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

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

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

Dissociation Quotients of Malonic Acid in Aqueous Sodium Chloride Media to 100°C1

The first and second molal dissociation quotients of malonic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of malonic acidJbimalonate solutions was measured relative to a standard aqueous HCI solution from 0 to 100°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a seven-term equation. This treatment yielded the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: log K1a = -2.852 ± 0.003. ΔH1̊a = 0.1 ±0.3 kJ-mol-1. ΔS1̊a = -54.4±1.0 J-mol-1-K-1 and ΔCp̊,1a = -185±20 J-mol-1-K-1. Measurements of the bimalonatelmalonate system were made over the same intervals of temperature and ionic strength. A similar regression of the present and previously published equilibrium quotients using a seven- term equation yielded the following values for the second acid dissociation equilibrium at 25°C: log K2a = -5.697 ± 0.001. ΔH2̊a = -5.13±0.11 kJ-mol-1, ΔS2̊a = -126.3±0.4 J-mol-1-K-1. and ΔCp̊,2a = -250+10 J-mol-1-K-1

Dissociation Quotients of Malonic Acid in Aqueous Sodium Chloride Media to 100°C1

The first and second molal dissociation quotients of malonic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of malonic acidJbimalonate solutions was measured relative to a standard aqueous HCI solution from 0 to 100°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a seven-term equation. This treatment yielded the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: log K1a = -2.852 ± 0.003. ΔH1̊a = 0.1 ±0.3 kJ-mol-1. ΔS1̊a = -54.4±1.0 J-mol-1-K-1 and ΔCp̊,1a = -185±20 J-mol-1-K-1. Measurements of the bimalonatelmalonate system were made over the same intervals of temperature and ionic strength. A similar regression of the present and previously published equilibrium quotients using a seven- term equation yielded the following values for the second acid dissociation equilibrium at 25°C: log K2a = -5.697 ± 0.001. ΔH2̊a = -5.13±0.11 kJ-mol-1, ΔS2̊a = -126.3±0.4 J-mol-1-K-1. and ΔCp̊,2a = -250+10 J-mol-1-K-1

THE GEOLOGIC CONTEXT OF WONDERSTONE: A COMPLEX, OUTCROP-SCALED PATTERN OF IRONOXIDE CEMENT

Although siderite is a widespread early diagenetic mineral in fluvial systems, it is unstable in oxidizing environments and destroyed in permeable rocks that experience uplift and exhumation. The products of siderite oxidation, however, (mm- to cm-scale rhombs, concretions, and complex bands of iron-oxide cement) are widespread in the rock record of fluvial systems. The fluvial channels of the Shinarump Member of the Chinle Formation in southern Utah and northern Arizona, U.S.A., provide an excellent suite of examples of diagenetic features produced by Triassic and Neogene oxidation of early diagenetic siderite. These diagenetic features also provide direct evidence of the level of the water table during deposition of the Shinarump member. Large, in situ, discoidal concretions containing preserved siderite are present in Shinarump floodplain siltstones. Rip-up clasts derived from the siltstones developed iron-oxide rinds during late-stage, near-surface oxidation. These two structures show that floodplain silts contained abundant organic matter and methanic pore water. Groundwater recharging through these silts carried reducing water through underlying sand bodies and discharged into active channels. Degassing of CO2 and methanogenesis caused rhombic crystals of siderite to precipitate in channel sands during these wet intervals. Some of this siderite may have been oxidized during dry intervals when groundwater circulation reversed, but most siderite in the channel sands was preserved until the Shinarump was exhumed during the Neogene. As oxygenated near-surface water entered joints in the lithified Shinarump, colonies of iron-oxidizing microbes living in the phreatic zone occupied redox boundaries and used the rhombic crystals of siderite in the sandstone and the spherulitic siderite in transported siltstone intraclasts as their sources of energy and carbon. The ferrous iron released from dissolving siderite within the intraclasts was oxidized at the siltstone–sandstone contact, generating rinded concretions similar to those in the Cretaceous Dakota Formation. Complex banding known as wonderstone was produced in the channel sandstones from oxidation of the rhombic siderite; the pattern is a combination of Liesegang bands and microbially mediated cements. The preserved rhombs are pseudomorphs after siderite crystals that were either oxidized during Triassic dry intervals, or escaped Neogene microbial oxidation in the phreatic zone, only to be oxidized abiotically in the vadose zone. Microbes are likely oxidizing Shinarump siderite a few kilometers down dip of outcrops with exposed wonderstone. At such locations, the Shinarump is in contact with overlying watersaturated Quaternary alluvium

