Sandstone Matrix Research Articles

An Effective Acid Combination for Enhanced Properties and Corrosion Control of Acidizing Sandstone Formation

To fulfill the demand of the world energy, more technologies to enhance the recovery of oil production are being developed. Sandstone acidizing has been introduced and it acts as one of the important means to increase oil and gas production. Sandstone acidizing operation generally uses acids, which create or enlarge the flow channels of formation around the wellbore. In sandstone matrix acidizing, acids are injected into the formation at a pressure below the formation fracturing pressure, in which the injected acids react with mineral particles that may restrict the flow of hydrocarbons. Most common combination is Hydrofluoric Acid - Hydrochloric with concentration (3% HF - 12% HCl) known as mud acid. But there are some problems associated with the use of mud acid i.e., corrosion, precipitation. In this paper several new combinations of acids were experimentally screened to identify the most effective combination. The combinations used consist of fluoboric, phosphoric, formic and hydrofluoric acids. Cores were allowed to react with these combinations and results are compared with the mud acid. The parameters, which are analyzed, are Improved Permeability Ratio, strength and mineralogy. The analysis showed that the new acid combination has the potential to be used in sandstone acidizing.

Selected Properties and Systematic Position of Soils Developed from Red Sandstones and Clays of the Lower Triassic Buntsandstein in the Nw Part of the Holy Cross Mountains (Poland) / Niektóre właściwości i pozycja systematyczna gleb wytworzonych z czerwonych piaskowców i iłów dolnego triasu w NW obrzeżeniu Gór Świętokrzyskich

AbstractThe aim of the study was to compare the properties of soils developed from the Lower Triassic Buntsandstein sediments in the north-western part of the Holy Cross Mountains (Poland). These are deposits of continental genesis and unique features such as red beds. Two representative soil pedons - the Bartków profile (pBK) developed from clay and the Góra Czerwona profile (pGC) developed from sandstone were selected for detailed analyzes. The morphology of profiles, their micromorphological features, mineralogical composition, and physico-chemical properties were examined. Most of the properties of the soils are a consequence of the original parent rock lithology. A specific feature of the morphology of the soils are the presence of red color (about 10R by the Munsell color scale) related to the presence of hematite. As shown by the XRD data, hematite is not the product of the current soil-forming processes, but it is a lithogenic component, which was inherited from the parent rock. Under the influence of climatic factors primary rock structure has been transformed into a new pedogenic one. Soils developed from clays have a characteristic angular blocky structure. Micromorphological analysis showed that an important role in the formation of soil structure involves geogenic susceptibility of Triassic clays to specific cuboid disintegration. This is indicated by the pore system of planes as an orthogonal nets visible in thin section. The soils developed from sandstone have a weak (unstable) subangular blocky structure. The main reason is the insufficient dispersion of the clay-ferruginous fraction from the sandstone matrix. Microscopic observations indicate that fine factions occurs as loose microaggregates, which results in a feature that smaller rock fragments and individual quartz grains are not bonded into soil aggregates. The studied soils are characterized by specific physical-chemical properties. Some of them strongly depend on the mineralogical properties of the soil substrate. Strong acidity (pH 3-4) and a very low content of base cations (below 1.0 cmol(+)kg-1) are due to a lack of carbonate minerals in sandstones and weak weathering of aluminium silicate. High exchangeable Al content in clay (16.5 cmol(+)kg-1) should be related to the geochemical properties of the red bed-type rocks such as the Lower Triassic Buntsandstein deposits. Soils developed from the Lower Triassic Buntsandstein clays have a sequence of genetic horizons: Ap, Bw, Bw/C, C and fulfill the criteria assigned to dystrophic typical brown soils (BDt) in the Polish Soil Classification (PSC 2011), whereas in the WRB they were classified as Endoeutric Chromic Cambisols (Loamic). Soils developed from the Lower Triassic Buntsandstein red sandstone can be classified as dystrophic humus brown soil (BDpr) in the PSC (2011). Within the WRB classification that soil can be assigned to Epidystric Chromic Endoleptic Cambisols.

