Plant Root Systems Preserved in the Permian Cedar Mesa Sandstone at Moki Dugway, Southeastern Utah

Rooted green plants represent the base of the food chain for most terrestrial ecosystems, but, compared to animal burrows, root systems are relatively rarely recognized in ancient sedimentary rocks. Plant roots that penetrate unconsolidated sand dunes, especially those containing not only quartz grains, but also abundant grains of calcite (CaCO3), are commonly replaced by fine crystals of calcite (Klappa, 1980). These structures (known by geologists as rhizoliths from the Greek for “root rock”) are one form of calcite cemented soil and sediment called caliche (figure 1). Caliche crystallizes well above the water table and its calcite crystals are tiny because of rapid evaporation of soil water. One source of the calcium (Ca) and carbonate (CO3) ions necessary for making the calcite of caliche is falling dust, and another source is the dissolution of calcite grains already in the soil. Caliche is widespread in semi-arid regions. In regions with abundant rainfall, available calcium and carbonate ions are rapidly flushed downward, out of the soil, preventing calcite crystals from growing in the root zone. In arid regions there is too little available soil water for crystal growth. Because plant roots in modern semi-arid settings are commonly preserved by caliche (figure 1), rhizoliths in ancient rocks are good indicators of semi-arid paleoclimates. The Early Permian (245-286 million year old) root systems preserved the Cedar Mesa Sandstone at Moki Dugway (figure 2) grew on low-relief land surfaces that formed when dune fields were flattened by wind erosion. A near-surface water table may have prevented further erosion of the Permian dune sand and allowed the land surface to be colonized by woody plants

Hexagonal Fracture Patterns On Navajo Sandstone Crossbeds At Yellow Knolls, Washington County

At this geosite, the main features of interest—remarkably uniform and beautiful fracture patterns dominantly composed of linked hexagons (fi gures 1 and 2)—are present on outcrops of the Jurassic Navajo Sandstone. Th e Navajo was deposited by large, southward- migrating desert dunes about 200 million years ago, but the fractures that defi ne the hexagons here are just a surfi cial veneer less than 20 inches (half a meter) deep. Th e fractures are a weathering phenomenon that developed under climate conditions similar to today’s. Steep thermal gradients develop in the sandstone because it is exposed to solar radiation and changing air temperature. Polygonal fracturing is present in other Navajo exposures in southern Utah, but only in non-bedded (homogeneous) rock. Th e beautiful, bedding-parallel fracture pattern developed here is very rare; it developed because the bedding planes in the rock at Yellow Knolls are unusually wide-spaced

A wealth of hallowed memories : The development of mission, saga, and distinctiveness at the Virginia Military Institute

This study seeks to discover the elements in Virginia Military Institute\u27s past that have proven most influential in guiding and preserving its present-day distinctive culture. Historical in nature, the study also incorporates theories from sociology and political science in analyzing the importance of events, people, and places surrounding Virginia Military between 1816 and 1890. Integral to the overarching theory behind this dissertation is the assumption that VMI\u27s history is closely linked with the history of Virginia and of the American South. In order to tie historical theory to the theory of the elite college, the hypothesis relies heavily on four texts: Burton Clark\u27s The Distinctive College, C. Vann Woodward\u27s The Burden of Southern History, W. J. Cash\u27s Mind of the South, and Bertram Wyatt-Brown\u27s Southern Honor.;Specifically, the study hypothesizes that Virginia Military was heavily reliant upon Virginia state government from the time of its founding in 1839 through the Civil War. However, the war provided the circumstances by which the Institute could claim its own place in history. The Battle of New Market, in which cadets from the Institute fought and died in support of the Confederate cause, gave VMI a substantive past separate from, yet tethered to, Virginia history and the history of the South. After the war, the Institute cultivated its own ideology and traditions, creating what Burton Clark terms an institutional saga. Self-realization of this saga, coupled with its external recognition by alumni, forged the distinctiveness exhibited by Virginia Military today. In turn, this distinctiveness, preserved by a conservative even reactionary ideology, created an institutional atmosphere reluctant to embrace change

