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Sample records for sandstone surface crust

  1. Chemical analysis of black crust on the Angkor sandstone at the Bayon temple, Cambodia

    NASA Astrophysics Data System (ADS)

    Song, Wonsuh; Oguchi, Chiaki; Waragai, Tetsuya

    2014-05-01

    The Angkor complex is the one of the greatest cultural heritages in the world. It is constructed in the early 12th century, designated as a world cultural heritage by UNESCO in 1992. The temples at the Angkor complex are mainly made of sandstone and laterite. However, due to the tropical climate, plants, lichens and various microorganisms are growing well on the rock surface. Black crusts are also easily found on the stone surface. The 21st technical session of the International Coordinating Committee for the Safeguarding and Development of the Historic Site of Angkor (ICC-Angkor) held in 2012 recommended that to preserve both the biofilms and the forest cover and to prohibit the biocides (chlorine-based) and organic biocides. However, there are many reports that lichens and microorganisms accelerate rock weathering. It is important to clarify that how the biofilm on the Angkor temples affect Angkor sandstones. We sampled Angkor sandstone covered by black crust at the Bayon temple, Angkor complex, and observed the section and the surface of the rock sample by using SEM. Surfaces of the samples are not polished in order to observe the original condition. The samples are coated with gold for 180 seconds. The depth of the black crust is up to 1 mm. Many filamentous materials were found on the black crust. Average energy-dispersive X-ray spectroscopy data of the five areas of ca. 20 μm ×15 μm in the black crusts shows that over 80 % of the filamentous materials are compounds of carbon. It seems that these materials are hyphae. The shape of the hypha is like a thread and its size is few μm in diameter and up to several centimeters in length. Black crusts are consisted of elements and compounds of carbon, Na, Mg, Al, Si, Cl, K, Ca, and Fe. Further research has to be done to find out the better and proper way of conservation for the Angkor complex.

  2. Biologically-initiated rock crust on sandstone: Mechanical and hydraulic properties and resistance to erosion

    NASA Astrophysics Data System (ADS)

    Slavík, Martin; Bruthans, Jiří; Filippi, Michal; Schweigstillová, Jana; Falteisek, Lukáš; Řihošek, Jaroslav

    2017-02-01

    Biocolonization on sandstone surfaces is known to play an important role in rock disintegration, yet it sometimes also aids in the protection of the underlying materials from rapid erosion. There have been few studies comparing the mechanical and/or hydraulic properties of the BIRC (Biologically-Initiated Rock Crust) with its subsurface. As a result, the overall effects of the BIRC are not yet well understood. The objective of the present study was to briefly characterize the BIRC from both the mineralogical and biological points of view, and especially to quantify the effect of the BIRC upon the mechanical and hydraulic properties of friable sandstone. The mineralogical investigation of a well-developed BIRC showed that its surface is enriched in kaolinite and clay- to silt-sized quartz particles. Total organic carbon increases with the age of the BIRC. Based on DNA sequencing and microscopy, the BIRC is formed by various fungi, including components of lichens and green algae. Using the method of drilling resistance, by measuring tensile strength, and based on water jet testing, it was determined that a BIRC is up to 12 times less erodible and has 3-35 times higher tensile strength than the subsurface friable sandstone. Saturated hydraulic conductivity of the studied BIRC is 15-300 times lower than the subsurface, and was measured to also decrease in capillary water absorption (2-33 times). Water-vapor diffusion is not significantly influenced by the presence of the BIRC. The BIRC thus forms a hardened surface which protects the underlying material from rain and flowing water erosion, and considerably modifies the sandstone's hydraulic properties. Exposing the material to calcination (550 °C), and experiments with the enzyme zymolyase indicated that a major contribution to the surface hardening is provided by organic matter. In firmer sandstones, the BIRC may still considerably decrease the rate of weathering, as it is capable of providing cohesion to strongly

  3. The cauliflower-like black crusts on sandstones: A natural passive sampler to evaluate the surrounding environmental pollution.

    PubMed

    Morillas, Héctor; Maguregui, Maite; García-Florentino, Cristina; Carrero, Jose Antonio; Salcedo, Isabel; Madariaga, Juan Manuel

    2016-05-01

    Black crust in buildings can be formed as a result of different kind of chemical and physical reactions between the stone surface and environmental factors (e.g. acid aerosols emitted to the atmosphere, airborne particulate matter, etc.). Moreover, biological colonizations can also be present on them. This kind of pathology is widely present in limestones, but fewer are the case study dealing with the characterization of black crusts on sandstones. In this work we present an innovative methodology based on the use of cauliflower-like black crusts formed on sandstone material as natural passive sampler to evaluate the environmental pollution related with the emission of natural (crustal particles and marine aerosol particles) and metallic elements in the airborne particulate matter from the surrounding atmosphere. To illustrate its usefulness, different cauliflower-like black crusts growing in areas protected from the rain growing in an historical construction, La Galea Fortress, made up of sandstone and placed in the Abra Bay (Getxo, Basque Country, Spain) were characterized. This area suffers the anthropogenic emissions coming from the surrounding industry, traffic, sea port, and the natural ones coming from the surrounding marine atmosphere. The applied analytical methodology began with a previous elemental in situ screening in order to evaluate and compare the presence of the metals trapped in black crusts from different orientations using a hand-held energy dispersive X-Ray Fluorescence spectrometer. After this preliminary study, samples of black crusts were taken in order to characterize them in the laboratory using molecular techniques (Raman spectroscopy and XRD) and elemental techniques (ICP-MS, SEM-EDS and micro energy dispersive X-Ray Fluorescence). With the last two elemental techniques, imaging analyses were performed at different lateral resolutions in order to observe the distribution of the metals and other kind of particles trapped in the black

  4. Surface coating for prevention of crust formation

    DOEpatents

    Kronberg, James W.

    1994-01-01

    A flexible surface coating which promotes the removal of deposits as they reach the surface by preventing adhesion and crust formation. Flexible layers are attached to each side of a flexible mesh substrate comprising of a plurality of zones composed of one or more neighboring cells, each zone having a different compressibility than its adjacent zones. The substrate is composed of a mesh made of strands and open cells. The cells may be filled with foam. Studs or bearings may also be positioned in the cells to increase the variation in compressibility and thus the degree of flexing of the coating. Surface loading produces varying amounts of compression from point to point causing the coating to flex as deposits reach it, breaking up any hardening deposits before a continuous crust forms. Preferably one or more additional layers are also used, such as an outer layer of a non-stick material such as TEFLON, which may be pigmented, and an inner, adhesive layer to facilitate applying the coating to a surface.

  5. Optical Characterization of Cryptoendolithic Chemical Biosignatures on Antarctic Sandstone Surfaces

    NASA Technical Reports Server (NTRS)

    Harju, Ellen R.

    2005-01-01

    We have used several non-destructive optical techniques to study the distribution of organic molecules on an Antarctic sandstone sample collected at Battleship Promontory. Cryptoendolithic microorganisms have been found to inhabit rocks in the dry valleys of Antarctica. These dry deserts are an Earth analog to Mars. Future Mars rovers may search for life in the rocks of Mars with similar instrumentation used in this study. Light microscopy was used to determine five distinct regions and to determine textures on the sample. Deep ultraviolet fluorescence spectroscopy was used to scan the rock for the presence of organic molecules. Organic molecules were present in three of the five regions but not in the crust. There were similarities between each region, but each region presented a unique signature. Raman spectroscopy identified the minerals present and also provided more definitive identifications of the organic molecules. X-ray diffraction was also used to definitively identify the minerals present and corroborate the Raman mineral results.

  6. Acoustic techniques for studying soil-surface seals and crusts

    USDA-ARS?s Scientific Manuscript database

    The impact of raindrops on a soil surface during a rainstorm may cause soil-surface sealing and upon drying, soil crusting. Soil-surface sealing is a result of the clogging of interaggregate pores by smaller suspended particles in the water and by structural deformation of the soil fabric, which red...

  7. Experimental Evidence of Truly Elastic Behavior of Artificial Sandstone Inside the Cementation Yield Surface

    NASA Astrophysics Data System (ADS)

    Trads, N.; Lade, P. V.

    2014-03-01

    Hollow cylinder specimens of cemented sand, i.e., artificial sandstone, were produced and tested by applying normal stresses and shear stresses such as to form closed stress loops to investigate the elastic behavior of the artificial sandstone. The entire process of fabrication of the hollow cylinder specimens, measurement techniques, measurements and analyses are presented to show that the artificial sandstone can be characterized as an elastic material inside the initial cementation yield surface. By applying closed stress loops in which the points of initiation of loading and the final points are identical, it has been shown that the artificially cemented sandstone behaves as a truly elastic material inside the initial cementation yield surface, because no residual energy was generated or dissipated. Furthermore, the isotropic elastic parameters have been determined for the artificially cemented sandstone.

  8. Contrasting effects of microbiotic crusts on runoff in desert surfaces

    NASA Astrophysics Data System (ADS)

    Kidron, Giora J.; Monger, H. Curtis; Vonshak, Ahuva; Conrod, William

    2012-02-01

    Microbiotic crusts (MCs) play an important role in surface hydrology by altering runoff yield. In order to study the crust's role on water redistribution, rainfall and runoff were measured during 1998-2000 at three sites within the northern Chihuahuan Desert, New Mexico, USA: the Sevilleta National Wildlife Refuge (SEV), the White Sands National Monument (WS), and the Jornada Experimental Range (JER). Whereas quartz and gypsum sand characterize the SEV and WS sites, respectively, both of which have high infiltration rates, silty alluvial deposits characterize the JER site. Runoff was measured in four pairs of 1.8-6.4 m 2 plots having MCs, one of which was scalped in each pair. No runoff was generated at WS, whether on the crusted or the scalped plots. Runoff was however generated at SEV and JER, being higher on the crusted plots at SEV and lower on the JER plots. The results were explained by the combined effect of (a) parent material and (b) the crust properties, such as species composition, microrelief (surface roughness) and exopolysaccharide (EPS) content (reflected in the ratio of carbohydrates to chlorophyll). Whereas the effective rainfall, the fines and the EPS content were found to explain runoff initiation, the effective rainfall and the crust microrelief were found to explain the amount of runoff at SEV and JER where runoff generation took place. The findings attest to the fundamental role of the parent material and the crust's species composition and properties on runoff and hence to the complex interactions and the variable effects that MCs have on dryland hydrology.

  9. Mineralogical controls on NMR rock surface relaxivity: A case study of the Fontainebleau Sandstone

    NASA Astrophysics Data System (ADS)

    Livo, Kurt

    Pore size distribution is derived from nuclear magnetic resonance, but is scaled by surface relaxivity. While nuclear magnetic resonance studies generally focus on the difficulty of determining pore size distribution in unconventional shale reservoirs, there is a lack of discussion concerning pure quartz sandstones. Long surface relaxivity causes complications analyzing nuclear magnetic resonance data for pore size distribution determination. Currently, I am unaware of research that addresses the complicated pore size distribution determination in long relaxing, pure sandstone formations, which is essential to accurate downhole petrophysical modeling. The Fontainebleau sandstone is well known for its homogenous mineralogical makeup and wide range of porosity and permeability. The Hibernia sandstone exhibits a similar mineralogy and is characterized by a similar and porosity-permeability range to the Fontainebleau sandstones, but with a significantly higher portion of clay minerals (1-6%). I present systematic petrophysical properties such as porosity, pore size distribution from nuclear magnetic resonance transverse relaxation times, permeability, and volumetric magnetic susceptibility to aide in characterization of the Fontainebleau sandstone. Analysis of collected nuclear magnetic resonance data is then compared to other petrophysical studies from literature such as helium porosity and permeability, magnetic susceptibility, and electrical conductivity. I find that the lack of impurities on the grain surfaces of pure quartz samples imparts a lower surface relaxivity as compared to clay containing sandstones and makes nuclear magnetic resonance analysis more complex. Thus, inverted nuclear magnetic resonance data from cleaner outcrop samples incorrectly models pore size distribution without accounting for wider surface relaxivity variation and is improperly used when characterizing the Fontainebleau sandstone. This is further supported by evidence from less

  10. Acoustic Techniques for Studying Soil-surface Seals and Crusts

    NASA Astrophysics Data System (ADS)

    Hickey, C. J.; Leary, D.; Dicarlo, D. A.

    2007-05-01

    The impact of raindrops on a soil surface during a rainstorm may cause soil-surface sealing and crusting. Soil- surface sealing is a result of the clogging in interaggregate pores by smaller suspended particles in the water, which reduces the infiltration capacity of soils. Soil-surface crusting refers to the increase in soil strength or mechanical stiffness associated with near surface compaction or densification. The formation of soil-surface seals and crusts have a profound influence on the erodability of soils, with the consensus being that the reduced hydraulic conductivity due to sealing is the more important factor. However, studies note that measured values of seal hydraulic conductivity are few. The reason so few measurements may be because the thickness of the altered surface layer is on the order of millimeters. For example Lee (2006) states that a soil-surface seal consist of two parts: a 0.1mm thick upper skin seal attributed to compaction by the rain drop impact and a deeper 1.5 mm "washed in" zone with decreased porosity due to the accumulation of particles. Bulk density profiles measured using X-radiography show maximum changes in the top 5 mm of the soil. The surface of the ground (soil) has an influence on the propagation of sound outdoors. The porosity, air flow- resistivity, and tortuosity of the ground are the properties, which characterize the influence of the ground on the airborne sound. The air flow-resistivity of a dry soil is equivalent to the hydraulic conductivity of a water-saturated soil. In this presentation we discuss two acoustic techniques, one with sensitivity to changes in hydraulic properties (sealing) and the other to changes in mechanical stiffness (crusting). These non-contact techniques excite the soil using a suspended loudspeaker to impinge acoustic energy from the air (sound) onto the sample. The response of the soil is quantified using a microphone to measure the total pressure above the soil surface and a laser Doppler

  11. Influence of surface crusting on infiltration of a loess plateau soil

    USDA-ARS?s Scientific Manuscript database

    Surface sealing and crusting are common widespread processes that occur in many cultivated soils worldwide, especially in arid and semiarid regions. Soil crusting negatively affects water infiltration, increases surface runoff, reduces seedling emergence, restricts air exchange between the soil and ...

  12. Colour changes of a historical Gotland sandstone caused by laser surface cleaning in ambient air and N2 flow

    NASA Astrophysics Data System (ADS)

    Jasińska, M.; Nowak, A.; Łukaszewicz, J. W.; Śliwiński, G.

    2008-07-01

    The surface discoloration due to laser cleaning was investigated for a historical Gotland sandstone. The difference in discoloration for cleaning performed in air and in the shielding environment of N2 flowing at low velocities was studied by means of colorimetry and scanning electron microscopy and energy dispersive X-ray spectroscopy techniques. For ablative removal of the natural as well as artificially applied encrustation a pulsed 1064-nm laser operated at a fluence of 0.5 J/cm2 was applied. It was observed that the natural colour variations (ΔL*=21; Δb*=23) of the stone can completely screen the laser-induced changes. Under conditions of shielding with nitrogen, darkening and yellowing slightly stronger than those occurring in the ambient air were revealed for the laser-cleaned, artificially crusted samples and the effect was independent of the gas-flow velocity. The observed difference confirmed the contribution of iron oxidation to the laser-induced yellowing and showed that the presence of oxygen in the ambient air affects favourably the cleaning by supporting removal of a variety of combustible surface remnants and crust components of organic as well as inorganic origin.

  13. Geochemistry of surface and subsurface waters in quartz-sandstones: significance for the geomorphic evolution of tepui table mountains (Gran Sabana, Venezuela)

    NASA Astrophysics Data System (ADS)

    Mecchia, Marco; Sauro, Francesco; Piccini, Leonardo; De Waele, Jo; Sanna, Laura; Tisato, Nicola; Lira, Jesus; Vergara, Freddy

    2014-04-01

    In situ measurements of discharge, pH, electric conductivity (EC), temperature, and SiO2 content have been carried out during five expeditions in the last 20 years on the summit plateaus, inside caves and along the rivers of the surrounding lowlands of three tepui massifs in Venezuela (Auyan, Roraima, and Chimanta). Additionally, detailed chemical analyses were performed on waters sampled in a newly discovered extensive quartz-sandstone cave system on the Auyan Tepui. Rock samples of the quartz-sandstone bedrock from different locations have been analysed to obtain their chemical composition with a wavelength dispersive X-ray fluorescence spectrometer. These data show that the majority of silica present in surface and subsurface water comes from dissolution of quartz and only in minor amount from hydrolysis of other silicate minerals. Probably the presence of a hardened crust of iron hydroxides limits the dissolution of silica on the top surface of tepuis. Dissolution in the subsurface, instead, is more significant and causes, in the long term, the “arenisation” of the quartz-sandstone and its subsequent removal by mechanical erosion. On the other hand, waters flowing on the arkosic rock outcropping on the lowland below the tepuis obtain their high dissolved silica content mainly from hydrolysis of silicates. The morphological evolution of these table mountains appears thus to be controlled mainly by the underground weathering of the quartz-sandstone, with the opening of deep fractures (grietas) and the collapse of large underground horizontal cave systems. Scarp retreat, instead, seems to be related to the higher weathering rate of the more arkosic formations underlying the quartz-sandstones.

  14. Mixed-Mode Fracture Behavior and Related Surface Topography Feature of a Typical Sandstone

    NASA Astrophysics Data System (ADS)

    Ren, L.; Xie, L. Z.; Xie, H. P.; Ai, T.; He, B.

    2016-08-01

    The geo-mechanical properties of reservoirs, especially the morphology of the rock surface and the fracture properties of rocks, are of great importance in the modeling and simulation of hydraulic processes. To better understand these fundamental issues, five groups of mixed-mode fracture tests were conducted on sandstone using edge-cracked semi-circular bend specimens. Accordingly, the fracture loads, growth paths and fracture surfaces for different initial mixities of the mixed-mode loadings from pure mode I to pure mode II were then determined. A surface topography measurement for each rough fracture surface was conducted using a laser profilometer, and the fractal properties of these surfaces were then investigated. The fracture path evolution mechanism was also investigated via optical microscopy. Moreover, the mixed-mode fracture strength envelope and the crack propagation trajectories of sandstone were theoretically modeled using three widely accepted fracture criteria (i.e., the MTS, MSED and MERR criterions). The published test results in Hasanpour and Choupani (World Acad Sci Eng Tech 41:764-769, 2008) for limestone were also theoretically investigated to further examine the effectiveness of the above fracture criteria. However, none of these criteria could accurately predict the fracture envelopes of both sandstone and limestone. To better estimate the fracture strength of mixed-mode fractures, an empirical maximum tensile stress (EMTS) criterion was proposed and found to achieve good agreement with the test results. Finally, a uniformly pressurized fracture model was simulated for low pressurization rates using this criterion.

  15. [Effects of soil crusts on surface hydrology in the semiarid Loess hilly area].

    PubMed

    Wei, Wei; Wen, Zhi; Chen, Li-Ding; Chen, Jin; Wu, Dong-Ping

    2012-11-01

    Soil crusts are distributed extensively in the Chinese Loess Plateau and play key roles in surface hydrological processes. In this study, a typical loess hilly region in Anjiagou catchment, Dingxi city, Gansu province was selected as the study region, and soil crusts in the catchment were investigated. Then, the hydrological effect of soil crusts was studied by using multi-sampling and hydrological monitoring experiments. Several key results were shown as follows. Firstly, compared with bared soil without crust cover, soil crusts can greatly reduce the bulk density, improve the porosity of soil, and raise the holding capacity of soil moisture which ranges from 1.4 to 1.9 times of that of bared soil. Secondly, the role of soil crust on rainfall interception was very significant. Moss crust was found to be strongest on rainfall interception, followed by synantectic crusts and lichen crusts. Bared soil without covering crusts was poorest in resisting rainfall splash. Thirdly, hydrological simulation experiments indicate that soil crusts play a certain positive role in promoting the water infiltration capacity, and the mean infiltration rate of the crusted soil was 2 times higher than that of the no-crust covered soils. While the accumulated infiltrated water amounts was also far higher than that of the bared soil.

  16. Evaluation of sandstone surface relaxivity using laser-induced breakdown spectroscopy

    NASA Astrophysics Data System (ADS)

    Washburn, Kathryn E.; Sandor, Magdalena; Cheng, Yuesheng

    2017-02-01

    Nuclear magnetic resonance (NMR) relaxometry is a common technique used to assess the pore size of fluid-filled porous materials in a wide variety of fields. However, the NMR signal itself only provides a relative distribution of pore size. To calculate an absolute pore size distribution from the NMR data, the material's surface relaxivity needs to be known. Here, a method is presented using laser-induced breakdown spectroscopy (LIBS) to evaluate surface relaxivity in sandstones. NMR transverse and longitudinal relaxation was measured on a set of sandstone samples and the surface relaxivity was calculated from the pore size distribution determined with MICP measurements. Using multivariate analysis, it was determined that the LIBS data can predict with good accuracy the longitudinal (R2 ∼ 0.84) and transverse (R2 ∼ 0.79) surface relaxivity. Analysis of the regression coefficients shows significant influence from several elements. Some of these are elements previously established to have an effect on surface relaxivity, such as iron and manganese, while others are not commonly associated with surface relaxivity, such as cobalt and titanium. Furthermore, LIBS provides advantages compared to current methods to calibrate surface relaxivity in terms of speed, portability, and sample size requirements. While this paper focuses on geological samples, the method could potentially be expanded to other types of porous materials.

  17. Evaluation of sandstone surface relaxivity using laser-induced breakdown spectroscopy.

    PubMed

    Washburn, Kathryn E; Sandor, Magdalena; Cheng, Yuesheng

    2017-02-01

    Nuclear magnetic resonance (NMR) relaxometry is a common technique used to assess the pore size of fluid-filled porous materials in a wide variety of fields. However, the NMR signal itself only provides a relative distribution of pore size. To calculate an absolute pore size distribution from the NMR data, the material's surface relaxivity needs to be known. Here, a method is presented using laser-induced breakdown spectroscopy (LIBS) to evaluate surface relaxivity in sandstones. NMR transverse and longitudinal relaxation was measured on a set of sandstone samples and the surface relaxivity was calculated from the pore size distribution determined with MICP measurements. Using multivariate analysis, it was determined that the LIBS data can predict with good accuracy the longitudinal (R(2)∼0.84) and transverse (R(2)∼0.79) surface relaxivity. Analysis of the regression coefficients shows significant influence from several elements. Some of these are elements previously established to have an effect on surface relaxivity, such as iron and manganese, while others are not commonly associated with surface relaxivity, such as cobalt and titanium. Furthermore, LIBS provides advantages compared to current methods to calibrate surface relaxivity in terms of speed, portability, and sample size requirements. While this paper focuses on geological samples, the method could potentially be expanded to other types of porous materials.

  18. Spatial and temporal distribution of cyanobacterial soil crusts in the Kalahari: Implications for soil surface properties

    NASA Astrophysics Data System (ADS)

    Thomas, A. D.; Dougill, A. J.

    2007-03-01

    Localised patterns of erosion and deposition in vegetated semi-arid rangelands have been shown to influence ecological change and biogeochemical cycles. In the flat, vegetated Kalahari rangelands of Southern Africa the factors regulating erodibility of the fine sand soils and the erosivity of wind regimes require further investigation. This paper reports on the spatial and temporal patterns of cyanobacterial soil crust cover from ten sites at five sampling locations in the semi-arid Kalahari and discusses the likely impact on factors regulating surface erodibility and erosivity. Cyanobacterial soil crust cover on Kalahari Sand varied between 11% and 95% of the ground surface and was higher than previously reported. Cover was inversely related to grazing with the lowest crust cover found close to boreholes and the highest in the Game Reserve and Wildlife Management Zone. In grazed areas, crusts form under the protective canopies of the thorny shrub Acacia mellifera. Fenced plot data showed that crusts recover quickly from disturbance, with a near complete surface crust cover forming within 15 months of disturbance. Crust development is restricted by burial by wind blown sediment and by raindrop impact. Crusts had significantly greater organic matter and total nitrogen compared to unconsolidated surfaces. Crusts also significantly increased the compressive strength of the surface (and thus decreased erodibility) and changed the surface roughness. Establishing exactly how these changes affect aeolian erosion requires further process-based studies. The proportion of shear velocity acting on the surface in this complex mixed bush-grass-crust environment will be the key to understanding how crusts affect erodibility.

  19. Soil surface disturbances in cold deserts: Effects on nitrogenase activity in cyanobacterial-lichen soil crusts

    USGS Publications Warehouse

    Belnap, Jayne

    1996-01-01

    CyanobacteriaMichen soil crusts can be a dominant source of nitrogen for cold-desert ecosystems. Effects of surface disturbance from footprints, bike and vehicle tracks on the nitrogenase activity in these crusts was investigated. Surface disturbances reduced nitrogenase activity by 30-100%. Crusts dominated by the cyanobacterium Microcoleus vaginatus on sandy soils were the most susceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichen Collema tenax was present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of nitrogenase activity reduction were affected by the degree of soil disruption and whether sites were dominated by cyanobacteria with or without heterocysts. Consequently, anthropogenic surface disturbances may have serious implications for nitrogen budgets in these ecosystems.

  20. Dynamical instability in surface permeability characteristics of building sandstones in response to salt accumulation over time

    NASA Astrophysics Data System (ADS)

    McCabe, S.; McKinley, J. M.; Gomez-Heras, M.; Smith, B. J.

    2011-07-01

    This paper explores how the surface permeability of sandstone blocks changes over time in response to repeated salt weathering cycles. Surface permeability controls the amount of moisture and dissolved salt that can penetrate in and facilitate decay. Connected pores permit the movement of moisture (and hence soluble salts) into the stone interior, and where areas are more or less permeable soluble salts may migrate along preferred pathways at differential rates. Previous research has shown that salts can accumulate in the near-surface zone and lead to partial pore blocking which influences subsequent moisture ingress and causes rapid salt accumulation in the near-surface zone. Two parallel salt weathering simulations were carried out on blocks of Peakmoor Sandstone of different volumes. Blocks were removed from simulations after 2, 5, 10, 20 and 60 cycles. Permeability measurements were taken for these blocks at a resolution of 20 mm, providing a grid of 100 permeability values for each surface. The geostatistical technique of ordinary kriging was applied to the data to produce a smoothed interpolation of permeability for these surfaces, and hence improve understanding of the evolution of permeability over time in response to repeated salt weathering cycles. Results illustrate the different responses of the sandstone blocks of different volumes to repeated salt weathering cycles. In both cases, after an initial subtle decline in the permeability (reflecting pore blocking), the permeability starts to increase — reflected in a rise in mean, maximum and minimum values. However, between 10 and 20 cycles, there is a jump in the mean and range permeability of the group A block surfaces coinciding with the onset of meaningful debris release. After 60 cycles, the range of permeability in the group A block surface had increased markedly, suggesting the development of a secondary permeability. The concept of dynamic instability and divergent behaviour is applied at the

  1. Scaling of sub-surface deformation in hypervelocity impact experiments on porous sandstone

    NASA Astrophysics Data System (ADS)

    Buhl, Elmar; Poelchau, Michael; Dresen, Georg; Kenkmann, Thomas

    2014-11-01

    Two hypervelocity impact experiments into dry sandstone (Seeberger Sandstein, ~ 23% porosity), performed under similar impact conditions but with different projectile sizes, have been analyzed to investigate the size scaling of impact damage. For one experiment a 2.5 mm steel projectile was impacted at 4.8 km s- 1 onto a sandstone cube of 20 cm side length. For the other experiment a 10 mm iron meteorite projectile was impacted at 4.6 km s- 1 onto a sandstone cube of 50 cm side length. The resulting kinetic impact energies of 773 and 42,627 J led to crater cavities of 7600 and 612,000 mm3. Investigation of thin sections along cross-sections through both craters revealed that the same deformation microstructures are present in both experiments. The occurrence of different microstructural patterns was mapped and zones of characteristic deformation were defined. This mapping was used to calculate the volumes of material deformed by specific mechanisms. Comparing the results, normalized to the size of the projectile, showed that the sub-surface damage is very similar in size, volume and geometry for both experiments. Analysis of deformation bands found in both experiments regarding their long axes orientation showed that these features are developed under shear deformation. Particle size distributions (PSD), expressed as power-law fits, were measured to quantify the impact damage. Comparison showed that the decay of the power-law exponents with increasing distance from the impact point source is similar for both experiments. Reconstruction of the loading path allowed to infer the stresses under which distinct deformation microstructures are developed.

  2. Flow of deep crust in orogens, associated surface dynamics, and the stabilization of continents

    NASA Astrophysics Data System (ADS)

    Teyssier, C. P.; Whitney, D. L.; Mulch, A.; Rey, P. F.

    2013-12-01

    Mountain building throws continental crust into an unstable state; subsequent stabilization of continental crust takes various forms, but flow of low-viscosity crust is the most common. Some of this low-viscosity crust remains at depth- it is the crust we see in the deep portions of Archean and Proterozoic cratons, typically granulite-migmatite terrains that have recorded ~10 kbar pressure, 600-800°C temperature, and intense deformation dominated by subhorizontal fabrics. In some places though, this deep crust reached the surface during the orogenic cycle. This is the case in the North American Cordillera where the deep crust leaked toward the surface and formed a series of metamorphic complexes that are cored by migmatite domes. Within the domes, complex structural overprints and decompression metamorphic paths indicate large-magnitude horizontal and vertical flow of partially molten crust relative to mantling rocks. No matter how the crust reached partial melting (thermal relaxation and/or heating) during continental under-thrusting, crustal thickening, lithosphere foundering, slab break-off, or slab window, the end result is one of an orogenic crust that contains a low viscosity layer at depth. This layer is mobile and opportunistic: it flows laterally and therefore helps keep a flat Moho; it may flow from a thick plateau and thicken the foreland region (mechanism of plateau growth); it fills gaps that open in the upper crust and therefore enhances orogenic collapse by transferring material from deep to shallow levels; ultimately, flow of this layer stabilizes the crust and may bring the end of orogeny. Thermal and mechanical numerical modeling can help evaluate quantitatively the relative importance of crust thickness, geothermal gradients, and tectonic boundary conditions in the evolution of orogenic systems. In the simple case of steady extension of a layered crust, results show that upper-crust extension is dynamically linked to lower crustal flow until

  3. Naturally weathered feldspar surfaces in the Navajo Sandstone aquifer, Black Mesa, Arizona: Electron microscopic characterization

    USGS Publications Warehouse

    Zhu, Chen; Veblen, D.R.; Blum, A.E.; Chipera, S.J.

    2006-01-01

    Naturally weathered feldspar surfaces in the Jurassic Navajo Sandstone at Black Mesa, Arizona, was characterized with high-resolution transmission and analytical electron microscope (HRTEM-AEM) and field emission gun scanning electron microscope (FEG-SEM). Here, we report the first HRTEM observation of a 10-nm thick amorphous layer on naturally weathered K-feldspar in currently slightly alkaline groundwater. The amorphous layer is probably deficient in K and enriched in Si. In addition to the amorphous layer, the feldspar surfaces are also partially coated with tightly adhered kaolin platelets. Outside of the kaolin coatings, feldspar grains are covered with a continuous 3-5 ??m thick layer of authigenic smectite, which also coats quartz and other sediment grains. Authigenic K-feldspar overgrowth and etch pits were also found on feldspar grains. These characteristics of the aged feldspar surfaces accentuate the differences in reactivity between the freshly ground feldspar powders used in laboratory experiments and feldspar grains in natural systems, and may partially contribute to the commonly observed apparent laboratory-field dissolution rate discrepancy. At Black Mesa, feldspars in the Navajo Sandstone are dissolving at ???105 times slower than laboratory rate at comparable temperature and pH under far from equilibrium condition. The tightly adhered kaolin platelets reduce the feldspar reactive surface area, and the authigenic K-feldspar overgrowth reduces the feldspar reactivity. However, the continuous smectite coating layer does not appear to constitute a diffusion barrier. The exact role of the amorphous layer on feldspar dissolution kinetics depends on the origin of the layer (leached layer versus re-precipitated silica), which is uncertain at present. However, the nanometer thin layer can be detected only with HRTEM, and thus our study raises the possibility of its wide occurrence in geological systems. Rate laws and proposed mechanisms should consider the

  4. Naturally weathered feldspar surfaces in the Navajo Sandstone aquifer, Black Mesa, Arizona: Electron microscopic characterization

    NASA Astrophysics Data System (ADS)

    Zhu, Chen; Veblen, David R.; Blum, Alex E.; Chipera, Stephen J.

    2006-09-01

    Naturally weathered feldspar surfaces in the Jurassic Navajo Sandstone at Black Mesa, Arizona, was characterized with high-resolution transmission and analytical electron microscope (HRTEM-AEM) and field emission gun scanning electron microscope (FEG-SEM). Here, we report the first HRTEM observation of a 10-nm thick amorphous layer on naturally weathered K-feldspar in currently slightly alkaline groundwater. The amorphous layer is probably deficient in K and enriched in Si. In addition to the amorphous layer, the feldspar surfaces are also partially coated with tightly adhered kaolin platelets. Outside of the kaolin coatings, feldspar grains are covered with a continuous 3-5 μm thick layer of authigenic smectite, which also coats quartz and other sediment grains. Authigenic K-feldspar overgrowth and etch pits were also found on feldspar grains. These characteristics of the aged feldspar surfaces accentuate the differences in reactivity between the freshly ground feldspar powders used in laboratory experiments and feldspar grains in natural systems, and may partially contribute to the commonly observed apparent laboratory-field dissolution rate discrepancy. At Black Mesa, feldspars in the Navajo Sandstone are dissolving at ˜10 5 times slower than laboratory rate at comparable temperature and pH under far from equilibrium condition. The tightly adhered kaolin platelets reduce the feldspar reactive surface area, and the authigenic K-feldspar overgrowth reduces the feldspar reactivity. However, the continuous smectite coating layer does not appear to constitute a diffusion barrier. The exact role of the amorphous layer on feldspar dissolution kinetics depends on the origin of the layer (leached layer versus re-precipitated silica), which is uncertain at present. However, the nanometer thin layer can be detected only with HRTEM, and thus our study raises the possibility of its wide occurrence in geological systems. Rate laws and proposed mechanisms should consider the

  5. Structural analysis of the fracture surface of a heterogeneous body (quartz sandstone)

    NASA Astrophysics Data System (ADS)

    Vettegren', V. I.; Mamalimov, R. I.; Kulik, V. B.; Patonin, A. V.; Ponomarev, A. V.; Sobolev, G. A.; Shcherbakov, I. P.

    2017-07-01

    The structure of surface layers of quartz sandstone with a thickness of 1 μm before and after destruction by a compressive stress is studied by methods of infrared, photoluminescent, and Raman spectroscopy. Before destruction, this layer contained quartz grains cemented with montmorrillonite and kaolinite. The grains are covered with a thin water layer and have crystallographic defects: Si-O-, self-trapped excitons, AlOH and LiOH compounds, [AlO4]- centers, etc. The destructed surface contains separate quartz grains with sizes of 2 μm and a reduced defect concentration. It is assumed that the defects reduce the strength of quartz grains, which are destroyed in the first turn.

  6. The origin of summertime crust and surface hoar formation at the WAIS Divide site, West Antarctica

    NASA Astrophysics Data System (ADS)

    Fegyveresi, J. M.; Alley, R. B.; Spencer, M. K.

    2013-12-01

    Summertime field observations at the WAIS Divide site, West Antarctica, indicate a very active surface. Over five consecutive seasons (2008-2013), daily surface measurements were made along with photography of the surface and of back-lit snowpits, where densities were measured. The Automatic Weather Station in the University of Wisconsin network was supplemented by various independent sensors deployed on site, including pyranometer sensor arrays and net-radiometers in order to better quantify the short-wave and long-wave radiation conditions surrounding near-surface metamorphism. Prominent 'glazed' crusts occur frequently. Surface and pit observations show that such crusts form in summertime during relative low-wind, low-humidity, high-temperature episodes that immediately follow a succession of strong wind events. During each documented case of formation, these episodes were also brought about during clear-sky days with maximum diurnal variability of incoming solar energy. Shallow firn temperature measurements indicate strong inversions during crust formation that likely lead to increased vapor transport. Furthermore, distinct hoar frost growth was observed on crusts that were exposed to multiple clear-sky days, likely as a result of increased insolation, humidity, and vertical vapor transport in the near-surface. There was no obvious indication of melt associated with glazed features during initial inspection. Examination of the WDC06A ice core and its associated ECM record indicates that numerous crusts are present very regularly throughout the core and in all seasons. Crusts are about 40% more abundant in summertime than in wintertime deposits, likely due to the formation of 'glazed' surfaces; formation mechanisms of the less-common wintertime crusts have not been observed and are not known. Over the ice-core record, there is little change in frequency of occurrence of wintertime crusts, but some changes in summertime, perhaps indicating changes in occurrence

  7. Microscopic surface wettability electrochemical characterization of tight sandstone with infrared spectra testing

    NASA Astrophysics Data System (ADS)

    Song, L.; Ning, Z. F.; Li, N.; Zhang, B.; Ding, G. Y.

    2017-08-01

    The distribution of charge density on the surface of microscopic tight oil is studied by using Stern double electric layer theory, and the mathematical flow model of polar fluid with micro powers in tight oil reservoir is established. The Fourier transform infrared (FTIR) were used to investigate the interaction of rock surface functional groups with fluids. The results show that: (1) When the external fluid of the polar group passes through the dense micro-nano pore, it will form an electric double layer on the surface of the rock, there will be a certain thickness of the liquid membrane, the fluid migration has a certain Of the electrical viscosity effect, will have a certain flow resistance. (2) The Fourier transform infrared spectroscopy of the Chang 7 tight reservoir rock samples exists and distributes different kinds of peaks. The left peak trend determines the presence of hydroxyl groups. The four fronts and types of the right side can be used to obtain that calcium carbonate CO3 2- exists. (3) There are CO3 2- and hydroxyl functional minerals in the Chang 7 tight sandstone samples. It is consistent with the basic mineral analysis measured by X-ray diffraction. When the external fluid affects the rock surface, the surface will occur in the physical van der Waals force and chemical bond interaction, so it will affect the flow of water on the surface.

  8. Surface tension of the core-crust interface of neutron stars with global charge neutrality

    NASA Astrophysics Data System (ADS)

    Rueda, Jorge A.; Ruffini, Remo; Wu, Yuan-Bin; Xue, She-Sheng

    2014-03-01

    It has been shown recently that taking into account strong, weak, electromagnetic, and gravitational interactions, and fulfilling the global charge neutrality of the system, a transition layer will happen between the core and crust of neutron stars, at the nuclear saturation density. We use relativistic mean field theory together with the Thomas-Fermi approximation to study the detailed structure of this transition layer and calculate its surface and Coulomb energy. We find that the surface tension is proportional to a power-law function of the baryon number density in the core bulk region. We also analyze the influence of the electron component and the gravitational field on the structure of the transition layer and the value of the surface tension, to compare and contrast with known phenomenological results in nuclear physics. Based on the above results we study the instability against Bohr-Wheeler surface deformations in the case of neutron stars obeying global charge neutrality. Assuming the core-crust transition at nuclear density ρcore≈2.7×1014 g cm-3, we find that the instability sets the upper limit to the crust density, ρcrustcrit≈1.2×1014 g cm-3. This result implies a nonzero lower limit to the maximum electric field of the core-crust transition surface and makes inaccessible a limit of quasilocal charge neutrality in the limit ρcrust=ρcore. The general framework presented here can be also applied to study the stability of sharp phase transitions in hybrid stars as well as in strange stars, both bare and with outer crust. The results of this work open the way to a more general analysis of the stability of these transition surfaces, accounting for other effects such as gravitational binding, centrifugal repulsion, magnetic field induced by rotating electric field, and therefore magnetic dipole-dipole interactions.

  9. Hydrology of the Ferron Sandstone aquifer and effects of proposed surface-coal mining in Castle Valley, Utah

    SciTech Connect

    Lines, G.C.

    1983-01-01

    The availability and quality of groundwater in the coal-bearing Ferron Sandstone, Utah, are evaluated. The report contains structure-contour, thickness and potentiometric-surface maps for the aquifer. Possible hydrologic effects of a proposed surface mine in the Energy Coalfield are also evaluated by use of a 3-dimensional digital-computer model of the aquifer and laboratory experiments that simulated leaching of overburden at the mine.

  10. Intertongued Dakota sandstone-Mancos shale members of surface and subsurface in San Juan basin, New Mexico and Colorado: eustatic, tectonic, and sedimentologic effects on depositional systems

    SciTech Connect

    Owen, D.E.; Walters, L.J. Jr.; Sparks, D.K.

    1988-02-01

    Three wedges of transgressive marine Mancos Shale, deposited off-shore, intertongue with four Dakota Sandstone units, largely shoreface deposits. Contacts between shoreface and offshore lithologies trend approximately north-south, with nonmarine Dakota main body sandstones to the west. Submarine bar sandstones trending northwest-southeast are locally developed near the shoreface-offshore transition. This succession was deposited during approximately 4 m.y. of the transgressive phase of the Greenhorn cyclothem. Each Dakota-Mancos sandstone-shale pair may represent (1) a fourth-order eustatic cycle or (2) regional tectonic and local sedimentologic overprints of two third-order Vail cycles. Detailed analyses of trace elements within shales and primary sedimentary structures and trace fossils of sandstones, combined with geophysical logs and regional paleontologic control, were invaluable in this first, basin-wide, surface and subsurface paleoenvironmental study of these complex strata. Dakota main body and basal fluvial sandstones were deposited by easterly flowing, meandering stream system. Overlying sets of extensively burrowed shoreface sandstones were deposited under prevailing southerly paleocurrents. The uppermost Dakota tongue (Twowells Sandstone) illustrates a dominant, but complex, regressive character and a seaward pinch-out, as well as a thin, upper transgressive phase in nearshore locations. Significant petroleum accumulations are contained in this sandstone.

  11. The role of moisture on controlling dust emissions from crusted supply-limited surfaces

    NASA Astrophysics Data System (ADS)

    King, James; Wiggs, Giles F. S.; Thomas, David S. G.; Washington, Richard

    2013-04-01

    Dust emissions from crusted surfaces are both highly variable and difficult to measure directly. Seasonal changes in surface soil moisture, temperature, evaporation, surface roughness, and sediment supply result in a highly complex surface condition that remains to be fully described in the context of wind erosion potential. A highly intensive project on Makgadikgadi Pan, Botswana using the PI-SWERL (portable wind tunnel) combined with surface measurements of crust and soil properties has led to a new understanding of the time sensitive controls on wind erosion from these surfaces. The PI-SWERL is a highly portable wind tunnel that applies a shear stress to the surface using a motor-controlled rotating annular blade and measures resulting dust emissions with a PM10 monitor (DustTrak TSI Inc.). We undertook a sequence of tests with the PI-SWERL to obtain both the wind erosion threshold (using a slowly increasing shear velocity) and a dust emission flux (using a constant shear velocity) across a 12 km by 12 km grid across the pan surface. A total of just over 1500 wind tunnel tests and 3000 correlated measurements of a variety of surface properties including crust thickness, surface and subsurface soil moisture, shearing strength (shear vane), normal stress resistance (penetrometer), and surface roughness were conducted in August 2011 and August through October 2012. Two sets of results are presented providing discussion on: 1) Spatial variations in surface characteristics 2) Temporal variation in the control of surface characteristics and climatic conditions on potential dust emissions. These results show that wind erosion potential is best described by measurements of normal stress resistance rather than shearing strength at low dust emission fluxes, but despite their frequent use in wind erosion studies of crusted surfaces neither metric provided a good explanation of higher dust emission fluxes. Surface soil moisture explained the most variation in both dust

  12. Stabilization of Desert Surfaces and Accumulation of Dust Under Biological Soil Crusts

    NASA Astrophysics Data System (ADS)

    Finstad, K. M.; Mcnicol, G.; Pfeiffer, M.; Amundson, R.

    2014-12-01

    Biological soil crusts (BSC) are known to play a critical role in the stabilization of desert surfaces by helping to protect sediment from wind and water erosion and aiding in the trapping of airborne particles. The crusts are often composed of cyanobacteria, algae, and fungi, and occupy the upper few cm of a soil. Due to their high tolerance of desiccation and ability to utilize fog and dew sources, BSC are able to exist in environments that may otherwise be too dry for vascular plants. In the hyperarid Atacama Desert, decades or more between measurable precipitation events has created a landscape devoid of macroscopic life. While precipitation is rare, coastal fog occurs regularly and microbial communities capable of utilizing fog and dew water are able to persist. Here we found cyanobacteria and lichen living in association with a thin sulfate and dust crust (~2 cm) covering the surface of 'dust plateaus'. Topographically the region is highly irregular and part of a largely erosional landscape. We hypothesized that these flat-topped plateaus are accretionary features that have been able to maintain dust accumulation for thousands of years as a result of the surface crusts. To test this hypothesis we conducted radiocarbon analysis of crusts and soil profiles at two sites approximately 30 km apart, one in a high fog zone and another in lower fog frequency zone. The radiocarbon analysis shows that sediment has been accumulating in the 'plateaus' for the past 15,000 years and that biological activity and rates of C cycling in the crust increase with increasing fog frequency and intensity. The ages of organic material in the dust decrease monotonically with decreasing soil thickness, suggestive of progressive upward growth by dust accumulation. Our data indicate that the BSC are capable of surviving in hyperarid the Atacama Desert, a Mars analogue, through the utilization of fog water, and that their presence can leave a visible geomorphic imprint on the landscape.

  13. Dust emissions from undisturbed and disturbed, crusted playa surfaces: cattle trampling effects

    USDA-ARS?s Scientific Manuscript database

    Dry playa lake beds can be significant sources of fine dust emission. This study used a portable field wind tunnel to quantify the PM10 emissions from a bare, fine-textured playa surface located in the far northern Chihuahua Desert. The natural, undisturbed crust and its subjection to two levels of ...

  14. Surface disturbance of cryptobiotic soil crusts: nitrogenase activity, chlorophyll content, and chlorophyll degradation

    USGS Publications Warehouse

    Belnap, Jayne; Harper, Kimball T.; Warren, Steven D.

    1994-01-01

    Cryptobiotic soil crusts are an important component of semiarid and arid ecosystems. An important role of these crusts is the contribution of fixed nitrogen to cold‐desert ecosystems. This study examines the residual effects of various intensities and combinations of different surface disturbances (raking, scalping, and tracked vehicles) on nitrogenase activity, chlorophyll content, and chlorophyll degradation in these soil crusts. Nine months after disturbance chlorophyll content of disturbed soils was not statistically different from undisturbed controls, except in the scalped treatments, indicating recovery of this characteristic is fairly quick unless surface material is removed. Differences in chlorophyll degradation among treatments were not statistically significant. However, nitrogenase activity in all treatments showed tremendous reductions, ranging from 77–97%, when compared to the control, indicating this characteristic is slow to recover. Consequently, assessment of crustal recovery from disturbance must include not only visual and biomass characteristics but other physiological measurements as well. Areas dominated by these crusts should be managed conservatively until the implications of crustal disturbance is better understood.

  15. Surface soil crust types, properties and their response to ameliorants in the irrigated field of Eastern Ethiopia

    NASA Astrophysics Data System (ADS)

    Kebede, F.; Mekonnen, E.; Taha, N.; Verdoodt, A.; Van Ranst, E.

    2012-04-01

    Soil crusting is a worldwide problem occurring under a wide range of soil and climatic conditions. Soil crusts affect seedling emergence and reduce the infiltration rate causing loss of water and crop yield. Field experiment was conducted in Kombolcha, East Harerge to identify soil crust types and soil ameliorants for crust management under basin and furrow irrigation conditions. The experiment was conducted on plots of 12 m2 (4 m x 3 m) and arranged in RCBD with three replicates. Eight treatment combinations were considered namely: the control (without amendment), FYM, chat residue (decayed leaves of Chata edulis) and sediment (sub surface inorganic material locally called 'decay dimma'). Additionally, field and laboratory methods were employed to study types of surface soil crust. The study revealed that still depositional crust and slaking structural crust types were found as major forms of soil crusts. They are formed from deposition of water suspension on to irrigated land and subsequent slaking of colloidal materials. Furthermore, plots amended with FYM and chat residues made compost were significantly (p < 0.05) improved their moisture content and infiltration rate over the sediment amended plots and the control. Results have also revealed that improvement of infiltration rate, bulk density, porosity and water holding capacity was attained over the compost amended plots. The study concludes that use of chat residue made compost, FYM and the locally known mineral sediment (dicay dimma) are reasonable resources for minimizing structural degradation. Keywords: Soil ameliorant, irrigation practices, organic compost, soil crust, water suspension, and

  16. Fusion Crust and the Measurement of Surface Ages of Antarctic Ordinary Chondrites

    NASA Technical Reports Server (NTRS)

    Akridge, Jannette M. C.; Benoit, Paul H.; Sears, Derek W. G.

    1997-01-01

    Natural thermoluminescence (TL) reflects radiation exposure and storage temperature. Meteorites generally exhibit thermoluminescence acquired during their long exposure to galactic cosmic rays in space. During atmospheric passage, temperatures are high enough to completely drain the TL, in the first mm of material under the fusion crust. We therefore refer to this surface layer as "fusion crust" although it does include some unmelted material just below the crust. When the meteorite lands on earth this drained layer will begin to build up natural TL once again due to radiation from cosmic rays and internal radionuclides. Cosmic ray annual dose is estimated to be between 0.04 and 0.06 rad/yr on the earth's surface in Antarctica while the internal radionuclides contribute only about 0.01 rad/yr. Therefore the total annual dose received by the meteorite while it is on the surface is between 0.05 and 0.07 rad/yr. If the meteorite is buried deeply in the ice it is effectively shielded from most cosmic rays and thus only internal radioactivity contributes to the annual dose.

  17. Fusion Crust and the Measurement of Surface Ages of Antarctic Ordinary Chondrites

    NASA Astrophysics Data System (ADS)

    Akridge, Jannette M. C.; Benoit, Paul H.; Sears, Derek W. G.

    1997-01-01

    Natural thermoluminescence (TL) reflects radiation exposure and storage temperature. Meteorites generally exhibit thermoluminescence acquired during their long exposure to galactic cosmic rays in space. During atmospheric passage, temperatures are high enough to completely drain the TL, in the first mm of material under the fusion crust. We therefore refer to this surface layer as "fusion crust" although it does include some unmelted material just below the crust. When the meteorite lands on earth this drained layer will begin to build up natural TL once again due to radiation from cosmic rays and internal radionuclides. Cosmic ray annual dose is estimated to be between 0.04 and 0.06 rad/yr on the earth's surface in Antarctica while the internal radionuclides contribute only about 0.01 rad/yr. Therefore the total annual dose received by the meteorite while it is on the surface is between 0.05 and 0.07 rad/yr. If the meteorite is buried deeply in the ice it is effectively shielded from most cosmic rays and thus only internal radioactivity contributes to the annual dose.

  18. Depth-Average Modeling Of Gravity-Driven Lava Flow With Surface Crust Development

    NASA Astrophysics Data System (ADS)

    Rempel, A. W.; Chen, J.

    2015-12-01

    Forecasts for the emplacement of lava and associated mitigation strategies rely upon the accurate portrayal of flow interactions with topographic features. Efficient and easily adaptable numerical treatments are needed that can predict flow paths and dominant behaviors to illuminate the underlying mechanisms without the obscuring influence of secondary effects. We implement depth-averaged finite element models in COMSOL that treat a given lava flow as a non-isothermal gravity current overlain by a growing surface crust. For model validation we use observations from analog experiments that use both isothermal and rapidly cooling fluids to simulate the interactions of lava flows with topographic obstacles. Under a broad range of relevant conditions, although the flow thickness is very small compared with its extent, the high Péclet number ensures that most of the flow depth remains nearly isothermal, with crust forming in a thermal boundary layer near the surface. This surface crust can exert a retarding force that limits flow extent and leads to thickening. The good agreement between model predictions and laboratory experiments provides confidence in the extensibility of our simulation strategy to ongoing efforts at examining additional flow processes, including flow stagnation and channelization.

  19. Deucalionis Regio, Mars: Evidence for a unique mineralogic endmember and a crusted surface

    NASA Technical Reports Server (NTRS)

    Merenyi, E.; Edgett, K. S.; Singer, R. B.

    1993-01-01

    A small equatorial region south of Sinus Meridiani, Deucalionis Regio, has been found spectrally distinct from other regions as seen in a high spectral resolution telescopic image of the meridian hemisphere of Mars. Analysis of Viking IRTM and other related data suggest that Deucalionis Regio has a crusted surface. The crust-bonding minerals may contribute to the spectral uniqueness of this region. Two independent analyses of spectral images, linear spectral mixing and supervised classification based on the spectral shapes, showed that in addition to the well-known spectral endmember regions in this image (western Arabia, south Acidalia, and Sinus Meridiani), Deucalionis Regio has spectral properties that are unique enough to make it a principle endmember unit. In those earlier works, Deucalionis Regio was referred to as 'Meridiani Border.' Analysis of thermal inertia, rock abundance, and albedo information derived from Viking images and Infrared Thermal Mapper (IRTM) data obtained 1977-80 also indicate that Deucalionis Regio has a surface of distinctly different physical properties when compared to Arabia, Sinus Meridiani, and Acidalia. Deucalionis Regio has a thermal inertia equivalent to the Martian average, a low rock abundance (less than 5 percent), and an intermediate albedo and color. Considerable effort by previous investigators has revealed a consistent model for the surface (upper few cm) properties of the endmember reigons Arabia, Sinus Meridiani, and Acidalia. Compared with these regions, we consider that Deucalionis Regio is not a region of either (1) unconsolidated, fine bright dust like Arabia, (2) considerable windblown unconsolidated sand like Sinus Meridiani, or (3) a rocky-and-sandy surface like Acidalia. Thus, we are forced to consider that either the surface of Deucalionis Regio is made of unconsolidated fine to medium sand (about 250 microns) of an unusual and previously unreported color and albedo, or that the surface is crusted, fine

  20. Surface wave dispersion across Tibet: Direct evidence for radial anisotropy in the crust

    NASA Astrophysics Data System (ADS)

    Duret, F.; Shapiro, N. M.; Cao, Z.; Levin, V. L.; Molnar, P. H.; Roecker, S.

    2010-12-01

    We analyze broadband records of May 12, 2008 Sichuan earthquake aftershocks from stations in western Tibet, to develop an average 1D shear-wave velocity model of the Tibetan crust. Previous study (Shapiro et al. (2004)) has revealed 10% to 20% radial anisotropy throughout the middle crust, suggesting that the Tibetan plateau has been deformed consistent with the notion of channel flow within the crust. However, this result was based on using a data set sampling large areas outside Tibet. In our study, we use records of selected strong aftershocks from May 12, 2008 Sichuan earthquake by seismic stations of an ongoing western Tibet PASSCAL experiment. This dataset samples exclusively the Tibetan plateau along an area extending ˜1500 km East-West, and ˜300 km North-South. We selected a set of 60 traces for Rayleigh waves and 53 traces for Love waves and applied the Frequency-Time Analysis to measure surface wave group velocities between 10 and 100 s, and combined them together to obtain average Rayleigh and Love wave group velocity dispersion curves, and their standard deviation. Rayleigh waves exhibit a clear Airy phase, with a marked minimum at ˜35 s, suggesting that the vertically polarized S-wave velocities in upper and middle crust are relatively low. Such minimum is not observed for Love waves, implying that horizontally polarized S-waves propagate faster than vertically polarized ones, and therefore suggesting that radial anisotropy characterizes the Tibetan plateau. We simultaneously inverted Rayleigh and Love wave dispersion curves using a Monte-Carlo method, to deduce an average 1D shear-wave velocity profile of the Tibetan crust and upper-mantle. When we did not introduce radial anisotropy, we found a relatively thick crust, with the Moho at ˜65 km, but were unable to fit both Rayleigh and Love wave dispersion curves within their error bars. Predicted Rayleigh waves were systematically faster than measured, and Love waves slower. To resolve this

  1. Modelling and interpreting biologically crusted dryland soil sub-surface structure using automated micropenetrometry

    NASA Astrophysics Data System (ADS)

    Hoon, Stephen R.; Felde, Vincent J. M. N. L.; Drahorad, Sylvie L.; Felix-Henningsen, Peter

    2015-04-01

    Soil penetrometers are used routinely to determine the shear strength of soils and deformable sediments both at the surface and throughout a depth profile in disciplines as diverse as soil science, agriculture, geoengineering and alpine avalanche-safety (e.g. Grunwald et al. 2001, Van Herwijnen et al. 2009). Generically, penetrometers comprise two principal components: An advancing probe, and a transducer; the latter to measure the pressure or force required to cause the probe to penetrate or advance through the soil or sediment. The force transducer employed to determine the pressure can range, for example, from a simple mechanical spring gauge to an automatically data-logged electronic transducer. Automated computer control of the penetrometer step size and probe advance rate enables precise measurements to be made down to a resolution of 10's of microns, (e.g. the automated electronic micropenetrometer (EMP) described by Drahorad 2012). Here we discuss the determination, modelling and interpretation of biologically crusted dryland soil sub-surface structures using automated micropenetrometry. We outline a model enabling the interpretation of depth dependent penetration resistance (PR) profiles and their spatial differentials using the model equations, σ {}(z) ={}σ c0{}+Σ 1n[σ n{}(z){}+anz + bnz2] and dσ /dz = Σ 1n[dσ n(z) /dz{} {}+{}Frn(z)] where σ c0 and σ n are the plastic deformation stresses for the surface and nth soil structure (e.g. soil crust, layer, horizon or void) respectively, and Frn(z)dz is the frictional work done per unit volume by sliding the penetrometer rod an incremental distance, dz, through the nth layer. Both σ n(z) and Frn(z) are related to soil structure. They determine the form of σ {}(z){} measured by the EMP transducer. The model enables pores (regions of zero deformation stress) to be distinguished from changes in layer structure or probe friction. We have applied this method to both artificial calibration soils in the

  2. Dust Emissions from Undisturbed and Disturbed, Crusted Playa Surfaces: Cattle Trampling Effect

    NASA Astrophysics Data System (ADS)

    Zobeck, T. M.; Baddock, M. C.; van Pelt, R.; Fredrickson, E. L.

    2009-12-01

    Dry playa lake beds can be a significant source of fine dust emissions during high wind events in arid and semiarid landscapes. The physical and chemical properties of the playa surface control the amount and properties of the dust emitted. In this study, we use a field wind tunnel to quantify the dust emissions from a bare, fine-textured playa surface located in the Chihuahua Desert at the Jornada Experimental Range, near Las Cruces, New Mexico, USA. We tested natural, undisturbed crusted surfaces and surfaces that had been subjected to two levels of domestic animal disturbance. The animal disturbance was provided by trampling produced from one and ten passes along the length of the wind tunnel by a 630 kg Angus-Hereford cross cow. The trampling broke the durable crust and created loose erodible material. Each treatment (natural crust, one pass, and ten passes) was replicated three times. A push-type wind tunnel with a 6 m long, 0.5 m wide, and 1 m high test section was used to generate dust emissions under controlled conditions. Clean medium sand was dropped onto the playa surface to act as an abrader material. The tunnel wind speed was equivalent to 15 m/s at a height of 2 m over a smooth soil surface. The tunnel was initially run for ten minutes, with no abrader added. A second 30 minute run was subsequently sampled as abrader was added to the wind stream. Dust and saltating material were collected using an isokinetic slot sampler at the end of the tunnel. Total airborne dust was collected on two 25 cm x 20 cm glass fiber filters (GFF) and measured using a GRIMM particle monitor every 6 sec throughout each test run. Disturbance by trampling generated increased saltating material and airborne dust. The amount of saltating material measured during the initial (no abrader added) run was approximately 70% greater and 5.8 times the amount of saltating material measured on the one pass and ten pass plots, respectively, compared with that observed on the undisturbed

  3. Visually assessing the level of development and soil surface stability of cyanobacterially dominated biological soil crusts

    USGS Publications Warehouse

    Belnap, J.; Phillips, S.L.; Witwicki, D.L.; Miller, M.E.

    2008-01-01

    Biological soil crusts (BSCs) are an integral part of dryland ecosystems and often included in long-term ecological monitoring programs. Estimating moss and lichen cover is fairly easy and non-destructive, but documenting cyanobacterial level of development (LOD) is more difficult. It requires sample collection for laboratory analysis, which causes soil surface disturbance. Assessing soil surface stability also requires surface disturbance. Here we present a visual technique to assess cyanobacterial LOD and soil surface stability. We define six development levels of cyanobacterially dominated soils based on soil surface darkness. We sampled chlorophyll a concentrations (the most common way of assessing cyanobacterial biomass), exopolysaccharide concentrations, and soil surface aggregate stability from representative areas of each LOD class. We found that, in the laboratory and field, LOD classes were effective at predicting chlorophyll a soil concentrations (R2=68-81%), exopolysaccharide concentrations (R2=71%), and soil aggregate stability (R2=77%). We took representative photos of these classes to construct a field guide. We then tested the ability of field crews to distinguish these classes and found this technique was highly repeatable among observers. We also discuss how to adjust this index for the different types of BSCs found in various dryland regions.

  4. A Close View Into the 3D Geometry of Grain-to-Grain Contacts and Surface Roughness in Sandstones Using Laser Scanning Confocal Microscopy

    NASA Astrophysics Data System (ADS)

    Menendez, B.; David, C.; Louis, L.; Martinez Nistal, A.

    2003-12-01

    Due to its sharp resolution (< 1 micron) and its ability in building 3D reconstructions from images scanned at various depths, laser scanning confocal microscopy (LSCM) is a powerful tool to render the three-dimensional geometry of microstructural features like pores, cracks and grains. This technique was used in particular to study the grain-to-grain contacts and grain surface topology at small scale in several sandstones. For that purpose, the rock samples to be studied were impregnated with a fluorescent dyed (Rhodamine B) resin in order to discriminate the void space from the grains. The next stage is then to make thin-sections with a thickness larger than usual (> 100 microns) that can be studied under LSCM. Three different sandstones have been studied: the Rothbach sandstone (Vosges mountains, Eastern France), the Bentheim sandstone (Germany) and the Darley Dale sandstone (UK). On each sample several three dimensional blocks have been investigated with size 228 by 152 microns and depths ranging from 35 to 100 microns. From each block, series of tens of parallel "virtual sections" have been recorded, separated by 1 or 2 microns in depth. We show on several examples the complex structure of grain-to-grain contacts which may be associated to the heterogeneity in cement distribution. In particular for the Rothbach sandstone, we found that the topology of the grain surfaces is dominated by the coating of clay particles which leads to a high surface roughness. Complementary SEM studies revealed that the clays are also present as cementing material between the grains. A thorough petrophysical study has shown that the anisotropy of P wave velocity in the Rothbach sandstone can be explained by an anisotropic distribution of cement: whereas this could not be confirmed from our LSCM and SEM analysis, we observed that the spatial distribution of contact lengths is anisotropic which explains qualitatively the spatial variability of P wave velocity. Finally we show

  5. A seismic reference model for the crust and uppermost mantle beneath China from surface wave dispersion

    NASA Astrophysics Data System (ADS)

    Shen, Weisen; Ritzwoller, Michael H.; Kang, Dou; Kim, YoungHee; Lin, Fan-Chi; Ning, Jieyuan; Wang, Weitao; Zheng, Yong; Zhou, Longquan

    2016-08-01

    Using data from more than 2000 seismic stations from multiple networks arrayed throughout China (CEArray, China Array, NECESS, PASSCAL, GSN) and surrounding regions (Korean Seismic Network, F-Net, KNET), we perform ambient noise Rayleigh wave tomography across the entire region and earthquake tomography across parts of South China and Northeast China. We produce isotropic Rayleigh wave group and phase speed maps with uncertainty estimates from 8 to 50 s period across the entire region of study, and extend them to 70 s period where earthquake tomography is performed. Maps of azimuthal anisotropy are estimated simultaneously to minimize anisotropic bias in the isotropic maps, but are not discussed here. The 3D model is produced using a Bayesian Monte Carlo formalism covering all of China, extending eastwards through the Korean Peninsula, into the marginal seas, to Japan. We define the final model as the mean and standard deviation of the posterior distribution at each location on a 0.5° × 0.5° grid from the surface to 150 km depth. Surface wave dispersion data do not strongly constrain internal interfaces, but shear wave speeds between the discontinuities in the crystalline crust and uppermost mantle are well determined. We design the resulting model as a reference model, which is intended to be useful to other researchers as a starting model, to predict seismic wave fields and observables and to predict other types of data (e.g. topography, gravity). The model and the data on which it is based are available for download. In addition, the model displays a great variety and considerable richness of geological and tectonic features in the crust and in the uppermost mantle deserving of further focus and continued interpretation.

  6. Response of Surface Soil Hydrology to the Micro-Pattern of Bio-Crust in a Dry-Land Loess Environment, China.

    PubMed

    Wei, Wei; Yu, Yun; Chen, Liding

    2015-01-01

    The specific bio-species and their spatial patterns play crucial roles in regulating eco-hydrologic process, which is significant for large-scale habitat promotion and vegetation restoration in many dry-land ecosystems. Such effects, however, are not yet fully studied. In this study, 12 micro-plots, each with size of 0.5 m in depth and 1 m in length, were constructed on a gentle grassy hill-slope with a mean gradient of 8° in a semiarid loess hilly area of China. Two major bio-crusts, including mosses and lichens, had been cultivated for two years prior to the field simulation experiments, while physical crusts and non-crusted bare soils were used for comparison. By using rainfall simulation method, four designed micro-patterns (i.e., upper bio-crust and lower bare soil, scattered bio-crust, upper bare soil and lower bio-crust, fully-covered bio-crust) to the soil hydrological response were analyzed. We found that soil surface bio-crusts were more efficient in improving soil structure, water holding capacity and runoff retention particularly at surface 10 cm layers, compared with physical soil crusts and non-crusted bare soils. We re-confirmed that mosses functioned better than lichens, partly due to their higher successional stage and deeper biomass accumulation. Physical crusts were least efficient in water conservation and erosion control, followed by non-crusted bare soils. More importantly, there were marked differences in the efficiency of the different spatial arrangements of bio-crusts in controlling runoff and sediment generation. Fully-covered bio-crust pattern provides the best option for soil loss reduction and runoff retention, while a combination of upper bio-crust and lower bare soil pattern is the least one. These findings are suggested to be significant for surface-cover protection, rainwater infiltration, runoff retention, and erosion control in water-restricted and degraded natural slopes.

  7. Quantifying Modern Recharge to the Nubian Sandstone Aquifer System: Inferences from GRACE and Land Surface Models

    NASA Astrophysics Data System (ADS)

    Mohamed, A.; Sultan, M.; Ahmed, M.; Yan, E.

    2014-12-01

    The Nubian Sandstone Aquifer System (NSAS) is shared by Egypt, Libya, Chad and Sudanand is one of the largest (area: ~ 2 × 106 km2) groundwater systems in the world. Despite its importance to the population of these countries, major hydrological parameters such as modern recharge and extraction rates remain poorly investigated given: (1) the large extent of the NSAS, (2) the absence of comprehensive monitoring networks, (3) the general inaccessibility of many of the NSAS regions, (4) difficulties in collecting background information, largely included in unpublished governmental reports, and (5) limited local funding to support the construction of monitoring networks and/or collection of field and background datasets. Data from monthly Gravity Recovery and Climate Experiment (GRACE) gravity solutions were processed (Gaussian smoothed: 100 km; rescaled) and used to quantify the modern recharge to the NSAS during the period from January 2003 to December 2012. To isolate the groundwater component in GRACE data, the soil moisture and river channel storages were removed using the outputs from the most recent Community Land Model version 4.5 (CLM4.5). GRACE-derived recharge calculations were performed over the southern NSAS outcrops (area: 835 × 103 km2) in Sudan and Chad that receive average annual precipitation of 65 km3 (77.5 mm). GRACE-derived recharge rates were estimated at 2.79 ± 0.98 km3/yr (3.34 ± 1.17 mm/yr). If we take into account the total annual extraction rates (~ 0.4 km3; CEDARE, 2002) from Chad and Sudan the average annual recharge rate for the NSAS could reach up to ~ 3.20 ± 1.18 km3/yr (3.84 ± 1.42 mm/yr). Our recharge rates estimates are similar to those calculated using (1) groundwater flow modelling in the Central Sudan Rift Basins (4-8 mm/yr; Abdalla, 2008), (2) WaterGAP global scale groundwater recharge model (< 5 mm/yr, Döll and Fiedler, 2008), and (3) chloride tracer in Sudan (3.05 mm/yr; Edmunds et al. 1988). Given the available global

  8. Development and hydrology of biological soil crusts -- first results from a surface inoculation experiment

    NASA Astrophysics Data System (ADS)

    Mykhailova, Larysa; Raab, Thomas; Gypser, Stella; Fischer, Thomas

    2016-04-01

    Representing a set of various micro-biocoenoses, biocrusts often reside in adjacent patches, which not necessarily relate to structural elements of the habitat, like (micro-) topography or vegetational patterns. Such biocrust patches may become more stable through the formation of mutually dependent ecohydrological regimes. For example, algal patches inhibiting infiltration and generating runoff alternate with runoff-receiving moss patches possessing high water holding capacities. Here, we preliminarily report on a lysimeter field experiment where natural biocrust isolates were used for surface inoculation to (I) prove stochastic vs. deterministic biocrust development and (II) to quantitatively relate biocrust development to soil hydrology. Lysimeter sand was collected from 3-4 m below surface at natural dune outcrops in south-eastern Brandenburg, Germany (Glashütte (GLA) and Neuer Lugteich (LUG)), where biocrust samples were collected at the respective dune bases. The lysimeters were designed to prevent runoff. In a completely randomized full-factorial design, three factors were considered. (A) Inocolum in three treatments (bare control, mosses, algae), (B) mineral substrate texture in two treatments (GLA: 55% and LUG: 79% particles >630 μm), and (C) surface compaction in two treatments (control, 41.5 kN m-2 for 30 seconds). The samples were kept dry and re-moistened to -60 hPa two days before inoculation. After a species inventory, the inoculate was isolated by gently washing off sand particles from the biocrust samples. Algal/lichen crusts were dominated by Zygogonium ericetorum and Cladonia sp. at both sites. All moss crusts were dominated by Polytrichum piliferum and Ceratodon purpureus, whereas Brachythecium albicans was present at GLA only. 20 g of homogenized moist inoculate were spread over the surface of each lysimeter (Ø 19 cm, 22 cm depth). We performed autochthonous inoculation, i.e. biocrust isolates collected from GLA were used for inoculation of

  9. [Surface roughness characteristics of biological soil crusts and its influencing factors in the hilly Loess Plateau region, China].

    PubMed

    Wang, Yuan; Zhao, Yun-Ge; Yao, Chun-Zhu; Zhang, Pei-Pei

    2014-03-01

    Soil surface roughness exerts profound influence on runoff and sediments yield from slopes. Biological soil crusts (BSCs) are ubiquitous living cover in the open spaces between plants in arid and semiarid ecosystems, which considerably impact the surface roughness. Aimed to determine the effect of biological crusts on the surface roughness and its influence factors, this study investigated the surface roughness of soil with BSCs at their different successional stages by using the chain method. Besides, the impacts of slope aspects, soil water content and freezing and thawing on surface roughness were also investigated. Then, the correlations between roughness and soil chemical and physical properties were evaluated. The results showed that soil surface roughness decreased at the initial successional stage of BSCs but increased along with BSCs' development in the region. Soil roughness tended to be stabile since BSCs developed ten years later. The roughness was reduced by 47.0% by the light cyanobacteria-dominated crust and 20.4% by the dark cyanobacteria-dominated crust (moss coverage < 20%), compared with the bare soil. Soil moisture significantly impacted surface roughness. The surface roughness of BSCs changed obviously with soil moisture in the early development, but only slightly in their later succession. Freezing-thawing also affected surface roughness with BSCs. Roughness was more susceptible to freezing-thawing in the early de- velopment of BSCs, with an increase of 29.7% compared with the bare soil. The surface roughness of late successional BSCs exhibited a slight change only after repeated freezing-thawing. The surface roughness of BSCs showed a statistically significant relationship with the coverage of moss (P < 0.1).

  10. Dust emissions from undisturbed and disturbed, crusted playa surfaces: Cattle trampling effects

    NASA Astrophysics Data System (ADS)

    Baddock, Matthew C.; Zobeck, Ted M.; Van Pelt, R. Scott; Fredrickson, Ed L.

    2011-06-01

    Dry playa lake beds can be significant sources of fine dust emission. This study used a portable field wind tunnel to quantify the PM 10 emissions from a bare, fine-textured playa surface located in the far northern Chihuahua Desert. The natural, undisturbed crust and its subjection to two levels of animal disturbance (one and ten cow passes) were tested. The wind tunnel generated dust emissions under controlled conditions for firstly an initial blow-off of the surface, followed by two longer runs with sand added to the flow as an abrader material. Dust was measured using a GRIMM particle monitor. For the study playa, no significant differences in PM 10 concentration and emission flux were found between the untrampled surface and following a single animal pass. This was the case for both the initial blow-offs and tests on plots under a steady abrader rate. Significantly higher dust loading was only associated with the effect of 10 animal passes. In the blow-offs, the higher PM 10 yield after 10 passes reflected the greater availability of easily entrainable fine particles. Under abrasion, the effect of the heaviest trampling increased the emission flux by a third and abrasion efficiency by around 50% more than values on the untrampled surface. This enhanced abrasion efficiency persisted for a 30 min period under abrasion before the positive effect of the disturbance was no longer evident. The findings highlight the role of a threshold of disturbance that determines if supply-limited surfaces will exhibit enhanced wind erosion or not after undergoing perturbation.

  11. Crusts: biological

    USGS Publications Warehouse

    Belnap, Jayne; Elias, Scott A.

    2013-01-01

    Biological soil crusts, a community of cyanobacteria, lichens, mosses, and fungi, are an essential part of dryland ecosystems. They are critical in the stabilization of soils, protecting them from wind and water erosion. Similarly, these soil surface communities also stabilized soils on early Earth, allowing vascular plants to establish. They contribute nitrogen and carbon to otherwise relatively infertile dryland soils, and have a strong influence on hydrologic cycles. Their presence can also influence vascular plant establishment and nutrition.

