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Purpose Small-scale runoff and soil redistribution processes are important factors in rainfall simulation studies. Therefore, the main objective of this study is to examine the feasibility of rare earth oxide (REO) tracking combined with 3D surface modelling and soil crust analysis by scanning electron microscopy. Materials and methods Four 40 mmh−1 rainfall simulations (divided into two blocks) were conducted on a Luvisol sample at 9% slope steepness. In a block, two successive simulations were run on a tilled, and then, on a crusted surface. Before the first rainfall simulation of a block, the tilled surface was prepared by hoeing and application of four REO tracers (Pr6O11 Sm2O3, Ho2O3 and Yb2O3) to the freshly tilled surface. REOs divided the parcel into two back, and two front sub-parcels. The REO runoff content was measured by XRF, while the redistributed REOs were measured by SEM on polished crust samples taken after the second experiment in each block. Additionally, before and after 3D models of the surface were created for determining runoff direction and redistribution pattern. Results and discussion According to the REO content of the soil loss samples, the soil washed down from the front sub-parcels, while back parcels started contributing to soil loss only during the second block experiments. The surface microtopography changed between the experiments. The runoff path from the back sub-parcels headed to one side of the parcel. This strong, cross-side runoff pattern explained the lack of the back sub-parcel REOs in the soil loss. Meanwhile, in the crust samples, several forms of the redistribution were identified. The REOs of the back sub-parcels were found in the samples that were collected in runoff paths, and the leaching pattern became traceable with REOs. Moreover, we were able to reconstruct the original surface easily on SEM images. Conclusions Small-scale redistribution and the role of the microtopography of the surface should be considered as an erosional factor in erosion studies in a more detailed way. Behaviour of the REO as a soil sediment tracer has great potential, although questions remain. REO tracing applied with runoff direction modelling and SEM analysis of soil crust samples was suitable to monitor the runoff path, and explain the soil redistribution pattern horizontally and vertically.

A temporary solution to massive anthropogenic CO2 emissions can be the capture of industrial CO2 from flue gas and sequestering it in geological formations. For safe and effective storage of CO2, interaction processes in the rock-pore fluid–CO2 system should be known. Investigation of natural CO2 accumulations provides valuable examples to what physical and chemical effects could be expected during CO2 influx at future CO2 storage sites. One of the key controlling factors of the processes occurring in natural CO2 reservoirs is the lithology of the storage rocks, which is primarily determined by the formation conditions of these rocks. In this respect, the lithologies of individual CO2 accumulation areas influence the processes between the host rock, the pore fluid, and the CO2 in different ways. In the current study, we focus on a well-studied natural CO2 storage reservoir, namely the Mihályi-Répcelak area, NW Hungary. We provide insight into the so far unstudied conglomerate reservoirs that represent a stratigraphically deeper reservoir unit with significantly different lithology and pore water compositions compared to the sandstone reservoirs. Our results indicate that dawsonite /NaAlCO3(OH)2/ formation also affected the conglomerate reservoirs, which indicates that at least part of the CO2 could be trapped in mineral form. An important role of salinity in reducing the CO2 mineral trapping capacity of the storage system is also demonstrated. Furthermore, H isotope analysis of diagenetic kaolinite was applied to trace the origin of the pore water that was present during the rock formation. Based on the data, dawsonite formation was induced by the flux of meteoric water that infiltrated during a warm and humid period and mixed with ascending CO2.

Particle size and shape are among the most important properties of sedimentary deposits. Objective and robust determination of granulometric features of sediments is a challenging problem, and has been standingin the focal point of sedimentary studies for many decades. In this study, we provide an overview of a new analytical approach to characterize particles from thin sections of sandstones by using 2D automated optical static image analysis. The analysed samples are originated from the turbiditic Lower Pannonian (Upper Miocene) sediments of Szolnok Formation. Sandstone samples were analysed from 1,500 to 2,250 m depth range. According to the previous studies: the detrital components are quartz, muscovite, dolomite, K-feldspar and plagioclase. Diagenetic minerals are mostly carbonates (calcite, Fe-dolomite, ankerite, siderite), clay minerals (illite, kaolinite), ankerite, siderite and kaolinite. As the discussed Szolnok Formation is considered as a potential CO2 storage system (to reduce atmospheric CO2 concentration), special attention has to be paid on grain size and shape alteration evaluation, since pore water-rock interactions affected by CO2 injection may cause changes in particle properties. The primarily aim of the present study was to develop a method for effective characterization of the particle size and shape of sandstones from thin sections. We have applied a Malvern Morphologi G3SE-ID automated optical static image analyser device, what is completed with a Raman spectrometer. Via the combined analysis of granulometry and chemical characterization, it was obvious that there were specific relationships among various grain shape parameters (e.g., circularity values correlate to width and length ratios, as well as to convexity) and the results indicated that based simply on particle shapes, muscovites can be effectively separated from other minerals. Quartz and feldspar grains showed the highest variability in shapes as these are detrital ones, and sometimes arrived as lithic fragments from which other parts were dissolved The size and shape of carbonate minerals depends highly on the original pore size and shape because these minerals are mainly diagenetic. The shape of detrital dolomites depends on diagenetic ankerite, as it replaces the rim of dolomites.