Research on the calculation method of shale and tuff content: taking tuffaceous reservoirs of X depression in the Hailar–Tamtsag Basin as an example

Shale content is known in reservoir evaluation as an important parameter in well logging. However, the log response characteristics are simultaneously affected by shale and tuff existing in tuffaceous sandstone reservoirs. Due to the fact that tuff content exerts an influence on the calculation of shale content, the former is equally important as the latter. Owing to the differences in the source and composition between shale and tuff, the calculation of tuff content using the same methods for shale content cannot meet the accuracy requirements of logging evaluation. The present study takes the tuffaceous reservoirs in the X depression of the Hailar–Tamtsag Basin as an example. The differences in the log response characteristics between shale and tuff are theoretically analyzed and verified using core analysis data. The tuff is then divided into fine- and coarse-grained fractions, according to the differences in the distribution of the radioactive elements, uranium, thorium and potassium. Next, a volume model suitable for tuffaceous sandstone reservoirs is established to include a sandstone matrix, shale, fine-grained tuff, coarse-grained tuff and pore. A comparison of three optimization algorithms shows that the particle swarm optimization (PSO) yields better calculation results with small mean errors. The resistivity differences among shale, fine-grained tuff and coarse-grained tuff are considered in the calculation of saturation. The water saturation of tuffaceous reservoirs is computed using the improved Poupon's equation, which is suitable for tuffaceous sandstone reservoirs with low water salinity. The method is used in well Y, and is shown to have a good application effect.

Thermomechanical Analysis of Different Types of Sandstone at Elevated Temperature

Many centuries ago, humans used to build their houses using wood, but due to natural hazards such as fire, humans have now shifted to the concept of building their houses and monuments using rock materials such as concrete, sandstone, bricks, etc. Managing fires or extinguishing them in time, the change in the physical properties of stone building materials at elevated temperature, and the variation in the strength and deformation of stone building materials with change in temperature remain debatable issues. Understanding the effect of fire on stone building materials such as sandstones would be helpful to evaluate whether fire-damaged monuments can be strengthened or should be demolished, or whether damaged parts should be replaced. For centuries, sandstone has been used not only in India but all over the world for several purposes. Widescale application of sandstone can be seen in different monuments, temples, and buildings in India, i.e., the Red Forts of Delhi and Agra, places and buildings in Fatehpur Sikri, Kota, Jaipur, Jodhpur, Buddhist Rameswaram temples in south India, the Indian parliament house, the presidential house, the supreme court building, etc. Globally, the White House in the USA is made of Aquia Sandstone, and Ayres rock (Uluru) in Australia, the world’s largest monolithic sacred site, is made of kosic sandstone (Allison and Bristow 1999; Allison and Goudie 1994; BRE 1945; Hajpal 1999, 2002a, b; Chakrabarti 1993; Chakrabarti et al. 1996; Dorn 2003; Fitzner et al. 2003; Goudie et al. 1992; Alm 1985). In particular, India has witnessed several fire incidents recently (Gorton Castle, Shimla 2014; Connaught Place, Delhi 2014; Surat, Gujarat 2014). Hence, the effect of temperature on the strength and deformation behavior of stone building materials such as sandstones needs to be studied in detail before construction of any monuments using these materials. Under the influence of high temperatures but below the melting point of sandstone, its microstructure rearranges, new microcracks develop, and preexisting ones become widespread and widen. Meanwhile, various physical and mineralogical changes take place in the rock matrix. After cooling down to air-dried temperature, thermally induced changes become permanent in some of the sandstone matrix. The effect of temperature on the physical and mechanical properties of rock has become an important area of study in the rock mechanics field. Over the last few years, various investigations have been carried out in this field to determine the complex behavior of rock under thermomechanical (TM) coupling (Alshayea et al. 2000; Hudson et al. 2005; Cheng and Arson 2014; Heuze 1983; Jaeger et al. 2007; Tian et al. 2012). That work measured the variation of physicomechanical parameters such as the modulus of rock deformation, Poisson ratio, tensile strength, compressive strength, cohesion, internal friction angle, viscosity, thermal expansion coefficients, etc. with temperature (Brede 1993; Xu et al. 2008; Somerton 1992; Dwivedi et al. 2008). & P. K. Gautam pgautam.embedded@gmail.com; neurogeneticamit@gmail.com

Comparison of Buffer Effect of Different Acids During Sandstone Acidizing

The most important concern of sandstone matrix acidizing is to increase the formation permeability by removing the silica particles. To accomplish this, the mud acid (HF: HCl) has been utilized successfully for many years to stimulate the sandstone formations, but still it has many complexities. This paper presents the results of laboratory investigations of different acid combinations (HF: HCl, HF: H3PO4 and HF: HCOOH). Hydrofluoric acid and fluoboric acid are used to dissolve clays and feldspar. Phosphoric and formic acids are added as a buffer to maintain the pH of the solution; also it allows the maximum penetration of acid into the core sample. Different tests have been performed on the core samples before and after the acidizing to do the comparative study on the buffer effect of these acids. The analysis consists of permeability, porosity, color change and pH value tests. There is more increase in permeability and porosity while less change in pH when phosphoric and formic acids were used compared to mud acid. From these results it has been found that the buffer effect of phosphoric acid and formic acid is better than hydrochloric acid.