Sandstones and Utah’s canyon country: Deposition, diagenesis, exhumation, and landscape evolution

South-central Utah’s prominent sandstones and deeply dissected landscapes are the focus of this four-day trip, which begins and ends in Grand Junction, Colorado. Studies of the apatite grains in sandstones adjacent to igneous intrusions are revealing new information on the timing and rate of Cenozoic erosion. Iron-oxide-cemented concretions in other rocks record how reduced-iron carbonates and subsurface microbes interacted when near-surface, oxygenated waters started to flush the reducing, CO2-rich waters from Colorado Plateau aquifers. New geochronologic techniques that are being applied to the plateau rocks have the potential to expand our knowledge of how diagenetic episodes relate to the evolving topography of this classic geologic setting

Cadmium Malonate Complexation in Aqueous Sodium Trifluoromethanesulfonate Media to 75°C; Including Dissociation Quotients of Malonic Acid

The molal formation quotients for cadmium-malonate complexes were measured potentiometrically from 5 to 75°C, at ionic strengths of 0.1, 0.3, 0.6 and 1.0 molal in aqueous sodium trifluoromethanesulfonate (NaTf) media. In addition, the stepwise dissociation quotients for malomc acid were measured in the same medium from 5 to 100°C, at ionic strengths of 0.1, 0.3, 0.6, and 1.0 molal by the same method. The dissociation quotients for malonic acid were modeled as a function of temperature and ionic strength with empirical equations formulated such that the equilibrium constants at infinite dilution were consistent, within the error estimates, with the malonic acid dissociation constants obtained in NaCl media. The equilibrium constants calculated for the dissociation of malonic acid at 25°C and infinite dilution are log K1a = -2.86 ± 0.01 and log K2a = -5.71 ± 0.01. A single Cd-malonate species, CdCH2C2O4, was identified from the complexation study and the formation quotients for this species were also modeled as a function of temperature and ionic strength. Thermodynamic parameters obtained by differentiating the equation with respect to temperature for the formation of CdCH2C2O4 at 25°C and infinite dilution are: log K = 3.45 ± 0.09, ΔH° = 7 ± 6 kJ-mol-1, ΔS° = 91 ± 22 J-K-1-mol-1, and ΔC°p = 400 ± 300J-K-1-mol-1

Jurassic earthquake sequence recorded by multiple generations of sand blows, Zion National Park, Utah

Earthquakes along convergent plate boundaries commonly occur in sequences that are complete within 1 yr, and may include 8–10 events strong enough to generate sand blows. Dune crossbeds within the Jurassic Navajo Sandstone of Utah (western United States) enclose intact and truncated sand blows, and the intrusive structures that fed them. We mapped the distribution of more than 800 soft-sediment dikes and pipes at two small sites. All water-escape structures intersect a single paleo-surface, and are limited to the upper portion of the underlying set of cross-strata and the lower portion of the overlying set. A small portion of one set of crossbeds that represents ~1 yr of dune migration encloses eight generations of eruptive events. We interpret these superimposed depositional and deformational structures as the record of a single shock-aftershock earthquake sequence. The completeness and temporal detail of this paleoseismic record are unique, and were made possible when sand blows repeatedly erupted onto lee slopes of migrating dunes. Similar records should be sought in modern dunefields with shallow water tables