  12. Biological soil crust and disturbance controls on surface hydrology in a semi-arid ecosystem

    USGS Publications Warehouse

    Faist, Akasha M; Herrick, Jeffrey E.; Belnap, Jayne; Van Zee, Justin W; Barger, Nichole N

    2017-01-01

    Biological soil crust communities (biocrusts) play an important role in surface hydrologic processes in dryland ecosystems, and these processes may then be dramatically altered with soil surface disturbance. In this study, we examined biocrust hydrologic responses to disturbance at different developmental stages on sandy soils on the Colorado Plateau. Our results showed that all disturbance (trampling, scalping and trampling+scalping) of the early successional light cyanobacterial biocrusts generally reduced runoff. In contrast, trampling well-developed dark-cyano-lichen biocrusts increased runoff and sediment loss relative to intact controls. Scalping did not increase runoff, implying that soil aggregate structure was important to the infiltration process. Well-developed, intact dark biocrusts generally had lower runoff, low sediment loss, and highest aggregate stability whereas the less-developed light biocrusts were highest in runoff and sediment loss when compared to the controls. These results suggest the importance of maintaining the well-developed dark biocrusts, as they are beneficial for lowering runoff and reducing soil loss and redistribution on the landscape. These data also suggest that upslope patches of light biocrust may either support water transport to downslope vegetation patches or alternatively this runoff may place dark biocrust patches at risk of disruption and loss, given that light patches increase runoff and thus soil erosion potential.

  13. On the state of stress in the near-surface of the earth's crust

    USGS Publications Warehouse

    Savage, W.Z.; Swolfs, H.S.; Amadei, B.

    1992-01-01

    Five models for near-surface crustal stresses induced by gravity and horizontal deformation and the influence of rock property contrasts, rock strength, and stress relaxation on these stresses are presented. Three of the models-the lateral constraint model, the model for crustal stresses caused by horizontal deformation, and the model for the effects of anisotropy-are linearly elastic. The other two models assume that crustal rocks are brittle or viscoelastic in order to account for the effects of rock strength and time on near-surface stresses. It is shown that the lateral constraint model is simply a special case of the combined gravity-and deformation-induced stress field when horizontal strains vanish and that the inclusion of the effect of rock anisotropy in the solution for crustal stresses caused by gravity and horizontal deformation broadens the range for predicted stresses. It is also shown that when stress levels in the crust reach the limits of brittle rock strength, these stresses become independent of strain rates and that stress relaxation in ductile crustal rocks subject to constant horizontal strain rates causes horizontal stresses to become independent of time in the long term. ?? 1992 Birkha??user Verlag.

  14. Hydraulic and nutritional feedback controls surface patchiness of biological soil crusts at a post-mining site.

    NASA Astrophysics Data System (ADS)

    Fischer, Thomas; Gypser, Stella; Subbotina, Maria; Veste, Maik

    2015-04-01

    In a recultivation area located in Brandenburg, Germany, five types of biocrusts (initial BSC1, developed BSC2 and BSC3, mosses, lichens) and non-crusted mineral substrate were sampled on tertiary sand deposited in 1985-1986 to investigate hydrologic properties of crust patches. It was the aim of the study to demonstrate that (I) two types of BSC with alternative nutritional and hydraulic feedback modes co-exist in one area and that (II) these feedback modes are synergic. The sites to sample were selected by expertise, trying to represent mixed sites dominated by mosses, by lichens, and by visually in the field observable surface properties (colour and crust thickness) for the non-crusted substrate and BSC1 to 3. The non-crusted samples contained minor incrustations of the lichen Placynthiella oligotropha, young leaflets of the moss Ceratodon purpureus, as well as very sparsely present individuals of the green algae Ulothrix spec., Zygogonium spec. and Haematococcus spec. The sample BSC1 was not entirely covered with microphytes, crust patches were smooth, and P. oligotropha was observed to develop on residues of C. purpureus and on unspecified organic detritus. BSC2 covered the surface entirely and was dominated by P. oligotropha and by Zygogonium spec. The sample BSC3 consisted of pad-like patches predominantly growing on organic residues. The moss sample was dominated by C. purpureus and Zygogonium spec. growing between the moss stemlets directly on the mineral surface, the lichen sample was dominated by Cladonia subulata with sparsely scattered individuals of C. purpureus. Hierarchical cluster analysis revealed that BSC2 was floristically and chemically most similar to the moss crust, whereas BSC3 was floristically and chemically most similar to the lichen crust. Crust biomass was lowest in the non-crusted substrate, increased to the initial BSC1 and peaked in the developed BSC2, BSC3, the lichens and the mosses. Water infiltration was highest on the substrate

  15. Evidence for Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars

    NASA Technical Reports Server (NTRS)

    Frey, H. V.; Frey, E. L.; Hartmann, W. K.; Tanaka, K. L. T.

    2003-01-01

    Even though the Early Noachian (EN) used in geologic mapping is undefined at the early end, it is often assumed in absolute chronologies to extend back to 4.6 BYA. We explored this assumption by searching for evidence of buried impact basins, in the largest occurrences of Early Noachian terrain. The hypothesis is that if such basins exist, they indicate crust which must predate the surface units mapped as the oldest on Mars, and those units must then be less than 4.6 BY old. Alternatively, if no such buried features are seen, then the surface units may represent crust of the same age below, which could in principle be as old as Mars. Here we show the former alternative is true. There must be crust older than the oldest mapped surface units. We also show that a number of Noachian terrains on Mars appear to have a common total (visible + buried) crater retention age. This might be either the age of the original (planet-wide?) crust of Mars, or may indicate crater saturation.

  16. Shear velocity structure of the crust and upper mantle of Madagascar derived from surface wave tomography

    NASA Astrophysics Data System (ADS)

    Pratt, Martin J.; Wysession, Michael E.; Aleqabi, Ghassan; Wiens, Douglas A.; Nyblade, Andrew A.; Shore, Patrick; Rambolamanana, Gérard; Andriampenomanana, Fenitra; Rakotondraibe, Tsiriandrimanana; Tucker, Robert D.; Barruol, Guilhem; Rindraharisaona, Elisa

    2017-01-01

    The crust and upper mantle of the Madagascar continental fragment remained largely unexplored until a series of recent broadband seismic experiments. An island-wide deployment of broadband seismic instruments has allowed the first study of phase velocity variations, derived from surface waves, across the entire island. Late Cenozoic alkaline intraplate volcanism has occurred in three separate regions of Madagascar (north, central and southwest), with the north and central volcanism active until <1 Ma, but the sources of which remains uncertain. Combined analysis of three complementary surface wave methods (ambient noise, Rayleigh wave cross-correlations, and two-plane-wave) illuminate the upper mantle down to depths of 150 km. The phase-velocity measurements from the three methods for periods of 8-182 s are combined at each node and interpolated to generate the first 3-D shear-velocity model for sub-Madagascar velocity structure. Shallow (upper 10 km) low-shear-velocity regions correlate well with sedimentary basins along the west coast. Upper mantle low-shear-velocity zones that extend to at least 150 km deep underlie the north and central regions of recent alkali magmatism. These anomalies appear distinct at depths <100 km, suggesting that any connection between the zones lies at depths greater than the resolution of surface-wave tomography. An additional low-shear velocity anomaly is also identified at depths 50-150 km beneath the southwest region of intraplate volcanism. We interpret these three low-velocity regions as upwelling asthenosphere beneath the island, producing high-elevation topography and relatively low-volume magmatism.

  17. Evidence for Shock Metamorphic Origin of Multiply-Striated Joint Surfaces (MSJS) in Sandstones of the Sinamwenda Meteorite Impact Structure, Zimbabwe

    NASA Astrophysics Data System (ADS)

    Master, S.; Reimold, W. U.; Brandt, D.

    1996-03-01

    The Sinamwenda Structure (17 degrees 11'42" S, 27 degrees 47'30"E) is a 220m-diameter postulated impact crater situated in western Zimbabwe. Although the surrounding rocks are flat-lying unjointed Middle Triassic (Karoo) sandstones, the rocks of the crater rim are characterised by steep or overturned bedding, abundant multiply-striated joint surfaces (MSJS), and strong microbrecciation. We show that the MSJS are the result of shock metamorphism of the coarse sandstones in the rim, because of the rare occurrence, on the striated surfaces only, of isolated grains of shocked quartz containing Planar Deformation Features (PDFs). The presence of shocked quartz with PDFs is regarded as proof of the impact origin of the Sinamwenda crater.

  18. Linking playa surface dust emission potential to feedbacks between surface moisture and salt crust expansion through high resolution terrestrial laser scanning measurements

    NASA Astrophysics Data System (ADS)

    Nield, J. M.; King, J.; Wiggs, G.

    2012-12-01

    The dust emissivity of salt pans (or playas) can be significant but is controlled by interactions between wind erosivity, surface moisture, salt chemistry and crust morphology. These surface properties influence the aeolian transport threshold and can be highly variable over both short temporal and spatial scales. In the past, field studies have been hampered by practical difficulties in accurately measuring properties controlling sediment availability at the surface in high resolution. Studies typically therefore, have investigated large scale monthly or seasonal change using remote sensing and assume a homogeneous surface when predicting dust emissivity. Here we present the first high resolution measurements (sub-cm) of salt crust expansion related to changes in diurnal moisture over daily and weekly time periods using terrestrial laser scanning (TLS, ground-based LiDAR) on Sua Pan, Botswana. The TLS measures both elevation and relative surface moisture change simultaneously, without disturbing the surface. Measurement sequences enable the variability in aeolian sediment availability to be quantified along with temporal feedbacks associated with crust degradation. On crusts with well-developed polygon ridges (high aerodynamic and surface roughness), daily surface expansion was greater than 30mm. The greatest surface change occurred overnight on the upper, exposed sections of the ridges, particularly when surface temperatures dropping below 10°C. These areas also experienced the greatest moisture variation and became increasingly moist overnight in response to an increase in relative humidity. In contrast, during daylight hours, the ridge areas were drier than the lower lying inter-ridge areas. Positive feedbacks between surface topography and moisture reinforced the maximum diurnal moisture variation at ridge peaks, encouraging crust thrusting due to overnight salt hydration, further enhancing the surface, and therefore, aerodynamic roughness. These feedbacks

  19. High thermal inertia surfaces and the physical nature of the upper martian crust

    NASA Astrophysics Data System (ADS)

    Edwards, C. S.; Bandfield, J. L.; Christensen, P. R.; Fergason, R. L.

    2008-12-01

    An investigation of martian high thermal inertia surfaces has been made using Thermal Emission Imaging System (THEMIS) one hundred meter per pixel nighttime temperature data. High thermal inertia surfaces or interpreted bedrock are defined as any pixel in a THEMIS image with a thermal inertia over 1200 J K- 1m-2s-1/2) and may refer to in situ rock exposures or rock-dominated surfaces. Three distinct morphologies, ranked from most to least common, are associated with these high inertia surfaces: 1) valley and crater walls associated with mass wasting and high surface slope angles, 2) crater floors related to melting and re-crystallization associated with large (typically >25 km), high energy impacts, 3) plains surface with compositions significantly more mafic than the surrounding regolith, possibly indicating that the martian regolith has been processed, both chemically and mechanically. Overall, Mars has very little exposed bedrock or rocky material with only 960 instances identified from 75°N to 75°S. In general, bedrock instances occur in lower albedo (<0.18), moderate thermal inertia (>350 J K-1m-2s-1/2), and relatively dust free (DCI <0.95) areas. While many locations on Mars satisfy these conditions and have expected morphologies (e.g. steep slopes in Valles Marineris), observed bedrock instances are surprisingly rare. Most instances are concentrated in the southern highlands, with very few located at high latitudes (>45°N and <58°S). The latitudinal asymmetry observed in this data indicates a process that preferentially destroys or masks bedrock at lower latitudes in the north. Several processes likely play a role in destroying or masking a majority of the bedrock on the planet, including enhanced mechanical breakdown associated with permafrost at high latitudes and chemical and/or mechanical weathering associated with the formation of regolith fines from mafic precursor material [Bandfield and Rogers, 2008]. This distinct lack of bedrock indicates that

  20. Hydrology of the Ferron sandstone aquifer and effects of proposed surface-coal mining in Castle Valley, Utah, with sections on stratigraphy and leaching of overburden

    USGS Publications Warehouse

    Lines, Gregory C.; Morrissey, Daniel J.; Ryer, Thomas A.; Fuller, Richard H.

    1983-01-01

    Coal in the Ferron Sandstone Member of the Mancos Shale of Cretaceous age has traditionally been mined by underground techniques in the Emery Coal Field in the southern end of Castle Valley in east-central Utah. However, approximately 99 million tons are recoverable by surface mining. Ground water in the Ferron is the sole source of supply for the town of Emery, but the aquifer is essentially untapped outside the Emery area.The Ferron Sandstone Member crops out along the eastern edge of Castle Valley and generally dips 2 ? to 10 ? to the northwest. Sandstones in the Ferron are enclosed between relatively impermeable shale in the Tununk and Blue Gate Members of the Mancos Shale. Along the outcrop, the Ferron ranges in thickness from about 80 feet in the northern part of Castle Valley to 850 feet in the southern part. The Ferron also generally thickens in the subsurface downdip from the outcrop. Records from wells and test holes indicate that the full thickness of the Ferron is saturated with water in most areas downdip from the outcrop area.Tests in the Emery area indicate that transmissivity of the Ferron sandstone aquifer ranges from about 200 to 700 feet squared per day where the Ferron is fully saturated. Aquifer transmissivity is greatest near the Paradise Valley-Joes Valley fault system where permeability has been increased by fracturing. Storage coefficient ranges from about 10 .6 to 10 -3 where the Ferron sandstone aquifer is confined and probably averages 5 x 10-2 where it is unconfined.

  1. Does the reactive surface area of sandstone depend on water saturation?—The role of reactive-transport in water film

    NASA Astrophysics Data System (ADS)

    Nishiyama, Naoki; Yokoyama, Tadashi

    2013-12-01

    To investigate how mineral-water reactive surface area changes depending on water saturation, flow-through dissolution experiments were performed using a sandstone core at various water saturations. Fontainebleau sandstone with an open porosity of 6.3%, consisting of ∼100% quartz, was used. The water saturation of the core was adjusted to 0%, 51%, or 100%, and at each saturation, water was infiltrated into the core at a constant pressure. The experimental results showed that the total amount of dissolved Si did not change with decreasing water saturation. It can be therefore concluded that virtually all of the mineral surfaces were wetted with water film and allowed the progression of dissolution; i.e., the reactive surface area was not affected by water saturation despite the presence of air in the pores. The results also suggested that the flushing rate of dissolved Si from the interior of the water film to the exterior was fast enough to keep the Si concentration in the film sufficiently lower than the equilibrium concentration of quartz. We derived a reactive-transport model describing dissolution and diffusion in water film. The model shows that the solute concentration in a film is a function of the film thickness, diffusion length, dissolution rate of the mineral, equilibrium concentration, and roughness factor. As for the Fontainebleau sandstone, film thicknesses of 7-18 nm and diffusion lengths of 300-600 μm were estimated. The reactive-transport calculation confirmed that the overall dissolution rate of our sandstone sample was almost unaffected by water saturation, owing to the high flushing efficiency of dissolved Si in water film, which agrees with the experimental result. Application of the model allows us to evaluate whether the reactive surface area and the dissolution rate change with water saturation for a given rock of interest.

  2. Shear velocity structure of crust and uppermost mantle in China from surface wave tomography using ambient noise and earthquake data

    NASA Astrophysics Data System (ADS)

    Xu, Zhen J.; Song, Xiaodong; Zheng, Sihua

    2013-10-01

    We present a 3D model of shear velocity of crust and upper mantle in China and surrounding regions from surface wave tomography. We combine dispersion measurements from ambient noise correlation and traditional earthquake data. The stations include the China National Seismic Network, global networks, and all the available PASSCAL stations in the region over the years. The combined data sets provide excellent data coverage of the region for surface wave measurements from 8 to 120 s, which are used to invert for 3D shear wave velocity structure of the crust and upper mantle down to about 150 km. We also derive new models of the study region for crustal thickness and averaged S velocities for upper, mid, and lower crust and the uppermost mantle. The models provide a fundamental data set for understanding continental dynamics and evolution. The tomography results reveal significant features of crust and upper mantle structure, including major basins, Moho depth variation, mantle velocity contrast between eastern and western North China Craton, widespread low-velocity zone in mid-crust in much of the Tibetan Plateau, and clear velocity contrasts of the mantle lithosphere between north and southern Tibet with significant E- W variations. The low velocity structure in the upper mantle under north and eastern TP correlates with surface geological boundaries. A patch of high velocity anomaly is found under the eastern part of the TP, which may indicate intact mantle lithosphere. Mantle lithosphere shows striking systematic change from the western to eastern North China Craton. The Tanlu Fault appears to be a major lithosphere boundary.

  3. How biological crusts are stabilizing the soil surface? The devolpment of organo-mineral interactions in the initial phase

    NASA Astrophysics Data System (ADS)

    Fischer, T.; Veste, M.; Wiehe, W.; Lange, P.

    2009-04-01

    First colonizers of new land surfaces are cryptogames which often form biological soil crusts (BSC) covering the first millimetre of the top soil in many ecosystems from polar to desert ecosystems. These BSC are assemblages of cyanobacteria, green algae, mosses, liverworts, fungi and/or lichens. The development of soil surface crusts plays a major role for the further vegetation pattern through changes to the physico-chemical conditions and influencing various ecosystem processes. We studied the development of BSC on quaternary substrate of an initial artificial water catchment in Lusatia, Germany. Due to lack of organic matter in the geological substrate, photoautotrophic organisms like green algae and cyanobacteria dominated the initial phases of ecosystem development and, hence, of organo-mineral ineractions. We combined SEM/EDX and FTIR microscopy to study the contact zone of extracellular polymeric substances (EPS) of green algae and cyanobacteria with quartz, spars and mica on a >40 µm scale in undisturbed biological soil crusts, which had a maximum thickness of approx. 2 mm. SEM/EDX microscopy was used to determine the spatial distribution of S, Ca, Fe, Al, Si and K in the profiles, organic compounds were identified using FTIR microscopy. Exudates of crust organisms served as cementing material between sand particles. The crust could be subdivided into two horizontal layers. The upper layer, which had a thickness of approx. 200 µm, is characterized by accumulation of Al and K, but absence of Fe in microbial derived organic matter, indicating capture of weathering products of feldspars and mica by microbial exudates. The pore space between mineral particles was entirely filled with organic matter here. The underlying layer can be characterized by empty pores and organo-mineral bridges between the sand particles. Contrarily to the upper layer of the crust, Fe, Al and Si were associated with organic matter here but K was absent. Highest similarity of the FTIR

  4. Constrain the crust and upper mantle structure beneath the equatorial Eastern Pacific Rise from ambient noise and earthquake surface waves

    NASA Astrophysics Data System (ADS)

    Gao, C.; Yao, H.; Gouedard, P.; Collins, J. A.; McGuire, J. J.; van der Hilst, R.

    2012-12-01

    In this study we combine ambient noise and earthquake surface waves to jointly constrain the crust and upper mantle shear velocity structure beneath the equatorial eastern Pacific Rise using data from ocean bottom seismometers deployed in 2008. We measure the inter-station Rayleigh-wave phase velocity dispersion curves of the fundamental mode in the period band 2 - 30 s and the first higher mode in the period band 3 - 7 s from vertical component ambient noise cross-correlation functions. We also determine the inter-station phase velocity dispersion curves in the period band 20 - 100 s from an earthquake-based surface-wave two-station method. The average dispersion data from both ambient noise and earthquake surface waves are used to determine the average shear velocity structure in the crust and upper mantle using a global searching Neighborhood algorithm. Our results reveal a pronounced low velocity zone in the upper mantle with the shear wave speed as slow as 3.85 km/s beneath the equatorial eastern Pacific Rise, possibly caused by a combination of high temperature and the presence of partial melt beneath the mid-ocean ridges. We will also measure Love wave dispersion curves from transverse component ambient noise cross-correlation functions and earthquake surface waves. Together with Rayleigh-wave dispersion measurements, we will determine the radial anisotropy to constrain the deformation of the crust and upper mantle beneath the equatorial eastern Pacific Rise.

  5. Continental like crust beneath the Andaman Island through joint inversion of receiver function and surface wave from ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Gupta, Sandeep; Borah, Kajaljyoti; Saha, Gokul

    2016-09-01

    We study shear wave velocity structure of the crust beneath the Andaman Island through joint inversion of the teleseismic receiver function and Rayleigh wave group velocity measurements from 10 broadband seismographs over the Island. The group velocities in the periods from 5 to 21 s are obtained using cross-correlation of six month's ambient seismic noise data recorded by these seismic stations. Joint inversion results show 2 to 6 km thick subsurface low shear velocity (Vs 1.3-2.5 km/s) layer followed by a 12-14 km thick layer of silicic material (average Vs 3.5 km/s). The lower crust is mapped as an 8-12 km thick mafic layer with Vs 4.0 km/s. Uppermost mantle shear wave velocity is 4.55 km/s. The near-surface low-velocity layer is interpreted as the Andaman flysch sediments. The crustal thickness beneath the Andaman Island varies from 24 km in the north to 32 km in the south. The shear wave velocity-depth results show that the crustal structure beneath the Andaman Island is akin to continental crust, possibly the Burma continental crust. The subducting Indian plate may lie down below this overriding plate.

  6. Crust and upper mantle heterogeneities in the southwest Pacific from surface wave phase velocity analysis

    NASA Astrophysics Data System (ADS)

    Pillet, R.; Rouland, D.; Roult, G.; Wiens, D. A.

    1999-02-01

    with most of previous studies: the tomographic imaging shows a large contrast between low and high phase velocities along the Solomon, New Hebrides and Fiji-Tonga trenches. The lowest phase velocity anomalies are distributed beneath northern and southern Fiji basins and the Lau basin (corresponding to the volume situated just above the dipping slabs), whereas the highest values are displayed beneath the Pacific plate and the eastern part of Indian plate downgoing under the North Fiji basin. At shorter periods, our results show that the phase velocity distributions are well correlated with the large structural crustal domains. The use of local temporary broadband stations in the central part of the studied area gives us the opportunity to observe surface waves showing well-dispersed trains, allowing extended velocity measurements down to 8 s although aliasing due to multipaths become important. The continental regions (Eastern Australia, New Guinea, Fiji islands and New Zealand) show low velocities which are likely due to thick continental crust, whereas the Tasmanian, D'Entrecasteaux, and the Northern and Southern Fiji basins are characterized by higher velocities suggesting thinner oceanic crust. Additional analysis including the anisotropic case and S-wave velocity inversion with depth is in progress.

  7. Freshly brewed continental crust

    NASA Astrophysics Data System (ADS)

    Gazel, E.; Hayes, J. L.; Caddick, M. J.; Madrigal, P.

    2015-12-01

    Earth's crust is the life-sustaining interface between our planet's deep interior and surface. Basaltic crusts similar to Earth's oceanic crust characterize terrestrial planets in the solar system while the continental masses, areas of buoyant, thick silicic crust, are a unique characteristic of Earth. Therefore, understanding the processes responsible for the formation of continents is fundamental to reconstructing the evolution of our planet. We use geochemical and geophysical data to reconstruct the evolution of the Central American Land Bridge (Costa Rica and Panama) over the last 70 Ma. We also include new preliminary data from a key turning point (~12-6 Ma) from the evolution from an oceanic arc depleted in incompatible elements to a juvenile continental mass in order to evaluate current models of continental crust formation. We also discovered that seismic P-waves (body waves) travel through the crust at velocities closer to the ones observed in continental crust worldwide. Based on global statistical analyses of all magmas produced today in oceanic arcs compared to the global average composition of continental crust we developed a continental index. Our goal was to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust. We suggest that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone, a process probably more common in the Achaean where most continental landmasses formed, can produce the starting material necessary for juvenile continental crust formation.

  8. Potential fate of SOC eroded from natural crusted soil surface under simulated wind driven storm

    NASA Astrophysics Data System (ADS)

    Xiao, Liangang; Fister, Wolfgang; Greenwood, Philip; Hu, Yaxian; Kuhn, Nikolaus J.

    2016-04-01

    Improving the assessment of the impact of soil erosion on carbon (C) cycling requires a better understanding of the redistribution of eroded sediment and associated soil organic carbon (SOC) across agricultural landscapes. Recent studies conducted on dry-sieved aggregates in the laboratory demonstrated that aggregation can profoundly skew SOC redistribution and its subsequent fate by accelerating settling velocities of aggregated sediment compared to mineral grains, which in turn can increase SOC mineralization into greenhouse gases. However, the erodibility of the soil in the field is more variable than in the laboratory due to tillage, crus formation, drying-wetting and freeze-thaw cycles, and biological effects. This study aimed to investigate the potential fate of the SOC eroded from naturally developed soil surface and to compare the observations with those made in the laboratory. Simulated, short, high intensity wind driven storms were conducted on a crusted loam in the field. The sediments were fractionated with a settling tube according to their potential transport distances. The soil mass, SOC concentration and cumulative 80-day CO2 emission of each fraction were identified. The results show: 1) 53% of eroded sediment and 62% of eroded SOC from the natural surface in the field would be deposited across landscapes, which is six times and three times higher compared to that implied by mineral grains, respectively; 2) the preferential deposition of SOC-rich fast-settling sediment potentially releases approximately 50% more CO2 than the same layer of the non-eroded soil; 3) the respiration of the slow-settling fraction that is potentially transported to the aquatic systems was much more active compared to the other fractions and the bulk soil. Our results confirm in general the conclusions drawn from laboratory and thus demonstrate that aggregation can affect the redistribution of sediment associated SOC under field conditions, including an increase in

  9. Heat flow and near-surface radioactivity in the Australian continental crust

    USGS Publications Warehouse

    Sass, J.H.; Jaeger, J.C.; Munroe, Robert J.

    1976-01-01

    Heat-flow data have been obtained at 44 sites in various parts of Australia. These include seven sites from the old (~ 2500 m.y.) Precambrian shield of Western Australia, seventeen from the younger (~ 600- 2000 m.y.) Precambrian rocks of South Australia, the Northern Territory, and Queensland, and twenty within the eastern Paleozoic and younger rocks. Thirty of the sites are located where no previous heat-flow data existed, and the remainder provide significant extensions or refinements of areas previously studied. Where the holes studied penetrated the crystalline basement rocks, or where the latter rocks were exposed within a few kilometers of the holes, the upper crustal radiogenic heat production has been estimated based on gamma-ray spectrometric determinations of U, Th, and K abundances. Three heat-flow provinces are recognized in Australia based on the linear relation (q = q* + DA0 ) between heat flow q and surface radioactivity A0. New data from the Western Australian shield support earlier studies showing that heat flow is low to normal with values ranging from 0.7 to 1.2 hfu and with the majority of values less than 1.0 hfu, and the parameters q* = 0.63 hfu and 0 = 4.5 km determined previously were confirmed. Heat flow in the Proterozoic shield of central Australia is quite variable, with values ranging between about l and 3 hfu. This variability is attributed mainly to variations in near-surface crustal radioactivity. The parameters of the heat-flow line are q* = 0.64 hfu and 0 = 11.1 km and moderately high temperatures are predicted for the lower crust and upper mantle. Previous suggestions of a band of l ow- to - normal heat flow near the coast in eastern Australia were confirmed in some areas, but the zone is interrupted in at least one region (the Sydney Basin), where heat flow is about 2.0 hfu over a large area. The reduced heat flow, q*, in the Paleozoic intrusive rocks of eastern Australia varies from about 0.8 to 2.0 hfu . This variability might

  10. Stability of clathrate hydrates in Martian crust

    NASA Astrophysics Data System (ADS)

    Gloesener, Elodie; Karatekin, Özgür; Dehant, Véronique

    2014-05-01

    Clathrate hydrates are crystalline compounds constituted by cages formed by hydrogen-bonded water molecules inside of which guest gas molecules are trapped. These materials are typically stable at high pressure and low temperature and are present on Earth mainly in marine sediments and in permafrost. Moreover, clathrate hydrates are expected to exist on celestial bodies like the icy moons Titan, Europa or Enceladus. Current conditions in the Martian crust are favourable to the presence of clathrate hydrates. In this study, we focused on the stability of methane and carbon dioxide clathrates in the Martian crust. We coupled the stability conditions of clathrates with a 1D thermal model in order to obtain the variations of the clathrate stability zone in the crust of Mars with time and for different crust compositions. Indeed, the type of soil directly controls the geothermal conditions and therefore the depth of clathrates formation. Unconsolidated soil acts as a thermal insulator and prevents the clathrates formation in the crust except on a small part of a few tens of meters thick. In contrast, sandstone or ice-cemented soil allows the clathrates formation with a stability zone of several kilometers. This is explained by the fact that they evacuate heat more efficiently and thus maintain lower temperatures. We also studied the stability zone of clathrates formed from a mixture of methane and hydrogen sulphide as well as from a mixture of methane and nitrogen. Contrary to the addition of N2, the addition of H2S to CH4 clathrates extends the stability zone and thus brings it closer to the surface. Therefore, mixed clathrates CH4-H2S will be more easily destabilized by changes in surface temperature than CH4 clathrates.

  11. Response of Surface Soil Hydrology to the Micro-Pattern of Bio-Crust in a Dry-Land Loess Environment, China

    PubMed Central

    Wei, Wei; Yu, Yun; Chen, Liding

    2015-01-01

    The specific bio-species and their spatial patterns play crucial roles in regulating eco-hydrologic process, which is significant for large-scale habitat promotion and vegetation restoration in many dry-land ecosystems. Such effects, however, are not yet fully studied. In this study, 12 micro-plots, each with size of 0.5 m in depth and 1 m in length, were constructed on a gentle grassy hill-slope with a mean gradient of 8° in a semiarid loess hilly area of China. Two major bio-crusts, including mosses and lichens, had been cultivated for two years prior to the field simulation experiments, while physical crusts and non-crusted bare soils were used for comparison. By using rainfall simulation method, four designed micro-patterns (i.e., upper bio-crust and lower bare soil, scattered bio-crust, upper bare soil and lower bio-crust, fully-covered bio-crust) to the soil hydrological response were analyzed. We found that soil surface bio-crusts were more efficient in improving soil structure, water holding capacity and runoff retention particularly at surface 10 cm layers, compared with physical soil crusts and non-crusted bare soils. We re-confirmed that mosses functioned better than lichens, partly due to their higher successional stage and deeper biomass accumulation. Physical crusts were least efficient in water conservation and erosion control, followed by non-crusted bare soils. More importantly, there were marked differences in the efficiency of the different spatial arrangements of bio-crusts in controlling runoff and sediment generation. Fully-covered bio-crust pattern provides the best option for soil loss reduction and runoff retention, while a combination of upper bio-crust and lower bare soil pattern is the least one. These findings are suggested to be significant for surface-cover protection, rainwater infiltration, runoff retention, and erosion control in water-restricted and degraded natural slopes. PMID:26207757

  12. Altitude and configuration of the potentiometric surface in the Triassic sandstones and shales, northeastern Chester County, Pennsylvania, September 1987 through January 1988

    USGS Publications Warehouse

    Senior, Lisa A.; Garges, John A.

    1989-01-01

    The altitude of the water levels in the Triassic sandstones and shales in northeastern Chester County is shown on a map at a scale of 1:24,000. The map is based on water levels in 173 non-pumping drilled and dug wells measured in 1956 and 1965, and on the altitude of two springs that were flowing in November and December 1987. Water level altitudes are contoured at an interval of 20 ft. The surface defined by the contoured water levels may approximately represent the water table. Water table altitudes range from 379 ft to less than 80 ft above sea level. (USGS)

  13. Sensitivity of elastic surface deformations caused by atmospheric, hydrologic, and oceanic loads to the Earth's crust and mantle properties

    NASA Astrophysics Data System (ADS)

    Dill, Robert; Klemann, Volker; Kaban, Mikhail; Dobslaw, Henryk; Thomas, Maik

    2016-04-01

    The elastic deformation of the Earth's surface due to atmospheric surface pressure, terrestrial water storage, and ocean bottom pressure on seasonal or shorter time scales is usually represented by a set of elastic load Love numbers or the corresponding Green's function, determined from a radial Earth structure like PREM. Thereby, the influence of local deviations of the Earth's crustal and mantle properties is assumed to be negligible. However, local Green's functions derived individually for 1° grid cells from the 3D crustal structure model CRUST1 show large variations for in particular smaller distance angles. The loading response due to small-scale surface loads extending over less than 2500km2 significantly depends on the heterogeneous shallow structure of the Earth. In this contribution, we discuss the influence of lateral variations in the crust and mantle structure on atmospheric, hydrologic, and oceanic surface loads with regard to their spatial scales and distribution. Non-tidal atmospheric loading is calculated from an atmospheric surface pressure time series covering four decades (1976 - 2015) based on 3-hourly atmospheric data of ECMWF that has been homogenized by mapping surface pressure to a common reference orography. Hydrological loading is calculated for daily terrestrial water storage from LSDM over the same time period, where the surface water compartment is mapped from the 0.5° model resolution to a 0.125° GIS-based river network. Ocean tidal loading is exemplarily calculated based on the FES2014 ocean tidal model (0.0625°). Especially along the coasts of the oceans; in regions with steep orographic gradients; and in areas with thick crustal layers or sediments we will show the significant influence of the Earth's structure on small-scale deformation features caused by surface loads.

  14. Evidence for Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars

    NASA Technical Reports Server (NTRS)

    Frey, H. V.; Frey, E. L.; Hartmann, W. K.; Tanaka, K. L. T.

    2004-01-01

    MOLA gridded data shows clear evidence for Quasi-Circular Depressions not visible on images in Early Noachian (EN) terrain units on Mars. We suggest these are buried impact basins that pre-date the superimposed craters whose high density makes these EN units the oldest visible at the surface of Mars. There is crust older than the oldest visible terrain units on Mars, and these EN units cannot date from 4.6 BYA. These and other Noachian units have similar total (visible + buried) crater retention ages, suggesting a common "pre-Noachian" crustal age OR crater saturation beyond which we cannot see.

  15. Evidence for the Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars

    NASA Technical Reports Server (NTRS)

    Frey, H. V.; Frey, E. L.; Hartmann, W. K.; Tanaka, K. L. T.

    2003-01-01

    MOLA gridded data shows clear evidence for Quasi-Circular Depressions not visible on images in Early Noachian (EN) terrain units on Mars. We suggest these are buried impact basins that pre-date the superimposed craters whose high density makes these EN units the oldest visible at the surface of Mars. There is crust older than the oldest visible terrain units on Mars, and these EN units cannot date from 4.6 BYA. These and other Noa-chian units have similar total (visible + buried) crater retention ages, suggesting a common "pre-Noachian" crustal age OR crater saturation beyond which we cannot see.

  16. Evidence for the Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars

    NASA Technical Reports Server (NTRS)

    Frey, H. V.; Frey, E. L.; Hartmann, W. K.; Tanaka, K. L. T.

    2003-01-01

    MOLA gridded data shows clear evidence for Quasi-Circular Depressions not visible on images in Early Noachian (EN) terrain units on Mars. We suggest these are buried impact basins that pre-date the superimposed craters whose high density makes these EN units the oldest visible at the surface of Mars. There is crust older than the oldest visible terrain units on Mars, and these EN units cannot date from 4.6 BYA. These and other Noa-chian units have similar total (visible + buried) crater retention ages, suggesting a common "pre-Noachian" crustal age OR crater saturation beyond which we cannot see.

  17. Survival of artificially inoculated Escherichia coli and Salmonella Typhimurium on the surface of raw poultry products subjected to crust freezing.

    PubMed

    Chaves, B D; Han, I Y; Dawson, P L; Northcutt, J K

    2011-12-01

    Escherichia coli and Salmonella spp. are ubiquitous in the poultry production environment, and hence, their transmission to poultry products is of concern. Industry has widely used freezing as a strategy to halt pathogen growth, and more recently, crust freezing has been suggested as a means to improve mechanical operations, quality, and safety of poultry products. The purpose of this study was to evaluate the effect of crust freezing on the survival of Escherichia coli and Salmonella Typhimurium that were artificially inoculated on the surface of raw poultry products with or without adhering skin. Ampicillin-resistant (AR) E. coli JM 109 and nalidixic acid-resistant (NAR) Salmonella Typhimurium were used in the experiments. A set of cultures was subjected to cold-shock stress by storage at 4°C for 10 d. After being either cold-shocked or non-cold-shocked, commercial chicken breasts without skin and chicken thighs with skin were inoculated in separate experiments with each bacterium. Samples were crust frozen at -85°C for 20 min or completely frozen at -85°C for 60 min. The E. coli and Salmonella Typhimurium were recovered on appropriate selective and nonselective media containing the corresponding antibiotic. Log reductions and extent of injury were calculated and treatments were compared using ANOVA. No significant differences were observed in the reduction of cold-shocked or non-cold-shocked bacteria on products with or without skin that were crust or completely frozen. The average reduction for E. coli was 0.15 log(10) cfu/mL of rinse, and for Salmonella Typhimurium 0.10 log(10) cfu/mL of rinse; therefore, none of the final reductions were greater than the desired target (1 log). Bacterial cell injury was not significantly different (P > 0.05) among any of the treatments. Data showed no practical significance for initial reduction of these pathogens from crust freezing and thus, this technology should not be considered as a strategy for the reduction of E

  18. Behavior of Sandstones Under Heat Treatment

    NASA Astrophysics Data System (ADS)

    Keppert, M.; Fořt, J.; Trník, A.; Koňáková, D.; Vejmelková, E.; Pokorný, J.; Svora, P.; Pavlík, Z.; Černý, R.

    2017-04-01

    Knowledge of materials behavior under heat treatment is of high importance in construction and safety engineering; tunnels represent a special field because of their specific safety issues. In the case of fire, tunnel structure and surrounding rock are subjected to extreme temperatures which induces irreversible changes in the material's microstructure and consequently its mechanical properties. Significant portion of the Earth's crust is formed by sandstones; this group of sedimentary rocks is highly variable in structure, composition and engineering properties. Quartz grains (alternatively together with other minerals) form the clastic part of sandstones; the space between clasts is filled by variable amount of cement and matrix which can contain particularly clay minerals, quartz and calcite. The porosity of sandstones is again highly variable from a nearly compact material to a highly porous one. The paper aims to find out and explain differences in response of various kinds of sandstones to heat treatment. The behavior of a representative set of sandstones under heat treatment was studied by TG/DSC, thermodilatometry and residual strength measurement. These experiments were accompanied by SEM and porosimetry measurement. The effect of increased temperature on the compressive strength was found to be crucially dependent on the nature of the cement and matrix present in the individual rock. The rocks with calcite cement which had high initial strength and low porosity were damaged by calcite decomposition. The siliceous sandstones were damaged by cracking due to thermally induced volume changes. In contrary, the strength of the clayey sandstones was even improved after the heat treatment. It can be concluded that behavior of sandstone under heat treatment is controlled by its composition and diagenesis.

  19. The sensitivity of surface mass loading displacement response to perturbations in the elastic structure of the crust and mantle

    NASA Astrophysics Data System (ADS)

    Martens, Hilary R.; Rivera, Luis; Simons, Mark; Ito, Takeo

    2016-05-01

    Surface mass loads generate a rich spectrum of deformation responses in the solid Earth that might be exploited to probe the material properties of the crust and mantle. Here we present a detailed examination of load-induced surface displacements and their sensitivities to systematic perturbations in elastic Earth structure. We compute Love numbers and displacement load Green's functions (LGFs) by integrating the equations of motion for spheroidal deformation of a radially heterogeneous and self-gravitating Earth. Sensitivity kernels are derived for individual Love numbers numerically using finite differences and quasi-analytically using calculus of variations. We then generate sensitivity kernels for displacement LGFs by systematically perturbing the preliminary reference Earth model. We find that displacement LGFs are most sensitive to elastic structural perturbations within 500 km depth from the surface and for short source-receiver distances. For separate perturbations to the shear modulus, bulk modulus, and density within the crust and mantle, the sensitivity kernels exhibit unique patterns, consistent with the possibility to constrain the parameters independently given a spatially distributed set of sufficiently accurate loading response observations. The sensitivity to density structure, however, is generally weak in comparison to elastic structure. We also examine the sensitivity of surface displacements caused by M2 ocean tidal loading (OTL) to systematic perturbations in the elastic moduli and density. Since OTL-induced surface displacements are load and site dependent, we focus on high-resolution profiles across Iceland as a case study. The sensitivity kernels constitute a key element in the formulation of the inverse problem with application to geodetic tomography.

  20. Deformation of Tibetan Crust and Mantle and the Uplift of the Plateau: Insights from Broadband Surface Waves

    NASA Astrophysics Data System (ADS)

    Agius, M. R.; Lebedev, S.

    2013-12-01

    Seismic deployments over the last two decades have produced dense broadband data coverage across the Tibetan Plateau. Yet, the lithospheric dynamics of Tibet is still debated, with very different end-member models advocated to this day. Uncertainties over the anomalies in seismic tomography models contribute to the uncertainty of their interpretations, ranging from the subduction of India as far as northern Tibet to subduction of Asia there and to extreme viscous thickening of the entire Tibetan lithosphere. Within the lithosphere itself, a low-viscosity layer in the mid-lower crust is evidenced by many observations. It is still unclear, however, whether this layer accommodates a large-scale channel flow (which may have uplifted northern and eastern Tibet, according to one model) or if, instead, deformation within it is similar to that observed at the surface (which implies different uplift mechanisms). Broad-band surface waves provide resolving power from the upper crust down to the asthenosphere, for both isotropic-average shear-wave speeds (proxies for composition and temperature) and the radial and azimuthal shear-wave anisotropy (indicative of the patterns of deformation and flow). We measured highly accurate Love- and Rayleigh-wave phase-velocity curves in broad period ranges (up to 5-200 s) for a few tens of pairs and groups of stations across Tibet, combining, in each case, hundreds to thousands of inter-station measurements, made with cross-correlation and waveform-inversion methods. Robust shear-velocity profiles were then determined by series of non-linear inversions, yielding depth-dependent ranges of shear speeds and radial anisotropy consistent with the data. Temperature anomalies in the upper mantle were estimated from shear-velocity ones using accurate petro-physical relationships. Azimuthal anisotropy in the crust and upper mantle was determined by surface-wave tomography and, also, by sub-array analysis targeting the anisotropy amplitude. Our

  1. New Perspectives on the Old Red Sandstone

    NASA Astrophysics Data System (ADS)

    Miall, Andrew D.

    The Old Red Sandstone is amongst the most distinctive and well-known stratigraphic units in the British Isles. It is mainly of Devonian age; in fact, its lower boundary was used to define the base of the Devonian until relatively recently and it was called "Old" back in the nineteenth century to distinguish it from a superficially similar succession of Triassic age named the New Red Sandstone. The Old Red Sandstone has long been known to be a non-marine syntectonic to post-tectonic deposit associated with the Caledonian Orogeny One of the most famous outcrops of the red sandstone is at Siccar Point in northeast England at one of several outcrops named "Hutton's unconformity" where it lies, with marked angularity on Silurian lithic sandstones and shales. It was at these outcrops, toward the end of the eigthteenth century that James Hutton first came to understand the meaning of angular unconformities as structures representing vast amounts of missing time during which major upheavals of the Earth's crust occurred.

  2. Controls on the chemical composition of saline surface crusts and emitted dust from a wet playa in the Mojave Desert (USA)

    USGS Publications Warehouse

    Goldstein, Harland L.; Breit, George N.; Reynolds, Richard L.

    2017-01-01

    Saline-surface crusts and their compositions at ephemeral, dry, and drying lakes are important products of arid-land processes. Detailed understanding is lacking, however, about interactions among locally variable hydrogeologic conditions, compositional control of groundwater on vadose zone and surface salts, and dust composition. Chemical and physical data from groundwater, sediments, and salts reveal compositional controls on saline-surface crusts across a wet playa, Mojave Desert, with bearing on similar settings elsewhere. The compositions of chemically and isotopically distinctive shallow (<3 m) water masses are recorded in the composition of associated salts. In areas with deeper and more saline groundwater, however, not all ions are transported through the vadose zone. Retention of arsenic and other elements in the vadose zone diminishes the concentrations of potentially toxic elements in surface salts, but creates a reservoir of these elements that may be brought to the surface during wetter conditions or by human disturbance. Selective wind-erosion loss of sulfate salts was identified by the compositional contrast between surface salt crusts and underlying groundwater. At the sub-basin scale, compositional links exist among groundwater, salt crusts, and dust from wet playas. Across the study basin, however, lateral variations in groundwater and solid-salt compositions are produced by hydrogeologic heterogeneity.

  3. Dust Emissions from Undisturbed and Disturbed, Crusted Playa Surfaces: Cattle Trampling Effect

    USDA-ARS?s Scientific Manuscript database

    Dry playa lake beds can be a significant source of fine dust emissions during high wind events in arid and semiarid landscapes. The physical and chemical properties of the playa surface control the amount and properties of the dust emitted. In this study, we use a field wind tunnel to quantify the...

  4. Periodic changes in shallow lunat crust caused by Sun's heating and thermal diffusivity near the surface

    NASA Astrophysics Data System (ADS)

    Tanimoto, T.; Eitzel, M.; Yano, T.

    2007-12-01

    Analysis of Apollo 17 data (continuous data from 1976 to 1977) by the cross-correlation approach for seismic noise led us to two new discoveries, one related to the source of noise and the other on the periodic changes in seismic parameters due to extreme temperature changes near the surface. It has been shown previously by Larose et al. (2005) that Green's functions, dominated by Rayleigh waves, can be retrieved from cross-correlation of seismic noise in Apollo 17 data. We first confirmed their correlation results and further analyzed the details in GreenA?"qfs functions. The first discovery is that the sources of noise that lead to construction of Green's functions are (most likely) thermal moonquakes. This is suggested in the Rayleigh-wave observations that show diurnal variation (29.5 days) in amplitudes, but one can directly confirm a correlation between the statistics of thermal moonquakes and Rayleigh wave amplitudes. This is in contrast to the terrestrial case where ocean-generated seismic noise plays a critical role in the cross-correlation approach. This has implications for future planetary seismology as many planets lack oceans but may have thermal quakes caused by drastic temperature changes near the surface. Second, diurnal temporal variations in group velocity are detected, showing a strong correlation with the temporal variation of lunar surface temperature. This can be explained by the Sun's thermal effects which cause changes in density and seismic velocities near the surface. These effects are measurable on the moon since surface temperature changes as much as 270 K within the diurnal period. Depending on the thermal diffusivity of the medium, the depth extent of this thermal effect varies considerably. Inversion for thermal diffusivity using the changes in group velocity dispersion resulted in an estimate 10**(-7) (m**2/s) for the upper few meters.

  5. Evidence for gas accumulation beneath the surface crust driving cyclic rise and fall of the lava surface at Halema`uma`u, Kilauea Volcano

    NASA Astrophysics Data System (ADS)

    Patrick, M. R.; Orr, T. R.; Wilson, D.; Sutton, A. J.; Elias, T.; Fee, D.; Nadeau, P. A.

    2010-12-01

    The ongoing eruption in Halema`uma`u crater, at the summit of Kilauea Volcano, has surpassed the two-year mark and is characterized by lava lake activity in the vent. As of August 2010, the lava lake is about 70 m in diameter and 180 m below the rim of a narrow vent cavity. Although the explosive events that typified the first year of activity have abated, episodic rise and fall of the lava surface remains common. Cycles of rise and fall range from several minutes to eight hours in duration and are characterized by a quiescent rise phase and violent, gas-charged fall, spanning a height change of 20-30 m. Several models have been proposed to explain the cyclic rise and fall of lava surfaces at basaltic volcanoes, which in some cases is referred to as “gas pistoning”. In one model, episodic rise and fall is driven by the ascent of gas slugs from depth. In another, the cyclic behavior is driven by gas accumulation beneath the surface crust, with each cycle terminated by an abrupt failure of the crust, resulting in gas release. Seismic and infrasound data, as well as gas and webcam monitoring, at Halema`uma`u over the past two years strongly support the gas accumulation model, based on several lines of evidence. First, gas emission rates drop significantly below background levels during the rise phase, and increase dramatically during the fall phase, suggesting a process of gas buildup and release as opposed to slug flow. Second, the rise phases can last several hours, which is longer than reasonable slug ascent times. Third, the rise rate decreases over time, and in many cases plateaus, as the lava reaches its high stand, which is contrary to the exponential increase expected for gas slugs. Fourth, webcam video has captured numerous instances where rockfalls piercing the surface crust initiate gas release and lava level drop, suggestive of gas accumulation at shallow levels. Lastly, FTIR (Fourier Transform Infrared Spectroscopy) data reveal changes in gas

  6. The Role of Gas-Silicate Chemisorption Reactions in Modifying Planetary Crusts and Surfaces

    NASA Astrophysics Data System (ADS)

    King, P. L.; Henley, R. W.; Wykes, J. L.; Renggli, C.; Troitzsch, U.; Clark, D.; O'Neill, H. S.

    2014-12-01

    Evidence for gas-solid reactions is found throughout the solar system: for example, sulfidation reactions in some meteorites and secondary phases coating lunar pyroclastic glasses. On Earth, the products of gas-solid reactions are documented in volcanic systems, metalliferous mineral deposits, impact craters, and on dust or meteorites after passage through the atmosphere - such reactions are also likely on the surfaces of Mars and Venus. To understand the chemical dynamics of such gas-solid reactions, we are undertaking systematic experiments and thermochemical modelling. Experiments were conducted in a vertical gas-mixing furnace at 600 - 800 °C and 1 bar, using SO2and a range of Ca-bearing materials: labradorite, feldspar glass and anorthosite (rock). In each case, anhydrite formed rapidly. In shorter experiments with labradorite, isolated anhydrite is observed surrounded by 'moats' of Ca-depleted silicate. In longer experiments, anhydrite is found as clusters of crystals that, in some cases, extend from the substrate forming precarious 'towers' (Figure). Anhydrite fills cracks in porous samples. We propose that the nucleation and rapid growth of anhydrite on the surface of these Ca-rich phases occurs by chemisorption of SO2(g) molecules with slightly negatively charged oxygen onto available near-surface calcium with slight positive charge. Anhydrite growth is sustained by SO2(g) chemisorption and Ca migration through the reacting silicate lattice, accelerated by increased bond lengths at high temperature. Significantly, the chemisorption reaction indicates that SO2 disproportionates to form both oxidized sulfur (as anhydrite) and a reduced sulfur species (e.g., an S* radical ion). On Earth, in the presence of H2O, the predominant reduced sulfur species is H2S, through an overall reaction: 3CaAl2Si2O8 + 4 SO2(g)+ H2O(g) → 3CaSO4 + 3Al2SiO5 + 3SiO2 + H2S(g)The reduced sulfur may react with gas phase Fe, Ni, Zn and Cu cluster compounds to form metal sulfides

  7. Effect of rainfall and tillage direction on the evolution of surface crusts, soil hydraulic properties and runoff generation for a sandy loam soil

    NASA Astrophysics Data System (ADS)

    Ndiaye, Babacar; Esteves, Michel; Vandervaere, Jean-Pierre; Lapetite, Jean-Marc; Vauclin, Michel

    2005-06-01

    The study was aimed at evaluating the effect of rainfall and tillage-induced soil surface characteristics on infiltration and runoff on a 2.8 ha catchment located in the central region of Senegal. This was done by simulating 30 min rain storms applied at a constant rate of about 70 mm h -1, on 10 runoff micro-plots of 1 m 2, five being freshly harrowed perpendicularly to the slope and five along the slope (1%) of the catchment. Runoff was automatically recorded at the outlet of each plot. Hydraulic properties such as capillary sorptivity and hydraulic conductivity of the sandy loam soil close to saturation were determined by running 48 infiltration tests with a tension disc infiltrometer. That allowed the calculation of a mean characteristic pore size hydraulically active and a time to ponding. Superficial water storage capacity was estimated using data collected with an electronic relief meter. Because the soil was subject to surface crusting, crust-types as well as their spatial distribution within micro-plots and their evolution with time were identified and monitored by taking photographs at different times after tillage. The results showed that the surface crust-types as well as their tillage dependent dynamics greatly explain the decrease of hydraulic conductivity and sorptivity as the cumulative rainfall since tillage increases. The exponential decaying rates were found to be significantly greater for the soil harrowed along the slope (where the runoff crust-type covers more than 60% of the surface after 140 mm of rain) than across to the slope (where crusts are mainly of structural (60%) and erosion (40%) types). That makes ponding time smaller and runoff more important. Also it was shown that soil hydraulic properties after about 160 mm of rain were close to those of untilled plot not submitted to any rain. That indicates that the effects of tillage are short lived.

  8. Soil fertility in deserts: a review on the influence of biological soil crusts and the effect of soil surface disturbance on nutrient inputs and losses

    USGS Publications Warehouse

    Reynolds, R.; Phillips, S.; Duniway, M.; Belnap, J.

    2003-01-01

    Sources of desert soil fertility include parent material weathering, aeolian deposition, and on-site C and N biotic fixation. While parent materials provide many soil nutrients, aeolian deposition can provide up to 75% of plant-essential nutrients including N, P, K, Mg, Na, Mn, Cu, and Fe. Soil surface biota are often sticky, and help retain wind-deposited nutrients, as well as providing much of the N inputs. Carbon inputs are from both plants and soil surface biota. Most desert soils are protected by cyanobacterial-lichen-moss soil crusts, chemical crusts and/or desert pavement. Experimental disturbances applied in US deserts show disruption of soil surfaces result in decreased N and C inputs from soil biota by up to 100%. The ability to glue aeolian deposits in place is compromised, and underlying soils are exposed to erosion. The ability to withstand wind increases with biological and physical soil crust development. While most undisturbed sites show little sediment production, disturbance by vehicles or livestock produce up to 36 times more sediment production, with soil movement initiated at wind velocities well below commonly-occurring wind speeds. Soil fines and flora are often concentrated in the top 3 mm of the soil surface. Winds across disturbed areas can quickly remove this material from the soil surface, thereby potentially removing much of current and future soil fertility. Thus, disturbances of desert soil surfaces can both reduce fertility inputs and accelerate fertility losses.

  9. Global-scale Joint Body and Surface Wave Tomography with Vertical Transverse Isotropy in the Crust and Mantle

    NASA Astrophysics Data System (ADS)

    Simmons, N. A.; Myers, S.

    2016-12-01

    A series of global-scale seismic images of Earth's crust and mantle have been produced in recent years for seismic event monitoring applications (LLNL-G3D series, Simmons et al. 2011, 2012, and 2015). These models primarily focused on the prediction of body wave travel times for a suite of P and S body wave phases, allowing for more accurate event location estimates for events occurring anywhere in the world (Myers et al. 2015). We are currently incorporating global surface wave observations in the form of Love and Rayleigh dispersion relationships across a broad frequency range, while also fitting crustal, regional, and teleseismic body waves simultaneously. It is well-known that in order to simultaneously fit Love, Rayleigh, and body waves, terms representing radial anisotropy are required to account for the observed velocity of waves with differing propagation directions and particle motions. Therefore, we model vertical Vp, vertical Vs as well as 3 anisotropy parameters defined at each point to account for vertical transverse isotropy (VTI). We will present the development details of this newest model, which represents the next stage in a fully integrated Earth model capable of predicting a wider variety of seismic wave propagation characteristics for monitoring applications. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-ABS-698621

  10. What Can Spectral Properties of Martian Surface and Snc Can Tell Us about the Martian Crust Composition and Evolution

    NASA Astrophysics Data System (ADS)

    Ody, A.; Poulet, F.; Baratoux, D.; Quantin, C.; Bibring, J. P.

    2014-12-01

    While the study of Martian meteorites can provide detailed information about the crust and mantle composition and evolution, remote-sensing observations, through the merging of compositional and geological data, allow highlighting planetary-scale trends of the Martian crustal evolution [1,2]. Recently, the analysis of the global distribution of mafic minerals [3] has put new constraints on the Martian crust formation and evolution. One of the major results is a past global event of olivine-bearing fissural volcanism that has filled craters and low depressions in the southern highlands and a large part of the Northern plains during the late Noachian/early Hesperian. Petrologic models show that this sudden increase of the olivine content at the Noachian-Hesperian boundary could be the result of a rapid thickening of the lithosphere at the end of the Noachian era [4]. A recent study based on the OMEGA/MEx data has shown that the spectral properties of the shergottites are similar to those of some Noachian and Hesperian terrains [5]. To contrary, the Nakhla spectral properties are very different from those of the observable surface and could be representative of Amazonian terrains buried under dust. These results are best explained with an old age of the shergottites [6] and with the present understanding of the evolution of magma composition at a planetary scale [7]. On the other hand, if shergottites are young [8], the similarities between the shergottites and ancient terrains implies that exceptional conditions of melting with respect to the ambient mantle (e.g., hot spots or water-rich mantle source) were responsible for the formation of these samples [9]. References: [1] McSween et al., 2009, Science, 324. [2] Ehlmann & Edwards 2014, AREPS, vol. 42. [3] Ody et al., 2013, JGR,117,E00J14. [4] Ody et al., 2014, 8th Inter. Conf. on Mars,#1190. [5] Ody et al., 2013, 44th LPSC, #1719. [6] Bouvier et al., 2009, EPSL, 280. [7] Baratoux et al., 2013, JGR, 118. [8] Nyquist

  11. Evolution of the continental crust.

    PubMed

    Hawkesworth, C J; Kemp, A I S

    2006-10-19

    The continental crust covers nearly a third of the Earth's surface. It is buoyant--being less dense than the crust under the surrounding oceans--and is compositionally evolved, dominating the Earth's budget for those elements that preferentially partition into silicate liquid during mantle melting. Models for the differentiation of the continental crust can provide insights into how and when it was formed, and can be used to show that the composition of the basaltic protolith to the continental crust is similar to that of the average lower crust. From the late Archaean to late Proterozoic eras (some 3-1 billion years ago), much of the continental crust appears to have been generated in pulses of relatively rapid growth. Reconciling the sedimentary and igneous records for crustal evolution indicates that it may take up to one billion years for new crust to dominate the sedimentary record. Combining models for the differentiation of the crust and the residence time of elements in the upper crust indicates that the average rate of crust formation is some 2-3 times higher than most previous estimates.

  12. Eolian sabkha sandstones in the Nugget Sandstone (Jurassic), Vernal area, Utah

    SciTech Connect

    Schenk, C.J.; Peterson, F. )

    1991-06-01

    The Jurassic Nugget Sandstone in the Vernal, Utah, area is characterized by thick (up to 25 m) sets of cross-stratified eolian dune sandstone separated by either erosional planar bounding surfaces or thin (mostly < 3 m) sandstones interpreted as sabkha sandstones. Structures in Nugget sabkha sandstones are predominantly wavy or irregular bedding and thin, remnant sets of dune cross-strata consisting of eolian ripple and avalanche strata. The types of sedimentary structures and erosional features in Nugget sabkha sandstones indicate a close relationship between sand deposition and erosion and fluctuations in the local water table. Thin, remnant eolian dune sets are common in Nugget sabkha sandstones. The remnant sets form when dunes migrating across a sabkha are partially wetted as the water table rises slightly (on a scale of tens of centimeters); the lower part of the dune with wetted sand remains on the sabkha as the rest of the dune continues to migrate. Typically, ripple strata of the dune apron and the toes of avalanche strata are preserved in dune remnants. The avalanche strata, being slightly coarser grained, are preferentially deflated, leaving microtopography. This topography is commonly filled in with ripple strata that form as dry sand again blows across the sabkha. Stacked sets of remnant dunes separated by erosional surfaces illustrate the control of sand deposition on eolian sabkhas by the local water table.

  13. Activity of Type I Methanotrophs Dominates under High Methane Concentration: Methanotrophic Activity in Slurry Surface Crusts as Influenced by Methane, Oxygen, and Inorganic Nitrogen.

    PubMed

    Duan, Yun-Feng; Reinsch, Sabine; Ambus, Per; Elsgaard, Lars; Petersen, Søren O

    2017-07-01

    Livestock slurry is a major source of atmospheric methane (CH), but surface crusts harboring methane-oxidizing bacteria (MOB) could mediate against CH emissions. This study examined conditions for CH oxidation by in situ measurements of oxygen (O) and nitrous oxide (NO), as a proxy for inorganic N transformations, in intact crusts using microsensors. This was combined with laboratory incubations of crust material to investigate the effects of O, CH, and inorganic N on CH oxidation, using CH to trace C incorporation into lipids of MOB. Oxygen penetration into the crust was 2 to 14 mm, confining the potential for aerobic CH oxidation to a shallow layer. Nitrous oxide accumulated within or below the zone of O depletion. With 10 ppmv CH there was no O limitation on CH oxidation at O concentrations as low as 2%, whereas CH oxidation at 10 ppmv CH was reduced at ≤5% O. As hypothesized, CH oxidation was in general inhibited by inorganic N, especially NO, and there was an interaction between N inhibition and O limitation at 10 ppmv CH, as indicated by consistently stronger inhibition of CH oxidation by NH and NO at 3% compared with 20% O. Recovery of C in phospholipid fatty acids suggested that both Type I and Type II MOB were active, with Type I dominating high-concentration CH oxidation. Given the structural heterogeneity of crusts, CH oxidation activity likely varies spatially as constrained by the combined effects of CH, O, and inorganic N availability in microsites. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

  14. Origin of the Nubian and similar sandstones

    USGS Publications Warehouse

    McKee, E.D.

    1963-01-01

    The Nubian Sandstone and similar sandstone bodies exposed across much of northern Africa and adjoining parts of Asia are characteristically formed of clean sand that is conspicuously cross stratified throughout. Such sandstone, here called Nubian-type sandstone, ranges from Cambrian through Cretaceous in age and its genesis has been interpreted in many ways. Studies of its primary structures, and of the direction of sand transport, based on statistical measurements of foreset dip directions, have contributed new data on its genesis. By far the most common structure in Nubian-type sandstone is a medium-scale planar-type cross stratification in which sets of evenly dipping cross beds are bounded by essentially flat-lying top and bottom surfaces to form tabular bodies. Other less numerous but typical structures are large-scale, truncated-wedge cross strata, trough-type cross strata, intraformational recumbent folds, small-scale ripple laminae, and dipping sets of tabular-planar cross beds. An analysis of these structures suggests that in the typical Nubian Sandstone of Cretaceous age eolian deposits are not represented and normal marine types probably also are lacking; flood plain, pond or lagoon, and other continental and marginal environments are indicated. In the Carboniferous rocks of Sinai Peninsula some beach sandstone and possibly some eolian, in addition to the types described, form part of the sequence. Direction of sand transport, as determined from cross-bed dips, was northerly in the Cretaceous Nubian of Libya, Sudan, and Egypt; easterly in the Jurassic Adigrat of Ethiopia; westerly in the Carboniferous of Sinai; northwesterly in the early Paleozoic of Jordan. ?? 1963 Ferdinand Enke Verlag Stuttgart.

  15. Sand and sandstone

    SciTech Connect

    Pettijohn, F.J.; Potter, P.E.; Siever, R.

    1987-01-01

    Here is a new, second edition of a classical textbook in sedimentology, petrology, and petrography of sand and sandstones. It has been extensively revised and updated, including: new techniques and their utility; new literature; new illustrations; new, explicitly stated problems for the student; and a wider scope.

  16. Distributions of REE, Nd, Hf and Pb isotopes in the surfaces of Fe-Mn crusts from across the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Chu, N.; Nesbitt, R. W.; German, C. R.; Halbach, P.

    2001-12-01

    Over the past decade, numerous studies have investigated radiogenic isotopes (i.e. Nd, Pb, Hf, Os) in marine Fe-Mn deposits in an attempt to infer changes in ocean circulation throughout the Cenozoic. The use of radiogenic isotopes as paleoceanographic proxies has been challenged recently by evidence that the isotopic composition of crusts from oceanic domains near major river systems (e.g. Amazon, Congo) or old cratonic areas (i.e. the North Atlantic area) could be influenced significantly by continental inputs. Therefore, for any given crust, it is difficult to deduce the extent to which changes in weathering processes rather than ocean circulation may be responsible for observed isotopic variations. This is partly due to the fact that the oceanic budgets for some of these elements remain poorly constrained. In particular, the influence of both the eastward aeolian transport of Chinese loess and the erosion of the young West-Pacific volcanic belt on the isotopic composition of Pacific water masses has been poorly documented. The deep Pacific Ocean is composed of 4 principal water masses: North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW), Pacific Deep Water (PDW) and Antarctic Bottom Water (AABW). AABW, the main source of PDW, flows northward and enters the Central Basin through the Samoan Passage, where it is diverted into two branches: eastward to Line Island Passage and westward through Wake Passage. We will present Nd, Hf and Pb isotopic ratios combined with REE data from the surfaces of 16 Fe-Mn crusts taken at different depths from key areas of the Pacific Ocean. Two crusts were collected from the Izu-Bonin back-arc basin in the western Pacific and, hence, are particularly suitable for monitoring the influence of both continental aeolian and weathering inputs. Two other groups of crusts are from north and south of the equatorial Pacific region. The southern group is situated at the exit of the Samoan Passage, whereas the northern

  17. Provenance and geochronology of Cenozoic sandstones of northern Borneo

    NASA Astrophysics Data System (ADS)

    van Hattum, M. W. A.; Hall, R.; Pickard, A. L.; Nichols, G. J.

    2013-10-01

    The Crocker Fan of Sabah was deposited during subduction of the Proto-South China Sea between the Eocene and Early Miocene. Collision of South China microcontinental blocks with Borneo in the Early Miocene terminated deep water sedimentation and resulted in the major regional Top Crocker Unconformity (TCU). Sedimentation of fluvio-deltaic and shallow marine character resumed in the late Early Miocene. The Crocker Fan sandstones were derived from nearby sources in Borneo and nearby SE Asia, rather than distant Asian and Himalayan sources. The Crocker Fan sandstones have a mature composition, but their textures and heavy mineralogy indicate they are first-cycle sandstones, mostly derived from nearby granitic source rocks, with some input of metamorphic, sedimentary and ophiolitic material. The discrepancy between compositional maturity and textural immaturity is attributed to the effects of tropical weathering. U-Pb ages of detrital zircons are predominantly Mesozoic. In the Eocene sandstones Cretaceous zircons dominate and suggest derivation from granites of the Schwaner Mountains of southern Borneo. In Oligocene sandstones Permian-Triassic and Palaeoproterozoic zircons become more important, and are interpreted to be derived from Permian-Triassic granites and Proterozoic basement of the Malay Tin Belt. Miocene fluvio-deltaic and shallow marine sandstones above the TCU were mostly recycled from the deformed Crocker Fan in the rising central mountain range of Borneo. The provenance of the Tajau Sandstone Member of the Lower Miocene Kudat Formation in north Sabah is strikingly different from other Miocene and older sandstones. Sediment was derived mainly from granitic and high-grade metamorphic source rocks. No such rocks existed in Borneo during the Early Miocene, but potential sources are present on Palawan, to the north of Borneo. They represent continental crust from South China and subduction-related metamorphic rocks which formed an elevated region in the Early

  18. Rock doughnut and pothole structures of the Clarens Fm. Sandstone in the Karoo Basin, South Africa: Possible links to Lower Jurassic fluid seepage

    NASA Astrophysics Data System (ADS)

    Grab, Stefan; Svensen, Henrik

    2011-08-01

    South Africa has a wealth of sandstone landforms, yet many of these have not been examined in detail to expand knowledge on their morphology and process origins. Here we present data on primary morphological statistics, rock hardness, surface roughness and petrographic investigations of rock doughnuts and associated pothole structures in Golden Gate Highlands National Park (GGHNP) and in the Witkop III complex, with the aim of using such data and field observations to argue their likely origins. Schmidt hammer R-values indicate consistently harder doughnut rims (mean = 48.7; n = 150) than the enclosed potholes (mean = 37.8; n = 150) and surrounding sandstone platform (mean = 39.7; n = 250). The petrography of Clarens Fm. Sandstone shows that the typical whitish sandstone is affected by intense chemical weathering. Pothole rims and the irregular reddish crust typical of the Witkop III outcrops show a secondary cementation by microcrystalline silica. Although preservation of old land surfaces is difficult to prove, small and circular pipe structures filled with calcite-cemented sand are present locally surrounding the Witkop III hydrothermal complex, and represent conduits for fluidized sand. Based on the morphologies of the Witkop III summit with the associated potholes and pipes, we hypothesize that they are remnants of morphologies created by Jurassic fluid seepage, with a superimposed and secondary silica cementation. Given that fluidization structures evidently occur in Clarens Fm. Sandstone, as is the case at Witkop, such mechanisms could possibly have contributed to the observed rock doughnut structures elsewhere on Clarens Fm. Sandstones, such as at the GGHNP where the rock doughnut morphological attributes are typical to landforms originating from fluid venting.

  19. Dynamic effects of wet-dry cycles and crust formation on the saturated hydraulic conductivity of surface soils in the constructed Hühnerwasser ("Chicken Creek") catchment

    NASA Astrophysics Data System (ADS)

    Hinz, Christoph; Schümberg, Sabine; Kubitz, Anita; Frank, Franzi; Cheng, Zhang; Nanu Frechen, Tobias; Pohle, Ina

    2016-04-01

    Highly disturbed soils and substrates used in land rehabilitation undergo rapid changes after the first wetting events which in turn can lead to ecosystem degradation. Such changes were detected during the early development of the constructed Hühnerwasser ("Chicken Creek") catchment in Lusatia, Germany. Surface substrates consisting of quaternary sandy sediments formed surface seals during the first rainfall events leading to reduced infiltration and substantially increased surface runoff. Subsequently biological soil crusts formed and stabilised the surface. The aim of this study is to investigate the factors that cause the hydraulic conductivity to decrease using undisturbed and disturbed soil samples. Based on the hypothesis that physical and biological crusts lower the hydraulic conductivity, the first set of experiments with undisturbed soil cores from the Hühnerwasser catchment were carried out to measure the saturated hydraulic conductivity using the constant head method. Measurements were done with intact cores and repeated after the surface crust was removed. As the quaternary glacial sediments tend to display hard setting behaviour, we further hypothesised that the mobilisation of fine particles within the cores lead to pore clogging and that wet-dry cycles will therefore decrease hydraulic conductivity. A second set of experiments using the same methodology consisted of five repeated measurements of hydraulic conductivity after each drying cycle. These measurements were done with undisturbed core samples as well as repacked cores in order to assess how dry packing affects the dynamics of the hydraulic conductivity somewhat similar to the situation during the first wetting after completion of the catchment construction. For all experiments, the temporal evolution of hydraulic conductivity was measured and the turbidity of the effluent was recorded. The results clearly demonstrated that the substrate is highly unstable. The first set of experiments

  20. Spectral Induced Polarization of Sandstones: Temperature Effects

    NASA Astrophysics Data System (ADS)

    Binley, A.; Kruschwitz, S.; Lesmes, D.

    2007-12-01

    There is growing interest in the use of spectral induced polarization (SIP) for a wide range of environmental applications, in particular those focused on hydrogeological investigations. Recent experimental work has demonstrated that the mean relaxation time of electrical impedance spectra measured in sandstones is linked to the grain surface area and strongly correlated to some measure of a dominant pore throat size. Such empirically derived relationships lead to potential models of SIP - hydraulic conductivity, which has immense value for the hydrological community. Furthermore, the links between surface area and electrical response may lead to other, equally exciting, applications, such as in characterizing geochemical reactivity of sediments. However, there is a need to understand the fundamental behavior of SIP in such porous media in order for such models to be applied usefully. In an attempt to address this, we focus here on the influence of temperature on the SIP behavior of a range of sandstones. Classical models of dielectric dispersion in colloids have proposed direct inverse relationships between relaxation time and temperature. Through a series of experimental trials we have studied this behavior: examining the impedance spectra (in the 1 mHz to 1 kHz range) of four different sandstones over a temperature range of 5 to 30 degrees Celsius. Analysis of the spectra with the widely used Pelton Cole-Cole model has confirmed hypothesized effects on a mean relaxation time but revealed that the responses to temperature change is a function of physical properties of the sandstone. In addition, the analysis has illustrated how temperature effects on surface complex conductivity of the sandstones differ as a function of pore fluid and formation factor. The results add to the growing experimental evidence of controls on spectral impedance in porous media and help ascertain generalized petrophysical models for a wide range of applications.

  1. Subduction of the Indian lithosphere beneath Tibet and deformation of the Tibetan crust and mantle, imaged with broad-band surface waves

    NASA Astrophysics Data System (ADS)

    Agius, Matthew R.; Lebedev, Sergei

    2013-04-01

    Seismic deployments over the last two decades have produced dense broadband data coverage across the Tibetan Plateau. Yet, the lithospheric dynamics of Tibet remains enigmatic, with even its basic features debated and with very different end-member models still advocated today. Most body-wave tomographic models do not resolve any high-velocity anomalies in the upper mantle beneath central and northern Tibet, which motivated the inference that the Indian lithosphere may sink into deep mantle beneath the Himalayas in the south, with parts of it possibly extruded laterally eastward. In contrast, surface-wave tomographic models all show pronounced high-velocity anomalies beneath much of Tibet at depths around 200 km. Uncertainties over the shapes and amplitudes of the anomalies, however, contribute to the uncertainty of their interpretations, ranging from the subduction of India or Asia to the extreme viscous thickening of the Tibetan lithosphere. Within the lithosphere itself, a low-viscosity layer in the mid-lower crust is evidenced by many observations. It is still unclear, however, whether this layer accommodates a large-scale channel flow (which may have uplifted eastern Tibet, according to one model) or if, instead, deformation within it is similar to that observed at the surface. Broad-band surface waves provide resolving power from the upper crust down to the asthenosphere, for both the isotropic-average shear-wave speeds (characterising the composition and thermal state of the lithosphere) and the radial and azimuthal shear-wave anisotropy (indicative, in an actively deforming region, of the current and recent flow). We measured highly accurate Love- and Rayleigh-wave phase-velocity curves in broad period ranges (up to 5-200 s) for a few tens of pairs and groups of stations across Tibet, combining, in each case, hundreds to thousands of inter-station measurements made with cross-correlation and waveform-inversion methods. Robust shear-velocity profiles were

  2. The Continental Crust.

    ERIC Educational Resources Information Center

    Burchfiel, B. Clark

    1983-01-01

    Continental crust underlies the continents, their margins, and also small shallow regions in oceans. The nature of the crust (much older than oceanic crust) and its dynamics are discussed. Research related to and effects of tectonics, volcanism, erosion, and sedimentation on the crust are considered. (JN)

  3. The Continental Crust.

    ERIC Educational Resources Information Center

    Burchfiel, B. Clark

    1983-01-01

    Continental crust underlies the continents, their margins, and also small shallow regions in oceans. The nature of the crust (much older than oceanic crust) and its dynamics are discussed. Research related to and effects of tectonics, volcanism, erosion, and sedimentation on the crust are considered. (JN)

  4. Blueberries on Earth and Mars: Correlations Between Concretions in Navajo Sandstone and Terra Meridiani on Mars.

    NASA Astrophysics Data System (ADS)

    Mahaney, W. C.; Milner, M. W.; Netoff, D.; Dohm, J.; Kalm, V.; Krinsley, D.; Sodhi, R. N.; Anderson, R. C.; Boccia, S.; Malloch, D.; Kapran, B.; Havics, A.