Transport of engineered silver (Ag) nanoparticles through partially fractured sandstones

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.

Nestolaite, CaSeO3·H2O, a new mineral from the Little Eva mine, Grand County, Utah, USA

AbstractNestolaite (IMA 2013-074), CaSeO3·H2O, is a new mineral species from the Little Eva mine, Grand County, Utah, USA. It is named in honour of the prominent Italian mineralogist and crystallographer Fabrizio Nestola. The new mineral was found on sandstone matrix as rounded aggregates up to 2 mm across and up to 0.05 μm thick consisting of tightly intergrown oblique-angled, flattened to acicular crystals up to 30 μm long and up to 7 μm (very rarely up to 15 μm) thick. Nestolaite associates with cobaltomenite, gypsum, metarossite, orschallite and rossite. The new mineral is light violet and transparent with a white streak and vitreous lustre. The Mohs hardness is 2½. Nestolaite is brittle, has uneven fracture and perfect cleavage on {100}. The measured and calculated densities areDmeas. = 3.18(2) g/cm3andDcalc.= 3.163 g/cm3. Optically, nestolaite is biaxial positive. The refractive indices are α = 1.642(3), β = 1.656(3), γ = 1.722(6). The measured 2Vis 55(5)° and the calculated 2Vis 51°. In transmitted light nestolaite is colourless. It does not show pleochroism but has strong pseudoabsorption caused by high birefringence. The chemical composition of nestolaite (wt.%, electronmicroprobe data) is: CaO 28.97, SeO2 61.14, H2O (calc.) 9.75, total 99.86. The empirical formula calculated on the basis of 4 O a.p.f.u. (atoms per formula unit) is Ca0.96Se1.02O3·H2O. The Raman spectrum is dominated by the Se–O stretching and O–Se–O bending vibrations of the pyramidal SeO3groups and O–H stretching modes of the H2O molecules. The mineral is monoclinic, space groupP21/c, witha= 7.6502(9),b= 6.7473(10),c= 7.9358(13) Å, β = 108.542 (12)°,V= 388.37(10) Å3andZ= 4. The eight strongest powder X-ray diffraction lines are [dobsin Å(hkl) (Irel)]: 7.277 (100)(100), 4.949 (110)(37), 3.767 (002)(29), 3.630 (200)(58), 3.371 (020)(24), 3.163 (02)(74), 2.9783 (21)(74) and 2.7231 (112)(31). The crystal structure of nestolaite was determined by means of the Rietveld refinement from the powder data toRwp= 0.019. Nestolaite possesses a layered structure consisting of CaΦ–SeO3sheets, composed of edge-sharing polyhedra. Adjacent sheets are held by H bonds emanating from the single (H2O) group within the sheets. The nestolaite structure is topologically unique.

Bluelizardite, Na7(UO2)(SO4)4Cl(H2O)2, a new uranyl sulfate mineral from the Blue Lizard mine, San Juan County, Utah, USA

*Corr esponding author Bluelizardite (IMA 2013-062), Na 7 (UO 2 )(SO 4 ) 4 Cl(H 2 O) 2 , is a new uranyl sulfate mineral from the Blue Lizard mine, San Juan County, Utah (USA). It was found in a sandstone matrix and is associated with chalcanthite, copiapite, ferrinatrite, gypsum, krohnkite, johannite, and several other new, unnamed Na- and Mg-containing uranyl sulfates. Bluelizardite is a supergene mineral formed by the post-mining weathering of uraninite. The mineral is monoclinic, C2/c, with a = 21.1507(6), b = 5.3469(12), c = 34.6711(9) A, β = 104.913(3)°, V = 3788.91(17) A 3 and Z = 8. Crystals are blades up to 0.4 mm long, flattened on {001}, elongated parallel to [010] and exhibiting the forms {100}, {001} and {111}. Bluel izardite is pale yellow and has a yellowish-white streak. It has good cleavage on {001} and uneven fracture. The Mohs hardness is estimated at 2. The calculated density based on the empirical formula is 3.116 g/cm 3 . Bluelizardite exhibits bright yellow-green fluorescence under both long- and short-wave UV radiation. The mineral is optically biaxial (–), with α = 1.515(1), β = 1.540(1) and γ = 1.545(1) (measured with white light). The measured 2V is 48(2)° and the calculated 2V is 47.6°. The mineral does not exhibit any dispersion or pleochroism. The optical orientation is X = b, Y ≈ a, Z ≈ c*. The empirical formula of bluelizardite is Na 6.94 (U 1.02 O 2 )(SO 4 ) 4.00 Cl 0.94 O 0.06 (H 2 O) 2 (based on 21 anions pfu). The Raman

