Silty Sediments Research Articles

Experimental and modeling investigations of hydrate phase equilibria in natural clayey-silty sediments

Rapid and accurate acquisition of hydrate phase equilibria in sediments is crucial for gas hydrate resource assessment and exploitation and hydrate-based technological applications. However, current models have significant limitations and deficiencies in predicting hydrate phase equilibria in sediments, especially clayey-silty sediments prevalent in nature. To this end, a unified hydrate phase equilibrium model was developed, which considers the combined inhibitions of surface adsorption, capillary effect, and salt solution. It is derived that water content and salinity can be used as direct input parameters to the model to estimate the hydrate dissociation temperature depression. Using the stepwise heating method, the hydrate dissociation conditions in various natural sediments were measured. It suggests that montmorillonite has the greatest dissociation temperature depression, followed by SA sediments and kaolin, while pore hydrates in silts exhibit almost the same thermodynamic equilibrium conditions as bulk hydrates unless the water content is below 15%. Special attention was also paid to the additional inhibition of surface adsorption on hydrate phase equilibria in sediments with salt solutions. This inhibition was found to be quite pronounced in clay-rich sediments, especially expansive clays, but essentially negligible in silty or sandy sediments. The maximum average error of 3.29% was observed between model predictions and measured data. Additionally, the amounts of clathrated water (CW), non-equilibrium unclathrated water (NEUW), and equilibrium unclathrated water (EUW) in sediments after the end of hydrate formation were determined using the model. It reveals that CW has the highest proportion in silts, reaching 68.9%, while only 0.231 in montmorillonite; in contrast, EUW is dominant in montmorillonite; NEUW seems to be independent of lithology but shows a strong dependence on the water content. It implies that silty sediments are more conductive to hydrate-based gas storage and CO2 sequestration than clayey sediments. This study provides some practical insights and implications for hydrate phase behaviors in natural sediments and can potentially be employed as a tool for phase equilibrium prediction with universality and accuracy.

Investigating Potential Links Between Fine-Grained Components in Loess and Westerly Airflow: Evidence From East and Central Asia

Loess is a ubiquitous, silty aeolian sediment common across the semiarid to subhumid regions in the Northern Hemisphere. As such, the physical characteristics of loess sediment, such as modal grain size and quartz crystallinity index, have the potential to inform us about dust transport pathways and corresponding atmospheric circulation responsible for entrainment, transport, and deposition. In this article, we combine detailed granularity analyses and non-parametric end-member modeling with investigations of the quartz crystallinity index of three loess deposits, extending from East to Central Asia, with the aim of identifying dust transport processes and the climate subsystems responsible for them. We find marked differences in the grain size characteristics of Eastern and Central Asian loess. Given potential linkages of fine particles to the westerly jet stream, here we focused on the fine-grained end-members in the loess. The fine-grained components of the Central Asian Bishkek (BSK) and Chashmanigar (CMG) loess may be derived from individual particles carried at high altitude by major climate subsystems such as the westerlies. However, similar quartz crystallinity indexes of fine- and coarse-grained components in the Central Asian loess indicated that surface-level wind strength might influence the releases from proximal-sourced regions and abundances in the upper atmosphere for the fine particles. By contrast, the fine-grained component of the East Asian [Fanshan18 (FS18)] loess seems to yield physical similarities to the Tertiary Red Clays underlying many loess stratigraphies, and has been interpreted to relate to transport associated with the East Asian winter monsoon. It was further supported by quartz crystallinity indexes of the <16 μm fractions in the FS18 loess, basically consistent with those of the deserts in North China, highlighting the near-surface northwesterly winter monsoon as the dominant transport dynamics of fine-grained dust. In addition, comparisons of quartz crystallinity indexes of fine-grained components between the East and Central Asian loess also suggest that variations in fine particles within the loess might not be related to transport by the higher-level westerlies, which is in disagreement with the previous model. Therefore, our results indicate that variations in fine-grained end-members in loess are difficult to reliably document the variabilities of higher-level westerlies.

