This study examined the evolution of trace metal and metalloid concentrations in the Cassidaigne canyon water column (Mediterranean Sea), at the Gardanne alumina plant discharge area, between 2016 and 2024. Following the 2015 ban on solid waste discharge, the plant progressively switched to the discharge at sea of a regulatory clarified effluent, resulting from filter-presses, CO2 treatment and biological unit implementations. Several anomalies in element concentrations at discrete depths in the water column above the outfall (station L1) reflected local environmental influences, such as submarine groundwater discharges and lithogenic inputs, including mistral-induced upwelling, remobilizing sediment. From 2016 to 2021, Al concentrations below 200 m depth resulted from the effluent-seawater mixing (the plume) and subsequent metals and metalloids removal and/or release during hydrotalcite particles formation and dissolution. Concretions at the outfall of the effluent (330 m depth) stopped forming after introduction of the CO2 treatment of the effluent in 2018. Despite occasional biological treatment disruptions leading to increased Al, V, and Cu concentrations at sea in 2020 and 2021, the effluent's chemical footprint remained globally confined in the first hundred meters above the outfall, without broader upper water column impact. Deep Al anomalies at a distant site (station K) in the canyon axis also indicated potential local remobilization from legacy bauxite deposits. Overall, both the plume and the historical residues appeared as localized but distinct sources of contamination. Particular renewed attention emerged from monitoring committees regarding ancient deposits, the spatial extent of which in the canyon far exceeds the chemical footprint of the effluent.

In the context of evaluating the environmental impact of deep-sea tailing practices, we conducted a case study on the Bayer effluent released into the Mediterranean Sea by the French Gardanne alumina plant. This effluent results from the filtration of red mud, which has previously been discharged into the Cassidaigne canyon for 55 years. In 2015, regulatory changes permitted the released of a filtered effluent instead of the slurry. This paper investigated the chemical impact on seawater composition a few months after this change. High metal concentrations were found in the upper 10 m above the outfall, i.e. the plume where the effluent mixes with seawater and forms hydrotalcite particles and concretions. Elevated Al concentrations at station L1 above the outfall indicated the plume presence and potential hydrotalcite dissolution up to 200 m depth, while a more distant station (L2) showed less impact, suggesting further Al remobilization from red muds previously deposited on the seafloor. Generally, metals and metalloids concentrations were within Mediterranean background levels, with some anomalies possibly linked to local submarine groundwater discharge.

The generation and migration of hydrogen and methane in serpentinizing environments represent fundamental processes with implications for deep carbon cycling, the origin of life, and emerging carbon-free energy resources. Here we present an integrated geochemical study of gas emissions from the Bulqiz & euml; chromite mine in Albania, where exceptional underground access to depths exceeding 1000 m enables direct investigation of one of Earth's most intense natural hydrogen systems (similar to 200 tones H-2/year). Through a comprehensive analysis of bulk and clumped isotopes, noble gases, molecular compositions, and structural controls, we report a novel occurrence of radiocarbon-bearing methane (3.76 +/- 0.06 pMC; similar to 26 ka) in any ophiolite globally. This discovery, combined with modern water ages (3H = 3.5 TU; 14C-DIC = 95.8 pMC) yet ancient gas signatures, reveals a dramatically decoupled fluid systems where meteoric water circulates rapidly within the mine while gas migrates slowly from depth. Methane clumped isotopes (Delta 13CH(3)D = 2.52 +/- 0.26 parts per thousand; Delta 12CH(2)D(2) = 9.95 +/- 1.6 parts per thousand) indicate a lack of isotopic equilibrium with H-2 (delta D-H-2 = -743.5 +/- 1.1 parts per thousand; Delta DD = 255 +/- 35 parts per thousand) and suggest formation from a single hydrogen source. They also show positive Delta(CH2D2)-C-12 deviations likely due to diffusion or mixing, and point to a microbial origin probability of less than 10 %. High delta C-13-CH4 values (-12.3 parts per thousand), complete isotopic reversal in C-2-C-4 alkanes, and Volatile Organic Compounds signatures further support a predominantly abiotic synthesis. Noble gas and nitrogen isotopes reveal mixing between atmospheric (80-85 %) and crustal (15-20 %) components with negligible mantle input, confirming an open system with active recharge. Most remarkably, gas emissions are structurally controlled and exclusively occur along a major fault zone intersecting the chromitite ore body, a spatial relationship observed in chromite mines globally. The presence of Fe-Ni alloys and platinum group elements in chromitite appears to catalyze CO2 reduction to methane at temperatures significantly lower than required for uncatalyzed abiotic synthesis. This catalytic effect, combined with optimal serpentinization conditions at 3-5 km depth, sustains extraordinary gas fluxes that cannot be explained by conventional models. The radiocarbon signature suggests either ongoing methane formation incorporating traces of modern carbon or reactivation of the system following regional deglaciation similar to 26,000 years ago. Our findings transform understanding of ophiolitic gas systems from fossil reservoirs to dynamic features cycling carbon on 10(4)-year rather than 10(6)-year timescales. The identification of chromitite as a key catalyst provides new targets for hydrogen exploration throughout the global ophiolite belt, while the demonstration of rapid carbon cycling establishes ophiolites as active participants in the contemporary carbon cycle. These results offer a new paradigm for natural hydrogen generation with immediate relevance to both Earth system science and the urgent search for carbon-free energy resources.