Lithofacies architecture of basaltic andesite lavas and their interaction with wet-sediment: Port a’ Chroinn, Kerrera, NW Scotland

Synopsis Lavas of the Lorne Plateau Volcanic Succession (LPVS) crop out on the island of Kerrera, NW Scotland, and were emplaced during the Devonian Period, synchronous with Old Red Sandstone (ORS) terrestrial sedimentation. These flows are discontinuously exposed for c . 3 km at Port a’ Chroinn, Kerrera, and typically comprise blocky, basal breccias, coherent, crystalline cores, and clinker flow tops, interpreted as basaltic andesite ’a’a lavas. Gradational zones are observed from coherent core, through highly vesicular core, to semi-coherent lava and normally graded clinker. Prismatically jointed, inflated pahoehoe lavas are also present, but have few characteristic morphological features. Localized domains of magma–sediment mingling occur at the bases of several lavas, with clasts of basaltic andesite within a sandstone matrix. These domains are interpreted as peperites, formed as lava flowed over and mingled with unconsolidated, wet sediment that had been deposited on the surfaces of underlying lavas during periods of volcanic quiescence.

Transport of Sporosarcina pasteurii in sandstone and its significance for subsurface engineering technologies

The development of microbially mediated technologies for subsurface remediation and rock engineering is steadily increasing; however, we are lacking experimental data and models to predict bacterial movement through rock matrices. Here, breakthrough curves (BTCs) were obtained to quantify the transport of the ureolytic bacterium, Sporosarcina pasteurii, through sandstone cores, as a function of core length (1.8–7.5cm), bacterial density (4×106 to 9×107cells/ml) and flow rate (5.8–17.5m/s). S. pasteurii was easily immobilised within the homogeneous sandstone matrix (>80%) in comparison to a packed sand column (<20%; under similar experimental conditions), and percentage recovery decreased almost linearly with increasing rock core length. Moreover, a decrease in bacterial density or flow rate enhanced bacterial retention. A numerical model based on 1D advection dispersion models used for unconsolidated sand was fitted to the BTC data obtained here for sandstone. Good agreement between data and model was obtained at shorter rock core lengths (<4cm), suggesting that physicochemical filtration processes are similar in homogeneous packed sand and sandstones at these lengths. Discrepancies were, however observed at longer core lengths and with varying flow rates, indicating that the attributes of consolidated rock might impact bacterial transport progressively more with increasing core length. Implications of these results on microbial mineralisation technologies currently being developed for sealing fluid paths in subsurface environment is discussed.

Meisserite, Na5(UO2)(SO4)3(SO3OH)(H2O), a new uranyl sulfate mineral from the Blue Lizard mine, San Juan County, Utah, USA