Physicochemical and structural characterisation of oil palm trunks (OPT) hydrochar made via wet torrefaction

This study evaluates the effect of wet torrefaction of OPT under autogenous pressures at 3 different relatively low temperatures (i.e. 180, 200, and 220 oC) and extended residence times (i.e. 3, 6, 9, 12, 18, 24, 48, and 72 h) on the hydrochar's physical, chemical, and structural properties. Logarithmic-like increase of HHV profile was observed at the highest temperature of 220 oC, in which a plateau was reached at 24 h. Between temperature and residence time, temperature gave a more significant influence on the characteristics of the produced biochar. The HHV of the biomass sample increases from 16.4 MJ kg−1 in raw OPT to the highest HHV of 26.9 MJ kg−1 when torrefied at 220 oC for 72 h. Van Krevelen analysis shows dehydration was the primary reaction pathway that occurred during wet torrefaction of OPT at 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h. Decarboxylation dominates the reaction when temperature and residence time was increased to 220 oC for 24 h, respectively. Further increasing the residence time to 48 and 72 h at 220 oC promotes demethylation as the dominant reaction. FTIR analysis reveals that most hemicellulose and parts of cellulose decomposed when OPT was subjected to lower temperature and/or residence time (i.e. 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h). However, increasing temperature to 220 oC and beyond 24 h resulted in carbon-rich and lignin-dense hydrochar, which was observed in powder XRD results where graphite nitrate peak at 2θ of 7.4o appears. Morphology analysis reveals that most of the hemicellulose and cellulose-rich parenchyma was removed when subjected to wet torrefaction at 220 oC for 24 h. The formation of microspheres from the repolymerisation of 5-HMF was observed in large quantities in OPT hydrochar treated at 220 oC for 72 h. Inorganic elemental analysis shows that wet torrefaction of OPT effectively removes K and Cl from the biomass. The removal of K increased with increased temperature, which may partially resolve the corrosion problems in combustion reactions related to silicate deposition. OPT hydrochar from WT under autogenous condition and relatively low temperature exhibits much more improved fuel properties compared to raw OPT.

Electrical resistivity structure in the Tocomar geothermal system obtained from 3-D inversion of audio-magnetotelluric data (Central Puna, NW Argentina)

The Tocomar Geothermal System is located in the Puna Plateau (NW Argentina), within the Central Puna Energy Hub, and is considered one of the most promising places to harness potential alternative of power and heat sources in the Central Andean Volcanic Zone (16-28 °S). It is related to the Calama-Olacapato-Toro lineament and to the Quaternary Tocomar volcanic centre. Moreover, it is surrounded by active and fossil geothermal manifestations, like hot-springs, travertines and siliceous sinter deposits. Despite some geological studies in the area, no geophysical investigations have targeted the geothermal fields along the Central Puna.In this work we present a 3-D inversion of audio-magnetotelluric data around the Tocomar Geothermal System. These data was obtained in the frequency range of 1000-0.1 Hz to map the main elements of the geothermal system (clay cap and potential reservoir) at depths of approximately 1000 m. To achieve this goal, previous geoelectrical studies, the local geology and the trend of the main structures were also considered. For the 3-D inversion process the ModEM code was used.The model shows a low-resistivity layer (less than 10 Ωm) at least 300 m thick, at a depth of about 200–500 m, aligned with both the strike of the Calama-Olacapato-Toro lineament and the local superficial geothermal manifestations (hot-springs and hydrothermally altered rocks). This low-resistivity layer is linked with the clay cap at the shallow depth of the geothermal reservoir. At depths greater than 800 m, a gradual increase in resistivity is observed related to a potential reservoir within the fractured Ordovician basement. The final 3-D resistivity model highly correlates with the conceptual models of high-temperature volcanic geothermal systems.

