Surficial Rock Research Articles

Direct dating of an ancient stone causeway at Karlslunde, Sjælland, Denmark: A combined approach using luminescence from the surfaces of granitic cobbles and coarse grains from disaggregated heated rocks

In 2017 part of an ancient stone causeway was uncovered at Karlslunde on the island of Sjælland, Denmark. With no artefacts found at the site, optically stimulated luminescence dating of coarse grains, grains derived from disaggregated rocks, and surficial rock chips obtained directly from granitic road cobbles were used to determine the time of construction. Some granitic road cobbles were visibly disaggregating at the time of excavation, and laboratory measurements revealed surprising strong fast component dominated quartz sensitivity from these samples. It was concluded that some of the rocks used in the causeway had been heated, presumably prior to incorporation in the structure. Dose recovery plateau experiments using sedimentary quartz and quartz grains recovered by gently disaggregating heated rocks suggested the use of a 220/180 °C preheat/cut-heat combination (DR ratio 0.999 ± 0.018; n = 40); this reduced the risk of thermal transfer in these young samples. IRSL signals were used for rocks that could not be disaggregated. The L/T burial profiles obtained from two unheated rocks (1 granite, 1 felsic gneiss) indicated they had been exposed for sufficient time for us to be confident of obtaining accurate IRSL ages. The post-IR IRSL180 signals were also measured in these two cobbles; the bleaching front was shallow and the signal was only sufficiently reset to allow accurate determination of De on one rock. After subtracting a residual, the dose recovery ratio results for the unheated rocks post-IR IRSL180 and IR50 were 1.006 ± 0.012 (n = 10) and 0.937 ± 0.007 (n = 10), respectively. In total 8 ages were accepted; 4 coarse grained sediment quartz ages from an unexcavated part of the road surface, 2 fading corrected IR50 ages from surface slices from non-disaggregated cobbles, and 2 quartz ages from disaggregated (apparently heated) cobbles. IRSL signals from the sedimentary and heated samples were used primarily to assess the degree of resetting of the quartz blue-stimulated OSL; both the post-IR IRSL and IR50 signals significantly over-estimated the quartz age. However, the sedimentary quartz ages, the heated cobble quartz ages and the fading corrected IR50 ages from the unheated road cobbles, are consistent and likely reflect a construction age of ∼2ka ago.

Seasonality of rockfall triggers and conditioning factors interpreted from a lidar-derived rockfall database

Relationships between rockfall and environmental factors have been the focus of considerable research over the last several decades. Many prior studies have not quantified rockfall volume due to challenges in volume estimation without the use of modern remote sensing methods, and the role of longer-term conditioning factors on rockfall activity is often not considered. As part of a broader effort to evaluate rockfall hazard for slopes along the heavily trafficked Interstate-70 corridor in Colorado, this study takes advantage of a high temporal resolution lidar-derived rockfall database consisting of over five years' worth of rockfall data at a particular cut slope to evaluate the relationship between rockfall activity and environmental factors. The combination of monitoring duration and spatiotemporal monitoring resolution used allows for evaluation of both triggering and conditioning factors. Correlations are evaluated between rockfall metrics and weather metrics at a seasonal scale as well as the scale of individual monitoring intervals. Based on the results, it is interpreted that surficial rock material is weakened each Winter by freezing processes, large amounts of rockfall occur in the Spring as a result of the slope thawing out, elevated rockfall activity continues over the Summer as surficial rocks destabilized by freezing processes in the previous Winter are fully dislodged, and rockfall activity significantly reduces in the Fall due to the number of unstable blocks available to fall being significantly reduced. From comparison with the literature, we conclude this cycle is relatively consistent with rockfall trends observed in alpine environments, while more temperate regions exhibit notably different trends in rockfall seasonality.