AbstractMeisserite (IMA2013-039), Na5(UO2)(SO4)3(SO3OH)(H2O), is a new uranyl sulfate mineral from the Blue Lizard mine, San Juan County, Utah (USA). It is named in honour of the prominent Swiss mineralogist Nicolas Meisser. The new mineral was found in a sandstone matrix and is associated with chalcanthite, copiapite, ferrinatrite, gypsum, johannite and another new Na-bearing uranyl sulfate, belakovskiite (IMA2013-075). Meisserite is a secondary mineral formed by the post-mining weathering of uraninite. The mineral is triclinic,P,a= 5.32317(10),b= 11.5105(2),c= 13.5562(10) Å, α = 102.864(7)°, β = 97.414(7)°, γ = 91.461(6)°,V= 801.74(6) Å3, andZ= 2. Crystals are prisms elongated on [100], up to 0.3 mm long, exhibiting the forms {010} and {001}. Meisserite is pale green to yellowish green, translucent to transparent and has a very pale yellow streak. It is brittle, with fair cleavage on {100} and {001}, and uneven fracture. The Mohs hardness is estimated at 2. Meisserite is somewhat hygroscopic and easily soluble in water. The calculated density based on the empirical formula is 3.208 g/cm3. Meisserite exhibits bright yellow green fluorescence under both long- and shortwave UV radiation. The mineral is optically biaxial (–), with α = 1.514(1), β = 1.546(1), γ = 1.557(1) (measured in white light). The measured 2V is 60(2)° and the calculated 2V is 60°. Dispersion isr &gt; v, perceptible, and the optical orientation isX≈a,Z≈c*. The mineral is pleochroic, withX(colourless) &lt;Y(pale yellow) ≈Z(pale greenish yellow). The empirical formula of meisserite (based on 19 O a.p.f.u.) is Na5.05(U0.94O2)(SO4)3[SO2.69(OH)1.31](H2O). The Raman spectrum is dominated by the symmetric stretching vibrations of UO22+, SO42–and also weaker O–H stretching vibrations. The eight strongest powder X-ray diffraction lines are [dobsin Å(hkl)Irel]: 13.15 (001) 81, 6.33 (02) 62, 5.64 (01,020) 52, 5.24 (100,012,01) 100, 4.67 (101) 68, 3.849 (1,102,022) 48, 3.614 (02,3) 41, and 3.293 (13,004) 43. The crystal structure of meisserite (R1= 0.018 for 3306 reflections withIobs&gt; 3σI) is topologically unique among known structures of uranyl minerals and inorganic compounds. It contains uranyl pentagonal bipyramids linked by SO4groups to form chains. Na+cations bond to O atoms in the chains and to an SO3OH group and an H2&gt;O group between the chains, thereby forming a heteropolyhedral framework.

The Trace FossilTeredolites longissimusKelly and Bromley, 1984, from the Eocene of Curaçao

The clavate boring Teredolites Leymerie is produced in wood by teredinid bivalves and occurs at various sites in the Cenozoic of the Antillean region. Most commonly, the enclosing lignic substrate rots away and preservation relies on the calcareous lining, an organic mold of the bioerosive structure. Teredolites longissimus Kelly and Bromley from the (probably Middle) Eocene of the Ceru di Cueba Formation of Curaçao is unusually well preserved and intertwined tubes occur in life associations in a calcareous sandstone matrix. The waterlogged, enclosing wood presumably sank to the seafloor and was buried. As it rotted away, sand slipped into the void and held the T. longissimus tubes in place.

Probing internal gradients dependence in sandstones with multi-dimensional NMR

Multi-dimensional NMR experiments at two magnetic field strengths (2 and 23MHz) are presented in this paper to study the dependence of effective internal gradients in water-saturated sandstone plugs. Special pulse sequence is designed to encode longitudinal relaxation time T1, internal gradient Gin and transverse relaxation time T2 in respective windows. Experimental three-dimensional data are processed with a fast 3D inversion algorithm. Within this one-shot experiment, the three-dimensional distribution function T1-Gin-T2 and projected one- and two-dimensional distributions monitor internal gradients through diffusion in pores and reveal how effective internal gradients scale with magnetic field. Contrasts in behavior of pore size components between the two field strengths, such as T1/T2 ratio increase in T2–T1 maps and signal up-shift in T1-Gin and T2-Gin maps, are associated with variations in effective internal gradients in porous media, so potentially indicating the physical dependence of internal gradients on static field strengths and on heterogeneity of the sandstone matrix.

Lower Permian stems as fluvial paleocurrent indicators of the Parnaíba Basin, northern Brazil