    2008-12-01

    Concretionary Fe-Mn-rich nodular authigenic constituents of Jurassic Navajo sandstone (moki marbles) bear a certain relationship to similar concretionary forms ('blueberries') observed on Mars. Their origin on Earth is considered to invoke variable redox conditions with underground fluids penetrating porous quartz-rich sandstone leading to precipitation of hematite and goethite-rich material from solution, generally forming around a central nucleus of fine particles of quartz and orthoclase, recently verified by XRD and SEM-EDS analyses. At the outer rim/inner nucleus boundary, bulbous lobes of fine-grained quartz often invade and fracture the outer rim armored matrix. The bulbous forms are interpreted to result from fluid explusion from the inner concretionary mass, a response to pressure changes accompanying overburden loading. Moki marbles, harder than enclosing rock, often weather out of in situ sandstone outcrops that form a surface lag deposit of varnished marbles that locally resemble desert pavement. The marbles appear morphologically similar to 'blueberries' identified on the martian surface in Terra Meridiani through the MER-1 Opportunity rover. On Earth, redox fluids responsible for the genesis of marbles may have emanated from deep in the crust (often influenced by magmatic processes). These fluids, cooling to ambient temperatures, may have played a role in the genesis of the cemented outer rim of the concretions. The low frequency of fungi filaments in the marbles, contrasts with a high occurrence in Fe-encrusted sands of the Navajo formation [1], indicating that microbial content is of secondary importance in marble genesis relative to the fluctuating influx of ambient groundwater. Nevertheless, the presence of filaments in terrestrial concretions hints at the possibility of discovering fossil/extant life on Mars, and thus should be considered as prime targets for future reconnaissance missions to Mars. 1] Mahaney, W.C., et al. (2004), Icarus, 171, 39-53.

  5. Continental crust generated in oceanic arcs

    NASA Astrophysics Data System (ADS)

    Gazel, Esteban; Hayes, Jorden L.; Hoernle, Kaj; Kelemen, Peter; Everson, Erik; Holbrook, W. Steven; Hauff, Folkmar; van den Bogaard, Paul; Vance, Eric A.; Chu, Shuyu; Calvert, Andrew J.; Carr, Michael J.; Yogodzinski, Gene M.

    2015-04-01

    Thin oceanic crust is formed by decompression melting of the upper mantle at mid-ocean ridges, but the origin of the thick and buoyant continental crust is enigmatic. Juvenile continental crust may form from magmas erupted above intra-oceanic subduction zones, where oceanic lithosphere subducts beneath other oceanic lithosphere. However, it is unclear why the subduction of dominantly basaltic oceanic crust would result in the formation of andesitic continental crust at the surface. Here we use geochemical and geophysical data to reconstruct the evolution of the Central American land bridge, which formed above an intra-oceanic subduction system over the past 70 Myr. We find that the geochemical signature of erupted lavas evolved from basaltic to andesitic about 10 Myr ago--coincident with the onset of subduction of more oceanic crust that originally formed above the Galápagos mantle plume. We also find that seismic P-waves travel through the crust at velocities intermediate between those typically observed for oceanic and continental crust. We develop a continentality index to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust globally. We conclude that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone--a process probably more common in the Archaean--can produce juvenile continental crust.

  6. Facies architecture of tidal shelf sandstone ridge: Tocito sandstone

    SciTech Connect

    Riley, G.W.; Nummedal, D. )

    1989-09-01

    The lithofacies architecture of a single Tocito Sandstone Lentil has been documented in outcrops near the Hogback oil field west of Farmington with a very detailed outcrop study. This isolated Tocito sand body is composed of a three-tiered hierarchy of linear ridge elements. The large-scale Tocito Sandstone Lentil is approximately 5 km wide, 30 km long, and up to 16 m thick. The lentil is composed of at least three smaller scale ridges, which are up to 1 km wide, of unknown length, and up to 16 m thick. The small-scale ridges are arranged such that each new ridge accreted on the landward margin of the previous ridge. These smaller scale ridges consist of an ordered arrangement of four basic lithofacies: (1) burrowed, muddy sandstone, (2) interbedded clean and muddy sandstone, (3) cross-bedded sandstone, and (4) ripple-bedded sandstone. burrowed, muddy sandstone is found at the base of the small-scale ridges, is laterally extensive, and is interpreted as forming downcurrent from the most active portion of the ridge. The cross-bedded sandstone forms ribbon-shaped sand bodies elongate in the direction of ridge elongation. Typically the sand ribbons are 100-300 m wide, 2-4 m thick, and up to 1 km long. Usually two or more combine to form a small-scale ridge. The interbedded sandstone is found above the cross-bedded lithofacies as well as between the sand ribbons. The ripple-bedded facies is always found at the top of the section and represents the waning stage of ridge growth. The resulting architecture is one of coalesced sand ribbons combining to form the small-scale ridges, and subsequently small-scale ridges accreting landward to form a composite Tocito Sandstone Lentil.

  7. Ancient sandstone condition assessment in relation to degradation, cleaning and consolidation phenomena

    NASA Astrophysics Data System (ADS)

    Drdácký, Miloš; Frankeová, Dita; Slížková, Zuzana

    2015-04-01

    Non-invasive methods for assessing the state of historic stone types rely on measurement of their surface or subsurface characteristics, which are supposed to correlate with objective physical characteristics. Such measurements are influenced by surface conditions of stone, as well as by previous conservation treatments. The authors performed a comprehensive study of characteristics and behaviour of typical sandstone types present in the Charles' Bridge in Prague as a preparatory work for its diagnostic and restoration in order to understand the problem of a large, important, and non-homogeneous (from the material point of view) historic structure, that was intended for repair interventions. The study itself took advantage of the combination of non-invasive, or considerately destructive methods and fully destructive tests, because it was possible to use damaged sandstone blocks, which were extracted from a masonry rail of the bridge before replacement with new elements. Stone characteristics were studied on test specimens prepared from materials in various conditions and after various interventions. Seven types of sandstone were tested in nine sets (degraded surface layer with a crust, degraded surface layer after cleaning, and unweathered core material; all three without any consolidation treatment, and all three after consolidation with two products based on silicic acid ester - Funcosil 100 and 300). The paper will present only selected results of experiments and the most important conclusions taken from the tests and their comparison. During experimental work the following characteristics were investigated: bending strength, modulus of elasticity, ultrasonic velocity, micro-drilling resistance, water uptake, porosity, frost resistance, hydric dilation and thermal dilation. The degraded stone had a rather strong variation of its characteristics along the depth profile from the surface inside the stone ashlar. Therefore, the stone samples were prepared in a form

  8. A statistical assessment of seismic models of the U.S. continental crust using Bayesian inversion of ambient noise surface wave dispersion data

    NASA Astrophysics Data System (ADS)

    Olugboji, T. M.; Lekic, V.; McDonough, W.

    2017-07-01

    We present a new approach for evaluating existing crustal models using ambient noise data sets and its associated uncertainties. We use a transdimensional hierarchical Bayesian inversion approach to invert ambient noise surface wave phase dispersion maps for Love and Rayleigh waves using measurements obtained from Ekström (2014). Spatiospectral analysis shows that our results are comparable to a linear least squares inverse approach (except at higher harmonic degrees), but the procedure has additional advantages: (1) it yields an autoadaptive parameterization that follows Earth structure without making restricting assumptions on model resolution (regularization or damping) and data errors; (2) it can recover non-Gaussian phase velocity probability distributions while quantifying the sources of uncertainties in the data measurements and modeling procedure; and (3) it enables statistical assessments of different crustal models (e.g., CRUST1.0, LITHO1.0, and NACr14) using variable resolution residual and standard deviation maps estimated from the ensemble. These assessments show that in the stable old crust of the Archean, the misfits are statistically negligible, requiring no significant update to crustal models from the ambient noise data set. In other regions of the U.S., significant updates to regionalization and crustal structure are expected especially in the shallow sedimentary basins and the tectonically active regions, where the differences between model predictions and data are statistically significant.

  9. Surface uplift due to thermo-rheological changes in the crust: The case of the southern margin of the Central Anatolian Plateau (S Turkey)

    NASA Astrophysics Data System (ADS)

    Fernández-Blanco, David; Bertotti, Giovanni; Cassola, Teodoro; Willett, Sean

    2016-04-01

    Late Miocene uplift of the southern margin of the Central Anatolian orogenic plateau (SCAP) can be explained with our proposed surface uplift mechanism. This new model is based on the dynamic interactions between the growth of the Anatolian accretionary subduction margin and thermo-rheological changes at the base of its crust. Our thermo-rheological uplift mechanism fits newly obtained structural data, as well as compiled geological and geophysical data along a 550km-long arc-perpendicular transect. This transect runs between the Cyprian Arc trench and central Turkey through the area of the Anatolian upper-plate with larger uplift, i.e. central south Turkey. Observed deformation patterns and associated vertical motions along this transect indicate distributed shortening in relation to the subduction of the Cyprus slab, which still underlies this area. In the middle sectors of the transect a pre-Miocene basement gently dipping southward underwent regional subsidence since Early Miocene times. After ~8 Ma, surface uplift took place in the area of the future SCAP, as recorded by disruption of marine deposition and the onset of erosion, whereas subsidence persisted to the south of it, in the Cilicia Basin. Overall N-S shortening during this period developed regional contractional structures along the margin: the S-verging Kyrenia thrust system in N Cyprus, the S-dipping thrusts in the center of the Cilicia Basin, and the large-wavelength S-dipping monocline in S Turkey. We tested our proposed mechanism with 2D thermo-mechanically coupled finite elements models. The models demonstrate that sediment accretion and deposition in the central Cyprus accretionary forearc basin system led to crustal thickening of the Anatolian upper-plate, which in turn forced a sedimentary "blanketing" effect. This sedimentary "blanketing" effect controlled the temperature gradient in the crust, with decreased temperatures within the blanket and increased underneath it. Higher temperatures

  10. Development, calibration, and performance of a novel biocrust wetness probe (BWP) measuring the water content of biological soil crusts and surface soils

    NASA Astrophysics Data System (ADS)

    Weber, Bettina; Berkemeier, Thomas; Ruckteschler, Nina; Caesar, Jennifer; Ritter, Holger; Heintz, Henno; Brass, Henning

    2015-04-01

    The surface layer of soils as transition zone between pedosphere and atmosphere plays a crucial role in exchange processes of nutrients, atmospheric gases and water. In arid and semiarid regions, this uppermost soil layer is commonly colonized by biological soil crusts (biocrusts), which cover about 46 million km2 worldwide being highly relevant in the global terrestrial carbon and nitrogen cycles. Their water status is of major concern, as activity of these poikilohydric organisms is directly controlled by their water content. On-site analyses of both bare and crusted soils thus are urgently needed to correctly model exchange processes of water, nutrients and trace gases at the soil surface. In this study we present the biocrust wetness probe (BWP), which is the first low-cost sensor to reliably measure the water content within biocrusts or the uppermost 5 mm of the substrate. Using a weak alternating current, the electrical conductivity is assessed and an automatic calibration routine allows calculating the water content and precipitation equivalent of the surface layer over time. During one year of continuous field measurements, 60 BWPs were installed in different types of biocrusts and bare soil to measure at 5-minute intervals in the Succulent Karroo, South Africa. All sensors worked reliably and responded immediately and individually upon precipitation events. Upon completion of field measurements, soil and biocrust samples were collected from all measurement spots to compile calibration curves in the lab. In most soil and biocrust samples the water content rose linearly with increasing electrical conductivity values and only for few samples an exponential relationship was observed. Measurements revealed characteristic differences in biocrust and soil wetness patterns, which affect both the water regime and physiological processes in desert regions. Thus BWPs turned out to be well suited sensors for spatio-temporal monitoring of soil water content, allowing

  11. Feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust

    NASA Astrophysics Data System (ADS)

    Korotev, Randy L.; Jolliff, Bradley L.; Zeigler, Ryan A.; Gillis, Jeffrey J.; Haskin, Larry A.

    2003-12-01

    We present new compositional data for six feldspathic lunar meteorites, two from cold deserts (Yamato 791197 and 82192) and four from hot deserts (Dhofar 025, Northwest Africa 482, and Dar al Gani 262 and 400). The concentrations of FeO (or Al 2O 3) and Th (or any other incompatible element) together provide first-order compositional information about lunar polymict samples (breccias and regoliths) and regions of the lunar surface observed from orbit. Concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft, although the derived concentrations have large uncertainties and some systematic errors compared to sample data. Within the uncertainties and errors in the concentrations derived from orbital data, the distribution of FeO and Th concentrations among lunar meteorites, which represent ˜18 source regions on the lunar surface, is consistent with that of 18 random samples from the surface. Approximately 11 of the lunar meteorites are low-FeO and low-Th breccias, consistent with large regions of the lunar surface, particularly the northern farside highlands. Almost all regoliths from Apollo sites, on the other hand, have larger concentrations of both elements because they contain Fe-rich volcanic lithologies from the nearside maria and Th-rich lithologies from the high-Th anomaly in the northwestern nearside. The feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands, and we provide such an estimate based on the eight most well-characterized feldspathic lunar meteorites. The variable but high (on average) Mg/Fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high-Mg/Fe feldspathic rocks such as magnesian granulitic breccia, not ferroan anorthosite. Geochemically, the high-Mg/Fe breccias appear to be

  12. Patterns of active surface deformation along the eastern margin of the Tibetan Plateau: a role for flow in the lower crust?

    NASA Astrophysics Data System (ADS)

    Kirby, E.

    2009-04-01

    The growth of high topography in eastern Tibet continues to challenge our conceptual understanding of how orogenic plateaus develop. Although numerous lines of evidence suggest that large regions of the eastern Tibetan Plateau attained their current elevation through flow and thickening in the lower crust (Royden et al., 2008), the great earthquake of 12 May 2008 in Sichuan Province clearly attests to significant deformation within the brittle portions of the crust. The magnitude and complexity of this rupture has led some to argue that crustal shortening accomplished during this event obviates the need for flow in the deep crust. Here, I address this question from a combination of perspectives that utilize geomorphic and exhumational proxies to characterize the rates and patterns of differential rock uplift across the plateau margin. The topographic margin of the plateau adjacent to and north of the Sichuan Basin is one of the more enigmatic mountain fronts in the world. Despite nearly 6km of relief between the peaks of the Longmen Shan and the Sichuan Basin, geodetic data prior to the earthquake revealed little to no shortening across this margin of the plateau (Burchfiel et al., 2008). How such topography can develop and be maintained in the face of limited shortening of the upper crust remains an outstanding problem. Some insight is provided by studies of the low-temperature cooling history of this region. Prior to Late Miocene time, the entirety of eastern Tibet experienced extremely slow denudation rates (20 - 50 m/Myr) since Mesozoic time. Such rates are consistent with the preservation of Mesozoic cooling ages from samples atop the plateau surface. Thermal histories of rocks exposed in the deep canyons of Sichuan reveal that rocks in the immediate hanging wall of the Sichuan rupture have been exhumed from 8-10 km depth, during the past 12- 14 Ma. Thus, the rapid erosion that presently characterizes the deeply-incised topographic margin of the plateau has

  13. Microtopography of manganese crusts

    NASA Astrophysics Data System (ADS)

    Morgan, Charles L.

    Quantitative examination of the seafloor surface roughness will be necessary for any design of equipment intended for use in collecting surface deposits such as cobalt-rich manganese crusts or nodules. Furthermore, it is an essential prerequisite to the confident interpretation of returns from high frequency side-scan and other acoustic systems. The objectives of the project were to develop the capability at the University of Hawaii of generating high resolution (less than 1 cm horizontal and vertical) topographic models of the seafloor from 35 mm stereo photographs; to produce such models from existing photographs of cobalt-rich manganese crust deposits; and to optimize the configuration of the existing Hawaii Undersea Research Laboratory (HURL) camera system for stereo photograph collection and correlation of acoustic data with the photographic ground-truth. These tasks were accomplished and have also led to the development of a follow-on project (MMTC/OBD Project 1512) dedicated to the simultaneous acquisition of both optical and side-scan acoustic data for future accurate determination of seabed microtopography.

  14. Joint inversion of long period waveform and surface wave dispersion data for crust and upper mantle structure using the Spectral Element Method

    NASA Astrophysics Data System (ADS)

    Lekic, V.; Romanowicz, B. A.

    2009-12-01

    Surface waves and overtones provide excellent constraints on crustal, upper mantle, and transition zone structure. They offer far better radial resolution of shallow structure than is possible with teleseismic body waves, while simultaneously having excellent global coverage and signal-to-noise ratios. Indeed, since its development a quarter century ago (Woodhouse and Dziewonski, 1984), the modeling of long period waveforms of surface waves and overtones using approximate techniques has made possible the development of high resolution models of upper mantle shear wave velocity and radial anisotropy. However, the ray- and perturbation theory that underlie these efforts can result in modeling errors that exceed the noise level of the observed waveforms (Panning et al., 2009). In the case of realistic crustal structure, the modeling inaccuracies can significantly contaminate the retrieved images of mantle velocity and radial anisotropy (Lekic et al., 2009). Fortunately, the development of computational techniques capable of fully modeling wave propagation through the complex, heterogeneous Earth (Spectral Element Method, SEM: e.g. Capdeville et al., 2003) enables us to move away from approximate techniques. Previously, we have applied SEM to the modeling of long period waveforms to construct a preliminary model of isotropic shear wavespeed and radial anisotropy in the upper mantle (Lekic and Romanowicz, 2008). Yet, the superior accuracy of the spectral element method SEM comes at a far greater computational cost than that associated with approximate techniques, especially because of the presence of thin layers in the crust. At the same time, inaccuracies in existing global crustal models like CRUST2 (Bassin et al., 2000) can contaminate the retrieved mantle images. Thus, there is a need for approaches that avoid the meshing of thin layers while increasing the accuracy of crustal corrections. Long period waveforms lack the resolution necessary for crustal inversion, so

  15. Sandstones of unexpectedly high diffusibility.

    PubMed

    Bashar, Khairul; Tellam, John H

    2011-03-25

    Measurements have been made of diffusion coefficients (D(i)=-mass flux/concentration gradient) using a double reservoir, steady-state method with two tracers, CaBr(2) and amino-G-acid, on intact samples of Triassic red-bed sandstone from northwest England. Diffusibility (D'=D(i)/diffusion coefficient in water) averages 0.124, ranging between 0.075 and 0.215 (porosity 0.1 to 0.24), very similar for the two tracers. Implied tortuosities (actual path length/straight line length) average 1.21 (range 1.06 to 1.47), with constrictivities close to 1. In comparison with limited red-bed sandstone data from elsewhere, these D' values are up to 4 times greater, and tortuosity correspondingly lower. Re-interpretation of formation factor data from previous studies on shallow sandstone samples also from northwest England confirms that diffusibility is significantly higher in these sandstones than others from similar palaeoenvironment/stratigraphic units. The lower tortuosities appear to result from the relatively high permeability, open fabric of the rock, properties likely to be present in shallow sandstone systems used for water supply. It is concluded that diffusion rates may, in some shallow freshwater-containing continental sandstone systems, be significantly greater than is implied by estimates of sandstone diffusibility current in the literature. Copyright © 2010 Elsevier B.V. All rights reserved.

  16. Building Archean cratons from Hadean mafic crust

    NASA Astrophysics Data System (ADS)

    O'Neil, Jonathan; Carlson, Richard W.

    2017-03-01

    Geologic processing of Earth’s surface has removed most of the evidence concerning the nature of Earth’s first crust. One region of ancient crust is the Hudson Bay terrane of northeastern Canada, which is mainly composed of Neoarchean felsic crust and forms the nucleus of the Northeastern Superior Province. New data show these ~2.7-billion-year-old rocks to be the youngest to yield variability in neodymium-142 (142Nd), the decay product of short-lived samarium-146 (146Sm). Combined 146-147Sm-142-143Nd data reveal that this large block of Archean crust formed by reworking of much older (>4.2 billion-year-old) mafic crust over a 1.5-billion-year interval of early Earth history. Thus, unlike on modern Earth, mafic crust apparently could survive for more than 1 billion years to form an important source rock for Archean crustal genesis.

  17. Composition of the Continental Crust

    NASA Astrophysics Data System (ADS)

    Rudnick, R. L.; Gao, S.

    2003-12-01

    The Earth is an unusual planet in our solar system in having a bimodal topography that reflects the two distinct types of crust found on our planet. The low-lying oceanic crust is thin (˜7 km on average), composed of relatively dense rock types such as basalt and is young (≤200 Ma old) (see Chapter 3.13). In contrast, the high-standing continental crust is thick (˜40 km on average), is composed of highly diverse lithologies (virtually every rock type known on Earth) that yield an average intermediate or "andesitic" bulk composition (Taylor and McLennan (1985) and references therein), and contains the oldest rocks and minerals yet observed on Earth (currently the 4.0 Ga Acasta gneisses (Bowring and Williams, 1999) and 4.4 Ga detrital zircons from the Yilgarn Block, Western Australia (Wilde et al., 2001)), respectively. Thus, the continents preserve a rich geological history of our planet's evolution and understanding their origin is critical for understanding the origin and differentiation of the Earth.The origin of the continents has received wide attention within the geological community, with hundreds of papers and several books devoted to the topic (the reader is referred to the following general references for further reading: Taylor and McLennan (1985), Windley (1995), and Condie (1997). Knowledge of the age and composition of the continental crust is essential for understanding its origin. Patchett and Samson (Chapter 3.10) review the present-day age distribution of the continental crust and Kemp and Hawkesworth (Chapter 3.11) review secular evolution of crust composition. Moreover, to understand fully the origin and evolution of continents requires an understanding of not only the crust, but also the mantle lithosphere that formed more-or-less contemporaneously with the crust and translates with it as the continents move across the Earth's surface. The latter topic is reviewed in Chapter 2.05.This chapter reviews the present-day composition of the

  18. Implications for the evolution of continental crust from Hf isotope systematics of Archean detrital zircons

    NASA Technical Reports Server (NTRS)

    Stevenson, Ross K.; Patchett, P. Jonathan

    1990-01-01

    Results from the fractionation of zircon by sedimentary processes into continental margin sandstone yield information on the preservation of preexisting continental crust in the form of zircon, making it possible to distinguish between the contrasting theories of gradual growth versus constant volume of continental crust over geologic time. In this work, Hf-176/Hf-177 ratios were determined for detrital zircon fractions from 2.0-2.5, 2.6-3.0, and pre-3.0 Gyr old sandstones from the Canadian-Shield, the North-Atlantic, the Wyoming, and the Kaapvaal Cratons. Results pointed to small amounts of continental crust prior to 3.0 Gyr ago and a rapid addition of continental crust between 2.5 and 3.0 Gyr ago, consistent with the gradual growth of continental crust, and giving evidence against no-growth histories.

  19. Implications for the evolution of continental crust from Hf isotope systematics of Archean detrital zircons

    NASA Technical Reports Server (NTRS)

    Stevenson, Ross K.; Patchett, P. Jonathan

    1990-01-01

    Results from the fractionation of zircon by sedimentary processes into continental margin sandstone yield information on the preservation of preexisting continental crust in the form of zircon, making it possible to distinguish between the contrasting theories of gradual growth versus constant volume of continental crust over geologic time. In this work, Hf-176/Hf-177 ratios were determined for detrital zircon fractions from 2.0-2.5, 2.6-3.0, and pre-3.0 Gyr old sandstones from the Canadian-Shield, the North-Atlantic, the Wyoming, and the Kaapvaal Cratons. Results pointed to small amounts of continental crust prior to 3.0 Gyr ago and a rapid addition of continental crust between 2.5 and 3.0 Gyr ago, consistent with the gradual growth of continental crust, and giving evidence against no-growth histories.

  20. Evaluation of black crust formation and soiling process on historical buildings from the Bilbao metropolitan area (north of Spain) using SEM-EDS and Raman microscopy.

    PubMed

    Calparsoro, Estefanía; Maguregui, Maite; Giakoumaki, Anastasia; Morillas, Héctor; Madariaga, Juan Manuel

    2017-04-01

    In the present work, several building materials suffering from black crusts and soiled surfaces were evaluated by scanning electron microscopy energy dispersive X-ray spectrometry (SEM-EDS) and micro-Raman spectroscopy. The goal was to examine the elemental and molecular composition, the distribution on the samples, and the morphology of endogenous and exogenous compounds on those black crusts and soiled surfaces. The black crusts were deposited over different building materials such as limestone, sandstone, and brick that constitute a small construction called "malacate" as well as over a limestone substrate of a cemetery gate. Both constructions are dated back to the beginning of the twentieth century. The samples of soiling were taken from the façade of a building constructed in the 1980s. The analytical evaluation allowed in a first stage the determination of the composition and the observation of the morphology of soiling and black crusts. In addition, the evaluation of the compositions of the soiling and black crusts of different grade and formation allowed the assessment of the main weathering phenomena that the buildings have suffered, which were found to be sulfate impact, marine aerosol impact, depositions of metallic particles, crustal particulate matter depositions, carbonaceous particles, biodeterioration, and vandalism.

  1. Pacific ferromanganese crust geology and geochemistry

    SciTech Connect

    Andreev, S.I.; Vanstein, B.G.; Anikeeva, L.I. )

    1990-06-01

    Cobaltiferous ferromanganese crusts form part of a large series of oceanic ferromanganese oxide deposits. The crusts show high cobalt (commonly over 0.4%), low nickel and copper sum (0.4-0.8%), considerably high manganese (18-20%), and iron (14-18%). Less abundant elements in crusts are represented by molybdenum and vanadium; the rare-earth elements cerium, lanthenum, and yttrium; and the noble metals platinum and rhodium. Co-rich crusts form at water depths of 600 to 2,500 m. Crust thicknesses range from millimeters to 15-17 cm, averaging 2-6 cm. The most favorable conditions for 4-10 cm thick crusts to occur is at water depths of 1,200-2,200 m. The crusts formed on basaltic, calcareous, siliceous, and breccia bedrock surfaces provided there were conditions preventing bottom sedimentation at them. If the sedimentation takes place, it may be accompanied by nodules similar in composition to the crusts. The most favorable topography for extensive crust formation is considered to be subdued (up to 20{degree}) slopes and summit platforms of conical seamounts, frequently near faults and their intersection zones. Subhorizontal guyot summits do not usually favor crust growth. Crust geochemistry is primarily defined by mineralogy and manganese hydroxides (vernadite)/iron ratio. The first associated group of compounds includes cobalt, nickel, molybdenum, vanadium, cerium, and titanium; the other is strontium, yttrium, cerium, and cadmium. The aluminosilicate phase is associated with titanium, iron, chromium, and vanadium; phosphate biogenic phase includes copper, nickel, zinc, lead, and barium. The crucial point in cobaltiferous crust formation is their growth rate on which is dependent the degree of ferromanganese matrix sorption saturation with cobalt. The optimum for cobalt-rich ferromanganese ores is the conditions facilitating long-term and continuous hydrogenic processes.

  2. Chemical characteristics (REE, etc.) of Paleozoic and Mesozoic graywackes and sandstones from Central Europe

    NASA Astrophysics Data System (ADS)

    Wedepohl, Karl Hans; Simon, Klaus

    2012-10-01

    During the Variscan orogeny in Central Europe, partial melting in the lower continental crust formed granitic magmas, which intruded into the upper crust and left compounds of Ca (plus Eu2+), Mg, etc. in the lower crust. From the late Paleozoic decomposition of the tonalitic upper crust, sedimentary graywackes were produced reflecting the composition of this crust. The repeated reworking of the sedimentary cover caused the formation of sands. Sandstones as their products of consolidation contain increasing fractions of quartz and decreasing feldspar from Carboniferous and Triassic to Cretaceous age. A distinct negative Eu anomaly characterizes the majority of these rocks. The latter is imprinted by the Variscan magmatism. Quartz as used for numerous Medieval wood ash glasses is marked for its Central European origin by a distinct negative Eu anomaly in contrast to many soda glasses produced outside Germany mostly with a small or none Eu anomaly.

  3. Habitability Of Europa's Crust

    NASA Astrophysics Data System (ADS)

    Greenberg, R.; Tufts, B. R.; Geissler, P.; Hoppa, G.

    Physical characterization of Europa's crust shows it to be rich in potentially habitable niches, with several timescales for change that would allow stability for organisms to prosper and still require and drive evolution and adaptation. Studies of tectonics on Europa indicate that tidal stress causes much of the surface cracking, that cracks pen- etrate through to liquid water (so the ice must be thin), and that cracks continue to be worked by tidal stress. Thus a global ocean is (or was until recently) well linked to the surface. Daily tidal flow (period~days) transports substances up and down through the active cracks, mixing surface oxidants and fuels (cometary material) with the oceanic reservoir of endogenic and exogenic substances. Organisms moving with the flow or anchored to the walls could exploit the disequilibrium chemistry, and those within a few meters of the surface could photosynthesize. Cracks remain active for at least ~10,000 yr, but deactivate as nonsynchronous rotation moves them to different stress regimes in less than a million yr. Thus, to survive, organisms squeezed into the ocean must migrate to new cracks, and those frozen in place must hibernate. Most sites remelt and would release captive organisms within about a million yr based on the prevalence of chaotic terrain, which covers nearly half of Europa. Linkage of the ocean to the surface also could help sustain life in the ocean by delivering oxidants and fuels. Suboceanic volcanism (if any) could provide additional sites and support for life, but is not necessary. Recent results support this model. We further constrain the non-synchronous rotation rate, demonstrate the plausibility of episodic melt-through, show that characteristics of pits and uplift features do not imply thick ice, and demonstrate polar wander, i.e. that the ice crust is detached from the solid interior and has slipped as a unit relative to the spin axis. Thus Europa's biosphere (habitable if not inhabited) likely

  4. Fast evolving conduits in clay-bonded sandstone: Characterization, erosion processes and significance for the origin of sandstone landforms

    NASA Astrophysics Data System (ADS)

    Bruthans, Jiri; Svetlik, Daniel; Soukup, Jan; Schweigstillova, Jana; Valek, Jan; Sedlackova, Marketa; Mayo, Alan L.

    2012-12-01

    In Strelec Quarry, the Czech Republic, an underground conduit network > 300 m long with a volume of ~ 104 m3 and a catchment of 7 km2 developed over 5 years by groundwater flow in Cretaceous marine quartz sandstone. Similar landforms at natural exposures (conduits, slot canyons, undercuts) are stabilized by case hardening and have stopped evolving. The quarry offers a unique opportunity to study conduit evolution in sandstone at local to regional scales, from the initial stage to maturity, and to characterize the erosion processes which may form natural landforms prior to stabilization. A new technique was developed to distinguish erodible and non-erodible sandstone surfaces. Based on measurements of relative erodibility, drilling resistance, ambient and water-saturated tensile strength (TS) at natural and quarry exposures three distinct kinds of surfaces were found. 1) Erodible sandstone exposed at ~ 60% of surfaces in quarry. This sandstone loses as much as 99% of TS when saturated. 2) Sub-vertical fracture surfaces that are non-erodible already prior to exposure at ground surface and which keep considerable TS if saturated. 3) Case hardened surfaces that start to form after exposure. In favorable conditions they became non-erodible and reach the full TS in just 6 years. An increase in the hydraulic gradient from ~ 0.005 to > 0.02 triggered conduit evolution, based on long-term monitoring of water table in 18 wells and inflows to the quarry. Rapidly evolving major conduits are characterized by a channel gradient of ~ 0.01, a flow velocity ~ 40 cm/s and sediment concentration ~ 10 g/l. Flow in openings with a discharge 1 ml/s and hydraulic gradient > 0.05 exceeds the erosion threshold and initiates piping. In the first phase of conduit evolution, fast concentrated flow mobilizes erodible sandstone between sets of parallel fractures in the shallow phreatic zone. In the second phase the conduit opening mainly expands vertically upward into the vadose zone by mass

  5. The Crust and Upper Mantle Structure of Northeastern Iran from Joint Waveform Tomography Imaging of Body and Surface Waves

    NASA Astrophysics Data System (ADS)

    Baker, B.; Roecker, S. W.; Priestley, K. F.; Tatar, M.

    2012-12-01

    The deformation resulting from the Arabian-Eurasian collision at the longitude of Iran is concentrated in the Zagros, Alborz and Kopeh Dagh Mountains. The Zagros and Alborz Mountains have been the focus of a number of studies but little is known about the structure of NE Iran and the Kopeh Dagh. The Kopeh Dagh form a linear intracontinental fold-and-thrust belt trending NW-SE between the stable Turkmenistan platform and Central Iran, and mark the northern limit to deformation in NE Iran. To the south of the Kopeh Dagh lie a series of elongated mountain ranges: the Binalud, which is a structural and geological eastward continuation of the Alborz, the Siah Kuh near Sabzevar and the Kuh-e-Sorkh near Kashmar. Between August 2006 and February 2008 we operated 17 broadband seismographs along a profile from Sarakhs, near the northeastern political border of Iran with Turkmenistan, across the Kopeh Dagh Mountains, to Yazd in Central Iran. We apply a combination of the teleseismic body wave waveform tomography technique of Roecker et al (2010) with an extension of this technique to surface waves (Roecker et al, 2011) to analyze this data to determine the elastic wavespeed structure of this area. The joint inversion of these different types of waves affords similar types of advantages that are common to combined surface wave dispersion/receiver function inversions in compensating for intrinsic weaknesses in horizontal and vertical resolution capabilities. We compare results recovered from a several different inverse methods, starting with simple gradient techniques to the more sophisticated pseudo-Hessian or L-BFGS approach, and find that the latter are generally more robust. Modelling of receiver functions and surface wave dispersion prior to the analysis is shown to be an efficacious way to generate starting models for this analysis.

  6. Microstructure of deformed graywacke sandstones

    SciTech Connect

    Dengler, L.A.

    1980-03-05

    Microsctures in low-permeability graywacke sandstones were studied by optical and scanning electron microscopy (SEM). SEM specimens were prepared by ion-bombardment of thick polished samples. The undeformed rock contains grains in a matrix composed primarily of authigenic chlorite and kaolinite. Chlorite platelets are randomly arranged in face-to-edge relation to one another. Kaolinite occurs as pseudohexagonal crystals stacked face-to-face in pore filling books. Uniaxial-stress experiments covered a range of confining pressures from .1 to 600 MPa. Below 50 MPa confining pressure, intergranular fracturing occurs within the fault zone and near the sample's cylindrical surface. Between 100 and 300 MPa confining pressure, fault zones contain highly fractured grains, gauge and slickensides on grain surfaces. At 600 MPa, the sample contains a diffuse shear zone of highly fractured grains and no well-defined fault. In all samples, the distribution of microcracks is heterogeneous. Different clay minerals exhibit different modes of deformation. Chlorite structure responds to applied stress by compaction, reducing both pore size and volume. Chlorite platelets are plastically deformed in even the least strained samples. Kaolinite does not deform plastically in any of the samples examined. Deformation of kaolinite is restricted to toppling of the book structure. Dilatant crack growth was studied in two samples unloaded prior to failure. Uniaxially-strained samples deform primarily along grain boundaries, producing intergranular cracks and realignment of chlorite platelets. Intragranular crack density is linearly related to axial-strain, although grains are less fractured than in uniaxially-stressed samples tested at equivalent mean pressures. Cracks are rarely longer than a grain diameter. Nuclear-explosively deformed samples were recovered after the Rio Blanco gas stimulation experiment. (JGB)

  7. The Crust and Upper Mantle Structure of the Iranian Plateau from Joint Waveform Tomography Imaging of Body and Surface Waves

    NASA Astrophysics Data System (ADS)

    Roecker, S. W.; Priestley, K. F.; Tatar, M.

    2014-12-01

    The Iranian Plateau forms a broad zone of deformation between the colliding Arabian and Eurasian plates. The convergence is accommodated in the Zagros Mountains of SW Iran, the Alborz Mountains of northern Iran, and the Kopeh Dagh Mountains of NE Iran. These deforming belts are separated by relatively aseismic depressions such as the Lut Block. It has been suggested that the Arabia-Eurasia collision is similar to the Indo-Eurasia collision but at a early point of development and therefore, it may provide clues to our understanding of the earlier stages of the continent-continent collision process. We present results of the analysis of seismic data collected along two NE-SW trending transects across the Iranian Plateau. The first profile extends from near Bushere on the Persian Gulf coast to near to the Iran-Turkmenistan border north of Mashad, and consists of seismic recordings along the SW portion of the line in 2000-2001 and recording along the NE portion of the line in 2003 and 2006-2008. The second profile extends from near the Iran-Iraq border near the Dezfel embayment to the south Caspian Sea coast north of Tehran. We apply the combined 2.5D finite element waveform tomography algorithm of Baker and Roecker [2014] to jointly invert teleseismic body and surface waves to determine the elastic wavespeed structures of these areas. The joint inversion of these different types of waves affords similar types of advantages that are common to combined surface wave dispersion/receiver function inversions in compensating for intrinsic weaknesses in horizontal and vertical resolution capabilities. We compare results recovered from a finite difference approach to document the effects of various assumptions related to their application, such as the inclusion of topography, on the models recovered. We also apply several different inverse methods, starting with simple gradient techniques to the more sophisticated pseudo-Hessian or L-BFGS approach, and find that the latter are

  8. Drought effect on biocrust resilience: High-speed winds result in crust burial and crust rupture and flaking.

    PubMed

    Kidron, Giora J; Ying, Wang; Starinsky, Abraham; Herzberg, Moshe

    2017-02-01

    Once established, biocrusts (known also as biological soil crusts or microbiotic crusts) are thought to be relatively resilient to wind erosion, with crust burial being considered as the main mechanism responsible for crust death. Thus far, to the best of our knowledge, crust flaking and rupture under natural conditions were not reported. We report herein a two-year study during two severe drought years (2010-2012) in a dunefield in the Negev Desert during which in addition to crust burial, crust rupture and flaking also took place. As for crust burial, it took place under sand sheets or coppice dunes (mounds). Subsequent removal of the coppice dunes by wind resulted in crust disintegration and erosion of the formerly buried crust and the formation of patches devoid of crusts termed herein 'erosion cirques'. As for crust flaking and rupture, it is explained by a large change in the properties of the extracellular polymeric substances (EPS) composing the crust. The EPS adherence and viscoelastic properties were monitored using a quartz crystal microbalance with dissipation monitoring (QCD-M) technology. EPS adherence and viscoelastic properties deduced from the QCM-D experiments suggest that crust coherence and elasticity, mediated by the EPS, were affected by droughts. Although crust flaking affected up to 25% of the interdunal surface, it is suggested that with continuous rain shortage, further crust flaking is likely to take place under continuous drought-driven dry surface conditions. This positive feedback mechanism, during which initially eroded crusts trigger additional crust erosion, may have severe consequences on the structure and function of drought-prone ecosystems, and may endanger the stability of dunefields, causing dust storms, triggering dune encroachment and declining air quality.

  9. Deep ancient fluids in the continental crust and their impact on near-surface economic, environmental and biological systems.

    NASA Astrophysics Data System (ADS)

    Ballentine, Christopher; Warr, Oliver; Sutcliffe, Chelsea; McDermott, Jill; Fellowes, Jonathan; Holland, Greg; Mabry, Jennifer; Sherwood Lollar, Barbara

    2016-04-01

    With a few exceptions the mobility of water, oil and gas, provides for an ephemeral view of subsurface fluids relative to geological or planetary timescales. Aquifers supplying water for drinking and irrigation have mean residence ages from hundreds to tens of thousands of years; Hydrothermal systems can be active for hundreds of thousands to millions of years forming key mineral reserves; Sedimentary basin formation expels fluids during compaction and generates oil and gas on times scales of millions to hundreds of millions of years. Within these exemplar systems biological activity can play a crucial role by mediating system oxidation state: releasing arsenic into shallow groundwaters; precipitating ore bodies; generating methane; and biodegrading oil. It is becoming increasingly apparent that fluids resident in fractures and porespace in the crystalline basement underlying many of these systems can have a mean residence time that ranges from tens to hundreds of millions of years [1,2] to billions of years [3,4]. These fluids are highly saline and trace element rich; they are abundant in nitrogen, hydrogen, methane and helium and can contain microbes that have uniquely adapted to these isolated environments [5]. We are actively expanding discovery of sites with fluids exhibiting extreme age and have recently shown that these systems contribute to half of the terrestrial hydrogen production; a key component in biosphere energy and carbon cycles [6]. Tectonic or thermal release of these fluids can result in helium deposits; possible ore body generation and the inoculation of near-surface systems with microbial biota protected in the deep surface; the controls and rate of fluid release to shallow systems can fundamentally change the nature of some shallow systems. These deep ancient fluids represent a little tapped scientific resource for understanding how life survives and evolves in such isolation, how life is transported and communicates in extremis together and

  10. Seismic velocity structure of the crust and shallow mantle of the Central and Eastern United States by seismic surface wave imaging

    USGS Publications Warehouse

    Pollitz, Fred; Mooney, Walter D.

    2016-01-01

    Seismic surface waves from the Transportable Array of EarthScope's USArray are used to estimate phase velocity structure of 18 to 125 s Rayleigh waves, then inverted to obtain three-dimensional crust and upper mantle structure of the Central and Eastern United States (CEUS) down to ∼200 km. The obtained lithosphere structure confirms previously imaged CEUS features, e.g., the low seismic-velocity signature of the Cambrian Reelfoot Rift and the very low velocity at >150 km depth below an Eocene volcanic center in northwestern Virginia. New features include high-velocity mantle stretching from the Archean Superior Craton well into the Proterozoic terranes and deep low-velocity zones in central Texas (associated with the late Cretaceous Travis and Uvalde volcanic fields) and beneath the South Georgia Rift (which contains Jurassic basalts). Hot spot tracks may be associated with several imaged low-velocity zones, particularly those close to the former rifted Laurentia margin.

  11. A McMC Method for the Inference of Radial and Azimuthal Anisotropy of the Crust and Upper Mantle from Surface-Wave Dispersion Curves

    NASA Astrophysics Data System (ADS)

    Ravenna, Matteo; Lebedev, Sergei

    2016-04-01

    We develop a Markov Chain Monte Carlo method for joint inversion of Rayleigh- and Love-wave dispersion curves that is able to yield robust radially and azimuthally anisotropic shear velocity profiles, with resolution to depths down to the transition zone. The probabilistic feature of the algorithm is a powerful tool that is able to provide error assessment of the shear velocity models, quantify non-uniqueness and address the issue of data noise estimation by treating it as an unknown parameter in the inversion. In a fixed dimensional Bayesian formulation, we choose to set the number of parameters relatively high, with a more dense parametrization in the uppermost mantle in order to have a good resolution of the Litosphere-Astenosphere Boundary region. We apply the MCMC algorithm to the inversion of surface-wave phase velocities accurately determined in broad period ranges in a few test regions. In the Baikal-Mongolia region we invert Rayleigh- and Love- wave dispersion curves for radially anisotropic structure (Vsv,Vsh) of the crust and upper mantle. In the Tuscany region, where we have phase velocity data with good azimuthal coverage, a different implementation of the algorithm is applied that is able to resolve azimuthal anisotropy; the Rayleigh wave dispersion curves measured at different azimuths have been inverted for the Vsv structure and the depth distribution of the 2-psi azimuthal anisotropy of the region, with good resolution down to asthenospheric depths.

  12. Eocene adakitic porphyries in the central-northern Qiangtang Block, central Tibet: Partial melting of thickened lower crust and implications for initial surface uplifting of the plateau

    NASA Astrophysics Data System (ADS)

    Ou, Quan; Wang, Qiang; Wyman, Derek A.; Zhang, Hai-Xiang; Yang, Jin-Hui; Zeng, Ji-Peng; Hao, Lu-Lu; Chen, Yi-Wei; Liang, He; Qi, Yue

    2017-02-01

    The time and mechanism of crustal thickening and initial surface uplift of the Tibetan Plateau remain highly controversial. Here we report on zircon U-Pb age, and mineral, element, and Sr-Nd isotope composition data for Eocene adakitic porphyries in the Laorite Co area of central-northern Qiangtang Block, central Tibet. Laser ablation-inductively coupled plasma-mass spectrometry zircon U-Pb age dating shows that the porphyries were generated at 42-41 Ma. All samples display adakitic geochemical characteristics, such as high SiO2 and Al2O3, and low Y and Yb contents, and high Sr/Y and La/Yb ratios with positive Sr and negligible Eu anomalies and Nb-Ta depletion. They also have low magnesium number (Mg #) (16-45) and high K2O (4.0-4.6 wt %) values, as well as high (87Sr/86Sr)i (0.7076-0.7080) and low ɛNd(t) (-5.9 to -4.4) values. These adakitic rocks were most probably generated by partial melting of thickened lower crust in the stability field of garnet, amphibole, and rutile but with relatively minor plagioclase. Moreover, such a crustal thickening process beneath this block likely occurred no later than the middle Eocene and was most probably caused by the southward subduction of the Songpan-Ganzi Block in the early Cenozoic. In addition, the occurrences of exposed adakitic porphyries unambiguously indicate that exhumation process occurred after their formation. Thus, these 42 Ma adakitic porphyries indicate the occurrence of significant exhumation since 42 Ma. Integrated with the thermochronological and paleoelevation data, we suggest that the initial surface uplift of the Qiangtang Block, triggered by crustal thickening, was underway by the middle Eocene ( 42 Ma).

  13. The Oceanic Crust.

    ERIC Educational Resources Information Center

    Francheteau, Jean

    1983-01-01

    The earth's oceanic crust is created and destroyed in a flow outward from midocean ridges to subduction zones, where it plunges back into the mantle. The nature and dynamics of the crust, instrumentation used in investigations of this earth feature, and research efforts/findings are discussed. (JN)

  14. The Oceanic Crust.

    ERIC Educational Resources Information Center

    Francheteau, Jean

    1983-01-01

    The earth's oceanic crust is created and destroyed in a flow outward from midocean ridges to subduction zones, where it plunges back into the mantle. The nature and dynamics of the crust, instrumentation used in investigations of this earth feature, and research efforts/findings are discussed. (JN)

  15. Sandstone Diagenesis at Gale Crater, Mars, As Observed By Curiosity

    NASA Astrophysics Data System (ADS)

    Siebach, K. L.; Grotzinger, J. P.; McLennan, S. M.; Hurowitz, J.; Kah, L. C.; Edgett, K. S.; Williams, R. M. E.; Wiens, R. C.; Schieber, J.

    2014-12-01

    The Mars Science Laboratory rover, Curiosity, has encountered a significant number of poorly-sorted and very well-lithified sandstones along its traverse on the floor of Gale Crater. We use images from the hand-lens imager (MAHLI) and elemental chemistry from the ChemCam laser-induced breakdown spectroscopy instrument (LIBS) and the alpha-particle x-ray spectrometer (APXS) to begin to constrain the diagenetic history of these sandstones, including lithification and possible later dissolution. Investigation of MAHLI images reveals that the sediments are poorly-sorted and show very low apparent porosity, generally less than ~5%. However, in some cases, such as the Gillespie Lake sandstone identified in Yellowknife Bay, this apparent porosity includes a significant fraction of void spaces larger than typical sediment grain sizes (~30% by number or 75% of void spaces by area). One possible explanation of these larger pits is that they represent recent removal of soft intraclasts by eolian abrasion. Another possibility is that later diagenetic fluids caused dissolution of more soluble grains, and production of secondary porosity. Investigation into the elemental chemistry of the sandstones has shown that they have a relatively unaltered basaltic bulk composition in spite of possessing a variety of secondary minerals and amorphous material, indicating isochemical diagenetic processes. The chemistry and mineralogy of the cement is not immediately evident based on the initial analyses; there is not a high percentage of salts or evaporative minerals that may easily cement near-surface sandstones. Furthermore, these sandstones lack textures and compositions consistent with pedogenic processes, such as calcrete, silcrete, or ferricrete. Instead, they may record burial and cementation at depth. Cement composition may be constrained through comparison to terrestrial basaltic sandstones, and studying chemical variations along ChemCam and APXS transects of the rocks.

  16. Operation Sandstone: 1948. Technical report

    SciTech Connect

    Berkhouse, L.H.; Hallowell, J.H.; McMullan, F.W.; Davis, S.E.; Jones, C.B.

    1983-12-19

    SANDSTONE was a three-detonation atmospheric nuclear weapon test series conducted during the spring of 1948 at Enewetak Atoll in the Marshall Islands. Report emphasis is on the radiological safety of the personnel. Available records on personnel exposure are summarized.

  17. Microphytic crusts: 'topsoil' of the desert

    USGS Publications Warehouse

    Belnap, Jayne

    1990-01-01

    Deserts throughout the world are the home of microphytic, or cryptogamic, crusts. These crusts are dominated by cyanobacteria, previously called blue-green algae, and also include lichens, mosses, green algae, microfungi and bacteria. They are critical components of desert ecosystems, significantly modifying the surfaces on which they occur. In the cold deserts of the Colorado Plateau (including parts of Utah, Arizona, Colorado, and New Mexico), these crusts are extraordinarily well-developed, and may represent 70-80% of the living ground cover.

  18. Architecture of a transgressive systems tract: Tocito sandstone, New Mexico

    SciTech Connect

    Nummedal, D.; Swift, D.J.P.; Kofron, B.

    1988-02-01

    A sequence boundary is identified at the erosional base of the seaward units of the Tocito Sandstone by (1) a hiatus spanning three Inoceramus faunal zones, (2) basal onlap in the sequence above the hiatus as mapped in a pattern of progressively farther landward extent of younger bentonites, and (3) abrupt shallowing of facies across the hiatus. Traced up the depositional dip, the sequence boundary continues beneath a coarse fluvial sandstone (Torrivio sandstone) as demonstrated by incision of this unit into an underlying strand plain, the Gallup Sandstone. Individual Tocito sand bodies climb successively higher in the stratigraphic section when traced updip. Underlying these inferred shelf sand ridges is a landward-thickening wedge of fluvial strata (Dilco Coal Member of the Crevasse Canyon Formation), the expected consequence of trapping of siliciclastics on the transgressive coastal plain. The retrogradational deposits (Borrego Pass sandstone) constitute parasequences within the overall transgressive systems tract of the Tocito depositional sequence. The Tocito sand bodies are underlain by a stair-stepping set of ravinement surfaces, cut during episodes of shoreface retreat. They are overlain by parasequence condensed sections which appear to merge seaward into a major regional condensed section within the calcareous lower part of the Mulatto shale member of the upper Mancos Shale.

  19. Origin of the Lunar Highland Crust

    NASA Technical Reports Server (NTRS)

    Lowman, P. D., Jr.

    2005-01-01

    Understanding the origin of the oldest lunar crust was a main scientific objective of the last three Apollo missions, 15, 16, and 17, all of which landed in or near highland exposures. Starting with Apollo 15, the astronauts took hundreds of 70 mm surface photographs. These pictures have been re-studied, and reveal pervasive layering in the lunar highland crust visited by the Apollo 15, 16, and 17 missions. Additional information is included in the original extended abstract.

  20. Contractional deformation of porous sandstone: Insights from the Aztec Sandstone, SE Nevada, USA

    NASA Astrophysics Data System (ADS)

    Fossen, Haakon; Zuluaga, Luisa F.; Ballas, Gregory; Soliva, Roger; Rotevatn, Atle

    2015-05-01

    Contractional deformation of highly porous sandstones is poorly explored, as compared to extensional deformation of such sedimentary rocks. In this work we explore the highly porous Aztec Sandstone in the footwall to the Muddy Mountain thrust in SE Nevada, which contains several types of deformation bands in the Buffington tectonic window: 1) Distributed centimeter-thick shear-enhanced compaction bands (SECBs) and 2) rare pure compaction bands (PCBs) in the most porous parts of the sandstone, cut by 3) thin cataclastic shear-dominated bands (CSBs) with local slip surfaces. Geometric and kinematic analysis of the SECBs, the PCBs and most of the CSBs shows that they formed during ∼E-W (∼100) shortening, consistent with thrusting related to the Cretaceous to early Paleogene Sevier orogeny of the North American Cordilleran thrust system. Based on stress path modeling, we suggest that the compactional bands (PCBs and SECBs) formed during contraction at relatively shallow burial depths, before or at early stages of emplacement of the Muddy Mountains thrust sheet. The younger cataclastic shear bands (CSBs, category 3), also related to E-W Sevier thrusting, are thinner and show larger shear offsets and thus more intense cataclasis, consistent with the initiation of cataclastic shear bands in somewhat less porous materials. Observations made in this work support earlier suggestions that contraction lead to more distributed band populations than what is commonly found in the extensional regime, and that shear-enhanced compaction bands are widespread only where porosity (and permeability) is high.

  1. Magnetic structure of the crust

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.

    1985-01-01

    The bibuniqueness aspect of geophysical interpretation must be constrained by geological insight to limit the range of theoretically possible models. An additional step in depth understanding of the relationship between rock magnetization and geological circumstances on a grand scale is required. Views about crustal structure and the distribution of lithologies suggests a complex situation with lateral and vertical variability at all levels in the crust. Volcanic, plutonic, and metamorphic processes together with each of the observed anomalies. Important questions are addressed: (1) the location of the magnetic bottom; (2) whether the source is a discrete one or are certain parts of the crust cumulatively contributing to the overall magnetization; (3) if the anomaly to some recognizable surface expression is localized, how to arrive at a geologically realistic model incorporating magnetization contrasts which are realistic; (3) in the way the primary mineralogies are altered by metamorphism and the resulting magnetic contracts; (4) the effects of temperature and pressure on magnetization.

  2. Experimental investigation on mechanical damage characteristics of sandstone under triaxial cyclic loading

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Ranjith, P. G.; Huang, Yan-Hua; Yin, Peng-Fei; Jing, Hong-Wen; Gui, Yi-Lin; Yu, Qing-Lei

    2015-05-01

    The mechanical damage characteristics of sandstone subjected to cyclic loading is very significant to evaluate the stability and safety of deep excavation damage zones. However to date, there are very few triaxial experimental studies of sandstone under cyclic loading. Moreover, few X-ray micro-computed tomography (micro-CT) observations have been adopted to reveal the damage mechanism of sandstone under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic loading tests and X-ray micro-CT observations were conducted to analyse the mechanical damage characteristics of sandstone with respect to different confining pressures. The results indicated that at lower confining pressures, the triaxial strength of sandstone specimens under cyclic loading is higher than that under monotonic loading; whereas at confining pressures above 20 MPa, the triaxial strength of sandstone under cyclic loading is approximately equal to that under monotonic loading. With the increase of cycle number, the crack damage threshold of sandstone first increases, and then significantly decreases and finally remains constant. Based on the damage evolution of irreversible deformation, it appears that the axial damage value of sandstone is all higher than the radial damage value before the peak strength; whereas the radial damage value is higher than the axial damage value after the peak strength. The evolution of Young's modulus and Poisson's ratio of sandstone can be characterized as having four stages: (i) Stage I: material strengthening; (ii) Stage II: material degradation; (iii) Stage III: material failure and (iv) Stage IV: structure slippage. X-ray micro-CT observations demonstrated that the CT scanning surface images of sandstone specimens are consistent with actual surface crack photographs. The analysis of the cross-sections of sandstone supports that the system of crack planes under triaxial cyclic loading is much more complicated than that under triaxial

  3. Weathering behavior investigations and treatment of Kom Ombo temple sandstone, Egypt - Based on their sedimentological and petrogaphical information

    NASA Astrophysics Data System (ADS)

    Temraz, Mostafa Gouda; Khallaf, Mohamed K.

    2016-01-01

    The Temple of Kom Ombo is a huge ancient Egyptian temple in Upper Egypt. It was built by Ptolemy VI Philometor (180-145 BC) and added to by subsequent Ptolemys. The structure of the temple is built of local sandstone attributed to the Quseir Formation of "Nubian Sandstone" group at Gebel el-Silsila. Sandstone samples from Kom Ombo temple were taken to verify the source rock of the quarried material. Optical Polarizing Microscope (OPM) and Scanning Electron Microscope (SEM) were used to determine the microstructure and physical properties of the sandstone. X-Ray diffraction (XRD) was carried out for the Sandstone samples to identify its mineralogical composition. The sandstone samples were treated with six polymeric products to determine changes in their physical and mechanical properties after penetration, consolidation of polymers within them. This sandstone is composed mainly of three quartz arenite microfacies (feldspathic, sublithic and calcareous) that are interpreted to have been deposited in fluvial to fluvial-marine environment. Silane polymers is showing a good penetration and filling pores between grains and recommended for treatment and conservation of the sandstone. Acrylic polymer shows random penetration of polymer and formation of a film of polymer on the surface of sandstone. Silo11 gave the best result in consolidation of sandstone samples then primal AC33. Wacker BS29 gave the best result in isolating process of sandstone samples, then wacker BS 290.

  4. Icelandic-type crust

    USGS Publications Warehouse

    Foulger, G.R.; Du, Z.; Julian, B.R.

    2003-01-01

    Numerous seismic studies, in particular using receiver functions and explosion seismology, have provided a detailed picture of the structure and thickness of the crust beneath the Iceland transverse ridge. We review the results and propose a structural model that is consistent with all the observations. The upper crust is typically 7 ?? 1 km thick, heterogeneous and has high velocity gradients. The lower crust is typically 15-30 ?? 5 km thick and begins where the velocity gradient decreases radically. This generally occurs at the V p ??? 6.5 km s-1 level. A low-velocity zone ??? 10 000 km2 in area and up to ??? 15 km thick occupies the lower crust beneath central Iceland, and may represent a submerged, trapped oceanic microplate. The crust-mantle boundary is a transition zone ???5 ?? 3 km thick throughout which V p increases progressively from ???7.2 to ???8.0 km s-1. It may be gradational or a zone of alternating high- and low-velocity layers. There is no seismic evidence for melt or exceptionally high temperatures in or near this zone. Isostasy indicates that the density contrast between the lower crust and the mantle is only ???90 kg m-3 compared with ???300 kg m-3 for normal oceanic crust, indicating compositional anomalies that are as yet not understood. The seismological crust is ???30 km thick beneath the Greenland-Iceland and Iceland-Faeroe ridges, and eastern Iceland, ???20 km beneath western Iceland, and ???40 km thick beneath central Iceland. This pattern is not what is predicted for an eastward-migrating plume. Low attenuation and normal V p/V s ratios in the lower crust beneath central and southwestern Iceland, and normal uppermost mantle velocities in general, suggest that the crust and uppermost mantle are subsolidus and cooler than at equivalent depths beneath the East Pacific Rise. Seismic data from Iceland have historically been interpreted both in terms of thin-hot and thick-cold crust models, both of which have been cited as supporting the plume

  5. Polygonal deformation bands in sandstone

    NASA Astrophysics Data System (ADS)

    Antonellini, Marco; Nella Mollema, Pauline

    2017-04-01

    We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are dm-wide zones of shear deformation bands that developed under shallow burial conditions in the lower portion of the Jurassic Entrada Fm (Utah, USA). The edges of the polygons are 1 to 5 meters long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain < 0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. Density inversion, that takes place where under-compacted and over-pressurized layers (Carmel Fm) lay below normally compacted sediments (Entrada Sandstone), may be an important process for polygonal deformation bands formation. The gravitational sliding and soft sediment structures typically observed within the Carmel Fm support this hypothesis. Soft sediment deformation may induce polygonal faulting in the section of the Entrada Sandstone just above the Carmel Fm. The permeability of the polygonal deformation bands is approximately 10-14 to 10-13 m2, which is less than the permeability of the host, Entrada Sandstone (range 10-12 to 10-11 m2). The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes.

  6. Tidal influence within Pennsylvanian sandstones

    SciTech Connect

    Archer, A.W. )

    1991-08-01

    Within Pennsylvanian-age strata of the Illinois basin, large-scale linear sand bodies have been previously interpreted as fluvial and deltaic in origin. Nonetheless, analyses of fine-scale sedimentology and bed forms within such sandstones and the associated shales indicate that tidal processes greatly influenced the depositional environments within such lithofacies. Recent work on Mid-Continent Pennsylvanian-age sandstones indicates the occurrence of similar depositional environments. Based upon the pervasive tidal influence observed within such strata, environmental analogs other than fluvial and deltaic bear consideration. In general, tidally influenced estuarine models seem particularly appropriate. Within such settings, the changeover from a fluvially dominated deposystem to tidally influenced estuary occurs during transgressive phases. Despite the tidal influence that can be interpreted from the sedimentology, the strata contain few, if any, marine indicators because of the low salinities that occurred during deposition. Ongoing work in the Mid-Continent indicates that Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian sands share a number of similarities with the tidally influenced environments delineated in the Illinois basin studies. Thus a tidal/estuarine interpretation might be a generalizable model for many Pennsylvanian sandstones. In addition, enhanced understanding of the siliciclastic parts of Mid-Continent cyclothems provides a more useful framework for documentation of carbonate/siliciclastic interrelationships. Oscillations of carbonate/siliciclastic environments may be more readily explainable by climatic cycles rather than by traditionally popular depth-related facies models.

  7. Magnetization of the Lunar Crust

    NASA Technical Reports Server (NTRS)

    Carley, R. A.; Whaler, K. A.; Purucker, M. E.; Halekas, J. S.

    2012-01-01

    Magnetic fields measured by the satellite Lunar Prospector show large scale features resulting from remanently magnetized crust. Vector data synthesized at satellite altitude from a spherical harmonic model of the lunar crustal field, and the radial component of the magnetometer data, have been used to produce spatially continuous global magnetization models for the lunar crust. The magnetization is expressed in terms of localized basis functions, with a magnetization solution selected having the smallest root-mean square magnetization for a given fit to the data, controlled by a damping parameter. Suites of magnetization models for layers with thicknesses between 10 and 50 km are able to reproduce much of the input data, with global misfits of less than 0.5 nT (within the uncertainties of the data), and some surface field estimates. The magnetization distributions show robust magnitudes for a range of model thicknesses and damping parameters, however the magnetization direction is unconstrained. These global models suggest that magnetized sources of the lunar crust can be represented by a 30 km thick magnetized layer. Average magnetization values in magnetized regions are 30-40 mA/m, similar to the measured magnetizations of the Apollo samples and significantly weaker than crustal magnetizations for Mars and the Earth. These are the first global magnetization models for the Moon, providing lower bounds on the magnitude of lunar crustal magnetization in the absence of multiple sample returns, and can be used to predict the crustal contribution to the lunar magnetic field at a particular location.

  8. The Tuscarora Sandstone is marine--At least in southwestern Virginia

    SciTech Connect

    Dorsch, J.; Driese, S.G. . Dept. of Geological Sciences)

    1993-03-01

    The Tuscarora Sandstone (Upper Ordovician-Lower Silurian) forms part of the Martinsburg-Shawangunk clastic wedge, which represents the fill of a peripheral foredeep formed during the Taconic orogeny in the central Appalachians. The Tuscarora Sandstone is split into the lower Tuscarora Sandstone (LT) and the upper Tuscarora Sandstone (UT) by the regional Tuscarora Unconformity (TU). The TU formed by isostatic basin rebound during a lull in Taconic compressional tectonism. The LT interfingers with red beds of the upper Juniata Fm., and caps a coarsening-upward trend which commenced within the Martinsburg Fm. The LT is dominated by high-angle cross-stratified sandstone with arthrophycus, Planolites, Cruziana, and abundant Rusophycus, Monocraterion, and Skolithos traces. The coarser-grained sandstone beds represent subaqueous dunes deposited in a storm-dominated shallow-marine environment. Interbedded mudstone represents fairweather deposits. Present-day distribution and thickness of the LT is governed by original depositional geometry and by erosional removal beneath the TU. The UT is bounded at its base by the TU and at its top by a marine flooding surface marking the onset of deposition of the Rose Hill Formation. The UT is composed of: (1) basal, cross-stratified, gravelly sandstone representing uppermost upper shoreface deposits; (2) high-angle cross-stratified sandstone representing storm-enhanced rip-current deposits of the upper shoreface; (3) hummocky cross-stratified sandstone representing storm deposits of the middle and lower shoreface; (4) dark-colored fine-grained mudstone to sandstone representing fairweather deposits of the upper shoreface. The storm-dominated shoreface deposits of the UT constitute a retrogradational parasequence formed during a tectonically induced relative sea-level rise. To the southwest of Wytheville, VA, the TU and LT disappear, and the white quartzarenite is more appropriately designated as Clinch Sandstone.

  9. The oceanic crust as a bioreactor

    NASA Astrophysics Data System (ADS)

    Staudigel, Hubert; Tebo, Bradley; Yayanos, Art; Furnes, Harald; Kelley, Katie; Plank, Terry; Muehlenbachs, Karlis

    Various lines of evidence suggest that large portions of hydrothermal systems in the oceanic crust acts like a giant bioreactor that mediates water-rock exchange and buffers the chemical composition of seawater. We review the current literature and present new chemical, biological and petrographic data on microbially mediated alteration of glass in the oceanic crust. Microbial alteration of glass displays characteristic bioalteration features, in particular in the alteration fronts around residual glass in the oceanic crust, suggesting that microbes take on an active role in its dissolution. Such features are found throughout the oceanic crust ranging in age from a few million to 170 Ma and they are found down to crustal depths of 500 m, possibly defining a Deep Oceanic Biosphere (DOB) that covers up to 2/3 of the earth's surface area. Microbial glass alteration substantially increases the active surface area of dissolving glass particles thereby enhancing the reaction rates during microbially aided dissolution. Microbially mediated glass alteration involves the establishment of two types of diffusion barriers including hydration rinds and biofilms that play an important role in mediating glass alteration. In particular biofilms may be very active by creating a localized chemical environment conducive to glass alteration, and by sequestering dissolved chemical inventory from solution. When compared with abiotic alteration of the oceanic crust, bio-alteration causes more rapid deposition of biotic and abiotic reaction products in the oceanic crust that result in a more effective removal of elements from seawater and a more rapid sealing of the oceanic crust. Thus, it is likely that microbial activity increases the fluxes of seawater components into the crust, while reducing the low—temperature flux of basalt components into seawater. However, much about the microbial activity and its relationships to the chemistry of hydrothermal systems still remains to be

  10. Corium crust strength measurements.

    SciTech Connect

    Lomperski, S.; Nuclear Engineering Division

    2009-11-01

    Corium strength is of interest in the context of a severe reactor accident in which molten core material melts through the reactor vessel and collects on the containment basemat. Some accident management strategies involve pouring water over the melt to solidify it and halt corium/concrete interactions. The effectiveness of this method could be influenced by the strength of the corium crust at the interface between the melt and coolant. A strong, coherent crust anchored to the containment walls could allow the yet-molten corium to fall away from the crust as it erodes the basemat, thereby thermally decoupling the melt from the coolant and sharply reducing the cooling rate. This paper presents a diverse collection of measurements of the mechanical strength of corium. The data is based on load tests of corium samples in three different contexts: (1) small blocks cut from the debris of the large-scale MACE experiments, (2) 30 cm-diameter, 75 kg ingots produced by SSWICS quench tests, and (3) high temperature crusts loaded during large-scale corium/concrete interaction (CCI) tests. In every case the corium consisted of varying proportions of UO{sub 2}, ZrO{sub 2}, and the constituents of concrete to represent a LWR melt at different stages of a molten core/concrete interaction. The collection of data was used to assess the strength and stability of an anchored, plant-scale crust. The results indicate that such a crust is likely to be too weak to support itself above the melt. It is therefore improbable that an anchored crust configuration could persist and the melt become thermally decoupled from the water layer to restrict cooling and prolong an attack of the reactor cavity concrete.

  11. Growth of the lower continental crust

    NASA Technical Reports Server (NTRS)

    Rudnick, Roberta L.

    1988-01-01

    One of the largest uncertainties in crustal composition and growth models is the nature of the lower continental crust. Specifically, by what processes is it formed and modified, and when is it formed, particularly in reference to the upper crust? The main reason for this lack of information is the scarcity of lower crustal rock samples. These are restricted to two types: rocks which outcrop in granulite facies terrains and granulite facies xenoliths which are transported to the earth's surface by young volcanics. The important conclusions arising from the xenolith studies are: the majority of mafic lower crustal xenoliths formed through cumulate process, resitic xenoliths are rare; and formation and metamorphism of the deep crust is intimately linked to igneous activity and/or orogeny which are manifest in one form or another at the earth's surface. Therefore, estimates of crustal growth based on surface exposures is representative, although the proportion of remobilized pre-existing crust may be significantly greater at the surface than in the deep crust.

  12. Dynamic triggering during rupture nucleation in sandstone

    NASA Astrophysics Data System (ADS)

    Chanard, K.; Nicolas, A.; Latour, S.; Hatano, T.; Vinciguerra, S.; Schubnel, A.

    2016-12-01

    Fluid induced stress perturbations in the crust at seismogenic depths can be caused by various sources, such as deglaciation unloading, magmatic intrusion or fluid injection and withdrawal. Numbers of studies have robustly shown their link to earthquake triggering. However, the role of small periodic stress variations induced by solid earth and oceanic tides or seasonal hydrology in the seismic cycle, of the order of a few kPa, remains unclear. Indeed, the existence or absence of correlation between these loading phenomena and earthquakes have been equally proposed in the literature. To investigate this question, we performed a set of triaxial deformation experiments on porous water-saturated Fontainebleau sandstones. Rock samples were loaded by the combined action of steps of constant stress (creep), intended to simulate tectonic loading and small sinusoidal pore pressure variations with a range of amplitudes, analogous to tides or seasonal loading. All tests were conducted at a regulated temperature of 35C and a constant 35 MPa confining pressure. Our experimental results show that (1) pore pressure oscillations do not seem to influence the deformation rate at which the rock fails, (2) they correlate with acoustic emissions. Even more interestingly, we observe a progressive increase of the correlation coefficient in time as the rock approaches failure. The correlation coefficient is also sensitive to the amplitude of pore pressure oscillations as larger oscillations produce higher correlation levels. Finally, we show that, in the last hours of creep before failure, acoustic emissions occur significantly more when the pore pressure is at its lowest. This suggest that the correlation of small stress perturbations and acoustic emissions depend on the state stress of a rock and the amplitude of the perturbations and that emissions occur more likely when cracks are unclamped.

  13. Raising the continental crust

    NASA Astrophysics Data System (ADS)

    Campbell, Ian H.; Davies, D. Rhodri

    2017-02-01

    The changes that occur at the boundary between the Archean and Proterozoic eons are arguably the most fundamental to affect the evolution of Earth's continental crust. The principal component of Archean continental crust is Granite-Greenstone Terranes (GGTs), with granites always dominant. The greenstones consist of a lower sequence of submarine komatiites and basalts, which erupted onto a pre-existing Tonalite-Trondhjemite-Granodiorite (TTG) crust. These basaltic rocks pass upwards initially into evolved volcanic rocks, such as andesites and dacites and, subsequently, into reworked felsic pyroclastic material and immature sediments. This transition coincides with widespread emplacement of granitoids, which stabilised (cratonised) the continental crust. Proterozoic supra-crustal rocks, on the other hand, are dominated by extensive flat-lying platform sequences of mature sediments, which were deposited on stable cratonic basements, with basaltic rocks appreciably less abundant. The siliceous TTGs cannot be produced by direct melting of the mantle, with most hypotheses for their origin requiring them to be underlain by a complimentary dense amphibole-garnet-pyroxenite root, which we suggest acted as ballast to the early continents. Ubiquitous continental pillow basalts in Archean lower greenstone sequences require the early continental crust to have been sub-marine, whereas the appearance of abundant clastic sediments, at higher stratigraphic levels, shows that it had emerged above sea level by the time of sedimentation. We hypothesise that the production of komatiites and associated basalts, the rise of the continental crust, widespread melting of the continental crust, the onset of sedimentation and subsequent cratonisation form a continuum that is the direct result of removal of the continent's dense amphibole-garnet-pyroxenite roots, triggered at a regional scale by the arrival of a mantle plume at the base of the lithosphere. Our idealised calculations suggest

  14. Preliminary evaluation of the basal sandstone in Tennessee for receiving injected wastes

    USGS Publications Warehouse

    Mulderink, Dolores; Bradley, M.W.

    1986-01-01

    The EPA is authorized, under the Safe Drinking Water Act, to administer the Underground Injection Control program. This program allows for the regulation of deep-well disposal of wastes and establishes criteria to protect underground sources of drinking water from contamination. The basal sandstone in Tennessee occurs west of the Valley and Ridge province at depths of 5,000 to 9,000 ft below land surface. The basal sandstone consists of about 30 to 750 ft of Cambrian sandstone overlying the crystalline basement complex. The basal sandstone is overlain and confined by shale and carbonate rocks of the Middle and Upper Cambrian Conasauga Group. Hydrologic data for the basal sandstone, available from only three sites (four wells) in Tennessee, indicate that the basal sandstone generally has low porosity and permeability with a few zones having enough permeability to accept injected fluids. Limited water quality data indicate the basal sandstone contains water with dissolved solids concentrations exceeding 10,000 mg/L. Since the dissolved-solids concentrations exceed 10,000 mg/L, the basal sandstone is not classified as an underground source of drinking water according to EPA regulations. (Author 's abstract)

  15. Petrology, diagnosis, and sedimentology of oil reservoirs in Upper Cretaceous Shannon Sandstone Beds, Powder River basin, Wyoming

    SciTech Connect

    Hansley, P.L.; Whitney, C.G.

