Dead Horse Point, Southeastern Utah

An intensive study of the Morrison formation in the Colorado Plateau region is being made by the U. S. Geological Survey on behalf of the Atomic Energy Commission. This report summarizes some of the results of three years' work. End_Page 1108------------------------------ In the Colorado Plateau the Morrison formation of Upper Jurassic age may be divided into two parts. The lower part consists of two gradational and intertonguing lithologic members--the Salt Wash sandstone member, present in southeastern Utah, western Colorado, and extending short distances into Arizona and New Mexico; and the Recapture shale member, present in northwestern New Mexico, northeastern Arizona, and extending a short distance into southeastern Utah. Both members consist predominantly of fluviatile deposits of sandstone and claystone with increasing proportions of sandstone and conglomerate near the main sources. The Salt Wash member was derived from sedimentary rocks, mainly from a southwesterly source, probably in western Arizona. The Recapture member was derived from sedimentary, igneous, and metamorphic rocks, mainly from a southern source, probably in west-central New Mexico. Away from these source areas the members become thinner and contain increasing proportions of claystone and limestone. The Salt Wash sandstone member generally is absent northeast of the crest of the ancestral Uncompahgre uplift and it loses its identity, except in a few places in the Central Colorado basin where discontinuous sandstone beds, considered to be Salt Wash, are present. The upper part of the Morrison formation likewise consists of two lithologic members--the Brushy Basin shale member and the Westwater Canyon sandstone member. The Brushy Basin member is present over all the Colorado Plateau except for a belt extending from south-central Utah to central New Mexico, where it is absent, partly as a result of pre-Dakota erosion. The Westwater Canyon member occupies the lower part of the Brushy Basin interval in southeastern Utah, northwestern New Mexico, and northeastern Arizona; it is thought to replace the Brushy Basin by gradation and intertonguing. The Westwater Canyon consists of fluviatile deposits of sandstone and minor claystone and represents a continuation of deposition similar to that of the lower part of the Morrison. It appears to have the sa e source and source rocks as the Recapture member. It also is conglomeratic near its source and becomes thinner and nonconglomeratic away from the source area. The Brushy Basin shale member is predominantly varicolored claystone with minor lenses of sandstone, conglomerate, and limestone, and consists in large part of fluviatile deposits. However, in lithologic characteristics, it contrasts sharply with the rest of the Morrison. The member may contain beds formed in ephemeral lakes or playas, and some of the material may have been contributed by ash falls. Evidence for the source of the Brushy Basin member is meager. End_of_Article - Last_Page 1109------------

Recent work on strata of Permian and Triassic age on the Colorado Plateau indicates that the unit originally defined as the Hoskinnini tongue of the Cutler formation extends into parts of southeastern Utah where it had not been previously reported. In addition, the Hoskinnini is correlated with part or all of the unit defined as the Tenderfoot member of the Moenkopi formation in the salt anticline region of east-central Utah and west-central Colorado. As a result of this work, the Hoskinnini is redefined as the Hoskinnini member of the Moenkopi formation. The Hoskinnini and laterally continuous strata in the Tenderfoot member are exposed within a north-northeast oriented area about 180 miles long and 50 miles wide extending from the Monument Valley area, in northeastern A izona and southeastern Utah, to west-central Colorado. Previously the Hoskinnini had been recognized only in the Monument Valley area. The Hoskinnini member and laterally continuous strata in the Tenderfoot member are pale reddish brown sandy siltstone grading to silty very fine-grained sandstone and contains disseminated fine, medium, and coarse quartz grains. The Hoskinnini is composed of horizontal beds, which generally range from 1 to 2 feet in thickness. Individual beds are marked by indistinct discontinuous wavy laminae bounded by grayish red claystone or siltstone films. The Hoskinnini is 50-120 feet thick in most areas. The combination of fine to coarse sand grains in a silt or very fine-grained asnd matrix and of discontinuous wavy laminae serves to differentiate the Hoskinnini member from the underlying and overlying strata. These features also make possible the correlation of the member with rocks not previously correlated with the Hoskinnini in southeastern Utah and adjoining parts of Colorado.