Cosmogenic 10Be in pyroxene: laboratory progress, production rate systematics, and application of the 10Be–3He nuclide pair in the Antarctic Dry Valleys

Abstract. Here, we present cosmogenic-10Be and cosmogenic-3He data from Ferrar dolerite pyroxenes in surficial rock samples and a bedrock core from the McMurdo Dry Valleys, Antarctica, with the goal of refining the laboratory methods for extracting beryllium from pyroxene, further estimating the 10Be production rate in pyroxene and demonstrating the applicability of 10Be–3He in mafic rock. The ability to routinely measure cosmogenic 10Be in pyroxene will open new opportunities for quantifying exposure durations and Earth surface processes in mafic rocks. We describe scalable laboratory methods for isolating beryllium from pyroxene, which include a simple hydrofluoric acid leaching procedure for removing meteoric 10Be and the addition of a pH 8 precipitation step to reduce the cation load prior to ion exchange chromatography. 10Be measurements in pyroxene from the surface samples have apparent 3He exposure ages of 1–6 Myr. We estimate a spallation production rate for 10Be in pyroxene, referenced to 3He, of 3.6 ± 0.2 atoms g−1 yr−1. 10Be and 3He measurements in the bedrock core yield initial estimates for parameters associated with 10Be and 3He production by negative-muon capture (f10∗=0.00183 and f3∗fCfD=0.00337). Next, we demonstrate that the 10Be–3He pair in pyroxene can be used to simultaneously resolve erosion rates and exposure ages, finding that the measured cosmogenic-nuclide concentrations in our surface samples are best explained by 2–8 Myr of exposure at erosion rates of 0–35 cm Myr−1. Finally, given the low 10Be in our laboratory blanks (average of 5.7 × 103 atoms), the reported measurement precision, and our estimated production rate, it should be possible to measure 2 g samples with 10Be concentrations of 6 × 104 and 1.5 × 104 atoms g−1 with 5 % and 15 % uncertainty, respectively. With this level of precision, Last Glacial Maximum to Late Holocene surfaces can now be dated with 10Be in pyroxene. Application of 10Be in pyroxene, alone or in combination with 3He, will expand possibilities for investigating glacial histories and landscape change in mafic rock.

Backwasting rock sheets of the Navajo Sandstone, Utah, USA

AbstractOn many Navajo Sandstone outcrops in southern Utah, steep, decimetre‐high scarps (downslope‐facing margins of rock sheets) interrupt smooth slopes covered by crustose lichens. Scarps form where sheeting joints and water emerge at the land surface. Weathering at scarp faces causes upslope backwasting of rock sheets and leaves behind smooth, unweathered rock surfaces that become stabilized by lichens. We hypothesize that subsurface, low‐angle, open fractures in porous and permeable rocks are barriers to downward flux of water through the vadose zone. Runoff and lateral flow through the uppermost rock sheets deliver water to scarps, inducing backwasting. Monitoring of temperature and water/ice content within two surficial rock sheets revealed that, in the winter of 2020–2021, snowmelt that entered lichen‐covered surfaces persisted for 64 days and underwent 46 freeze/thaw cycles. Water gained from summer rains remained for a maximum of 11 days. Flaking rock and dangling lichen crusts that overhang scarps indicate backwasting is now active. We conclude that freeze/thaw cycles (rather than salt precipitation) drive backwasting at our study sites, all of which are located more than 1400 m above sea level where the climate is relatively cool, and snowfalls are frequent. Backwasting would likely be more rapid and extensive under a cooler, wetter (periglacial) climate. Although broad, gently sloping, lichen‐covered rock sheets dominate the land surface, they are not downwasting; weathering is instead restricted to the near‐vertical, lichen‐free, backwasting scarps.

Morphological and mineralogical characterization of surficial weathering on calcarenite rocks in the rupestrian system of “San Michele delle Grotte” at Gravina in Puglia (Bari, Apulia)

San Michele delle Grotte is a rupestrian cave excavated into the “Calcarenite di Gravina” formation, resting over the Cretaceous formation of “Calcare di Altamura”. Both rock types show evident instability features and intense surficial rock weathering. A detailed mineralogical and morphologic characterization of Calcarenite di Gravina Fm. samples has been carried out by means of optical and petrographic microscope (OM and PM), scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). In thin section, bioclastic packstone to grainstone fabrics were observed. In the surficial portion of the rock it is possible to find biological colonizations and efflorescences: the first are dominated by algae covering the calcite substrate, whilst the efflorescences contain mainly sulfates such as syngenite, gypsum and arcanite, and other salts including niter and sylvine. A distinctive enhance of microporosity on the rock surface immediately at the contact with the biological colonizations and efflorescences was observed. A high abundance of biological colonizations was found where the hostrock is well exposed to light, whereas efflorescences prevail in the innermost parts of the cavity. Efflorescences may originate from both anthropogenic air pollution (wet and dry airborne deposition that provides sulfate and nitrate anions) and circulation of soil water whose composition can be modified, for instance, by fertilizers. Analysis of the weathering conditions of calcarenite rocks is a crucial factor in determining the likely possibility of failures and collapses in underground environments.