    1990-01-01

    This paper reports on a study of the petrology of the Shannon Sandstone Member that indicates diagenetic alterations of outcrop and near-surface sandstones cannot be used to predict the diagenesis of deeply buried sandstones. Textural relations show that oil migrated to reservoirs late in the postdepositional history of the Shannon. Petrologic and sedimentologic data suggest that an alternative depositional model (for example, a nearshore rather than mid-shelf setting) should be considered for the Shannon.

  16. Oxygen consumption in subseafloor basaltic crust

    NASA Astrophysics Data System (ADS)

    Orcutt, B. N.; Wheat, C. G.; Hulme, S.; Edwards, K. J.; Bach, W.

    2012-12-01

    Oceanic crust is the largest potential habitat for life on Earth and may contain a significant fraction of Earth's total microbial biomass, yet little is known about the form and function of life in this vast subseafloor realm that covers nearly two-thirds of the Earth's surface. A deep biosphere hosted in subseafloor basalts has been suggested from several lines of evidence; yet, empirical analysis of metabolic reaction rates in basaltic crust is lacking. Here we report the first measure of oxygen consumption in young (~ 8 Ma) and cool (<25 degrees C) basaltic crust, calculated from modeling oxygen and strontium profiles in basal sediments collected during Integrated Ocean Drilling Program (IODP) Expedition 336 to 'North Pond', a sediment 'pond' on the western flank of the Mid-Atlantic Ridge (MAR), where vigorous fluid circulation within basaltic crust occurs. Dissolved oxygen concentrations increased towards the sediment-basement interface, indicating an upward diffusional supply from oxic fluids circulating within the crust. A parametric reaction-transport model suggests oxygen consumption rates on the order of 0.5-500 nmol per cubic centimeter fluid per day in young and cool basaltic crust, providing sufficient energy to support a subsurface crustal biosphere.

  17. Building Archean cratons from Hadean mafic crust.

    PubMed

    O'Neil, Jonathan; Carlson, Richard W

    2017-03-17

    Geologic processing of Earth's surface has removed most of the evidence concerning the nature of Earth's first crust. One region of ancient crust is the Hudson Bay terrane of northeastern Canada, which is mainly composed of Neoarchean felsic crust and forms the nucleus of the Northeastern Superior Province. New data show these ~2.7-billion-year-old rocks to be the youngest to yield variability in neodymium-142 ((142)Nd), the decay product of short-lived samarium-146 ((146)Sm). Combined (146-147)Sm-(142-143)Nd data reveal that this large block of Archean crust formed by reworking of much older (>4.2 billion-year-old) mafic crust over a 1.5-billion-year interval of early Earth history. Thus, unlike on modern Earth, mafic crust apparently could survive for more than 1 billion years to form an important source rock for Archean crustal genesis. Copyright © 2017, American Association for the Advancement of Science.

  18. Kinetics of the crust thickness development of bread during baking.

    PubMed

    Soleimani Pour-Damanab, Alireza; Jafary, A; Rafiee, Sh

    2014-11-01

    The development of crust thickness of bread during baking is an important aspect of bread quality and shelf-life. Computer vision system was used for measuring the crust thickness via colorimetric properties of bread surface during baking process. Crust thickness had a negative and positive relationship with Lightness (L (*) ) and total color change (E (*) ) of bread surface, respectively. A linear negative trend was found between crust thickness and moisture ratio of bread samples. A simple mathematical model was proposed to predict the development of crust thickness of bread during baking, where the crust thickness was depended on moisture ratio that was described by the Page moisture losing model. The independent variables of the model were baking conditions, i.e. oven temperature and air velocity, and baking time. Consequently, the proposed model had well prediction ability, as the mean absolute estimation error of the model was 7.93 %.

  19. Pore-throat sizes in sandstones, tight sandstones, and shales

    USGS Publications Warehouse

    Nelson, Philip H.

    2009-01-01

    Pore-throat sizes in silidclastic rocks form a continuum from the submillimeter to the nanometer scale. That continuum is documented in this article using previously published data on the pore and pore-throat sizes of conventional reservoir rocks, tight-gas sandstones, and shales. For measures of central tendency (mean, mode, median), pore-throat sizes (diameters) are generally greater than 2 μm in conventional reservoir rocks, range from about 2 to 0.03 μm in tight-gas sandstones, and range from 0.1 to 0.005 μm in shales. Hydrocarbon molecules, asphaltenes, ring structures, paraffins, and methane, form another continuum, ranging from 100 Å (0.01 μm for asphaltenes to 3.8 A (0.00038 μm) for methane. The pore-throat size continuum provides a useful perspective for considering (1) the emplacement of petroleum in consolidated siliciclastics and (2) fluid flow through fine-grained source rocks now being exploited as reservoirs.

  20. Shelf sandstones of Twowells tongue, Dakota Sandstone, northwestern New Mexico

    SciTech Connect

    Wolter, N.R.; Nummedal, D.

    1988-01-01

    The Dakota Sandstone of northwestern New Mexico is composed of basal continental strata and three marine sandstone tongues, which intertongue was the Mancos Shale. The late Cenomanian Twowells tongue was the last tongue deposited in the Dakota transgressive systems tract. This tongue is most commonly gradationallly underlain by the Whitewater Arroyo shale tongue and abruptly overlain by the Rio Salado tongue of the Mancos Shale. Data collected from 85 outcrop sections and 180 electric well logs, from the San Juan, Acoma, and Zuni Basins, indicates that the Twowells tongue represents three phases of marine deposition. The White-water Arroyo shale tongue, the muddy burrowed facies, and the horizontally bedded facies of the Twowells tongue represent a shoaling-upward sequence (regressive phase) of shelf and shoreface deposition. The regressive phase is sharply overlain by an inferred transgressive cross-bedded facies. Erosional scour and an extensive pebble lag mark the contact between the regressive and the transgressive facies. In the Acoma basin, the transgressive cross-bedded facies describes a north-south oriented shelf-sand ridge 32 km long, 18 km wide, and 32 m thick.

  1. Ophiolites and oceanic crust

    USGS Publications Warehouse

    Moores, E.M.; Jackson, E.D.

    1974-01-01

    OPHIOLITES consist of a pseudostratiform sequence, of harzburgite, tectonite, ultramafic and mafic cumulates sometimes including gabbro and quartz diorite (plagiogranite) intrusions, dolerite dyke swarms, pillow lava 1, and deep-sea sediments2-4. This assemblage occurs in all Phanerozoic mountain systems and is interpreted as fossil oceanic crust and uppermost mantle5-10. Outstanding problems include differences between the chemical properties of Ophiolites and rocks thought to represent present-day oceanic crust11,12, the lack in some complexes of recognised dyke swarms or cumulates, and the relative thinness of ophiolite mafic rocks compared with standard oceanic crustal sections5,8,13. ?? 1974 Nature Publishing Group.

  2. Phase separation in the crust of accreting neutron stars.

    PubMed

    Horowitz, C J; Berry, D K; Brown, E F

    2007-06-01

    Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus.

  3. Phase separation in the crust of accreting neutron stars

    SciTech Connect

    Horowitz, C. J.; Berry, D. K.; Brown, E. F.

    2007-06-15

    Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus.

  4. A complex investigation of building sandstones from Saxony (Germany)

    SciTech Connect

    Goetze, Jens Siedel, Heiner

    2007-11-15

    The present paper provides a methodology for the investigation and characterization of building sandstones. This analytical scheme was designed for distinguishing mature arenites, which in general show very similar properties and are difficult to distinguish. This is shown for Cretaceous sandstones from various occurrences in Saxony (Germany), which have been used for centuries as building materials. The procedure is mainly based on the combination of macroscopic rock description, thin section polarizing microscopy (phase composition, texture, grain-size distribution) and cathodoluminescence (CL) microscopy (quartz types, feldspar and kaolinite content) coupled with image analysis, scanning electron microscopy (accessories, pore cement, diagenetic grain surface features), and analysis of pore space data. Sometimes, additional data from X-ray diffraction or chemical analyses (major and trace elements) can be used. Especially in the case of quartz rich arenites, CL is a powerful tool for provenance analysis. The detailed analysis of sandstone material in most cases allows us to assign historically used building material to a specific sandstone occurrence. These results are important for both interpreting the weathering behaviour of the building material and the conservation, reconstruction and stone replacement of historical monuments.

  5. Transdomes sampling of lower and middle crust

    NASA Astrophysics Data System (ADS)

    Teyssier, C. P.; Whitney, D. L.; Roger, F.; Rey, P. F.

    2015-12-01

    Migmatite transdomes are formed by lateral and upward flow of partially molten crust in transtension zones (pull-apart structures). In order to understand the flow leading to this type of domes, 3D numerical models were set-up to simulate the general case of an extensional domain located between two strike-slip faults (pull-apart or dilational bridge). Results show that upper crust extension induces flow of the deep, low-viscosity crust, with rapid upward movement of transdome material when extension becomes localized. At this point a rolling hinge detachment allows rapid removal of upper crust. The internal structure of transdomes includes a subvertical high strain zone located beneath the zone of localized upper crust extension; this shear zone separates two elongate subdomes of foliation that show refolded/sheath folds. Lineation tends to be oriented dominantly subhorizontal when the amount of strike-slip motion is greater than the amount of upward flow of dome rocks. Models also predict nearly isothermal decompression of transdome material and rapid transfer of ~50 km deep rocks to the near surface. These model results are compared to the structural and metamorphic history of several transdomes, and in particular the Variscan Montagne Noire dome (French Massif Central) that consists of two domes separated by a complex high strain zone. The Montagne Noire dome contains ~315 Ma eclogite bodies (U-Pb zircon age) that record 1.4 GPa peak pressure. The eclogite bodies are wrapped in highly sheared migmatite that yield 314-310 Ma monazite ages interpreted as the metamorphism and deformation age. Based on these relations we conclude that the Montagne Noire transdome developed a channel of partially molten crust that likely entrained eclogite bodies from the deep crust (~50 km) before ascending to the near-surface. One implication of this work is that the flowing crust was deeply seated in the orogen although it remained a poor recorder of peak pressure of metamorphism

  6. Surface to subsurface cross sections showing correlation of the Dakota Sandstone, Burro Canyon (?) Formation, and upper part of the Morrison Formation in the Chama-El Vado area, Chama Basin, Rio Arriba County, New Mexico

    USGS Publications Warehouse

    Ridgley, Jennie L.

    1987-01-01

    This report shows the correlation of the Dakota Sandstone, Burro Canyon(?) Formation, and the upper part of the Morrison Formation in the Chama basin from E1 Cerro dome, just west of Chama, to El Vado Reservoir. Criteria needed to recognize these formations both at the outcrop and in the subsurface is also included. 

  7. Biological Soil Crusts: Webs of Life in the Desert

    USGS Publications Warehouse

    Belnap, Jayne

    2001-01-01

    Although the soil surface may look like dirt to you, it is full of living organisms that are a vital part of desert ecosystems. This veneer of life is called a biological soil crust. These crusts are found throughout the world, from hot deserts to polar regions. Crusts generally cover all soil spaces not occupied by green plants. In many areas, they comprise over 70% of the living ground cover and are key in reducing erosion, increasing water retention, and increasing soil fertility. In most dry regions, these crusts are dominated by cyanobacteria (previously called blue-green algae), which are one of the oldest known life forms. Communities of soil crusts also include lichens, mosses, microfungi, bacteria, and green algae. These living organisms and their by-products create a continuous crust on the soil surface. The general color, surface appearance, and amount of coverage of these crusts vary depending on climate and disturbance patterns. Immature crusts are generally flat and the color of the soil, which makes them difficult to distinguish from bare ground. Mature crusts, in contrast, are usually bumpy and dark-colored due to the presence of lichens, mosses, and high densities of cyanobacteria and other organisms.

  8. Provenance and weathering depth of carbonaceous gotland sandstone by use of carbon and oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Åberg, G.; Löfvendahl, R.; Stijfhoorn, D.; Råheim, A.

    Carbon and oxygen isotope ratios of carbonates (calcite) from different sites and stratigraphic levels of the Gotland sandstone show that it might be possible to fingerprint the different quarries. Preliminary tests of nine samples of Gotland sandstone from different buildings show that the laser microprobe is an excellent tool for estimating depth of weathering on this carbonaceous sandstone. Analyses perpendicular to the stone surface gave a similar trend for the carbon and oxygen isotope ratios, although changes go deeper with δ13C than δ18O. Depth of weathering is controlled by exposure, location, biologic overgrowth and salt efflorescence. The effect of earlier conservation treatment with linseed oil can also be traced.

  9. Earthquakes in Stable Continental Crust.

    ERIC Educational Resources Information Center

    Johnston, Arch C.; Kanter, Lisa R.

    1990-01-01

    Discussed are some of the reasons for earthquakes which occur in stable crust away from familiar zones at the ends of tectonic plates. Crust stability and the reactivation of old faults are described using examples from India and Australia. (CW)

  10. Earthquakes in Stable Continental Crust.

    ERIC Educational Resources Information Center

    Johnston, Arch C.; Kanter, Lisa R.

    1990-01-01

    Discussed are some of the reasons for earthquakes which occur in stable crust away from familiar zones at the ends of tectonic plates. Crust stability and the reactivation of old faults are described using examples from India and Australia. (CW)

  11. Neutron star crusts

    NASA Technical Reports Server (NTRS)

    Lorenz, C. P.; Ravenhall, D. G.; Pethick, C. J.

    1993-01-01

    We calculate properties of neutron star matter at subnuclear densities using an improved nuclear Hamiltonian. Nuclei disappear and the matter becomes uniform at a density of about 0.6n(s), where n(s) of about 0.16/cu fm is the saturation density of nuclear matter. As a consequence, the mass of matter in the crusts of neutron stars is only about half as large as previously estimated. In about half of that crustal mass, nuclear matter occurs in shapes very different from the roughly spherical nuclei familiar at lower densities. The thinner crust and the unusual nuclear shape have important consequences for theories of the rotational and thermal evolution of neutron stars, especialy theories of glitches.

  12. Psoriasis or crusted scabies.

    PubMed

    Goyal, N N; Wong, G A

    2008-03-01

    We describe a case of a 67-year-old woman with a 1-year history of nail thickening and a non-itchy erythematous scaly eruption on the fingertips. She was diagnosed with psoriasis and started on methotrexate after having had no response to topical calcipotriol. The diagnosis was reviewed after it was revealed by another consultant that the patient's husband had been attending dermatology clinics for several years with chronic pruritus, which had been repeatedly thought to be due to scabies. Our patient was found to have crusted scabies after a positive skin scraping showed numerous mites. She was treated with topical permethrin, keratolytics and oral ivermectin. We also review the literature on crusted scabies and its management, with recommendations.

  13. Mars Crust: Made of Basalt

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-05-01

    By combining data from several sources, Harry Y. (Hap) McSween (University of Tennessee), G. Jeffrey Taylor (University of Hawaii) and Michael B. Wyatt (Brown University) show that the surface of Mars is composed mostly of basalt not unlike those that make up the Earth's oceanic crust. McSween and his colleagues used data from Martian meteorites, analyses of soils and rocks at robotic landing sites, and chemical and mineralogical information from orbiting spacecraft. The data show that Mars is composed mostly of rocks similar to terrestrial basalts called tholeiites, which make up most oceanic islands, mid-ocean ridges, and the seafloor beneath sediments. The Martian samples differ in some respects that reflect differences in the compositions of the Martian and terrestrial interiors, but in general are a lot like Earth basalts. Cosmochemistst have used the compositions of Martian meteorites to discriminate bulk properties of Mars and Earth, but McSween and coworkers' synthesis shows that the meteorites differ from most of the Martian crust (the meteorites have lower aluminum, for example), calling into question how diagnostic the meteorites are for understanding the Martian interior.

  14. Elemental composition of the Martian crust.

    PubMed

    McSween, Harry Y; Taylor, G Jeffrey; Wyatt, Michael B

    2009-05-08

    The composition of Mars' crust records the planet's integrated geologic history and provides clues to its differentiation. Spacecraft and meteorite data now provide a global view of the chemistry of the igneous crust that can be used to assess this history. Surface rocks on Mars are dominantly tholeiitic basalts formed by extensive partial melting and are not highly weathered. Siliceous or calc-alkaline rocks produced by melting and/or fractional crystallization of hydrated, recycled mantle sources, and silica-poor rocks produced by limited melting of alkali-rich mantle sources, are uncommon or absent. Spacecraft data suggest that martian meteorites are not representative of older, more voluminous crust and prompt questions about their use in defining diagnostic geochemical characteristics and in constraining mantle compositional models for Mars.

  15. Elemental Composition of the Martian Crust

    NASA Astrophysics Data System (ADS)

    McSween, Harry Y.; Taylor, G. Jeffrey; Wyatt, Michael B.

    2009-05-01

    The composition of Mars’ crust records the planet’s integrated geologic history and provides clues to its differentiation. Spacecraft and meteorite data now provide a global view of the chemistry of the igneous crust that can be used to assess this history. Surface rocks on Mars are dominantly tholeiitic basalts formed by extensive partial melting and are not highly weathered. Siliceous or calc-alkaline rocks produced by melting and/or fractional crystallization of hydrated, recycled mantle sources, and silica-poor rocks produced by limited melting of alkali-rich mantle sources, are uncommon or absent. Spacecraft data suggest that martian meteorites are not representative of older, more voluminous crust and prompt questions about their use in defining diagnostic geochemical characteristics and in constraining mantle compositional models for Mars.

  16. Deep-ocean ferromanganese crusts and nodules

    USGS Publications Warehouse

    Hein, James R.; Koschinsky, Andrea

    2014-01-01

    Ferromanganese crusts and nodules may provide a future resource for a large variety of metals, including many that are essential for emerging high- and green-technology applications. A brief review of nodules and crusts provides a setting for a discussion on the latest (past 10 years) research related to the geochemistry of sequestration of metals from seawater. Special attention is given to cobalt, nickel, titanium, rare earth elements and yttrium, bismuth, platinum, tungsten, tantalum, hafnium, tellurium, molybdenum, niobium, zirconium, and lithium. Sequestration from seawater by sorption, surface oxidation, substitution, and precipitation of discrete phases is discussed. Mechanisms of metal enrichment reflect modes of formation of the crusts and nodules, such as hydrogenetic (from seawater), diagenetic (from porewaters), and mixed diagenetic–hydrogenetic processes.

  17. Lower-Crustal and Upper-Mantle Seismicity beneath Aleutian Arc Volcanoes: A Temporal Link for Magmatic Processes between the Lower-Crust and the Surface

    NASA Astrophysics Data System (ADS)

    Power, J. A.; Stihler, S. D.; Ketner, D. M.; Haney, M. M.; Prejean, S. G.; Parker, T. J.

    2013-12-01

    Since 1989 the Alaska Volcano Observatory has identified more than 1,200 seismic events at upper-mantle to mid-crustal depths beneath 27 active Aleutian arc volcanic centers. Epicenters typically scatter broadly around the volcanoes at distances of as much as 25 km from the closest volcanic vent. Hypocenters for these events range typically from 15 to 45 km and the average depth is 25.1 km (σ1 = 8.1 km). Magnitudes of located events range from -0.25 to 2.9 and the average magnitude is 1.22 (σ1 = 0.5). Seismicity at these depths is unusual as it is generally considered below the brittle-ductile transition and suggests the involvement of pressurized fluids. These events provide some of the only direct evidence of the time history of magmatic processes in the lower-crust and upper-mantle, a portion of the magma pathway that is traditionally difficult to observe. The waveforms of these events exhibit the full range in frequency content typically seen in volcanic environments from broad spectrum (1 to 15 Hz) brittle failure, volcano-tectonic earthquakes, to peaked spectra (1 to 4 Hz), fluid resonance or long-period events. Most of the events are long-period or low-frequency in character and often have extended codas. These events occur both as solitary events and in sequences lasting from 2 to 30 minutes containing 3 to 10 individual events. Within the sequences individual events are often separated by volcanic tremor that shares the same spectral character as the seismic events themselves. All Aleutian arc volcanoes with suitable instrumentation and long-term monitoring exhibit some level of mid-crustal to upper-mantle seismicity. Spurr, Westdahl, Aniakchak and Akutan have the highest rates of upper-mantle to mid-crustal seismicity. Recent eruptions at Redoubt (2009) and Shishaldin (1999) were preceded by increases in lower-crustal seismicity as were episodes of unrest at Mount Spurr (2005), Trident (2008) and Little Sitkin (2012). The 1992 eruption of Mount Spurr

  18. Reservoir sandstone bodies in lower Silurian Clinton sandstone interval, eastern Ohio

    SciTech Connect

    Coogan, A.H.

    1987-09-01

    The stratigraphic relationships of the sandstones, shales, limestones, dolomites, and related beds of the Lower Silurian Clinton sandstone interval in Ohio have been examined using several thousand well logs from Medina County to Coshocton County in eastern Ohio. This north-south band of counties lies semiparallel to the north-northeast-trending depositional edge of the Clinton lower deltaic and coastal plain. Continuous and discontinuous bar sandstones with patterns similar to barrier island deposits are found at the edge of the deltaic plain. The thicker sandstone reservoirs in these deposits have been prolific oil and gas pools. The discontinuous bar sands are more common, however, and where drilling is sparse or where only the cleaner sandstones are mapped, these bar sands appear as isolated, thick, porous sandstone bodies. Examples exist in Holmes and Wayne Counties, Ohio. Elongate, nearly straight, narrow sandstone bodies occur on the lower deltaic plain, and were deposited in channels that were fluvial or partly estuarine. The channel sandstones are less than 1000 ft wide, extend for distances up to 10 mi and can be seen in Coshocton, Summit, and Medina Counties. The reservoirs in these sandstones are prolific oil and gas producers, but they are not easy to locate. At the seaward end of the elongate channel, sandstones are thick, localized sand bodies that fit in the sedimentological picture as river mouth bars. An example from Medina County illustrates this reservoir geometry at the site of excellent oil production from the Clinton interval.

  19. Uranium migration through intact sandstone cores

    NASA Astrophysics Data System (ADS)

    Read, D.; Lawless, T. A.; Sims, R. J.; Butter, K. R.

    1993-06-01

    Uranium is often considered to be a mobile radioelement in the natural environment owing to its tendency to form stable complexes with a number of aqueous anions, particularly in oxidising milieu. A series of infiltration experiments were devised to investigate this migration behaviour under rigidly controlled laboratory conditions. Intact cores of Permo-Triassic Clashach Sandstone were pre-equilibrated with synthetic groundwater solutions and continuous flow-through of uranium monitored together with pH and concentrations of other ions. Prior to performing each experiment a simulation was carried out using a one-dimensional coupled chemical transport code, encompassing a thermodynamic description of the electrical double layer. These calculations together with electron microscopy indicated the potential role played by iron oxyhydroxide grain coatings in retarding the uranium plume. Thus, a second series of experiments was initiated on pre-acidified cores from which all surface exposed iron had been removed, allowing an assessment of the retention capacity of non-ferric components. Taken together, the data clearly illustrate the strong affinity of aqueous uranium species for natural surfaces even under strongly oxidising conditions. The success of the model in predicting a priori the dominant trends in uranium migration behaviour is encouraging and may aid in prioritising analytical requirements for investigations in more complex geochemical situations than those studied here.

  20. Crust formation and its effect on the molten pool coolability

    SciTech Connect

    Park, R.J.; Lee, S.J.; Sim, S.K.

    1995-09-01

    Experimental and analytical studies of the crust formation and its effect on the molten pool coolability have been performed to examine the crust formation process as a function of boundary temperatures as well as to investigate heat transfer characteristics between molten pool and overlying water in order to evaluate coolability of the molten pool. The experimental test results have shown that the surface temperature of the bottom plate is a dominant parameter in the crust formation process of the molten pool. It is also found that the crust thickness of the case with direct coolant injection into the molten pool is greater than that of the case with a heat exchanger. Increasing mass flow rate of direct coolant injection to the molten pool does not affect the temperature of molten pool after the crust has been formed in the molten pool because the crust behaves as a thermal barrier. The Nusselt number between the molten pool and the coolant of the case with no crust formation is greater than that of the case with crust formation. The results of FLOW-3D analyses have shown that the temperature distribution contributes to the crust formation process due to Rayleigh-Benard natural convection flow.

  1. Investigating the effect of unloading on artificial sandstone behaviour using the Discrete Element Method

    NASA Astrophysics Data System (ADS)

    Huang, Yueqin; Cheng, Yi Pik; Coop, Matthew

    2017-06-01

    The Discrete Element Method (DEM) was used to simulate the mechanical behaviour of a reservoir sandstone. Triaxial tests were carried out using 3D-DEM to simulate the stress-strain behaviour of a sandstone with comparisons made between the numerical tests and the laboratory tests. The influence of isotropic unloading was investigated, which was found to have impacts on bond breakages and was successfully captured in the 3D shearing processes. It was found that bond breakages correlated strongly with the stress-strain behaviour of the sandstone affecting the peak strength. It was also found that unloading affected the bond breakages, which then changed the mechanical behaviour of sandstone. The tangent stiffnesses of simulated virgin and cored samples under different confining stresses were compared. From the tangent stiffnesses, gross yield envelopes and the yielding surfaces for unloaded samples and virgin samples were plotted and analysed in detail.

  2. Physical constraints on dolomite crust formation, Ambergris Cay Belize

    SciTech Connect

    Birdwell, B.A.; Bischoff, W.D.; Mazzullo, S.J. )

    1990-05-01

    Dolomitic crusts forming on a peritidal flat on Ambergris Cay, Belize, occur beneath surface sediment adjacent to, but not within, small saline (60-90 ppt) ponds. Upper crusts, 2-12 cm thick forming at or slightly below the water table (approximately equivalent to lagoon water level) are areally restricted by (1) ponds where sediment lies below 20-50 cm of water, (2) high and relatively dry areas where sediment accumulation of more than 15 cm above water level supports diverse vegetation, and (3) low areas affected by mangrove encroachment where preexisting crusts are perforated by roots and displaced. The lower crusts occur immediately above the Pleistocene in lows beneath the Holocene sediment and on exposed Pleistocene surfaces. Estimates from x-ray diffraction analysis indicate 80-100% dolomite content within the upper crusts and 50-60% dolomite content in the lower crusts. Unlithified sediment above and below the upper crust contain up to 80% dolomite. Compositions range from Ca{sub 56}, Mg{sub 44} in the upper crusts to Ca{sub 60} Mg{sub 40} in the lower crusts. There is no correlation between stoichiometry and ordering in the dolomites; all are poorly ordered as indicated by very weak (015) and (021) superstructure peaks. Where crusts are not 100% dolomite, the dolomite is evident as euhedral cements within pores, especially within foraminiferal tests, and as micrite along algal laminations and walls of burrows. However, preliminary examinations with scanning electron microscopy and energy dispersive x-ray mapping show that magnesium enrichment is pervasive within these crusts and may represent Mg-enrichment of calcite as an intermediate stage in dolomite formation.

  3. Aleutian basin oceanic crust

    USGS Publications Warehouse

    Christeson, Gail L.; Barth, Ginger A.

    2015-01-01

    We present two-dimensional P-wave velocity structure along two wide-angle ocean bottom seismometer profiles from the Aleutian basin in the Bering Sea. The basement here is commonly considered to be trapped oceanic crust, yet there is a change in orientation of magnetic lineations and gravity features within the basin that might reflect later processes. Line 1 extends ∼225 km from southwest to northeast, while Line 2 extends ∼225 km from northwest to southeast and crosses the observed change in magnetic lineation orientation. Velocities of the sediment layer increase from 2.0 km/s at the seafloor to 3.0–3.4 km/s just above basement, crustal velocities increase from 5.1–5.6 km/s at the top of basement to 7.0–7.1 km/s at the base of the crust, and upper mantle velocities are 8.1–8.2 km/s. Average sediment thickness is 3.8–3.9 km for both profiles. Crustal thickness varies from 6.2 to 9.6 km, with average thickness of 7.2 km on Line 1 and 8.8 km on Line 2. There is no clear change in crustal structure associated with a change in orientation of magnetic lineations and gravity features. The velocity structure is consistent with that of normal or thickened oceanic crust. The observed increase in crustal thickness from west to east is interpreted as reflecting an increase in melt supply during crustal formation.

  4. Diagenetic history of fluvial and lacustrine sandstones of the Hartford Basin (Triassic Jurassic), Newark Supergroup, USA

    NASA Astrophysics Data System (ADS)

    Wolela, A. M.; Gierlowski-Kordesch, E. H.

    2007-04-01

    The early introduction of clays into continental sandstones has been attributed to mechanical infiltration by percolation of clay-rich surface waters into grain framework or cutans formed from pedogenic processes. The discovery of pedogenic mud aggregates as traction-load mud in ancient fluvial deposits suggests that permeability and porosity of terrigenous sandstones can be influenced at deposition and control early diagenetic patterns. This study compares diagenesis in fluvial (subaerially exposed) sandstones with lacustrine (subaqueous) sandstones in a Triassic-Jurassic continental rift basin (Hartford Basin, Newark Supergroup). Diversity of diagenetic minerals and sequence of diagenetic alteration can be directly related to depositional environment. The fluvial sandstones in the New Haven Arkose, East Berlin Formation, and Shuttle Meadow Formation of the Hartford Basin are dominated by concretionary calcite and early calcite cement, infiltrated clays (illite-smectite), pedogenic mud aggregates (smectite and illite-smectite), grain coating clays (illite/hematite, illite-chlorite/hematite), quartz overgrowths, late stage carbonate cements (calcite, ferroan calcite), pore-filling clays (illite, kaolinite with minor amounts of smectite, smectite-chlorite, illite-smectite) and hematite. However, pedogenic processes in these fluvial sandstones retarded the development of quartz and feldspar overgrowths, and carbonate authigenesis, as well as the quality of diagenetically enhanced porosity. Dark gray-black lacustrine (subaqueous) sandstones and mudrocks in the East Berlin and Shuttle Meadow Formations are dominated by pyrite, concretionary dolomite and early dolomite cement, radial grain coating clays (smectite-chlorite, illite-smectite), late stage carbonate cements (dolomite, ferroan dolomite, ankerite), albite and pore-filling clays (smectite-chlorite, illite-smectite, illite-chlorite). Clay minerals exist as detrital, mechanically infiltrated, and neoformed clay

  5. [Crusted scabies: A review].

    PubMed

    Jouret, G; Bounemeur, R; Presle, A; Takin, R

    2016-04-01

    Crusted scabies is a rare and severe form of infestation by Sarcoptes scabies var. hominis. It is characterized by profuse hyperkeratosis containing over 4000 mites per gram of skin, with treatment being long and difficult. The condition is both direct and indirectly contagious. It has a central role in epidemic cycles of scabies, the incidence of which is on the rise in economically stable countries. Recent discoveries concerning the biology of mites, the pathophysiology of hyperkeratosis and the key role of IL-17 in this severe form open up new therapeutic perspectives. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

  6. The influence of biological soil crusts on dew deposition in Gurbantunggut Desert, Northwestern China

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Zhang, Yuan-ming; Downing, Alison; Cheng, Jun-hui; Zhou, Xiao-bing; Zhang, Bing-chang

    2009-12-01

    SummaryDew is an important source of moisture for plants, biological soil crusts, invertebrates and small vertebrates in desert environments. In this paper, measurements were taken to investigate the effects of three different types of biological soil crusts (cyanobacteria, lichen and moss) and bare sand on dew deposition in the Gurbantunggut Desert. Dew quantities were measured using micro-lysimeters with a diameter of 6 cm and a height of 3.5 cm. The results showed that the total amount of dew deposited increased with the development of soil crusts, from bare sand to cyanobacterial crust to lichen crust to moss crust. The average amount of dew deposited daily on the moss crust was the highest of all and it was significant higher than the other three soil surfaces (lichen crust, cyanobacterial crust and bare sand) ( p < 0.05). During the period of the study, for each type of crust studied, the maximum amount of dew recorded was several times greater than the minimum. Moss crust was characterized by having the greatest amount of dew at dawn and also the maximum amount of dew deposited, whereas bare sand yielded the lowest amount of dew, with lichen crust and cyanobacterial crust exhibiting intermediate values. However, this was not the case for dew duration, as bare sand retained moisture for the longest period of time, followed by cyanobacterial crust, moss crust and finally lichen crust. Dew continued to condense even after sunrise. Furthermore, the differences in dew deposition may be partially attributed to an effect of the biological soil crusts on surface area. This study demonstrates the important effect of biological soil crusts upon dew deposition and may assist in evaluating the role of dew in arid and semi-arid environments.

  7. Jumbling, oozing, underplating, and delamination of Himalayan-Tibetan crust

    NASA Astrophysics Data System (ADS)

    Song, X.; Xu, Z.

    2010-12-01

    The modes of deformation of crust and mantle lithosphere after the Indian-Eurasian collision has been a long standing debate. Here we present high resolution imaging results from ambient noise surface wave tomography using Hi-CLIMB array data in western Tibet (roughly along 85 deg east). The combination of our much improved regional shear-wave velocity model (presented separately by Xu et al. in this meeting) and the dense array allows us to image the deformation of the crust along the profile in unprecedented details. The lndian crust is observed to subduct and underplate the Tibetan crust to between Yaluzangbu Suture and Banggong-Niujiang Suture, where it is highly deformed and delaminated. The crust in the region is highly deformed as evidenced by irregular shapes of velocity heterogeneities. A continuous low velocity zone is present in the mid-crust, which seems to ooze and tunnel through the crust and emerge near the surface at the Himalayan front. The observation provides a direct support for the channel flow and ductile extrusion model for the evolution of the Himalayan-Tibetan crust.

  8. Location of Mars Sandstone Target Windjana

    NASA Image and Video Library

    2014-04-25

    In this Mars Reconnaissance Orbiter view of the Curiosity rover mission waypoint called the Kimberley, the red dot indicates the location of a sandstone target, Windjana, selected for close-up inspection.

  9. Knobbly Textured Sandstone on Mount Sharp, Mars

    NASA Image and Video Library

    2016-03-11

    Patches of Martian sandstone visible in this view from NASA Curiosity Mars rover have a knobbly texture due to nodules apparently more resistant to erosion than the host rock in which some are still embedded.

  10. The Mafic Lower Crust of Neoproterozoic age beneath Western Arabia: Implications for Understanding African Lower Crust

    NASA Astrophysics Data System (ADS)

    Stern, R. J.; Mooney, W. D.

    2011-12-01

    We review evidence that the lower crust of Arabia - and by implication, that beneath much of Africa was formed at the same time as the upper crust, rather than being a product of Cenozoic magmatic underplating. Arabia is a recent orphan of Africa, separated by opening of the Red Sea ~20 Ma, so our understanding of its lower crust provides insights into that of Africa. Arabian Shield (exposed in W. Arabia) is mostly Neoproterozoic (880-540 Ma) reflecting a 300-million year process of continental crustal growth due to amalgamated juvenile magmatic arcs welded together by granitoid intrusions that make up as much as 50% of the Shield's surface. Seismic refraction studies of SW Arabia (Mooney et al., 1985) reveal two layers, each ~20 km thick, separated by a well-defined Conrad discontinuity. The upper crust has average Vp ~6.3 km/sec whereas the lower crust has average Vp ~7.0 km/sec, corresponding to a granitic upper crust and gabbroic lower crust. Neogene (<30 ma) lava fields in Arabia (harrats) extend over 2500 km, from Yemen to Syria. Many of these lavas contain xenoliths, providing a remarkable glimpse of the lower-crustal and upper-mantle lithosphere beneath W. Arabia. Lower crustal xenoliths brought up in 8 harrats in Saudi Arabia, Jordan, and Syria are mostly 2-pyroxene granulites of igneous (gabbroic, anorthositic, and dioritic) origin. They contain plagioclase, orthopyroxene, and clinopyroxene, and a few contain garnet and rare amphibole and yield mineral-equilibrium temperatures of 700-900°C. Pyroxene-rich and plagioclase-rich suites have mean Al2O3 contents of 13% and 19%, respectively: otherwise the two groups have similar elemental compositions, with ~50% SiO2 and ~1% TiO2, with low K2O (<0.5%) and Na2O (1-3%). Both groups show tholeiitic affinities, unrelated to their alkali basalt hosts. Mean pyroxene-rich and plagioclase-rich suites show distinct mean MgO contents (11% vs. 7%), Mg# (67 vs. 55), and contents of compatible elements Ni (169 vs. 66 ppm

  11. Nitrogen fixation in biological soil crusts from southeast Utah, USA

    USGS Publications Warehouse

    Belnap, J.

    2002-01-01

    Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus, but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in a similar fashion to climate conditions. Without precipitation within a week of collection, no NA was recorded, regardless of other conditions being favorable. Low (26??C) temperatures precluded NA, even if soils were moist. If rain or snow melt had occurred 3 or less days before collection, NA levels were highly correlated with daily average temperatures of the previous 3 days (r2=0.93 for Collema crusts; r2=0.86 for dark crusts and r2=0.83 for light crusts) for temperatures between 1??C and 26??C. If a precipitation event followed a long dry period, NA levels were lower than if collection followed a time when soils were wet for extended periods (e.g., winter). Using a combination of data from a recording weather datalogger, time-domain reflectometry, manual dry-down curves, and N fixation rates at different temperatures, annual N input from the different crust types was estimated. Annual N input from dark crusts found at relatively undisturbed sites was estimated at 9 kg ha-1 year-1. With 20% cover of the N-fixing soil lichen Collema, inputs are estimated at 13 kg ha-1 year-1. N input from light crusts, generally indicating soil surface disturbance, was estimated at 1.4 kg ha-1 year-1. The rates in light crusts are expected to be highly variable, as

  12. Don’t bust the biological soil crust: Preserving and restoring an important desert resource

    Treesearch

    Sue Miller; Steve Warren; Larry St. Clair

    2017-01-01

    Biological soil crusts are a complex of microscopic organisms growing on the soil surface in many arid and semi-arid ecosystems. These crusts perform the important role of stabilizing soil and reducing or eliminating water and wind erosion. One of the largest threats to biological soil crusts in the arid and semi-arid areas of the western United States is mechanical...

  13. A two scale analysis of tight sandstones

    NASA Astrophysics Data System (ADS)

    Adler, P. M.; Davy, C. A.; Song, Y.; Troadec, D.; Hauss, G.; Skoczylas, F.

    2015-12-01

    Tight sandstones have a low porosity and a very small permeability K. Available models for K do not compare well with measurements. These sandstones are made of SiO_2 grains, with a typical size of several hundreds of micron. These grains are separated by a network of micro-cracks, with sizes ranging between microns down to tens of nm. Therefore, the structure can be schematized by Voronoi polyhedra separated by plane and permeable polygonal micro-cracks. Our goal is to estimate K based on a two scale analysis and to compare the results to measurements. For a particular sample [2], local measurements on several scales include FIB/SEM [3], CMT and 2D SEM. FIB/SEM is selected because the peak pore size given by Mercury Intrusion Porosimetry is of 350nm. FIB/SEM imaging (with 50 nm voxel size) identifies an individual crack of 180nm average opening, whereas CMT provides a connected porosity (individual crack) for 60 nm voxel size, of 4 micron average opening. Numerical modelling is performed by combining the micro-crack network scale (given by 2D SEM) and the 3D micro-crack scale (given by either FIB/SEM or CMT). Estimates of the micro-crack density are derived from 2D SEM trace maps by counting the intersections with scanlines, the surface density of traces, and the number of fracture intersections. K is deduced by using a semi empirical formula valid for identical, isotropic and uniformly distributed fractures [1]. This value is proportional to the micro-crack transmissivity sigma. Sigma is determined by solving the Stokes equation in the micro-cracks measured by FIB/SEM or CMT. K is obtained by combining the two previous results. Good correlation with measured values on centimetric plugs is found when using sigma from CMT data. The results are discussed and further research is proposed. [1] Adler et al, Fractured porous media, Oxford Univ. Press, 2012. [2] Duan et al, Int. J. Rock Mech. Mining Sci., 65, p75, 2014. [3] Song et al, Marine and Petroleum Eng., 65, p63

  14. Provenance of Norphlet sandstone, northern Gulf Coast

    SciTech Connect

    Ryan, W.P.; Ward, W.C.; Kuglar, R.L.

    1987-09-01

    The Upper Jurassic Norphlet sandstone of the northern Gulf Coast is predominantly subarkose, with some arkose in the eastern area and sublitharenite and quartzarenite in the western area. Despite great depths of burial and despite feldspar and rock-fragment constituents, diagenesis has not appreciably altered the composition of Norphlet sandstone. Therefore, reconstruction of original composition of Norphlet sandstone presented little difficulty. Variation in detrital modes of the Norphlet suggests compositionally distinct source terranes. Samples from Florida, Alabama, and Mississippi reflect the influence of metamorphic and plutonic rocks of the Appalachian Piedmont Province and of Triassic-Jurassic volcanic rocks. Sandstones in east Texas, northern Louisiana, and southern Arkansas were derived from sedimentary and metasedimentary rocks of the Ouachita system. The Arbuckle Mountains and Llano uplift may have supplied trace amounts of quartzo-feldspathic and volcanic-rock fragments to the extreme western part of the study area. Norphlet sandstones represent a mixture of collision-orogen-derived sediment from the Appalachian and/or Ouachita system and continental-block-derived sediment from paleohighs and uplifts within the Gulf basin. However, Norphlet sandstones plot in the craton-interior and transitional-continental fields on Q-F-L and QM-F-Lt tectonic-provenance diagrams, because of mineralogically mature source rocks, elimination of unstable grains by abrasion and sorting during deposition, and/or sediment mixing from different source terranes.

  15. Porosity prediction in sandstones using erosional unconformities

    SciTech Connect

    Shanmugam, G.

    1989-03-01

    Erosional unconformities of subaerial origin are created by tectonic uplifts and eustatic sea level fall. Most erosional unconformities developed on sandstones are planes of increased porosity because uplifted sandstones are exposed to undersaturated CO/sub 2/-charged meteoric waters that result in dissolution of unstable framework grains and cements. The chemical weathering of sandstones is intensified in humid regions by the heavy rainfall, soil zones, lush vegetation, and accompanying voluminous production of organic and inorganic acids. Erosional unconformities are considered hydrologically open systems because of abundant supply of fresh meteoric water and relatively unrestricted transport of dissolved constituents away from the site of dissolution, causing a net gain in porosity near unconformities. Thus, porosity in sandstones tends to increase toward overlying unconformities. Such porosity trends have been observed in hydrocarbon-bearing sandstone reservoirs in Alaska, Algeria, Australia, China, Libya, Netherlands, Norwegian North Sea, Norwegian Sea, and Texas. A common attribute of these reservoirs is that they were all subaerially exposed under heavy rainfall conditions. An empirical model has been developed for the Triassic and Jurassic sandstone reservoirs in the Norwegian North Sea on the basis of the observed relationship that shows an increase in porosity in these reservoirs with increasing proximity to the overlying base of Cretaceous unconformity. An important practical attribute of this model is that it allows for the prediction of porosity in the neighboring undrilled areas by recognizing the base of Cretaceous unconformity in seismic reflection profiles and by constructing subcrop maps.

  16. Oxygen distribution and potential ammonia oxidation in floating, liquid manure crusts.

    PubMed

    Nielsen, Daniel Aa; Nielsen, Lars P; Schramm, Andreas; Revsbech, Niels P

    2010-01-01

    Floating, organic crusts on liquid manure, stored as a result of animal production, reduce emission of ammonia (NH3) and other volatile compounds during storage. The occurrence of NO2- and NO3- in the crusts indicate the presence of actively metabolizing NH3-oxidizing bacteria (AOB) which may be partly responsible for this mitigation effect. Six manure tanks with organic covers (straw and natural) were surveyed to investigate the prevalence and potential activity ofAOB and its dependence on the O2 availability in the crust matrix as studied by electrochemical profiling. Oxygen penetration varied from <1 mm in young, poorly developed natural crusts and old straw crusts, to several centimeters in the old natural crusts. The AOB were ubiquitously present in all crusts investigated, but nitrifying activity could only be detected in old natural crusts and young straw crust with high O2 availability. In old natural crusts, total potential NH3 oxidation rates were similar to reported fluxes of NH3 from slurry without surface crust. These results indicate that old, natural surface crusts may develop into a porous matrix with high O2 availability that harbors an active population of aerobic microorganisms, including AOB. The microbial activity may thus contribute to a considerable reduction of ammonia emissions from slurry tanks with well-developed crusts.

  17. Analysis of environmental factors determining development and succession in biological soil crusts.

    PubMed

    Lan, Shubin; Wu, Li; Zhang, Delu; Hu, Chunxiang

    2015-12-15

    Biological soil crusts play important ecological functions in arid and semi-arid regions, while different crust successional patterns appeared in different regions. Therefore in this study, the environmental conditions between Shapotou (with cyanobacterial, lichen and moss crusts) and Dalate Banner (with only cyanobacterial and moss crusts) regions of China were compared to investigate why lichen crusts only appeared in Shapotou; at the same time, artificial moss inoculation was conducted to find out the environmental factors promoting crust succession to moss stage. The results showed lichen crusts always developed from cyanobacterial crusts, which provide not only the stable soil surface, but also the biomass basis for lichen formation; furthermore, addition of crust physicochemical characteristics (primarily silt content) play a facilitating effect on lichen emergence (R(2)=0.53). The inoculation experiment demonstrated early crust soil surface and enough water holding content (>4%) provided the essential guarantee for moss germination. Our results show that there is heterogeneity in crust succession in different regions, which may be mainly affected by the ambient soil microenvironments. It is concluded that a positive feedback mechanism is expected between crust succession and ambient soil microenvironments; while a negative feedback mechanism forms between crust succession and free living cyanobacteria and algae.

  18. Tungsten Stable Isotope Compositions of Ferromanganese Crusts

    NASA Astrophysics Data System (ADS)

    Abraham, K.; Barling, J.; Hein, J. R.; Schauble, E. A.; Halliday, A. N.

    2014-12-01

    We report the first accurate and precise data for mass-dependent fractionation of tungsten (W) stable isotopes, using a double spike technique and MC-ICPMS. Results are expressed relative to the NIST 3136 W isotope standard as per mil deviations in 186W/184W (δ186W). Although heavy element mass-dependent fractionations are expected to be small, Tl and U both display significant low temperature isotopic fractionations. Theoretical calculations indicate that W nuclear volume isotopic effects should be smaller than mass-dependent fractionations at low temperatures. Hydrogenetic ferromanganese (Fe-Mn) crusts precipitate directly from seawater and have been used as paleoceanographic recorders of temporal changes in seawater chemistry. Crusts are strongly enriched in W and other metals, and are a promising medium for exploring W isotopic variability. Tungsten has a relatively long residence time in seawater of ~61,000 years, mainly as the tungstate ion (WO42-). Water depth profiles show conservative behaviour. During adsorption on Fe-Mn crusts, W species form inner-sphere complexes in the hexavalent (W6+) state. The major host phase is thought to be Mn oxides and the lighter W isotope is expected to be absorbed preferentially. Surface scrapings of 13 globally distributed hydrogenetic Fe-Mn crusts display δ186W from -0.08 to -0.22‰ (±0.03‰, 2sd). A trend toward lighter W isotope composition exists with increasing water depth (~1500 to ~5200m) and W concentration. One hydrothermal Mn-oxide sample is anomalously light and Mn nodules are both heavy and light relative to Fe-Mn crusts. Tungsten speciation depends on concentration, pH, and time in solution and is not well understood because of the extremely slow kinetics of the reactions. In addition, speciation of aqueous and/or adsorbed species might be sensitive to pressure, showing similar thermodynamic stability but different effective volumes. Thus, W stable isotopes might be used as a water-depth barometer in

  19. Dunlin group sequence stratigraphy in the northern North Sea: A model for Cook sandstone deposition

    SciTech Connect

    Marjanac, T.; Steel, R.J.

    1997-02-01

    The Dunlin Group in the northern North Sea, consisting of the Johansen, Amundsen, Burton, Cook, and Drake formations of late Sinemurian-Toarcian age, hosts important hydrocarbon reservoirs in the Cook Formation sandstones. The Johansen Formation is associated with a relative fall of sea level and is interpreted to be a large sandstone delta confined within a broad incised valley at the base of the group. During a later stage of relative sea level rise, the finer grained Amundsen and Burton formations were deposited. The overlying Cook Formation consists of four sandstone tongues, each of which is characterized by a lower zone of sharp-based, upward-coarsening, thinly bedded shoreface sandstones and siltstones (reflecting forced regression during falling relative sea level) and an erosively based upper zone of thin tidal flat and thick deltaic/estuarine sandstones (reflecting lowstand incision, as well as initial progradation and subsequent transgressive backfill of estuaries during relative sea level rise). The Drake Formation shales were deposited during continued relative sea level rise. Several types of erosional surfaces are recognized within the studied succession: (1) sequence boundaries occur at the base of the Johansen Formation and within the Cook Formation, and represent the bottoms of incised valleys that truncate the underlying shoreface deposits; (2) regressive surfaces of marine erosion occur at the base of Cook Formation units and truncate the underlying Burton and Drake shales, siltstones, and mudstones; (3) transgressive tidal channel (tidal ravinement) surfaces within the Cook Formation underlie the estuarine sandstones of the incised valley fills; (4) wave ravinement surfaces truncate the tops of estuarine sandstones and are overlain by thin transgressive lags that grade upward into the overlying black shales.

  20. Evolution of faults in sandstone and their permeability

    SciTech Connect

    Antonellini, M.; Du, Yijun; Aydin, At.; Pollard, D.D. )

    1992-01-01

    In many porous sandstones world over, major fault types initiate and propagate as localized bands of deformation. Individual bands have shear displacements up to a few cm, and compaction perpendicular to the bands. Although the initiation and propagation of faults are problematic, the authors here propose that the maximum distortional strain energy density (D-criterion) can be used successfully to simulate a band fault propagation as well as the interaction and linkage of the adjacent segments. Deformation bands tend to localize into zones that have distinct patterns repeating in a broad range of scale. Some zones are associated with slip surfaces that mark the loss of cohesion between two surfaces. The authors demonstrate the particulars of individual zones and slip surfaces including their patterns and distribution for several well-known sandstones in extensional and compressional settings within Colorado Plateau. They investigate also the relationship between mappable fault patterns and the geometry and kinematics of a major detachment at Cache Valley in Arches National Park, southeastern Utah, using a Discrete Element Model. Zones of bands have permeabilities 3 to 5 order of magnitude smaller than that of parent rocks making them highly effective barriers against fluid flow. In contrast, slip surfaces are likely to be conduits with high permeability along the surface. In light of the fact that a majority of energy resources are in sandstones and that the structures described above occur also in unconsolidated sediments as potential aquifers and contamination sites, these structures and their geometries as well as the deformation processes responsible for their formation have significant implications for societal problems.

  1. Moho vs crust-mantle boundary: Evolution of an idea

    NASA Astrophysics Data System (ADS)

    O'Reilly, Suzanne Y.; Griffin, W. L.

    2013-12-01

    The concept that the Mohorovicic Discontinuity (Moho) does not necessarily coincide with the base of the continental crust as defined by rock-type compositions was introduced in the early 1980s. This had an important impact on understanding the nature of the crust-mantle boundary using information from seismology and from deep-seated samples brought to the surface as xenoliths in magmas, or as tectonic terranes. The use of empirically-constrained P-T estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment. The xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere, and revealed that the crust-mantle boundary in off-craton regions commonly is transitional over a depth range of about 5-20 km. Early seismic-reflection data showed common layering near the Moho, correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust-mantle boundary. Developments in seismology, petrophysics and experimental petrology have refined interpretation of lithospheric domains. The expansion of in situ geochronology (especially zircon U-Pb ages and Hf-isotopes; Os isotopes of mantle sulfides) has defined tectonic events that affected whole crust-mantle sections, and revealed that the crust-mantle boundary can change in depth through time. However, the nature of the crust-mantle boundary in cratonic regions remains enigmatic, mainly due to lack of key xenoliths or exposed sections. The observation that the Moho may lie significantly deeper than the crust-mantle boundary has important implications for modeling the volume of the crust. Mapping the crust using seismic techniques alone, without consideration of the petrological problems, may lead to an overestimation of crustal thickness by 15-30%. This will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust-formation processes

  2. Deformation of Reservoir Sandstones by Elastic versus Inelastic Deformation Mechanisms

    NASA Astrophysics Data System (ADS)

    Pijnenburg, R.; Verberne, B. A.; Hangx, S.; Spiers, C. J.

    2016-12-01

    Hydrocarbon or groundwater production from sandstone reservoirs can result in surface subsidence and induced seismicity. Subsidence results from combined elastic and inelastic compaction of the reservoir due to a change in the effective stress state upon fluid extraction. The magnitude of elastic compaction can be accurately described using poroelasticity theory. However inelastic or time-dependent compaction is poorly constrained. Specifically, the underlying microphysical processes controlling sandstone compaction remain poorly understood. We use sandstones recovered by the field operator (NAM) from the Slochteren gas reservoir (Groningen, NE Netherlands) to study the importance of elastic versus inelastic deformation processes upon simulated pore pressure depletion. We conducted conventional triaxial tests under true in-situ conditions of pressure and temperature. To investigate the effect of applied differential stress (σ1 - σ3 = 0 - 50 MPa) and initial sample porosity (φi = 12 - 24%) on instantaneous and time-dependent inelastic deformation, we imposed multiple stages of axial loading and relaxation. The results show that inelastic strain develops at all stages of loading, and that its magnitude increases with increasing value of differential stress and initial porosity. The stress sensitivity of the axial creep strain rate and microstructural evidence suggest that inelastic compaction is controlled by a combination of intergranular slip and intragranular cracking. Intragranular cracking is shown to be more pervasive with increasing values of initial porosity. The results are consistent with a conceptual microphysical model, involving deformation by poro-elasticity combined with intergranular sliding and grain contact failure. This model aims to predict sandstone deformation behavior for a wide range of stress conditions.

  3. Thermalization time and specific heat of the neutron stars crust

    SciTech Connect

    Fortin, M.; Grill, F.; Margueron, J.; Page, Dany; Sandulescu, N.

    2010-12-15

    We discuss the thermalization process of the neutron star's crust described by solving the heat-transport equation with a microscopic input for the specific heat of baryonic matter. The heat equation is solved with initial conditions specific to a rapid cooling of the core. To calculate the specific heat of inner-crust baryonic matter, that is, nuclear clusters and unbound neutrons, we use the quasiparticle spectrum provided by the Hartree-Fock-Bogoliubov approach at finite temperature. In this framework, we analyze the dependence of the crust thermalization on pairing properties and on cluster structure of inner-crust matter. It is shown that the pairing correlations reduce the crust thermalization time by a large fraction. The calculations show also that the nuclear clusters have a non-negligible influence on the time evolution of the surface temperature of the neutron star.

  4. "Sydney sandstone": Heritage Stone from Australia

    NASA Astrophysics Data System (ADS)

    Cooper, Barry; Kramar, Sabina

    2014-05-01

    Sydney is Australia's oldest city being founded in 1788. The city was fortunate to be established on an extensive and a relatively undeformed layer of lithified quartz sandstone of Triassic age that has proved to be an ideal building stone. The stone has been long identified by geologists as the Hawkesbury Sandstone. On the other hand the term "Sydney sandstone" has also been widely used over a long period, even to the extent of being utilised as the title of published books, so its formal designation as a heritage stone will immediately formalise this term. The oldest international usage is believed to be its use in the construction of the Stone Store at Kerikeri, New Zealand (1832-1836). In the late 19th century, public buildings such as hospitals, court houses as well as the prominent Sydney Town Hall, Sydney General Post Office, Art Gallery of New South Wales, State Library of New South Wales as well as numerous schools, churches, office building buildings, University, hotels, houses, retaining walls were all constructed using Sydney sandstone. Innumerable sculptures utilising the gold-coloured stone also embellished the city ranging from decorative friezes and capitals on building to significant monuments. Also in the late 19th and early 20th century, Sydney sandstone was used for major construction in most other major Australian cities especially Melbourne, Adelaide and Brisbane to the extent that complaints were expressed that suitable local stone materials were being neglected. Quarrying of Sydney sandstone continues today. In 2000 it was recorded noted that there were 33 significant operating Sydney sandstone quarries including aggregate and dimension stone operations. In addition sandstone continues to be sourced today from construction sites across the city area. Today major dimension stone producers (eg Gosford Quarries) sell Sydney sandstone not only into the Sydney market but also on national and international markets as cladding and paving products

  5. Depositional environments of Upper Triassic sandstones, El Borma oil field, southwestern Tunisia

    SciTech Connect

    Bentahar, H.; Ethridge, F.G. )

    1991-03-01

    El Borma oil field in southwestern Tunisia is located on the Algerian border and produces from five Upper Triassic sandstone reservoirs at depths ranging from 2,300 to 2,400 m. The 250 km{sup 2} field has recoverable reserves of 770 mm bbl of equivalent oil. Reservoir sandstones rest unconformably on south-dipping Lower Devonian clastic deposits. Silurian shale represents the major oil source rock and the field is capped by 550 m of shale, carbonate, and evaporite. Hercynian, topography below the reservoir sandstones comprises an 18 km wide, northeast-oriented paleovalley. Each of the four lower reservoir sandstones, bounded by a lower scour surface and a basal lag deposit, is commonly discontinuous and separated by lenticular shale beds. These 5 to 15 m thick sandstones display in channels flowing to the northeast. The overlying 12 m thick transgressive marine dolomitic shale contains carbonized bivalves and is capped by a paleosoil with root structures and siderite cement indicating subaerial exposure. The clay-rich and locally bioturbated uppermost reservoir sandstone was probably deposited in a tidally influenced estuary. Overall, the Upper Triassic reservoirs at El Borma consists of valley-fill estuary deposits that were formed during transgression of the sea from the northeast.

  6. Demagnetization of Martian Crust by Large Impacts

    NASA Astrophysics Data System (ADS)

    Mohit, P. S.; Arkani-Hamed, J.

    2001-12-01

    The magnetic anomaly map of Mars derived from Mars Global Surveyor magnetic data shows no magnetic signature inside large basins such as Hellas, Argyre and Isidis, but it does show some appreciable anomalies over the immediate surroundings of these basins. This implies that the large impacts that produced these giant basins demagnetized the entire crust beneath the basins. To investigate the extent of the impact effects, we first assess the excavation by determining the crustal thickness beneath the basins under the assumption that the observed gravity anomaly arises from the surface topography and the undulation of the crust-mantle interface. Using the resulting crustal structure, we then model the neighboring small magnetic anomalies to determine the degradation of crustal magnetization as a function of distance from the impact site. This provides a means to constrain the extent of the shock effects and the initial temperature distribution immediately after the impact. The impacts have generated shock pressures of about 3 GPa at the edge of the basins, implying that shock was a major factor in the demagnetization of the crust beneath the basins. The magnetic effects of the initial shock wave and the heat resulting from isentropic decompression following the impact are then investigated. We also modeled the thermal evolution of the crust beneath the basins and possible remagnetization of small source bodies in the surroundings to establish that the impacts occurred in the absence of the core field.

  7. Seismic anisotropy in the continental crust of northwestern Canada

    NASA Astrophysics Data System (ADS)

    Dalton, Colleen A.; Gaherty, James B.

    2013-04-01

    Most studies of the seismic structure of continental crust assume that the wave speeds are isotropic at seismic wavelengths. The ability to measure surface wave propagation speed from the cross-correlation of ambient seismic noise provides new opportunities to image the crust and uppermost mantle. We investigate radial anisotropy in the continental crust of northwestern Canada from group-velocity curves of Love and Rayleigh waves obtained from ambient-noise cross-correlation. We test the null hypothesis that the Love and Rayleigh group-speed curves can be simultaneously fit by an earth model containing isotropic seismic velocities throughout the crust. Group velocity is predicted for 200 000 one-dimensional earth models, which are generated by randomly varying the crustal shear velocity and radial anisotropy within a prescribed range. The goodness-of-fit of the predictions is assessed by comparison with two sets of observed dispersion curves that correspond to two tectonically distinct terranes: the Archean/early Proterozoic craton and the transition from craton to Cordillera. The majority of best-fitting models contain VSH > VSV (4-5 per cent) in the middle crust. The finding that the middle/lower crust is seismically anisotropic across a large swath of northwestern Canada, combined with recent observations of anisotropic crust in much of the western United States, suggests that anisotropy may be ubiquitous in the continental crust.

  8. The evolution of Mercury's crust: a global perspective from MESSENGER.

    PubMed

    Denevi, Brett W; Robinson, Mark S; Solomon, Sean C; Murchie, Scott L; Blewett, David T; Domingue, Deborah L; McCoy, Timothy J; Ernst, Carolyn M; Head, James W; Watters, Thomas R; Chabot, Nancy L

    2009-05-01

    Mapping the distribution and extent of major terrain types on a planet's surface helps to constrain the origin and evolution of its crust. Together, MESSENGER and Mariner 10 observations of Mercury now provide a near-global look at the planet, revealing lateral and vertical heterogeneities in the color and thus composition of Mercury's crust. Smooth plains cover approximately 40% of the surface, and evidence for the volcanic origin of large expanses of plains suggests that a substantial portion of the crust originated volcanically. A low-reflectance, relatively blue component affects at least 15% of the surface and is concentrated in crater and basin ejecta. Its spectral characteristics and likely origin at depth are consistent with its apparent excavation from a lower crust or upper mantle enriched in iron- and titanium-bearing oxides.

  9. GREYBULL SANDSTONE PETROLEUM POTENTIAL ON THE CROW INDIAN RESERVATION, SOUTH-CENTRAL MONTANA

    SciTech Connect

    David A. Lopez

    2000-12-14

    Evaluation of the Lower Cretaceous Greybull Sandstone on the Crow Indian Reservation for potential stratigraphic traps in the valley-fill sandstone was the focus of this project. The Crow Reservation area, located in south-central Montana, is part of the Rocky Mountain Foreland structural province, which is characterized by Laramide uplifts and intervening structural basins. The Pryor and Bighorn mountains, like other foreland uplifts, are characterized by asymmetrical folds associated with basement-involved reverse faults. The reservation area east of the mountains is on the northwestern flank of the Powder River Basin. Therefore, regional dips are eastward and southeastward; however, several prominent structural features interrupt these regional dips. The nearly 4,000 mi{sup 2} reservation is under explored but has strong potential for increased oil and gas development. Oil and gas production is well established in the Powder River Basin of Wyoming to the south as well as in the areas north and west of the reservation. However, only limited petroleum production has been established within the reservation. Geologic relations and trends indicate strong potential for oil and gas accumulations, but drilling has been insufficient for their discovery. The Greybull Sandstone, which is part of the transgressive systems tract that includes the overlying Fall River Sandstone, was deposited on a major regional unconformity. The erosional surface at the base of the Greybull Sandstone is the +100 Ma, late Aptian-Early Albian regional unconformity of Weimer (1984). This lowstand erosional surface was controlled by a basin-wide drop in sea level. In areas where incised Greybull channels are absent, the lowstand erosional unconformity is at the base of the Fall River Sandstone and equivalent formations. During the pre-Greybull lowstand, sediment bypassed this region. In the subsequent marine transgression, streams began to aggrade and deposit sand of the lower Greybull Sandstone

  10. Origins of massive-type sandstones in braided river systems

    NASA Astrophysics Data System (ADS)

    Martin, Charlotte A. L.; Turner, Brian R.

    1998-07-01

    This study details largely ignored massive-type, predominantly structureless sandstones preserved within braided fluvial successions of Carboniferous to Triassic age. Architectural element analysis reveals that these sediments were deposited within sand-dominated perennial systems of low braiding index. Cross-stratified braid bar deposits are interbedded with, and laterally equivalent to geometrically distinct, largely structureless massive-type sandbodies identified as two separate architectural elements: channel-like (SMC) and sheet-like (SMS). Sub-divisions within these broad categories define six geometric units which are texturally distinct from each other and from the structured sediments of the same lithological unit. Since massive-type sandstone elements have many features in common with the deposits of highly concentrated, laminar sediment/water flows, they are interpreted in terms of similar depositional processes. SMC elements form elongate channel-like features which trend both at high angles to, and parallel with, the palaeoflow of host fluvial channels. The lower bounding surfaces of SMC elements may be either erosive or non-erosive, and describe symmetrical cross-sections with margins dipping <50°. Concentric laminae are preserved parallel to the scour margins which grade into a structureless sandstone fill. Diffuse laminae and water escape structures are commonly preserved in the upper portion of these elements, which are interpreted as the deposits of sandy debris flows related to fluvial bank and/or bar collapse. SMS elements form sandsheets up to 8 m in thickness which may be traced >250 m parallel and transverse to the fluvial palaeoflow direction established from cross-stratified sandstones of adjacent architectural elements. The basal surface of SMS elements may either be undulose (where the sandbodies are termed SMSU) or erosional (where they are termed SMSE). Internally SMSU elements preserve parallel laminae marginal to basal scours

  11. Assessing level of development and successional stages in biological soil crusts with biological indicators.

    PubMed

    Lan, Shubin; Wu, Li; Zhang, Delu; Hu, Chunxiang

    2013-08-01

    Biological soil crusts (BSCs) perform vital ecosystem services, but the difference in biological components or developmental level still affects the rate and type of these services. In order to differentiate crust successional stages in quantity and analyze the relationship between crust developmental level and successional stages, this work determined several biological indicators in a series of different developmental BSCs in the Shapotou region of China. The results showed that crust developmental level (level of development index) can be well indicated by crust biological indicators. Photosynthetic biomass was the most appropriate to differentiate crust successional stages, although both photosynthetic biomass and respiration intensity increased with the development and succession of BSCs. Based on of the different biological compositions, BSCs were quantificationally categorized into different successional stages including cyanobacterial crusts (lichen and moss coverages <20 %), lichen crusts (lichen coverage >20 % but moss coverage <20 %), semi-moss crusts (moss coverage >20 % but <75 %), and moss crusts (moss coverage >75 %). In addition, it was found that cyanobacterial and microalgal biomass first increased as cyanobacterial crusts formed, then decreased when lots of mosses emerged on the crust surface; however nitrogen-fixing cyanobacteria and heterotrophic microbes increased in the later developmental BSCs. The structural adjustment of biological components in the different developmental BSCs may reflect the requirement of crust survival and material transition.

  12. Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic

    USGS Publications Warehouse

    Koschinsky, A.; Halbach, P.; Hein, J.R.; Mangini, A.

    1996-01-01

    Hydrogenetic ferromanganese crusts reflect the chemical conditions of the seawater from which they formed. Fine-scale geochemical analysis of crust layers in combination with age determinations can therefore be used to investigate paleoceanographic changes which are recorded in geochemical gradients in the crusts. At Tropic seamount (off northwest Africa), uniform crust growth influenced by terrigenous input from the African continent occurred during approximately the past 12 Ma. Phosphatization of these crusts is minor. In contrast, crusts from Lion seamount, located between Madeira and the Portuguese coast, display a much more variable growth history. A pronounced increase in Ni, Cu, and Zn is observed in some intervals of the crusts, which probably reflects increased surface productivity. A thick older phosphatized generation occurs in many samples. Hydrographic profiles indicate that Mediterranean outflow water (MOW) may play an important role in the composition of these crusts. 10Be dating of one sample confirms that the interruption of the MOW during the Messinian salinity crisis (6.2-5 Ma ago) resulted in changes in element composition. Sr-isotope dating of the apatite phase of the old crust generation has been carried out to obtain a minimum age for the older generation of Atlantic crusts and to determine whether crust phosphatization in the Atlantic can be related to phosphatization episodes recorded in Pacific crusts. The preliminary data show that the old phosphatized crust generation might be as old as approximately 30-40 Ma.

  13. Continental crust: a geophysical approach

    SciTech Connect

    Meissner, R.

    1986-01-01

    This book develops an integrated and balanced picture of present knowledge of the continental crust. Crust and lithosphere are first defined, and the formation of crusts as a general planetary phenomenon is described. The background and methods of geophysical studies of the earth's crust and the collection of related geophysical parameters are examined. Creep and friction experiments and the various methods of radiometric age dating are addressed, and geophysical and geological investigations of the crustal structure in various age provinces of the continents are studied. Specific tectonic structures such as rifts, continental margins, and geothermal areas are discussed. Finally, an attempt is made to give a comprehensive view of the evolution of the continental crust and to collect and develop arguments for crustal accretion and recycling. 647 references.

  14. The fate of Ceres' original crust

    NASA Astrophysics Data System (ADS)

    Roberts, James H.; Rivkin, Andrew S.

    2015-11-01

    The bulk density of Ceres implies that water ice comprises a substantial fraction of Ceres’ interior. However, water ice is not stable at Ceres orbital distance and if exposed would have a loss rate of 1 km Myr-1 or more. The near-hydrostatic shape of Ceres, and relatively low melting point of ice suggests that the interior is at least partly differentiated. Because Ceres’ surface remains exposed to space, it radiates very effectively, and models predicting differentiation retain an undifferentiated crust. This would be denser than the ice shell beneath it resulting in an unstable stratification. This has led to expectations that the crust would founder and the surface of Ceres might be very smooth and relaxed. But could the crust have remained to the present day?Here, we model global-scale overturn on Ceres using both analytical two-layer linear stability analyses, and numerical models to predict the most unstable wavelength, and growth timescales for Rayleigh-Taylor instabilities. We find that for a 10 km-thick crust above a 75 km-thick ice layer, instabilities grow fastest at spherical harmonic degree l=4. The growth timescale is a function of the viscosity of the upper layer. This timescale is less than the age of the solar system unless the effective viscosity of the crust is > 1024 Pa s. We conclude that the crust of Ceres could remain at the surface if it either has some finite elastic strength over a ~800 km length scale, or is an unconsolidated regolith with a large, (> 50%) macro-porosity, such that the regolith is buoyant relative to water ice.Neither end-member for the crustal strength precludes convective activity in the underlying ice layer. However we note that a thick, porous regolith is a fantastic insulator and may promote heating of the interior and potential foundering of the regolith if the top of the ice becomes too warm. This possibility can be evaluated by models of thermal evolution (e.g., Castillo-Rogez et al., 2010). An episode of

  15. Development of a Thermodynamically Consistent Constitutive Framework for Castlegate Sandstone

    NASA Astrophysics Data System (ADS)

    Richards, M. C.; Ingraham, M. D.; Issen, K. A.

    2014-12-01

    Development of accurate field-scale deformation models requires use of a constitutive framework that is capable of representing material behavior, and can be calibrated using available mechanical response data. This study focuses on the formulation of such a constitutive framework for Castlegate sandstone, which is a high porosity fluvial-deposited reservoir analog rock. In developing a constitutive framework, researchers must balance the complexity of the mathematics required to represent all aspects of mechanical response, with the ease of implementation. Central to this effort is identifying and modeling the most fundamental material behaviors. For Castlegate sandstone, experimentalists (e.g., AGU Abstract 30068, Issen et al.) report three behaviors that are essential in characterizing deformation response: 1) dependence of the moduli on stress (nonlinearity), 2) evolution of the moduli with plastic strain, and 3) non-normality of the plastic strain increment to the yield surface (non-associativity). This work employs the principles of hyperplasticity (e.g., Houlsby and Puzrin, 2006) to develop a thermodynamically sound constitutive framework for Castlegate sandstone. This requires selection of two potentials: 1) a thermodynamic potential (i.e., internal energy, enthalpy, Helmholtz function, or Gibbs' function) and 2) a dissipation function or yield surface. Furthermore, the elastic, plastic, and coupled strain increments are derived from these potentials. This study uses a Gibbs' function to define expressions for the evolution of the elastic moduli, from which elastic and coupled strain increments are determined. The yield surface in dissipative stress-space is used to derive the plastic strain increments. A key result of this formulation is that normality is predicted in dissipative stress space; this result is evaluated against experimental data from work discussed in AGU Abstract 30068, Issen et al.

  16. Evaporative losses from soils covered by physical and different types of biological soil crusts

    USGS Publications Warehouse

    Chamizo, S.; Cantón, Y.; Domingo, F.; Belnap, J.

    2013-01-01

    Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well-developed biological soil crusts than in physical or poorly developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared with the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (<6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils.

  17. Development of Shear Banding in Berea Sandstone

    NASA Astrophysics Data System (ADS)

    Riedel, J. J.; Labuz, J. F.

    2004-05-01

    Closed-loop, servo-controlled testing was used to investigate the development of shear failure in Berea sandstone under low confining pressure. The experiments were performed with the University of Minnesota Plane-Strain Apparatus, designed to allow the failure plane to propagate in an unrestricted manner. Deformation was imposed into the strain softening regime and controlled so that the specimens remained intact. Thin-section microscopy provided direct observation in, adjacent to, and around the tip of the rupture zone. The shear band appeared to initiate near a stress concentration, either the corner of the specimen or, when present, an imperfection (3 mm diameter hole) introduced into the specimen. Intragranular microcracking was the dominant observable failure mechanism. The intensity of grain cracking was greatest near the initiation point and decreased as the failure surface was traced towards the tip. Areas of high crack density also appeared to have the greatest amount of grain size reduction and there seemed to be a larger amount of pore space. In areas where intragranular microcracks were distinguishable, (e.g. near the tip of the rupture zone), microcracks showed very little or no shear displacement, suggesting the features were not reoriented after formation. Microcrack orientations showed a dominant direction of -16 degrees from the maximum principal stress direction and -26 degrees from the failure surface. A numerical imaging technique was developed to provide an efficient means for analyzing the relative porosity of epoxy-impregnated thin-sections. The code was set up to receive a digital image (*.bmp), where three parameters (R, G, and B) describe the color of each pixel. The intensity of the R channel consistently defined the boundary of grain and pore space and was used to differentiate blue pore space from the white grains composing the matrix. Porosity increase within the rupture zone was 3-4 grain diameters wide. An absence of notable

  18. Dakota sandstone facies, western Oklahoma panhandle

    SciTech Connect

    Atalik, E.; Mansfield, C.F.

