47 to 59 m. Integration of sediment size, bedforms type, and channel depth were used to estimate the discharge of the river, which is on the order of < 400 m3/s. This suggests that the Ferron deltas were characterized by small, steep-gradient “dirty” rivers, which is consistent with the hyperpycnal nature of linked downstream deltaic systems.

Sedimentology and Paleontology of the Upper Cretaceous Wahweap Formation sag ponds adjacent to syndepositional normal faults, Grand Staircase-Escalante National Monument, Utah

During the development of the East Kaibab monocline, listric normal faulting related to outer arc influenced the sedimentation style of the Upper Cretaceous Wahweap Formation. The initiation of the Laramide Orogeny was therefore recorded in the sedimentary record of south-central Utah. Evidence for this includes the preservation of sag ponds adjacent to two of the normal faults in our study area, which developed when fault movement created topographic features. Ancient sag-pond deposits are likely under-identified in the rock record. This study demonstrates their significance and potential for unraveling fault histories.The northern, younger, sag-pond deposit is located at the boundary between the upper and capping sandstone members of the Wahweap Formation, and consists of sandstone dikes and sills hosted in gray mudstones and siltstones with no discernable invertebrate fauna, but some small macerated flora. The second southern sag-pond fill, is located at the base of the upper member. The sag pond is older, larger in area, and contains a thicker deposit. In contrast to the northern sag-pond deposit siltstones and mudstones are gray and visiblity structureless. Within the southern sag pond there are a series of fossil horizons consisting mainly of juvenile unionid bivalves, a lesser number of gastropods, and macerated plants. Comparison of the two preserved Upper Cretaceous sag-pond deposits suggests two distinct responses to fault movement, perhaps governed by fault kinematics, manifested in sedimentation style and type; the impact of faunal invertebrate invasion; and post-sedimentation deformation.

Greater palaeobiodiversity in conifer seed cones in the Upper Jurassic Morrison Formation of Utah, USA

Although fossil conifer wood, leaves, and pollen have been known from the Upper Jurassic Morrison Formation of the Western Interior of North America for many decades, only a few conifer seed cones have been described as carbonaceous compressions and casts with little internal structure. Recently, however, over 60 silicified seed cones with preserved internal anatomy were amassed by collectors from 11 localities in northeastern and southern Utah and brought to the attention of palaeobotanists. Here we describe the silicified cones from Utah and compare them to one another in size, gross morphology and internal construction. The fossil material is sorted into five new morphotypes of seed cone. Morphotype 1 pertains to Araucariaceae, Morphotype 2 is most likely Pinaceae, and Morphotype 5 is Cheirolepidiaceae. The familial affinity of Morphotypes 3 and 4 cannot be determined at this time. Comparative size analysis based on volume calculations shows that Morphotypes 2, 3, 4 and 5 are extremely small, smaller than any Mesozoic araucarian seed cone, and that Morphotype 1 falls within the range of small fossil araucarian cones. Most cone-bearing localities are situated to the northwest, west, and south of Hanksville in southcentral Utah. With regard to palaeobiodiversity, if Araucaria delevoryasii Gee from Wyoming is included, there are now six morphotypes of seed cones that represent at least three conifer families in Utah and Wyoming. Because many conifers are arborescent and form forests, the new fossil evidence suggests that species-diverse conifer forests or woodlands were a major type of vegetation in the Morrison Formation during the Late Jurassic.

Iron precipitation in a natural CO2 reservoir: Jurassic Navajo Sandstone in the northern San Rafael Swell, UT, USA

AbstractDiagenetic iron (oxyhydr)oxide minerals are common precipitates expected in CO2 reservoirs, and these minerals record fluid flow for application to carbon capture and sequestration (CSS). Multiple mineralogy and spectroscopy analyses on a pore to meter scale characterize a well‐exposed, lithologically controlled, iron (oxyhydr)oxides reaction front in the Jurassic Navajo Sandstone. Dolomite is the most prevalent cement (up to 23 area%), followed by only several percent or less of iron (oxyhydr)oxides, kaolinite, illite, and gypsum cements. Bulk geochemistry based on diagenetic mineralogies in the reaction front is compared with the water chemistry from nearby modern spring effluent emanating from the Navajo Sandstone to conclude that similar fluids (i.e., CO2‐charged, saline waters containing hydrocarbons) are responsible for the precipitation. A second comparison of bulk geochemistry and diagenetic mineralogies of the reaction front with data from other abundant Navajo Sandstone concretions in the Spencer Flat region (in south central Utah) shows that reservoir fluids likely vary spatially and temporally in the porous and permeable Navajo Sandstone. CO2 injection into porous and permeable, quartz arenite, saline aquifers will likely result in minor clay and abundant dolomite precipitation that will significantly decrease porosity.