Relationships of Vegetation to Environment in Canyonlands National Park

The vegetation of Canyonlands National Park, Utah, has been described from 157 samples located throughout the Park. Species frequency, density and cover were recorded along with measurements of soil thickness, slope, aspect, elevation and geologic substrate at each site. Measurements of soil texture, pH, and electrical conductivity were taken for a representative subsample. A map of the vegetation of the Park was made by relating the sample points to their corresponding spectral signatures on vertical aerial photographs and locating boundaries between vegetation units by means of changes in photo signatures. Vegetation in these arid to semi-arid environments appears to be strongly related to particular combinations of regolith thickness, bedrock composition and depth to water table. Elevation and slope exposure control vegetation patterns to a much smaller extent. Vegetational units are distinct, and can be readily visualized. The six units mapped, in order of relative importance, (area covered) were: blackbrush, juniper-pinyon woodlands, semi-desert grasslands, sagebrush-fourwing saltbush shrublands, salt-desert shrublands and riparian tall shrublands. These vegetational units are related to specific combinations of environmental factors. Boundaries between units are sharp vegetationally and environmentally. Moisture availability appears to be the key factor, but effective soil moisture is largely controlled by regolith/bedrock relationships. Grasslands predominate at all elevations where regolith is over 50 cm in thickness and there is no access of plant roots to the water table. Regolith that is uniformly thinner than 50 cm supports vegetation dominated by blackbrush (Coleogyne ramosissima). Sandy areas that provide immediate root access to the water table support thickets of Salix, Tamarix, and other riparian shrubs. Shrublands dominated by Atrinlex canescens and Artemisia tridentata occur on thicker sand deposits with seasonal root access to capillary water. Where competent bedrock is exposed and joints are developed, Pinus edulis, Juniperus osteosperroa and various upland shrubs dominate. Several species of Atrinlex dominate the salt-desert shrublands where clayey shales crop out. Historical grazing use by domestic livestock has altered the composition and cover in grasslands, chiefly in the southern part of the Park. Elsewhere, grassland modification is slight because of more difficult access. other vegetation types have experienced less obvious changes. The many abandoned roads within the Park date chiefly from extensive mineral exploration in the early 1950\u27s. Secondary succession on these disturbed areas is extremely slow

Burrows Dug by Large Vertebrates into Rain-Moistened Middle Jurassic Sand Dunes: A Reply

Odier (2007) is concerned with two issues: (1) I did not cite his work on burrows in the Navajo Sandstones of southeastern Utah in my article (Loope 2006), and (2) he believes I amwrong in interpreting the structures preserved in the Entrada Sandstone as burrows. On the first issue, I failed to cite both his 2004 abstract and the newly published book that he sent me in October 2006. My article was accepted on June 12, 2006; I returned the proofs on August 23; and the issue was published online on October 4, 2006. The timing of these events makes it clear why I did not cite the book. I did not cite the abstract because that would have necessitated airing my reservations about his interpretations. Since the middle 1970s, I have been aware of abundant cylindrical structures of likely biogenic origin in the Navajo Sandstone, and at the 2004 Geological Society of America meeting, I learned that Odier was interpreting these structures as mammal burrows. In my view, his interpretation could be correct, but, because the preferentially cemented (concretionary) features weather out of structureless sandstone, very little detail is available for study. For instance, in any one cylinder, the diameter commonly varies widely. What was the original diameter of the burrow (or the plant root)? Because bedding planes are absent, this simple question cannot be answered. In the “Conclusions” section of my article on burrows within the Entrada Sandstone, I emphasize the importance of thinlaminated sandstone to the preservation and recognition of biogenic structures; disruptions of this lamination by either physical or biogenic processes provide abundant clues that are simply unavailable in structureless sandstones. On the second issue, Odier (2007) states that the structures in the Entrada Sandstone that I interpret as burrows cannot be burrows because of the crossbedding that is present inside several of them. Instead, he interprets them as “wells” formed by heavy rain falling on dune sand. Many sedimentologists have been interested in the effects of heavy rain on subaerially exposed sand. Clifton (1977) described rain-impact ripples with wavelengths of about 1 cm that form transverse to the wind direction. Rain-wetted blocks of cohesive sand sometimes move down steep lee faces of dunes (Bigarella et al. 1969; Hunter et al. 1983; Loope et al. 2001). I am not aware, however, of reports of rain events that excavate 3-m-long, 50- cm-wide cylindrical voids that are inclined 15°–20° to the horizontal and cut dune crossbeds at a high angle. Figure 8 in my article shows the origin of the internal crossbeds: wind-blown sand drifted into the open burrow throats. For high-resolution, color images of these structures, please see http://www.geosciences.unl.edu/∼dloope/