    1984-04-01

    The Cretaceous Dakota Sandstone in Cimarron County comprised three sandstone units and intervening mudrocks; it overlies the Kiowa Shale Member of the Purgatoire Formation. Deposits include shoreface, beach (foreshore) and dune, estuarine and tidal channel, marine marginal bay and swamp/marsh in a generally progradational sequences associated with marine regression in the Western Interior. The shoreface sand, characterized by ripple lamination, bioturbation and the trace fossils Teichichnus and Thalassinoides, is fine-grained, 5-10 m (15-30 ft) thick and grades into the underlying Kiowa Shale. Beach and associated dune deposits are 2-5 m (6-16 ft) thick, medium to fine-grained, medium to thick-bedded, tabular-planar cross-bedded, and lenticular; cross-bed paleocurrent headings are northeasterly and northwesterly. Estuarine channel deposits are 3-5 m (10 to 16 ft) thick, trough to tabular-planar cross-bedded, and medium to coarse-grained with local conglomerate overlying the scoured base which commonly cuts into the Kiowa Shale or overlying shoreface sandstone; rip-up clasts and wood pieces are common but trace fossils are rare; southeasterly and southwesterly paleocurrents predominate. Tidal channel deposits are thinner (up to 2 m of 6 ft) and finer grained (medium to fine-grained) that the estuarine channel deposits; they occur within fine-grained sandstone and mudrock sequences, are trough cross-bedded, and commonly contain trace fossils (e.g., Skolithos) and wood fragments. Marine marginal (tidal flat or bay.) deposits comprise fine-grained sandstone, siltstone and interbedded shale, that are 1-3m (3-10 ft) thick with abundant burrows, small ripple marks, and parallel lamination. These grade into the fine to very fine-grained sandstones, siltstones, shales, and coals of the swamp/marsh deposits that are 1-5m (3-16 ft) thick and contain ripple marks, burrows, other trace fossils, and parallel lamination.

  19. Evidence of Non-Linear Elasticity of the Crust from the Mw7.6 Manyi (Tibet) Earthquake Surface Displacement Field

    NASA Technical Reports Server (NTRS)

    Peltzer, G.; Crampe, F.; King, G.

    1999-01-01

    Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 7.6 Manyi earthquake of 8 November 1997 produces a 170 km-long surface break with up to 7m of left-lateral slip, reactivating a North 76 degrees East quaternary fault in western Tibet.

  20. Stress in a stratified crust overlying a buried screw dislocation

    NASA Astrophysics Data System (ADS)

    Leary, Peter C.

    1985-01-01

    A Haskell matrix solution to the equation of stress equilibrium is used to describe the crustal response to a screw dislocation source lying beneath a uniform elastic crust capped by a region of layered rigidity. The solution is used to illustrate the effect a stratified crustal rigidity has on the near surface in situ stress field. Without accounting for this effect, it is possible to overestimate the deep tectonic stress levels inferred from in situ vertical gradients measured in the uppermost crust.

  1. Magnetic Sources in the Crust of Mars

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This is a simple schematic representation of localized magnetic sources in the crust of Mars, buried beneath the surface, and revealed by observation of the magnetic field (blue) extending up to satellite altitude (about 120 kilometers). Most of our close passes to date - for which we have data - reveal the presence of one or more magnetic anomalies close to the path of the spacecraft. Since the sources must be close to the path of the satellite, we can only infer that the crust of Mars is strewn with similar magnetic anomalies, awaiting discovery. Where we can obtain enough data - that is to say, spaced more or less evenly in longitude with a spacing comparable to our periapsis altitude - we can construct a detailed image of the magnetic state of the Martian crust. We can then perhaps learn about the history of the now-extinct early Mars dynamo and the evolution of the surface of Mars.

    The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO. JPL is an operating division of California Institute of Technology (Caltech).

  2. Composition of weakly altered Martian crust

    NASA Technical Reports Server (NTRS)

    Mustard, J. F.; Murchie, S. L.; Erard, S.

    1993-01-01

    The mineralogic and chemical composition of weakly altered crust remains an unresolved question for Mars. Dark regions hold clues to the composition since they are thought to comprise surface exposures of weakly altered crustal materials. Understanding the in situ composition of relatively pristine crustal rocks in greater detail is important for investigating basic volcanic processes. Also, this will provide additional constraints on the chemical pathways by which pristine rocks are altered to produce the observed ferric iron-bearing assemblages and inferred clay silicate, sulphate, and magnetic oxide phases. Reflectance spectra of dark regions obtained with the ISM instrument are being used to determine the basic mineralogy of weakly altered crust for a variety of regions on Mars.

  3. Longshore-drift dispersed, storm-generated cross-stratified sandstone from some Cretaceous shallow marine strata, Rocky Mountain region

    SciTech Connect

    Gustason, E.R. )

    1990-05-01

    Most Cretaceous shallow marine strata of the Rocky Mountain region are characterized by asymmetrical upward-coarsening and upward-thickening sequences. The strata typically contain similar lithofacies (i.e., normally graded planar parallel laminated claystone, siltstone, and sandstone; hummocky cross-stratified sandstone; symmetrical and asymmetrical ripple cross-lamination; and trough and planar tublar cross-stratified sandstone) and display an upward increase in the thickness and frequency of sharp-based sandstone beds that grade into amalgamated cross-stratified sandstone. Most workers agree that sharp-based sandstone beds and hummocky cross-stratified sandstone are storm generated. However, the origin of trough and planar tabular cross-stratified sandstone is controversial. Most workers interpret these sedimentary structures as deposited from either storm-generated traction currents or combined flow currents on the shelf, tide-generated traction currents, or tidally dispersed, storm-generated suspension clouds. Detailed analysis of three-dimensional outcrops has revealed several significant features of these sedimentary structures that indicate they may have been deposited by longshore drift dispersed, storm-generated suspension clouds. Sets of trough and planar cross-stratified sandstone form medium-scale discontinuous, irregularly shaped sand bodies, bound by erosional surfaces and composed of unidirectional dip-oriented cross strata. Individual cross stratum commonly have a sigmoidal shape, are bound by either reactivation surfaces or mudstone drapes, and contain normally graded concordant laminae. Top-set laminae, are truncated by the upper set boundary, whereas bottom-set laminae, become asymptotic to the lower set boundary and commonly are reworked and overlain by wave generated, ripple cross-lamination or mudstone drapes.

  4. Impact Metamorphism of Sandstones at Amguid Crater, Algeria

    NASA Astrophysics Data System (ADS)

    Sahoui, R.; Belhai, D.

    2016-08-01

    Amguid is a 450 m diameter sample crater; it is emplaced in Lower Devonian sandstones.We have carried out a petrographic study in order to investigate shock effects recorded in these sandstones and define shock stages in Amguid.

  5. The potential roles of biological soil crusts in dryland hydrologic cycles

    USGS Publications Warehouse

    Belnap, J.

    2006-01-01

    Biological soil crusts (BSCs) are the dominant living cover in many drylands of the world. They possess many features that can influence different aspects of local hydrologic cycles, including soil porosity, absorptivity, roughness, aggregate stability, texture, pore formation, and water retention. The influence of biological soil crusts on these factors depends on their internal and external structure, which varies with climate, soil, and disturbance history. This paper presents the different types of biological soil crusts, discusses how crust type likely influences various aspects of the hydrologic cycle, and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world. Most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers. Unfortunately, this greatly complicates interpretation of the results. Applied disturbances alter many soil features such as soil texture, roughness, aggregate stability, physical crusting, porosity, and bulk density in ways that would not necessarily be the same if crusts were not naturally present. Combined, these studies show little agreement on how biological crusts affect water infiltration or runoff. However, when studies are separated by biological crust type and utilize naturally occurring differences among these types, results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff, have mixed effects in and regions, and increase infiltration and reduce runoff in semiarid cool and cold drylands. However, more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff. We especially need studies that control for sub-surface soil features such as bulk density, micro- and macropores, and biological crust structure. Unlike

  6. Composition and origin of ferromanganese crusts from equatorial western Pacific seamounts

    NASA Astrophysics Data System (ADS)

    Wang, Guozhi; Jansa, Luba; Chu, Fengyou; Zou, Can; Sun, Guosheng

    2015-04-01

    In the equatorial western Pacific, iron-manganese oxyhydroxide crusts (Fe-Mn crusts) and nodules form on basaltic seamounts and on the top of drowned carbonate platform guyots that have been swept free of pelagic sediments. To date, the Fe-Mn crusts have been considered to be almost exclusively of abiotic origin. However, it has recently been suggested that these crusts may be a result of biomineralization. Although the Fe-Mn crust textures in the equatorial western Pacific are similar to those constructed by bacteria and algae, and biomarkers also document the existence of bacteria and algae dispersed within the Fe-Mn crusts, the precipitation, accumulation and distribution of elements, such as Fe, Mn, Ni and Co in Fe-Mn crusts are not controlled by microbial activity. Bacteria and algae are only physically incorporated into the crusts when dead plankton settle on the ocean floor and are trapped on the crust surface. Geochemical evidence suggests a hydrogenous origin of Fe-Mn crusts in the equatorial western Pacific, thus verifying a process for Fe-Mn crusts that involves the precipitation of colloidal phases from seawater followed by extensive scavenging of dissolved trace metals into the mineral phase during crust formation.

  7. Towards a better understanding of tetrachloroethene entry pressure in the matrix of Permo-Triassic sandstones.

    PubMed

    Gooddy, Daren C; Bloomfield, John P; Harrold, Gavin; Leharne, Steven A

    2002-12-01

    The pressure required for a chlorinated solvent to enter a geological medium can be calculated given knowledge of the characteristic pore size of the medium and the interfacial tension (IFT) and contact angle of the solvent-water-rock system. Using a centrifuge-based method, capillary pressure-saturation curves have been determined for 30 water-saturated samples of Permo-Triassic sandstones for the solvent tetrachloroethene (PCE). These curves have been successfully fitted using the van Genuchten function to determine PCE entry pressure for each of the sandstone samples. A plot of PCE entry pressures against average pore diameter shows a linear relationship in log-log space; however, observed values for PCE entry pressure are significantly lower than would be expected theoretically for a sandstone-PCE-water system. This may be explained either by a decrease in the IFT or an increase in the contact angle. The IFT may decrease during contact with sandstones due to hysteresis effects during imbibition and drainage of fluids, but this is unlikely to be sufficient to account for the low entry pressures observed. Therefore, it is inferred that the low observed PCE entry pressures are due to higher than expected PCE contact angles, and that the average pore-throat surface of the sandstones is more solvent wetting than would be expected. A weak acid extraction indicates the presence of calcite and dolomite in the sandstone cores, and a correlation is observed between carbonate content per unit porosity and a reduction in PCE entry pressure. It is suggested that these mineral phases are responsible for observed wettability changes and a conceptual model is proposed. One consequence of the lower observed entry pressures is that solvents are likely to penetrate deeper into the matrix of water-saturated sandstones than previously expected.

  8. "The Ruins": Large cold seep sandstone chimneys in the upper Miocene Santa Margarita Sandstone, Scotts Valley, CA

    NASA Astrophysics Data System (ADS)

    Schwartz, H.; Bazan, C.; Perry, F.; Garrison, R. E.

    2012-12-01

    In 1856 a peculiar letter in a San Francisco newspaper reported the discovery of an ancient ruin on a sandy hillside in Scotts Valley, CA (Santa Cruz County). The purported "great and magnificent structure" consisted of 50 sandstone columns, some of which were said to be capped by a dome. Exploration of the site by speculators and treasure hunters in the 1850's produced no artifacts or evidence of human activity and regrettably resulted in removal or destruction of most of the original columns. Despite its depletion, and subsequent assessment as a wholly geological phenomenon, the locality is still known locally as "The Ruins". In order to evaluate the origin of the distinctive cementation at the Ruins we mapped its remaining features and collected samples for petrographic, XRD and stable isotope analysis. The site, presently located on private property, consists of at least 12 columns and numerous flattened, discontinuous slabs of well indurated sandstone exposed over ~160 square meters. Stratigraphically it is in the uppermost part of the upper Miocene Santa Margarita Sandstone, 7-15 m below its contact with the overlying Santa Cruz Mudstone. The columns range from 0.5-2 m in diameter and the tallest rises 1.5 m above the surface. All of the columns are distinctly chimney-like, with circular cross sections and hollow central cavities that in some cases are partially filled with separately cemented rings. They describe a SW-NE linear trend on the south side of a hill. A horizon of sandstone slabs, 0.2-1.7 m in length, stratigraphically overlies the chimneys at the top of the hill. Both chimneys and slabs consist of coarse-grained, moderately-sorted sandstone cemented by sparry low-Mg calcite. Most samples also contain abundant remains of the echinoid Astrodapsis spatiosus. δ18O values range from -5.15‰ (chimney) to -2.32‰ (slab); δ13C values range from -19.89‰ (chimney) to -1.95‰ (slab). Stable isotope values seem tied to location rather than contrasting

  9. Fractures and stresses in Bone Spring sandstones

    SciTech Connect

    Lorenz, J.C.; Warpinski, N.R.; Sattler, A.R.; Northrop, D.A.

    1990-09-01

    This project is a collaboration between Sandia National Laboratories and Harvey E. Yates Company being conducted under the auspices of the Oil Recovery Technology Partnership. The project seeks to apply perspectives related to the effects of natural fractures, stress, and sedimentology to the simulation and production of low-permeability gas reservoirs to low-permeability oil reservoirs as typified by the Bone Spring sandstones of the Permian Basin, southeast New Mexico. This report presents the results and analysis obtained in 1989 from 233 ft of oriented core, comprehensive suite of logs, various in situ stress measurements, and detailed well tests conducted in conjunction with the drilling of two development wells. Natural fractures were observed in core and logs in the interbed carbonates, but there was no direct evidence of fractures in the sandstones. However, production tests of the sandstones indicated permeabilities and behavior typical of a dual porosity reservoir. A general northeast trend for the maximum principal horizontal stress was observed in an elastic strain recovery measurements and in strikes of drilling-induced fractures; this direction is subparallel to the principal fracture trend observed in the interbed carbonates. Many of the results presented are believed to be new information for the Bone Spring sandstones. 57 figs., 18 tabs.

  10. Differential Erosion at Work on Martian Sandstones

    NASA Image and Video Library

    2014-03-24

    Sandstone layers with varying resistance to erosion are evident in this Martian scene recorded by the Mast Camera on NASA Curiosity Mars rover on Feb. 25, 2014, about one-quarter mile about 400 meters from a planned waypoint called the

  11. Crust Formation in Aluminum Cells

    NASA Astrophysics Data System (ADS)

    Oedegard, R.; Roenning, S.; Rolseth, S.; Thonstad, J.

    1985-11-01

    This paper examines the catalytic effects offlourides on the ϒ→α-Al2O3 phase transformation by heat treating commercial alumina samples with 2wt% additions of different flouride compounds. The various additives were ranked according to their effect on transformation temperature. Experiments were conducted to explain the high temperature coherence of crusts. The findings indicate that an alumina network is formed during ϒ→α phase transformation, which reinforces the crust on top of the cryolite bath.

  12. Hydrogeology of a Transboundary Sandstone Aquifer, Quebec - New York

    NASA Astrophysics Data System (ADS)

    Nastev, M.; Lamontagne, C.; Morin, R.; Williams, J.; Lavigne, M.; Croteau, A.; Tremblay, T.; Godin, R.; Dagenais, M.; Rouleau, A.

    2005-12-01

    The Potsdam sandstone aquifer of Cambrian age straddles southern Quebec and northern New York in a region known for its abundant and good quality groundwater, a resource that recently has been coveted by several bottling companies. The potential conflicts and concerns of the mainly rural and groundwater dependent population about the possible overuse of this resource has led the Quebec Ministry of Environment, Geological Survey of Canada and the U. S. Geological Survey to jointly carry out a transboundary hydrogeological study of the Potsdam sandstone aquifer. The Potsdam sandstone aquifer consists of a lower unit of arkose and conglomerate and an upper unit of well-cemented quartz arenite. The thickness of the regional aquifer ranges from nil at the base of Adirondacks to more than 500 m near the St. Lawrence River. Glacial till, littoral sand and gravel, and marine silt and clay discontinuously overlie the aquifer. The aquifer's water budget is characterized by low rates of surface runoff and high rates of infiltration and sub-surface runoff. Major recharge areas are present at higher altitudes near and to the south of the border. Strong downward hydraulic gradients in these areas result in cascading water and water-level depths of more than 30 m in deep wells. Bedding in the Potsdam sandstone is gently dipping with fractures along sub-horizontal bedding planes forming major flow conduits. Bedrock folds and faults, mainly developed by east-west compression during the Appalachian orogenies, locally complicates aquifer geometry and groundwater flow. Hydraulic tests (pump, slug, flowmeter and straddle packer) indicate similar horizontal transmissivities in the lower and upper aquifer units. However, differences in lithology and structure of the aquifer units impose some apparent differences in hydraulic properties and groundwater flow patterns. In the lower unit, regional flow appears to be sustained by a limited number of laterally extensive bedding-plane fractures

  13. Quantitative evaluation of decay patterns on artificially weathered sandstone specimens

    NASA Astrophysics Data System (ADS)

    Prikryl, Richard

    2017-04-01

    Natural stone affected by weathering processes exhibits development of specific weathering forms / patterns. These features are controlled by numerous factors; however, their extent is generally considered to be proportional to weathering grade. The recent study focused on possible quantitative evaluation of the decay patterns on artificially weathered sandstones and on correlation of the extent of decay forms with conventionally used parameters such as weight loss or porosity increase. Macroscopically visible decay patterns were recorded after completion of certain number of cycles of freezing/thawing and/or salt crystallization applied to several types of building sandstones. By using prismatic specimens, the preservation of (1) corners, (2) edges, and (3) flat surfaces plus overall integrity of specimens were captured by digital photography. Individual photos were processed by means of image analysis software to quantify % loss of original shape (i.e. rounding of corners and edges, material loss on flat surfaces, etc.), and formation of cracks. Obtained data were correlated with results of non-destructive measurements of selected physical properties such as porosity, ultrasonic velocity or weight loss.

  14. Water depth-composition trends in ferromanganese crusts adjacent to the California margin compared to those in equatorial Pacific crusts

    NASA Astrophysics Data System (ADS)

    Conrad, T. A.; Hein, J. R.

    2013-12-01

    Ferromanganese (Fe-Mn) crusts have been used as proxies for paleo-seawater chemistry; however, element concentrations and growth rates in crusts can vary depending on the region, latitude, and water depth. Here we will look at 130 Fe-Mn crusts from seven seamounts adjacent to the California (CA) margin to explore trends in composition with water depth and latitude. Crusts were collected by ROV, resulting in a dataset with exact water depth and location coordinates. Water depth ranges from 570 to 3,934 m along a 700-km transect running roughly parallel to the CA margin. Crust samples used for comparison were collected by dredging along transects following the Gilbert Ridge and Tokelau Seamounts in the western equatorial Pacific, with water depths ranging from about 1,500 to 4,800 m. In addition to variations with latitude and water depth, element concentrations in CA margin crusts are influenced by high primary productivity in surface waters, terrestrial input, and upwelling along the continental margin. Elements associated with terrestrial input, including Na, Si, Al, K, Pb, and particularly Th, are enriched in CA margin crusts relative to crusts from the equatorial Pacific transects. Si is also associated with the biogenic phase, as are P, Ba, and Cu but these elements are lower in CA margin crusts. Ba is a proxy for primary productivity. CA margin crusts show Ba increasing with increasing water depth, while equatorial Pacific crusts show the inverse trend. In equatorial Pacific crusts, Ba correlates with decreasing latitude, which reflects increasing proximity to the high productivity zone of equatorial upwelling; additionally, local obstructional upwelling associated with primary productivity around seamounts and islands enhances the productivity signal. Cu, which is associated with the manganese oxide phase, in addition to the biogenic phase, also increases with water depth along the CA margin; this is consistent with the seawater profile for dissolved Cu. In

  15. Radial spreading of viscous-gravity currents with solidifying crust

    NASA Technical Reports Server (NTRS)

    Fink, Jonathan H.; Griffiths, Ross W.

    1990-01-01

    In the present investigation of solidifying-crust effects on the dynamics and surface morphology of radial viscous-gravity currents, polyethylene glycol inflows into the base of a tank holding a cold sucrose solution are used as analogs. As the radial current advanced away from the inlet, its surface solidified and deformed through a combination of folding anf fracturing. When cooling was sufficiently rapid, solid crust formed and caused the spreading rate to increase; progressively colder experiments revealed a sequence of surface morphologies resembling features of cooling lava flows and lava lakes, including multiarmed rift structures with shear offsets and bulbous lobate forms resembling pillow lavas on the ocean floor.

  16. Radial spreading of viscous-gravity currents with solidifying crust

    NASA Technical Reports Server (NTRS)

    Fink, Jonathan H.; Griffiths, Ross W.

    1990-01-01

    In the present investigation of solidifying-crust effects on the dynamics and surface morphology of radial viscous-gravity currents, polyethylene glycol inflows into the base of a tank holding a cold sucrose solution are used as analogs. As the radial current advanced away from the inlet, its surface solidified and deformed through a combination of folding anf fracturing. When cooling was sufficiently rapid, solid crust formed and caused the spreading rate to increase; progressively colder experiments revealed a sequence of surface morphologies resembling features of cooling lava flows and lava lakes, including multiarmed rift structures with shear offsets and bulbous lobate forms resembling pillow lavas on the ocean floor.

  17. Paleoshorelines in the Upper Cretaceous Point Lookout Sandstone, southern San Juan Basin, New Mexico

    USGS Publications Warehouse

    Zech, R.S.

    1982-01-01

    LANDSAT images and aerial photography reveal several parallel linear features as much as 17 km long and 0.7 km wide. Detailed cross sections normal to a linear feature show it to be an exhumed paleoshoreline containing several overlapping sandstone units. Each unit tends to pinchout into the shales of the overlying Menefee Formation, showing a range of depositional environments including upper shoreface, foreshore, washover and eolian. Paleogeomorphic elements, predominately beach ridges and interridge swales, shape the upper surface of the sandstone and produce a relief as great as 4.2 m. The various components found in the paleoshoreline create a trellis-like drainage pattern that contrasts with the regional dendritic drainage pattern; the resulting linear feature is easily discernible on aerial photography and LANDSAT images. The rapid lithologic and thickness changes of the sandstone bodies in these linear features provide excellent potential as stratigraphic trap for hydrocarbons. Paleoshoreline facies are likely to be preserved in areas of thickest marginal marine regressive sand accumulation and similar paleoshoreline systems may be preserved at depth in the Point Lookout (Sandstone) or other Cretaceous sandstones.

  18. The effect of fluid saturation on the dynamic shear modulus of tight sandstones

    NASA Astrophysics Data System (ADS)

    Li, Dongqing; Wei, Jianxin; Di, Bangrang; Ding, Pinbo; Shuai, Da

    2017-10-01

    Tight sandstones have become important targets in the exploration of unconventional oil and gas reservoirs. However, due to low porosity, low permeability, complex pore structure and other petrophysical properties of tight sandstones, the applicability of Gassmann’s fluid substitution procedure becomes debatable. Aiming at this problem, this paper attempts to explore the applicability of Gassmann’s theory in tight sandstones. Our focus is to investigate the sensitivity of dynamic shear modulus to fluid saturation and the possible mechanism. Ultrasonic velocity in dry and saturated tight sandstone samples was measured in the laboratory under an effective pressure within the range of 1-60 MPa. This study shows that the shear modulus of the water-saturated samples appears to either increase or decrease, and the soft porosity model (SPM) can be used to quantitatively estimate the variation of shear modulus. Under the condition of in situ pressure, samples dominated by secondary pores and microcracks are prone to show shear strengthening with saturation, which is possibly attributed to the local flow dispersion. Samples that mainly have primary pores are more likely to show shear weakening with saturation, which can be explained by the surface energy mechanism. We also find good correlation between changes in shear modulus and inaccurate Gassmann-predicted saturated velocity. Therefore, understanding the variation of shear modulus is helpful to improving the applicability of Gassmann’s theory in tight sandstones.

  19. Depositional facies, diagenesis, and reservoir quality of Ivishak sandstone (Sadlerochit Group), Prudhoe Bay field

    SciTech Connect

    McGowen, J.H.; Bloch, S.

    1985-02-01

    The Sadlerochit Group is a large fan-delta system comparable in size to the modern Kosi River wet alluvial fan of Nepal and India. Braided-stream processes distributed chert gravel and quartz and chert sand in radial fashion to construct the subaerial part of the fan delta. Fluvial energy, slope of the fan surface, and grain size decrease in a north to south basinward direction. There is also a decrease in scale of sedimentation units from source area seaward. Facies of the subaerial fan delta can be broadly categorized as midfan delta (alternating conglomerate and sandstone), distal fan-delta (chiefly sandstone), and abandoned channel-fill, overbank, and pond facies (mudstone, siltstone, fine-grained sandstone). Seaward of the subaerial fan delta are the delta-front and prodelta facies. Subaerial fan-delta and delta-front facies compose the Ivishak sandstone, which grades basinward into the Kavik shale, a prodelta facies. Diagenetic effects were gradually superimposed on the sediments deposited in the Sadlerochit fan-delta system. The sedimentary facies, and in particular their textural characteristics, seem to control the side and degree of diagenesis, including enhancement of porosity and permeability. Comparison of permeability trends among the facies of the Ivishak sandstone with permeability patterns displayed by unconsolidated sands with analogous grain size and texture, indicates that the general trends that existed in the Ivishak sediments are still recognizable in spite of the diagenetic overprint.

  20. Non-cyanobacterial diazotrophs mediate dinitrogen fixation in biological soil crusts during early crust formation

    PubMed Central

    Pepe-Ranney, Charles; Koechli, Chantal; Potrafka, Ruth; Andam, Cheryl; Eggleston, Erin; Garcia-Pichel, Ferran; Buckley, Daniel H

    2016-01-01

    Biological soil crusts (BSCs) are key components of ecosystem productivity in arid lands and they cover a substantial fraction of the terrestrial surface. In particular, BSC N2-fixation contributes significantly to the nitrogen (N) budget of arid land ecosystems. In mature crusts, N2-fixation is largely attributed to heterocystous cyanobacteria; however, early successional crusts possess few N2-fixing cyanobacteria and this suggests that microorganisms other than cyanobacteria mediate N2-fixation during the critical early stages of BSC development. DNA stable isotope probing with 15N2 revealed that Clostridiaceae and Proteobacteria are the most common microorganisms that assimilate 15N2 in early successional crusts. The Clostridiaceae identified are divergent from previously characterized isolates, though N2-fixation has previously been observed in this family. The Proteobacteria identified share >98.5% small subunit rRNA gene sequence identity with isolates from genera known to possess diazotrophs (for example, Pseudomonas, Klebsiella, Shigella and Ideonella). The low abundance of these heterotrophic diazotrophs in BSCs may explain why they have not been characterized previously. Diazotrophs have a critical role in BSC formation and characterization of these organisms represents a crucial step towards understanding how anthropogenic change will affect the formation and ecological function of BSCs in arid ecosystems. PMID:26114889

  1. Provenance, tectonics and palaeoclimate of Proterozoic Chandarpur sandstones, Chattisgarh basin: A petrographic view

    NASA Astrophysics Data System (ADS)

    Datta, Basudeb

    2005-06-01

    Sandstones of early Neoproterozoic Chandarpur Group, Chattisgarh Supergroup, central India display progressive change towards greater textural and mineralogical maturity from base to top of the succession. The clay-silt matrix decreases, sorting of sand grains improves, frequency of rounded grains increases, monocrystalline quartz content increases with concomitant decrease in polycrystalline quartz, feldspar and rock fragments. The trend of variations in different mineralogical and textural attributes, however, exhibits inflections at different stratigraphic levels. The sandstones of the basal Lohardih Formation are alluvial fan deposits, characterized by high matrix and feldspar content, iron-oxide impregnated highly angular grains and poor sorting. Petrographic properties collectively indicate that the sandstones were derived from a weathered granitic crust under a humid climatic condition. Abundance of well rounded grains within the alluvial fan and overlying braided fluvial deposit indicates prolonged wind action during episodes of high aridity. The shallow marine deposit overlying the fluvial deposits in the upper part of the Lohardih Formation exhibits bed-to-bed variation in the frequency of angular grains, feldspar content and overall maturity suggesting environmentally controlled segregation of sediments. The abrupt appearance of coarse-grained immature sandstones with concomitant reappearance of iron-oxide impregnated/altered feldspar grains in the upper part of the shelf deposits of the Chaporadih Formation point to a phase of tectonic uplift that possibly triggered a regression. Continued regression and peneplanation heralded the deposition of supermature medium-grained purple quartzarenite of the upper shoreface Kansapathar Formation in the uppermost part of the Chandarpur succession under a hot desertic climatic condition. The provenance analysis revealed that the Chandarpur clastics were derived from granites and granite-gneisses of a continental

  2. Van Horn Sandstone, Trans-Pecos Texas: Evidence for Late Cambrian rifting along southern North America

    SciTech Connect

    Hongshuan, Ye; Soegaard, K. . Programs in Geosciences)

    1993-02-01

    The Van Horn Sandstone in the Trans-Pecos region of west Texas is interpreted as a rift sequence which developed in response to Cambrian breakup along the southern margin of the North American continent. The Van Horn Sandstone consists exclusively of braided alluvial sediments and occupies relatively small isolated basins in the vicinity of the town of Van Horn. The sandstone is in structural unconformable contact above intensely deformed Precambrian sediments which are < 1,123 Ma old. The Van Horn Sandstone is overlain by more than 650 meters of earliest Ordovician to Mississippian shallow-marine shelf sediments. Geohistory analysis of the overlying Paleozoic shelf sediments indicates that subsidence was driven by thermal contraction of the crust and that the shallow-marine sediments represent a drift sequence. Subsidence history curves correspond with theoretical thermal decay curves where [beta] = 1.2 and suggest that thermal subsidence commenced in Late Cambrian time about 510 Ma ago. Increased crustal attenuation, resulting in development of an ocean basin, occurred between Van Horn and the original location of deep water sediments presently exposed in the Marathon uplift to the south. Proposed Late Cambrian breakup south of Van Horn is coeval with rifting in the southern Oklahoma aulachogen and Rome trough in the Appalachian Mountains, but post-dates the main Late Proterozoic rifting event between 625 and 555 Ma along the eastern and western freeboard of North American. The significance of diachronous rifting in Eocambrian-Cambrian time is unclear at present but has consequences for fragmentation of the late Precambrian supercontinent Rodinia'.

  3. Reservoir characterization of Mesaverde (Campanian) bedload fluvial meanderbelt sandstones, northwestern Colorado

    SciTech Connect

    Jones, J.R. Jr.

    1984-04-01

    Reservoir characterization of Mesaverde meanderbelt sandstones is used to determined directional continuity of permeable zones. A 500-m (1600 ft) wide fluvial meanderbelt in the Mesaverde Group is exposed as laterally continuous 3-10-m (10-33-ft) high sandstone cliffs north of Rangely, Colorado. Forty-eight detailed measured sections through 3 point bar complexes oriented at right angles to the long axis of deposition and 1 complex oriented parallel to deposition were prepared. Sections were tied together by detailed sketches delineating and tracing major bounding surfaces such as scours and clay drapes. These complexes contain 3 to 8 multilateral sandstone packages separated by 5-20 cm (2-8 in.) interbedded siltstone and shale beds. Component facies are point bars, crevasse splays, chute bars, and floodplain/overbank deposits. Two types of lateral accretion surfaces are recognized in the point bar facies. Gently dipping lateral accretions containing fining-upward sandstone packages. Large scale trough cross-bedding at the base grades upward into ripples and plane beds. Steeply dipping lateral accretion surfaces enclose beds characterized by climbing ripple cross laminations. Bounding surfaces draped by shale lags can seal vertically stacked point bars from reservoir communication. Scoured boundaries allow communication in some stacked point bars. Crevasse splays showing climbing ripples form tongues of very fine-grained sandstone which flank point bars. Chute channels commonly cut upper point bar surfaces at their downstream end. Chute facies are upward-fining with small scale troughs and common dewatering structures. Siltstones and shales underlie the point bar complexes and completely encase the meanderbelt system. Bounding surfaces at the base of the complexes are erosional and contain large shale rip-up clasts.

  4. Hawaiian submarine manganese-iron oxide crusts - A dating tool?

    USGS Publications Warehouse

    Moore, J.G.; Clague, D.A.

    2004-01-01

    Black manganese-iron oxide crusts form on most exposed rock on the ocean floor. Such crusts are well developed on the steep lava slopes of the Hawaiian Ridge and have been sampled during dredging and submersible dives. The crusts also occur on fragments detached from bedrock by mass wasting, on submerged coral reefs, and on poorly lithified sedimentary rocks. The thickness of the crusts was measured on samples collected since 1965 on the Hawaiian Ridge from 140 dive or dredge localities. Fifty-nine (42%) of the sites were collected in 2001 by remotely operated vehicles (ROVs). The thinner crusts on many samples apparently result from post-depositional breakage, landsliding, and intermittent burial of outcrops by sediment. The maximum crust thickness was selected from each dredge or dive site to best represent crusts on the original rock surface at that site. The measurements show an irregular progressive thickening of the crusts toward the northwest-i.e., progressive thickening toward the older volcanic features with increasing distance from the Hawaiian hotspot. Comparison of the maximum crust thickness with radiometric ages of related subaerial features supports previous studies that indicate a crust-growth rate of about 2.5 mm/m.y. The thickness information not only allows a comparison of the relative exposure ages of two or more features offshore from different volcanoes, but also provides specific age estimates of volcanic and landslide deposits. The data indicate that some of the landslide blocks within the south Kona landslide are the oldest exposed rock on Mauna Loa, Kilauea, or Loihi volcanoes. Crusts on the floors of submarine canyons off Kohala and East Molokai volcanoes indicate that these canyons are no longer serving as channelways for downslope, sediment-laden currents. Mahukona volcano was approximately synchronous with Hilo Ridge, both being younger than Hana Ridge. The Nuuanu landslide is considerably older than the Wailau landslide. The Waianae

  5. Characterizing flow pathways in a sandstone aquifer at multiple depths

    NASA Astrophysics Data System (ADS)

    Medici, Giacomo; West, Jared; Mountney, Nigel

    2017-04-01

    Sandstone aquifers are commonly assumed to represent porous media characterized by a permeable matrix. However, such aquifers may be heavily fractured where rock properties and timing of deformation favour brittle failure and crack opening. In many aquifer types, fractures associated with faults, bedding planes and stratabound joints represent preferential pathways for fluids and contaminants. This presentation reports well-test results and outcrop-scale studies that reveal how strongly lithified siliciclastic rocks may be entirely dominated by fracture flow at shallow depths (≤ 150 m), similar to limestone and crystalline aquifers. The Triassic St Bees Sandstone Formation of the UK East Irish Sea Basin represents an optimum succession for study of the influence of both sedimentary and tectonic aquifer heterogeneities in a strongly lithified sandstone aquifer-type. This sedimentary succession of fluvial origin accumulated in rapidly subsiding basins, which typically favour preservation of complete depositional cycles, including fine-grained mudstone and silty sandstone layers of floodplain origin interbedded with sandstone-dominated fluvial channel deposits. Vertical joints in the St Bees Sandstone Formation form a pervasive stratabound system whereby joints terminate at bedding-parallel discontinuities. Additionally, normal faults are present through the succession and record development of open-fractures in their damage zones. Here, the shallow aquifer (depth ≤150 m BGL) was characterized in outcrop and well tests. Fluid temperature, conductivity and flow-velocity logs record inflows and outflows from normal faults, as well as from pervasive bed-parallel fractures. Quantitative flow logging analyses in boreholes that cut fault planes indicate that zones of fault-related open fractures typically represent ˜ 50% of well transmissivity. The remaining flow component is dominated by bed-parallel fractures. However, such sub-horizontal fractures become the

  6. Soil CO2 and O2 concentrations in shale and sandstone catchments of central Pennsylvania.

    NASA Astrophysics Data System (ADS)

    Hill, L. Z.; Kaye, J. P.; Brantley, S.

    2016-12-01

    In order to increase understanding of parent material controls on biogeochemical processes, we monitored the depth distribution of soil CO2 and O2 concentrations in central Pennsylvania in two watersheds on different lithologies. We deployed gas monitoring instrumentation on two catena transects, one located on sandstone and the other on shale. As expected, with increasing soil depth, O2 concentrations decreased while pCO2 increased. Over the year of monitoring, CO2 concentrations varied between the shale and sandstone locations. When soils were consistently wet (e.g. September and October 2015) pCO2 at 25 cm below the soil surface was 2 to 3 times greater on the sandstone ridgetop and north-facing mid-slope than its shale counter-parts. During the rest of the growing season, CO2 and O2 concentrations varied more by topographical position than with lithology, as the valley floor positions in both catenas had the highest pCO2 for a given depth. Both infrequent manual sampling from many gas access tubes and continuous sampling by a limited number of buried sensors documented these patterns. Because these sites are in close proximity with similar temperature and precipitation, we hypothesize that elevated pCO2 in the surface of sandstone-derived soils (relative to shale) is a result of a thicker organic horizon and differences in the associated heterotrophic respiration. At depth, the higher pCO2 at the sandstone site may be due to a combination of carbon availability and constraints of diffusion. Adjacent forests underlain by shale and sandstone parent materials are prevalent throughout the Appalachian Mountains and if our sites are representative of this region, processes related to soil CO2 and O2, including weathering rates, nutrient cycling, microbial productivity, root growth, and soil respiration may differ markedly in these adjacent forests.

  7. Three-dimensional morphology of pores and cracks in intact and mechanically deformed sandstones

    NASA Astrophysics Data System (ADS)

    Menendez, B.; David, C.; Wong, T.-F.; Martinez-Nistal, A.

    2003-04-01

    We have studied four different sandstones under confocal laser scanning microscopy (CLSM). In order to discriminate the void space from the grains, the samples were impregnated with a fluorescent dyed (Rhodamine B) resin and thin-sections with a thickness larger than usual were prepared and studied with CSLM. Two different kinds of samples have been studied: mechanically deformed samples of Darley Dale and Berea sandstones and intact samples of Rothbach and Bentheim sandstones. On each sample several three dimensional blocks have been investigated with size 228 by 152 microns and depths ranging from 35 to 100 microns. From each block a series of tens of parallel "virtual sections" has been recorded, separated by 1 or 2 microns in depth. First we show some examples on Darley Dale and Berea sandstone samples deformed in triaxial experiments. Rotating animations are built from series of 3D views of reconstructed crack networks taken step by step for different block orientations. When put together these 3D views nicely simulate a rotation of the 3D block. To create and run the animations we used the Confocal Assistant free software on a PC. Spectacular 3D animations representing crack networks in mechanically deformed samples are obtained this way in a very short time: some examples will be shown on the screen. Secondly we show on a poster some static 3D reconstructions of the pore and/or crack networks obtained using the Slicer Dicer software. For the intact samples we observe that pore (or grain) walls are smoother in Bentheim sandstone whereas in Rothbach sandstone the presence of a significant amount of coating clay minerals results in a visible surface roughness. Some differences in pore size and pore shape were also observed, with a more homogeneous distribution in Bentheim sandstone than in Rothbach sandstone. In both sandstones we observe the classical pore-to-throats junctions. Complex contact geometry between adjacent grains are sometimes observed. In the

  8. Sea level and paleotectonic controls on distribution of reservoir sandstone of Lower Cretaceous Muddy Sandstone, Hilight Field, Powder River basin, Wyoming

    SciTech Connect

    Wheeler, D.M.; Gustason, E.R.

    1987-05-01

    To date, over 74 million bbl of oil have been produced from stratigraphic traps at Hilight field. Production is primarily from thin but stratigraphically complex fluvial and shallow marine sandstone of the Lower Cretaceous Muddy Sandstone. The deposition and preservation of these reservoirs were controlled by the interplay between sea level and tectonics. The Muddy Sandstone in Hilight field was deposited during a late Albian sea level rise. It onlaps an erosional surface, developed during the preceding sea level drop, including a dendritic valley system cut deeply into the underlying Skull Creek Shale. In this area, the Muddy consists of four members that are bounded by transgressive disconformities. These members were deposited during stillstands in the overall rise of sea level. The lower two members consist of fluvial and fluvial-estuarine deposits which fill the valley system; the upper two members consist of fluvial-deltaic and barrier island deposits. Three northeast-trending lineaments transect Hilight field. These lineaments are interpreted to represent basement faults that experienced recurrent movement during Muddy deposition. Relative structural downdrop controlled the orientation of drainages that cut the Hilight valley system. Recurrent movement provided structural and topographic lows within which relatively thick fluvial-deltaic and barrier island sandstones were deposited and preserved. Thinner sequences were deposited and subsequently eroded on adjacent structural and topographic highs.

  9. Structure and Composition of the Lunar Crust

    NASA Astrophysics Data System (ADS)

    Spudis, P. D.; Bussey, D. B. J.; Hawke, B. R.

    1999-01-01

    , the average lunar highlands composition is, as long suspected, that of "anorthositic norite", a mixed rock type, somewhat similar to many of the lunar meteorites (e.g,., ALHA 81005 and more mafic than pure ferroan anorthosite. Anorthosite proper does occur on the Moon; it is found almost exclusively within the inner rings of multiring basins. These basins span a range of ages and distributions. Mafic provinces occur in the central Procellarum region of the front side and on the floor of the South Pole Aitken Basin. In these areas, the lunar surface is "highland basaltic" composition (FeO about 9-10 wt%). Additional highland basaltic areas occur in the vicinity of nearside basins, such as Serenitatis. The major lunar "hot spot" of high Th concentration (about 10 ppm) occurs within a broad, oval depression approximately coincident with Oceanus Procellarum. Slightly less elevated amounts (about ppm) are associated with the basaltic floor of SPA Basin on the farside. Aside from this, Th highs are isolated and minor. On the basis of the new global data, as well as from our continuing study of the composition of basin ejecta to probe the deep crust, we have modified slightly our existing crustal model to accommodate the new findings. We propose a three-layer model of crustal configuration. The uppermost zone, down to depths of about 15-20 km, consists of mega breccia of mostly anorthositic norite composition (FeO about 4-6 wt%; Al2O3 about 26 wt%). This zone is neither laterally or vertically uniform, displaying anomalous compositional zones at scales of tens to hundreds of kilometers, but is remarkably homogeneous at planetwide scales. In bulk composition, it resembles the "ferroan anorthositic norite" suite of mixed rocks described by Lindstorm et al. and many of the highlands regolith breccias found as lunar meteorites. It is also similar to the average crustal composition inferred by Taylor , on the basis of Apollo granulitic breccias and limited orbital chemical data

  10. Algal biomass and primary production within a temperate zone sandstone

    SciTech Connect

    Bell, R.A.; Sommerfeld, M.R. )

    1987-02-01

    The use of dimethyl sulfoxide (DMSO) to extract chlorophyll a and {sup 14}C-labelled photosynthate from endolithic algae of sparsely vegetated, cold temperate grasslands on the Colorado Plateau in Arizona has yielded the first estimates of biomass and photosynthesis for this unusual community. These subsurface microorganisms are found widespread in exposed Coconino Sandstone, a predominant formation in this cold temperate region. The endolithic community in Coconino Sandstone, composed primarily of coccoid blue-green and coccoid/sarcinoid green algae, yielded a biomass value (as chlorophyll a content) of 87 mg m{sup {minus}2} rock surface area and a photosynthetic rate of 0.37 mg CO{sub 2} dm{sup {minus}2} hr{sup {minus}1} or 0.48 mg CO{sub 2} mg{sup {minus}1} chl a hr{sup {minus}1}. The endolithic algal community contributes moderate biomass (5-10%) and substantial photosynthesis (20-80%) to the sparse grassland ecosystem.

  11. Effective pressure law for permeability of E-bei sandstones

    NASA Astrophysics Data System (ADS)

    Li, M.; Bernabé, Y.; Xiao, W.-I.; Chen, Z.-Y.; Liu, Z.-Q.

    2009-07-01

    Laboratory experiments were conducted to determine the effective pressure law for permeability of tight sandstone rocks from the E-bei gas reservoir, China. The permeability k of five core samples was measured while cycling the confining pressure pc and fluid pressure pf. The permeability data were analyzed using the response-surface method, a statistical model-building approach yielding a representation of k in (pc, pf) space that can be used to determine the effective pressure law, i.e., peff = pc - κpf. The results show that the coefficient κ of the effective pressure law for permeability varies with confining pressure and fluid pressure as well as with the loading or unloading cycles (i.e., hysteresis effect). Moreover, κ took very small values in some of the samples, even possibly lower than the value of porosity, in contradiction with a well-accepted theoretical model. We also reanalyzed a previously published permeability data set on fissured crystalline rocks and found again that the κ varies with pc but did not observe κ values lower than 0.4, a value much larger than porosity. Analysis of the dependence of permeability on effective pressure suggests that the occurrence of low κ values may be linked to the high-pressure sensitivity of E-bei sandstones.

  12. Preserving Native American petroglyphs on porous sandstone

    USGS Publications Warehouse

    Grisafe, D.A.

    1996-01-01

    A new method of chemical treatment is proposed to improve the durability of soft, porous sandstones onto which Native American petroglyphs have been carved. Cores of Dakota Sandstone from the Faris Cave site, located along the Smoky Hill River in Ellsworth County, Kansas, were treated with ethyl silicate dissolved in a lightweight ketone carrier, and some cores were subsequently treated with a combination of ethyl silicate and silane using the same solvent. Measurement of the resulting physical properties, when compared to untreated cores, indicate the treatments substantially increased the compressive strength and freeze-thaw resistance of the stone without discoloring the stone or completely sealing the pore system. The treatment increases the durability of the stone and provides a method for preserving the petroglyphs at the site. After treating test panels at the site, the petroglyphs were treated in like manner.

  13. Fractures and stresses in Bone Spring sandstones

    SciTech Connect

    Warpinski, N.R.; Sattler, A.R.; Lorenz, J.C.; Northrop, D.A.

    1992-06-01

    This project was a collaboration between Sandia National Laboratories and the Harvey E. Yates Company (Heyco), Roswell, NM, conducted under the auspices of Department of Energy's Oil Recovery Technology Partnership. The project applied Sandia perspectives on the effects of natural fractures, stress, and sedimentology for the stimulation and production of low permeability gas reservoirs to low permeability oil reservoirs, such as those typified by the Bone Spring sandstones of the Delaware Basin, southeast New Mexico. This report details the results and analyses obtained in 1990 from core, logs, stress, and other data taken from three additional development wells. An overall summary gives results from all five wells studied in this project in 1989--1990. Most of the results presented are believed to be new information for the Bone Spring sandstones.

  14. Lava crusts and flow dynamics

    NASA Technical Reports Server (NTRS)

    Kilburn, C. R. J.

    1993-01-01

    Lava flows can be considered as hot viscous cores within thinner, solidified crusts. Interaction between crust and core determines a flow's morphological and dynamical evolution. When the lava core dominates, flow advance approaches a steady state. When crusts are the limiting factor, advance is more irregular. These two conditions can be distinguished by a timescale ratio comparing rates of core deformation and crustal formation. Aa and budding pahoehoe lavas are used as examples of core- and crustal-dominated flows, respectively. A simple model describes the transition between pahoehoe and aa flow in terms of lava discharge rate, underlying slope, and either the thickness or velocity of the flow front. The model shows that aa morphologies are characterized by higher discharge rates and frontal velocities and yields good quantitative agreement with empirical relations distinguishing pahoehoe and aa emplacement on Hawaii.

  15. Numerical modeling of subduction, accretion, and collision of island arc crust onto continental crust

    NASA Astrophysics Data System (ADS)

    Tetreault, J. L.; Buiter, S.

    2011-12-01

    Arc-continent collision occurs when a subducting continent collides into the island arc on the overriding plate or when the island arc is on the subducting plate with an overriding continent. In addition to arc-continent collision, the latter case can lead to full subduction of the arc or accretion parts of arc crust. Accreted terranes composed of arc crustal material are present in the geological record as imbricated slices of crustal rocks or crustal blocks intermingled with accretionary prism rocks. We use numerical experiments to test the importance of different mechanical parameters of the arc crust that allow the arc to subduct, accrete, or collide with an overriding continent. Our experiments specifically focus on the effects of lithospheric buoyancy and detachment layers in the arc crust on subduction geodynamics. We examine the geodynamics of island arc-continent interaction using thermo-mechanical experiments that incorporate a free surface and viscous-plastic rheology. In our numerical experiments, subduction is allowed to freely evolve by including a low viscosity subduction channel. We vary buoyancy and detachment layers for an island arc located on the subducting oceanic plate with an overriding continental plate. The rheological structure of the island arc is represented with upper, middle, and lower crust layers illustrative of the seismic crustal structure of modern arcs. Lithospheric buoyancy is varied by changing the island arc crustal thickness and density. We impose various detachment layers in the arc crust to examine the effect on subduction, accretion, or collision. A basal detachment layer represents the ultramafic crust-mantle transition layer that is posited to founder due to high densities or serve as a weak delamination layer during collision. Detachment layers at other depths represent layers weakened by backarc rifting. Our numerical experiments show that the influence of detachment layers outweighs buoyancy when testing the ability

  16. Reduction of acrylamide content in bread crust by starch coating.

    PubMed

    Liu, Jie; Liu, Xiaojie; Man, Yong; Liu, Yawei

    2017-06-16

    A technique of starch coating to reduce acrylamide content in bread crust was proposed. Bread was prepared in accordance with a conventional procedure and corn or potato starch coating was brushed on the surface of the fermented dough prior to baking. Corn starch coating caused a decrease in acrylamide of 66.7% and 77.1% for the outer and inner crust, respectively. The decrease caused by the potato starch coating was 68.4% and 77.4%, respectively. Starch coating reduced asparagine content significantly (43.4-82.9%; P < 0.01)in both the outer and inner crust. A lower temperature (difference of 10-20 °C) in combination with a higher moisture content (maximum difference of 8%) of bread crust were a result of starch coating, which effectively shortened the time span (4-8 min) over which acrylamide could form and accumulate. The present study demonstrates that starch coating could be a simple, effective and practical application for reducing acrylamide levels in bread crust without changing the texture and crust color of bread. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

  17. Experimental research on seismoelectric effects in sandstone

    NASA Astrophysics Data System (ADS)

    Peng, Rong; Wei, Jian-Xing; Di, Bang-Rang; Ding, Pin-Bo; Liu, Zi-Chun

    2016-09-01

    The seismoelectric effects induced from the coupling of the seismic wave field and the electromagnetic field depend on the physical properties of the reservoir rocks. We built an experimental apparatus to measure the seismoelectric effects in saturated sandstone samples. We recorded the seismoelectric signals induced by P-waves and studied the attenuation of the seismoelectric signals induced at the sandstone interface. The analysis of the seismoelectric effects suggests that the minimization of the potential difference between the reference potential and the baseline potential of the seismoelectric disturbance area is critical to the accuracy of the seismoelectric measurements and greatly improves the detectability of the seismoelectric signals. The experimental results confirmed that the seismoelectric coupling of the seismic wave field and the electromagnetic field is induced when seismic wave propagating in a fluid-saturated porous medium. The amplitudes of the seismoelectric signals decrease linearly with increasing distance between the source and the interface, and decay exponentially with increasing distance between the receiver and the interface. The seismoelectric response of sandstone samples with different permeabilities suggests that the seismoelectric response is directly related to permeability, which should help obtaining the permeability of reservoirs in the future.

  18. Matrix versus fracture permeability in a regional sandstone aquifer (Wajid sandstone, SW Saudi Arabia)

    NASA Astrophysics Data System (ADS)

    Al Ajmi, Hussain; Hinderer, Matthias; Rausch, Randolf; Hornung, Jens; Bassis, Alexander; Keller, Martin; Schüth, Christoph

    2014-06-01

    Sandstones are often characterized as fractured aquifers. We present a case study of the Wajid sandstone, which forms a regional aquifer system in SW Saudi Arabia, where matrix, fracture, and large-scale hydraulic conductivities are coincident. The measurements deal with different scales and methods and are based on porosity and permeability measurements in the laboratory, as well as pumping tests in the field. Porosities of the sandstone samples in general are high and range between less than 5 % and more than 45 %. Gas permeabilities for strongly cemented samples are < 1 mD, whereas most samples range in between 500 and 5,000 mD. There is only a weak anisotropy with preference of the horizontal x-, y-directions. Hydraulic conductivities of the matrix samples (5.5 · 10-6 m/s and 1.1 · 10-5 m/s for the Upper and Lower Wajid sandstone, respectively) were in the same order of magnitude compared to hydraulic conductivities derived from pumping tests (8.3 · 10-5 m/s and 2.2 · 10-5 m/s for the Upper and Lower Wajid sandstone, respectively).

  19. Palaeomagnetism and the continental crust

    SciTech Connect

    Piper, J.D.A.

    1987-01-01

    This book is an introduction to palaeomagnetism offering treatment of theory and practice. It analyzes the palaeomagnetic record over the whole of geological time, from the Archaean to the Cenozoic, and goes on to examine the impact of past geometries and movements of the continental crust at each geological stage. Topics covered include theory of rock and mineral magnetism, field and laboratory methods, growth and consolidation of the continental crust in Archaean and Proterozoic times, Palaeozoic palaeomagnetism and the formation of Pangaea, the geomagnetic fields, continental movements, configurations and mantle convection.

  20. Grebull sandstone pool (Lower Cretaceous) on Elk Basin thrust-fold complex, Wyoming and Montana

    SciTech Connect

    Stone, D.S.

    1984-07-01

    The Elk Basin field in the northern Bighorn basin is a giant structural trap with cumulative production surpassing 500 million bbl, principally from a Paleozoic common pool. Abundant well data and seismic information have been used in a stratigraphic and structural study focusing on the Greybull (Lower Cretaceous) gas pool and on deeper formations along this structural complex. These data support an interpretation of the Elk Basin field as a thrust-fold complex, underlain by a listric thrust fault zone which probably emanates from Precambrian basement at an angle of 45/sup 0/ or less. The fault steepens upward and dies out in steeply dipping Mesozoic clastics that are attenuated and cut by extensional faults at the surface. The little known Greybull Sandstone pool at Elk Basin field, which is now used for gas storage, was discovered in 1920, and contained estimated primary recoverable reserves of 54 bcf of gas at an average depth of about 2500 ft (760 m). The Greybull lies stratigraphically between the Dakota and Morrison Formations, and is composed of two distinct sandstone units, called A and B at the North Clark's Fork field in southern Montana. The lower B unit at Elk Basin is a fluvial river-channel deposit which ranges up to 150 ft (45 m) in thickness and nearly 2 mi (3 km) in width. The upper A unit is a series of shoreline sandstone deposits oriented northwest-southeast. Individual, porous A sandstone bodies range from a few feet to more than 20 ft (6 m) in thickness at Elk Basin. These two Greybull Sandstone units are part of a common gas pool covering about 2000 acres (800 ha.) of the crestal closure of the Elk Basin anticline. Seismic modeling indicates that Greybull Sandstone channels over 60 ft (18 m) thick may be detected by reflection character changes in CDP seismic data.

  1. CO2 Wettability of the Mt. Simon Sandstone and Implications for Predicting Pore Scale Transport

    NASA Astrophysics Data System (ADS)

    Botto, J.; Werth, C. J.; Valocchi, A. J.

    2015-12-01

    Geological sequestration of CO2 is an emerging technology for mitigating atmospheric accumulation of CO2. A large demonstration of this technology was performed in the Illinois Basin under the direction of the Midwest Geological Sequestration Consortium. A key challenge is predicting the migration pathways of CO2 in the Mt. Simon Sandstone of the Illinois Basin, which is a function of reservoir permeability and wettability. The primary goal of this effort is to measure the CO2 wettability of rock samples from the Mt. Simon Sandstone, and to determine how this wettability is affected by the different mineral components comprising the samples. Contact angle measurements of CO2 in brine on pure minerals present in the Mt. Simon sandstone, and on the Mt. Simon sandstone itself, will be presented. The effects of surface roughness and surface charge of the samples on contact angle will also be presented. Implications of the results on predicting wettability in real reservoirs will be discussed, as well as the effects of wettability on predicting the migration of CO2 at the pore scale.

  2. Seastacks buried beneath newly reported Lower Miocene sandstone, northern Santa Barbara County, California

    SciTech Connect

    Fritsche, A.E.; Hanna, F.M.

    1985-04-01

    Three large, isolated exposures of a light-gray, coarse-grained, thick-bedded sandstone unit occur in the northern San Rafael Mountains of Santa Barbara County, California. These rocks are moderately fossiliferous and contain Vertipecten bowersi, Amussiopecten vanvlecki, Aequipecten andersoni, Otrea howelli, shark teeth, whale bones, and regular echinoid spines. The fossils indicate that the sandstone unit, although previously reported as upper(.) Miocene, correlates best with the lower Miocene Vaqueros Formation. This unit was deposited in angular unconformity on a Cretaceous, greenish-gray turbidite sequence of interbedded sandstone and shale, and onlaps the unconformity erosion surface from west to east, the unit being thicker in the west and older at its base. The underlying Cretaceous sandstone beds are well indurated, and during the eastward transgression of the early Miocene sea, they resisted wave erosion and stood as seastacks offshore of the advancing coastline, thus creating a very irregular topographic surface upon which the Vaqueros Formation was deposited. Some seastacks were as much as 4 m tall, as indicated by inliers of Cretaceous rock surrounded by 4-m thick sections of the Vaqueros Formation.

  3. Time-dependent brittle creep in Darley Dale sandstone

    NASA Astrophysics Data System (ADS)

    Heap, M. J.; Baud, P.; Meredith, P. G.; Bell, A. F.; Main, I. G.

    2009-07-01

    The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's crust. The chemical influence of pore water promotes time-dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Here, we report results from a study of time-dependent brittle creep in water-saturated samples of Darley Dale sandstone (initial porosity, 13%) under triaxial stress conditions. Results from conventional creep experiments show that axial strain rate is heavily dependent on the applied differential stress. A reduction of only 10% in differential stress results in a decrease in strain rate of more than two orders of magnitude. However, natural sample variability means that multiple experiments must be performed to yield consistent results. Hence we also demonstrate that the use of stress-stepping creep experiments can successfully overcome this issue. We have used the stress-stepping technique to investigate the influence of confining pressure at effective confining pressures of 10, 30, and 50 MPa (while maintaining a constant 20 MPa pore fluid pressure). Our results demonstrate that the stress corrosion process appears to be significantly inhibited at higher effective pressures, with the creep strain rate reduced by multiple orders of magnitude. The influence of doubling the pore fluid pressure, however, while maintaining a constant effective confining pressure, is shown to influence the rate of stress corrosion within the range expected from sample variability. We discuss these results in the context of microstructural analysis, acoustic emission hypocenter locations, and fits to proposed macroscopic creep laws.

  4. Mobility of partially molten crust, heat and mass transfer, and the stabilization of continents

    NASA Astrophysics Data System (ADS)

    Teyssier, Christian; Whitney, Donna L.; Rey, Patrice F.

    2017-04-01

    The core of orogens typically consists of migmatite terrains and associated crustal-derived granite bodies (typically leucogranite) that represent former partially molten crust. Metamorphic investigations indicate that migmatites crystallize at low pressure (cordierite stability) but also contain inclusions of refractory material (mafic, aluminous) that preserve evidence of crystallization at high pressure (HP), including HP granulite and eclogite (1.0-1.5 GPa), and in some cases ultrahigh pressure (2.5-3.0 GPa) when the continental crust was subducted (i.e. Norwegian Caledonides). These observations indicate that the partially molten crust originates in the deep crust or at mantle depths, traverses the entire orogenic crust, and crystallizes at shallow depth, in some cases at the near-surface ( 2 km depth) based on low-T thermochronology. Metamorphic assemblages generally show that this nearly isothermal decompression is rapid based on disequilibrium textures (symplectites). Therefore, the mobility of partially molten crust results in one of the most significant heat and mass transfer mechanisms in orogens. Field relations also indicate that emplacement of partially molten crust is the youngest major event in orogeny, and tectonic activity essentially ceases after the partially molten crust is exhumed. This suggests that flow and emplacement of partially molten crust stabilize the orogenic crust and signal the end of orogeny. Numerical modeling (open source software Underworld; Moresi et al., 2007, PEPI 163) provides useful insight into the mechanisms of exhumation of partially molten crust. For example, extension of thickened crust with T-dependent viscosity shows that extension of the shallow crust initially drives the mobility of the lowest viscosity crust (T>700°C), which begins to flow in a channel toward the zone of extension. This convergent flow generates channel collision and the formation of a double-dome of foliation (two subdomes separated by a steep

  5. Is Ishtar Terra a thickened basaltic crust?

    NASA Technical Reports Server (NTRS)

    Arkani-Hamed, Jafar

    1992-01-01

    The mountain belts of Ishtar Terra and the surrounding tesserae are interpreted as compressional regions. The gravity and surface topography of western Ishtar Terra suggest a thick crust of 60-110 km that results from crustal thickening through tectonic processes. Underthrusting was proposed for the regions along Danu Montes and Itzpapalotl Tessera. Crustal thickening was suggested for the entire Ishtar Terra. In this study, three lithospheric models with total thicknesses of 40.75 and 120 km and initial crustal thicknesses of 3.9 and 18 km are examined. These models could be produced by partial melting and chemical differentiation in the upper mantle of a colder, an Earth-like, and a hotter Venus having temperatures of respectively 1300 C, 1400 C, and 1500 C at the base of their thermal boundary layers associated with mantle convection. The effects of basalt-granulite-eclogite transformation (BGET) on the surface topography of a thickening basaltic crust is investigated adopting the experimental phase diagram and density variations through the phase transformation.

  6. Use of single-grain geochemistry of cryptic tuffs and volcaniclastic sandstones improves the tephrostratigraphic framework of Olduvai Gorge, Tanzania

    NASA Astrophysics Data System (ADS)

    McHenry, Lindsay J.; Stollhofen, Harald; Stanistreet, Ian G.

    2013-09-01

    Single-grain geochemical composition of volcaniclastic sandstones can be a potential tool to improve correlations of mixed pyroclastic/epiclastic deposits. To test this, trachytic tuffs of the paleoanthropologically important FLK, FLK N, and FLK NN sites of Pleistocene Olduvai Gorge Bed I (Tanzania) are used as an established tephrostratigraphic framework against which to test volcaniclastic sandstone correlations. Fluvio-lacustrine sandstones and tuff samples were collected from eight archeological trenches between Tuffs IB and ID across a 500-m transect, including Leakey's famous Zinjanthropus (FLK) and OH 7/OH 8 (FLK NN) sites. A previously unknown, thin, fine, mineralogically unique, black trachyandesitic fallout ash was discovered below Tuff IC. Compositions of individual augite, feldspar and titanomagnetite grains from sandstones between Tuffs IB and IC reveal some IB-equivalent material, and a new compositional assemblage distinct from the sandwiching marker tuffs. Mineral compositions of the "tripartite" volcaniclastic sandstone between Tuffs IC and ID are similar to ID. Volcaniclastic sandstone grain fingerprints further refine correlations between fluvio-lacustrine sections within the area, providing support for proposed high-resolution stratigraphic reconstruction of the Zinjanthropus and OH 7/OH 8 land surfaces. This method might be applied to other sections where pyroclastic particles are admixed but distinct tuffs are not preserved.

  7. Influence of high-frequency strandline cycles on internal reservoir geometry: Point Lookout sandstone, New Mexico and Colorado

    SciTech Connect

    Wright, R.

    1989-03-01

    High-frequency (< 100,000 years) transgressive-regressive strandline couplets that form basic building blocks of individual marine shoreface sandstones strongly influence strandline migration pattern and internal reservoir geometry. At reservoir scale, couplets average 7-10 m thick and are characterized by repetitive stacking of genetically related sandstone-mud rock packages. Individual cycles, or architectural elements, correlate in 3-D outcrop for at least 30 km, are locally bundled into larger discrete packages of five to eight constituent cycles, and are distinguishable in well logs. Contrary to long-held opinion, many of these cycles are not asymmetric. Rather, they contain thin (< 3 m) transgressive systems tracts that are overlain by thicker (< 7 m) regressive systems tracts and which are separated from one another by a pronounced downdip surface. Transgressive mud rocks fine upward from siltstone to clay-shale and coarsen landward less than 10 km into thinly interbedded sandstones with abundant siderite lags. Regressive mud rocks coarsen upward and landward into prograding shoreface sandstones that may overlie transgressive sandstones in proximal positions. Landward facies transitions within transgressive and regressive components of a single cycle vary, resulting in complex lithofacies interlayering. The significance for reservoir studies is that repeated transgressive systems tracts form predictable intraformational stratigraphic markers which may influence both horizontal and vertical fluid migration pathways. Importantly, the standard vertical profile fails to properly interpret transgressive deposits (especially sandstones) in the absence of a well-constrained lateral model.

  8. Microenvironments and microscale productivity of cyanobacterial desert crusts

    USGS Publications Warehouse

    Garcia-Pichel, F.; Belnap, Jayne

    1996-01-01

    We used microsensors to characterize physicochemical microenvironments and photosynthesis occurring immediately after water saturation in two desert soil crusts from southeastern Utah, which were formed by the cyanobacteria Microcoleus vaginatus Gomont, Nostoc spp., and Scytonema sp. The light fields within the crusts presented steep vertical gradients in magnitude and spectral composition. Near-surface light-trapping zones were formed due to the scattering nature of the sand particles, but strong light attenuation resulted in euphotic zones only ca. 1 mm deep, which were progressively enriched in longer wavelengths with depth. Rates of gross photosynthesis (3.4a??9.4 mmol O2A?ma??2A?ha??1) and dark respiration (0.81a??3.1 mmol Oa??2A?ma??2A?ha??1) occurring within 1 to several mm from the surface were high enough to drive the formation of marked oxygen microenvironments that ranged from oxygen supersaturation to anoxia. The photosynthetic activity also resulted in localized pH values in excess of 10, 2a??3 units above the soil pH. Differences in metabolic parameters and community structure between two types of crusts were consistent with a successional pattern, which could be partially explained on the basis of the microenvironments. We discuss the significance of high metabolic rates and the formation of microenvironments for the ecology of desert crusts, as well as the advantages and limitations of microsensor-based methods for crust investigation.

  9. Radiogenic heat production in the continental crust

    NASA Astrophysics Data System (ADS)

    Jaupart, Claude; Mareschal, Jean-Claude; Iarotsky, Lidia

    2016-10-01

    The thermal structure and evolution of continents depend strongly on the amount and distribution of radioactive heat sources in the crust. Determining the contribution of crustal rocks beneath a superficial layer is a major challenge because heat production depends weakly on major element composition and physical properties such as seismic wavespeed and density. Enriched granitic intrusives that lie at the current erosion level have a large impact on the surface heat flux but little influence on temperatures in the deep crust. Many lower crustal rocks that are poor in heat producing elements are restites from ancient orogenic events, implying that enrichment of the upper crust was achieved at the expense of deeper crustal levels. For the same total heat production, concentrating heat sources in an upper layer acts to reduce temperatures in the lower crust, thereby allowing stabilization of the crust. The present-day structure of the crust is a consequence of orogeny and should not be adopted for thermal models of the orogenic event itself. This review summarizes information extracted from large data sets on heat flow and heat production and provides estimates of crustal stratification and heat production in several geological provinces. Analysis of global and regional data sets reveals the absence of a positive correlation between surface heat flow and crustal thickness, showing that the average crustal heat production is not constant. Differences of heat flow between geological provinces are due in large part to changes of crustal structure and bulk composition. Collating values of the bulk crustal heat production in a few age intervals reveals a clear trend of decrease with increasing age. This trend can be accounted for by radioactive decay, indicating that thermal conditions at the time of crustal stabilization have not changed significantly. For the average crustal thickness of 40 km, Moho temperatures are near solidus values at the time of stabilization

  10. GALENICALS IN THE TREATMENT OF CRUSTED SCABIES

    PubMed Central

    Sugathan, P; Martin, Abhay Mani

    2010-01-01

    Crusted scabies is rare. It is a therapeutic challenge, as the common drugs used against scabies are unsatisfactory. The successful use of galenicals in a 10-year-old girl with crusted scabies is reported. PMID:20606896

  11. Collescipoli - An unusual fusion crust glass. [chondrite

    NASA Technical Reports Server (NTRS)

    Nozette, S.

    1979-01-01

    An electron microprobe study was conducted on glass fragments taken from the fusion crust and an internal glass-lined vein in the H-5 chondrite Collescipoli. Microprobe analyses of the glasses revealed an unusual fusion crust composition, and analyses of glass from inside the meteorite showed compositions expected for a melt of an H-group chondrite. Studies of fusion crusts by previous workers, e.g., Krinov and Ramdohr, showed that fusion crusts contain large amounts of magnetite and other oxidized minerals. The Collescipoli fusion crusts do contain these minerals, but they also contain relatively large amounts of reduced metal, sulphide, and a sodium-rich glass. This study seems to indicate that Collescipoli preserved an early type of fusion crust. Oxidation was incomplete in the fusion crust melt that drained into a crack. From this study it is concluded that fusion crust formation does not invariably result in complete oxidation of metal and sulphide phases.

  12. MAGNETIC FIELD-DECAY-INDUCED ELECTRON CAPTURES: A STRONG HEAT SOURCE IN MAGNETAR CRUSTS

    SciTech Connect

    Cooper, Randall L.; Kaplan, David L. E-mail: dkaplan@kitp.ucsb.edu

    2010-01-10

    We propose a new heating mechanism in magnetar crusts. Magnetars' crustal magnetic fields are much stronger than their surface fields; therefore, magnetic pressure partially supports the crust against gravity. The crust loses magnetic pressure support as the field decays and must compensate by increasing the electron degeneracy pressure; the accompanying increase in the electron Fermi energy induces nonequilibrium, exothermic electron captures. The total heat released via field-decay electron captures is comparable to the total magnetic energy in the crust. Thus, field-decay electron captures are an important, if not the primary, mechanism powering magnetars' soft X-ray emission.

  13. Failure mode and weakening effect of water on sandstone

    NASA Astrophysics Data System (ADS)

    Baud, Patrick; Zhu, Wenlu; Wong, Teng-Fong

    2000-07-01

    Previous studies have shown that brittle strength of a rock is generally reduced in the presence of water. However, for siliciclastic rocks, there is a paucity of data on the waterweakening behavior in the cataclastic flow regime. To compare the weakening effect of water in the brittle faulting and cataclastic flow regime, triaxial compression experiments were conducted on the Berea, Boise, Darley Dale, and Gosford sandstones (with nominal porosities ranging from 11% to 35%) under nominally dry and saturated conditions at room temperature. Inelastic behavior and failure mode of the nominal dry samples were qualitatively similar to those of water-saturated samples. At elevated pressures, shear localization was inhibited, and all the samples failed by strain hardening. The compactive yield strengths (associated with the onset of shear-enhanced compaction) in the saturated samples were lower than those in the dry samples deformed under comparable pressure conditions by 20% to 70%. The reductions of brittle strength in the presence of water ranged from 5% to 17%. The water-weakening effects were most and least significant in the Gosford and Berea sandstones, respectively. The relation between water weakening and failure mode is consistently explained by micromechanical models formulated on the basis that the specific surface energy in the presence of water is lowered than that in vacuum by the ratio λ. In accordance with the Hertzian fracture model the initial yield stress in the compactive cataclastic flow regime scales with the grain-crushing pressure, which is proportional to λ3/2. In the brittle faulting regime, damage mechanics models predict that the uniaxial compressive strength scales with λ1/2. In the presence of water the confined brittle strength is lower due to reductions of both the specific surface energy and friction coefficient.

  14. Anatomy of an ancient aeolian sandstone on Mars: the Stimson formation, Gale crater, Mars

    NASA Astrophysics Data System (ADS)

    Gupta, Sanjeev; Banham, Steven; Rubin, David; Watkins, Jessica; Sumner, Dawn; Grotzinger, John P.; Lewis, Kevin; Edgett, Kenneth S.; Edgar, Lauren; Stack, Kathryn; Day, McKenzie; Ewing, Ryan; Lapotre, Mathieu

    2016-10-01

    Since landing in 2012, the Mars Science Laboratory's (MSL) rover Curiosity has traversed the plains and foothills of Aeolis Mons (informally known as Mt. Sharp) investigating the environments preserved in the stratigraphic record of Gale crater. Recently, the Curiosity team has been investigating the Stimson formation, a sandstone exhibiting abundant crossbedding that drapes the underlying Murray formation mudstones. The contact between the Stimson and underlying Murray formation exhibits several meters relief over several 100 m hundred metres where encountered thus far. The Stimson is observed to onlap onto this contact, indicating that accumulating Stimson sandstones unconformably onlapped or buried local palaeotopography.Facies and architectural elements observed within the Stimson are interpreted to represent deposition within an ancient dune field. The Stimson formation is typically composed of decimeter-scale and meter-scale crossbedded sandstones, (exhibiting wind-ripple lamination and well rounded particles up to granule size). Architectural elements are visible in outcrops oriented perpendicular to the regional northwest dip. These consist of undulating surfaces parallel to the regional dip with observed lateral extents up to 30 m that truncate underlying cross-sets and commonly act as basal surfaces to overlying cross-sets. Undulating surfaces are interpreted possibly to be deflationary supersurfaces, which formed in response to deflation or dune-field stabilisation across a regional extent. Surfaces inclined relative to the regional dip ascend between supersurfaces towards the north east at an observed angle of 3-4°. These surfaces are interpreted to be dune bounding surfaces, which are preserved when dunes climb as a result of dune-field aggradation. Aggradation of the system during the duration of the dune field's existence possibly occurred as a response to episodic increases of sediment supply into the basin, allowing dunes to climb and preserving

  15. Vista from Curiosity Shows Crossbedded Martian Sandstone

    NASA Image and Video Library

    2015-09-11

    Large-scale crossbedding in the sandstone of this ridge on a lower slope of Mars' Mount Sharp is common in petrified sand dunes. The scene combines multiple images taken with both cameras of the Mast Camera (Mastcam) on Curiosity on Aug. 27, 2015, during the 1,087th Martian day, or sol of the rover's work on Mars. It spans from east, at left, to south-southwest. Figure 1 includes a scale bar of 200 centimeters (about 6.6 feet). Sets of bedding laminations lie at angles to each other. Such crossbedding is common in wind-deposited sandstone of the U.S. Southwest. An example from Utah is pictured at http://3dparks.wr.usgs.gov/zion/html2/3d153.html. The sandstone in the image from Mars is part of the Stimson unit on Mount Sharp. The color of the Mastcam mosaic has been approximately white-balanced to resemble how the scene would appear under daytime lighting conditions on Earth. The component images in the center and upper portion of the mosaic are from Mastcam's right-eye camera, which is equipped with a 100-millimeter-focal-length telephoto lens. Images used in the foreground and at far left and right were taken with Mastcam's left-eye camera, using a wider-angle, 34-millimeter lens. Malin Space Science Systems, San Diego, built and operates Curiosity's Mastcam. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, built the rover and manages the project for NASA's Science Mission Directorate, Washington. For more information about Curiosity, visit http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl . http://photojournal.jpl.nasa.gov/catalog/PIA19818

  16. Relation between crust development and heterocyclic aromatic amine formation when air-roasting a meat cylinder.

    PubMed

    Kondjoyan, Alain; Chevolleau, Sylvie; Portanguen, Stéphane; Molina, Jérôme; Ikonic, Predrag; Clerjon, Sylvie; Debrauwer, Laurent

    2016-12-15

    The meat crust that develops during cooking is desired by consumers for its organoleptic properties, but it is also where heterocyclic aromatic amines (HAs) are formed. Here we measured HAs formation during the development of a colored crust on the surface of a beef meat piece. HAs formation was lower in the crust than previously measured in meat slices subjected to the same air jet conditions. This difference is explained by a lower average temperature in the colored crust than in the meat slices. Temperature effects can also explain why colored crust failed to reproduce the plateauing and decrease in HAs content observed in meat slices. We observed a decrease in creatine content from the center of the meat piece to the crust area. In terms of the implications for practice, specific heating conditions can be found to maintain a roast beef meat aspect while dramatically reducing HAs content. Copyright © 2016 Elsevier Ltd. All rights reserved.