Estimating soil organic carbon levels in cultivated soils from satellite image using parametric and data-driven methods

ABSTRACT Soil organic carbon (SOC) is one of the key soil components for cultivated soils. SOC is regularly monitored and mapped to improve the quality, health, and productivity of the soil. However, traditional SOC-level monitoring is expensive for land managers and farmers. Estimating SOC using satellite imagery provides an easy, efficient, and cost-effective way to monitor surface SOC levels. The objective of this study was to estimate the surface SOC distribution in selected soils of Major Land Resource Areas (MLRA), 102A (Rolling Till Plain, Brookings County, SD), and 103 (Central Iowa and Minnesota Till Prairies, Lac qui Parle County, MN), using satellite imagery with different resolutions (Landsat 8 and PlanetScope). The dominant soils in the study area are Haplustolls, Calciustolls, and Endoaquolls, which are formed in silty sediments, local silty alluvium, and till. Landsat 8 and PlanetScope spectral bands were used to develop SOC prediction models. Parametric and data-driven methods were employed to predict the SOC. Multiple linear regression and Linear Spatial Mixed Model (LSMM) were used on the Landsat 8 and PlanetScope data. In addition to the parametric models, Regression Trees and Random Forest were also employed on both satellite data. The results showed that reduced LSMM provided the lowest RMSE, which are 0.401 and 0.367 for Landsat 8 and PlanetScope, respectively. Furthermore, the random forest has the highest RPD and RPIQ for Landsat 8 (RPD of 2.67 and RPIQ of 2.49) and PlanetScope (RPD of 2.85 and RPIQ of 3.7). In all cases, models obtained from PlanetScope are better than those obtained from Landsat 8.

Characteristics of the Sediment Gravity Flow Triggered by Wave-Induced Liquefaction on a Sloping Silty Seabed: An Experimental Investigation

The sloping silty sediments in estuarine deltas are frequently affected by extreme storms, and they are prone to liquefaction instability. The unstable liquefied sediments of the slopes can subsequently form a sediment gravity flow (SGF), which can seriously endanger offshore engineering facilities. To better understand the characteristics and mechanism of wave-induced liquefied sediment gravity flow (WILSGF), a flume experiment was conducted to reproduce the formation, movement, and deposition processes of the WILSGF and analyze their controlling factors using natural silty sediment samples collected from the Yellow River Delta in China. The results show that the mass of the WILSGF comes from the sediment in the liquefied layer, and the movement of the WILSGF in these experiments was significantly affected by the wave orbital velocity and the relative outflow position. At the initial stage of the formation of the WILSGF, the phase and amplitude of the WILSGF were the same as those of waves, and the maximum velocity of the WILSGF reached 2.39 cm/s. The velocity of the WILSGF decreased continuously with the downward evolution of the liquefaction interface. When the liquefaction depth reached its maximum value, there was no WILSGF. We also found that the median particle size of the WILSGF was greater than that of the original seabed due to wave-induced seabed coarsening and the intrusion of ambient water. This study has guiding significance for in-depth understanding and prediction of the geological hazards caused by WILSGF.

Genesis of Convolutions in Lacustrine Complexes in Regions with Comparatively Low (Baltic Shield) and High (Tien Shan) Paleoseismic Activity

Abstract —Structural and lithological comparison of intraformational plicative liquefaction deformations (convolutions) in Late Quaternary lacustrine complexes of the Baltic Shield (sediments of small glacial lakes) and the Tien Shan (sediments of a large stationary basin in the Issyk-Kul depression) is carried out in order to clarify their genesis. These regions have sharply different levels of seismotectonic activity, which makes it possible to most fully determine the role of a seismic factor in the formation of bedding disturbances. Convolutions in the Baltic Shield are represented by load casts, flame structures, pseudonodules, and regular folds with more pronounced anticlinal bends. It is shown that convolutions occur here only in the most liquefied soils (siltstones and fine-grained sands) with low cohesion and fluid permeability in the case of unstable (increased density and coarsening of the sediment from bottom to top) or neutral (homogeneous composition) stratification of weakly consolidated sediments, and the ratio of the widths of the synclinal and anticlinal parts of the folds (Ksyn) for these structures is 1.0–7.5. These signs point to the formation of disturbances because of a spontaneous instability or an instability initiated by weak mechanical influences in the sedimentary stratum under conditions of a normal vertical gradient of the sediment viscosity. Deformations in the second region are structures typical of the Baltic Shield, columnar structures of deep interpenetration of layers, diapirs, and clastic dikes. There are also flexural folds with Ksyn ≈ 1, which formed at a higher degree of sediment consolidation than the actual liquefaction structures. The convolutions of the Issyk-Kul depression are developed not only in sand–silty sediments but also in relatively lowly liquefied soils (clay, gravel, and pebbles). These structures formed under both unstable and stable density stratification of the sediment (for example, clay-on-sand), and Ksyn = 0.3–2.5. Thus, the formation of convolute structures in the Issyk-Kul depression is impossible without strong dynamic impacts on stratified sediments during their accumulation. The results obtained make it possible to substantiate the predominantly diagenetic (convective and landslide) genesis of convolutions in the lacustrine complexes of the Baltic Shield and the seismogenic genesis in the limnogenic deposits of the Tien Shan. A number of new criteria for identifying seismites are proposed, which determines the practical significance of the study.