The Origin of Shinarump Wonderstone, Hildale, Washington County

Southern Utah’s “wonderstone” is Shinarump sandstone, variably cemented and stained with iron oxide, forming intricate patterns reminiscent of landscapes. It is cut and sold as absorbent drink coasters and decorative objects, and is seen in rock shops across the country. The wonderstone pattern comprises thick bands of iron oxide mineralization that fills pore space (referred to as iron oxide cement or IOC) and more delicate bands of iron oxide mineralization that coats sand grains but does not fill pore space (referred to as iron oxide stain or IOS) (figure 1). The wonderstone pattern is of interest to geologists because it formed after the Shinarump sandstone was deposited from iron that was transported in aqueous solution. The iron that now resides in the cement and stain occurs as oxidized iron (iron-III) minerals (e.g., goethite and hematite). Significant amounts of iron-III can be transported in aqueous solution only under very unusual conditions. On the other hand, if an electron is added to iron-III, the resultant reduced iron (iron-II) can be transported readily in aqueous solutions. But iron-II forms a different group of minerals, typically pyrite (FeS2) and siderite (FeCO3) that do not have the characteristic red color of the wonderstone cement and stain. How was the iron that now resides in the wonderstone transported to its current location? What was the chemical mechanism for removing the iron from natural waters and fixing it as iron-III minerals? The typical explanation for the wonderstone pattern is that the bands of iron oxide cement and stain are Liesegang bands. Liesegang bands were discovered originally by chemists and are a form of chemical self-organization that produces bands of insoluble material from the mixing of two solutions. The conventional interpretation is that when pyrite is exposed to oxygen-rich groundwater the pyrite will dissolve, producing a strongly acidic, iron-rich solution. Iron-III will migrate in solution toward the source of oxygen. This aqueous iron-III will then precipitate as the solution is neutralized to form the Liesegang bands of iron oxide cement. This conventional interpretation was developed before geologists recognized the importance of microbes to processes that occur at low temperature. Our interpretation is that iron was introduced to the rock as iron- II shortly after sediment deposition and formed the mineral siderite. As the Colorado Plateau experienced uplift more oxygen-rich groundwaters invaded the Shinarump Sandstone. Iron-oxidizing bacteria thrive by transferring an electron from iron-II to oxygen to make iron-III. Energy is released during this transfer that the bacteria use to survive (in the same way that humans transfer electrons from the carbon in food to oxygen and survive using the energy released in those reactions). The IOC was produced through dissolution of siderite followed by oxidation of aqueous iron-II by microbes at a succession of oxidation-reduction interfaces. The IOC bands mark the position of interfaces where iron-oxidizing bacteria converted aqueous iron II to iron-III with a consequent precipitation of iron III oxide. We consider the iron oxide staining, on the other hand, to be Liesegang produced by the inter-diffusion of iron II and oxygen after the bands of cement were produced. See Kettler and others (2015) for a more complete description of the processes. The outcrops and blocks of wonderstone in this quarry provide a good summary of the evidence that falsifies the pyrite oxidation hypothesis in favor of our hypothesis

Surficial fractures in the Navajo sandstone, south-western USA: the roles of thermal cycles, rainstorms, granular disintegration, and iterative cracking

Deep (\u3e 5 m) sheeting fractures in the Navajo sandstone are evident at numerous sites in southern Utah and derive from tectonic stresses. Strong diurnal thermal cycles are, however, the likely triggers for shallow (\u3c 0.3 m) sheeting fractures. Data from subsurface thermal sensors reveal that large temperature differences between sensors at 2 and 15 cm depth on clear summer afternoons are as great as those that trigger sheeting fractures in exposed California granite. Extensive polygonal patterns in the Navajo sandstone are composed of surface-perpendicular fractures and were produced by contractile stresses. Numerous studies have shown that porewater diminishes the tensile strength of sandstone. Based on our thermal records, we propose that cooling during monsoonal rainstorms triggers polygonal fracturing of temporarily weakened rock. On steep outcrops, polygonal patterns are rectilinear and orthogonal, with T-vertices. Lower-angle slopes host hexagonal patterns (defined by the dominance of Y-vertices). Intermediate patterns with rectangles and hexagons of similar scale are common. We posit that outcropping fractures are advancing downward by iterative steps, and that hexagons on sandstone surfaces (like prismatic columns of basalt) have evolved from ancestral orthogonal polygons of similar scale. In lava flows, fractures elongate intermittently as they follow a steep thermal gradient (the source of stress) as it rapidly moves through the rock mass. In our model, a steep, surficial thermal gradient descends through unfractured sandstone, but at the slow pace of granular disintegration. Through time, as the friable rock on stable slopes erodes, iterative cracking advances into new space. Hexagonal patterns form as new fractures, imperfectly guided by the older ones, propagate in new directions, and vertices drift into a configuration that minimizes the ratio of fracture length to polygon area

Iron Mobility in Desert Sandstone Aquifers: The Possible Role of Siderite

Jordanians and a large number of refugees are drinking radiumcontaminated water from a sandstone aquifer. The problem is that this water passed through sandstone of the Disi Formation only after carbon dioxide and methane had bleached the sandstone, dissolving the Iron-oxide coatings and liberating heavy metals and radionuclides . The Iron that once coated the grains migrated to form Iron bands in the lower Um Ishrin Formation. The major practical significance of this study involves water quality. The movement of Iron sandstone aquifers can drastically change groundwater chemistry; understanding how and when this movement takes place will help in locating safe supplies of drinking water. Hypothesis: The rhombic, Iron-rich structures in the Jordanian sandstones are the altered remains of nowdissolved siderite crystals. It is important to figure out the elemental composition of the possible pseudomorphs, and to get a better look at their form