  17. Poncho field - Cretaceous J sandstone stratigraphic traps - Denver basin, Colorado

    SciTech Connect

    Ethridge, F.G.; Ziegler, J.R.

    1983-08-01

    Distributary channel and delta destructional sandstones of Early Cretaceous age are important reservoirs for stratigraphic traps in the J sandstone at Poncho field, Adams and Arapahoe Counties, Colorado. Cores and logs from the field area reveal a lowermost, nonproductive, northeast-trending delta front sandstoe (J-3); a middle complex of southeast- and east-trending, productive distributary channel sandstones (J-2) that grade into tightly cemented delta fringe marine sediments to the southeast and northeast; and an upper, northeast trending, productive delta destructional sandstone (J-1). Vertical and lateral sequences of sedimentary structures, textures, trace fossil assemblages, and geometry and trend of sandstone bodies suggest that these units were part of a wave-dominated delta complex that prograded to the east and southeast from the area of Lonetree field. Thin section and SEM analyses reveal that the principal cements in both reservoir sandstones are quartz overgrowths, kaolinite, and chlorite, and that the bulk of the porosity is secondary and related to dissolution of carbonate cement and feldspar grains. Porosities and permeabilities are most variable and lowest in the nonproductive delta front sandstones, averaging 15% and 7 md; variable and intermediate in the productive distributary channel sandstones, averaging 16% and 28 md; and most uniform and highest in the overlying delta destructional sandstones, averaging 21% and 88 md.

  18. An evaluation of alternative chemical classifications of sandstones

    USGS Publications Warehouse

    Lindsey, D.A.

    1999-01-01

    Chemical classification of sandstone is worth attempting because modern analytical methods are producing extensive data sets on rock composition. Previous compilations and statistical studies have demonstrated the application of chemical data to problems in sandstone petrology, but classification has been largely ignored. Chemical data has value for classification, but the limitations of using chemical data for classification must be identified. Consideration of the processes of sandstone formation permits formulation of classification guidelines and systems for classification. Alternative systems for chemical classification can be then evaluated for their power to identify major types of sandstones and to facilitate genetic interpretation.

  19. Discolored Fracture Zones in Martian Sandstone

    NASA Image and Video Library

    2015-12-17

    This view from NASA's Curiosity Mars rover shows an example of discoloration closely linked to fractures in the Stimson formation sandstone on lower Mount Sharp. The pattern is evident along two perpendicular fractures. Curiosity's Navigation Camera (Navcam) acquired the component images of this mosaic on Aug. 23, 2015, during the 1.083rd Martian day, or sol, of the mission. The location is along the rover's path between "Marias Pass" and "Bridger Basin." In this region, the rover has found fracture zones to be associated with rock compositions enriched in silica, relative to surrounding bedrock. http://photojournal.jpl.nasa.gov/catalog/PIA20268

  20. The velocity structure of the lunar crust.

    NASA Technical Reports Server (NTRS)

    Kovach, R. L.; Watkins, J. S.

    1973-01-01

    Seismic refraction data, obtained at the Apollo 14 and 16 sites, when combined with other lunar seismic data, allow a compressional wave velocity profile of the lunar near-surface and crust to be derived. The regolith, although variable in thickness over the lunar surface, possesses surprisingly similar seismic properties. Underlying the regolith at both the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is low-velocity brecciated material or impact derived debris. Key features of the lunar seismic velocity profile are: (1) velocity increases from 100 to 300 m/sec in the upper 100 m to about 4 km/sec at 5 km depth, (2) a more gradual increase from about 4 km/sec to about 6 km/sec at 25 km depth,(3) a discontinuity at a depth of 25 km, and (4) a constant value of about 7 km/sec at depths from 25 km to about 60 km.

  1. Seismic amplitude anomalies associated with thick First Leo sandstone lenses, eastern Powder River basin, Wyoming.

    USGS Publications Warehouse

    Balch, A.H.; Lee, M.W.; Miller, J.J.; Ryder, R.T.

    1981-01-01

    Several new discoveries of oil production in the Leo sandstone, an economic unit in the Pennsylvanian middle member of the Minnelusa formation, eastern Powder River basin, Wyoming-Nebraska-South Dakota, have renewed exploration interest in this area. Vertical seismic profiles (VSP) and model studies suggested that a measurable seismic amplitude anomaly is frequently associated with the thick First Leo sandstone lenses. To test this concept, a surface reflection seismic profile was run between two wells about 12 miles apart. The First Leo was present and productive in one well and thin and barren in the other. The surface profile shows the predicted amplitude anomaly at the well where a thick lens is known to exist. Two other First Leo amplitude anomalies also appear on the surface seismic profile between the two wells, which may indicate the presence of additional lenses.-Authors

  2. Fe and O isotope composition of meteorite fusion crusts: Possible natural analogues to chondrule formation?

    NASA Astrophysics Data System (ADS)

    Hezel, Dominik C.; Poole, Graeme M.; Hoyes, Jack; Coles, Barry J.; Unsworth, Catherine; Albrecht, Nina; Smith, Caroline; RehkäMper, Mark; Pack, Andreas; Genge, Matthew; Russell, Sara S.

    2015-02-01

    Meteorite fusion crust formation is a brief event in a high-temperature (2000-12,000 K) and high-pressure (2-5 MPa) regime. We studied fusion crusts and bulk samples of 10 ordinary chondrite falls and 10 ordinary chondrite finds. The fusion crusts show a typical layering and most contain vesicles. All fusion crusts are enriched in heavy Fe isotopes, with δ56Fe values up to +0.35‰ relative to the solar system mean. On average, the δ56Fe of fusion crusts from finds is +0.23‰, which is 0.08‰ higher than the average from falls (+0.15‰). Higher δ56Fe in fusion crusts of finds correlate with bulk chondrite enrichments in mobile elements such as Ba and Sr. The δ56Fe signature of meteorite fusion crusts was produced by two processes (1) evaporation during atmospheric entry and (2) terrestrial weathering. Fusion crusts have either the same or higher δ18O (0.9-1.5‰) than their host chondrites, and the same is true for Δ17O. The differences in bulk chondrite and fusion crust oxygen isotope composition are explained by exchange of oxygen between the molten surface of the meteorites with the atmosphere and weathering. Meteorite fusion crust formation is qualitatively similar to conditions of chondrule formation. Therefore, fusion crusts may, at least to some extent, serve as a natural analogue to chondrule formation processes. Meteorite fusion crust and chondrules exhibit a similar extent of Fe isotope fractionation, supporting the idea that the Fe isotope signature of chondrules was established in a high-pressure environment that prevented large isotope fractionations. The exchange of O between a chondrule melt and an 16O-poor nebula as the cause for the observed nonmass dependent O isotope compositions in chondrules is supported by the same process, although to a much lower extent, in meteorite fusion crusts.

  3. Microbial Community Analysis of Fresh and Old Microbial Biofilms on Bayon Temple Sandstone of Angkor Thom, Cambodia

    PubMed Central

    Lan, Wensheng; Li, Hui; Wang, Wei-Dong; Katayama, Yoko

    2010-01-01

    The temples of Angkor monuments including Angkor Thom and Bayon in Cambodia and surrounding countries were exclusively constructed using sandstone. They are severely threatened by biodeterioration caused by active growth of different microorganisms on the sandstone surfaces, but knowledge on the microbial community and composition of the biofilms on the sandstone is not available from this region. This study investigated the microbial community diversity by examining the fresh and old biofilms of the biodeteriorated bas-relief wall surfaces of the Bayon Temple by analysis of 16S and 18S rRNA gene sequences. The results showed that the retrieved sequences were clustered in 11 bacterial, 11 eukaryotic and two archaeal divisions with disparate communities (Acidobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, Proteobacteria; Alveolata, Fungi, Metazoa, Viridiplantae; Crenarchaeote, and Euyarchaeota). A comparison of the microbial communities between the fresh and old biofilms revealed that the bacterial community of old biofilm was very similar to the newly formed fresh biofilm in terms of bacterial composition, but the eukaryotic communities were distinctly different between these two. This information has important implications for understanding the formation process and development of the microbial diversity on the sandstone surfaces, and furthermore to the relationship between the extent of biodeterioration and succession of microbial communities on sandstone in tropic region. Electronic supplementary material The online version of this article (doi:10.1007/s00248-010-9707-5) contains supplementary material, which is available to authorized users. PMID:20593173

  4. The influence of biological soil crusts on mineral uptake by associated vascular plants

    USGS Publications Warehouse

    Harper, K.T.; Belnap, Jayne

    2001-01-01

    Soil surfaces dominated by cyanobacteria and cyanolichens (such as Collema sp.) are widespread in deserts of the world. The influence of these biological soil crusts on the uptake of bioessential elements is reported for the first time for six seed plants of the deserts of Utah. This sample almost doubles the number of species for which the influence of biological soil crusts on mineral uptake of associated vascular plants is known. These new case studies, and others previously published, demonstrate that cyanobacterial or cyanobacteria- Collema crusts significantly alter uptake by plants of many bioessential elements. In studies now available, these crusts always increase the N content of associated seed plants. Uptake of Cu, K, Mg, and Zn is usually (>70% of reported cases) increased in the presence of the biological soil crusts. Soil crusts are generally negatively associated with Fe and P levels in associated seed plant tissue, while plant tissue levels of Ca, Mn, and Na are positively as often as negatively associated with the presence of soil crusts. Increases in bioessential elements in vascular plant tissue from biologically-crusted areas are greatest for short-lived herbs that are rooted primarily within the surface soil, the horizon most influenced by crustal organisms. The mineral content of a deeply rooted shrub (Coleogyne ramosissima) was less influenced by co-occurrence of biological soil crusts.

  5. Mineralogy and diagenesis of low-permeability sandstones of Late Cretaceous age, Piceance Creek Basin, northwestern Colorado

    USGS Publications Warehouse

    Hansley, Paula L.; Johnson, Ronald C.

    1980-01-01

    This report presents preliminary results of a mineralogic and diagenetic study of some low-permeability sandstones from measured surface sections and cores obtained from drill holes in the Piceance Creek Basin of northwestern Colorado. A documentation of the mineralogy and diagenetic history will aid in the exploration for natural gas and in the development of recovery technology in these low-permability sandstones. These sandstones are in the nonmarine upper part of the Mesaverde Formation (or Group) of Late Cretaceous age and are separated from overlying lower Tertiary rocks by a major regional unconformity. Attention is focused on the sandstone units of the Ohio Creek Member, which directly underlies the unconformity; however, comparisons between the mineralogy of the Ohio Creek strata and that of the underlying sandstone units are made whenever possible. The Ohio Creek is a member of the Hunter Canyon Formation (Mesaverde Group) in the southwestern part of the basin, and the Mesaverde Formation in the southern and central parts of the basin. The detrital mineralogy is fairly constant throughout all of these nonrnarine Cretaceous sandstone units; however, in the southeastern part of the basin, there is an increase in percentage of feldspar, quartzite, and igneous rock fragments in sandstones of the Ohio Creek Member directly underlying the unconformity. In the southwestern part of the basin, sandstones of the Ohio Creek Member are very weathered and are almost-entirely comprised of quartz, chert, and kaolinite. A complex diagenetic history, partly related to the overlying unconformity, appears to be responsible for transforming these sandstones into potential gas reservoirs. The general diagenetic sequence for the entire Upper Cretaceous interval studied is interpreted to be (early to late): early(?) calcite cement, chlorite, quartz overgrowths, calcite cement, secondary porosity, analcime (surface only), kaolinite and illite, and late carbonate cements

  6. Role of biological soil crusts in desert hydrology and geomorphology: Implications for military training operations

    Treesearch

    Steven D. Warren

    2014-01-01

    Biological soil crusts, composed of soil surfaces stabilized by a consortium of cyanobacteria, algae, fungi, lichens, and/or bryophytes, are common in most deserts and perform functions of primary productivity, nitrogen fixation, nutrient cycling, water redistribution, and soil stabilization. The crusts are highly susceptible to disturbance. The degree of perturbation...

  7. Windblown soil crust formation under light rainfall in a semiarid region

    USDA-ARS?s Scientific Manuscript database

    Many soils in arid and semi-arid regions of the world are affected by crusting, the process of forming a compact layer or thin mantle of consolidated material at the soil surface. Our objective was to evaluate the effect of rainfall quantity on crust formation of five soil types prominent in the Col...

  8. The nature of orogenic crust in the central Andes

    NASA Astrophysics Data System (ADS)

    Beck, Susan L.; Zandt, George

    2002-10-01

    The central Andes (16°-22°S) are part of an active continental margin mountain belt and the result of shortening of the weak western edge of South America between the strong lithospheres of the subducting Nazca plate and the underthrusting Brazilian shield. We have combined receiver function and surface wave dispersion results from the BANJO-SEDA project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure. The major results are as follows: (1) The crust supporting the high elevations is thick and has a felsic to intermediate bulk composition. (2) The relatively strong Brazilian lithosphere is underthrusting as far west (65.5°W) as the high elevations of the western part of the Eastern Cordillera (EC) but does not underthrust the entire Altiplano. (3) The subcrustal lithosphere is delaminating piecemeal under the Altiplano-EC boundary but is not completely removed beneath the central Altiplano. The Altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation, leading to lower crustal flow and flat topography. In contrast, in the high-relief, inland-sloping regions of the EC and sub-Andean zone, the upper crust is still strongly coupled across the basal thrust of the fold-thrust belt to the underthrusting Brazilian Shield lithosphere. Subcrustal shortening between the Altiplano and Brazilian lithosphere appears to be accommodated by delamination near the Altiplano-EC boundary. Our study suggests that orogenic reworking may be an important part of the "felsification" of continental crust.

  9. Wettability Alteration of Sandstones by Silica Nanoparticle Dispersions with Light and Heavy Crude Oil

    NASA Astrophysics Data System (ADS)

    Pales, A. R.; Huibers, B. M. J.; Bai, L.; Li, C.; Mu, L.; Ladner, D.; Daigle, H.; Darnault, C. J. G.

    2016-12-01

    In enhanced oil recovery (EOR), nanoparticles with their unique physico-chemical properties present a promising method for altering wettability. Nanoparticles could create a water-wet surface in a reservoir rather than an oil-wet one which would ease petroleum recovery. This research examines how uncoated silica nanoparticles alter the wettability of two sandstone surfaces, Berea and Boise, by measuring the contact angle and interfacial tension of different systems as an indicator of wettability. The silica nanoparticles were suspended in brine and brine plus a nonionic surfactant at concentrations of 0, 0.001, and 0.01 wt%. The differential impact on heavy and light crude oils was characterized as well. The study showed that surfactants had a greater impact on interfacial tension (IFT). The IFT decreased with the introduction of surfactants by 79% and 54% for light and heavy crude oils respectively. This reduction in IFT translates to less pressure needed for petroleum recovery. For the contact angle, images collected depict the reduction of contact angle with increased nanoparticle concentration across all oil, sandstone, and reservoir types. In addition to the images taken, the contact angles measured significantly decreased when nanoparticles were introduced with reductions reaching up to 93% between 0 and 0.001 wt% nanoparticles with light oil on the Berea sandstone. As nanoparticle concentration increased, the sandstones became increasingly water-wet for both oil types, and the increasing concentration impacted the light crude oil more than the heavy crude oil. The research evinced that nanoparticles can be used with surfactants in light and heavy crude oil systems to increase the hydrophilicity of Berea and Boise sandstones.

  10. Dynamics of Pre-3 Ga Crust-Mantle Evolution

    NASA Astrophysics Data System (ADS)

    Patchett, P. J.; Chase, C. G.; Vervoort, J. D.

    2004-05-01

    During 3.0 to 2.7 Ga, the Earth's crust underwent a non-uniformitarian change from a pre-3.0 Ga environment where long-term preservation of cratons was rare and difficult, to post-2.7 Ga conditions where cratons were established and new continental crust generation took place largely at craton margins. Many models view the Earth's surface during pre-3 Ga time as broadly equivalent to the post 2.7 Ga regime. Any such uniformitarian or gradual evolution cannot explain the conundrum that only a tiny amount of pre-3 Ga crust is preserved today coupled with the fact that very little pre-3 Ga crust was incorporated into the large amount of new craton that came into existence during 3.0-2.7 Ga. If large volumes of pre-3 Ga continental crust existed, it disappeared either just prior to 3 Ga, or during 3.0-2.7 Ga. To explain sudden appearance of surviving but dominantly juvenile continental crust in a model where continents were large prior to 3 Ga, it would be necessary either that pre-3 Ga continent was recycled into the mantle at sites systematically different from those where new 3.0-2.7 Ga crust was made, or that widespread continent destruction preceded the 3.0-2.7 Ga crustal genesis. From expected mantle overturn in response to the heat budget, it is likely that most pre-3 Ga crust was both more mafic and shorter-lived than after 3 Ga. Although Nd and Hf ratios for pre-3 Ga rocks are uncertain due to polymetamorphism, it appears that depleted upper mantle was widespread by 2.7 Ga, even pre-3 Ga. Depletion may have been largely achieved by formation, subduction and storage of mafic crust for periods of 200-500 m.y. The rapid change to large surviving continents during 3.0-2.7 Ga was due to declining mantle overturn, and particularly to development of the ability to maintain subduction in one zone of the earth's surface for the time needed to allow evolution to felsic igneous rock compositions. In as much as storage of subducted slabs is probably occurring today, and

  11. Soil stabilization by biological soil crusts in arid Tunisia

    NASA Astrophysics Data System (ADS)

    Guidez, Sabine; Couté, Alain; Bardat, Jacques

    2015-04-01

    As part of the fight against desertification (LCD) in arid Tunisia, we have been able to highlight the important role played by biological soil crusts (BSC) in soil stabilization. The identification of the major species of cyanobacteria, lichens and bryophytes, their adaptation and terrestrial colonization strategies in this high climatic constraints area through their morpho-anatomical criteria have been set. In addition to their biological composition, their internal arrangement (i.e. texture and microstructure) reflects the structural stability of BSC against erosion. Precisely, the aggregative power of cyanobacteria and their ways of moving inside a soil, the capacity of mosses to grow through the sediments and lichens ability to bind at particles on surface, thus stabilizing the substrate have been demonstrated. Then, the three biological components ability to capture soil particles has been widely illustrated, proving the major environmental contribution of BSC in arid areas biological crusts formation, providing that soils will experience an increase of organic matter and fine particles rates subsequently gaining faster and better stability. Although the thickness and the morphology of crusts are related to the cover rates of these different biological components, the water properties of the latter, studied at the environmental SEM, illustrate their important role in altering the water cycle. Thus, the mixed crusts, i.e. with good presence of three biological components, cause the highest runoff rates by their ability to retain the water and spread on the surface. In spite of a swelling coefficient in presence of water higher than cryptogams, the cyanobacterial crusts located in newly stabilized areas of our studied region, remain finally insufficiently dense to impact surface hydrology. But, we showed after all that the cyanobacteria, pioneer species, have a certain environmental role. The lichen crusts cause a increased runoff because the lichens have a

  12. Recovery rates of cryptobiotic crusts: inoculant use and assessment methods

    USGS Publications Warehouse

    Belnap, Jayne

    1993-01-01

    Recovery rates of cyanobacterial-lichen soil crusts from disturbance were examined. Plots were either undisturbed or scalped, and scalped plots were either inoculated with surrounding biological crust material or left to recover naturally. Natural recovery rates were found to be very slow. Inoculation significantly hastened recovery for the cyanobacterial/green algal component, lichen cover, lichen species richness, and moss cover. Even with inoculation, however, lichen and moss recovery was minimal. Traditional techniques of assessing recovery visually were found to underestimate time for total recovery. Other techniques, such as extraction of chlorophyll a from surface soil and measurement of sheath material accumulation, were used and are discussed.

  13. Initiation and propagation of mixed mode fractures in granite and sandstone

    NASA Astrophysics Data System (ADS)

    Rück, Marc; Rahner, Roman; Sone, Hiroki; Dresen, Georg

    2017-10-01

    We investigate mixed mode fracture initiation and propagation in experimentally deformed granite and sandstone. We performed a series of asymmetric loading tests to induce fractures in cylindrical specimens at confining pressures up to 20 MPa. Loading was controlled using acoustic emission (AE) feedback control, which allows studying quasi-static fracture propagation for several hours. Location of acoustic emissions reveals distinct differences in spatial-temporal fracture evolution between granite and sandstone samples. Before reaching peak stress in experiments performed on granite, axial fractures initiate first at the edge of the indenter and then propagate through the entire sample. Secondary inclined fractures develop during softening of the sample. In sandstone, inclined shear fractures nucleate at peak stress and propagate through the specimen. AE source type analysis shows complex fracturing in both materials with pore collapse contributing significantly to fracture growth in sandstone samples. We compare the experimental results with numerical models to analyze stress distribution and energy release rate per unit crack surface area in the samples at different stages during fracture growth. We thereby show that for both rock types the energy release rate increases approximately linearly during fracture propagation. The study illuminates how different material properties modify fracture initiation direction under similar loading conditions.

  14. Transport of Organic Contaminants Mobilized from Coal through Sandstone Overlying a Geological Carbon Sequestration Reservoir

    SciTech Connect

    Zhong, Lirong; Cantrell, Kirk J.; Bacon, Diana H.; Shewell, Jesse L.

    2014-02-01

    Column experiments were conducted using a wetted sandstone rock installed in a tri-axial core holder to study the flow and transport of organic compounds mobilized by scCO2 under simulated geologic carbon storage (GCS) conditions. The sandstone rock was collected from a formation overlying a deep saline reservoir at a GCS demonstration site. Rock core effluent pressures were set at 0, 500, or 1000 psig and the core temperature was set at 20 or 50°C to simulate the transport to different subsurface depths. The concentrations of the organic compounds in the column effluent and their distribution within the sandstone core were monitored. Results indicate that the mobility though the core sample was much higher for BTEX compounds than for naphthalene. Retention of organic compounds from the vapor phase to the core appeared to be primarily controlled by partitioning from the vapor phase to the aqueous phase. Adsorption to the surfaces of the wetted sandstone was also significant for naphthalene. Reduced temperature and elevated pressure resulted in greater partitioning of the mobilized organic contaminants into the water phase.

  15. Earthquakes in stable continental crust

    SciTech Connect

    Johnson, A.C.; Kanter, L.R. )

    1990-03-01

    Earthquakes can strike even in stable crust, well away from the familiar earthquake zones at the edges of tectonic plates, but their mere occurrence is both a source of concern in planning critical facilities such as nuclear power plants. The authors sought answers to two major questions: Just how much seismic activity does take place within the stable parts of continents And are there specific geologic features that make some areas of stable crust particularly susceptible to earthquakes They began by studying North America alone, but it soon became clear that the fairly short record of these rare events on a single continent would not provide enough data for reliable analysis. Hence, they decided to substitute space for time--to survey earthquake frequency and distribution in stable continental areas worldwide. This paper discusses their findings.

  16. The sandstone's chromatic alteration of the florentine cultural heritage

    NASA Astrophysics Data System (ADS)

    Vettori, S.; Pecchioni, E.; Cantisani, E.; Ricci, M.; Fratini, F.; Garzonio, C. A.

    2012-04-01

    Pietra Serena is one of the materials more used in Florentine architecture. It is a sandstone that outcrops in the hills north of the city in the municipality of Fiesole and it has been employed mainly for ornamental purposes. This litotype belongs to the the Macigno Formation (Oligocene Upper- Miocene Lower) which consists of beds of turbiditic sandstones separated by pelitic levels which are the finest components of each single turbidity layer. Petrographically, Pietra Serena can be defined as a medium-coarse-grained greywacke made of quartz, feldspars, micas, fragments of metamorphic and magmatic rocks. The clayey matrix is quite abundant, mainly composed by illite, kaolinite and chlorite-vermiculite (present only in some quarries). It is well known that the processes of decay of the sandstones are related to the type of matrix, the amount of cement, the kind of clay minerals and to the pore size distribution, which lead to water infiltrations, swelling of the clay minerals, separation of the clayey matrix, with resulting exfoliation and peeling of the stone artefacts. Pietra Serena has a bluish-grey colour in fresh cut, but many times it is easily oxidized acquiring an ochraceous-reddish brown colour on buildings. Such changes in colour, appear to be due in part to the oxidation of iron, proceeding very quickly from the surface to the inside, though the cohesion is not affected. It is possible to hypothesize that the chromatic changes not necessarily involve a progressive state of alteration of the artefact, but they may often to represents a natural patina acquired with the time. Nevertheless it is necessary to remember that the oxidized layer and its hardness could also be the result of treatments performed in the past. In Florence, several monuments and buildings are affected by such phenomenon, in particular it is possible to note an intense and diffuse reddish colouring on the Pietra Serena utilized for columns and for façade's decorations. In this work

  17. Evaluation of stratigraphic relations of sandstone-producing reservoirs in upper Council Grove and Chase groups (Permian) in north-central Oklahoma

    SciTech Connect

    Chaplin, J.R. )

    1989-08-01

    Poor well control and the absence of surface stratigraphic control made previous interpretations of the stratigraphic relations of sandstone-producing reservoirs tenuous. Recent extensive analyses of surface outcrops and well and core data support the contention that the major sandstone-producing reservoirs can be physically correlated with formations in the outcrop section. Sandstone bodies within the upper Council Grove Group include Neva sand and Blackwell sand (Neva Limestone), Hotson-Kisner sand (Eskridge Shale), and the Whitney-Hodges sand. The Whitney-Hodges sand correlates, in part, with the Speiser Shale (Garrison Formation) of the outcrop section. However, previous usage suggested tentative correlations with sandstone bodies stratigraphically lower in the section. These sands were probably deposited in channels that were, in part, fluvial, tidal, or estuarine. Production from the Chase Group occurs locally within channelform sandstone bodies referred to as the Hoy-Matfield sand. These sands appear to be equivalent, occupying essentially the position of the Kinney Limestone Member (Matfield Shale) of the outcrop section. Detailed core-hole data at and in the vicinity of Kaw Dam, southeastern Kay County, and outcrops along the shoreline of Kaw Lake at Kaw City, Kay County, clearly demonstrate the facies distribution of the Hoy sand. Core-hole data has also delineated additional potential sandstone reservoirs within and near or at the top of the Fort Riley Limestone Member (Barneston Limestone). The Wolfe sand, a producing sandstone locally, occupies a stratigraphic position within the Doyle Shale.

  18. Anisotropy of permeability in faulted porous sandstones

    NASA Astrophysics Data System (ADS)

    Farrell, N. J. C.; Healy, D.; Taylor, C. W.

    2014-06-01

    Studies of fault rock permeabilities advance the understanding of fluid migration patterns around faults and contribute to predictions of fault stability. In this study a new model is proposed combining brittle deformation structures formed during faulting, with fluid flow through pores. It assesses the impact of faulting on the permeability anisotropy of porous sandstone, hypothesising that the formation of fault related micro-scale deformation structures will alter the host rock porosity organisation and create new permeability pathways. Core plugs and thin sections were sampled around a normal fault and oriented with respect to the fault plane. Anisotropy of permeability was determined in three orientations to the fault plane at ambient and confining pressures. Results show that permeabilities measured parallel to fault dip were up to 10 times higher than along fault strike permeability. Analysis of corresponding thin sections shows elongate pores oriented at a low angle to the maximum principal palaeo-stress (σ1) and parallel to fault dip, indicating that permeability anisotropy is produced by grain scale deformation mechanisms associated with faulting. Using a soil mechanics 'void cell model' this study shows how elongate pores could be produced in faulted porous sandstone by compaction and reorganisation of grains through shearing and cataclasis.

  19. Compaction of Norphlet sandstones, Rankin County, Mississippi

    SciTech Connect

    McBride, E.F.

    1987-09-01

    Fabric and porosity changes resulting from compaction were studied in sandstones from three cores sampled at depths between 15,900 and 22,500 ft. Point counts of 30 thin sections indicate that 0.4% of the rock volume was lost by ductile grain deformation and 3% by pressure solution at both grain contacts and at widely spaced stylolites. Pre-cement porosities of eolian sandstone range from 27 to 35% (mean = 29%), indicating that a total of from 10 to 18% porosity (mean = 16%) was lost by compaction (assuming 45% initial porosity). The difference between the total porosity loss and the sum of the other two processes is assumed to be the porosity lost by grain rearrangement (mean = 12.6%). The amount of pressure solution at grain contacts for each well is independent of depth, temperature, and amount of both quartz cement and total cement. Stylolites transect both grains and cements, which indicates they formed late in the diagenetic sequence. Silica released by pressure solution at quartz grain contacts could not be the sole source and was probably not even the major source of quartz cement in the formation, because cementation by quartz preceded the episode of strong pressure solution. In addition, the volume of silica released by pressure solution appears to have been inadequate to provide the volume of quartz cement present.

  20. Metamorphism in the Martian crust

    NASA Astrophysics Data System (ADS)

    McSween, Harry Y.; Labotka, Theodore C.; Viviano-Beck, Christina E.

    2015-04-01

    Compositions of basaltic and ultramafic rocks analyzed by Mars rovers and occurring as Martian meteorites allow predictions of metamorphic mineral assemblages that would form under various thermophysical conditions. Key minerals identified by remote sensing roughly constrain temperatures and pressures in the Martian crust. We use a traditional metamorphic approach (phase diagrams) to assess low-grade/hydrothermal equilibrium assemblages. Basaltic rocks should produce chlorite + actinolite + albite + silica, accompanied by laumontite, pumpellyite, prehnite, or serpentine/talc. Only prehnite-bearing assemblages have been spectrally identified on Mars, although laumontite and pumpellyite have spectra similar to other uncharacterized zeolites and phyllosilicates. Ultramafic rocks are predicted to produce serpentine, talc, and magnesite, all of which have been detected spectrally on Mars. Mineral assemblages in both basaltic and ultramafic rocks constrain fluid compositions to be H2O-rich and CO2-poor. We confirm the hypothesis that low-grade/hydrothermal metamorphism affected the Noachian crust on Mars, which has been excavated in large craters. We estimate the geothermal gradient (>20 °C km-1) required to produce the observed assemblages. This gradient is higher than that estimated from radiogenic heat-producing elements in the crust, suggesting extra heating by regional hydrothermal activity.

  1. Continental crust beneath southeast Iceland

    PubMed Central

    Torsvik, Trond H.; Amundsen, Hans E. F.; Trønnes, Reidar G.; Doubrovine, Pavel V.; Gaina, Carmen; Kusznir, Nick J.; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D.; Griffin, William L.; Werner, Stephanie C.; Jamtveit, Bjørn

    2015-01-01

    The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland—and especially the Öræfajökull volcano—is characterized by a unique enriched-mantle component (EM2-like) with elevated 87Sr/86Sr and 207Pb/204Pb. Here, we demonstrate through modeling of Sr–Nd–Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2–6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume. PMID:25825769

  2. Continental crust beneath southeast Iceland.

    PubMed

    Torsvik, Trond H; Amundsen, Hans E F; Trønnes, Reidar G; Doubrovine, Pavel V; Gaina, Carmen; Kusznir, Nick J; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D; Griffin, William L; Werner, Stephanie C; Jamtveit, Bjørn

    2015-04-14

    The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland--and especially the Öræfajökull volcano--is characterized by a unique enriched-mantle component (EM2-like) with elevated (87)Sr/(86)Sr and (207)Pb/(204)Pb. Here, we demonstrate through modeling of Sr-Nd-Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2-6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume.

  3. KTB and the electrical conductivity of the crust

    NASA Astrophysics Data System (ADS)

    Haak, V.; Simpson, F.; Bahr, Karsten; Bigalke, J.; Eisel, M.; Harms, U.; Hirschmann, G.; Huenges, E.; Jödicke, H.; Kontny, A.; Kück, J.; Nover, G.; Rauen, A.; Stoll, J.; Walther, J.; Winter, H.; Zulauf, G.; Wolfgang, J.

    1997-08-01

    The German Continental Deep Drilling Program (KTB) drilled two holes through crystalline rocks which are rich in both high-salinity fluids and graphite accumulated along shear zones. Analyses of a large number of borehole measurements yield models for the electrical resistivity of the upper and middle crust in the vicinity of the KTB holes. High observed resistivity, of more than 105Ωm in the lowermost part of the 9000 m deep main hole, in a rather ``wet'' crust, indicates that effective mechanisms exist to cut down connections between fluid accumulations and therefore that fluids are not the likely cause of high-conductivity anomalies. On the other hand, graphite accumulations appear to be connected along shear lineaments over hundreds of meters or more. Structural, mineralogical, and geochemical studies suggest a tectonic model which explains the deposition of graphite as the relic and witness of a shearing process that occurred during the late Variscan (Upper Carboniferous) thrusting. This process took place while this part of the crust resided at temperatures between 240° and 380°C. Subsequent independent reverse faulting lifted this part to the Earth's surface. Our conclusion is that the KTB case indicates how high electrical conductivities in the upper crust, which originated from the middle to lower crust, are caused by graphite accumulations, rather than by fluids, and that these anomalies are related to shearing processes. Such graphite accumulations may exist elsewhere and may be of relevance in the context of present-day midcrustal conductors.

  4. Building icelandic igneous crust by repeated melt injections

    NASA Astrophysics Data System (ADS)

    Greenfield, Tim; White, Robert S.

    2015-11-01

    Observations of microseismicity provide a powerful tool for mapping the movement of melt in the crust. Here we record remarkable sequences of earthquakes 20 km below the surface in the normally ductile crust in the vicinity of Askja Volcano, in northeast Iceland. The earthquakes occur in swarms consisting of identical waveforms repeating as frequently as every 8 s for up to 3 h. We use template waveforms from each swarm to detect and locate earthquakes with an automated cross-correlation technique. Events are located in the lower crust and are inferred to be the result of melt being injected into the crust. During melt intrusion high strain rates are produced in conjunction with high pore fluid pressures from the melt or exsolved carbon dioxide. These cause brittle failure on high-angle fault planes located at the tips of sills. Moment tensor solutions show that most of the earthquakes are opening cracks accompanied by volumetric increases. This is consistent with the failure causing the earthquakes by melt injection opening new tensile cracks. Analysis of the magnitude distribution of earthquakes within a swarm reveals a complicated relationship between the imposed strain rates and the fluids that cause brittle failure. The magnitude of the earthquakes is controlled by the distance fluids can migrate along a fault, whereas the frequency of the events is controlled by the strain rate. Faults at the tips of sills act to focus melt transport between sills and so must be an important method of transporting melt through the lower crust.

  5. Composition of the Lower Crust Identified at Basin Rings

    NASA Astrophysics Data System (ADS)

    Pieters, C. M.; Head, J. W.; Dhingra, D.; Isaacson, P.; Klima, R.; Petro, N.; Taylor, L. A.

    2011-10-01

    In contrast to the extensively mixed lunar megaregolith [e.g., 6], materials exposed along the inner ring of several impact basins exhibit compositionally distinct mineral lithologies. We interpret these rocktypes to be deep-seated materials brought to the surface and exposed by the basin forming event. An initial survey of such materials using data from the Moon Mineralogy Mapper (M3) reveals compositions expected from the lunar samples (anorthosite, norites, troctolites), as well as new and unusual lithologies (pink spinel anorthosite, pyroxenite, and perhaps dunite). A simple magma ocean model is consistent with remote observations and samples from the upper crust, but is inadequate to describe our observations of the lower crust. We are beginning to glimpse the actual complexity of lunar lower crust evolution.

  6. The Mendocino crustal conveyor: Making and breaking the California crust

    USGS Publications Warehouse

    Furlong, K.P.; Lock, J.; Guzofski, C.; Whitlock, J.; Benz, H.

    2003-01-01

    The northward migration of the Mendocino triple junction has resulted in a fundamental modification of the crust of coastal California. As a consequence of viscous coupling between the southern edge of the Gorda slab and the base of the North American crust beneath the Coast Ranges of central and northern California, the crust of coastal California was first thickened and then thinned. This viscous coupling and ephemeral crustal thickening has produced a distinctive pattern of uplift that allows us to map the three-dimensional extent of crustal modification. This pattern of crustal deformation has combined with the strain field of the developing San Andreas fault system to produce the observed pattern of near-surface deformation. The rapid rise in heat flow south of the triple junction observed in the northern Coast Ranges is a direct consequence of development and removal of the crustal welt that migrated with the triple junction.

  7. Sequence stratigraphy and onlap relationships of a stratigraphic trap, Lower Cretaceous Muddy Sandstone, Hilight field, Powder River basin, Wyoming

    SciTech Connect

    Wheeler, D.M.; Gustason, E.R. )

    1989-09-01

    In Hilight field more than 74 million bbl of oil and 244 bcf of gas have been produced from thin fluvial and shallow marine sandstones of the Lower Cretaceous Muddy Sandstone. In this area the Muddy was deposited during a late Albian sea level rise and onlaps a lowstand subaerial surface of erosion including a dendritic valley system incised into the underlying Skull Creek Shale. Transgressive valley-fill deposits of the Muddy Sandstone in the Hilight field area consist of four regionally correlative, time-bounded, back-stepping, progradational units. The retrogradational nature of these units indicates they belong in a transgressive systems tract rather than a lowstand wedge, as is often implied for valley-fill sequences. Each unit is capped by a regionally extensive marine flooding surface. The contact between units is placed at the surface representing maximum flooding or at the correlative horizon landward of the maximum transgression. Two of these contacts include thin bentonite beds which substantiate the time-stratigraphic interpretation. Petroleum is trapped in each unit by the onlap of reservoir sandstone facies against the lowstand surface of erosion on the impermeable Skull Creek Shale. Top seals are formed by mudstones at the base of overlying units or by the Shell Creek Shale, which overlies the Muddy Sandstone above a regionally extensive marine flooding surface. Reservoir heterogeneity is explained by lateral facies changes within each unit. The lateral and vertical distribution of reservoir-quality sandstone in the Muddy sequence in this area can be used as a model to predict occurrences in similar sequences elsewhere.

  8. Snow and Ice Crust Changes over Northern Eurasia since 1966

    NASA Astrophysics Data System (ADS)

    Bulygina, O.; Groisman, P. Y.; Razuvaev, V.; Radionov, V.

    2009-12-01

    When temperature of snow cover reaches zero Celsius first time since its establishment, snowmelt starts. In many parts of the world this process can be lengthy. The initial amount of heat that “arrives” to the snowpack might be insufficient for complete snowmelt, during the colder nights re-freeze of the melted snow may occur (thus creating the ice crust layers), and a new cold front (or the departure of the warm front that initiated melt) can decrease temperatures below the freezing point again and stop the snowmelt completely. It well can be that first such snowmelt occurs in winter (thaw day) and for several months thereafter snowpack stays on the ground. However, even the first such melt initiates a process of snow metamorphosis on its surface changing snow albedo and generating snow crust as well as on its bottom generating ice crust. Once emerged, the crusts will not disappear until the complete snowmelt. Furthermore, these crusts have numerous pathways of impact on the wild birds and animals in the Arctic environment as well as on domesticated reindeers. In extreme cases, the crusts may kill some wild species and prevent reindeers’ migration and feeding. Ongoing warming in high latitudes created situations when in the western half of Eurasian continent days with thaw became more frequent. Keeping in mind potential detrimental impacts of winter thaws and associated with them snow/ice crust development, it is worthwhile to study directly what are the major features of snow and ice crust over Eurasia and what is their dynamics. For the purpose of this study, we employed the national snow survey data set archived at the Russian Institute for Hydrometeorological Information. The dataset has routine snow surveys run throughout the cold season each decade (during the intense snowmelt, each 5 days) at all meteorological stations of the former USSR, thereafter, in Russia since 1966. Prior to 1966 snow surveys are also available but the methodology of

  9. Low-Reflectance Material in Mercury's Crust

    NASA Astrophysics Data System (ADS)

    Denevi, B. W.; Robinson, M. S.; Murchie, S. L.; Blewett, D. T.; Holsclaw, G. M.; McClintock, W. E.; McCoy, T. J.; McNutt, R. L.; Solomon, S. C.

    2008-12-01

    Mercury's reflectance and spectral slope are broadly similar to that of the lunar nearside. However, a host of Earth-based measurements and spacecraft data indicate that the composition and physical makeup of their surfaces may exhibit significant differences. Apollo samples and orbital remote sensing show that the lunar nearside surface is generally high in FeO (6 to 20 wt %) while the farside surface abundance is somewhat lower (3 to 10 wt %). Earth-based remote sensing of Mercury indicates that its surface contains less than 6 wt % FeO and perhaps even lower than 3 wt %. The reflectance of the Moon, and most likely Mercury, is controlled to first order by variations in iron and titanium abundances. If Mercury's ferrous iron content is much lower than that of the lunar nearside, then why is its reflectance comparable (0.019 vs. 0.021 at phase angle 65°, respectively)? Two-color vidicon observations by Mariner 10 revealed patchy low-reflectance, relatively blue units within Mercury's crust. Hapke and coworkers first speculated that opaque minerals (most likely ilmenite) could explain the color and reflectance of this low-reflectance component. Multispectral image data obtained by MESSENGER during its January 2008 flyby of Mercury covered new terrain and provided higher resolution, better signal-to-noise ratio, and extended wavelength coverage above that obtained by Mariner 10. The new data confirmed the existence of the low-reflectance material (LRM) and its relatively blue color and provide much better geologic context to interpret the origin of this material. MESSENGER multispectral data show the LRM to be widespread across the surface and to occur at depth within the crust. Three key observations show the vertical distribution of LRM. First the rims and floors of 100-km-scale craters within the Caloris basin are composed of LRM, streamers of LRM occur in ejecta traceable back to outcrops in crater floors (e.g. Mozart), and large continuous sections of ejecta

  10. Ejection behavior characteristics in experimental cratering in sandstone targets

    NASA Astrophysics Data System (ADS)

    Sommer, Frank; Reiser, Fiona; Dufresne, Anja; Poelchau, Michael H.; Hoerth, Tobias; Deutsch, Alex; Kenkmann, Thomas; Thoma, Klaus

    2013-01-01

    Within the frame of the MEMIN research unit (Multidisciplinary Experimental and Numerical Impact Research Network), impact experiments on sandstone targets were carried out to systematically study the influence of projectile mass, velocity, and target water saturation on the cratering and ejection processes. The projectiles were accelerated with two-stage light-gas guns (Ernst-Mach-Institute) onto fine-grained targets (Seeberger sandstone) with about 23% porosity. Collection of the ejecta on custom-designed catchers allowed determination of particle shape, size distribution, ejection angle, and microstructures. Mapping of the ejecta imprints on the catcher surface enabled linking of the different patterns to ejection stages observed on high-speed videos. The increase in projectile mass from 0.067 to 7.1 g correlates with an increase in the total ejected mass; ejecta angles, however, are similar in range for all experiments. The increase in projectile velocity from 2.5 to 5.1 km s-1 correlates with a total ejecta mass increase as well as in an increase in comminution efficiency, and a widening of the ejecta cone. A higher degree of water saturation of the target yields an increase in total ejecta mass up to 400% with respect to dry targets, higher ejecta velocity, and a steeper cone. These data, in turn, suggest that the reduced impedance contrast between the quartz grains of the target and the pores plays a primary role in the ejecta mass increase, while vaporization of water determines the ejecta behavior concerning ejecta velocity and particle distribution.

  11. Reservoir characterization of Pennsylvanian Sandstone Reservoirs. Annual report

    SciTech Connect

    Kelkar, M.

    1992-09-01

    This annual report describes the progress during the second year of a project on Reservoir Characterization of Pennsylvanian Sandstone Reservoirs. The report is divided into three sections: (i) reservoir description and scale-up procedures; (ii) outcrop investigation; (iii) in-fill drilling potential. The first section describes the methods by which a reservoir can be characterized, can be described in three dimensions, and can be scaled up with respect to its properties, appropriate for simulation purposes. The second section describes the progress on investigation of an outcrop. The outcrop is an analog of Bartlesville Sandstone. We have drilled ten wells behind the outcrop and collected extensive log and core data. The cores have been slabbed, photographed and the several plugs have been taken. In addition, minipermeameter is used to measure permeabilities on the core surface at six inch intervals. The plugs have been analyzed for the permeability and porosity values. The variations in property values will be tied to the geological descriptions as well as the subsurface data collected from the Glen Pool field. The third section discusses the application of geostatistical techniques to infer in-fill well locations. The geostatistical technique used is the simulated annealing technique because of its flexibility. One of the important reservoir data is the production data. Use of production data will allow us to define the reservoir continuities, which may in turn, determine the in-fill well locations. The proposed technique allows us to incorporate some of the production data as constraints in the reservoir descriptions. The technique has been validated by comparing the results with numerical simulations.

  12. Wind erodibility response of physical and biological crusts to rain and flooding

    NASA Astrophysics Data System (ADS)

    Aubault, H.; Bullard, J. E.; Strong, C. L.; Ghadiri, H.; McTainsh, G. H.

    2015-12-01

    Soil surface crusts are important controllers of the small-scale wind entrainment processes that occur across all dust source regions globally. The crust type influences water and wind erosion by impacting infiltration, runoff, threshold wind velocity and surface storage capacity of both water and loose erodible material. The spatial and temporal patterning of both physical and biological crusts is known to change with rainfall and flooding. However, little is known about the impact of differing water quantity (from light rainfall through to flooding) on soil crusting characteristics (strength, roughness, sediment loss). This study compares the response of two soil types (loamy sand - LS, sandy loam - SL) with and without BSCs to three different rainfall events (2mm, 8mm, 15mm). Two BSC treatments were used one that simulated a young cyanobacteria dominated crust and an older flood induced multi species biological crust. For both soil types, soil surface strength increased with increasing rainfall amount with LS having consistently higher resistance to rupture than SL. Regardless of texture, soils with BSCs were more resistant and strength did not change in response to rainfall impact. Soil loss due to wind erosion was substantially higher on bare LS (4 times higher) and SL (3 times higher) soils compared with those with BSCs. Our results also show that young biological crust (formed by the rainfall event) have reduced soil erodibility with notably greater strength, roughness and reduced sediment losses when compared to soils with physical crust. Interestingly though, the erodibility of the old BSC did not differ greatly from that of the young BSC with respect to strength, roughness and sediment loss. This raises questions regarding the rapid soil surface protection offered by young colonising cyanobacteria crusts. Further analyses exploring the role of biological soil crusts on surface response to rainfall and wind saltation impact are ongoing.

  13. Study of adsorption Ag and Pb in liquid sample using Berea sandstone by commercial laser-induced breakdown spectroscopy (LIBS)

    NASA Astrophysics Data System (ADS)

    Suyanto, H.; Wendri, N.; Agustiningrum, U.; Manurung, M.

    2016-11-01

    Qualitative and quantitative analysis of Pb and Ag elements in liquid samples had been done by commercial laser-induced breakdown spectroscopy (LIBS) using adsorption method on a Berea Sandstone. The aim of this study is to identify the thickness of the Berea Sandstone for adsorbing Pb and Ag elements in liquid. The experiment was started with characterizing the Berea Sandstone that contains Si, Na, H, Li, K, Ca, O, N, Be, Ti, Al, Mg and Ba. Some of these elements have ability to adsorb Pb and Ag elements in the liquid. To prove this phenomenon, it is required to look for the experiment parameter optimum conditions such as laser energy, adsorption time and sample temperature. The experiment was conducted by dropping 2 ml standard liquid containing 1000 ppm of Pb and Ag to the Berea Sandstone surface. The result showed that the parameter optimum conditions for analyzing Pb and Ag elements in liquid sample with adsorption method were adsorption delay-time of 15 minutes, laser energy of 120 mJ and sample heating of 80 °C. The next experiment was focused on the number of adsorption as a function of depth. The data showed that Pb and Ag elements in liquid sample of 2 ml, 1000 ppm were fully adsorbed by the Berea Sandstone until the depth of 0.372 mm and 10.40 mm from the surface, respectively. The data also showed that the limit of detection predicted to about 22.76 ppm.

  14. The impact of additives found in industrial formulations of TCE on the wettability of sandstone.

    PubMed

    Harrold, Gavin; Lerner, David N; Leharne, Stephen A

    2005-11-01

    The wettability of aquifer rocks is a key physical parameter which exerts an important control on the transport, residual trapping, distribution and eventual fate of chlorinated hydrocarbon solvents (CHSs) released into the subsurface. Typically chlorinated solvents are assumed to be non-wetting in water saturated rocks and unconsolidated sediments. However industrially formulated solvent products are often combined with basic additives such as alkylamines to improve their performance; and the mineral surfaces of aquifer rocks and sediments usually possess a range of acid and hydrogen-bonding adsorption sites. The presence of these sites provides a mechanism whereby the basic additives in CHSs can be adsorbed at the solvent phase/solid phase interface. Given the amphiphilic molecular structure of these additives, this may result in changes in the wetting conditions of the solid phase. The aim of this study was therefore to test this conjecture for two classes of additives (alkylamines and quaternary ammonium salts) that are often encountered in industrial solvent formulations. Wettability assessments were made on sandstone cores by means of measurements of spontaneous and forced water drainage and spontaneous and forced water imbibition and through contact angle measurements on a smooth quartz surface. No solvent/additive combination produced solvent wetting conditions, though dodecylamine and octadecylamine significantly reduced the water wetting preference of sandstone which frequently resulted in neutral wetting conditions. The large volume of spontaneous water drainage observed in wettability experiments involving cetyltrimethylammonium bromide and octadecyltrimethylammonium bromide, suggested that the sandstone cores in these tests remained strongly water wetting. However equilibrium static contact angles of around 60 degrees were measured on quartz suggesting that the sandstone surfaces should be close to neutral wetting conditions. This paradox was finally

  15. Diagenesis of the Almond sandstone in the Washakie Basin

    SciTech Connect

    Yin, Peigui; Liu, Jie; Surdam, C.R. . Dept. of Geology and Geophysics)

    1992-01-01

    The marginal marine and nonmarine Almond sandstones are mostly sublitharenite, litharenite, and lithic arkose. The sandstones are fine-to very-fine-grained, and are well-sorted. The framework composition, authigenic minerals, and porosity and permeability distributions in the Almond sandstones are different below and above 8,000 feet, resulting in a variation in hydrocarbon reservoir types. The shallow conventional reservoirs are permeable, producing both liquid oil and gas, whereas the deep gas-bearing sandstones are very tight and overpressured. Porosity of the shallow Almond sandstones have been significantly enhanced by dissolution of the feldspar grains and lithic fragments. Quartz overgrowth cement and authigenic clay rims have occluded most of the intergranular pores, as well as the previously leached pores. The Almond sandstones have been buried deeper than their present depths. The sandstones in each part of the Washakie Basin have experienced different uplift and subsidence. Reconstruction of the burial history and diagenetic modeling are essential steps for understanding the diagenetic evolution of the Almond sandstones.

  16. Sequestration of volatiles in the martian crust through hydrated minerals

    NASA Astrophysics Data System (ADS)

    Mustard, J. F.; Ehlmann, B. L.; Poulet, F.; Fraeman, A. A.; Carter, J.

    2011-12-01

    The magnitude and history of volatile reservoirs is a key question in understanding Mars' evolution. The volumes of reservoirs for water through time have been estimated on the basis of morphology (e.g. Carr 1996) and modeling while the volume of active identifiable modern reservoirs such as the polar caps, the near-surface cryosphere, and the atmosphere are reasonably well known. One reservoir that has been hypothesized but not examined is the crust where water would be in the form of hydrous minerals. The OMEGA and CRISM experiments on Mars Express and Mars Reconnaissance Orbiter respectively, have shown that phyllosilicate minerals are commonly observed in the Noachian crust of Mars. Modeling has shown that depending on the location the abundance of clays and phyllosilicates can exceed 50% but more typically is less or absent, particularly in the Hesperian and younger terrains (Poulet 2007). Phyllosilicate-bearing outcrops have been observed in the deepest wall exposures of Valles Marineris (8 km below the rim) and in the central peaks of impact craters as large of 100 km. Modeling suggests that the porosity of the crust in maintained to approximate 8-10 km depth permitting the circulation of water to this depth and formation of phyllosilicate and other hydrated minerals. Based on these and other observations it is evident that at least the top 10 km of the crust can be considered to contain hydrated silicate minerals. These observations also show that phyllosilicates are globally present in Noachian crust. We use altered oceanic crust as an analog for the amount of alteration on Mars. Analyses show that the average volume fraction of hydrous phases in the lower oceanic crust is 10%. Simple calculations show this results in a water content of between 1 - 3%. If the upper 10 km of the martian crust is altered to this extent then a global equivalent thickness (GET) of water of 0.3 to 0.9 km is stored in the crust due to alteration minerals. This is comparable to

  17. Short-term coastal cycles in Upper Cretaceous Point Lookout Sandstone, southeastern San Juan basin, New Mexico

    SciTech Connect

    Wright, R.

    1986-08-01

    The Point Lookout Sandstone offers an excellent opportunity to study short-term (100,000-year) cyclic strandline events in the rock record. Although thin (30 to 60 m in the study area), this sandstone is divisible into numerous genetic strandline sequences separated from one another by distinct transgressive surfaces. Individual progradational sequences do not form major sandstone benches and are distinguished only through correlation of subtle transgressive surfaces. Transgressive surfaces are recognized where offshore mudstones sharply overlie transition or shoreface deposits. Such surfaces trace updip into progressively thinner mudstone partings that separate stacked shoreface sandstones. Presence of these mudstone partings suggest that a physical shift in mud-line position accompanied transgression. A probable explanation for the landward mud-line shift is entrapment of coarse sediment in estuaries and/or aggrading fluvial systems. Knowledge of such partings in subsurface strata is critical to understanding fluid migration through these reservoir sandstones. Delineation of short-term transgressive-regressive couplets in the Point Lookout Sandstone facilitates detailed reconstruction of local paleoshoreline trends. Because of short-term nature of individual cycles, variation in coastal morphology is resolvable at a scale of 100,000 years or less. Paleogeographic maps for each cycle, constructed at points of maximum transgression and maximum preserved progradation, define local shoreline irregularities that resulted from migration of a fluvial-dominated deltaic complex along the coastline. The occurrence of the fluvial delta in the area suggests autocyclicity as an important factor in deposition of these strata. Any significant allocyclic component must yet be determined by regional correlation.

  18. Threshold friction velocity of crusted windblown soils in the Columbia Plateau

    NASA Astrophysics Data System (ADS)

    Sharratt, B. S.; Vaddella, Venkata

    2014-12-01

    Wind erosion processes are governed by soil physical properties and surface characteristics. Erosion is initiated when the friction velocity exceeds the threshold friction velocity (u∗t) of soils. Although u∗t is influenced by soil physical properties such as wetness and crusting, there is little information available on the effect of soil crusting on u∗t. Knowledge of the relationship between soil crusting and u∗t is required to improve our ability to predict wind erosion and PM10 (particulates ⩽10 μm in aerodynamic diameter) emissions from crusted soils. Threshold friction velocity was assessed on five soil types commonly found across the Columbia Plateau. These soils were obtained from agricultural fields, placed in trays, subject to various rainfall amounts to promote crust formation, and then exposed to winds inside a wind tunnel. Emission of soil particulates and PM10 as a function of wind speed were monitored by saltation and aerosol sensors. Threshold friction velocity was determined by systematically increasing wind speed until we observed an increase in airborne particulate or PM10 concentration. Threshold friction velocity increased with the development of a soil crust; u∗t increased exponentially with an increase in crust strength and thickness. The relationship between u∗t and crust thickness was influenced by clay content. The relationship between u∗t and crust strength and thickness should be considered when simulating wind erosion of agricultural soils.

  19. Sensitivity of desert cryptograms to air pollutants: soil crusts and rock lichens

    USGS Publications Warehouse

    Belnap, J.

    1991-01-01

    Parks throughout the West are being faced with increasing air pollution threats from current or proposed industries near their boundaries. For this reason, it is important to understand the effects these industries may have on desert ecosystems. Rock lichens can be excellent biomonitors, acting as early warning systems of impending damage to other components of the desert ecosystem. Cryptogamic crusts, consisting mostly of cyanobacteria and lichens, may not only be excellent bioindicators, but also are an essential part of the desert ecosystem. Their presence is critical for soil stability as well as for the contribution of nitrogen to the ecosystem in a form available to higher plants. Air pollutants, such as emissions from coal-fired power plants, may threaten the healthy functioning of these non-vascular plants. The purpose of this study is to determine if, in fact, air pollutants do have an impact on the physiological functioning of cryptogamic crusts or rock lichens in desert systems and, if so, to what extent. Some results have already been obtained. Both rock lichens and cryptogamic crusts exhibit physiological damage in the vicinity of the Navajo Generating Station in Page, Arizona. Increased electrolyte leakage and chlorophyll degradation, along with reduced nitrogen fixation, have been found. Preliminary studies comparing sensitivity between substrates indicate that crusts on limestone and sandstone substrates may be more sensitive than those on gypsum.

  20. Genetic stratigraphy and reservoir characterization of the Spiro sandstone, Red Oak Field, Arkoma Basin, southeastern Oklahoma

    SciTech Connect

    Horn, B.W. )

    1996-01-01

    The Lower Atokan Spiro sandstone is a mixed carbonate-silicilastic reservoir that produces hydrocarbons from three discrete stratigraphic intervals at the Red Oak Field. Reservoir-quality sandstones develop in the seaward stepping sub-Spiro sequence (highstand system tract), landward stepping Foster [open quote]channel,[close quotes] and upper Spiro depositional sequences (transgressive and highstand system tract). The sub-Spiro and Foster [open quote]channel[close quote] sequences are separated by regional unconformity interpreted as a sequence boundary. Regressive marine shoreface cycles, genetically related to the sub-Spiro shale, comprise the lowermost producing interval. Fluvial/estuarine valley-fill (Foster channel) sandstones progressively onlap the sequence boundary overlying the regressive shoreface cycles and juxtapose reservoir-quality sandstones of different sequences, creating a complex reservoir architecture. Upper Spiro reservoir sandstones are developed within marine shoreface cycles that are deposited in a landward-stepping succession (highstand systems tract) following the drowning of incised paleovalleys. These aggradational / retrogradational successions downlap onto the valley-fill and sub-Spiro sequences representing the final stages of Spiro deposition prior to the high stand of sea level during Middle Atokan time. Regional stratigraphic correlations demonstrate progressive basinward truncation of the sub-Spiro regressive shoreface cycles by an erosional surface, creating a network of incised paleovalleys across the Pennsylvanian shelf. Based on core, well log, and outcrop interpretations, the magnitude of the facies offset across this sequence boundary indicates that a significant volume of reservoir-quality sediment has been partitioned basinward of the current producing areas.

  1. Supply-limited horizontal sand drift at an ephemerally crusted, unvegetated saline playa

    USGS Publications Warehouse

    Gillette, Dale A.; Niemeyer, T.C.; Helm, P.J.

    2001-01-01

    A site at Owens Dry Lake was observed for more than 4 years. The site was a vegetation-free saline playa where the surface formed "ephemeral crusts," crusts that form after rainfall. Sometimes these crusts were destroyed and often a layer of particles on the crust would engage in vigorous aeolian activity. Three "phases" of active sand drifting are defined as almost no movement (extreme supply limitation), loose particles on crust with some degree of sand drift (moderate supply limitation), and unlimited source movement corresponding to a destroyed surface crust (unlimited supply). These "phases" occurred 45, 49, and 6% of the time, respectively. The accumulation of loose particles on the crust was mostly the result of in situ formation. Crusted sediments with loose particles on top can exhibit mass flux rates about the same as for noncrusted sediments. Crusted sediments limit or eliminate sand drift in two conditions: for rough crusts that effect a sufficiently high threshold friction velocity (above the wind friction velocity) and for limited amounts of loose particles on the crust where particle supply is less than would be transported in normal saltation for a thick sandy surface. These "supply-limited" cases are similar to wind erosion of limited spilled material on a hard concrete surface. We quantified "supply limitation" by defining a "potential" or "supply unlimited" sand drift function Q = AG where A represents supply limitation that decreases as the particle source is depleted. Here Q is the mass of sand transported through a surface perpendicular to the ground and to the wind and having unit width during time period t, and G = ??? u*(u*2 - u*t2) dt for u* > u*t. G is integrated for the same time period t as for Q, u* is the friction velocity of the wind, and u*t is the threshold friction velocity of the wind. Hard crusts (usually formed in the summer) tended to show almost no change of threshold friction velocity with time and often gave total

  2. Evaporative sodium salt crust development and its wind tunnel derived transport dynamics under variable climatic conditions

    NASA Astrophysics Data System (ADS)

    Nield, Joanna M.; McKenna Neuman, Cheryl; O'Brien, Patrick; Bryant, Robert G.; Wiggs, Giles F. S.

    2016-12-01

    Playas (or ephemeral lakes) can be significant sources of dust, but they are typically covered by salt crusts of variable mineralogy and these introduce uncertainty into dust emission predictions. Despite the importance of crust mineralogy to emission potential, little is known about (i) the effect of short-term changes in temperature and relative humidity on the erodibility of these crusts, and (ii) the influence of crust degradation and mineralogy on wind speed threshold for dust emission. Our understanding of systems where emission is not driven by impacts from saltators is particularly poor. This paper describes a wind tunnel study in which dust emission in the absence of saltating particles was measured for a suite of climatic conditions and salt crust types commonly found on Sua Pan, Botswana. The crusts were found to be non-emissive under climate conditions characteristic of dawn and early morning, as compared to hot and dry daytime conditions when the wind speed threshold for dust emission appears to be highly variable, depending upon salt crust physicochemistry. Significantly, sodium sulphate rich crusts were found to be more emissive than crusts formed from sodium chloride, while degraded versions of both crusts had a lower emission threshold than fresh, continuous crusts. The results from this study are in agreement with in-situ field measurements and confirm that dust emission from salt crusted surfaces can occur without saltation, although the vertical fluxes are orders of magnitude lower (∼10 μg/m/s) than for aeolian systems where entrainment is driven by particle impact.

  3. Provenance of sandstones in the Golconda terrane, north central Nevada

    SciTech Connect

    Jones, E.A. )

    1991-02-01

    The upper Paleozoic Golconda terrane of north-central Nevada is a composite of several structurally bounded subterranes made of clastic, volcanic, and carbonate rocks. The clastic rocks provide important clues for the interpretation of the provenance and paleogeographic settings of the different lithologic assemblages found in these subterranes. Two petrographically distinct sandstones are identified in the Golconda terrane in the Osgood Mountains and the Hot springs Range of north-central Nevada. The sandstone of the Mississippian Farrel Canyon Formation, part of the Dry Hills subterrane, is characterized by quartzose and sedimentary and lithic-rich clasts with a small feldspar component. in contrast, the sandstone of the Permian Poverty Peak (II) subterrane is a silty quartzarenite with no lithic component, and a very limited feldspar component. The sandstone of the Farrel Canyon Formation is similar to nonvolcanic sandstones reported from elsewhere in the Golconda terrane. Modal data reflect a provenance of a recycled orogen and permit the interpretation that it could have been derived from the antler orogen as has been proposed for other sandstones of the golconda terrane. The sandstone of the Poverty Peak (II) subterrane is more mature than any of the other sandstones in either the Golconda terrane, the Antler overlap sequence, or the Antler foreland basin sequence. Modal data put the Poverty Peak (II) sandstone in the continental block provenance category. The distinct extrabasinal provenances represented in these different sandstones support the idea that the Golconda basin was made up of complex paleogeographic settings, which included multiple sources of extrabasinal sediment.

  4. Oceanic Crust in the Canada Basin of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Hutchinson, Deborah; Chian, Deping; Jackson, Ruth; Lebedeva-Ivanova, Nina; Shimeld, John; Li, Qingmou; Mosher, David; Saltus, Richard; Oakey, Gordon

    2015-04-01

    Canada Basin show the topography of the basement surface varies with the crustal types determined by the velocity data. The top of oceanic crust is generally a weak reflection with a high-relief blocky character, and rare deeper reflections. The top of transitional crust is a low-relief, bright reflection with numerous subparallel bright reflections that extend as much as .5 km deeper. The areas of continental crust show grabens possibly associated with rifting. Previously published longer offset wide-angle reflection/refraction experiments in the southern Canada Basin are consistent with the lack of oceanic layer 3 velocities and the depth to Moho based on our interpretation of the sonobuoy profiles. Our new sonobuoy results show a restricted area of oceanic crust centered within the middle of Canada Basin. This result has implications for plate reconstruction models, which now must close a smaller area and must also account for the poorly known but finite extension in the transitional crust.

  5. History of the earth's crust

    SciTech Connect

    Eicher, D.L.; Mcalester, A.L.; Rottman, M.L.

    1984-01-01

    The history of the earth's crust since its formation 4.6 Gyr ago is traced in an introductory textbook, with consideration of the global climate and the general outline of biological evolution. The methodology of paleogeology is introduced, and the origin of the solar system, the accumulation and differentiation of the earth, the beginnings of life, and the history of the moon are examined. Separate chapters are then devoted to the Precambrian, Paleozoic, Mesozoic, and Cenozoic earth. Photographs, maps, diagrams, and drawings are provided. 49 references.

  6. Juxtaposition of different fault rocks into fault cores in sandstone-dominated formations

    NASA Astrophysics Data System (ADS)

    Philit, Sven; Soliva, Roger; Ballas, Grégory; Chemenda, Alexandre; Castilla, Raymi

    2017-04-01

    We analyze normal faults in porous quartz sandstones at two sites to characterize the juxtaposition of three well-known processes along faults: cataclasis, brecciation and smearing. At the first study site (Jurassic sandstone in Utah, USA), deformation structures formed during a single tectonic episode, displacing sandstones including 10-60 cm thick layers of silt and clay from 2 to 6 m. We observe that cataclastic deformation takes place and thickens along the sandstone/sandstone juxtaposition producing clusters of deformation bands up to tens of centimeters in thickness. With further displacement, the cluster is shifted against the developing silt/clay smear that provides reduced strength. A displacement of 2 meters is sufficient to create a major slip-surface along the clusters of deformation bands. The presence of thin layers of silt/clay therefore induces a fault core made of two adjacent types of fault rocks, namely cataclastic deformation and smear. At the second study site (Permian sandstone in Scotland, UK), two overprinting episodes of faulting occurred within an evolving sandstone lithology. The studied fault is of seismic scale and accommodates a total displacement of 20 to 50 m. Structural analysis based on macroscopic and microscopic observations allows showing a first stage of cataclastic deformation occurring in unlithified sandstone. A second subsequent stage of faulting corresponds to brecciation formed in hardened material (cemented sandstone and cataclastic structure). The breccia currently comprises over 40% of oxides in its composition of meteoric income. In this case, the diagenetic evolution of the sandstone permitted the juxtaposition of these two types of fault rocks. The process of cataclasis causes a porosity reduction of 32 to >90% of the initial porosity and a permeability reduction of 2 to 5 orders of magnitude compared to the host rock. Silts and clays do not undergo significant porosity and permeability reduction through smearing

  7. The significance of slab-crusted lava flows for understanding controls on flow emplacement at Mount Etna, Sicily

    NASA Astrophysics Data System (ADS)

    Guest, John E.; Stofan, Ellen R.

    2005-04-01

    Slab-crusted flows on Mount Etna, Sicily are defined here as those whose crust has ridden on the flow core without significant disruption or deformation and have a high length to width ratio. They typically erupt from ephemeral boccas as late-stage products on dominantly aa flow fields, such as that of the 1983 eruption on Mount Etna. Slab-crusted flows tend to inflate mainly as they approach and after they reach the maximum length of slab-crust formation, the flow interior acting as a preferential pathway for injecting lava under a stable crust. Coalescence of vesicles under successive crusts causes separation between core and crust giving a new cooling surface within the flow, on which ropy surfaces (and occasionally aa textures) of limited areal extent may develop. Slab-crusted flows tend to form at ephemeral boccas together with other surface textural types including toes, ropy pahoehoe sheets and aa flows. This suggests that, on Etna, slab-crusted flows form from lava of the same rheological properties as both aa and pahoehoe textured flows. They do not represent a transition between aa and pahoehoe as argued for toothpaste flows in Hawaii. We conclude that slab-crusted flows on Etna owe their morphology to a relatively high critical ratio of effusion rate to advance rate, related to vent cross-sectional area and the slope over which the flow forms.

  8. Attenuation of Landfill Leachate In Unsaturated Sandstone

    NASA Astrophysics Data System (ADS)

    Butler, A. P.; Brook, C.; Godley, A.; Lewin, K.; Young, C. P.

    Landfill leachate emanating from old "dilute and disperse" sites represents a potential (and in many cases actual) threat to the integrity of groundwater. Indeed, this concern has been included in EU legislation (80/86/EEC), where key contaminants (e.g. ammonia, various toxic organic compounds and heavy metals) are explicitly highlighted in terms of their impact on groundwater. In the UK, whilst there are a substantial number of unlined landfills sited on major aquifers, many of these are in locations where there is a substantial unsaturated zone. Thus, there exists the opportunity for the modification and attenuation of contaminants prior to it encountering the water table. An understanding of likely changes in leachate content and concentrations at such sites will enable a more comprehensive assessment of the potential risks and liabilities posed by such sites to be evaluated. The Burntstump landfill, situated 8 km north of Nottingham (UK), is sited on an outcrop of Sherwood sandstone. The fine friable sand has been quarried since the 1960s and the excavated volume used to store municipal waste. Filling at the site commenced in the mid 1970s and originally was unlined. In 1978 the first of what was to become a series of boreholes was installed within an area of roughly 5 m radius over one of the original waste cells. Cores of the waste and underlying sandstone were extracted and analysed for a range of physical and chemical parameters. The most recent set of analyses were obtained in 2000. The series of investigations therefore provide an important record of leachate migration and modification through the unsaturated zone for over twenty years. The progression of the leachate front is clearly delineated by the chloride concentration profile with an average velocity of around 1.6 m.yr-1. Combining this value with an average (and reasonably uniform) measured moisture content of about 7% gives a mean inter-granular specific discharge of 110 mm.yr-1. An interesting

  9. Constraints on the Composition and Petrogenesis of the Martian Crust

    NASA Technical Reports Server (NTRS)

    McSween, Harry Y., Jr.; Grove, Timothy L.; Wyatt, Michael B.

    2003-01-01

    Spectral interpretation that silicic rocks are widespread on Mars implies that Earth's differentiated crust is not unique. Evaluation of observations bearing on the composition of the Martian crust (Martian meteorite petrology and a possible crustal assimilant, analysis of Mars Pathfinder rocks, composition of Martian fines, interpretation of spacecraft thermal emission spectra, and inferred crustal densities) indicates that the crust can be either basalt plus andesite or basalt plus weathering products. New calculated chemical compositions for Thermal Emission Spectrometer (TES) global surface units indicate that surface type 1 has basaltic andesite composition and surface type 2 has the composition of andesite. If these materials represent volcanic rocks, their calc-alkaline compositions on a FeO*/MgO versus silica diagram suggest formation by hydrous melting and fractional crystallization. On Earth, this petrogenesis requires subduction, and it may suggest an early period of plate tectonics on Mars. However, anorogenic production of andesite might have been possible if the primitive Martian mantle was wet. Alternatively, chemical weathering diagrams suggest that surface type 2 materials could have formed by partial weathering of surface type 1 rocks, leading to depletion in soluble cations and mobility of silica. A weathered crust model is consistent with the occurrence of surface type 2 materials as sediments in a depocenter and with the alpha proton X-ray spectrometer (APXS) analysis of excess oxygen suggesting weathering rinds on Pathfinder rocks. If surface type 1 materials are also weathered or mixed with weathered materials, this might eliminate the need for hydrous melting, consistent with a relatively dry Martian mantle without tectonics.