RUSSELL REVIEW Are plant roots only “in” soil or are they “of” it? Roots, soil formation and function

AbstractRoots are near‐ubiquitous components of soils globally but have often been regarded as separate from the soil rather than a substantial factor in determining what soil is and how it functions. The start of rapid soil formation commenced about 400 million years ago with the emergence of vascular plants and the evolution of roots and associated microbes. Roots and associated microorganisms contribute significantly to soil formation by altering rocks and soil minerals through a variety of biogeochemical processes and supply carbon to a depth that can have long residence times. Living root inputs of carbon via rhizodeposits are more efficient than shoot and root litter inputs in forming slow‐cycling, mineral‐associated soil organic carbon pools. The current functionality of soils in providing food and fuel and fibres, supplying plant nutrients, filtering water and flood regulation, and disease suppression are all dependent on the activities of plant roots. Roots are actively communicating and collaborating with other organisms for mutual benefit, and the signals underlying this modulation of the rhizosphere microbiome are being identified. In this review I examine how plant roots (an organ not an organism) affect soil formation and function and conclude that, from several perspectives, roots are not just “in” soil but “of” it and that definitions of soil should recognise this. A possible definition is: “Soils are altered surficial rock or sediment, composed of organic matter, minerals, fluids, and organisms whose formation and functionality are influenced by biogeochemical weathering and interactions of these components with plant roots.”HighlightsPaleoclimatic and paleosoil research shows the key role of roots and mycorrhiza in soil formation.Deep roots and living root inputs are substantial contributors to long‐term C storage.Root/microbe signalling facilitates mutualistic symbioses, nutrient uptake and disease suppression.Definitions of soil should explicitly include roots as an important component of the soil system.

Reconstruction of Surficial Rock Blocks by Means of Rock Structure Modelling of 3D TLS Point Clouds: The 2013 Long-Chang Rockfall

Terrestrial laser scanning (TLS) enables the digital representation of rock outcrops with unprecedented resolution and accuracy. Currently, extracting full-scale block structures from raw TLS data (e.g. for assessing rockfall source areas) requires special techniques. This contribution describes processing methods for reconstructing three-dimensional representations of blocky rock masses from raw point cloud data. The developed workflow involves extracting structural and topographical details, fitting location-dependent discontinuities bounding the rock blocks, and reconstructing the block array embedded in three-dimensional geomorphology. The method is applied to a case study of the 2013 Long-Chang rockfall located in the Guizhou Province of China. Based on these initial results, the workflow will be applied to rockfall source evaluations throughout the karstified Kaili region within Guizhou.

Relaxation Response of Critically Stressed Macroscale Surficial Rock Sheets

Rock environments both underground and on Earth’s surface show indications of energetic macroscale fracture. In tunnels and excavations, these manifest as rockbursts—energetic explosions of rock that can damage engineering projects, and may pose ongoing financial and safety risk as rock stresses adjust during post-failure relaxation. In natural settings at the surface, evidence for rockbursts exist in the form of tent-like structures of ruptured exfoliation sheets, but few direct observations of such events exist, precluding the analysis of how natural rock formations may evolve after rupture. Here we investigate the post-failure evolution of a granitic rock dome following rapid fracture events (i.e., surficial rockbursts) that occurred in California, USA during 2014–2016. Building upon previous work that showed a thermal stress origin for the observed fracturing, we investigate the return to background stress conditions (i.e., stress relaxation) observed in both short- (week, month) and long-term (multi-year) rock deformation trends. Acoustic emissions, deformation, and environmental monitoring data indicate that partially detached rock sheets forming the surface of the dome undergo fracture aperture closing during cooling periods, concurrent with reduction of rock stress by the source of forcing (i.e., thermal stress). However, with sufficient critical and/or subcritical fracture, our observations also show that rock sheets can become decoupled from the source of stress, resulting in a long-term return to background stress conditions. Our results provide insight into the cyclic and likely ephemeral nature of rock fracture in surficial rock domes, as well as in underground rockburst environments.