Sedimentary transport processes and pore water- rock interaction may cause dissolution and precipitation of different minerals. These processes influence the particle shapes and grain size. In this paper we analyzed thin sections of sandstones with 2D image analysis (Morphologi G3ID) to specify the most characteristic shapes of the different minerals and pores.The studied samples originated from the Pannonian Basin, which was filled by delta and fluvial sediments in the Late Miocene. The previous studies show that the detrital minerals are quartz, muscovite, dolomite, K-feldspar and plagioclase. The main diagenetic minerals are carbonates (calcite, Fe-dolomite, ankerite, siderite) and clay minerals (illite, kaolinite).We measured the sandstone samples by Morphologi G3ID, which is a method of 2D image analysis combined with chemical characterization (Raman spectrometer). The results show that HS circularity (high sensitive) is in correlation with aspect ratio, furthermore, convexity and HS circularity also showed interdependency. According to the results, based on morphological parameters muscovites form a well separable group (HS circularity ~ 0.36; aspect ratio ~0.36, convexity ~0.86). The quartz and feldspar grains show high variability of the shapes (HS circularity: ~0.2-0.9, aspect ratio: 0.2-1, convexity: 0.8-1), because these minerals are detrital minerals and sometimes arrived as lithic fragments, from which one part dissolved. The shape of carbonate minerals can be described with the following parameters: HS circularity 0.3-0.8, aspect ratio 0.3-0.8 and convexity 0.8-1. The shape of carbonate minerals depends on the original pore size and shapes, because these minerals are mainly of diagenetic origin. Dolomite is detrital, however the shape of these grains depends on the diagenetic ankerite, because ankerite replaces the rim of dolomite.

One of the challenges of the present century is to limit the greenhouse gas emissions for the mitigation of climate change which is possible for example by a transitional technology, CO2 geological storage. Clay minerals are considered to be responsible for the low permeability and sealing capacity of caprocks sealing off stored CO2. However, their reactions are not well understood for complex simulations. This work aims to create a kinetic geochemical model of Na-montmorillonite standard SWy-2 supported by solution and mineral composition results from batch experiments. Such experimentally validated numerical models are scarce. Four 70-hours experiments have been carried out at atmospheric conditions, and with CO2 supercritical phase at 100 bar and 80 °C. Solution samples have been taken during and after experiments and their compositions were measured by ICP-OES. The treated solid phase has been analyzed by XRD and ATR-FTIR and compared to in-parallel measured references (dried SWy-2). Kinetic geochemical modelling of the experimental conditions has been performed by software PHREEQC. Experiments and models show fast reactions under the studied conditions and increased reactivity in presence of scCO2. Solution composition results cannot be described by the change of the uncertain reactive surface area of mineral phases. By considering the clay standard’s cation exchange capacity divided proportionally among interlayer cations of Na-montmorillonite, the measured variation can be described on an order of magnitude level. It is furthermore indicated that not only the interlayer cations take part in this process but a minor proportion of other, structural ions as well, differently in the reference and scCO2 environments.

Eleven unique core samples from the National Radioactive Waste Repository of Hungary, Bataapati were studied in this work. The samples all cross the granite–concrete interface and have been drilled from around 275 m depth from the surface, 1–15 months after concrete injection. Phase analytical techniques, optical microscopy, SEM-EDS and Raman-spectroscopy were used for the analysis of interactions between granitic rock and cementitious building material. Newly formed phases, Ca-carbonates and titanite, were observed at the interface. Carbonation may reduce the porosity and permeability in the contact zone. The presence of titanite indicates the changing geochemical and thermodynamical constrains along the reaction front of granite–concrete, furthermore, it may help in the validation of future geochemical models. The cementitious material is seen to penetrate among the sheets of biotite mineral in granite which process is probable to cause the attachment of granite and concrete.

