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

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

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

INTERACTIONS OF A PALEOCENE RIVER, A RISING FOLD, AND EARLY-DIAGENETIC CONCRETIONS

The relative rates of sediment accumulation, erosion, and structural uplift determine whether a growing fold develops positive topographic relief, is beveled by antecedent streams, or is buried under thick growth strata. When folds rise in subsiding basins, upward, convergent flow of groundwater through the permeable growth strata that underlie antecedent streams enhances the flux of ions required for concretion growth. Early diagenetic concretions that grow in such alluvial strata may constitute the only clasts larger than sand size available for transport when antecedent streams become erosive. The first reworked concretions deposited by these streams should accurately mark the transition from aggradation to erosion as folds rise into the paths of streams. In this situation, the ability to differentiate reworked from in situ concretions is crucial. The west-vergent Simpson Ridge anticline, a N–S-trending, thick-skinned Laramide structure in east-central Wyoming, separates the larger Hanna basin from the Carbon basin. Near the north nose of this anticline, in situ ironoxide- rich concretions are abundant in folded Paleocene strata (Ferris Formation) and, just to the east, large, reworked, iron-rich concretions are abundant in younger, more gently dipping conglomerates in the basal Hanna Formation of the backlimb. Smaller reworked concretions are also present near the base of the Hanna Formation at least 7 km south of the anticlinal nose and just east of the fold’s axis. At the anticlinal nose, in situ (non-reworked) concretions up to 3 m X 1 m X 1 m are abundant at the top of an ~ 7- km-thick sequence of sandstones and siltstones that constitute the Late Cretaceous–early Paleocene Ferris Formation. Reworked concretions are absent in the strata hosting these in situ concretions, but reworked concretionary clasts up to 2 m in diameter are present in exposures of conglomerates in the lowermost Hanna Formation that lie just above the in situ Ferris concretions and southeast of the anticlinal nose. These early-diagenetic concretions were originally cemented by siderite (FeCO3). Oxidation of some small, rinded siderite-cemented clasts took place after their fluvial transport into the Hanna Formation, but abundant angular, un-rinded, iron-oxide-cemented clasts indicate that many large, in situ siderite concretions had resided in the vadose zone before they were entrained. The distribution of reworked concretions and the orientations of crossbeds show that antecedent Hanna streams eroded a swath at least 5 km wide across the rising structure. These streams transported Ferris Formation concretions southeastward into the Carbon basin, and deposited them in a conglomeratic sandstone body in the Hanna Formation. Large calcitecemented concretions, many with a pipe-like morphology, then grew within Hanna crossbeds. In many cases, these in situ concretions enclose transported, iron-rich concretions, but there is no evidence any calcite-cemented concretions were reworked. The NW–SE alignment of the pipes record southeastward flow of groundwater and thus also provide evidence (together with the orientation of the crossbeds) of the original continuity of the Hanna Formation across the anticline. Reworked concretions reveal the interplay of deposition, diagenesis, and erosion. Due to convergent groundwater flow over growing anticlines, early diagenetic concretions, both in situ and as reworked clasts, are especially likely to be found in growth strata

Sheeting joints and polygonal patterns in the Navajo Sandstone, southern Utah: Controlled by rock fabric, tectonic joints, buckling, and gullying

Sheeting joints are ubiquitous in outcrops of the Navajo Sandstone on the west-central Colorado Plateau, USA. As in granitic terrains, these are opening- mode fractures and form parallel to land surfaces. In our study areas in south-central Utah, liquefaction during Jurassic seismic events destroyed stratification in large volumes of eolian sediment, and first-order sheeting joints are now preferentially forming in these structureless (isotropic) sandstones. Vertical cross-joints abut the land-surface-parallel sheeting joints, segmenting broad (tens of meters) rock sheets into equant, polygonal slabs ~5 m wide and 0.25 m thick. On steeper slopes, exposed polygonal slabs have domed surfaces; eroded slabs reveal an onion-like internal structure formed by 5-m-wide, second-order sheeting joints that terminate against the crossjoints, and may themselves be broken into polygons. In many structureless sandstone bodies, however, the lateral extent of first-order sheeting joints is severely limited by pre-existing, vertical tectonic joints. In this scenario, non-conjoined sheeting joints form extensive agglomerations of laterally contiguous, polygonal domes 3–6 m wide, exposing exhumed sheeting joints. These laterally confined sheeting joints are, in turn, segmented by short vertical cross-joints into numerous small (~0.5 m) polygonal rock masses. We hypothesize that the sheeting joints in the Navajo Sandstone form via contemporaneous, land-surface-parallel compressive stresses, and that vertical cross-joints that delineate polygonal masses (both large and small) form during compression-driven buckling of thin, convex-up rock slabs. Abrasion of friable sandstone during runoff events widens vertical tectonic joints into gullies, enhancing land-surface convexity. Polygonal rock slabs described here provide a potential model for interpretation of similar-appearing patterns developed on the surface of Mars

Iron concretions in the Cretaceous Dakota Formation

The Cretaceous Dakota Formation contains abundant iron oxide concretions. The precursors to the iron concretions are siderite (FeCO3) nodules that formed in a reducing floodplain environment. A variety of concretion morphologies formed when the precursor siderite nodules were dissolved by oxidizing groundwater in a paleoaquifer. Iron-oxidizing bacteria are able to oxidize aqueous Fe(II) to Fe(III) oxy-hydroxide at microaerophilic and neutrophilic conditions. This study investigated these concretions to determine if there was a microbial element in their formation and to characterize the concretion morphologies present in the Dakota. This is important for complete paleoenvironment interpretations and astrobiology pursuits

The footprints of ancient CO2-driven flow systems: Ferrous carbonate concretions below bleached sandstone

Iron-rich carbonates and the oxidized remains of former carbonates (iron-oxide concretions) underlie bleached Navajo Sandstone over large portions of southern Utah. Iron in the carbonates came from hematite rims on sand grains in the upper Navajo that were dissolved when small quantities of methane accumulated beneath the sealing Carmel Formation. As a second buoyant gas (CO2 derived from Oligocene–Miocene magmas) reached the seal and migrated up dip, it dissolved in the underlying water, enhancing the solution’s density. This water carried the released ferrous iron and the methane downward. Carbonates precipitated when the descending, reducing water degassed along fractures. The distribution of a broad array of iron-rich features made recognition of the extent of the ancient fl ow systems possible. Although siderite is not preserved, dense, rhombic, mm-scale, iron-oxide pseudomorphs after ferrous carbonates are common. Distinctive patterns of iron oxide were also produced when large (cm-scale), poikilotopic carbonate crystals with multiple iron-rich zones dissolved in oxidizing waters. Rhombic pseudomorphs are found in the central cores of small spheroids and large (meter-scale), irregular concretions that are defi ned by thick, tightly cemented rinds of iron-oxide–cemented sandstone. The internal structure and distribution of these features reveal their origins as ironcarbonate concretions that formed within a large-scale fl ow system that was altered dramatically during Neogene uplift of the Colorado Plateau. With rise of the Plateau, the iron-carbonate concretions passed upward from reducing formation water to shallow, oxidizing groundwater fl owing parallel to modern drainages. Finally they passed into the vadose zone. Absolute dating of different portions of these widespread concretions could thus reveal uplift rates for a large portion of the Plateau. Iron-rich masses in other sedimentary rocks may reveal fl ow systems with similar histories