Vibration Safety Criteria for Surficial Rock Mass of Open Pit Slope Affected by Underground Mining Blasting Operations

Introduction: Blasting vibration velocity is an important index to evaluate the stability of mine slopes under blasting operations. Objective: In order to determine the blasting vibration safety criteria for slope rock mass scientifically and reasonably, the influence of stress waves on surficial rock mass of mine slopes was analyzed when stress waves propagate to the slope surface, and mathematical models for blasting vibration safety criteria are proposed based on the ultimate tensile stress criterion, the ultimate shear stress criterion and the Mohr-Coulomb criterion. Results and Conclusion: Combined with the field blasting operations during the open-pit to underground mining in Daye iron mine, the blasting vibration safety criteria is calculated. It is obtained that the blasting vibration safety criteria for the north slope and the south slope are 11.08cm/s and 10.20cm/s respectively. The results agree well with the Safety Regulations for Blasting in China and provide a reference to determine blasting vibration safety criteria for other similar projects.

Electrical resistivity dynamics beneath a fractured sedimentary bedrock riverbed in response to temperature and groundwater–surface water exchange

Abstract. Bedrock rivers occur where surface water flows along an exposed rock surface. Fractured sedimentary bedrock can exhibit variable groundwater residence times, anisotropic flow paths, and heterogeneity, along with diffusive exchange between fractures and rock matrix. These properties of the rock will affect thermal transients in the riverbed and groundwater–surface water exchange. In this study, surface electrical methods were used as a non-invasive technique to assess the scale and temporal variability of riverbed temperature and groundwater–surface water interaction beneath a sedimentary bedrock riverbed. Conditions were monitored at a semi-daily to semi-weekly interval over a full annual period that included a seasonal freeze–thaw cycle. Surface electromagnetic induction (EMI) and electrical resistivity tomography (ERT) methods captured conditions beneath the riverbed along a pool–riffle sequence of the Eramosa River in Canada. Geophysical datasets were accompanied by continuous measurements of aqueous specific conductance, temperature, and river stage. Time-lapse vertical temperature trolling within a lined borehole adjacent to the river revealed active groundwater flow zones along fracture networks within the upper 10 m of rock. EMI measurements collected during cooler high-flow and warmer low-flow periods identified a spatiotemporal riverbed response that was largely dependent upon riverbed morphology and seasonal groundwater temperature. Time-lapse ERT profiles across the pool and riffle sequence identified seasonal transients within the upper 2 and 3 m of rock, respectively, with spatial variations controlled by riverbed morphology (pool versus riffle) and dominant surficial rock properties (competent versus weathered rock rubble surface). While the pool and riffle both exhibited a dynamic resistivity through seasonal cooling and warming cycles, conditions beneath the pool were more variable, largely due to the formation of river ice during the winter season. We show that surface electrical resistivity methods have the capacity to detect and resolve electrical resistivity transience beneath a fractured bedrock riverbed in response to porewater temperature and specific conductance fluctuations over a complete annual cycle.

The compositional and physical properties of localized lunar pyroclastic deposits

Lunar localized pyroclastic deposits are low albedo deposits with areas <2500km2. These deposits were difficult to study before the turn of the millennium because of the lack of available high spatial-resolution data. With the launch of the Lunar Reconnaissance Orbiter, Kaguya, and Chaandrayan-1, new sets of diverse high spatial-resolution data are now available. Using several of these data sets, we conducted a study of 34 localized pyroclastic deposits globally. For each localized pyroclastic deposit, we examined topography to estimate pyroclastic volume and juvenile proportions, S-band radar backscatter, thermal-infrared-derived measures of surficial rock abundance and regolith density, and mineral abundances. Our goals are to (1) quantitatively characterize the physical and mineralogical properties of each localized pyroclastic deposit, (2) investigate the physical and mineralogical variations among localized pyroclastic deposits, (3) compare these properties of localized (<2500km2) to regional pyroclastic deposits (>2500km2), and (4) provide useful parameters for future volcanological modeling. From this study, we find that: (1) localized pyroclastic deposits exhibit low relief structures, (2) the surface rock abundance and circular polarization ratio of localized pyroclastic deposits display a wide range of values (0.2–0.5% and 0.3–0.6, respectively), (3) the glass abundance of localized pyroclastic deposits vary between ∼0 and ∼80wt.%, (4) there are four types of localized pyroclastic deposits based upon the surface rock abundance and glass abundance parameters, (5) pyroclastic deposits within the same floor-fractured crater tend to have similar properties, and (6) localized pyroclastic deposits are diverse with respect to regional pyroclastic deposits, but a subset of localized pyroclastic deposits have similar physical and mineralogical properties to regional pyroclastic deposits.