A very thick Permian section in the Wasatch Mountains east of Provo, Utah, has been disclosed by field work of the Geological Survey in 1937 and 1938. This section appears to have special significance, for it offers promise of providing a key to the correlation of the Permian sequence of the southern Rocky Mountains and the Colorado Plateau with that of the northern Rocky Mountain region. The correlations and some of the age assignments of the Permian sequence of the Provo region suggested in this paper represent only tentative opinions and may be modified after the fossil collections from this area have been completely studied. The Permian of southwestern Colorado and southeastern Utah consists of the Cutler formation (redbeds), above, and the Rico formation (redbeds and limestone), below; the Rico overlies the Pennsylvanian Hermosa formation. On the west, in southeastern Utah and northeastern Arizona, thick light-colored sandstone units are intercalated in the redbeds of the Cutler formation. Still farther west at the Grand Canyon in Arizona the Permian consists, in ascending order, of the Supai and Hermit formations (redbeds), the Coconino sandstone (light-colored, cross-bedded), and the marine Kaibab limestone at the top. Beds definitely of Pennsylvanian age are absent in part of the Grand Canyon region and the Permian rests on the Mississippian Redwall limestone. The Supai, Hermit, Coconino, and at least part of the Kaibab are believed to be continuous with, and essentially equivalent to, the Cutler formation. The Permian is unconformably overlain by Triassic beds--Moenkopi formation in southeastern Utah and northeastern Arizona and Dolores formation in southwestern Colorado. The Permian deposits of western Wyoming, Idaho, and northern Utah, have generally been included in the Phosphoria formation, but in northwestern Wyoming they are placed in the Embar formation by many geologists; near Park City in northeastern Utah they are included in the Park City formation; and in parts of Wyoming they have been in part included in the Chugwater formation. In its typical region in southeastern Idaho, the Phosphoria consists of an upper chert and limestone--the Rex chert member--and a lower phosphatic shale member. It is overlain by the Woodside shale of Lower Triassic age and underlain by the Wells formation of Pennsylvanian age. At the top of the Wells formation is a limestone generally thought to be of Pennsylvanian age. The lower part of the Park City formation in north-central Utah is considered by many geologists to be equivalent to the limestone at the top of the Wells formation farther north. The upper part of the Park City formation includes the phosphatic shale and upper cherty limestone that have been assigned to the Phosphoria formation farther north. The Park City formation has accordingly been considered by most geologists s in part of Pennsylvanian and in part of Permian age. End_Page 617------------------------------ Fig. 1. Index map showing location of sections presented in Figures 2-6 and of region included in Figure 7. End_Page 618------------------------------ Between these two regions, in the vicinity of Provo, Utah, a series of rocks with a maximum thickness of more than 4,000 feet is included in the Permian, though the assignment of the two lowest units to the Permian is tentative. These rocks rest with probable unconformity on a tremendously thick Pennsylvanian section and are unconformably overlain by the Lower Triassic Woodside shale. Limestone at the base of the sequence considered Permian, in the Provo section, has a maximum thickness of nearly 1,500 feet but is absent locally. It has no counterpart in lithology in the Permian rocks of the Colorado Plateau to the south or in the Permian rocks that crop out toward the north in Utah, Idaho, and Wyoming. A red to gray sandstone, 600-1,000 feet thick, that overlies, and is gradational i to, this limestone is similar in lithology to the Coconino sandstone and is tentatively correlated with it. Overlying the sandstone are nearly 2,000 feet of strata composed of a lower gray cherty limestone about 600 feet thick, an upper cherty limestone 600 to 1,100 feet thick, and an intervening black phosphatic shale about 200 feet thick. These rocks are considered by the writers to be the equivalent of the Park City formation. The discovery in them of a fauna that has in it definite Kaibab elements beneath typical Phosphoria faunas and lithology, suggests that the Kaibab is, at least in part, equivalent to the lower limestone and that the phosphatic black shale and upper limestone may not be represented by contemporaneous deposits in the Grand Canyon region of Arizona. It also casts d ubt upon the correlation of the lower part of the Park City formation in northern Utah with the limestone at the top of the Pennsylvanian Wells formation in southeastern Idaho.