Carbonaceous residues in the Southern Uplands accretionary prism of Ireland and Scotland

Carbonaceous residues occur in mudstones and turbidites of the Lower Paleozoic accretionary prism in Ireland and Scotland (Longford-Down, Southern Uplands). The accretionary prism was host to fluid migration during both the Lower Paleozoic and Carboniferous–Triassic, so the age of the carbonaceous fluids is uncertain. Raman spectroscopy data for the carbonaceous residues in the Lower Paleozoic rocks indicate palaeotemperatures similar to those measured in their host rocks, and much higher than those in the Carboniferous cover rocks or in residues in the cover rocks. These data show that residues in the prism rocks are of Lower Paleozoic age, and were not contributed by younger mineralizing fluids. The residues represent hydrocarbons generated from source rocks in the prism that were part of the Ordovician–Silurian deposits of the Iapetus Ocean.

Thermal imagery of woodland tree canopies provides new insights into drought-induced tree mortality

Our understanding of how water dynamics determines the probability of tree mortality during drought is incomplete. Here we help address this shortcoming by coupling approaches from the disciplines of ecophysiology, geophysics and remote sensing in a woodland ecosystem undergoing protracted drying. Water uptake and use strategies varied between the dominant canopy species of the ecosystem. At one extreme were species that tightly regulate their water status, which is broadly consistent with the definition of isohydry. The higher leaf temperatures revealed by thermal imagery of these isohydric species are likely a reflection of reduced latent cooling owing to a stringent control of transpiration rate. Where silty sediments occur in the root zone, this strategy may have the effect of limiting the water sources available to these species during prolonged drought because of an insufficient hydraulic gradient for water uptake. In contrast were species that allowed their water status to fluctuate, operating in a fashion more consistent with anisohydry. For these species, latent cooling owing to relatively high transpiration rates maintained leaf temperatures near, or below, the ambient air temperature. The resulting drawdown in leaf water potential between soil and leaves in these anisohydric species may generate a sufficient hydraulic gradient to enable water uptake from silty soil during seasonal or prolonged droughts. In this way the spatial distribution of fine textured soil could indicate areas where the isohydric hydraulic control strategy is disadvantageous during prolonged droughts or where annual soil water recharge has fallen below a critical threshold.

Layering and reservoir modeling of Silurian uppermost Tannezuft and Acacus reservoirs in the Tunisian Ghadames Basin: Inferred static model and prolific layers

Upper Silurian sediments of the uppermost Tannezuft Formation and the overlying Acacus A Unit in the Ghadames Basin of Southern Tunisia are considered as an important oil and gas target. For that, four wells, spanning these reservoirs, are evaluated herein. The study uses well logging tools via the Interactive Petrophysics (IP) software to determine hydrocarbon bearing layers. A static model is also inferred.The studied interval shows twenty-four sand bodies associated to the four petrophysical packages (T0 to T3) of the Uppermost Tannezuft and the nine petrophysical packages of the Acacus A (A1 to A9). Sand bodies show variable thicknesses (from 1.5 to 38m) and are laterally correlated following a North-West (NW) to South-East (SE) trend. They are composed of stacked thin bedded alternating sands and shales. The petrophysical packages A5 (A5-1 and A5a-2) and A9 (A9a and A9b) of the Acacus A are identified as the most interesting layers.The computed petrophysical parameters of the sand bodies reveal a clay volume ranging between 8% and 29% with an average of 22%. The effective porosity ranges from 10% to 29%. Relatively high-water saturation is depicted in most sand bodies reaching up to 63%. In addition, and due to the complex matrix composition, relatively low permeabilities characterize reservoirs zones (an average of 20mD). The integration of all data using the IP software reveals significant accumulations of gas condensates. The volumetric assessment via static modeling using the Petrel software indicates that the A9b unit is, predominantly, the most prolific reservoir.