Natural CO2 reservoirs provide an opportunity to study long-term fluid-rock interactions, which are essential to reassure the safety of mineral storage of carbon-dioxide. The Mihalyi-Repcelak field (Pannonian Basin, Central Europe) is one of the largest natural CO2-bearing reservoirs in Europe (25 Mt). The CO2 was trapped in Neogene sandstones, which contain various carbonate minerals (dolomite, ankerite, siderite, dawsonite). To reveal the origin of the parent fluid, from which these minerals precipitated, dawsonite and siderite were separated by a new physical method to minimise the uncertainties in the analysis of their stable isotope composition. The δ13CDaw values range from +1.3‰ to +1.6‰ and the calculated δ13CCO2 values in equilibrium with dawsonite (−4.8‰ - –2.0‰) overlap with the carbon isotope compositions of the local CO2 and the European Subcontinental Lithospheric Mantle (−3.9‰ - –2.1‰). This indicates that the dawsonite-forming CO2 had a magmatic origin. The siderite data indicates that some formed from the magmatic CO2, possibly simultaneously with dawsonite (−6.0‰ - –3.9‰), whereas the rest (−8.4‰ - –6.1‰) formed either from a fractionated CO2 with magmatic origin or before the CO2 invasion. The hydrogen isotope composition of structural OH− of dawsonite (−57‰ to −74‰) was determined and was used to estimate the origin of the interacting porewater. The calculated porewater data (δD: −69‰ - –103‰ and δ18O: −1.4‰ - +4.7‰) indicate that the parent fluid was meteoric water modified by water-rock interaction. Our data allows estimation of the total amount of CO2 stored in the dawsonite-bearing sandstone reservoir to be 25 kg/m3, well in line with previous modelling works, which gives a total of 2.01 × 106 t of CO2, higher than previous estimates. We suggest that individual mineral analysis complemented by hydrogen isotope analysis is to be employed to effectively trace in-reservoir fluid-rock interactions in CO2 reservoirs and provide valuable input data for geochemical modelling for better predicting conditions for mineral storage of CO2.

When CO2 is injected into a subsurface reservoir, it undergoes structural-stratigraphic, residual, dissolution and mineral trapping mechanisms. Among these, the most permanent and preferable is the mineral trapping, in which carbonate minerals build the CO2 into their structures. In this study the amount of CO2 trapped in minerals was estimated from both analytical data of and thermodynamic geochemical models for a natural CO2 occurrence. Models underestimate the amount of trapped CO2 to be 0.004 tons/m3 reservoir in comparison with measured amount of dawsonite and other carbonates in rock samples indicating that 0.02-0.18 tons CO2 is trapped in one m3 reservoir.

Stable isotope systems provide exceptional insight into fluid-solid interactions occurring in the sub-surface. We provide detailed insight into the stable isotope distribution of carbonate minerals in a natural CO 2 reservoir system from Mihalyi-Repcelak area, NW-Hungary. Several types of measurements and calculations have been applied for the estimation of CO 2 and H 2 O isotopic composition in equilibrium with dawsonite. The estimated δ 13 C of CO 2 exhibit values around -4.5 to -2.6 ‰ overlapping with assumed magmatic values and the presently measured gas data confirming magmatic origin, whereas we may assume that the water present during carbonate formation likely had meteoric origin.

Low permeability caprock prevents migration of injected CO 2 towards the surface and potable water reservoirs. As a result of geochemical reactions among caprock minerals and CO 2 -saturated pore water, physical properties such as porosity, permeability and tortuosity may change, which could affect the sealing capability of caprocks. Due to the common high clay mineral content of caprocks, the reactivity of these minerals should be well-studied at CO 2 -saturated reservoir conditions. The main aim of this study is to understand better the geochemical behavior of CO 2 –brine–clay mineral system by using laboratory experiments at reservoir conditions on reference clays.

The caprock is the only physical barrier in the migration path of CO2 during CO2 geological storage. For this reason, caprock integrity is one of the most important factors regarding the long-term safe underground storage of CO2. As a result of geochemical reactions, among the caprock minerals and CO2 saturated pore water, the physical properties of caprocks such as porosity and permeability may change, which could affect their sealing capacity. Natural CO2 occurrences can help to understand these long-term reactions under storage conditions on geological timescale.