Selected Analyses of a Utah/NOAA Cooperative Research Program Conducted in Utah During the 1982-83 Winter Season

A major weather modification research program was conducted in south central Utah during the 1982-83 winter season. This research was conducted in a "piggyback" fashion upon an on-going operational program being conducted in Utah. The goal of the operational weather modification program in Utah is to increase higher elevation snowpack in much of central and southern Utah to provide augmented streamflow to a variety of irrigation water users.

Milankovitch-Scale Sequence Stratigraphy and Stepped Forced Regressions of the Turonian Ferron Notom Deltaic Complex, South-Central Utah, U.S.A

Abstract Laterally extensive outcrops in south-central Utah of the Turonian Ferron Notom Delta Complex and its bounding shales contain numerous chronometrically age-dated bentonite beds. The chronometry enables estimation of rates of accommodation and accumulation change. Integration of 56 measured sections and walking and tracing of beds allowed rigorous application of the concept of shoreline trajectory, using the lower bentonites as stratigraphic datums. Geometric stratal relationships along with facies dislocations were used to define high-frequency sequences and systems tracts. Forty-three parasequences were grouped into 18 parasequence sets, five simple sequences, and one sequence set. Parasequence sets show repeated, aggradational–progradational, degradational, progradational–aggradational, and retrogradational stacking patterns, which match the recently developed accommodation succession model. The chronometric analysis shows that the high-frequency sequences are Milankovitch-scale (approximately 100,000 yr), and record sea-level falls of up to 50 meters. The most complete sequence set, sequence set 3, shows clear evidence of a prolonged and stepped forced regression, with two additional higher-frequency sequences (possibly 40 kyr cycles), forming a forced regressive sequence set. This matches previous observations that valley systems, associated with the sequence boundaries, are compound, and also record higher-frequency cut-and-fill cycles. Among the various controlling factors causing cyclicity, such as shoreline autoretreat, delta-lobe switching, and allogenic controls such as climate, tectonics, and eustasy, we hypothesize that glacio-eustasy is the most likely control on the cyclicity of Ferron deposition, overprinted on a tectonically active basin. Gradual build-up of glaciers are hypothesized as a possible explanation of the punctuated downsteps observed in the forced regressive sequence set 3.

Gravel-capped benches above northern tributaries of the Escalante River, south-central Utah

Andesitic boulder deposits mantle straths cut in sedimentary bedrock high above the northern tributaries of the Escalante River in south-central Utah. The andesitic gravel deposits are derived from the southern escarpments of Boulder Mountain and Aquarius Plateau. The sedimentology and geomorphic expression of these deposits suggest they are from slurry-flow mass movements that have been reworked by fluvial processes. The andesitic boulders are significantly tougher than the local sedimentary bedrock and cause boulder armoring and topographic inversion. The andesitic boulders are also effective tools for fluvial incision when transported across weaker bedrock. Cosmogenic 3 He exposure-age dating of some of the largest boulders exposed on the treads of four different deposits range from 303 ± 48 to 1395 ± 241 ka. The tallest boulders exposed on the deposit surfaces tend to yield the oldest exposure ages, suggesting that boulder erosion and deposit erosion are controlling the exposure-age populations and indicating that even the oldest exposure ages from a given deposit are likely minimum age estimates. Using the oldest exposure age from each surface, we estimate maximum Escalante River northern tributary incision rates of 151–323 m Ma −1 for the period since 0.6–1.4 Ma.

Pollen accumulation in lake sediments during historic spruce beetle disturbances in subalpine forests of southern Utah, USA

Paleoecological reconstructions using lake sediments provide important information about ecological dynamics and forest disturbance processes that occurred prior to the historic period of scientific observation. In high-altitude and high-latitude ecosystems where landscape-scale disturbances recur at time intervals exceeding observation in many regions, e.g. western North America, reconstructed environmental data are essential in providing context for land managers. During the most recent two decades eruptive populations of bark beetles ( Dendroctonus spp.) have rapidly and profoundly altered subalpine forest ecosystems across western North America. Outbreaks of these insects are unprecedented in scale and severity, at least historically. Currently, little information exists about these destructive outbreaks and in general, the information that exists, does not extend beyond the most recent few centuries. The research presented here examines sedimentary pollen records from six subalpine basins affected by severe spruce beetle ( D. rufipennis) epidemics during the 20th century in the high-elevation plateaus and mountain ranges of south-central Utah. Reciprocal exchanges in dominance between pollen abundance of host spruce ( Picea engelmannii) and non-host subalpine fir ( Abies lasiocarpa) associated with historic outbreaks are conspicuous. Calculating simple ratios of host and non-host pollen accumulations offers a useful metric to visually identify spruce beetle outbreaks using sedimentary records. However, supporting lines of evidence may be required to identify these disturbances with greater certainty over the Holocene. Our data and findings provide a platform with which to begin exploration of other paleoecological proxy methods for the ultimate purpose of generating more temporally extensive reconstructions of bark beetle disturbances using sedimentary records.