CMAS corrosion and thermal cycling fatigue resistance of alternative thermal barrier coating materials and architectures: A comparative evaluation

The corrosion of ceramic thermal barrier coatings (TBCs) by molten silicate deposits, usually known as “CMAS” from their main constituents (CaO-MgO-Al2O3-SiO2), is an issue of increasing concern in modern gas turbines as the turbine inlet temperatures are increased to enhance thermodynamic efficiency. Because conventional ZrO2-7wt%Y2O3 (7YSZ) dissolves quite readily in a CMAS melt, many alternative materials have been proposed, but there are not many comparative studies among them. Multi-layer architectures featuring a tougher 7YSZ bottom layer and a more brittle, but more CMAS corrosion-resistant top layer have also been proposed; therefore, a comparison among these architectures is also in order. In this paper we studied comparatively the resistance to CMAS corrosion and to thermal cycling fatigue (an essential pre-requisite for any TBC system) of Gd2Zr2O7, ZrO2–55wt%Y2O3 and Gd/Yb/Y co-doped ZrO2, both in the form of single, dense-vertically cracked (DVC) layers deposited by plasma spraying onto an MCrAlY bond coat, and as top layers with a bottom layer of either porous or DVC 7YSZ. It was found that Gd2Zr2O7 resists CMAS corrosion, without any grain-boundary dissolution, slightly better than does ZrO2–55wt%Y2O3. They both develop a solid Gd- or Y-apatite layer (respectively) at the interface with the CMAS melt, driven by the rather large difference in optical basicity between these compounds and CMAS itself, but the Y-apatite layer is less continuous and, therefore, a bit less protective. Gd/Yb/Y co-doped ZrO2, instead, suffers as much grain-boundary dissolution in contact with molten CMAS as does 7YSZ. A Gd2Zr2O7/porous 7YSZ system would therefore exhibit simultaneously high resistance to CMAS dissolution and to thermal cycling fatigue, although there is a risk that the CMAS melt might infiltrate the segmentation macro-cracks and the microcracks of the Gd2Zr2O7 layer and undermine the porous 7YSZ bottom layer.

Lithological Signatures of Early Carboniferous Events in the Northeastern Siberian Craton (Western Verkhoyansk Region)

Abstract The paper focuses on presumable sources of coarse carbonate material transported into the Visean Northern Kharaulakh basin. The sand to pebble components of the Krestyakh conglomerate unit originated by medium and distant transport by debris flows (turbidity currents) along submarine canyons from the place of their initial littoral deposition to relatively deep accommodation basins. The carbonate material was most likely derived from Ordovician, Silurian, and Devonian sediments, which are currently represented by their analogs in Kotelny Island. The sediments of the Northern Kharaulakh basin store a record of two geological events: (1) middle Visean collision of Siberia with the Laurussian supercontinent and rifting of some terranes off the Siberian сraton, and (2) late Visean collision of the Kara terrane with the northern margin of Siberia.