Microarthropod communities associated with biological soil crusts in the Colorado Plateau and Chihuahuan deserts

New uranium-lead (U-Pb) analyses of carbonate deposits in the Navajo Sandstone in southeastern Utah (USA) yielded dates of 200.5 ± 1.5 Ma (earliest Jurassic, Hettangian Age) and 195.0 ± 7.7 Ma (Early Jurassic, Sinemurian Age). These radioisotopic ages—the first reported from the Navajo erg and the oldest ages reported for this formation—are critical for understanding Colorado Plateau stratigraphy because they demonstrate that initial Navajo Sandstone deposition began just after the Triassic and that the base of the unit is strongly time-transgressive by at least 5.5 m.y.

Subalpine habitats in sky islands in the Southwestern USA are currently facing large-scale transformations. Lichens have widely been used as bioindicators of environmental change. On the Colorado Plateau, fruticose lichens occur in patchy, disconnected populations, including unique lichen-draped conifer sites in subalpine forests in the La Sal Mountains in southeastern Utah. Here, we document the distribution and fungal diversity within these lichen communities. We find that lichen-draped conifer sites in the La Sal Mountains are restricted to only three known, small areas in Picea englemannii forests above 3000 m above sea level, two of which have recently been impacted by wildfire. We document 30 different species of lichen-forming fungi in these communities, several which represent the first reports from the Colorado Plateau. We also characterize mycobiont haplotype diversity for the fruticose lichens Evernia divaricata, Ramalina sinensis, and multiple Usnea species. We also report a range of diverse fungi associated with these lichens, including genetic clusters representing 22 orders spanning seven classes of Ascomycetes and fewer clusters representing Basidiomycetes. Our results provide a baseline for ongoing monitoring and help to raise awareness of unique lichen communities and other biodiversity in the region.

EcosphereVolume 13, Issue 12 e4352 COVER IMAGEOpen Access Cover Image First published: 04 December 2022 https://doi.org/10.1002/ecs2.4352AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract COVER PHOTO: The Colorado Plateau is world renowned for spectacular geology and landforms, such as shown here from Canyonlands National Park in southeastern Utah, USA. However, as with drylands globally, the Colorado Plateau is increasingly threatened by climate and land use change. Duniway et al. (Ecosphere, Volume 13, Issue 11, Article e4273; doi: 10.1002/ecs2.4273) used a network of 135 long-term vegetation-monitoring sites in three national parks and characterized connections between geology, geomorphology, soils, climate, and dryland plant communities. The authors found that soil depth, aridity, lithology, and soil salinity were some of the most important landscape variables governing plant community composition and present a novel framework that links the geologic and geomorphic evolution of landscapes with the distribution of soils and plant communities that can guide ecosystem management. Photo credit: Christopher Benson. Volume13, Issue12December 2022e4352 RelatedInformation

Vertebrate trace fossils are common in Upper Triassic deposits across the American southwest. These ichnofauna are dominated by Grallator, Brachychirotherium, and Pseudotetrasauropus, and lack ichnotaxa traditionally considered to be Early Jurassic in age, such as Eubrontes and Anomoepus. While known from Indian Creek and Lisbon Valley, Utah, vertebrate trace fossils have not been previously reported from Comb Ridge, Utah. This is significant considering that lithostratigraphic work has been ongoing at Comb Ridge since the 1990s in the elsewhere fossiliferous ‘Big Indian Rock Beds’, in the US Highway 163 roadcut that transects Comb Ridge. 2016 fieldwork by the Museums of Western Colorado: Dinosaur Journey recovered two sandstone slabs that had been dislodged from a river channel sand in the Church Rock Member of the Chinle Formation. The slabs preserve the first documented Triassic vertebrate trace fossils from Comb Ridge: a single pes impression of the ichnogenus Grallator, and several manus and at least one pes impression of a small archosaur. We tentatively refer this second track set to the ichnogenus Brachychirotherium. Taken together, these specimens provide evidence for a more diverse vertebrate fauna in the Church Rock Member of the Chinle Formation at Comb Ridge than indicated by the current body fossil record.