The purpose of this study was to investigate the results of re-interpreted old well-logs and porosity and permeability measurements of core samples from a natural CO 2 occurrence in NW-Hungary. The reservoirs formed in Neogene sediments over a basement high. We compared the estimated physical properties based on well logging and the results of core sample analysis. The goal of our investigation was to give a distribution of hydrogeological properties in the in Mihalyi –Repcelak area. We outlined the paleoenvironment of the reservoirs and caprocks searching for the explanation of the formation of this natural CO 2 storage.

The Special Collection of papers in this issue of Astrobiology provide an overview of the characteristics and potential for future exploration of the Ojos del Salado volcano, located in the Andes Mountains in front of the Atacama Desert in northern Chile. The main benefits of this site compared with others are the combination of strong UV radiation, the presence of permafrost, and geothermal activity within a dry terrain. The interaction between limited snow events and wind results in snow patches buried under a dry soil surface. This leads to ephemeral water streams that only flow duringdaytime hours. On this volcano, which has the highest located subsurface temperature monitoring systems reported to date, seasonal melting of the permafrost is followed by fast percolation events. This is due to the high porosity of these soils. The results are landforms that shaped by the strong winds. At this site, both thermal springs and lakes (the latter arising from melting ice) provide habitats for life; a 6480m high lake heated by volcanic activity shows both warm and cold sediments that contain a number of different microbial species, including psychrophiles. Where the permafrost melts, thawing ponds have formed at 5900m that is dominated by populations of Bacteroidetes and Proteobacteria, while in the pond sediments and the permafrost itself Acidobacteria, Actinobacteria, Bacteroidetes, Patescibacteria, Proteobacteria, and Verrucomicrobia are abundant. In turn, fumaroles show the presence of acidophilic iron-oxidizers and iron-reducing species. In spite of the extreme conditions reported at Ojos del Salado, this site is easily accessible., Comment: Accepted in Astrobiology Special Issue 2020. 04. 10

The volume of soil organic matter (SOM) changes, owing to variations in tillage systems. Conservation tillage (CT) is a useful method for recovering the SOM content of crop fields. However, little is known about the SOM composition of silt- and clay-associated and aggregate-occluded organic matter (OM). The present study aimed at determining the SOM compositions of various SOM fractions in the same Luvisol in a native forest and under ploughing and CT. SOM fractions (silt and clay associated, sand and aggregates associated, restricted OM) were characterized using diffuse reflectance Fourier transform infrared (FTIR) spectroscopy. The size of both the aggregate-occluded and resistant SOM pools increased, owing to the shift in the tillage system to CT for 15 years. As a general trend, the soil organic carbon content was inversely proportional to aromaticity under both crop fields, which supported the preferential mineralization of aliphatic components in each fraction. The shift in the tillage system could trigger rapid qualitative changes even in the stable restricted carbon pools, nevertheless, it was difficult to distinguish between the role of OM and the mineral composition in the FTIR spectra. In particular, the clay-related organic-mineral complexes could trigger difficulties in the traditional interpretation methods.

A study was conducted on the sorption of 17α-ethynylestradiol (EE2) on five soils formed under different redox conditions: an Arenosol (A_20) with fully aerobic conditions, two Gleysol samples (G_20 and G_40) with suboxic and anoxic conditions and two Histosols (H_20 and H_80) with mostly anoxic conditions. The soils were characterized on the basis of total organic carbon (TOC), specific surface area (SSA) and the Fourier transform infrared spectra of the humic acid and humin fractions (the soil remaining after alkali extraction) of the soil. The maximum adsorption capacity of the soils (Qmax) ranged from 10.7 to 83.6 mg/g in the order G_20 > H_20 > G_40 > A_20 > H_80, which reflected the organic matter content of the soils. The sorption isotherms were found to be nonlinear for all the soil samples, with Freundlich n values of 0.45–0.68. The strong nonlinearity found in the adsorption of the H_80 samples could be attributed to their high hard carbon content, which was confirmed by the high aromaticity of the humin fraction. The maximum sorption capacity (Qmax) of the soils did not increase indefinitely as the organic carbon content of the soils rose. There could be two reasons for this: (i) the large amount of organic matter may reduce the number of binding sites on the surface, and (ii) the decrease in SSA with increasing soil OC content may limit the ability to adsorb EE2 molecules. In anaerobic soil samples, where organic matter accumulation is pronounced, the amount of aromatic and phenolic compounds was higher than in better aerated soil profiles. Strong correlations were found between the amount of aromatic and phenolic compounds in the organic matter and the adsorption of EE2 molecules, indicating that π-π interaction and H-bonding are the dominant sorption mechanisms.