Isotopic signatures of magmatic fluids and seawater within silicic submarine volcanic deposits

Addressing questions of magma ascent, volcanic eruption dynamics, and volatile fluxes requires accurate measurement of magmatic water concentrations in volcanic glass. Glass in volcanic rocks in the deep-sea environment can experience rehydration (addition of external water) across a range of temperatures, and from different sources (e.g., seawater and hydrothermal fluids), which can lead to overestimation of magmatic-H2O. This study used H and O isotopes (δD and δ18O) to identify sources of rehydration in pumice and lava from the deep-sea 2012 volcanic eruption of Havre volcano, Kermadec Arc, and from a variety of older (tens to thousands of years) silicic submarine deposits across the Izu-Bonin Arc and Lau Basin. We find that old seafloor pumices were rehydrated up to 6 wt.% H2O by the diffusion of cold seawater over 100s to 1000s of years, and thus, enriched in δD, bulk-δ18O, and water-in-glass (wig) δ18O up to −30‰, +9‰ and −5‰ respectively. By contrast, the young Havre deposits exhibit a much wider range of both isotopic enrichment and depletion with δD = −50 to −120‰, δ18Obulk = +5.7 to +6.2‰, and δ18Owig = −10 to +4‰, depending on the eruptive units. Using magmatic degassing and vapor δD-H2O modeling, a volatile-melt δ18O-geothermometer, and previous textural studies of Havre 2012 deposits, we identify multiple high-temperature rehydration sources, timescales, and mechanisms. δD-depleted pumices were likely rehydrated by vapor co-existing in bubbles and vesicles at temperatures around and below the glass transition (320–670 °C) over timescales of a few minutes during clast cooling above the eruptive vent. Conversely, δD-enriched Havre pumice and lava from different deposits were most likely rehydrated by heated, δD-enriched seawater at glass temperatures > 100 °C. These results provide a natural confirmation of recent experimental findings, which tackle the fundamentals of H and O diffusion and isotope exchange in silicate materials at temperatures of 100–400 °C. Addressing the effects of rehydration, and thus accuracy of H2O measurements, in volcanic glasses and crystals is important for improving our understanding of conduit processes during volcanic eruptions, and the kinetics of glass hydration and alteration.

Protocol for selecting exemplary silicate deposit compositions for evaluating thermal and environmental barrier coatings

AbstractA protocol for selecting representative silicate compositions for comparative testing of gas turbine coating materials is presented. It begins with a curated dataset of compositions of engine deposits and naturally occurring siliceous debris including volcanic ashes, sands, and dusts. The compositions are first reduced to the five major oxides—those of Ca, Mg, Fe, Al, and Si—and then distilled further using principal component analysis and k‐means clustering. The process ultimately yields four classes of possible deposits with common chemical characteristics. Each class is represented by a composition centroid and a range in Ca:Si ratios. Key thermophysical properties of the possible deposits are calculated and related to the glass network connectivity, characterized by the Si:O ratio. Finally, deposits from each of these classes are compared in terms of their reactions with prototypical thermal and environmental barrier oxides, with due consideration of the effects of composition variations within each deposit class. The protocol is, in principle, adaptable to datasets compiled by OEMs and researchers in gas turbine coatings.

A Comprehensive Methodology for Monitoring Evaporitic Mineral Precipitation and Hydrochemical Evolution of Saline Lakes: The Case of Lake Magadi Soda Brine (East African Rift Valley, Kenya).