Wind erosion potential of lacustrine and alluvial soils before and after disturbance in the eastern Great Basin, USA: Estimating threshold friction velocity using easier-to-measure soil properties

Abstract Disturbance of lacustrine and alluvial soils could increase aeolian dust emissions in the eastern Great Basin, but little is known about the susceptibility of these land surfaces to wind erosion. Threshold friction velocity (u∗t), a necessary parameter to estimate wind erosion potential, is difficult to accurately measure; methods to estimate u∗t from alternate measurements would be useful. We measured u∗t and sediment production rate with a portable wind tunnel, and quantified relationships between u∗t and eleven easier-to-measure soil surface properties for both undisturbed and disturbed lacustrine and alluvial soils in Snake Valley, Utah. Soil surface type and disturbance significantly influenced u∗t, sediment production rate, and the relationships between u∗t and easier-to-measure soil surface properties. Only soils with surficial rock fragments and weak physical crusts reached u∗t before disturbance, whereas all surface types reached u∗t following disturbance. Soils with weak physical crusts had the lowest average u∗t and highest average sediment production rate before and after disturbance. Surprisingly, however, disturbance reduced sediment production rate. Soils with weak physical crusts and surficial rock cover are likely the most susceptible to wind erosion and subsequent dust generation both before and after disturbance. Silt concentration and penetrometer resistance were significant predictors of u∗t in undisturbed soils with weak physical crusts and surficial rock cover. Following disturbance, clay concentration and aggregate stability were significant predictors for soils with hard salt crusts and surficial rock cover. Prediction of u∗t using alternate measurements is promising, but u∗t measurement uncertainty must be considered.

Impact of the Dakota Aquifer on major-ion chemistry of Rock Creek discharge, eastern Nebraska, Midwest region

Examination of historical water-quality data (major cations and anions and total dissolved solids [TDS]) for Rock Creek, located in eastern Nebraska’s saline wetlands north of the Platte River, revealed that concentrations of sodium (Na), chloride (Cl), and TDS increased significantly in the downstream reach below the town of Ceresco, exceeding the U.S. Environmental Protection Agency (USEPA) secondary drinking water standards of 250 mg/L for Cl and 500 mg/L for TDS. Research into the probable source(s) of these inorganic constituents revealed that the Dakota Formation of Late Cretaceous age subcrops in the study area and typically yields water with elevated concentrations of Na, Cl, and TDS in southeastern Nebraska. This brackish to saline water upwells to the surficial aquifer and Rock Creek streambed. Additionally, the significant levels of Na and Cl correlate well with the occurrence of unique saline wetlands along Rock Creek downstream from Ceresco. Public-domain geochemical speciation software codes (Visual MINTEQ and NETPATH) were used to characterize and investigate aqueous geochemistry of Rock Creek discharge and to calculate mixing proportions of Dakota Formation water and stream discharge. The NETPATH output suggests that 3.3%–18% of discharge in Rock Creek approximately 10 km (6.2 mi) southeast of Ceresco, Nebraska, originates from the Dakota Formation and probably the underlying Pennsylvanian bedrock. Hopefully, this paper will be the impetus for an up-to-date, comprehensive, and geochemical-rich data investigation of the Dakota Aquifer’s impact on the inorganic water quality of Rock Creek.

Travertine precipitation in the Paleoproterozoic Kuetsjärvi Sedimentary Formation, Pechenga Greenstone Belt, NE Fennoscandian Shield