Foreland basin structural growth recorded in the Turonian Ferron Sandstone of the Western Interior Seaway Basin, USA

Tectonic forcing of stratigraphic architecture is likely in foreland basins. Tectonic driving forces are increasingly being invoked to explain stratigraphic patterns in the Cretaceous Western Interior Seaway Basin of North America, yet the evidence is largely circumstantial, and the details of driving forces remain elusive. In this paper I show direct stratigraphic evidence for syndepositional growth of a structural arch with at least 50 m of relief during accumulation of the upper Turonian Ferron Sandstone in south-central Utah, United States. Progressive growth of the arch was superimposed on several high-frequency stratal cycles that were driven by a more regionally extensive process (geodynamic or eustatic) and that produced laterally amalgamated sandstone bodies in a depositional strike-parallel orientation (north-south). All of this stratigraphy was then truncated by a more or less planar erosion surface (sequence boundary) that can be traced physically over at least 67 km north-south. This surface was later tilted northward, such that the upper member of the Ferron Sandstone thins progressively southward from 50 to 10 m over 67 km. The facies juxtapositions revealed by the Ferron Sandstone could, if seen in exposure of limited lateral extent, be wrongly interpreted as recording regionally extensive relative sea-level drops and potentially used in error as evidence for substantial eustatic sea-level falls during the Turonian. The folding and tilting documented in this study can be clearly attributed to geodynamic and/or tectonic driving forces, likely related to migration of a forebulge.

Using gas chromatography to determine winter diets of greater sage‐grouse in Utah

AbstractSagebrush (Artemisia spp.) constitutes the majority (&gt;99%) of sage‐grouse (Centrocercus spp.) winter diets. Thus, identification and protection of important winter habitats is a conservation priority. However, not all sagebrush may be alike. More information is needed regarding sage‐grouse sagebrush winter dietary preferences for application to management. The objective of our research was to determine if chemical analysis of fecal pellets could be used to characterize winter sage‐grouse diets as a substitute for more invasive methods. We collected and analyzed fecal pellets and sagebrush samples from 29 different sage‐grouse flock locations in northwestern and southcentral Utah. Using gas chromatography, we were able to identify crude terpene profiles that were unique to Wyoming sagebrush (A. tridentata wyomingensis) and black sagebrush (A. nova). We subsequently used the profiles to determine sagebrush composition of sage‐grouse fecal pellets, thus reflecting sage‐grouse winter diets. This technique provides managers with a tool to determine which species or subspecies of sagebrush may be important in the winter diets of sage‐grouse populations. © 2011 The Wildlife Society.

Follow the water: Connecting a CO2 reservoir and bleached sandstone to iron-rich concretions in the Navajo Sandstone of south-central Utah, USA: REPLY

Follow the water: Connecting a CO2 reservoir and bleached sandstone to iron-rich concretions in the Navajo Sandstone of south-central Utah, USA: REPLY

Follow the water: Connecting a CO2 reservoir and bleached sandstone to iron-rich concretions in the Navajo Sandstone of south-central Utah, USA: COMMENT

Concretions comprise an important diagenetic record of fluid flow in the Jurassic Navajo Sandstone (Utah, United States). Mobilization and transport of chemically reduced Fe+2 in solution likely occurs via groundwater with CH4 or other hydrocarbons as reducing agents ([Beitler et al., 2003][1]; [

Morphologic Clues to the Origins of Iron Oxide–Cemented Spheroids, Boxworks, and Pipelike Concretions, Navajo Sandstone of South-Central Utah, U.S.A.

AbstractConcretions cemented by iron oxide are abundant and diverse in the Jurassic Navajo Sandstone of southern Utah. Some of these structures are considered terrestrial analogs for concretions imaged on Mars. The Navajo concretions can be spheroidal, pipelike, or tabular with multicompartmented boxworks. These iron oxide concretions typically display a rinded structure: dense sandstone rinds cemented by iron oxide surround pale, iron-poor sandstone cores. Within a single structure, the iron-rich rinds may be single or multiple. Pseudomorphs of siderite are present in local residual, iron-rich cores of boxworks. Workers in the late nineteenth through mid-twentieth centuries, many of whom found evidence for siderite precusors, concluded that many spherical, rinded, iron oxide-cemented concretions were formed by centripetal precipitation of iron oxide inward from the perimeter of the concretion; in contrast, the walls of pipelike concretions of iron oxide grew centrifugally outward. We interpret the Navajo...