A comprehensive biostratinomic study was carried out with abundant stems from the Lower Permian Motuca Formation of the intracratonic Parnaíba Basin, central-north Brazil. The fossils represent a rare tropical to subtropical paleofloristic record in north Gondwana. Tree ferns dominate the assemblages (mainly Tietea, secondarily Psaronius), followed by gymnosperms, sphenophytes, other ferns and rare lycophytes. They are silica-permineralized, commonly reach 4 m length (exceptionally more than 10 m), lie loosely on the ground or are embedded in the original sandstone or siltstone matrix, and attract particular attention because of their frequent parallel attitudes. Many tree fern stems present the original straight cylindrical to slightly conical forms, other are somewhat flattened, and the gymnosperm stems are usually more irregular. Measurements of stem orientations and dimensions were made in three sites approximately aligned in a W–E direction in a distance of 27.3 km at the conservation unit “Tocantins Fossil Trees Natural Monument”. In the eastern site, rose diagrams for 54 stems indicate a relatively narrow azimuthal range to SE. These stems commonly present attached basal bulbous root mantles and thin cylindrical sandstone envelopes, which sometimes hold, almost adjacent to the lateral stem surface, permineralized fern pinnae and other small plant fragments. In the more central site, 82 measured stems are preferentially oriented in the SW–NE direction, the proportion of gymnosperms is higher and cross-stratification sets of sandstones indicate paleocurrents mainly to NE and secondarily to SE. In the western site, most of the 42 measured stems lie in E–W positions. The predominantly sandy succession, where the fossil stems are best represented, evidences a braided fluvial system under semiarid conditions. The low plant diversity, some xeromorphic features and the supposedly almost syndepositional silica impregnation of the plants are coherent with marked dry seasons. Thick mudstones and some coquinites below and above the sandy interval may represent lacustrine facies formed in probably more humid conditions. The taphonomic history of the preserved plants began with exceptional storms that caused fast-flowing high water in channels and far into the floodplains. In the eastern site region, many tree ferns only fell, thus sometimes covering and protecting plant litter and leaves from further fragmentation. Assemblages of the central and western sites suggest that the trees were uprooted and transported in suspension (floating) parallel to the flow. Heavier ends of stems (according to their form or because of attached basal bulbous root mantle or large apical fronds) were oriented to upstream because of inertial forces. During falling water stage, the stems were stranded on riverbanks, usually maintaining the previous transport orientation, and were slightly buried. The perpendicular or oblique positions of some stems may have been caused by interference with other stems or shallow bars. Rare observed stems were apparently waterlogged before the final depositional process and transported as bedload. The differences of interpreted channel orientations between the three sites are expected in a braided fluvial system, considering the very low gradients of the basin and the work scale in the order of tens of kilometers. The mean direction of the drainage probably was to east and the flows apparently became weaker downstream. This study seems to provide reliable data for paleocurrent interpretations, especially considering areas with scarce preserved sedimentary structures.

Mobilization of aluminum by the acid percolates within unsaturated zone of sandstones

The area of the Black Triangle has been exposed to extreme levels of acid deposition in the twentieth century. The chemical weathering of sandstones found within the Black Triangle became well-known phenomenon. Infiltration of acid rain solutions into the sandstone represents the main input of salt components into the sandstone. The infiltrated solutions--sandstone percolates--react with sandstone matrix and previously deposited materials such as salt efflorescence. Acidic sandstone percolates pH 3.2-4.8 found at ten sites within the National Park Bohemian Switzerland contained high Al-tot (0.8-10 mg L(-1)) concentrations and high concentrations of anions SO4 (5-66 mg L(-1)) and NO3 (2-42 mg L(-1)). A high proportion (50-98 %) of Al-tot concentration in acid percolates was represented by toxic reactive Al(n+). Chemical equilibrium modeling indicated as the most abundant Al species Al(3+), AlSO4 (+), and AlF(2+). The remaining 2-50 % of Al-tot concentration was present in the form of complexes with dissolved organic matter Al-org. Mobilization and transport of Al from the upper zones of sandstone causes chemical weathering and sandstone structure deterioration. The most acidic percolates contained the highest concentrations of dissolved organic material (estimated up to 42 mg L(-1)) suggesting the contribution of vegetation on sandstone weathering processes. Very low concentrations of Al-tot in springs at BSNP suggest that Al mobilized in unsaturated zone is transported deeper into the sandstone. This process of mobilization could represent a threat for the water quality small-perched aquifers.

Brazilian Geological Sandstone Characterization and its Utilization as Aggregate in Structural Concrete

The sandstone extraction is an essential activity to the production of specific products. It is employed in the civil construction sector. However, there is still a deficiency in physical and geological characterization. This research develops two experiments in the sandstone matrix located in São Carlos region (City of São Paulo State – Brazil). The first experiment is related to the geological aspect of the specific sandstone. It identified the geographic location and investigated the porosity and absorption rates of the Brazilian sandstone rock, besides verifying its compressive strength. The purpose was to identify and evaluate possibilities of sandstone use in the structural concrete composition. The second experiment tested the concrete strength with this aggregate. Some quantities of crushed sandstone were used as fine aggregate in the manufactured concrete. The experiments presented sandstone properties and sandstone aggregate possibilities in concrete composition. The present study is a result of an undergraduate project, aiming to contribute with new information on the Brazilian sandstone characterization and concrete strength application with the sedimentary aggregate. This work showed some possibilities to use this type of yellow and red sandstone as aggregate.