Lake Magadi, East African Rift Valley, is a hyperalkaline and saline soda lake highly enriched in Na+, K+, CO32–, Cl–, HCO3–, and SiO2 and depleted in Ca2+ and Mg2+, where thick evaporite deposits and siliceous sediments have been forming for 100 000 years. The hydrogeochemistry and the evaporite deposits of soda lakes are subjects of growing interest in paleoclimatology, astrobiology, and planetary sciences. In Lake Magadi, different hydrates of sodium carbonate/bicarbonate and other saline minerals precipitate. The precipitation sequence of these minerals is a key for understanding the hydrochemical evolution, the paleoenvironmental conditions of ancient evaporite deposits, and industrial crystallization. However, accurate determination of the precipitation sequence of these minerals was challenging due to the dependency of the different hydrates on temperature, water activity, pH and pCO2, which could induce phase transformation and secondary mineral precipitation during sample handling. Here, we report a comprehensive methodology applied for monitoring the evaporitic mineral precipitation and hydrochemical evolution of Lake Magadi. Evaporation and mineral precipitations were monitored by using in situ video microscopy and synchrotron X-ray diffraction of acoustically levitated droplets. The mineral patterns were characterized by ex situ Raman spectroscopy, X-ray diffraction, and scanning electron microscopy. Experiments were coupled with thermodynamic models to understand the evaporation and precipitation-driven hydrochemical evolution of brines. Our results closely reproduced the mineral assemblages, patterns, and textural relations observed in the natural setting. Alkaline earth carbonates and fluorite were predicted to precipitate first followed by siliceous sediments. Among the salts, dendritic and acicular trona precipitate first via fractional crystallization—reminiscent of grasslike trona layers of Lake Magadi. Halite/villiaumite, thermonatrite, and sylvite precipitate sequentially after trona from residual brines depleted in HCO3–. The precipitation of these minerals between trona crystals resembles the precipitation process observed in the interstitial brines of the trona layers. Thermonatrite precipitation began after trona equilibrated with the residual brines due to the absence of excess CO2 input. We have shown that evaporation and mineral precipitation are the major drivers for the formation of hyperalkaline, saline, and SiO2-rich brines. The discrepancy between predicted and actual sulfate and phosphate ion concentrations implies the biological cycling of these ions. The combination of different in situ and ex situ methods and modeling is key to understanding the mineral phases, precipitation sequences, and textural relations of modern and ancient evaporite deposits. The synergy of these methods could be applicable in industrial crystallization and natural brines to reconstruct the hydrogeochemical and hydroclimatic conditions of soda lakes, evaporite settings, and potentially soda oceans of early Earth and extraterrestrial planets.

Pore-scale observations of natural hydrate-bearing sediments via pressure core sub-coring and micro-CT scanning

Both intra-pore hydrate morphology and inter-pore hydrate distribution influence the physical properties of hydrate-bearing sediments, yet there has been no pore-scale observations of hydrate habit under pressure in preserved pressure core samples so far. We present for the first time a pore-scale micro-CT study of natural hydrate-bearing cores that were acquired from Green Canyon Block 955 in UT-GOM2-1 Expedition and preserved within hydrate pressure–temperature stability conditions throughout sub-sampling and imaging processes. Measured hydrate saturation in the sub-samples, taken from units expected to have in-situ saturation of 80% or more, ranges from 3 ± 1% to 56 ± 11% as interpreted from micro-CT images. Pore-scale observations of gas hydrate in the sub-samples suggest that hydrate in silty sediments at the Gulf of Mexico is pore-invasive rather than particle displacive, and hydrate particles in these natural water-saturated samples are pore-filling with no evidence of grain-coating. Hydrate can form a connected 3D network and provide mechanical support for the sediments even without cementation. The technical breakthrough to directly visualize particle-level hydrate pore habits in natural sediments reported here sheds light on future investigations of pressure- and temperature-sensitive processes including hydrate-bearing sediments, dissolved gases, and other biochemical processes in the deep-sea environment.

Adsorption of Cd(II), Pb(II) and Ni(II) onto natural sediments from the Gulf of Aqaba Jordan

ABSTRACT Carbonate and silicate natural sediments from the gulf of Aqaba-Jordan have been used to study adsorption of nickel(II), lead(II) and cadmium(II) ions, separately, from aqueous solutions. Both sediment types were characterised by FTIR, XRD and SEM. Adsorption of these metal ions were investigated using batch technique as a function of initial concentration of metal cations, adsorbent dosage, initial pH, contact time and temperature. The metal uptake enhanced with increasing pH until a maximum removal at pH 8.0 for Ni, 5.0 for Pb and 6.0 for Cd. Kinetic study shows that the adsorption obeys a pseudo-second-order kinetic model. The adsorption isothermal behaviour of the metal ions uptake onto carbonate and silicate sediments were examined using Langmuir, Freundlich and Dubinin–Radushkevich (D-R) adsorption isotherms. The maximum adsorption capacity obtained by Langmuir isotherm model (25°C) onto carbonate sediments was 2.64, 4.41 and 4.15 mg/g for Ni(II), Pb(II) and Cd(II), respectively. While the adsorption onto silicate sediments was 2.57, 3.56 and 3.15 mg/g, respectively. These adsorption values on carbonate sediments comparing to silicate sediments were attributed to some physical and chemical properties of both sediments, especially the higher permeability and porosity for carbonate sediments. Thermodynamic functions, ΔG*, ΔH* and ΔS* were determined. Negative ΔG* values show that the adsorption process of these metal ions onto both sediments is spontaneous. While the positive ΔH* values indicate that adsorptions are endothermic, and the positive values of entropy ΔS* suggest that the adsorption is driven by increasing of randomness. Conservative calculations using the data in this study and some other from the literature shows that the shallow sediments would adsorb roughly 7 × 10 16 kg of heavy metals that may be introduced into the sea through different anthropogenic activities.