The Moenkopi formation of Triassic age is widely exposed in the salt anticline region in southeastern Utah and southwestern Colorado* The distribution of the Moenkopi is that of a blanket of irregular thickness several large holes wrn in it,, due chiefly to pre-Chinle erosion* Four members of contrasting lithology have been mapped in the Moenkopi in the salt anticline region. In ascending order these members ares l) the Tenderfoot member^ composed dominantly of muddy or silty poorly sorted sandstone | 2) the Ali Baba member 9 composed of interstratified arkosie conglomeratic sandstone and fissile siltstone| 3) the Sewemup member $ composed dominantly of fissile siltstone with minor beds of conglomeratic sandstone and gypsum 5 and 4) the Pariott member composed of interstratified sandstone and siltstone* Part of the Tenderfoot member of the Moenkopi formation correlates the Hoskinnini member of the Moenkopi formation of southeastern Utahj, a unit which may be either Permian or Early Triassic in age or possibly both. If equivalents of the type Moenkopi of northeastern Arizona are present in the salt anticline region, they may include the upper part of the Sewemup member and part or all of the Pariott The Moenkopi formation of Trlassie age, a unit long recognized on the Colorado Plateau (Ward, 1901, p0 4-03-4-041 Gregory, 1917, p. 23-31$ and McKee, 1954-) was first delimited in the salt anticline region of southeastern Utah and southwestern Colorado (fig. l) Baker and others (1927, p. 796-798)„ It was subsequently mapped in the Utah part of the region by Baker (1933) and by Dane (1935), who extended stratigraphie observations on the Moenkopi Into adjacent parts of Colorado. Dane (1935, p, 51) noted and called attention to an unusually thick section of the Moenkopi formation in Sinbad Valley, Colorado. In 194-8, mapping -was begun In the vicinity of Sinbad Valley, Colo., by the senior author under a program of mapping undertaken by the U. S. Geological Survey on behalf of the Division of Ra¥ Materials of the TJ 0 Ba Atomic Energy Commission* In order to determine the nature of the unusual lateral changes in thickness of the Moenkopi formation, three members were distinguished and mapped In Sinbad Valley, -where the formation Is composed of three major units of contrasting lithology (Shoemaker, 1955 and 1956). Subsequently the units were traced northward (by the senior author) to the vicinity of Gateway, Colo. (Cater, 1955a), southward into Paradox Valley, Colo. (Shoemaker, 1956), and westward into the areas previously mapped by Baker and Dane in Utah (Shoemaker, 1952), A fourth member was recognized in Utah<, In 1952, additional field and laboratory work was undertaken In collaboration the junior author to complete a study of the Moenkopi throughout the salt anticline region. The purpose of these notes is to set forth the salient features of the stratigraphy of the Moenkopi formation of this region and to supplement new

Natural hybridization between Arizona singleleaf pinyon (Pinus monophylla subsp. fallax [Little] Zavarin) and Colorado pinyon (P. edulis Engelm.) was studied in northwestern Arizona, using morphological characters. The array of phenotypes indicated introgression of both species. In the Grand Canyon hybridization occurred between elevationally stratified populations of the taxa where flowering phenology was overlapping. Colorado pinyon showed evidence of introgression in the western Grand Canyon area and up the Colorado River canyon into southeastern Utah, as well as southeastward below the Colorado Plateau. Long-distance pollen dispersal may be responsible for introgression into southeastern Utah, and hybridization in northwestern Arizona may have started during the Late Pleistocene.