Implications of carbonate-like geochemical signatures in a sandstone aquifer: Radium and strontium isotopes in the Cambrian Jordan aquifer (Minnesota, USA)

Water–rock interaction in sandstone aquifers can potentially mobilize U-and Th-series radionuclides, resulting in elevated levels of radioactive constituents such as radium (Ra) in groundwater. Previous studies have delineated the sources of Ra in groundwater by assuming that 228Ra/226Ra of groundwater parallels the 232Th/238U activity ratio of aquifer solids. We present an integrated geochemical and isotopic study of groundwater and aquifer solids for major and trace elements, radium (224Ra, 226Ra, 228Ra), strontium isotopes (87Sr/86Sr), and tritium in the Cambrian Jordan quartz sandstone aquifer of southeastern Minnesota (USA). The Jordan aquifer, part of the Cambrian–Ordovician aquifer system of the upper midwestern USA, is characterized by a wide range of Ra activities in groundwater. Uniform Ca–Mg–HCO3− major element composition and patterns in 87Sr/86Sr indicate that interaction with carbonate minerals controls water chemistry. At least one contributing Sr source is radiogenic, yielding 87Sr/86Sr ratios up to 0.71347. Radium-226 activities exhibit especially large variations (<1–418mBqL−1), and the highest radium activities occupy a 100-km-long north–south region. Consistent with the carbonate-like elemental and Sr isotope signatures, 226Ra activity (median 85mBqL−1) is higher than 228Ra (median 47mBqL−1), yielding low 228Ra/226Ra ratios (median 0.5) that would be expected from a lithology preferentially containing U relative to Th, such as carbonate rocks. Collectively, results indicate the primary source of radium to the aquifer is alpha recoil from aquifer solids rather than external inputs of high-Ra waters, indicated by (1) similar 228Ra/226Ra ratios in aquifer solids and groundwater, including low, carbonate-like values in the high-226Ra samples; (2) some association between whole-rock 226Ra levels and groundwater 226Ra activities; and (3) groundwater 224Ra/228Ra averaging near unity. Furthermore, hydrogeologic setting (e.g. presence or absence of overlying carbonate units) is inconsistent with systematic inputs of high-Ra waters from overlying carbonate aquifers. The most proximate source of carbonate material in the sandstone aquifer seems to be the calcite and dolomite cement that yields different geochemical and isotopic fingerprints than silicate minerals would impart. Whole-rock 226Ra/238U≈1 implies that any U enrichment in the carbonate cement occurred at least 350,000years ago. High groundwater Ra activities relative to solids are attributable to anoxic conditions that play a role in maintaining inefficient radium removal for a fresh groundwater system, indicated by the estimated dimensionless whole-rock Ra distribution coefficient of 150–920 (median 560). Coprecipitation of Ra into barite is a potential but unquantified Ra removal mechanism. Overall, radium in the Jordan aquifer provides an example of a naturally-occurring trace element of health significance that may be derived not mainly from the quartz sandstone matrix, but from carbonate material such as calcite and dolomite cement. Especially when combined with complementary tracers such as 87Sr/86Sr, this study demonstrates the usefulness of the 228Ra/226Ra ratio as an indicator of the key mineral phases (silicate vs. carbonate) involved in supplying radium to groundwater.

Geological relationships of basalts, andesites and sand injectites at the base of the Paraná volcanic province, Torres, Brazil