Precambrian travertines, tufas and speleothems either formed rarely or they have not been identified in previous studies. In the absence of high pCO2 soils in Paleoproterozoic, karst solution and speleothem formation occurred by processes distinct from those commonly found in present-day low temperature karst environments. However, the high pCO2 atmosphere could itself have encouraged karst formation. The Paleoproterozoic Kuetsjärvi Sedimentary Formation of the Pechenga Greenstone Belt, NW Russia, includes abundant terrestrial carbonate precipitates. These precipitates were sampled from a drillcore representing a complete section of the ca. 120-m-thick formation and were investigated for C and O isotopes, acid-soluble elemental contents and petrography. The newly obtained results were used to constrain the origins of the precipitates and to illuminate different terrestrial carbonate types. The investigated drillcore includes abundant small-scale cavities and veins, which are commonly filled with dolomite and quartz. Dolomite crusts are found both in the cavities and on bedding/erosional surfaces. Dolomite cements coat uneven surfaces and surficial rock fragments. The surficial dolomite crusts form distinct and discrete layers, whereas the cements do not. The cavity and vein fills are likely post-depositional in origin, whereas the surficial dolomite crusts and dolomite cements are likely syn-depositional precipitates. The investigated precipitates often show δ13C values lower than those reported from their host rocks, suggesting the influence of an external carbon source. Petrographic features and geochemical data suggest dissolution and precipitation of carbonate material originating from deep-sourced CO2-bearing fluids, likely at high earth surface temperatures.

Detection of Alteration Induced by Onshore Gas Seeps from ASTER and WorldView-2 Data

Hydrocarbon seeps cause chemical and mineralogical changes at the surface, which can be detected by remote sensing. This paper aims at the detection of mineral alteration induced by gas seeps in a marly limestone formation, SW Iran. For this purpose, the multispectral Advance Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the high spatial resolution WorldView-2 (WV-2) data were utilized for mapping surficial rock alteration. In addition, the potential of Visible Near Infrared (VNIR) bands of the WV-2 and its high spatial resolution for mapping alterations was determined. Band ratioing, principal component analysis (PCA), data fusion and the boosted regression trees (BRT) were applied to enhance and classify the altered and unaltered marly limestone formation. The alteration zones were identified and mapped by remote sensing analyses. Integrating the WV-2 into the ASTER data improved the spatial accuracy of the BRT classifications. The results showed that the BRT classification of the multiple band imagery (created from ASTER and WV-2) using regions of interest (ROIs) around field data provides the best discrimination between altered and unaltered areas. It is suggested that the WV-2 dataset can provide a potential tool along higher spectral resolution data for mapping alteration minerals related to hydrocarbon seeps in arid and semi-arid areas.

Groundwater development in hardrock terrain using morphometric analysis

The occurrence of several water crises in India over the years has resulted in the formulation of strategies that promote sustainable development of groundwater resources. For such planning efforts, the evaluation of groundwater recharge zones is a vital component of the water balance equation. Therefore, this study presents a systematic scientific analysis of various morphometric parameters relating to groundwater flow in hard rock terrain. The numerical classification scheme presented herein constitutes an integrated approach that shows how to leverage basic watershed information to evaluate prospective sites and measures at various scales for the purposes of water resources development and management. We have used our morphometric analysis of the Mamundiyar watershed of southern India to demonstrate the use of this classification scheme as a helpful tool in the watershed development planning process. The results of this relative ranking of Mamundiyar subbasins, using various parameters that are ultimately indicative of surficial rock permeability, show the usefulness of this classification scheme in identifying suitable rainfall infiltration sites. Together with an evaluation of the various hydrogeologic conditions in a given basin, this type of numerical classification scheme can be developed and applied to properly identify recharge sites in the planning stages of sustainable watershed development, as well as in already active watersheds, perhaps where extractive industries are working or certain land use practices exist, to evaluate potential relationships between hydrogeologic regimes and these anthropogenic activities.

Integrated hyperspectral remote sensing, geochemical and isotopic studies for understanding hydrocarbon-induced rock alterations

The main objective of this work was to determine if there are characteristic mineral assemblages and chemical changes in areas affected by hydrocarbon microseepages. For this purpose remote sensing was utilized for mapping surficial rock alterations, and geochemical tools were used to understand the alteration processes. The key area chosen for this type of work were altered and unaltered Wingate Sandstone outcrops in Lisbon Valley, Utah. The Spectral Angle Mapper method was applied on HyMap hyperspectral data to classify the extent of altered and unaltered outcrops, as well as to map the changes in mineral content within the outcrops. The Spectral Feature Fitting method was used to identify lithological changes in the area. Reflectance spectroscopy, thin section studies, major, minor, and trace element analyses, and stable carbon and oxygen studies on both bleached (altered) and unbleached (unaltered) samples were successfully used to delineate areas of similar rock composition and relate changes due to hydrocarbons leaking from underlying petroleum reservoirs. Unbleached Wingate Sandstone samples had higher hematite and feldspar content than bleached Wingate samples, which were characterized by larger amounts of clay, calcite, and pyrite. Some bleached samples also had higher concentrations of elements (U, Mo) characteristic of hydrocarbon-related reducing environments, and were depleted in 13C when compared to the unbleached samples. Based on these results, the following model of chemical reactions is suggested for diagnostic changes within Wingate Sandstone. Hydrocarbon-induced reducing environment caused the transformation of sulfate ion (obtained from groundwater or from oxidation of H2S) to sulfide ion, resulting in the reduction of hematite to pyrite. The released hydrogen ion from this reaction reacted with available feldspars in the rock, leading to precipitation of kaolinite. These conditions favor the reaction between bicarbonate ion and Ca2+ ions that can be obtained from the groundwater, leading to precipitation of calcite in pore spaces left open after the reduction and removal of hematite.