Effects of Livestock Grazing on Infiltration and Erosion Rates Measured on Chained and Unchained Pinyon-Juniper Sites in Southeastern Utah

Mudlumps in the Monitor Butte Member of the Upper Triassic Chinle Formation are the product of syndepositional deformation in lacustrine, delta-front, and prodelta deposits. Diapirism in lacustrine and delta deposits caused intraformational folds and faults that were penecontemporaneous with sedimentation. Deposition of the Shinarump, Monitor Butte, and Moss Back Members of the Chinle Formation in southeastern Utah was in a complex fluvial-lacustrine system, in which fluvial channel systems with abundant wetland floodplain environments flowed generally west into a large lake. Intraformational deformation occurred in lacustrine and deltaic units near the lake margin. Lacustrine deposits in and near the upper part of Glen Canyon are locally well exposed and are composed of red and purple bentonitic mudstone, which, in places, contain ostracodes, and burrowed, sandy limestone. Prodelta deposits are composed of gray and purple bentonitic mudstone. These lacustrine and prodelta deposits contain high-angle reverse faults, locally vertical beds, and diapiric strata interpreted as mudlumps. Delta-front deposits comprise green, micaceous and carbonaceous, coarsening upward sequences of foresetbedded siltstone and sandstone that dip as much as 28° and are as much as 24 m thick. Rapid progradation of the delta front over prodelta and lacustrine sediments produced overloading and subsequent deformation by diapirism. The mechanism of formation of the Monitor Butte mudlumps appears to have been similar to that proposed for modern Mississippi River delta mudlumps. The processes that formed the mudlumps in the vicinity of Glen Canyon may be the same processes that produced the vertical and contorted bedding that is more poorly exposed in the Monitor Butte Member elsewhere on the Colorado Plateau.

Late Quaternary Fossils of Poa fendleriana (Muttongrass): Holocene Expansions of Apomicts

How plant populations, communities, and ecosystems respond to climate change is a critical focus in ecology today. The responses of introduced species may be especially rapid. Current models that incorporate temperature and precipitation suggest that future Bromus tectorum invasion risk is low for the Colorado Plateau. With a field warming experiment at two sites in southeastern Utah, we tested this prediction over 4 years, measuring B. tectorum phenology, biomass, and reproduction. In a complimentary greenhouse study, we assessed whether changes in field B. tectorum biomass and reproductive output influence offspring performance. We found that following a wet winter and early spring, the timing of spring growth initiation, flowering, and summer senescence all advanced in warmed plots at both field sites and the shift in phenology was progressively larger with greater warming. Earlier green-up and development was associated with increases in B. tectorum biomass and reproductive output, likely due early spring growth, when soil moisture was not limiting, and a lengthened growing season. Seeds collected from plants grown in warmed plots had higher biomass and germination rates and lower mortality than seeds from ambient plots. However, in the following two dry years, we observed no differences in phenology between warmed and ambient plots. In addition, warming had a generally negative effect on B. tectorum biomass and reproduction in dry years and this negative effect was significant in the plots that received the highest warming treatment. In contrast to models that predict negative responses of B. tectorum to warmer climate on the Colorado Plateau, the effects of warming were more nuanced, relied on background climate, and differed between the two field sites. Our results highlight the importance of considering the interacting effects of temperature, precipitation, and site-specific characteristics such as soil texture, on plant demography and have direct implications for B. tectorum invasion dynamics on the Colorado Plateau.

ABSTRACT. Springs located on the Colorado Plateau are highly threatened and represent a small percentage of the landscape; yet they are disproportionately important to diverse native flora and fauna. The relationships between anthropogenic disturbance, aquatic macroinvertebrate species composition, and environmental variables at these springs have received little study. We selectively visited 40 sandstone springs in southeastern Utah and southwestern Colorado to span a range of impacts. We classified the springs into impact categories based on a spring impact score, and we measured biodiversity (aquatic macroinvertebrates), water chemistry (nutrients, dissolved O2, pH, specific conductivity, temperature, turbidity, coliform bacteria [Escherichia coli]), physical characters (solar radiation, substrate, vegetation cover, bank stability, discharge), and presence of anthropogenic disturbance. Escherichia coli abundance was higher in high impact categories, and turbidity increased with increasing disturbance. ...