The Cretaceous interaction of the heated, giant Guarani aquifer with lavas, dikes and sills of the Paraná volcanic province is here evaluated based on the description of the large exposures in Torres, southernmost Brazil. Chalcedony silicified sandstone dikes, sills and breccias containing volcanic clasts in a sandstone matrix are common in the Paraná volcanic province. Sandstone layers mark either the contact between lava flows or the base of the vertically-jointed, massive core. In Torres, one basaltic andesite and one andesite lava flow of the low-Ti Gramado type, and basalt and basaltic andesite sills and dikes, are correlated over 10km with rocks in the Graxaim quarry. Scintillometric emission rates vary systematically with contents of K, Th and U and are characteristic of each lava or intrusive rock. Major and trace elements are also characteristic of each lava. Three large outcrops of breccias display angular, amygdaloidal volcanic clasts immersed in a silicified sandstone matrix. No evidence was found of high temperature (1150°C) interaction of the lava with the loose, erg of the Botucatu Formation, such as fluidal volcanic clasts, quenched rims or thermal recrystallization of the sand; only a thin (5mm) layer of thermally modified sand is present on top of a paleodune in Torres.In Torres, the interaction of andesite with wet sand occurred after degassing of the lava, because the breccia clasts are amygdaloidal. All evidence points to hydrothermal processes for the formation of the breccias, such as lozenge fractures filled with silicified sandstone, preserved detrital characteristics of the sandstone grains and cold (below 130°C) contact between the volcanic rock and the sand. Most significant is the timing of sand intrusion, because thin (1mm) dikes of silicified sandstone cut fractures in the rock and the zeolite-filled amygdales. The sandstone dikes, sills and breccias are interpreted as a result of the ascent of overpressured heated water and its vapor from the huge, underlying Guarani aquifer, carrying fluidized sand and continuously silicifying the intruded sand. The three breccias are sills intruded into cold lava flows. The description and correlation of the magmatic bodies and the field relationships of the silicified sandstones establish the stratigraphy of the Paraná volcanic province in Torres and elucidate the processes responsible for the injection and effusion of sand in the Cretaceous.

Sandstone matrix olistostrome deposited on intra-subduction complex serpentinite, Franciscan Complex, western Marin County, California

Detailed field mapping in the Franciscan Complex in western Marin County, California, offers insight into the origins and development of mélanges, as well as accretionary complex architecture. From structurally high to low, the study area units comprise a structurally high sandstone matrix olistostrome, serpentinite, a structurally intermediate sandstone matrix olistostrome, Early Cretaceous Nicasio Reservoir Terrane greenstone, and coherent Cretaceous greywacke, all exhibiting prehnite–pumpellyite burial metamorphism. The structurally high sandstone matrix olistostrome includes volcanic blocks up to 700m in diameter and chert blocks up to 100m in diameter, whereas the structurally intermediate olistostrome unit comprises a lithic-rich sandstone matrix enclosing volcanic blocks 1–20m in diameter. The youngest detrital zircons in the high olistostrome and the coherent greywacke have U–Pb ages of ≈20m.y. older than the inferred depositional ages of the units themselves, suggesting that the bulk of the detritus comprising these units was derived by exposure and sedimentary recycling of significantly older, previously accreted sediments. The matrix of both olistostrome units exhibits minimal strain with weak local development of pressure solution cleavage. These findings demonstrate introduction of Franciscan exotic blocks and development of Franciscan block-in-matrix fabrics through sedimentary sliding and support sedimentary interpretations for more highly strained shale and serpentinite matrix mélanges. Additionally, these data suggest that sandstone matrix olistostromes/mélange may constitute a larger part of the Franciscan and other accretionary complexes than previously believed.The structurally high olistostrome preserves a depositional contact on serpentinite, verifying an intra-subduction complex origin for the serpentinite. The serpentinite lacks block-in-matrix structure and likely represents a tectonically emplaced unit derived from the subducting plate as a coherent nappe, rather than a sedimentary serpentinite deposit. Multi-kilometer scale west-vergent overturned folds with subhorizontal fold axes deform the nappes of the field area, and a later generation of open, northeast-trending folds overprints the earlier folds.

Histological, chemical, and morphological reexamination of the “heart” of a small Late Cretaceous Thescelosaurus

A three-dimensional, iron-cemented structure found in the anterior thoracic cavity of articulated Thescelosaurus skeletal remains was hypothesized to be the fossilized remains of the animal's four-chambered heart. This was important because the finding could be interpreted to support a hypothesis that non-avian dinosaurs were endothermic. Mammals and birds, the only extant organisms with four-chambered hearts and single aortae, are endotherms. The hypothesis that this Thescelosaurus has a preserved heart was controversial, and therefore, we reexamined it using higher-resolution computed tomography, paleohistological examination, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy. This suite of analyses allows for detailed morphological and chemical examination beyond what was provided in the original work. Neither the more detailed examination of the gross morphology and orientation of the thoracic "heart" nor the microstructural studies supported the hypothesis that the structure was a heart. The more advanced computed tomography showed the same three areas of low density as the earlier studies with no evidence of additional low-density areas as might be expected from examinations of an ex situ ostrich heart. Microstructural examination of a fragment taken from the "heart" was consistent with cemented sand grains, and no chemical signal consistent with a biological origin was detected. However, small patches of cell-like microstructures were preserved in the sandstone matrix of the thoracic structure. A possible biological origin for these microstructures is the focus of ongoing investigation.