  10. Soil crusts to warm the planet

    NASA Astrophysics Data System (ADS)

    Garcia-Pichel, Ferran; Couradeau, Estelle; Karaoz, Ulas; da Rocha Ulisses, Nunes; Lim Hsiao, Chiem; Northen, Trent; Brodie, Eoin

    2016-04-01

    Soil surface temperature, an important driver of terrestrial biogeochemical processes, depends strongly on soil albedo, which can be significantly modified by factors such as plant cover. In sparsely vegetated lands, the soil surface can also be colonized by photosynthetic microbes that build biocrust communities. We used concurrent physical, biochemical and microbiological analyses to show that mature biocrusts can increase surface soil temperature by as much as 10 °C through the accumulation of large quantities of a secondary metabolite, the microbial sunscreen scytonemin, produced by a group of late-successional cyanobacteria. Scytonemin accumulation decreases soil albedo significantly. Such localized warming had apparent and immediate consequences for the crust soil microbiome, inducing the replacement of thermosensitive bacterial species with more thermotolerant forms. These results reveal that not only vegetation but also microorganisms are a factor in modifying terrestrial albedo, potentially impacting biosphere feedbacks on past and future climate, and call for a direct assessment of such effects at larger scales. Based on estimates of the global biomass of cyanobacteria in soil biocrusts, one can easily calculate that there must currently exist about 15 million metric tons of scytonemin at work, warming soil surfaces worldwide

  11. What do we really know about Earth's early crust?

    NASA Astrophysics Data System (ADS)

    Rudnick, R. L.; Tang, M.

    2016-12-01

    The oldest minerals on Earth, the detrital Hadean Jack Hills zircons from western Australia, show evidence for their crystallization from hydrous, low temperature, granitic magmas. However, considerable debate centers on whether the parental melts are minimum-melt granites formed in subduction zone settings and implying widespread, evolved continental crust (e.g., Harrison, 2009, AREPS), or crystallized from the last differentiates of mafic magmas (Darling et al., 2009, Geology), or even late differentiates of impact melt sheets on a largely water-covered Earth (Kenny et al., 2016, Geology). Another means by which to interrogate the nature of Earth's early crust is through analyses of ancient fine-grained terrigenous sedimentary rocks such as shales or glacial diamictites, which provide averages of the surface of the Earth that is exposed to chemical weathering and erosion. From these studies it has long been known that Archean crust contained a higher proportion of mafic rocks. However, only recently has that proportion been constrained based on a change in the average MgO content of the upper continental crust from 15 wt.% at 3.2 Ga, to 4 wt.% at 2.6 Ga (Tang et al., 2016, Science). These data for terrigeneous sediments require the pre 3.2 Ga crust to be dominated by mafic rocks (only 10-40% `granite' s.l.) and to be high-standing and susceptible to subareal weathering and erosion, implying the mafic crust was thick (see Tang and Rudnick, this meeting). The dramatic transition that occurred in upper crustal composition between 3.2 and 2.6 Ga likely marks the onset of widespread subduction as a means of generating voluminous granite.

  12. Impacts of biological soil crust disturbance and composition on C and N loss from water erosion

    USGS Publications Warehouse

    Barger, N.N.; Herrick, J.E.; Van Zee, J.; Belnap, J.

    2006-01-01

    In this study, we conducted rainfall simulation experiments in a cool desert ecosystem to examine the role of biological soil crust disturbance and composition on dissolved and sediment C and N losses. We compared runoff and sediment C and N losses from intact late-successional dark cyanolichen crusts (intact) to both trampled dark crusts (trampled) and dark crusts where the top 1 cm of the soil surface was removed (scraped). In a second experiment, we compared C and N losses in runoff and sediments in early-successional light cyanobacterial crusts (light) to that of intact late-successional dark cyanolichen crusts (dark). A relatively high rainfall intensity of approximately 38 mm per 10-min period was used to ensure that at least some runoff was generated from all plots. Losses of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and ammonium (NH 4+ ) were significantly higher from trampled plots as compared to scraped and intact plots. Sediment C and N losses, which made up more than 98% of total nutrient losses in all treatments, were more than 4-fold higher from trampled plots relative to intact plots (sediment C g/m2, intact = 0.74, trampled = 3.47; sediment N g/m2, intact = 0.06, trampled = 0.28). In light crusts, DOC loss was higher relative to dark crusts, but no differences were observed in dissolved N. Higher sediment loss in light crusts relative to dark crusts resulted in 5-fold higher loss of sediment-bound C and N. Total C flux (sediment + dissolved) was on the order of 0.9 and 7.9 g/m2 for dark and light crusts, respectively. Sediment N concentration in the first minutes after runoff from light crusts was 3-fold higher than the percent N of the top 1 cm of soil, suggesting that even short-term runoff events may have a high potential for N loss due to the movement of sediments highly enriched in N. Total N loss from dark crusts was an order of magnitude lower than light crusts (dark = 0.06 g N/m2, light = 0.63 g/m2). Overall, our

  13. Study of Hydrogen and Oxygen and Its Reaction With Host Elements in Sandstone by Laser-Induced Breakdown Spectroscopy (LIBS)

    NASA Astrophysics Data System (ADS)

    Suyanto, Hery

    2017-05-01

    A study of hydrogen and oxygen and its reaction with host elements in a sandstone has been done by laser-induced breakdown spectroscopy (LIBS). The sandstone was irradiated by Nd-YAG laser (1064 nm, 7 ns) with varied energy of 60 mJ till 140 mJ in surrounding air gas pressure of 1 atm and produced plasma. The emission intensities of hydrogen H I 656.2 nm and oxygen O I 777.2 nm in the plasma were captured by HR 2500+ spectrometer and displayed in intensity as a function of wavelength. The data show that the emission intensities of hydrogen and oxygen increase with increasing laser energy at a gradient of 5.4 and 11.8 respectively every increasing laser energy of 20 mJ. To characterize the reaction process between hydrogen and oxygen with the host elements of the sandstone, a 0.2 ml demineralized water was dropped on the sandstone surface and was analyzed as a function of delay time reaction and temperature. The data show that the oxidation reaction between host elements and oxygen occurred after 25 minutes that the oxygen emission intensity increases and the hydrogen emission intensity decreases. Another data also show that the increasing temperature of sandstone until 80 C increased intermolecular bond between oxygen and host element and dehydrogenation took place after reaching this temperature

  14. Characteristics of deltaic deposits in the Cretaceous Pierre Shale, Trinidad Sandstone, and Vermejo Formation, Raton Basin, Colorado.

    USGS Publications Warehouse

    Flores, R.M.; Tur, S.M.

    1982-01-01

    Detailed facies analyses of closely spaced measured surface sections in the Trinidad and adjacent areas of Colorado reflect deposition in the river-influenced delta. That this deltaic system was accompanied by abandonment of subdeltas is indicated by a destructional-deltaic facies of heavily bioturbated, carbonaceous sandstones, siltstones, and shales best recorded in the delta front deposits of the Trinidad Sandstone. Coal accumulation of the Vermejo deposits nevertheless remained primarily controlled by persistent organic sedimentation in interdistributary backswamps. These backswamps, which accumulated thick, lenticular coals, were formed during the normal constructional phase of the delta plain. -from Authors

  15. Diazotrophic Community Structure and Function in Two Successional Stages of Biological Soil Crusts from the Colorado Plateau and Chihuahuan Desert

    PubMed Central

    Yeager, Chris M.; Kornosky, Jennifer L.; Housman, David C.; Grote, Edmund E.; Belnap, Jayne; Kuske, Cheryl R.

    2004-01-01

    The objective of this study was to characterize the community structure and activity of N2-fixing microorganisms in mature and poorly developed biological soil crusts from both the Colorado Plateau and Chihuahuan Desert. Nitrogenase activity was approximately 10 and 2.5 times higher in mature crusts than in poorly developed crusts at the Colorado Plateau site and Chihuahuan Desert site, respectively. Analysis of nifH sequences by clone sequencing and the terminal restriction fragment length polymorphism technique indicated that the crust diazotrophic community was 80 to 90% heterocystous cyanobacteria most closely related to Nostoc spp. and that the composition of N2-fixing species did not vary significantly between the poorly developed and mature crusts at either site. In contrast, the abundance of nifH sequences was approximately 7.5 times greater (per microgram of total DNA) in mature crusts than in poorly developed crusts at a given site as measured by quantitative PCR. 16S rRNA gene clone sequencing and microscopic analysis of the cyanobacterial community within both crust types demonstrated a transition from a Microcoleus vaginatus-dominated, poorly developed crust to mature crusts harboring a greater percentage of Nostoc and Scytonema spp. We hypothesize that ecological factors, such as soil instability and water stress, may constrain the growth of N2-fixing microorganisms at our study sites and that the transition to a mature, nitrogen-producing crust initially requires bioengineering of the surface microenvironment by Microcoleus vaginatus. PMID:14766579

  16. Diazotrophic Community Structure and Function in Two Successional Stages of Biological Soil Crusts from the Colorado Plateau and Chihuahuan Desert

    USGS Publications Warehouse

    Yeager, C.M.; Kornosky, J.L.; Housman, D.C.; Grote, E.E.; Belnap, J.; Kuske, C.R.

    2004-01-01

    The objective of this study was to characterize the community structure and activity of N2-fixing microorganisms in mature and poorly developed biological soil crusts from both the Colorado Plateau and Chihuahuan Desert. Nitrogenase activity was approximately 10 and 2.5 times higher in mature crusts than in poorly developed crusts at the Colorado Plateau site and Chihuahuan Desert site, respectively. Analysis of nifH sequences by clone sequencing and the terminal restriction fragment length polymorphism technique indicated that the crust diazotrophic community was 80 to 90% heterocystous cyanobacteria most closely related to Nostoc spp. and that the composition of N2-fixing species did not vary significantly between the poorly developed and mature crusts at either site. In contrast, the abundance of nifH sequences was approximately 7.5 times greater (per microgram of total DNA) in mature crusts than in poorly developed crusts at a given site as measured by quantitative PCR. 16S rRNA gene clone sequencing and microscopic analysis of the cyanobacterial community within both crust types demonstrated a transition from a Microcoleus vaginatus-dominated, poorly developed crust to mature crusts harboring a greater percentage of Nostoc and Scytonema spp. We hypothesize that ecological factors, such as soil instability and water stress, may constrain the growth of N2-fixing microorganisms at our study sites and that the transition to a mature, nitrogen-producing crust initially requires bioengineering of the surface microenvironment by Microcoleus vaginatus.

  17. Compaction Bands Around Unstable Wellbores In Porous Sandstone and Their Dependence On Grain Bonding

    NASA Astrophysics Data System (ADS)

    Haimson, B.; Klaetsch, A.

    porosity Berea and St. Peter sandstones sutured contacts are limited to relatively small areas of the grain surface. Such contacts are readily severed at stress levels lower than quartz-grain strength, yielding debonded but intact compaction bands. On the other hand, sutured contacts in the 12% St. Peter are considerably more extensive, covering most of the grain surfaces, and rendering the strength of the matrix equal to that of individual grains. Hence, the compaction band here contains both debonded and crushed grains.

  18. Diagenetic analogs to hematite regions on Mars: examples from Jurassic sandstones of southern Utah, USA

    NASA Astrophysics Data System (ADS)

    Beitler, Brenda; Chan, Marjorie A.; Parry, William T.; Ormo, Jens O.; Komatsu, Goro

    2004-11-01

    Diagenetic hematite concretions are common in the eolian Jurassic Navajo Sandstone in southern Utah (and some correlative units in Arizona and Nevada). The zones of alteration formed by structurally and stratigraphically influenced subsurface groundwater flow and localized iron oxide precipitation within porous sedimentary rocks. In many geologic systems on Earth, iron is a sensitive fluid flow indicator1. Mobilization and precipitation of iron oxides and sulfides requires specific variations in fluid chemistry. Precipitation of iron oxides in discrete concretionary zones further requires specific host rock characteristics. These characteristic color variations and zones of mineralization in the Jurassic Navajo Sandstone occur in a variety of cementation patterns with structural and stratigraphic relationships that have been well documented. Iron for the concretions is likely sourced internally from hematite grain coatings. Near surface, meteoric waters and processes of weathering commonly distribute disseminated iron films that impart a pink to orange-red color to the sandstone early in the depositional or burial history. The disseminated iron oxides are commonly mobilized and removed by reducing fluids, leaving the sandstone white. When these fluids mix with oxidizing groundwater in the Utah example, concentrated hematite precipitates, typically in the form of spherical balls. Many other concretion geometries commonly occur where anisotropy and preferential fluid flow pathways exist. Some of these shapes include pipes, sheets, bulbs, angular bricks, and repetitive bands. The differing geometries appear to be primarily a function of permeability barriers and pathways. Both sandstone coloration and the presence of hematite concretions (+/- other iron oxide minerals) record evidence of past fluid flow and reactions in subsurface sedimentary rocks. These are products of low-temperature, near-surface, hydrologic, chemical diagenetic reactions. Biomediation can also

  19. Evolution of Fractal Parameters through Development Stage of Soil Crust

    NASA Astrophysics Data System (ADS)

    Ospina, Abelardo; Florentino, Adriana; Tarquis, Ana Maria

    2016-04-01

    Soil surface characteristics are subjected to changes driven by several interactions between water, air, biotic and abiotic components. One of the examples of such interactions is provided through biological soil crusts (BSC) in arid and semi-arid environments. BSC are communities composed of cyanobacteria, fungi, mosses, lichens, algae and liverworts covering the soil surface and play an important role in ecosystem functioning. The characteristics and formation of these BSC influence the soil hydrological balance, control the mass of eroded sediment, increase stability of soil surface, and influence plant productivity through the modification of nitrogen and carbon cycle. The site of this work is located at Quibor and Ojo de Agua (Lara state, Venezuela). The Quibor Depression in Venezuela is a major agricultural area being at semi-arid conditions and limited drainage favor the natural process of salinization. Additionally, the extension and intensification of agriculture has led to over-exploitation of groundwater in the past 30 years (Méndoza et al., 2013). The soil microbial crust develops initially on physical crusts which are mainly generated since wetting and drying, being a recurrent feature in the Quíbor arid zone. The microbiotic crust is organic, composed of macro organisms (bryophytes and lichens) and microorganisms (cyanobacteria, fungi algae, etc.); growing on the ground, forming a thickness no greater than 3 mm. For further details see Toledo and Florentino (2009). This study focus on characterize the development stage of the BSC based on image analysis. To this end, grayscale images of different types of biological soil crust at different stages where taken, each image corresponding to an area of 12.96 cm2 with a resolution of 1024x1024 pixels (Ospina et al., 2015). For each image lacunarity and fractal dimension through the differential box counting method were calculated. These were made with the software ImageJ/Fraclac (Karperien, 2013

  20. CHIC - Coupling Habitability, Interior and Crust

    NASA Astrophysics Data System (ADS)

    Noack, Lena; Labbe, Francois; Boiveau, Thomas; Rivoldini, Attilio; Van Hoolst, Tim

    2014-05-01

    We present a new code developed for simulating convection in terrestrial planets and icy moons. The code CHIC is written in Fortran and employs the finite volume method and finite difference method for solving energy, mass and momentum equations in either silicate or icy mantles. The code uses either Cartesian (2D and 3D box) or spherical coordinates (2D cylinder or annulus). It furthermore contains a 1D parametrised model to obtain temperature profiles in specific regions, for example in the iron core or in the silicate mantle (solving only the energy equation). The 2D/3D convection model uses the same input parameters as the 1D model, which allows for comparison of the different models and adaptation of the 1D model, if needed. The code has already been benchmarked for the following aspects: - viscosity-dependent rheology (Blankenbach et al., 1989) - pseudo-plastic deformation (Tosi et al., in preparation phase) - subduction mechanism and plastic deformation (Quinquis et al., in preparation phase) New features that are currently developed and benchmarked include: - compressibility (following King et al., 2009 and Leng and Zhong, 2008) - different melt modules (Plesa et al., in preparation phase) - freezing of an inner core (comparison with GAIA code, Huettig and Stemmer, 2008) - build-up of oceanic and continental crust (Noack et al., in preparation phase) The code represents a useful tool to couple the interior with the surface of a planet (e.g. via build-up and erosion of crust) and it's atmosphere (via outgassing on the one hand and subduction of hydrated crust and carbonates back into the mantle). It will be applied to investigate several factors that might influence the habitability of a terrestrial planet, and will also be used to simulate icy bodies with high-pressure ice phases. References: Blankenbach et al. (1989). A benchmark comparison for mantle convection codes. GJI 98, 23-38. Huettig and Stemmer (2008). Finite volume discretization for dynamic

  1. Beyond KTB - electrical conductivity of the deep continental crust

    NASA Astrophysics Data System (ADS)

    Glover, Paul W. J.; Vine, F. J.

    1995-01-01

    aqueous fluids and/or contains interconnected grain surface films of graphite. The experimental data are consistent with a three layer crust consisting of an aqueous fluid saturated acidic uppermost layer, above an aqueous fluid saturated amphibolite mid-crust, and a granulite lowermost crust, which may or may not be saturated with aqueous fluids, but if not, requires the presence of an additional conduction mechanism such as conduction through thin graphite films.

  2. The evolution of the early lunar crust

    NASA Astrophysics Data System (ADS)

    Hess, P. C.; Parmentier, E. M.

    1997-03-01

    In the framework of the plutonic and tectonic processes that acted to create the current configuration of the lunar crust, attention is given to the problems as to why (1) the crust is vertically zoned; (2) there are no plutonic equivalents to mare basalt; and (3) the evolution of lunar crust would shape subsequent and younger volcanic events. The existence of mascons by 3.9 By shows that the entire crust had strengthened, and could support far greater stresses than those generated by mafic plutons.

  3. Pulsar glitches: the crust is not enough.

    PubMed

    Andersson, N; Glampedakis, K; Ho, W C G; Espinoza, C M

    2012-12-14

    Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the nondissipative entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid, effectively reducing the moment of inertia associated with the angular momentum reservoir. Combining the latest observational data for prolific glitching pulsars with theoretical results for the crust entrainment, we find that the required superfluid reservoir exceeds that available in the crust. This challenges our understanding of the glitch phenomenon, and we discuss possible resolutions to the problem.

  4. Geochemical characteristics and metal element enrichment in crusts from seamounts of the Western Pacific

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoyu; Zhu, Kechao; Du, Yong; Zhang, Fuyuan; Zhang, Weiyan; Ren, Xiangwen; Jiang, Binbin; Huang, Dasong

    2016-03-01

    Elemental geochemistry is an essential part of understanding mineralization mechanisms. In this paper, a data set of 544 cobalt crust samples from seamounts of the Western Pacific are used to study the enrichment characteristics of metal elements. REE normalization is utilized to reveal the origin of the crusts; effects of water depth on Co enrichment and impacts of phosphatization on mineral quality are discussed to obtain the evolution of these marine mineral deposits, which gives support to further resource assessment. Conclusions are reached as follows: 1) Elemental abundances, inter-element relationships, and shale-normalized REE patterns for phosphate-poor crusts from different locations reflect hydrogenetic origin of the crusts. EFs (enrichment coefficients) of REE exhibit exponential increase from surface sediments to phosphorite to polymetallic nodules to crusts, suggesting that the improved degree of hydrogeneous origin induces the enrichment of REE. 2) The crusts in the Western Pacific, formed through hotspot produced guyots trails, have relatively lower REE than those in the Mid-Pacific. The latter could be attributed to the peculiar submarine topography of seamounts formed by intraplate volcanism. 3) The non-phosphatized younger crust layers have 40% higher Co than the phosphatized older layers. This indicates the modification of the elemental composition in these crusts by phosphatization. A general depletion of hydroxide-dominated elements such as Co, Ni, and Mn and enrichment of P, Ca, Ba, and Sr is evident in phosphatized crusts, whereas non-phosphatized younger generation crusts are rich in terrigenous aluminosilicate detrital matter. 4) Co increases above the carbonate compensation depth (CCD) from less than 0.53% to over 0.65% in seamount regions with water depth of less than 2,500 m, suggesting the significance of the dissolution of carbonate in the sea water column to the growth and composition of crusts.

  5. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics

    NASA Astrophysics Data System (ADS)

    Tang, Ming; Chen, Kang; Rudnick, Roberta L.

    2016-01-01

    The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago.

  6. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics.

    PubMed

    Tang, Ming; Chen, Kang; Rudnick, Roberta L

    2016-01-22

    The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago. Copyright © 2016, American Association for the Advancement of Science.

  7. Evidence for mechanical coupling and strong Indian lower crust beneath southern Tibet.

    PubMed

    Copley, Alex; Avouac, Jean-Philippe; Wernicke, Brian P

    2011-04-07

    How surface deformation within mountain ranges relates to tectonic processes at depth is not well understood. The upper crust of the Tibetan Plateau is generally thought to be poorly coupled to the underthrusting Indian crust because of an intervening low-viscosity channel. Here, however, we show that the contrast in tectonic regime between primarily strike-slip faulting in northern Tibet and dominantly normal faulting in southern Tibet requires mechanical coupling between the upper crust of southern Tibet and the underthrusting Indian crust. Such coupling is inconsistent with the presence of active 'channel flow' beneath southern Tibet, and suggests that the Indian crust retains its strength as it underthrusts the plateau. These results shed new light on the debates regarding the mechanical properties of the continental lithosphere, and the deformation of Tibet. ©2011 Macmillan Publishers Limited. All rights reserved

  8. Temperature dependent elasticity and damping in dehydrated sandstone

    NASA Astrophysics Data System (ADS)

    Darling, T. W.; Struble, W.

    2013-12-01

    Work reported previously at this conference, outlining our observation of anomalously large elastic softening and damping in dehydrated Berea sandstone at elevated temperatures, has been analysed to study shear and compressional effects separately. Modeling of the sample using COMSOL software was necessary to identify modes, as the vibration spectrum of the sample is poorly approximated by a uniform isotropic solid. The first torsional mode of our evacuated, dry, core softens at nearly twice the rate of Young's modulus modes (bending and compressional) and is also damped nearly twice as strongly as temperature increases. We consider two possible models for explaining this behavior, based on the assumption that the mechanical properties of the sandstone are dominated by the framework of quartz grains and polycrystalline cementation, neglecting initially the effects of clay and feldspar inclusions. The 20cm x 2.54cm diameter core is dry such that the pressure of water vapor in the experiment chamber is below 1e-6 Torr at 70C, suggesting that surface water beyond a small number of monolayers is negligible. Our models consider (1) enhanced sliding of grain boundaries in the cementation at elevated temperature and reduced internal water content, and (2) strain microcracking of the cementatioin at low water content due to anisotropic expansion in the quartz grains. In model (1) interfaces parallel to polyhedral grain surfaces were placed in the cement bonds and assigned frictional properties. Model (2) has not yet been implemented. The overall elasticity of a 3-D several-grain model network was determined by modeling quasistatic loading and measuring displacements. Initial results with a small number of grains/bonds suggests that only the first model provides softening and damping for all the modes, however the details of the effects of defect motioin at individual interfaces as the source for the frictional properties is still being evaluated. Nonlinear effects are

  9. Two scale analysis applied to low permeability sandstones

    NASA Astrophysics Data System (ADS)

    Davy, Catherine; Song, Yang; Nguyen Kim, Thang; Adler, Pierre

    2015-04-01

    Low permeability materials are often composed of several pore structures of various scales, which are superposed one to another. It is often impossible to measure and to determine the macroscopic properties in one step. In the low permeability sandstones that we consider, the pore space is essentially made of micro-cracks between grains. These fissures are two dimensional structures, which aperture is roughly on the order of one micron. On the grain scale, i.e., on the scale of 1 mm, the fissures form a network. These two structures can be measured by using two different tools [1]. The density of the fissure networks is estimated by trace measurements on the two dimensional images provided by classical 2D Scanning Electron Microscopy (SEM) with a pixel size of 2.2 micron. The three dimensional geometry of the fissures is measured by X-Ray micro-tomography (micro-CT) in the laboratory, with a voxel size of 0.6x0.6x0.6microns3. The macroscopic permeability is calculated in two steps. On the small scale, the fracture transmissivity is calculated by solving the Stokes equation on several portions of the measured fissures by micro-CT. On the large scale, the density of the fissures is estimated by three different means based on the number of intersections with scanlines, on the surface density of fissures and on the intersections between fissures per unit surface. These three means show that the network is relatively isotropic and they provide very close estimations of the density. Then, a general formula derived from systematic numerical computations [2] is used to derive the macroscopic dimensionless permeability which is proportional to the fracture transmissivity. The combination of the two previous results yields the dimensional macroscopic permeability which is found to be in acceptable agreement with the experimental measurements. Some extensions of these preliminary works will be presented as a tentative conclusion. References [1] Z. Duan, C. A. Davy, F

  10. Geology of the Ferron Sandstone coalbed gas {open_quotes}fairway,{close_quotes} central Utah

    SciTech Connect

    Tabet, D.E.; Hucka, B.P.; Sommer, S.N.

    1996-12-31

    A major new coalbed gas play with as many as 1,000 wells already proposed is being developed in the Upper Cretaceous Ferron Sandstone of central Utah. The Ferron consists of a vertically stacked sequence of as many as seven fluvial-deltaic sandstones and laterally equivalent interdistributary coal swamp units. A new total-net-coal isopach map for the Ferron, compiled from the review of hundreds of well records, shows the greatest accumulation of coal generally occurs in a 6-to 10-mile-wide band, or fairway, directly to the west (landward) of the fluvial-deltaic sandstones. This fairway can be traced a distance of at least 80 miles, heading southwest from the vicinity of Price to the southeast corner of Sevier County. The fairway is interrupted roughly every 8-to-12 miles along its length by deltaic, distributary-channel systems. Well samples of Ferron coal were examined microscopically to determine vitrinite reflectance and maturity level. Near-surface coals, on the east side of the fairway, have vitrinite reflectance measurements as low as 0.5 percent. Reflectance values increase to the west, reaching a maximum of 0.71 percent. The maturity of coals with vitrinite reflectance readings between 0.5 and 0.71 percent is the early stage in which thermogenic methane generation begins. Examination of drill-hole data also shows that the coal fairway exists at shallow to moderate depths, ranging from surface exposures to 8,000 feet deep.

  11. Geology of the Ferron Sandstone coalbed gas [open quotes]fairway,[close quotes] central Utah

    SciTech Connect

    Tabet, D.E.; Hucka, B.P.; Sommer, S.N. )

    1996-01-01

    A major new coalbed gas play with as many as 1,000 wells already proposed is being developed in the Upper Cretaceous Ferron Sandstone of central Utah. The Ferron consists of a vertically stacked sequence of as many as seven fluvial-deltaic sandstones and laterally equivalent interdistributary coal swamp units. A new total-net-coal isopach map for the Ferron, compiled from the review of hundreds of well records, shows the greatest accumulation of coal generally occurs in a 6-to 10-mile-wide band, or fairway, directly to the west (landward) of the fluvial-deltaic sandstones. This fairway can be traced a distance of at least 80 miles, heading southwest from the vicinity of Price to the southeast corner of Sevier County. The fairway is interrupted roughly every 8-to-12 miles along its length by deltaic, distributary-channel systems. Well samples of Ferron coal were examined microscopically to determine vitrinite reflectance and maturity level. Near-surface coals, on the east side of the fairway, have vitrinite reflectance measurements as low as 0.5 percent. Reflectance values increase to the west, reaching a maximum of 0.71 percent. The maturity of coals with vitrinite reflectance readings between 0.5 and 0.71 percent is the early stage in which thermogenic methane generation begins. Examination of drill-hole data also shows that the coal fairway exists at shallow to moderate depths, ranging from surface exposures to 8,000 feet deep.

  12. Stratigraphic sequence of a transgressive barrier-bar system, Red Fork sandstone, Wakita trend, Grant County, Oklahoma

    SciTech Connect

    O'Reilly, K.L.

    1987-08-01

    The stratigraphic sequence of the Red Fork sandstone (Boggy Formation, Krebs Group) along the Wakita trend, north-central Oklahoma, is interpreted as a transgressive barrier-bar system. The Red Fork sands were deposited along the northern shelf of the Anadarko basin in an elongate belt about 1-7 km wide. Within the belt, the sandstone forms podlike bodies ranging from 1 to 16 km long. The Red Fork is positioned in a generally onlapping sequence of strata, from the Inola Limestone Member at the base to the Tiawah (Pink) Limestone Member at the top. Shales that are interpreted as lagoonal deposits underlie and have a sharp contact with the Red Fork. To the north, the underlying shale is variegated green and red, and contains abundant rootlets and woody detritus; shale to the south is dark-gray and contains abundant brachiopod fragments. Glauconitic siltstone and shale overlie and have a gradational contact with the Red Fork sandstone. Sedimentation of the Red Fork sand was apparently localized on an east-west-striking hinge formed by increasing dip on the surface of the Inola. Shale overlying the Inola thickens to the south, forming a relatively flat surface upon which Red Fork deposition occurred. No evidence exists of valleys or channels cutting into shale underlying the Red Fork sandstone. Sedimentary structures in the Red Fork sandstone support interpretation of the stratigraphic sequence as a barrier-bar complex. Sandstone geometry and the nature of the encasing rocks are distinctly characteristic of transgressive barrier-bar systems.

  13. Excavation and melting of the Hadean continental crust by Late Heavy Bombardment

    NASA Astrophysics Data System (ADS)

    Shibaike, Yuhito; Sasaki, Takanori; Ida, Shigeru

    2016-03-01

    No Hadean rocks have ever been found on Earth's surface except for zircons-evidence of continental crust, suggesting that Hadean continental crust existed but later disappeared. One hypothesis for the disappearance of the continental crust is excavation/melting by the Late Heavy Bombardment (LHB), a concentration of impacts in the last phase of the Hadean eon. In this paper, we calculate the effects of LHB on Hadean continental crust in order to investigate this hypothesis. Approximating the size-frequency distribution of the impacts by a power-law scaling with an exponent α as a parameter, we have derived semi-analytical expressions for the effects of LHB impacts. We calculated the total excavation/melting volume and area affected by the LHB from two constraints of LHB on the Moon, the size of the largest basin during LHB, and the density of craters larger than 20 km. We also investigated the effects of the value of α. Our results show that LHB does not excavate/melt all of Hadean continental crust directly, but over 70% of the Earth's surface area can be covered by subsequent melts in a broad range of α. If there have been no overturns of the continental crust until today, LHB could be responsible for the absence of Hadean rocks because most of Hadean continental crust is not be exposed on the Earth's surface in this case.

  14. Magnetization of the oceanic crust: TRM or CRM?

    NASA Technical Reports Server (NTRS)

    Raymond, C. A.; Labrecque, J. L.

    1987-01-01

    A model was proposed in which chemical remanent magnetization (CRM) acquired within the first 20 Ma of crustal evolution may account for 80% of the bulk natural remanent magnetization (NRM) of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low temperature alteration. The CRM intensity and direction are controlled by the post-emplacement polarity history. This model explains several independent observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness discrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis, and the enhanced magnetization of the Cretaceous Quiet Zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Further studies indicate varying rates of TRM decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer.

  15. A Comparison of Microbial Communities from Deep Igneous Crust

    NASA Astrophysics Data System (ADS)

    Smith, A. R.; Flores, G. E.; Fisk, M. R.; Colwell, F. S.; Thurber, A. R.; Mason, O. U.; Popa, R.

    2013-12-01

    Recent investigations of life in Earth's crust have revealed common themes in organism function, taxonomy, and diversity. Capacities for hydrogen oxidation, carbon fixation, methanogenesis and methanotrophy, iron and sulfur metabolisms, and hydrocarbon degradation often predominate in deep life communities, and crustal mineralogy has been hypothesized as a driving force for determining deep life community assemblages. Recently, we found that minerals characteristic of the igneous crust harbored unique communities when incubated in the Juan de Fuca Ridge flank borehole IODP 1301A. Here we present attached mineral biofilm morphologies and a comparison of our mineral communities to those from a variety of locations, contamination states, and igneous crustal or mineralogical types. We found that differences in borehole mineral communities were reflected in biofilm morphologies. Olivine biofilms were thick, carbon-rich films with embedded cells of uniform size and shape and often contained secondary minerals. Encrusted cells, spherical and rod-shaped cells, and tubes were indicative of glass surfaces. We also found that the attached communities from incubated borehole minerals were taxonomically more similar to native, attached communities from marine and continental crust than to communities from the aquifer water that seeded it. Our findings further support the hypothesis that mineralogy selects for microbial communities that have distinct phylogenetic, morphological, and potentially functional, signatures. This has important implications for resolving ecosystem function and microbial distributions in igneous crust, the largest deep habitat on Earth.

  16. Cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the Pacific sea floor

    USGS Publications Warehouse

    Manheim, F. T.; Lane-Bostwick, C. M.

    1988-01-01

    Ferromanganese oxide crusts, which accumulate on unsedimented surfaces in the open ocean1-6, derive most of their metal content from dissolved and particulate matter in ambient bottom water7,8, in proportions modified by the variable scavenging efficiency of the oxide phase for susceptible ions9. They differ in this respect from abyssal nodules, much of whose metals are remobilized from host sediments. Here we present maps of cobalt concentration and inferred accumulation rate of ferromanganese crusts from the Pacific Ocean. We propose that depletion of cobalt in Pacific crusts measures the location and intensity of submarine hydrothermal discharge. Use of the 'cobalt chronometer', an algorithm inversely relating cobalt content and crust growth rate, permits mapping of the accumulation rate of ferromanganese crusts with only indirect recourse to radioactivity-based dating methods. These maps show that crusts in hydrothermal areas grow from two to more than four orders of magnitude faster than in the Central Pacific Ocean. Cobalt-enriched crusts are found where water masses are most isolated from continental-coastal and hydrothermal sources of metals, now and in the past. This relationship can resolve the problem of cobalt enrichment in crusts without recourse to hypotheses invoking special cobalt sources or enrichment mechanisms. ?? 1988 Nature Publishing Group.

  17. Local structures of Ca, Ti and Fe in meteorite fusion crusts

    NASA Astrophysics Data System (ADS)

    Tobase, T.; Yoshiasa, A.; Hiratoko, T.; Hongu, H.; Isobe, H.; Nakatsuka, A.; Arima, H.; Sugiyama, K.

    2016-05-01

    The local structures of meteorite fusion crusts were studied by Ca, Ti and Fe K-edge XANES and EXAFS spectroscopy. The surface of meteorites were melted and volatilized with extreme high temperature and large temperature gradient when meteorites were rushed into atmosphere. This study indicated that meteorite fusion crusts have unique local structures. The local structures of fusion crusts differ from tektites especially in intensity of the shoulder in the rising flank of the edge in Ca XANES spectra. It is consistent with chemical composition change by the volatilization of Si at fusion during atmospheric entry. The high estimated Fe3+/ (Fe2++Fe3+) ratio in meteorite fusion crusts indicates that meteorite fusion crusts are formed into atmospheric oxidation condition. The Ca-O distances in meteorite fusion crusts are 2.612.66 A and are extremely longer than in other natural glasses. The fusion crusts have unique local structure since they experienced extremely high temperature and short quenching time. The XAFS method is effective in distinction of meteorite fusion crusts and classification of natural glass.

  18. [Ecological effect of hygroscopic and condensate water on biological soil crusts in Shapotou region of China].

    PubMed

    Pan, Yan-Xia; Wang, Xin-Ping; Zhang, Ya-Feng; Hu, Rui

    2013-03-01

    By the method of field experiment combined with laboratory analysis, this paper studied the ecological significance of hygroscopic and condensate water on the biological soil crusts in the vegetation sand-fixing area in Shapotou region of China. In the study area, 90% of hygroscopic and condensate water was within the 3 cm soil depth, which didn' t affect the surface soil water content. The hygroscopic and condensate water generated at night involved in the exchange process of soil surface water and atmosphere water vapor, made up the loss of soil water due to the evaporation during the day, and made the surface soil water not reduced rapidly. The amount of the generated hygroscopic and condensate water had a positive correlation with the chlorophyll content of biological soil crusts, indicating that the hygroscopic and condensate water could improve the growth activity of the biological soil crusts, and thus, benefit the biomass accumulation of the crusts.

  19. Europium mass balance in polymict samples and implications for plutonic rocks of the lunar crust

    NASA Technical Reports Server (NTRS)

    Korotev, Randy L.; Haskin, Larry A.

    1988-01-01

    The mean concentrations of Sm and Eu in the lunar surface crust were analyzed by correlating the Sm concentration and the Sm/Eu ratio with Th concentration obtained from published data on a large number of polymict samples from various locations in the lunar highlands, and using the value of 0.91 microg/g for the mean Th concentration of the highlands surface crust obtained by the orbiting gamma-ray experiments. The mean concentration of Sm in the lunar surface crust was found to be between 2 and 3 microg/g, and that of Eu between 0.7 and 1.2 microg/g. The results indicate that there is no significant enrichment or depletion of Eu, compared to Sm, relative to chondritic abundances; i.e., there is no significant 'Eu anomaly' in average upper crust, contrary to predictions by some earlier investigators.

  20. Integrated Studies of Impact-Basin Ejecta as Probes of the Lunar Crust: Imbrium and Serenitatis

    NASA Technical Reports Server (NTRS)

    Jolliff, Brad L.; Haskin, Larry A.

    1998-01-01

    The large, late, basin impacts on the Earth side of the Moon fundamentally reshaped the structure of the crust, its surface morphology, and the composition of the megaregolith and surface soils. The latest (except for Orientale on the western limb) and largest was the Imbrium impact, which produced massive ejecta deposits over much of the Procellarum region and beyond, and ejected material that mixed with surface regolith nearly Moonwide. The basins serve as natural probes into the lunar crust; therefore, understanding the nature and composition of ejecta produced by them provides information about the crust at depth. Gravity data allow modeling of the structure of the crust beneath the basins, and from such models one can infer depths of excavation and the nature of crustal response following impact.

  1. Influence of temperature and water on subcritical crack growth in sandstone

    NASA Astrophysics Data System (ADS)

    Nara, Yoshitaka; Yoneda, Tetsuro; Kaneko, Katsuhiko

    2010-05-01

    Understanding time-dependent brittle deformation due to slow crack growth is important in many geological applications. Time-dependent fracture propagation has been invoked as the key mechanism responsible for the increase in seismicity preceding earthquake ruptures and volcanic eruptions. In addition, when designing sub-surface structures in the rock mass, such as repositories for radioactive waste and underground power plants, it is essential to consider their long-term stability. In order to ensure long-term stability, it is necessary to evaluate the long-term strength of the rock. In turn, this requires an understanding of time-dependent fracture propagation such as subcritical crack growth. Environmental dependence of subcritical crack growth in igneous rocks has been studied well. However, that in sedimentary rocks has not been clarified yet. In this study, the effects of the temperature and water on subcritical crack growth in sandstone were investigated. Berea sandstone and Shirahama sandstone were used as rock samples. The load relaxation method of Double Torsion (DT) testing method was used to measure the crack velocity and the stress intensity factor under controlled environmental conditions. In water, it was shown that the crack velocity at a given stress intensity factor increased when the temperature increased. This agrees well with the theory of stress corrosion. In air, however, it was shown that the change of the crack velocity at a given stress intensity factor was not clear when the temperature increased under a constant relative humidity. On the other hand, the crack velocity at a given stress intensity factor increased by several orders of magnitude when the relative humidity increased threefold or fourfold under a constant temperature. This increase is much larger than that expected from the conventional concept based on the theory of stress corrosion. Additionally, the increase of the crack velocity was larger for Shirahama sandstone which

  2. Archaeal and bacterial communities in deep-sea hydrogenetic ferromanganese crusts on old seamounts of the northwestern Pacific.

    PubMed

    Nitahara, Shota; Kato, Shingo; Usui, Akira; Urabe, Tetsuro; Suzuki, Katsuhiko; Yamagishi, Akihiko

    2017-01-01

    Deep-sea ferromanganese crusts are found ubiquitously on the surface of seamounts of the world's oceans. Considering the wide distribution of the crusts, archaeal and bacterial communities on these crusts potentially play a significant role in biogeochemical cycling between oceans and seamounts; however little is known about phylogenetic diversity, abundance and function of the crust communities. To this end, we collected the crusts from the northwest Pacific basin and the Philippine Sea. We performed comprehensive analysis of the archaeal and bacterial communities of the collected crust samples by culture-independent molecular techniques. The distance between the sampling points was up to approximately 2,000 km. Surrounding sediments and bottom seawater were also collected as references near the sampling points of the crusts, and analyzed together. 16S rRNA gene analyses showed that the community structure of the crusts was significantly different from that of the seawater. Several members related to ammonia-oxidizers of Thaumarchaeota and Betaproteobacteria were detected in the crusts at most of all regions and depths by analyses of 16S rRNA and amoA genes, suggesting that the ammonia-oxidizing members are commonly present in the crusts. Although members related to the ammonia-oxidizers were also detected in the seawater, they differed from those in the crusts phylogenetically. In addition, members of uncultured groups of Alpha-, Delta- and Gammaproteobacteria were commonly detected in the crusts but not in the seawater. Comparison with previous studies of ferromanganese crusts and nodules suggests that the common members determined in the present study are widely distributed in the crusts and nodules on the vast seafloor. They may be key microbes for sustaining microbial ecosystems there.

  3. Archaeal and bacterial communities in deep-sea hydrogenetic ferromanganese crusts on old seamounts of the northwestern Pacific

    PubMed Central

    Usui, Akira; Urabe, Tetsuro; Suzuki, Katsuhiko; Yamagishi, Akihiko

    2017-01-01

    Deep-sea ferromanganese crusts are found ubiquitously on the surface of seamounts of the world’s oceans. Considering the wide distribution of the crusts, archaeal and bacterial communities on these crusts potentially play a significant role in biogeochemical cycling between oceans and seamounts; however little is known about phylogenetic diversity, abundance and function of the crust communities. To this end, we collected the crusts from the northwest Pacific basin and the Philippine Sea. We performed comprehensive analysis of the archaeal and bacterial communities of the collected crust samples by culture-independent molecular techniques. The distance between the sampling points was up to approximately 2,000 km. Surrounding sediments and bottom seawater were also collected as references near the sampling points of the crusts, and analyzed together. 16S rRNA gene analyses showed that the community structure of the crusts was significantly different from that of the seawater. Several members related to ammonia-oxidizers of Thaumarchaeota and Betaproteobacteria were detected in the crusts at most of all regions and depths by analyses of 16S rRNA and amoA genes, suggesting that the ammonia-oxidizing members are commonly present in the crusts. Although members related to the ammonia-oxidizers were also detected in the seawater, they differed from those in the crusts phylogenetically. In addition, members of uncultured groups of Alpha-, Delta- and Gammaproteobacteria were commonly detected in the crusts but not in the seawater. Comparison with previous studies of ferromanganese crusts and nodules suggests that the common members determined in the present study are widely distributed in the crusts and nodules on the vast seafloor. They may be key microbes for sustaining microbial ecosystems there. PMID:28235095

  4. Luna 24 - Lateral heterogeneity in the lunar crust

    NASA Technical Reports Server (NTRS)

    Warner, J. L.; Simonds, C. H.; Mcgee, P. E.; Cochran, A.

    1978-01-01

    Results of petrological investigations of Luna 24 soil samples are compared with data from Apollo and other Luna missions in order to determine the large scale composition of the lunar surface and crust. Modal analysis of the 90 to 150 micron soil fraction and electron microprobe analysis of glass spheres and fragments of the Luna 24 core sample are presented. High and low MgO mare basalt compositional clusters are found, suggesting the derivation of southern Mare Crisium basalts from two magmas. A model of Luna 24 soils as being composed of a mixture of glass-poor mare material and glass-rich highland material is found to be consistent with glass and agglutinate modal abundances. Comparisons show that potassium, and by inference all lithophile trace elements, are depleted on the eastern limb of the moon relative to the central nearside. The observed depletion is interpreted to be characteristic of the underlying crust and mantle as well as the surface.

  5. Ejecta Dynamics during Hypervelocity Impacts into Dry and Wet Sandstone

    NASA Astrophysics Data System (ADS)

    Hoerth, T.; Schäfer, F.; Thoma, K.; Poelchau, M.; Kenkmann, T.; Deutsch, A.

    2011-03-01

    Hypervelocity impact experiments into dry and water saturated porous Seeberger sandstone were conducted at the two-stage light gas accelerator at the Ernst-Mach-Institute (EMI) and the ejecta dynamics were analyzed.

  6. Resonant Ultrasound Spectroscopy studies of Berea sandstone at high temperature

    SciTech Connect

    Davis, Eric S.; Sturtevant, Blake T.; Sinha, Dipen N.; Pantea, Cristian

    2016-09-04

    Resonant Ultrasound Spectroscopy was used in this paper to determine the elastic moduli of Berea sandstone from room temperature to 478 K. Sandstone is a common component of oil reservoirs, and the temperature range was chosen to be representative of typical downhole conditions, down to about 8 km. In agreement with previous works, Berea sandstone was found to be relatively soft with a bulk modulus of approximately 6 GPa as compared to 37.5 GPa for α-quartz at room temperature and pressure. Finally, it was found that Berea sandstone undergoes a ~17% softening in bulk modulus between room temperature and 385 K, followed by an abnormal behavior of similar stiffening between 385 K and 478 K.

  7. Resonant Ultrasound Spectroscopy studies of Berea sandstone at high temperature

    DOE PAGES

    Davis, Eric S.; Sturtevant, Blake T.; Sinha, Dipen N.; ...

    2016-09-04

    Resonant Ultrasound Spectroscopy was used in this paper to determine the elastic moduli of Berea sandstone from room temperature to 478 K. Sandstone is a common component of oil reservoirs, and the temperature range was chosen to be representative of typical downhole conditions, down to about 8 km. In agreement with previous works, Berea sandstone was found to be relatively soft with a bulk modulus of approximately 6 GPa as compared to 37.5 GPa for α-quartz at room temperature and pressure. Finally, it was found that Berea sandstone undergoes a ~17% softening in bulk modulus between room temperature and 385more » K, followed by an abnormal behavior of similar stiffening between 385 K and 478 K.« less

  8. Martian Sandstone Target Windjana Before and After Brushing

    NASA Image and Video Library

    2014-04-29

    This image from an animation shows a patch of sandstone scrubbed with the Dust Removal Tool, a wire-bristle brush, on NASA Curiosity Mars rover. This rock target is called Windjana, after a gorge in Western Australia.

  9. Nodules of Cemented Sand Grains Within Martian Sandstone

    NASA Image and Video Library

    2016-03-11

    This view from NASA Curiosity shows nodules exposed in sandstone that is part of the Stimson geological unit on Mount Sharp, Mars. The nodules can be seen to consist of grains of sand cemented together.

  10. Pressure sensitivity of low permeability sandstones

    USGS Publications Warehouse

    Kilmer, N.H.; Morrow, N.R.; Pitman, J.K.

    1987-01-01

    Detailed core analysis has been carried out on 32 tight sandstones with permeabilities ranging over four orders of magnitude (0.0002 to 4.8 mD at 5000 psi confining pressure). Relationships between gas permeability and net confining pressure were measured for cycles of loading and unloading. For some samples, permeabilities were measured both along and across bedding planes. Large variations in stress sensitivity of permeability were observed from one sample to another. The ratio of permeability at a nominal confining pressure of 500 psi to that at 5000 psi was used to define a stress sensitivity ratio. For a given sample, confining pressure vs permeability followed a linear log-log relationship, the slope of which provided an index of pressure sensitivity. This index, as obtained for first unloading data, was used in testing relationships between stress sensitivity and other measured rock properties. Pressure sensitivity tended to increase with increase in carbonate content and depth, and with decrease in porosity, permeability and sodium feldspar. However, scatter in these relationships increased as permeability decreased. Tests for correlations between pressure sensitivity and various linear combinations of variables are reported. Details of pore structure related to diagenetic changes appears to be of much greater significance to pressure sensitivity than mineral composition. ?? 1987.

  11. Plagioclase flotation and lunar crust formation

    NASA Technical Reports Server (NTRS)

    Walker, D.; Hays, J. F.

    1977-01-01

    Anorthitic plagioclase floats in liquids parental to the lunar highlands crust. The plagioclase enrichment that is characteristic of lunar highlands rocks can be the result of plagioclase flotation. Such rocks would form a gravitationally stable upper crust on their parental magma.

  12. Diagenesis Along Fractures in an Eolian Sandstone, Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Ming, D. W.; Yen, A. S.; Rampe, E. B.; Grotzinger, J. P.; Blake, D. F.; Bristow, T. F.; Chipera, S. J.; Downs, R.; Morris, R. V.; Morrison, S. M.; Vaniman, D. T.; Gellert, R.; Sutter, B.; Treiman, A. H.

    2016-01-01

    The Mars Science Laboratory rover Curiosity has been exploring sedimentary deposits in Gale crater since August 2012. The rover has traversed up section through approx.100 m of sedimentary rocks deposited in fluvial, deltaic, lacustrine, and eolian environments (Bradbury group and overlying Mount Sharp group). The Stimson formation lies unconformable over a lacustrine mudstone at the base of the Mount Sharp group and has been interpreted to be a cross-bedded sandstone of lithified eolian dunes. Mineralogy of the unaltered Stimson sandstone consists of plagioclase feldspar, pyroxenes, and magnetite with minor abundances of hematite, and Ca-sulfates (anhydrite, bassanite). Unaltered sandstone has a composition similar to the average Mars crustal composition. Alteration "halos" occur adjacent to fractures in the Stimson. Fluids passing through these fractures have altered the chemistry and mineralogy of the sandstone. Silicon and S enrichments and depletions in Al, Fe, Mg, Na, K, Ni and Mn suggest aqueous alteration in an open hydrologic system. Mineralogy of the altered Stimson is dominated by Ca-sulfates, Si-rich X-ray amorphous materials along with plagioclase feldspar, magnetite, and pyroxenes, but less abundant in the altered compared to the unaltered Stimson sandstone and lower pyroxene/plagioclase feldspar. The mineralogy and geochemistry of the altered sandstone suggest a complicated history with several (many?) episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline).

  13. The Middle Jurassic Entrada Sandstone near Gallup, New Mexico

    USGS Publications Warehouse

    Robertson, J.F.; O'Sullivan, R. B.

    2001-01-01

    Near Gallup, New Mexico, the Middle Jurassic Entrada Sandstone consists of, in ascending order, the Iyanbito Member, the Rehoboth Member, and an upper sandstone member. The Rehoboth Member is named herein to replace the middle siltstone member, with a type section located 26 km east of Gallup. The Iyanbito Member has been erroneously equated with the Wingate Sandstone of northeast Arizona, and the Rehoboth Member has been miscorrelated with the Dewey Bridge Member of the Entrada in Utah. The Dewey Bridge is an older unit that does not extend into New Mexico. The Iyanbito Member, east of Gallup, overlies the J-2 unconformity and the eroded tops of the Owl Rock and Petrified Forest Members of the Chinle Formation. The Wingate Sandstone of the Lower Jurassic Glen Canyon Group overlies the J-0 unconformity and the underlying Rock Point Member (topmost unit) of the Chinle Formation in northeast Arizona. Both the Wingate Sandstone and the Rock Point Member are missing east of Gallup below the J-2 unconformity. Similarly, the Wingate is missing southwest of Gallup, near Lupton, Arizona, but the Rock Point Member is present and underlies the Iyanbito from Zuni northward to Toadlena, New Mexico. The Wingate and other formations of the Glen Canyon Group thin and wedge out southward and eastward in northeast Arizona. The J-2 unconformity truncates the Wingate Sandstone and the underlying J-0 unconformity, 5 km north of Toadlena.

  14. Neutron star inner crust: Nuclear physics input

    SciTech Connect

    Steiner, Andrew W.

    2008-03-15

    A fully self-consistent model of the neutron star inner crust based upon models of the nucleonic equation of state at zero temperature is constructed. The results nearly match those of previous calculations of the inner crust given the same input equation of state. The extent to which the uncertainties in the symmetry energy, the compressibility, and the equation of state of low-density neutron matter affect the composition of the crust are examined. The composition and pressure of the crust is sensitive to the description of low-density neutron matter and the nuclear symmetry energy, and the latter dependence is nonmonotonic, giving larger nuclei for moderate symmetry energies and smaller nuclei for more extreme symmetry energies. Future nuclear experiments may help constrain the crust and future astrophysical observations may constrain the nuclear physics input.

  15. Transgressive parasequences in Cretaceous upper Frontier (Wall Creek) sandstone

    SciTech Connect

    Huff, M.C. )

    1989-09-01

    Transgression during the upper Turonian in the area of the present-day Powder River basin was episodic: initial sea level rise, followed by a gradual overtaking of sea level rise by sedimentation rate, then another sea level rise to higher than it was before. Most of the parasequences produced consist of a transgressive lag directly overlain by coarsening-upward progradational deposits. Others are more complex. These more complex parasequences are composed of a transgressive lag overlain by fining-upward transgressive sediments overlain by coarsening-upward regressive deposits. A condensed section or omission surface separating the transgressive portion from the regressive portion is rarely found. Several such packages are found stacked vertically in areas that were near the basin margin. Farther paleolandward, part of the record preserved in the marine parasequences was removed by erosion. In the deeper parts of the basin, the condensed section encompasses part or all of the record. Capping the last progradational deposit in some locations in a shelf sand ridge. Understanding the details of sequence stratigraphy increases the accuracy of its use for predicting where to find reservoir sandstones. Certain Wall Creek facies, such as shelf sand ridges, are important petroleum reservoirs in the Powder River basin.

  16. Crust and upper mantle of Kamchatka from teleseismic receiver functions

    NASA Astrophysics Data System (ADS)

    Levin, Vadim; Park, Jeffrey; Brandon, Mark; Lees, Jonathan; Peyton, Valerie; Gordeev, Evgenii; Ozerov, Alexei

    2002-11-01

    Teleseismic receiver functions (RFs) from a yearlong broadband seismological experiment in Kamchatka reveal regional variations in the Moho, anisotropy in the supra-slab mantle wedge, and, along the eastern coast, Ps converted phases from the steeply dipping slab. We analyze both radial- and transverse-component RFs in bin-averaged epicentral and backazimuthal sweeps, in order to detect Ps moveout and polarity variations diagnostic of interface depth, interface dip, and anisotropic fabric within the shallow mantle and crust. At some stations, the radial RF is overprinted by near-surface resonances, but anisotropic structure can be inferred from the transverse RF. Using forward modeling to match the observed RFs, we find Moho depth to range between 30 and 40 km across the peninsula, with a gradational crust-mantle transition beneath some stations along the eastern coast. Anisotropy beneath the Moho is required to fit the transverse RFs at most stations. Anisotropy in the lower crust is required at a minority of stations. Modeling the amplitude and backazimuthal variation of the Ps waveform suggests that an inclined axis of symmetry and 5-10% anisotropy are typical for the crust and the shallow mantle. The apparent symmetry axes of the anisotropic layers are typically trench-normal, but trench-parallel symmetry axes are found for stations APA and ESS, both at the fringes of the central Kamchatka depression. Transverse RFs from east-coast stations KRO, TUM, ZUP and PET are fit well by two anisotropic mantle layers with trench-normal symmetry axes and opposing tilts. Strong anisotropy in the supra-slab mantle wedge suggests that the mantle "lithosphere" beneath the Kamchatka volcanic arc is actively deforming, strained either by wedge corner flow at depth or by trenchward suction of crust as the Pacific slab retreats.

  17. Soil nematode communities are ecologically more mature beneath late- than early-successional stage biological soil crusts

    USGS Publications Warehouse

    Darby, B.J.; Neher, D.A.; Belnap, J.

    2007-01-01

    Biological soil crusts are key mediators of carbon and nitrogen inputs for arid land soils and often represent a dominant portion of the soil surface cover in arid lands. Free-living soil nematode communities reflect their environment and have been used as biological indicators of soil condition. In this study, we test the hypothesis that nematode communities are successionally more mature beneath well-developed, late-successional stage crusts than immature, early-successional stage crusts. We identified and enumerated nematodes by genus from beneath early- and late-stage crusts from both the Colorado Plateau, Utah (cool, winter rain desert) and Chihuahuan Desert, New Mexico (hot, summer rain desert) at 0-10 and 10-30 cm depths. As hypothesized, nematode abundance, richness, diversity, and successional maturity were greater beneath well-developed crusts than immature crusts. The mechanism of this aboveground-belowground link between biological soil crusts and nematode community composition is likely the increased food, habitat, nutrient inputs, moisture retention, and/or environmental stability provided by late-successional crusts. Canonical correspondence analysis of nematode genera demonstrated that nematode community composition differed greatly between geographic locations that contrast in temperature, precipitation, and soil texture. We found unique assemblages of genera among combinations of location and crust type that reveal a gap in scientific knowledge regarding empirically derived characterization of dominant nematode genera in deserts soils and their functional role in a crust-associated food web. ?? 2006 Elsevier B.V. All rights reserved.

  18. Ecological succession, hydrology and carbon acquisition of biological soil crusts measured at the micro-scale.

    PubMed

    Tighe, Matthew; Haling, Rebecca E; Flavel, Richard J; Young, Iain M

    2012-01-01

    The hydrological characteristics of biological soil crusts (BSCs) are not well understood. In particular the relationship between runoff and BSC surfaces at relatively large (>1 m(2)) scales is ambiguous. Further, there is a dearth of information on small scale (mm to cm) hydrological characterization of crust types which severely limits any interpretation of trends at larger scales. Site differences and broad classifications of BSCs as one soil surface type rather than into functional form exacerbate the problem. This study examines, for the first time, some hydrological characteristics and related surface variables of a range of crust types at one site and at a small scale (sub mm to mm). X-ray tomography and fine scale hydrological measurements were made on intact BSCs, followed by C and C isotopic analyses. A 'hump' shaped relationship was found between the successional stage/sensitivity to physical disturbance classification of BSCs and their hydrophobicity, and a similar but 'inverse hump' relationship exists with hydraulic conductivity. Several bivariate relationships were found between hydrological variables. Hydraulic conductivity and hydrophobicity of BSCs were closely related but this association was confounded by crust type. The surface coverage of crust and the microporosity 0.5 mm below the crust surface were closely associated irrespective of crust type. The δ (13)C signatures of the BSCs were also related to hydraulic conductivity, suggesting that the hydrological characteristics of BSCs alter the chemical processes of their immediate surroundings via the physiological response (C acquisition) of the crust itself. These small scale results illustrate the wide range of hydrological properties associated with BSCs, and suggest associations between the ecological successional stage/functional form of BSCs and their ecohydrological role that needs further examination.

  19. Ecological Succession, Hydrology and Carbon Acquisition of Biological Soil Crusts Measured at the Micro-Scale

    PubMed Central

    Tighe, Matthew; Haling, Rebecca E.; Flavel, Richard J.; Young, Iain M.

    2012-01-01

    The hydrological characteristics of biological soil crusts (BSCs) are not well understood. In particular the relationship between runoff and BSC surfaces at relatively large (>1 m2) scales is ambiguous. Further, there is a dearth of information on small scale (mm to cm) hydrological characterization of crust types which severely limits any interpretation of trends at larger scales. Site differences and broad classifications of BSCs as one soil surface type rather than into functional form exacerbate the problem. This study examines, for the first time, some hydrological characteristics and related surface variables of a range of crust types at one site and at a small scale (sub mm to mm). X-ray tomography and fine scale hydrological measurements were made on intact BSCs, followed by C and C isotopic analyses. A ‘hump’ shaped relationship was found between the successional stage/sensitivity to physical disturbance classification of BSCs and their hydrophobicity, and a similar but ‘inverse hump’ relationship exists with hydraulic conductivity. Several bivariate relationships were found between hydrological variables. Hydraulic conductivity and hydrophobicity of BSCs were closely related but this association was confounded by crust type. The surface coverage of crust and the microporosity 0.5 mm below the crust surface were closely associated irrespective of crust type. The δ 13C signatures of the BSCs were also related to hydraulic conductivity, suggesting that the hydrological characteristics of BSCs alter the chemical processes of their immediate surroundings via the physiological response (C acquisition) of the crust itself. These small scale results illustrate the wide range of hydrological properties associated with BSCs, and suggest associations between the ecological successional stage/functional form of BSCs and their ecohydrological role that needs further examination. PMID:23119058

  20. Energy conservation in the earth's crust and climate change.

    PubMed

    Mu, Yao; Mu, Xinzhi

    2013-02-01

    Among various matters which make up the earth's crust, the thermal conductivity of coal, oil, and oil-gas, which are formed over a long period of geological time, is extremely low. This is significant to prevent transferring the internal heat of the earth to the thermal insulation of the surface, cooling the surface of the earth, stimulating biological evolution, and maintaining natural ecological balance as well. Fossil energy is thermal insulating layer in the earth's crust. Just like the function of the thermal isolation of subcutaneous fatty tissue under the dermis of human skin, it keeps the internal heat within the organism so it won't be transferred to the skin's surface and be lost maintaining body temperature at low temperatures. Coal, oil, oil-gas, and fat belong to the same hydrocarbons, and the functions of their thermal insulation are exactly the same. That is to say, coal, oil, and oil-gas are just like the earth's "subcutaneous fatty tissue" and objectively formed the insulation protection on earth's surface. This paper argues that the human large-scale extraction of fossil energy leads to damage of the earth's crust heat-resistant sealing, increasing terrestrial heat flow, or the heat flow as it is called, transferring the internal heat of the earth to Earth's surface excessively, and causing geotemperature and sea temperature to rise, thus giving rise to global warming. The reason for climate warming is not due to the expansion of greenhouse gases but to the wide exploitation of fossil energy, which destroyed the heat insulation of the earth's crust, making more heat from the interior of the earth be released to the atmosphere. Based on the energy conservation principle, the measurement of the increase of the average global temperature that was caused by the increase of terrestrial heat flow since the Industrial Revolution is consistent with practical data. This paper illustrates "pathogenesis" of climate change using medical knowledge. The

  1. Post-glacial ocean acidification and the decline of reefal microbial crusts

    NASA Astrophysics Data System (ADS)

    Riding, R.; Liang, L.; Braga, J.

    2011-12-01

    Data from Pacific, Indian Ocean and Caribbean coral reefs indicate marked Late Pleistocene to Holocene decline in the maximum thickness of microbial carbonate crusts in reef cavities. Using estimated values of pH, temperature, CO2, and ionic composition, we calculated calcite saturation ratio (Ωcalcite) of tropical surface seawater for the past 16 Ka. This shows a declining trend of Ωcalcite, paralleling that of reefal microbial crust thickness. We suggest that thinning of reefal microbial crusts could reflect decrease in seawater carbonate saturation due to ocean acidification in response to deglacial CO2 increase. Previously, decline in reefal microbial crusts, for example at Tahiti in the Pacific Ocean, has mainly been attributed to changes in nutrient supply associated with ocean upwelling and/or terrestrial run-off. Ocean acidification does not preclude such effects on microbial crust development produced by localized changes, but two features in particular are consistent with a global link with carbonate saturation state. Firstly, post-glacial decline in reefal microbial crust thickness affected tropical coral reefs in several oceans. Secondly, seawater carbonate saturation is a major long-term control on microbial carbonate abundance; microbially-induced biocalcification requires elevated seawater saturation for CaCO3 minerals and can be expected to fluctuate with carbonate saturation. In addition to compiling published crust thickness data, we measured thicknesses of microbial carbonate crusts in cavities in Tahiti reefs sampled by Integrated Ocean Drilling Program coring in 2005. This indicates halving of maximum crust thickness, during the same period as steep decline in mean-ocean calcite saturation, near the Pleistocene-Holocene transition. Reefal microbial crusts have been common since skeletal reefs became widespread during the Ordovician Period, 475 Ma ago. The habitat for cryptic crusts expanded as scleractinian corals developed cavernous

  2. Geometric and sedimentologic characteristic of Mid-Miocene lowstand reservoir sandstones, offshore northwest Java, Indonesia

    SciTech Connect

    Lowry, P.; Kusumanegara, Y.; Warman, S.

    1996-12-31

    Numerous reservoirs in the Upper Cibulakan Formation (Mid-Miocene) of the Offshore Northwest Java shelf occur in sharp-based sandbodies that range from less than 1 m up to 10 m in thickness. Well-log derived net-sand isopach and seismic amplitude maps of these sandbodies depict elongate features, that are 1-2 km wide and 5-8 km long. The orientation of the longest axis of these sandbodies is predominantly north-south. Conventional cores reveal that these sandbodies are burrowed to completely bioturbated sandstones. Common trace fossils associated with these sandbodies include Ophiomorpha, Teichichnus and Thalassinoides. The lower contact of these sands is typically sharp and is commonly associated with a Glossifungites surface and siderite mud clasts. Overlying and underlying mudstones are relatively devoid of burrowing. Benthonic foraminifera assemblages within these mudstones indicate inner to outer neritic conditions in a relatively restricted marine setting. The upper contact of these sandstones is gradational over a 0.5 to 1m interval. Sandbodies of the same age and similar facies were observed in outcrops in onshore west Java. Here, they can be observed to pinch out over a distance of 500 m. The lower bounding contact appears discordant with underlying interbedded sandstones and mudstones. Several of the sandstones contain abundant accumulations of the large, open marine, benthonic foraminifera Cycloclypeus and Lepidocyclina. Occasionally the concentration of these large foraminifera form limestones within the sharp-based sandbodies. These bioclastic deposits commonly exhibit planar-tabular and trough cross-stratification. The sandbodies are interpreted as having been emplaced during relative falls in sea-level within a large Mid-Miocene embayment. Our understanding of their geometry and sedimentologic characteristics is leading to a more effective exploitation strategy for these sandbodies in the Offshore Northwest Java area.

  3. Factors Affecting the Kinetics of Salt Crystallization and Related Damage in Sandstone

    NASA Astrophysics Data System (ADS)

    Shahidzadeh, N.; Desarnaud, J.; Hannelore, D.; Molari, L.; Miranda, S.; Cnudde, V.

    2014-12-01

    Salt contaminated stones or masonry materials are often observed to deteriorate under environmental conditions due to crystallization of salts, the importance of which is expected to increase in the future due to global climate change. When environmental conditions such as humidity or exposure to rain or rising damp vary, salts in contact with water (liquid or vapor) can dissolve and cause damage to the material by re-crystallization upon drying. The detailed mechanisms of the damaging processes have been investigated for several decades now. However there are still open questions such as why a given salt can lead to damage in some environmental conditions and not in others. We present both macroscopic and microscopic experiments assessing the importance of the kinetics of salt crystallization for NaCl on damage in sandstone with environmental fluctuations, i.e. wetting/drying and humidity cycling. NaCl contaminated sandstones are put in contact with liquid water and water vapor until complete saturation, followed by drying at different relative humidities. Advanced techniques such as high resolution X-ray computed tomography and Scanning Electron Microscopy are used to study the kinetics of salt growth in the porous network. Our results show that the kinetics of recrystallization after deliquescence (contact with water vapor) and rewetting of salt contaminated sandstones leads to very different crystallization patterns. With humidity cycling, recrystallization promotes the formation of localised bigger cubic crystals at the subsurface of the stone whereas rewetting leads to efflorescence in the form of large localised cauliflowers at the surface. The different growth dynamics also affects the drying behaviour of the sandstones. These results reveal for the first time the major role of the crystallization dynamics in the way a given salt causes damage in some environmental conditions and not in other.

  4. Numerical simulation of multi-dimensional NMR response in tight sandstone

    NASA Astrophysics Data System (ADS)

    Guo, Jiangfeng; Xie, Ranhong; Zou, Youlong; Ding, Yejiao

    2016-06-01

    Conventional logging methods have limitations in the evaluation of tight sandstone reservoirs. The multi-dimensional nuclear magnetic resonance (NMR) logging method has the advantage that it can simultaneously measure transverse relaxation time (T 2), longitudinal relaxation time (T 1) and diffusion coefficient (D). In this paper, we simulate NMR measurements of tight sandstone with different wettability and saturations by the random walk method and obtain the magnetization decays of Carr-Purcell-Meiboom-Gill pulse sequences with different wait times (TW) and echo spacings (TE) under a magnetic field gradient, resulting in D-T 2-T 1 maps by the multiple echo trains joint inversion method. We also study the effects of wettability, saturation, signal-to-noise ratio (SNR) of data and restricted diffusion on the D-T 2-T 1 maps in tight sandstone. The results show that with decreasing wetting fluid saturation, the surface relaxation rate of the wetting fluid gradually increases and the restricted diffusion phenomenon becomes more and more obvious, which leads to the wetting fluid signal moving along the direction of short relaxation and the direction of the diffusion coefficient decreasing in D-T 2-T 1 maps. Meanwhile, the non-wetting fluid position in D-T 2-T 1 maps does not change with saturation variation. With decreasing SNR, the ability to identify water and oil signals based on NMR maps gradually decreases. The wetting fluid D-T 1 and D-T 2 correlations in NMR diffusion-relaxation maps of tight sandstone are obtained through expanding the wetting fluid restricted diffusion models, and are further applied to recognize the wetting fluid in simulated D-T 2 maps and D-T 1 maps.

  5. Evaporation front compared with crust thickness in potato deep-fat frying.

    PubMed

    Lioumbas, John S; Karapantsios, Thodoris D

    2012-01-01

    The various theoretical approaches that have been proposed for modeling heat and mass transport during deep-fat frying of potatoes provide a rather ambiguous view of the relation between the propagation of the evaporation front inside the food and the evolution of crust thickness. This can be partly attributed to the unavailability of detailed experimental information concerning the temperature field inside the developing crust to validate the models. The objective of the present work is to experimentally study the relation between crust thickness evolution and evaporation front propagation and how this varies with frying conditions. To achieve this goal, a special device has been constructed that permits (1) only 1 side of a potato stick to be exposed to hot oil, and (2) accurate and stable placement of miniature thermocouples in prescribed positions under but very close to the potato surface. Temperature recordings inside the developing crust allowed identification of different heating regimes during frying and a rough estimation of the evaporation front propagation. In addition, crust thickness was determined at intermittent time intervals by 2 independent methods (1) microphotography and (2) a micrometer. Comparison of the evaporation front propagation with crust thickness evolution indicates an interrelationship roughly up to the end of the boiling regime (bubble-end point). After this moment, the propagation of the evaporation front is faster than the evolution of crust thickness. Understanding the role of parameters that determine crust formation is of paramount importance since crust characteristics such as thickness and texture dictate the sensory perception of fried foods. This study aims to quantify the relationship between such parameters (that is, crust evolution and the propagation of the evaporation front inside the food) and to examine how frying conditions (oil temperature and frying duration) affect it. In addition, the present findings may be of

  6. Fault-fracture strain in Wingate Sandstone

    NASA Astrophysics Data System (ADS)

    Jamison, William R.

    The Laramide deformation of the Triassic Wingate Sandstone along the northeast flank of the Uncompahgre uplift has occurred by faulting at various scales. Macroscopically smooth flexures of beds within the Wingate occur by small displacements across a myriad of intraformational, mesoscale faults. The deformation resultant from these small faults may be approximated by a strain tensor, provided the measurement domain satisfies certain size criteria. Equivalent strain (ɛ) measurements, obtained from 22 locations in the East Kodel's Canyon, range from 1% to 15.5% (the maximum contractional strains range from -0.9% to -13.4%). The faults producing this strain have displacements ranging from a fraction of a millimeter to 18.5 cm. The fault intensity increases with increasing ɛ, although in a distinctly non-linear fashion. At low strains, incremental increases in the deformation produce additional, small displacement faults. At larger strains, incremental increases in the deformation occur via progressive displacement along existing faults. The principal strain axes are consistently non-coaxial with the inferred principal stresses (average σ1Λɛ1 is 18.5°). This non-coaxiality results from the non-uniform development of the conjugate fault systems. This same inequality of the conjugate systems produces a non-zero rotation tensor, ω, but ω is not related to σ1Λɛ1. The non-uniform development of conjugate shears (and the associated non-coaxiality of σ1 and ɛ1) may be an intrinsic characteristic of a Coulomb material.

  7. Biological soil crusts as an integral component of desert environments

    USGS Publications Warehouse

    Belnap, Jayne; Weber, Bettina

    2013-01-01

    The biology and ecology of biological soil crusts, a soil surface community of mosses, lichens, cyanobacteria, green algae, fungi, and bacteria, have only recently been a topic of research. Most efforts began in the western U.S. (Cameron, Harper, Rushforth, and St. Clair), Australia (Rogers), and Israel (Friedmann, Evenari, and Lange) in the late 1960s and 1970s (e.g., Friedmann et al. 1967; Evenari 1985reviewed in Harper and Marble 1988). However, these groups worked independently of each other and, in fact, were often not aware of each other’s work. In addition, biological soil crust communities were seen as more a novelty than a critical component of dryland ecosystems. Since then, researchers have investigated many different aspects of these communities and have shown that although small to microscopic, biological soil crusts are critical in many ecological processes of deserts. They often cover most of desert soil surfaces and substantially mediate inputs and outputs from desert soils (Belnap et al. 2003). They can be a large source of biodiversity for deserts, as they can contain more species than the surrounding vascular plant community (Rosentreter 1986). These communities are important in reducing soil erosion and increasing soil fertility through the capture of dust and the fixation of atmospheric nitrogen and carbon into forms available to other life forms (Elbert et al. 2012). Because of their many effects on soil characteristics, such as external and internal morphological characteristics, aggregate stability, soil moisture, and permeability, they also affect seed germination and establishment and local hydrological cycles. Covering up to 70% of the surface area in many arid and semi-arid regions around the world (Belnap and Lange 2003), biological soil crusts are a key component within desert environments.

  8. The Seismic Structure of the Crust of Madagascar

    NASA Astrophysics Data System (ADS)

    Wysession, M. E.; Andriampenomanana Ny Ony, F. S. T.; Tsiriandrimanana, R.; Pratt, M. J.; Aleqabi, G. I.; Wiens, D. A.; Nyblade, A.; Shore, P.; Rambolamanana, G.; Tilmann, F. J.