Microspheres in the Silurian of the Altai Mountains: Morphology, Chemical Composition, Biomineralization, and Genesis

The study of Silurian sediments in the central part of the Altai Mountains (Gorny Altai) by limestone dissolution has revealed two groups of spherical objects; large microspheres 90–120 µm and small nanofossils (nanospheres) 5–18 µm in diameter. Their double-layered walls are composed of standard-sized siderite microcrystals replaced by goethite. The Altai microspheres have a low Ca content (<0.5 wt %) so cannot be interpreted as calcispheres. The Altai Silurian microspheres and nanofossils (nanospheres) are tentatively attributed to biomineralized remains of loricae (shell-like envelopes) of various euglenoid alga generations.

Isotopic geochemical characteristics and identification indexes of shale gas hydraulic fracturing flowback/produced water

China is rich in shale gas resources, which are mainly distributed in densely populated southern marine carbonate areas. The geological and surface conditions are complex, the ecological environment is fragile, and water resources are scarce or unevenly distributed. Therefore, large-scale fracturing mining has high pressure of water resources utilization and serious risk of water environment pollution. In this paper, the geochemical characteristics of traditional and non-traditional stable isotopes such as hydrogen, oxygen, boron, lithium, strontium in shale gas hydraulic fracturing flowback/produced water (FP water) were comprehensively analyzed. The results show that, the hydrogen and oxygen isotopic composition of the FP water in Sichuan Basin, China has similar evolution trend with the produced water of conventional wells from Cambrian, Permian and Triassic Xujiahe, Jialingjiang and Leikoupo formations, but different from that of the Sinian conventional produced water. It indicates that the FP water in Sichuan Basin is a mixture of fracturing injected fluid and formation brine retained in Silurian shale. The saline end member is close to the formation water of Cambrian, but with higher δ11B values. The FP water in Sichuan Basin has δ11B values close to that of the Marcellus FP water, and both are derived from the evaporated seawater. The δ11B values of FP water in Sichuan Basin have overlap with that of the conventional produced water from different strata, so it can not be precisely distinguished. However, the δ11B and B/Cl values of the FP water in Sichuan Basin can be clearly distinguished from the river and the FP water from non-marine facies shale in Qaidam Basin. The FP water in Sichuan Basin has slightly higher δ7Li values than that of the Marcellus FP water, but has overlap with that of the Yangtze River. The average value of 87Sr/86Sr of FP water is 0.7197 in Weiyuan and 0.7193 in Changning, which is much higher than that of the produced water from conventional wells in different formations. This is because the Silurian shale is affected by terrestrial siliceous sediments and the underlying Sr-rich fluids. As a result, 87Sr/86Sr values measured in the Silurian strata in southern Sichuan Basin are high, which makes 87Sr/86Sr values become an effective index to distinguish shale gas fracturing FP water from conventional gas well produced water and shallow groundwater in Sichuan Basin.

Study of Unconventional Reservoirs in the North-East of Sakhalin

According to the results of geological fieldworks in the north-east of Sakhalin Island on the Schmidt Peninsula and in the Pogranichny Depression, Cenozoic outcrops were studied in order to explore the siliceous deposits of the Pilskaya formation. Samples were taken for analytical studies, small structural forms that are indicators of tectonic stress, were studied. It is shown that the fracture intensity depends on the lithology, the position of the observation point relative to disjunctive and/or plicative structures. A sharp nonuniformity of the stress field in the vicinity of the Pogranichny Depression is noted, reflected in the nature of the bedding planes, structural discontinuities and parageneses.