Contributions to atmospheric dust production of natural and anthropogenic emissions in a recreational area designated for off-road vehicular activity (Nellis Dunes, Nevada, USA)

Wind erosion measurements and experiments with off-road vehicles (ORV) were conducted in the Nellis Dunes Recreation Area (NDRA) near Las Vegas, Nevada. Wind erosion was measured during one complete year. ORV emissions were measured for 3 types of vehicles (dirt bikes, dune buggies, 4-wheelers) and for various driving speeds up to 56kmh−1. This study investigates the mutual contributions of wind erosion and ORV in the total emission of dust in NDRA. The highest emissions generated by wind erosion occur in the sandy areas, and especially in the sand dunes. These areas produce only very little dust during ORV driving. By far the most ORV dust is generated in areas of silt and rock-covered silt, where protective surface crusts and surficial rock layers are destroyed by the driving and large reservoirs of emittable dust are available in the top layer. On an annual basis the amounts of dust produced in NDRA are almost equal for wind erosion and ORV. Management in the NDRA is complicated by the intense wind erosion in the sand dunes. Even while ORV driving does not create significant emissions in these areas, drivers can potentially inhale large amounts of dust produced locally by wind erosion.

Heave of a surficial rock layer due to pressures generated by injected fluids

This paper examines the problem of heave developed in a surface or caprock layer of a storage formation due to the injection of pressurized fluids at depth. The problem is of interest to the deep geologic disposal of hazardous wastes and the geologic sequestration of carbon dioxide by injection. The paper develops a mathematical model that assumes elastic behavior of the storage medium while the surface rock layer is modeled as a thin plate. Elastic solutions are developed for the axisymmetric flexure deflections of the surface layer during internal pressurization over a flat circular region. The model provides a convenient tool for the preliminary estimation of the influence of injection pressures on the integrity of surface rock layers.

Use of habitat features, edges and harvest treatments by spruce grouse in subalpine forest

Winter use of habitat features, edges and alternative forest harvest types by spruce grouse ( Falcipennis canadensis) was measured at the Sicamous Creek Silvicultural Systems site in high-elevation forest in south-central British Columbia, Canada. Habitat relationships and edge effects were tested at five other validation sites. Winter use by grouse was indicated by droppings in habitat plots or edge transects conducted shortly after snowmelt. Assumptions of using droppings to indicate grouse occurrence were assessed. Grouse high-use areas (100 m-radius) were distinguished from areas available overall by higher densities but lower basal areas of fir and spruce trees, presence of surficial rock and sparse shrub cover. Plots of 0.01 ha used by grouse within high-use areas were distinguished from unused plots by these same habitat features, plus greater canopy cover and more relatively short trees. Knolls were preferred topography types, as predicted by this habitat model. Use of forest was reduced within 10 m of recently harvested openings of 0.1, 1 and 10 ha, and within 20 m of older large openings. Use increased with proximity to open wetlands until 20 m from the wetland, paralleling predicted habitat quality, then declined nearer to the edge despite high predicted quality. Percent decline in winter occurrence of grouse was similar to the percent timber removed (33%) in harvest treatments with 0.1, 1 and 10 ha openings, but a more pronounced decline occurred in uniform partial cuts, where uniform thinning lowered predicted habitat quality. Recommendations to maintain winter habitat for spruce grouse in managed high-elevation forests include maintaining forest patches on knolls or other poor growing sites and around wetlands, ensuring some retained area >10 m from harvested and natural edges, and avoiding widespread use of uniform partial cutting.