    2015-12-01

    The structure of Madagascar's crust is determined using both body wave receiver functions as well as an analysis of surface waves using ambient-noise and two-plane-wave earthquake surface waves analyses. The primary data used are from the 2011-2013 MACOMO (Madagascar, the Comoros, and Mozambique) broadband seismic array from the PASSCAL program of IRIS (Incorporated Research Institutions for Seismology), funded by the NSF. Additional data came from the RHUM-RUM project (led by G. Barruol and K. Sigloch), the Madagascar Seismic Profile (led by F. Tilmann), and the GSN. The crustal structure of Madagascar, which had previously only been inferred from a gravity survey assuming isostasy, shows a strong correlation with its tectonic history. Crustal thicknesses are greatest, reaching 45 km, along the spine of Madagascar's mountains, which run north-south across the island. Crustal thicknesses thin to the east and west, which are both regions of tectonic separation, however, with very different results. Extensive crustal thinning occurred along the western coasts of Madagascar when the island rifted away from mainland Africa beginning 160 Ma ago. The crust is as thin as 20 km here, but the thickness of basin sediments is as great as 9 km, with the crystalline basement continental crust thinning to 12 km at its thinnest. Along the east coast, the crustal thickness is within the 33-38 km range, but it is thickest in the two places where mesoarchaean crust was rifted off from the Indian subcontinent when it broke away from Madagascar. Surface wave studies show that velocities beneath Madagascar are generally slow, when compared to global models such as AK135. This appears to be due to the occurrence of Cenozoic intraplate volcanism in three regions of Madagascar (north, central, and southwest), each of which has strong underlying seismic low-velocity anomalies in the lithospheric mantle and asthenosphere.

  9. Global occurrence of tellurium-rich ferromanganese crusts and a model for the enrichment of tellurium

    USGS Publications Warehouse

    Hein, J.R.; Koschinsky, A.; Halliday, A.N.

    2003-01-01

    Hydrogenetic ferromanganese oxyhydroxide crusts (Fe-Mn crusts) precipitate out of cold ambient ocean water onto hard-rock surfaces (seamounts, plateaus, ridges) at water depths of about 400 to 4000 m throughout the ocean basins. The slow-growing (mm/Ma) Fe-Mn crusts concentrate most elements above their mean concentration in the Earth's crust. Tellurium is enriched more than any other element (up to about 50,000 times) relative to its Earth's crustal mean of about 1 ppb, compared with 250 times for the next most enriched element. We analyzed the Te contents for a suite of 105 bulk hydrogenetic crusts and 140 individual crust layers from the global ocean. For comparison, we analyzed 10 hydrothermal stratabound Mn-oxide samples collected from a variety of tectonic environments in the Pacific. In the Fe-Mn crust samples, Te varies from 3 to 205 ppm, with mean contents for Pacific and Atlantic samples of about 50 ppm and a mean of 39 ppm for Indian crust samples. Hydrothermal Mn samples have Te contents that range from 0.06 to 1 ppm. Continental margin Fe-Mn crusts have lower Te contents than open-ocean crusts, which is the result of dilution by detrital phases and differences in growth rates of the hydrogenetic phases. Correlation coefficient matrices show that for hydrothermal deposits, Te has positive correlations with elements characteristic of detrital minerals. In contrast, Te in open-ocean Fe-Mn crusts usually correlates with elements characteristic of the MnO2, carbonate fluorapatite, and residual biogenic phases. In continental margin crusts, Te also correlates with FeOOH associated elements. In addition, Te is negatively correlated with water depth of occurrence and positively correlated with crust thickness. Q-mode factor analyses support these relationships. However, sequential leaching results show that most of the Te is associated with FeOOH in Fe-Mn crusts and ???10% is leached with the MnO2. Thermodynamic calculations indicate that Te occurs

  10. What makes the desert bloom? Contribution of dust and crusts to soil fertility on the Colorado Plateau

    Treesearch

    Jayne Belnap; Richard Reynolds; Marith Reheis; Susan L. Phillips

    2001-01-01

    Eolian dust (windblown silt and clay) and biological soil crusts are both important to ecosystem functioning of arid lands. Dust furnishes essential nutrients, influences hydrology, contributes to soil formation, and renders surfaces vulnerable to erosion. Biological soil crusts contribute directly to soil fertility by fixing carbon and nitrogen, and indirectly by...

  11. Decay of sandstone monuments in Petra (Jordan): Gravity-induced stress as a stabilizing factor

    NASA Astrophysics Data System (ADS)

    Řihošek, Jaroslav; Bruthans, Jiří; Mašín, David; Filippi, Michal; Schweigstillova, Jana

    2016-04-01

    As demonstrated by physical experiments and numerical modeling the gravity-induced stress (stress in further text) in sandstone massive reduces weathering and erosion rate (Bruthans et al. 2014). This finding is in contrast to common view that stress threatens stability of man-made monuments carved to sandstone. Certain low- levels of gravity-induced stress can in fact stabilize and protect these forms against weathering and disintegration. The purpose of this investigation is to evaluate the effect of the stress on weathering of sandstone monuments at the Petra World Heritage Site in Jordan via field observations, salt weathering experiments, and physical and numerical modeling. Previous studies on weathering of Petra monuments have neglected the impact of stress, but the ubiquitous presence of stress-controlled landforms in Petra suggests that it has a substantial effect on weathering and erosion processes on man-made monuments and natural surfaces. Laboratory salt weathering experiments with cubes of Umm Ishrin sandstone from Petra demonstrated the inverse relationship between stress magnitude and decay rate. Physical modeling with Strelec locked sand from the Czech Republic was used to simulate weathering and decay of Petra monuments. Sharp forms subjected to water erosion decayed to rounded shapes strikingly similar to tombs in Petra subjected to more than 2000 years of weathering and erosion. The physical modeling results enabled visualization of the recession of monument surfaces in high spatial and temporal resolution and indicate that the recession rate of Petra monuments is far from constant both in space and time. Numerical modeling of stress fields confirms the physical modeling results. This novel approach to investigate weathering clearly demonstrates that increased stress decreases the decay rate of Petra monuments. To properly delineate the endangered zones of monuments, the potential damage caused by weathering agents should be combined with stress

  12. Effects of chemically active solutions on shearing behavior of a sandstone

    NASA Astrophysics Data System (ADS)

    Feucht, L. J.; Logan, John M.

    1990-03-01

    To evaluate the effect of chemical solutions on the frictional properties of a quartz-rich sandstone, triaxial compression tests have been performed on a sandstone saturated with distilled water solutions of NaCl, CaCl 2 and Na 2SO 4 at varying ionic strengths and pH values. The sandstone, although containing 90% quartz, also bears about 7% clay. Results from these tests indicate that the presence of water alone reduces the ultimate strength by 33%. The NaCl solution of low ionic strength (0.2 M) produces similar reductions in strength. The samples saturated with NaCl solutions of intermediate ionic strength (1.0 M) are up to 20% stronger than those samples saturated with distilled water. The samples saturated with solutions of the high ionic strength (5.0 M) display the greatest weakening (41-46%) from the case of the dry specimen; this is a reduction of up to 20% compared to the water-saturated sample. Reductions in ultimate strength due to changes in pH are only apparent for samples saturated with solutions of intermediate ionic strength. Results from the samples saturated with the divalent solutions show strength reductions of up to 52% compared to dry specimens. In addition, the tests demonstrate that the presence of either cations or anions appears to produce an equivalent weakening in the samples. In all cases the samples saturated with the solutions of intermediate ionic strength (1.0 M) display the greatest ultimate strength. Results from fracture tests on intact specimens indicate that the ultimate strength of nominally dry samples is approximately 15% greater than that of samples from all other environments. There is no discernable difference between the strengths of specimens saturated with distilled water and those treated with more chemically active solutions. Scanning electron microscopic observations of the friction surfaces demonstrate that those solutions which produce the weakest mechanical behavior generate either very rough surfaces (high ionic

  13. Europium mass balance in polymict samples and implications for plutonic rocks of the lunar crust

    SciTech Connect

    Korotev, R.L.; Haskin, L.A. )

    1988-07-01

    From correlations of SM concentration and Sm/Eu ratio with Th concentration for a large number of polymict samples from various locations in the lunar highlands and the value of 0.91 {mu}g/g for the mean Th concentration of the highlands surface crust obtained by the orbiting gamma-ray experiments. The authors estimate the mean concentrations of Sm and Eu in the lunar surface crust to be between 2 and 3 {mu}g/g Sm and 0.7 and 1.2 {mu}g/g Eu. The compositional trends indicate that there is no significant enrichment or depletion of Eu, on the average, compared to Sm relative to chondritic abundances, i.e., there is no significant Eu anomaly in average upper crust. Although rich in plagioclase ({approximately}70%), the upper crust does not offer evidence for a gross vertical separation of plagioclase from the final liquid from which it crystallized. This and the chondritic ratio of Eu/Al in average highlands material imply that the net effect of the processes that led to formation of the lunar crust was to put most of the Al and incompatible elements in the crust. Among plutonic rocks, only plagioclase in rocks from the magnesian suite can supply the excess Eu in the polymict rocks. Owing to the intermediate value of the mean Mg/Fe ratio of the crust, a significant fraction of the mafic rocks of the lunar highlands must have lower Mg/Fe ratios than the norites and troctolites of the magnesian-suite of plutonic rocks. A large fraction of the plagioclase in the lunar crust is associated not with ferroan anorthosite, but with more mafic rocks. There is little evidence in the Eu data that the lunar crust ever consisted of a thick shell of nearly pure plagioclase, as envisioned in some formulations of the magma ocean model of its formation.

  14. Continental Lower Crust: Wavespeeds, Composition, and Relamination

    NASA Astrophysics Data System (ADS)

    Hacker, B. R.; Kelemen, P. B.; Behn, M. D.

    2015-12-01

    The composition of much of Earth's lower continental crust is enigmatic. The available heat-flow and wavespeed constraints can be satisfied if lower continental crust elsewhere contains anywhere from 49 to 62 wt% SiO2 (similar to andesite and dacite), with high to moderate concentrations of K, Th and U. Beneath shields and platforms, Vp suggests that 20-30% of lower crust is mafic. A large fraction of this material could be denser than peridotite. In these settings the underlying upper mantle is too cold to permit development of a convective instability. High Vp lithologies in these settings may be the result of mafic underplating, or slow metamorphic growth of large proportions of garnet. Vp from lower crust of Paleozoic-Mesozoic orogens indicates a smaller amount of mafic rock and little or no material that is denser than peridotite. Beneath rifts, arcs, and volcanic plateaux and beneath continent-collision zones, ~10-20% of lower crust is mafic, and about half that is denser than peridotite. The inferred gravitational instability and high Moho temperatures suggest that the mafic lower crust in these regions may be temporary. During sediment subduction, subduction erosion, arc subduction, and continent subduction, mafic rocks become eclogite and may continue to descend into the mantle, whereas more silica-rich rocks are transformed into felsic gneisses that are less dense than peridotite but more dense than continental upper crust. These more-felsic rocks may rise buoyantly, undergo decompression melting and melt extraction, and may be relaminated to the base of the crust. As a result of this refining/differentiation process, such relatively felsic rocks could form much of lower crust.

  15. 3D visualization of liquefaction-induced dune collapse in the Navajo Sandstone, Utah, USA

    NASA Astrophysics Data System (ADS)

    Ford, Colby; Nick, Kevin; Bryant, Gerald

    2015-04-01

    The eolian Navajo Sandstone outcrop on the Canyon Overlook Trail in Zion National Park in Southern Utah is dissected by modern erosion in a way which reveals a great deal of the three-dimensional architecture of a major soft-sediment deformation event. The feature is bounded below by a well-developed interdune complex made up of two superimposed carbonate lenses, above by an irregular truncational surface, and incorporates 3 - 10 m of sandstone over an approximately 2 km area. The material above the deformed interval is undeformed cross-bedded sandstone, with crossbeds downlapping onto the surface of truncation. The stratigraphic confinement of deformation and the irregularity of the upper bounding surface suggests a deformation process which created topography, which was in turn covered by the next upwind dune before it could be eroded flat. The deformed material itself is laterally segmented by a stacked succession of shear surfaces, which all strike approximately perpendicular to the paleo-wind direction and dip at decreasing angles in the down paleo-wind direction. These factors point to the collapse of a major dune into the downwind interdune area, likely initiated by liquefaction in the interdune complex. The foundering of the dune's toe into the liquefied area created a powerful lateral stress field which did not extend significantly into the subsurface. The dune collapse process has been used in the past to describe other soft-sediment deformation features in the Navajo Sandstone, but this site provides a wealth of physical details which were not previously associated with dune collapse. Shear surfaces originate in the interdune deposit as slip between laminae, then the cohesive muds provided support as they were thrust upward to angles of up to 50 degrees. The margins of the site also contain important paleoenvironmental indicators. Dinosaur tracks are exposed both at the extreme upwind and downwind margins of the interdune deposit in and slightly above

  16. Two phase damage theory and the failure enveloppes of sandstone

    NASA Astrophysics Data System (ADS)

    Ricard, Y.; Bercovici, D.

    2003-04-01

    Using a classical averaging approach, we derive a two-phase theory to describe the deformation of a porous material made of a matrix containing voids. The presence and evolution of surface energy at the interface between the solid matrix and voids is taken into account with non-equilibrium thermodynamic considerations that allow storage of deformational work as surface energy on growing or newly created voids. This treatment leads to a simple description of isotropic damage that can be applied to low-cohesion media such as sandstone. In particular, the theory yields two possible solutions wherein samples can either ``break" by shear localization with dilation (i.e., void creation), or undergo shear-enhanced compaction (void collapse facilitated by deviatoric stress). For a given deviatoric stress and confining pressure, the dominant solution is the one with the largest absolute value of the dilation rate, |Γ|, which thus predicts that shear-localization and dilation occur at low effective pressures, while shear-enhanced compaction occurs at larger effective pressure. Stress trajectories of constant |Γ| represent potential failure envelopes that are ogive (Gothic-arch) shaped curves wherein the ascending branch represents failure by dilation and shear-localization, and the descending branch denotes shear-enhanced compactive failure. The theory further predicts that the onset of dilation preceding shear-localization and failure necessarily occurs at the transition from compactive to dilational states and thus along a line connecting the peaks of constant-|Γ| ogives. Finally, the theory implies that while shear-enhanced compaction first occurs with increasing deviatoric stress (at large effective pressure), dilation will occur at higher deviatoric stresses. All these predictions in fact compare very successfully with various experimental data. Indeed, the theory leads to a normalization where all the data of failure envelopes and dilation thresholds collapse to a

  17. Cratering on Ceres: Implications for its crust and evolution.

    PubMed

    Hiesinger, H; Marchi, S; Schmedemann, N; Schenk, P; Pasckert, J H; Neesemann, A; O'Brien, D P; Kneissl, T; Ermakov, A I; Fu, R R; Bland, M T; Nathues, A; Platz, T; Williams, D A; Jaumann, R; Castillo-Rogez, J C; Ruesch, O; Schmidt, B; Park, R S; Preusker, F; Buczkowski, D L; Russell, C T; Raymond, C A

    2016-09-02

    Thermochemical models have predicted that Ceres, is to some extent, differentiated and should have an icy crust with few or no impact craters. We present observations by the Dawn spacecraft that reveal a heavily cratered surface, a heterogeneous crater distribution, and an apparent absence of large craters. The morphology of some impact craters is consistent with ice in the subsurface, which might have favored relaxation, yet large unrelaxed craters are also present. Numerous craters exhibit polygonal shapes, terraces, flowlike features, slumping, smooth deposits, and bright spots. Crater morphology and simple-to-complex crater transition diameters indicate that the crust of Ceres is neither purely icy nor rocky. By dating a smooth region associated with the Kerwan crater, we determined absolute model ages (AMAs) of 550 million and 720 million years, depending on the applied chronology model.

  18. Cratering on Ceres: Implications for its crust and evolution

    USGS Publications Warehouse

    Hiesinger, H.; Marchi, S.; Schmedemann, N.; Schenk, P.; Pasckert, J. H.; Neesemann, A.; O'Brien, D. P.; Kneissl, T.; Ermakov, A.; Fu, R.R.; Bland, M. T.; Nathues, A.; Platz, T.; Williams, D.A.; Jaumann, R.; Castillo-Rogez, J. C.; Ruesch, O.; Schmidt, B.; Park, R.S.; Preusker, F.; Buczkowski, D.L.; Russell, C.T.; Raymond, C.A.

    2016-01-01

    Thermochemical models have predicted that Ceres, is to some extent, differentiated and should have an icy crust with few or no impact craters. We present observations by the Dawn spacecraft that reveal a heavily cratered surface, a heterogeneous crater distribution, and an apparent absence of large craters. The morphology of some impact craters is consistent with ice in the subsurface, which might have favored relaxation, yet large unrelaxed craters are also present. Numerous craters exhibit polygonal shapes, terraces, flowlike features, slumping, smooth deposits, and bright spots. Crater morphology and simple-to-complex crater transition diameters indicate that the crust of Ceres is neither purely icy nor rocky. By dating a smooth region associated with the Kerwan crater, we determined absolute model ages (AMAs) of 550 million and 720 million years, depending on the applied chronology model.

  19. Properties of phonons in the neutron star crust

    NASA Astrophysics Data System (ADS)

    di Gallo, L.; Oertel, M.

    2010-12-01

    Neutron stars are compact objects, created in supernova explosions at the end of the life of massive stars. They contain matter under extreme conditions, in particular concerning the density : starting from a lattice of (neutron rich) nuclei in the crust one reaches nuclear matter at several times the density of atomic nuclei in the center. One way to understand this object is to confront theoretical modelisation with observations. Among observations of pulsars there is the thermal emission of its surface. This observable, which depend on the heat transport properties, is very sensitive to the superfluid and superconducting character of the different sutructures inside the star. The presentation is focussed on the inner crust, where we can find an interesting nuclear structure called the ``Pasta Phase". Its excitation spectrum within a superfluid hydrodynamics approach will be discussed in view of calculating the contribution to the heat capacity.

  20. Cratering on Ceres: Implications for its crust and evolution

    NASA Astrophysics Data System (ADS)

    Hiesinger, H.; Marchi, S.; Schmedemann, N.; Schenk, P.; Pasckert, J. H.; Neesemann, A.; O'Brien, D. P.; Kneissl, T.; Ermakov, A. I.; Fu, R. R.; Bland, M. T.; Nathues, A.; Platz, T.; Williams, D. A.; Jaumann, R.; Castillo-Rogez, J. C.; Ruesch, O.; Schmidt, B.; Park, R. S.; Preusker, F.; Buczkowski, D. L.; Russell, C. T.; Raymond, C. A.

    2016-09-01

    Thermochemical models have predicted that Ceres, is to some extent, differentiated and should have an icy crust with few or no impact craters. We present observations by the Dawn spacecraft that reveal a heavily cratered surface, a heterogeneous crater distribution, and an apparent absence of large craters. The morphology of some impact craters is consistent with ice in the subsurface, which might have favored relaxation, yet large unrelaxed craters are also present. Numerous craters exhibit polygonal shapes, terraces, flowlike features, slumping, smooth deposits, and bright spots. Crater morphology and simple-to-complex crater transition diameters indicate that the crust of Ceres is neither purely icy nor rocky. By dating a smooth region associated with the Kerwan crater, we determined absolute model ages (AMAs) of 550 million and 720 million years, depending on the applied chronology model.

  1. Regional diagenetic variations in Middle Pennsylvanian foreland basin sandstones of the southern Appalachians: Comparison to passive margin Cenozoic sandstones of the Gulf of Mexico

    SciTech Connect

    Milliken, K.L. . Dept. of Geological Science)

    1992-01-01

    Water/rock interactions recorded by authigenic phases in lithic-rich sandstones of the southern Appalachian basin, in the region of the Pine Mountain Overthrust (PMO), began with early post-depositional burial, extended through deeper burial and temperatures > 100 C during the Alleghenian orogeny, and continued through uplift and exposure at the modern weathering surface. Early-formed carbonate in the form of highly localized calcite concretions preserves IGVs greater than 30% and has widely ranging trace element concentrations. Later-formed calcite is characterized by relative low trace element concentrations in sandstones of low IGV. Precipitation of kaolinite cement and grain replacements partially overlapped formation of early carbonate and quartz cement. Dissolution and albitization of detrital feldspars are the primary types of grain alteration observed. Complete loss of the detrital feldspar assemblage is observed only around the eastern end of the PMO where a portion of the feldspar loss is recorded as quartz-replaced grains. Compaction due to ductile behavior of phyllosilicate-rich rock fragments and pressure solution of detrital quartz has reduced IGV to an average of around 11% below the PMO and 6% above the fault. In general, these foreland basin sandstones manifest authigenic phases and sequences of diagenetic events similar to those observed in the passive margin Gulf of Mexico sedimentary basin. The most striking diagenetic differences between the two basins are seen in terms of the comparative amounts of compaction (greater in the foreland basin) and grain alteration (less in the foreland basin) which most likely relate to primary differences in the texture and mineralogy of the sediments.

  2. Velocity model of the shallow lunar crust

    NASA Astrophysics Data System (ADS)

    Gangi, A. F.

    1980-01-01

    The travel times of the seismic waves obtained for the Apollo-14 and -16 active seismic experiments and the Apollo-16 grenade launches are shown to be consistent with a powder-layer model of the shallow lunar crust. The velocity variation with depth determined from these data is: V(z) = approximately 110 z to the 1/6 power m/sec for z less than 10 meters and V(z) is nearly = to 250 m/sec for z greater than 10 meters. The velocity values found for the 10 meter depth are similar to those found by Kovach, et al. (1972). The z to the 1/6 power depth dependence for the velocity of the topmost layer is that predicted on the basis of a powder layer (Gangi, 1972). The Amplitude variation of the direct waves as a function of source-to-receiver separation, x, is A(x) = A(o)x to the -n power exp(-ax) where 1.5 n 2.2 and a is nearly = to 0.047 neper/m. Velocity-spectra analyses of the direct, surface-reflected, bottom-reflected and refracted waves give results that are consistent with the velocity model inferred from the traveltime data.

  3. Strong neutrino cooling by cycles of electron capture and β- decay in neutron star crusts.

    PubMed

    Schatz, H; Gupta, S; Möller, P; Beard, M; Brown, E F; Deibel, A T; Gasques, L R; Hix, W R; Keek, L; Lau, R; Steiner, A W; Wiescher, M

    2014-01-02

    The temperature in the crust of an accreting neutron star, which comprises its outermost kilometre, is set by heating from nuclear reactions at large densities, neutrino cooling and heat transport from the interior. The heated crust has been thought to affect observable phenomena at shallower depths, such as thermonuclear bursts in the accreted envelope. Here we report that cycles of electron capture and its inverse, β(-) decay, involving neutron-rich nuclei at a typical depth of about 150 metres, cool the outer neutron star crust by emitting neutrinos while also thermally decoupling the surface layers from the deeper crust. This 'Urca' mechanism has been studied in the context of white dwarfs and type Ia supernovae, but hitherto was not considered in neutron stars, because previous models computed the crust reactions using a zero-temperature approximation and assumed that only a single nuclear species was present at any given depth. The thermal decoupling means that X-ray bursts and other surface phenomena are largely independent of the strength of deep crustal heating. The unexpectedly short recurrence times, of the order of years, observed for very energetic thermonuclear superbursts are therefore not an indicator of a hot crust, but may point instead to an unknown local heating mechanism near the neutron star surface.

  4. Strong neutrino cooling by cycles of electron capture and decay in neutron star crusts

    SciTech Connect

    Schatz, Hendrik; Gupta, Sanjib; Moeller, Peter; Beard, Mary; Brown, Edward; Deibel, A. T.; Gasques, Leandro; Hix, William Raphael; Keek, Laurens; Lau, Rita; Steiner, Andrew M; Wiescher, Michael

    2013-01-01

    The temperature in the crust of an accreting neutron star, which comprises its outermost kilometre, is set by heating from nuclear reactions at large densities, neutrino cooling and heat transport from the interior. The heated crust has been thought to affect observable phenomena at shallower depths, such as thermonuclear bursts in the accreted envelope. Here we report that cycles of electron capture and its inverse, decay, involving neutron-rich nuclei at a typical depth of about 150 metres, cool the outer neutron star crust by emitting neutrinos while also thermally decoupling the surface layers from the deeper crust. This Urca mechanism has been studied in the context of white dwarfs13 and type Ia supernovae, but hitherto was not considered in neutron stars, because previous models1, 2 computed the crust reactions using a zero-temperature approximation and assumed that only a single nuclear species was present at any given depth. The thermal decoupling means that X-ray bursts and other surface phenomena are largely independent of the strength of deep crustal heating. The unexpectedly short recurrence times, of the order of years, observed for very energetic thermonuclear superbursts are therefore not an indicator of a hot crust, but may point instead to an unknown local heating mechanism near the neutron star surface.

  5. Mineralogy of the lunar crust: Results from Clementine

    NASA Astrophysics Data System (ADS)

    Tompkins, Stefanie; Pieters, Carle M.

    1999-01-01

    The central peaks of 109 impact craters across the Moon are examined with Clementine UVVIS camera multispectral data. The craters range in diameter from 40 to 180 km, and are believed to have exhumed material from 5 - 30 km beneath the surface to form the peaks, including both upper and lower crustal rocks depending on whether craters have impacted into highlands or basins. Representative five-color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral parameters, including the "key ratio" (which is related to mafic mineral abundance) and "spectral curvature" (linked to absorption band shape, which distinguishes between low- and high-Ca pyroxene and olivine). The spectral parameters are correlated to mineralogical abundances, related in turn to highland plutonic rock compositions. The derived rock compositions for the various central peaks are presented in a global map. From these results, it is evident that the lunar crust is compositionally diverse, both globally and at local 100-m scales found within individual sets of central peaks. While the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure, they also indicate a more anorthositic crust than generally assumed, with a bulk plagioclase content of ~81%, evolving from "pure" anorthosite near the surface towards more mafic, low-Ca pyroxene-rich compositions with depth (comparable to anorthositic norite). Evidence for mafic plutons occurs in both highlands and basins, and represent all mafic highland rock types. However, the lower crust is more compositionally diverse than the highlands, with both a greater range of rock types and more diversity within individual sets of central peaks.

  6. No evidence for Hadean continental crust within Earth's oldest evolved rock unit

    NASA Astrophysics Data System (ADS)

    Reimink, J. R.; Davies, J. H. F. L.; Chacko, T.; Stern, R. A.; Heaman, L. M.; Sarkar, C.; Schaltegger, U.; Creaser, R. A.; Pearson, D. G.

    2016-10-01

    Due to the acute scarcity of very ancient rocks, the composition of Earth's embryonic crust during the Hadean eon (>4.0 billion years ago) is a critical unknown in our search to understand how the earliest continents evolved. Whether the Hadean Earth was dominated by mafic-composition crust, similar to today's oceanic crust, or included significant amounts of continental crust remains an unsolved question that carries major implications for the earliest atmosphere, the origin of life, and the geochemical evolution of the crust-mantle system. Here we present new U-Pb and Hf isotope data on zircons from the only precisely dated Hadean rock unit on Earth--a 4,019.6 +/- 1.8 Myr tonalitic gneiss unit in the Acasta Gneiss Complex, Canada. Combined zircon and whole-rock geochemical data from this ancient unit shows no indication of derivation from, or interaction with, older Hadean continental crust. Instead, the data provide the first direct evidence that the oldest known evolved crust on Earth was generated from an older ultramafic or mafic reservoir that probably surfaced the early Earth.

  7. Chemical complexity of hotspots caused by cycling oceanic crust through mantle reservoirs

    NASA Astrophysics Data System (ADS)

    Li, Mingming; McNamara, Allen K.; Garnero, Edward J.

    2014-05-01

    Lavas erupted at ocean island hotspots such as Hawaii have diverse geochemical signatures. These ocean island basalts are thought to be derived from many sources with different chemical compositions within Earth's mantle and contain components of more primitive, less degassed material, as well as several recycled oceanic crustal components. Furthermore, the recycled oceanic crustal components display vastly different ages. The various components may be derived from different mantle reservoirs that are entrained and carried to the surface by mantle plumes, but it is unclear how individual plumes could successively sample each of these reservoirs or why the recycled oceanic crust would have variable ages. Here we use high-resolution numerical simulations to investigate the interaction between mantle plumes, subducted oceanic crust and a more primitive lower mantle reservoir. In our simulations, some subducted oceanic crust is entrained directly into mantle plumes, but a significant fraction of the crust--up to 10%--enters the more primitive reservoirs. As a result, mantle plumes entrain a variable combination of relatively young oceanic crust directly from the subducting slab, older oceanic crust that has been stirred with ancient more primitive material and background, depleted mantle. Cycling of oceanic crust through mantle reservoirs can therefore reconcile observations of different recycled oceanic crustal ages and explain the chemical complexity of hotspot lavas.

  8. Fractal Scaling of Particle Size Distribution and Relationships with Topsoil Properties Affected by Biological Soil Crusts

    PubMed Central

    Gao, Guang-Lei; Ding, Guo-Dong; Wu, Bin; Zhang, Yu-Qing; Qin, Shu-Gao; Zhao, Yuan-Yuan; Bao, Yan-Feng; Liu, Yun-Dong; Wan, Li; Deng, Ji-Feng

    2014-01-01

    Background Biological soil crusts are common components of desert ecosystem; they cover ground surface and interact with topsoil that contribute to desertification control and degraded land restoration in arid and semiarid regions. Methodology/Principal Findings To distinguish the changes in topsoil affected by biological soil crusts, we compared topsoil properties across three types of successional biological soil crusts (algae, lichens, and mosses crust), as well as the referenced sandland in the Mu Us Desert, Northern China. Relationships between fractal dimensions of soil particle size distribution and selected soil properties were discussed as well. The results indicated that biological soil crusts had significant positive effects on soil physical structure (P<0.05); and soil organic carbon and nutrients showed an upward trend across the successional stages of biological soil crusts. Fractal dimensions ranged from 2.1477 to 2.3032, and significantly linear correlated with selected soil properties (R2 = 0.494∼0.955, P<0.01). Conclusions/Significance Biological soil crusts cause an important increase in soil fertility, and are beneficial to sand fixation, although the process is rather slow. Fractal dimension proves to be a sensitive and useful index for quantifying changes in soil properties that additionally implies desertification. This study will be essential to provide a firm basis for future policy-making on optimal solutions regarding desertification control and assessment, as well as degraded ecosystem restoration in arid and semiarid regions. PMID:24516668

  9. Transport of engineered silver (Ag) nanoparticles through partially fractured sandstones.

    PubMed

    Neukum, Christoph; Braun, Anika; Azzam, Rafig

    2014-08-01

    Transport behavior and fate of engineered silver nanoparticles (AgNP) in the subsurface is of major interest concerning soil and groundwater protection in order to avoid groundwater contamination of vital resources. Sandstone aquifers are important groundwater resources which are frequently used for public water supply in many regions of the world. The objective of this study is to get a better understanding of AgNP transport behavior in partially fractured sandstones. We executed AgNP transport studies on partially fissured sandstone drilling cores in laboratory experiments. The AgNP concentration and AgNP size in the effluent were analyzed using flow field-flow fractionation mainly. We employed inverse mathematical models on the measured AgNP breakthrough curves to identify and quantify relevant transport processes. Physicochemical filtration, time-dependent blocking due to filling of favorable attachment sites and colloid-facilitated transport were identified as the major processes for AgNP mobility. Physicochemical filtration was found to depend on solute chemistry, mineralogy, pore size distribution and probably on physical and chemical heterogeneity. Compared to AgNP transport in undisturbed sandstone matrix reported in the literature, their mobility in partially fissured sandstone is enhanced probably due to larger void spaces and higher hydraulic conductivity. Copyright © 2014 Elsevier B.V. All rights reserved.

  10. Fault-related Silurian Clinton sandstone deposition in Ohio

    SciTech Connect

    Coogan, A.H. )

    1988-08-01

    Mapping the thickness of the Silurian Clinton sandstone reservoir and associated shale, sandstone, and carbonate facies in the subsurface of 40 counties in eastern Ohio reveals a general correspondence between major patterns of deposition and the location of faults that strike parallel with or subparallel to the depositional trends. Clinton delta-front sandstones, which occur along a line from Hocking and Perry Counties, through Knox, Holmes, and Wayne Counties northeast to Lake County, Ohio, parallel a line of major change in magnetic intensity in the basement, which is interpreted here to be the juncture between the more stable, less subsiding central Ohio carbonate bank and the more subsiding western edge of the Appalachian basin. The principal Clinton deltaic lobes occur in east-central and northeastern Ohio. The Clinton sandstone interval is thinner and starved of coarse clastic sediment close to the Rome trough, which is located along the southeasternmost Ohio border. Sediment distribution patterns indicate that deltaic deposits of Clinton sandstone were captured in the subsiding Rome trough at the border of southern Ohio during the Early Silurian. Farther north, deltaic sediments spread out across eastern Ohio to reach an elongate depocenter caused by minor subsidence at the central Ohio platform edge. There, deltaic sands intermittently filled the delta-edge trough, and spilled out as thin shelf sands onto the more stable platform, a site of predominantly mixed shale and carbonate deposition during the Early Silurian.

  11. Transport of engineered silver (Ag) nanoparticles through partially fractured sandstones

    NASA Astrophysics Data System (ADS)

    Neukum, Christoph; Braun, Anika; Azzam, Rafig

    2014-08-01

    Transport behavior and fate of engineered silver nanoparticles (AgNP) in the subsurface is of major interest concerning soil and groundwater protection in order to avoid groundwater contamination of vital resources. Sandstone aquifers are important groundwater resources which are frequently used for public water supply in many regions of the world. The objective of this study is to get a better understanding of AgNP transport behavior in partially fractured sandstones. We executed AgNP transport studies on partially fissured sandstone drilling cores in laboratory experiments. The AgNP concentration and AgNP size in the effluent were analyzed using flow field-flow fractionation mainly. We employed inverse mathematical models on the measured AgNP breakthrough curves to identify and quantify relevant transport processes. Physicochemical filtration, time-dependent blocking due to filling of favorable attachment sites and colloid-facilitated transport were identified as the major processes for AgNP mobility. Physicochemical filtration was found to depend on solute chemistry, mineralogy, pore size distribution and probably on physical and chemical heterogeneity. Compared to AgNP transport in undisturbed sandstone matrix reported in the literature, their mobility in partially fissured sandstone is enhanced probably due to larger void spaces and higher hydraulic conductivity.

  12. Tertiary age for upper Nubian sandstone formation, central Sudan

    SciTech Connect

    Prasad, G.; Lejal-Nicol, A.; Vaudois-Mieja, N.

    1986-02-01

    In central and northern Sudan, oil exploration is now active in the basins containing sediments of the Nubian Sandstone Formation. On the evidence of planned pipeline construction, significant volumes of oil appear to have been discovered in southwestern Sudan. A newly discovered flora from the upper Nubian Sandstone Formation near Khartoum in central Sudan is Tertiary in age. The flora is well preserved, and comprises leaves, flowers, and fruits, many not yet described. At the generic level, they are comparable to forms that are known fro the Eocene to Miocene. Aquatic plants indicate a lacustrine paleoenvironment; humid tropical forests thrived on the lakeshores. The Nubian Sandstone Formation of Sudan had been considered to be entirely of Cretaceous age; this new flora shifts the upper boundary into the Tertiary. The Tertiary Hudi Chert, found in scattered outcrops in the region of Atbara, was considered to overlie the Nubian Sandstone Formation. The authors suggest that the Hudi Chert is partly age equivalent to the Tertiary upper Nubian Sandstone at Jebel Mudaha.

  13. What Hf isotopes in zircon tell us about crust-mantle evolution

    NASA Astrophysics Data System (ADS)

    Iizuka, Tsuyoshi; Yamaguchi, Takao; Itano, Keita; Hibiya, Yuki; Suzuki, Kazue

    2017-03-01

    The 176Lu-176Hf radioactive decay system has been widely used to study planetary crust-mantle differentiation. Of considerable utility in this regard is zircon, a resistant mineral that can be precisely dated by the U-Pb chronometer and record its initial Hf isotope composition due to having low Lu/Hf. Here we review zircon U-Pb age and Hf isotopic data mainly obtained over the last two decades and discuss their contributions to our current understanding of crust-mantle evolution, with emphasis on the Lu-Hf isotope composition of the bulk silicate Earth (BSE), early differentiation of the silicate Earth, and the evolution of the continental crust over geologic history. Meteorite zircon encapsulates the most primitive Hf isotope composition of our solar system, which was used to identify chondritic meteorites best representative of the BSE (176Hf/177Hf = 0.282793 ± 0.000011; 176Lu/177Hf = 0.0338 ± 0.0001). Hadean-Eoarchean detrital zircons yield highly unradiogenic Hf isotope compositions relative to the BSE, providing evidence for the development of a geochemically enriched silicate reservoir as early as 4.5 Ga. By combining the Hf and O isotope systematics, we propose that the early enriched silicate reservoir has resided at depth within the Earth rather than near the surface and may represent a fractionated residuum of a magma ocean underlying the proto-crust, like urKREEP beneath the anorthositic crust on the Moon. Detrital zircons from world major rivers potentially provide the most robust Hf isotope record of the preserved granitoid crust on a continental scale, whereas mafic rocks with various emplacement ages offer an opportunity to trace the Hf isotope evolution of juvenile continental crust (from εHf[4.5 Ga] = 0 to εHf[present] = + 13). The river zircon data as compared to the juvenile crust composition highlight that the supercontinent cycle has controlled the evolution of the continental crust by regulating the rates of crustal generation and intra

  14. Dynamics of Crust Dissolution and Gas Release in Tank 241-SY-101

    SciTech Connect

    SD Rassat; CW Stewart; BE Wells; WL Kuhn; ZI Antoniak; JM Cuta; KP Recknagle; G Terrones; VV Viswanathan; JH Sukamto; DP Mendoza

    2000-01-26

    Due primarily to an increase in floating crust layer thickness, the waste level in Hanford Tank 241-SY-101 (SY-101) has grown appreciably, and the flammable gas volume stored in the crust has become a potential hazard. To remediate gas retention in the crust and the potential for buoyant displacement gas releases from the nonconnective layer at the bottom of the tank, SY-101 will be diluted to dissolve a large fraction of the solids that allow the waste to retain gas. In this work we develop understanding of the state of the tank waste and some of its physical properties, investigate how added water will be distributed in the tank and affect the waste, and use the information to evaluate mechanisms and rates of waste solids dissolution and gas release. This work was completed to address these questions and in support of planning and development of controls for the SY-101 Surface Level Rise Remediation Project. Particular emphasis is given to dissolution of and gas release from the crust, although the effects of back-dilution on all waste layers are addressed. The magnitude and rates of plausible gas release scenarios are investigated, and it is demonstrated that none of the identified mechanisms of continuous (dissolution-driven) or sudden gas release, even with conservative assumptions, lead to domespace hydrogen concentrations exceeding the lower flammability limit. This report documents the results of studies performed in 1999 to address the issues of the dynamics, of crust dissolution and gas release in SY-101. It contains a brief introduction to the issues at hand; a summary of our knowledge of the SY-101 crust and other waste properties, including gas fractions, strength and volubility; a description of the buoyancy and dissolution models that are applied to predict the crust response to waste transfers and back dilution; and a discussion of the effectiveness of mixing for water added below the crust and the limited potential for significant stratification

  15. Origin of High Electrical Conductivity in the Lower Continental Crust: A Review

    NASA Astrophysics Data System (ADS)

    Yang, Xiaozhi

    2011-11-01

    Electromagnetic measurements have demonstrated that the lower continental crust has remarkable electrical anomalies of high conductivity and electrical anisotropy on a global scale (probably with some local exceptions), but their origin is a long-standing and controversial problem. Typical electrical properties of the lower continental crust include: (1) the electrical conductivity is usually 10-4 to 10-1 S/m; (2) the overlying shallow crust and underlying upper mantle are in most cases less conductive; (3) the electrical conductivity is statistically much higher in Phanerozoic than in Precambrian areas; (4) horizontal anisotropy has been resolved in many areas; and (5) in some regions there appear to be correlations between high electrical conductivity and other physical properties such as seismic reflections. The explanation based on conduction by interconnected, highly conductive phases such as fluids, melts, or graphite films in grain boundary zones has various problems in accounting for geophysically resolved electrical conductivity and other chemical and physical properties of the lower crust. The lower continental crust is dominated by mafic granulites (in particular beneath stable regions), with nominally anhydrous clinopyroxene, orthopyroxene, and plagioclase as the main assemblages, and the prevailing temperatures are mostly 700-1,000°C as estimated from xenolith data, surface heat flow, and seismic imaging. Pyroxenes have significantly higher Fe content in the lower crust than in the upper mantle (peridotites), and plagioclase has higher Na content in the lower crust than in the shallow crust (granites). Minerals in the lower continental crust generally contain trace amounts of water as H-related point defects, from less than 100 to more than 1,000 ppm H2O (by weight), with concentrations usually higher than those in the upper mantle. Observations of xenolith granulites captured by volcano-related eruptions indicate that the lower continental crust is

  16. Closer Look at Lunar Highland Crust

    NASA Image and Video Library

    2012-12-05

    This image depicting the porosity of the lunar highland crust was derived using bulk density data from NASA GRAIL mission and independent grain density measurements from NASA Apollo moon mission samples as well as orbital remote-sensing data.

  17. Drilling to gabbro in intact ocean crust.

    PubMed

    Wilson, Douglas S; Teagle, Damon A H; Alt, Jeffrey C; Banerjee, Neil R; Umino, Susumu; Miyashita, Sumio; Acton, Gary D; Anma, Ryo; Barr, Samantha R; Belghoul, Akram; Carlut, Julie; Christie, David M; Coggon, Rosalind M; Cooper, Kari M; Cordier, Carole; Crispini, Laura; Durand, Sedelia Rodriguez; Einaudi, Florence; Galli, Laura; Gao, Yongjun; Geldmacher, Jörg; Gilbert, Lisa A; Hayman, Nicholas W; Herrero-Bervera, Emilio; Hirano, Nobuo; Holter, Sara; Ingle, Stephanie; Jiang, Shijun; Kalberkamp, Ulrich; Kerneklian, Marcie; Koepke, Jürgen; Laverne, Christine; Vasquez, Haroldo L Lledo; Maclennan, John; Morgan, Sally; Neo, Natsuki; Nichols, Holly J; Park, Sung-Hyun; Reichow, Marc K; Sakuyama, Tetsuya; Sano, Takashi; Sandwell, Rachel; Scheibner, Birgit; Smith-Duque, Chris E; Swift, Stephen A; Tartarotti, Paola; Tikku, Anahita A; Tominaga, Masako; Veloso, Eugenio A; Yamasaki, Toru; Yamazaki, Shusaku; Ziegler, Christa

    2006-05-19

    Sampling an intact sequence of oceanic crust through lavas, dikes, and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid-ocean ridges, but it has been an elusive goal of scientific ocean drilling for decades. Recent drilling in the eastern Pacific Ocean in Hole 1256D reached gabbro within seismic layer 2, 1157 meters into crust formed at a superfast spreading rate. The gabbros are the crystallized melt lenses that formed beneath a mid-ocean ridge. The depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid-ocean ridges: Melt lenses occur at shallower depths at faster spreading rates. The gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas, precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by Hole 1256D.

  18. The breaking strain of neutron star crust

    SciTech Connect

    Kadau, Kai; Horowitz, C J

    2009-01-01

    Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Due to the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gTavitational wave radiation could limit the spin periods of some stars and might be detectable in large scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in Magnetar Giant and Micro Flares.

  19. Two-point correlation functions to characterize microgeometry and estimate permeabilities of synthetic and natural sandstones

    SciTech Connect

    Blair, S.C.; Berge, P.A.; Berryman, J.G.

    1993-08-01

    We have developed an image-processing method for characterizing the microstructure of rock and other porous materials, and for providing a quantitative means for understanding the dependence of physical properties on the pore structure. This method is based upon the statistical properties of the microgeometry as observed in scanning electron micrograph (SEM) images of cross sections of porous materials. The method utilizes a simple statistical function, called the spatial correlation function, which can be used to predict bounds on permeability and other physical properties. We obtain estimates of the porosity and specific surface area of the material from the two-point correlation function. The specific surface area can be related to the permeability of porous materials using a Kozeny-Carman relation, and we show that the specific surface area measured on images of sandstones is consistent with the specific surface area used in a simple flow model for computation of permeability. In this paper, we discuss the two-point spatial correlation function and its use in characterizing microstructure features such as pore and grain sizes. We present estimates of permeabilities found using SEM images of several different synthetic and natural sandstones. Comparison of the estimates to laboratory measurements shows good agreement. Finally, we briefly discuss extension of this technique to two-phase flow.

  20. Microbial community on oceanic ferro-manganese crusts from Takuyo-Daigo Seamount and Ryusei Seamount

    NASA Astrophysics Data System (ADS)

    Nitahara, S.; Kato, S.; Yamagishi, A.

    2012-12-01

    Background and Purpose Iron and manganese oxide deposits are often found on deep seafloor. Rocks covered with these oxides are called ferro-manganese crusts (Mn crusts), and are ubiquitously distributed on deep seafloor (Rona 2003). Because Mn crusts contain rare metals such as Co, Pt and rare earth element, it can be resources in the future. Mn crusts and microbes on Mn crusts may contribute to material, especially carbon and nitrogen circulation between hydrosphere and lithosphere. Mechanism of Mn crust formation is not completely understood. Wang et al. propose a model that microorganisms associate with initial Mn mineral deposition (Wang et al., 2011). There is a possibility that microbes may contribute to formation of Mn crust relying on their ability to oxidize Fe and Mn. However, there is limited information about diversity, spatial distribution and abundance of microbes on Mn crust surface. Our purpose is to clarify microbial community composition, spatial distribution, diversity and abundance of microbes on Mn crusts collected from Takuyo-Daigo seamount and Ryusei seamount. Method We collected Mn crusts, sediments and ambient seawater from Takuyo-Daigo seamount at the depth of 1200 m, 1419 m, 2209 m and 2991 m during NT09-02 cruise in Feb 2009 and Ryusei seamount at the depth of 1194 m, 2079 m during KY11-02 in Feb 2011 with remotely operated vehicle Hyper-Dolphin (JAMSTEC). Genomic DNA was extracted from each sample using Fast DNA kit for soil (Qbiogene). Partial 16S rRNA gene and amoA gene were amplified by PCR with prokaryote-universal primer set (Uni516F-Uni1407R) and bacterial and archaeal amoA specific primer sets. PCR products were cloned. The nucleotide sequences of randomly selected clones were determined. We performed phylogenetic and statistical analysis to determine microbial community compositions, and estimated diversity indices. We also estimated the copy numbers of 16S rRNA and amoA genes of Bacteria and Archaea by quantitative PCR. Results

  1. Numerical Simulations of the Incremental Intrusion of Granitic Magma into Continental Crust

    NASA Astrophysics Data System (ADS)

    Cao, W.; Kaus, B. J.; Paterson, S. R.

    2012-12-01

    We have employed the visco-elasto-plastic Finite-Element & Marker-in-cell code, MILAMIN_VEP, to carry out a 2D modeling study of the incremental intrusion of granitic magma into continental crust. Algorithms of multiple pulses of magma and pseudo-diking are implemented into the code. New magma of an initial circular shape is regularly replenished at "magma source" regions at sub-crustal depths. Pseudo-dikes of rectangular shapes are added at location where the maximum differential stress along the melt-solid interface is greater than an assigned tensile strength of the surrounding solid host rock. Preliminary results show that when diking and multiple pulses of magma are included, later pulses of magma rise higher and faster and even reach the Earth's surface in some cases by taking advantage of the pre-heated low-viscosity pathways created by earlier dikes and pulses of magma. Host rocks display bedding rotation, and downward flow at two sides of a growing magma chamber but show discordantly truncation when magma ascend through the weak channels made by dikes. The effect of the thermal structure of the crust was tested as well. In a cold crust, "diking" is critical in breaking the high-viscosity crust, guiding the direction of magma rising, and facilitating later magma pulses to form chambers. In a warmer crust, magma rises in the form of diapirs, after which dikes take over in transporting later pulses of magma to the surface. The simulations also suggest that a magma chamber incrementally constructed by multiple magma bathes is a very dynamic environment featuring intra-chamber convection and recycling previous batches of magma. In simulations without diking and multiple pulses, magma is unable to reach the shallow crust. Instead, it is stuck in the middle crust, as the viscosity of the upper crust is too large to permit rapid motion, and at the same time magma-induced stresses are insufficient to deform the upper crust in a plastic manner. Intra

  2. Workshop on the Growth of Continental Crust

    NASA Technical Reports Server (NTRS)

    Ashwal, Lewis D. (Editor)

    1988-01-01

    Constraints and observations were discussed on a fundamental unsolved problem of global scale relating to the growth of planetary crusts. All of the terrestrial planets were considered, but emphasis was placed on the Earth's continental crust. The title of each session is: (1) Extraterrestrial crustal growth and destruction; (2) Constraints for observations and measurements of terrestrial rocks; (3) Models of crustal growth and destruction; and (4) Process of crustal growth and destruction.

  3. Characteristics of deltaic deposits in the Cretaceous Pierre shale. Trinidad sandstone, and Vermejo formation. Raton Basin, Colorado

    SciTech Connect

    Flores, R.M.; Tur, S.M.

    1982-04-01

    The depositional models previously described for the regressive sequence of Upper Cretaceous Pierre Shale, Trinidad Sandstone, and Vermejo Formation lithologies in the Raton Basin, Colorado, indicate to some degree the constructional--and destructional--deltaic characteristics of the sequence. However, the relationships of specific deltaic environments and deltaic abandonment phases to coal accumulation and distribution in the Vermejo Formation are not well understood. Detailed facies analyses of closely spaced measured surface sections in the Trinidad and adjacent areas of Colorado reflect deposition in the river-influenced delta. That this deltaic system was accompanied by abandonment of subdeltas is indicated by a destructional-deltaic facies of heavily bioturbated, carbonaceous sandstones, siltstones, and shales best recorded in the delta front deposits of the Trinidad Sandstone. This destructional-deltaic facies commonly separates overlapped distributary mouth-bar sandstones. Like their modern counterparts in the Mississippi delta system, the abandoned delta-front deposits are affected by wave reworking, as indicated by their mature and clean characteristics, although associated offshore barrier islands apparently were not formed. Perhaps the difference between these modern and ancient deltaic deposits is related to associated basinal processes attendant to a uniformly subsiding system in the highly muddy prodeltaic depositional environment in the Raton Basin. Although abandonment of subdeltas had a limited influence on the characteristics of the Vermejo coal deposits, coal accumulation nevertheless remained primarily controlled by persistent organic sedimentation in interdistributary backswamps.

  4. Changes of petrophysical properties of sandstones due to interaction with carbon dioxide, a laboratory study

    NASA Astrophysics Data System (ADS)

    Nover, Georg; von der Gönna, Jutta; Heikamp, Stephanie; Köster, Jens

    2013-04-01

    dissolution at narrow pore throats thus causing a higher degree of interconnection of the pore system and a shift of the phase angle that indicates changes of the geometry of the pore surface area. The uniaxial compressive strength was measured before and after scCO2-treatment on a set of homogeneous sandstones from Neidenbach. These data were compared with natural analogues, e.g. bleached and unbleached sandstones from the Hessian depression. The uniaxial compressive strength of untreated and scCO2-treated samples were found to fit the range reported for sandstones.

  5. Early formation of evolved asteroidal crust.

    PubMed

    Day, James M D; Ash, Richard D; Liu, Yang; Bellucci, Jeremy J; Rumble, Douglas; McDonough, William F; Walker, Richard J; Taylor, Lawrence A

    2009-01-08

    Mechanisms for the formation of crust on planetary bodies remain poorly understood. It is generally accepted that Earth's andesitic continental crust is the product of plate tectonics, whereas the Moon acquired its feldspar-rich crust by way of plagioclase flotation in a magma ocean. Basaltic meteorites provide evidence that, like the terrestrial planets, some asteroids generated crust and underwent large-scale differentiation processes. Until now, however, no evolved felsic asteroidal crust has been sampled or observed. Here we report age and compositional data for the newly discovered, paired and differentiated meteorites Graves Nunatak (GRA) 06128 and GRA 06129. These meteorites are feldspar-rich, with andesite bulk compositions. Their age of 4.52 +/- 0.06 Gyr demonstrates formation early in Solar System history. The isotopic and elemental compositions, degree of metamorphic re-equilibration and sulphide-rich nature of the meteorites are most consistent with an origin as partial melts from a volatile-rich, oxidized asteroid. GRA 06128 and 06129 are the result of a newly recognized style of evolved crust formation, bearing witness to incomplete differentiation of their parent asteroid and to previously unrecognized diversity of early-formed materials in the Solar System.

  6. Frozen magma lenses below the oceanic crust.

    PubMed

    Nedimović, Mladen R; Carbotte, Suzanne M; Harding, Alistair J; Detrick, Robert S; Canales, J Pablo; Diebold, John B; Kent, Graham M; Tischer, Michael; Babcock, Jeffrey M

    2005-08-25

    The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies.

  7. Effective Thermal Conductivity Modeling of Sandstones: SVM Framework Analysis

    NASA Astrophysics Data System (ADS)

    Rostami, Alireza; Masoudi, Mohammad; Ghaderi-Ardakani, Alireza; Arabloo, Milad; Amani, Mahmood

    2016-06-01

    Among the most significant physical characteristics of porous media, the effective thermal conductivity (ETC) is used for estimating the thermal enhanced oil recovery process efficiency, hydrocarbon reservoir thermal design, and numerical simulation. This paper reports the implementation of an innovative least square support vector machine (LS-SVM) algorithm for the development of enhanced model capable of predicting the ETCs of dry sandstones. By means of several statistical parameters, the validity of the presented model was evaluated. The prediction of the developed model for determining the ETCs of dry sandstones was in excellent agreement with the reported data with a coefficient of determination value ({R}2) of 0.983 and an average absolute relative deviation of 0.35 %. Results from present research show that the proposed LS-SVM model is robust, reliable, and efficient in calculating the ETCs of sandstones.

  8. Optical coherence tomography for vulnerability assessment of sandstone.

    PubMed

    Bemand, Elizabeth; Liang, Haida

    2013-05-10

    Sandstone is an important cultural heritage material, in both architectural and natural settings, such as neolithic rock art panels. The majority of deterioration effects in porous materials such as sandstone are influenced by the presence and movement of water through the material. The presence of water within the porous network of a material results in changes in the optical coherence tomography signal intensity that can be used to monitor the wetting front of water penetration of dry porous materials at various depths. The technique is able to detect wetting front velocities from 1 cm s(-1) to 10(-6) cm s(-1), covering the full range of hydraulic conductivities likely to occur in natural sandstones from pervious to impervious.

  9. Giant stromatolites and a supersurface in the Navajo Sandstone, Capitol Reef National Park, Utah

    NASA Astrophysics Data System (ADS)

    Eisenberg, Len

    2003-02-01

    At Capitol Reef National Park, Utah, 5-m-high stromatolites are present locally on interdune carbonate lenses in the Early Jurassic Navajo Sandstone. The stromatolites display both finely laminated and fenestral internal fabrics, and grew along south-facing interdune margins. These stromatolites formed during a high-water-table episode engendered by a dune-dammed paleodrainage in a stabilized Navajo erg. These stromatolites, and the thick interdune section associated with them, suggest a hiatus in erg accumulation and the presence of a super bounding surface.

  10. Stone temperature and moisture variability under temperate environmental conditions: Implications for sandstone weathering

    NASA Astrophysics Data System (ADS)

    McAllister, Daniel; Warke, Patricia; McCabe, Stephen

    2017-03-01

    Temperature and moisture conditions are key drivers of stone weathering processes in both natural and built environments. Given their importance in the breakdown of stone, a detailed understanding of their temporal and spatial variability is central to understanding present-day weathering behaviour and for predicting how climate change may influence the nature and rates of future stone decay. Subsurface temperature and moisture data are reported from quarry fresh Peakmoor Sandstone samples exposed during summer (June-July) and late autumn/early winter (October-December) in a mid-latitude, temperate maritime environment. These data demonstrate that the subsurface thermal response of sandstone comprises numerous short-term (minutes), low magnitude fluctuations superimposed upon larger-scale diurnal heating and cooling cycles with distinct aspect-related differences. The short-term fluctuations create conditions in the outer 5-10 mm of stone that are much more 'energetic' in comparison to the more subdued thermal cycling that occurs deeper within the sandstone samples. Data show that moisture dynamics are equally complex with a near-surface region (5-10 mm) in which frequent moisture cycling takes place and this, combined with the thermal dynamism exhibited by the same region, may have significant implications for the nature and rate of weathering activity. Data indicate that moisture input from rainfall, particularly when it is wind-driven, can travel deep into the stone where it can prolong the time of wetness. This most often occurs during wetter winter months when moisture input is high and evaporative loss is low but can happen at any time during the year when the hydraulic connection between near-surface and deeper regions of the stone is disrupted with subsequent loss of moisture from depth slowing as it becomes reliant on vapour diffusion alone. These data illustrate the complexity of temperature and moisture conditions in sandstone exposed to the 'moderate

  11. Evolving morphology of thermochemical piles caused by accumulation of subducted oceanic crust

    NASA Astrophysics Data System (ADS)

    Li, M.; McNamara, A. K.

    2015-12-01

    Seismic tomography results have shown two large low shear velocity provinces (LLSVPs) in the lowermost mantle beneath Africa and Pacific. The LLSVPs have been hypothesized to be caused by large-scale compositional heterogeneity. Two hypotheses have been proposed for the origin of this compositional heterogeneity: (1) primordial material formed during Earth's early differentiation, and (2) accumulations of subducted oceanic crust on the core-mantle boundary (CMB). Previous geodynamical calculations often show that stable thermochemical piles caused by primordial material have sharp boundaries. So, if the accumulation of subducted oceanic crust has different morphology than that of piles caused by primordial material, we may be able to constrain the origin of compositional heterogeneity from high resolution seismic observations of the boundaries of LLSVPs.Here, we performed geodynamic calculations to investigate the morphology of accumulation of subducted oceanic crust on the CMB. We found that the ability of subducted oceanic crust to accumulate on the CMB and the sharpness of the boundaries of the accumulations both strongly depends on the crustal thickness. A thick (e.g., ~30 km) oceanic crust produced from the early hot mantle can form into large-scale accumulations on the CMB, but with fuzzy and diffuse top boundaries. However, as the oceanic crust becomes thinner, it becomes more difficult to accumulate on the CMB, and the top boundaries of the accumulations of subducted oceanic crust also gradually become sharp, more like that of piles caused by primordial material. Thus, a sharp top boundaries of LLSVPs in the present-day Earth does not guarantee that they are caused by piles of primordial material. In addition, as the oceanic crust becomes thinner, more subducted oceanic crust is entrained and recycled to shallow depth, which may have important implications for geochemical observations on Earth's surface.

  12. Samples from the Jurassic ocean crust beneath Gran Canaria, La Palma and Lanzarote (Canary Islands)

    NASA Astrophysics Data System (ADS)

    Schmincke, Hans-Ulrich; Klügel, Andreas; Hansteen, Thor H.; Hoernle, Kaj; van den Bogaard, Paul

    1998-11-01

    Gabbro and minor metabasalt fragments of MORB composition were found on three of the seven Canary Islands. On Gran Canaria, they occur as metamorphosed (greenschist facies) metabasalt and metagabbro clasts in Miocene fanglomerates and sandstones overlying the shield basalts. On Lanzarote and La Palma, MORB gabbros occur as xenoliths in Pleistocene and historic basanite scoria cones and lava flows. The MORB xenoliths are interpreted as fragments of layers 2 and 3 of the underlying Mesozoic oceanic crust, based on mineral compositions (An-rich plagioclase, Ti- and Al-poor clinopyroxene, ± orthopyroxene ± olivine), depleted major and trace element signatures, and Jurassic ages (ca. 180 Ma) determined on single primary plagioclase and secondary amphibole crystals using the 40Ar/ 39Ar laser technique. The Lanzarote gabbros are very mafic (mg# 87 to 89 in clinopyroxene), moderately deformed, and highly depleted. Gran Canaria gabbros are more evolved (mg# 69 to 83 in clinopyroxene) and texturally mostly isotropic. La Palma MORB gabbros have a range of compositions (mg# 68 to 83 in clinopyroxene), some rocks being strongly metasomatized by interaction with basanite magma. The occurrence of MORB fragments on Lanzarote provides definite evidence that oceanic crust beneath the Canary Island archipelago continues at least as far east as the eastern Canary Islands. We postulate that MORB gabbros on Lanzarote which are commonly associated with peridotite xenoliths, represent the base of oceanic layer 3 where gabbros and peridotites were possibly tectonically interleaved. Such tectonic mixing would explain the enigmatic seismic velocities in this area. Gabbro xenoliths from La Palma were derived from within layer 3, probably from wall rock close to magma reservoirs emplaced during the Pleistocene/Holocene growth of La Palma. The Gran Canaria xenoliths are interpreted to represent the metamorphosed layer 2 and upper layer 3. The abundance of lower crustal xenoliths emphasizes

  13. Synkinematic quartz cementation in partially open fractures in sandstones

    NASA Astrophysics Data System (ADS)

    Ukar, Estibalitz; Laubach, Stephen E.; Fall, Andras; Eichhubl, Peter

    2014-05-01

    Faults and networks of naturally open fractures can provide open conduits for fluid flow, and may play a significant role in hydrocarbon recovery, hydrogeology, and CO2 sequestration. However, sandstone fracture systems are commonly infilled, at least to some degree, by quartz cement, which can stiffen and occlude fractures. Such cement deposits can systematically reduce the overall permeability enhancement due to open fractures (by reducing open fracture length) and result in permeability anisotropies. Thus, it is important to identify the factors that control the precipitation of quartz in fractures in order to identify potential fluid conduits under the present-day stress field. In many sandstones, quartz nucleates syntaxially on quartz grain or cement substrate of the fracture wall, and extends between fracture walls only locally, forming pillars or bridges. Scanning electron microscope cathodoluminescence (SEM-CL) images reveal that the core of these bridges are made up of bands of broken and resealed cement containing wall-parallel fluid inclusion planes. The fluid inclusion-rich core is usually surrounded by a layer of inclusion-poor clear quartz that comprises the lateral cement. Such crack-seal textures indicate that this phase was precipitating while the fractures were actively opening (synkinematic growth). Rapid quartz accumulation is generally believed to require temperatures of 80°C or more. Fluid inclusion thermometry and Raman spectroscopy of two-phase aqueous fluid-inclusions trapped in crack-seal bands may be used to track the P-T-X evolution of pore fluids during fracture opening and crack-seal cementation of quartz. Quartz cement bridges across opening mode fractures in the Cretaceous Travis Peak Formation of the tectonically quiescent East Texas Basin indicate individual fractures opened over a 48 m.y. time span at rates of 16-23 µm/m.y. Similarly, the Upper Cretaceous Mesaverde Group in the Piceance Basin, Colorado contains fractures that

  14. Buoyancy and Dissolution of the Floating Crust Layer in Tank 241-SY-101 During Transfer and Back-Dilution

    SciTech Connect

    CW Stewart; JH Sukamto; JM Cuta; SD Rassat

    1999-11-22

    To remediate gas retention in the floating crust layer and the potential for buoyant displacement gas releases from below the crust, waste will be transferred out of Hanford Tank 241-SY-101 (SY-101) in the fall of 1999 and back-diluted with water in several steps of about 100,000 gallons each. To evaluate the effects of back-dilution on the crust a static buoyancy model is derived that predicts crust and liquid surface elevations as a function of mixing efficiency and volume of water added during transfer and back-dilution. Experimental results are presented that demonstrate the basic physics involved and verify the operation of the models. A dissolution model is also developed to evaluate the effects of dissolution of solids on crust flotation. The model includes dissolution of solids suspended in the slurry as well as in the crust layers. The inventory and location of insoluble solids after dissolution of the soluble fraction are also tracked. The buoyancy model is applied to predict the crust behavior for the first back-dilution step in SY-101. Specific concerns addressed include conditions that could cause the crust to sink and back-dilution requirements that keep the base of the crust well above the mixer pump inlet.

  15. Diagenetic pathways for sandstones: The role of initial composition

    SciTech Connect

    Harris, N.B.

    1995-09-01

    The initial composition of a clastic section is critical in determining the diagenetic reactions that a sandstone will undergo during burial, reactions which strongly influence its reservoir properties. The role of initial composition is illustrated for Middle Jurassic sandstones of northwest Europe (including the Brent sandstone of the North Sea) and Tertiary sandstones of the Gulf of Mexico. The composition of the former evolves from arkose to quartz arenite, with massive dissolution first of plagioclase and subsequently K-feldspar. As the bulk composition changes, the suite of clay minerals changes from kaolinite-dominated to illite-dominated, suite of clay minerals changes from kaolinite-dominated to illite-dominated, typically accompanied by a pronounced decrease in permeability. The Gulf of Mexico sandstones are also initially arkoses. Their composition, however, evolves toward a mixture of quartz and compositionally pure albite. Kaolinite remains the dominant authigenic clay within the sandstones; however detrital clays change from a Na-rich, smectitic mixed layer clay to a K-rich, illitic mixed layer clay. The contrasting diagenetic pathways result from differing mineralogy in the clastic section. The smectite-rich mudstones in the Gulf of Mexico provide a powerful sink for potassium and source of sodium. The resulting low potassium activity results in K-feldspar dissolution; it also prevents illite formation, while high sodium activity stabilizes albite. The Middle Jurassic clastic section in northwest Europe contains relatively little smectite, thus lacks the potassium sink and sodium source. Sodium activity is low, so plagioclases preferentially dissolve. K-feldspars also dissolve, but the potassium here is available for illite formation.

  16. Microbial contamination of two urban sandstone aquifers in the UK.

    PubMed

    Powell, Karen L; Taylor, Richard G; Cronin, Aidan A; Barrett, Mike H; Pedley, Steve; Sellwood, Jane; Trowsdale, Sam A; Lerner, David N

    2003-01-01

    Development of urban groundwater has historically been constrained by concerns about its quality. Rising urban water tables and overabstraction from rural aquifers in the UK have led to a renewed interest in urban groundwater, particularly the possibility of finding water of acceptable quality at depth. This study assessed the microbial quality of groundwater collected from depth-specific intervals over a 15-month period within the Permo-Triassic Sherwood Sandstone aquifers underlying the cities of Nottingham and Birmingham. Sewage-derived bacteria (thermotolerant coliforms, faecal streptococci and sulphite-reducing clostridia) and viruses (enteroviruses, Norwalk-like viruses, coliphage) were regularly detected to depths of 60 m in the unconfined sandstone and to a depth of 91 m in the confined sandstone. Microbial concentrations varied temporally and spatially but increased frequency of contamination with depth coincided with geological heterogeneities such as fissures and mudstone bands. Significantly, detection of Norwalk-like viruses and Coxsackievirus B4 in groundwater corresponded with seasonal variations in virus discharge to the sewer system. The observation of low levels of sewage-derived microbial contaminants at depth in the Triassic Sandstone aquifer is explained by the movement of infinitesimal proportions of bulk (macroscopic) groundwater flow along preferential pathways (e.g., fissures, bedding planes). The existence of very high microbial populations at source (raw sewage) and their extremely low detection limits at the receptor (multilevel piezometer) enable these statistically extreme (microscopic) flows to be traced. Rapid penetration of microbial contaminants into sandstone aquifers, not previously reported, highlights the vulnerability of sandstone aquifers to microbial contamination.

  17. Pervasive Layering in the Lunar Highland Crust: Evidence from Apollos 15, 16,and 17

    NASA Technical Reports Server (NTRS)

    Lowman, Paul D., Jr.; Yang, Tiffany

    2005-01-01

    This paper presents results of a photogeologic reconnaissance of 70 mm photographs taken on the lunar surface during the Apollo 15, 16, and 17 missions, whose primary objective was to investigate the lunar highland crust. Photographs at all three sites, notably the Apennine Front, show pervasive layered structure. These layers are easily distinguished from lighting artifacts, and are considered genuine crustal structures. Their number, thickness, and extent implies that they are lava flows, not ejecta blankets or intrusive features. They appear to be the upper part of the earliest lunar crust, possibly forming a layer tens of kilometers thick. Remote sensing studies (X-ray fluorescence and reflectance spectroscopy), indicate that the highland crust is dominantly a feldspathic basalt. It is concluded that the highland layers represent a global crust formed by eruptions of high-alumina basalt in the first few hundred million years of the Moon's history.

  18. Deformation and rupture of the oceanic crust may control growth of Hawaiian volcanoes

    USGS Publications Warehouse

    Got, J.-L.; Monteiller, V.; Monteux, J.; Hassani, R.; Okubo, P.

    2008-01-01

    Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot-spot activity below the Pacific Plate. Despite the apparent simplicity of the parent process - emission of magma onto the oceanic crust - the resulting edifices display some topographic complexity. Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown. Here we use seismological investigations and finite-element mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities. Further studies are needed to determine whether such processes occur in other active intraplate volcanoes. ??2008 Nature Publishing Group.

  19. Deformation and rupture of the oceanic crust may control growth of Hawaiian volcanoes.

    PubMed

    Got, Jean-Luc; Monteiller, Vadim; Monteux, Julien; Hassani, Riad; Okubo, Paul

    2008-01-24

    Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot-spot activity below the Pacific Plate. Despite the apparent simplicity of the parent process--emission of magma onto the oceanic crust--the resulting edifices display some topographic complexity. Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown. Here we use seismological investigations and finite-element mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities. Further studies are needed to determine whether such processes occur in other active intraplate volcanoes.

  20. Fluvial-deltaic sedimentation and stratigraphy of the ferron sandstone

    USGS Publications Warehouse

    Anderson, P.B.; Chidsey, T.C.; Ryer, T.A.

    1997-01-01

    East-central Utah has world-class outcrops of dominantly fluvial-deltaic Turonian to Coniacian aged strata deposited in the Cretaceous foreland basin. The Ferron Sandstone Member of the Mancos Shale records the influences of both tidal and wave energy on fluvial-dominated deltas on the western margin of the Cretaceous western interior seaway. Revisions of the stratigraphy are proposed for the Ferron Sandstone. Facies representing a variety of environments of deposition are well exposed, including delta-front, strandline, marginal marine, and coastal-plain. Some of these facies are described in detail for use in petroleum reservoir characterization and include permeability structure.

  1. Hydrogeology of the Potsdam Sandstone in northern New York

    USGS Publications Warehouse

    Williams, John H.; Reynolds, Richard J.; Franzi, David A.; Romanowicz, Edwin A.; Paillet, Frederick L.

    2010-01-01

    The Potsdam Sandstone of Cambrian age forms a transboundary aquifer that extends across northern New York and into southern Quebec. The Potsdam Sandstone is a gently dipping sequence of arkose, subarkose, and orthoquartzite that unconformably overlies Precambrian metamorphic bedrock. The Potsdam irregularly grades upward over a thickness of 450 m from a heterogeneous feldspathic and argillaceous rock to a homogeneous, quartz-rich and matrix-poor rock. The hydrogeological framework of the Potsdam Sandstone was investigated through an analysis of records from 1,500 wells and geophysical logs from 40 wells, and through compilation of GIS coverages of bedrock and surficial geology, examination of bedrock cores, and construction of hydrogeological sections. The upper several metres of the sandstone typically is weathered and fractured and, where saturated, readily transmits groundwater. Bedding-related fractures in the sandstone commonly form sub-horizontal flow zones of relatively high transmissivity. The vertical distribution of sub-horizontal flow zones is variable; spacings of less than 10 m are common. Transmissivity of individual flow zones may be more than 100 m2/d but typically is less than 10 m2/d. High angle fractures, including joints and faults, locally provide vertical hydraulic connection between flow zones. Hydraulic head gradients in the aquifer commonly are downward; a laterally extensive series of sub-horizontal flow zones serve as drains for the groundwater flow system. Vertical hydraulic head differences between shallow and deep flow zones range from 1 m to more than 20 m. The maximum head differences are in recharge areas upgradient from the area where the Chateauguay and Chazy Rivers, and their tributaries, have cut into till and bedrock. Till overlies the sandstone in much of the study area; its thickness is generally greatest in the western part, where it may exceed 50 m. A discontinuous belt of bedrock pavements stripped of glacial drift extends

  2. Natural and Laboratory-Induced Compaction Bands in Aztec Sandstone

    NASA Astrophysics Data System (ADS)

    Haimson, B. C.; Lee, H.

    2002-12-01

    The Aztec sandstone used in this research is from the Valley of Fire State Park area, Nevada. This Jurassic aeolian sandstone is extremely weak (uniaxial compressive strength of 1-2 MPa); porosity averages 26%; grains are subrounded and have a bimodal size distribution (0.1 mm and 0.5 mm); its mineral composition (K. Sternlof, personal comm.) is 93% quartz, 5% k-spar, and 2% kaolinite, Fe carbonate and others; grain bonding is primarily through suturing. Sternlof et al. (EOS, November, 2001) observed substantial exposure of mainly compactive deformation bands in the Aztec sandstone. We studied an SEM image of a compaction band found in a hand sample of the Aztec sandstone. We also conducted a drilling test in a 130x130x180 mm prismatic specimen subjected to a preset far-field true triaxial stress condition (\\sigmah = 15 MPa, \\sigmav = 25 MPa, \\sigmaH = 40 MPa). Drilling of a 20 mm dia. vertical hole created a long fracture-like thin tabular breakout along the \\sigmah springline and perpendicular to \\sigmaH direction. SEM analysis of the zones ahead of the breakout tips revealed narrow bands of presumed debonded intact grains interspersed with grain fragments. We infer that the fragments were formed from multiple splitting or crushing of compacted grains in the band of high compressive stress concentration developed along the \\sigmah springline. SEM images away from the breakout tip surroundings showed no such fragments. SEM study of the natural compaction band showed a similar arrangement of mainly intact grains surrounded by grain fragments. Using the Optimas optical software package, we found the percentage of pore area within the band ahead of the breakout tips to average 17%; outside of this zone it was 23%. In the natural compaction band pore area occupied 8.5% of the band; in the host rock adjacent to the compaction band it averaged 19%. These readings strongly suggest porosity reduction due to compaction in both cases. The close resemblance between the

  3. Elevated Uranium in Aquifers of the Jacobsville Sandstone

    NASA Astrophysics Data System (ADS)

    Sherman, H.; Gierke, J.

    2003-12-01

    The EPA has announced a new standard for uranium in drinking water of 30 parts per billion (ppb). This maximum contaminant level (MCL) takes effect for community water supplies December 2003. The EPA's ruling has heightened awareness among residential well owners that uranium in drinking water may increase the risk of kidney disease and cancer and h