The Gardanne alumina plant in Southern France modified its production process in late 2015 and implemented effluent treatment systems to ensure that discharges into the sea complied with environmental regulations, which were due to come into effect by 2021. This study investigated metal concentrations in effluent samples collected at the plant (2016-2024) and in the associated plume at sea (2016-2021), within 10 m above the outfall, when the effluent mixes with seawater. Filtered (F) and unfiltered (NF) samples were analyzed by ICP-MS to determine concentrations of Al, As, Co, Cu, Cr, Fe, Mn, Ni, Pb, Ti, and V. A major decrease in Al was observed in 2019 in the effluent, following the installation of a CO₂ treatment station in 2018, which neutralized the pH and reduced metal concentrations. Several metal concentrations also exceeded thresholds in 2020 and 2021 due to technical issues during effluent treatment. By 2021, metal concentrations in the effluent met regulatory standards. At the pipeline outfall, mixing of the effluent with seawater was leading to the formation of hydrotalcites that scavenged metals, especially Al. This process ceased once the effluent was neutralized, leading to the release of metals previously trapped in concretions. Close to the outfall, metal concentrations in the plume reflected a nearly undiluted effluent. In contrast, by 2021, the effluent contribution 10 m above the outfall was less than 1 %. Further investigation of the full water column will help to determine the overall dispersion of the effluent.

Deep crustal production of hydrogen (H2) is a potential source of primary energy if recoverable accumulations in geological formations are sufficiently large. We report direct measurements of an elevated outgassing rate of 84% (by volume) of H2 from the deep underground Bulqizë chromite mine in Albania. A minimum of 200 tons of H2 is vented annually from the mine's galleries, making it one of the largest recorded H2 flow rates to date. We cannot attribute the flux solely to the release of paleo-fluids trapped within the rocks or to present-day active and pervasive serpentinization of ultramafic rocks; rather, our results demonstrate the presence of a faulted reservoir deeply rooted in the Jurassic ophiolite massif. This discovery suggests that certain ophiolites may host economically useful accumulations of H2 gas.

Abstract This study provides a comprehensive characterization of various hydrothermal systems in Southern Peru ranging from the faulted Precordillera's steep topography up to the volcanic High Cordillera (>4,000 m asl). The objective is to investigate thermal anomalies that may potentially serve as new geothermal resources. Our integrated approach combines: (a) geochemistry from 14 hot springs sampled throughout the Tacna region, and (b) 3D numerical modeling of coupled groundwater and heat transfer considering topography and faults embedded in homogeneous permeability. Water and gas analysis indicates that the springs located near volcanoes discharge Na‐K‐Cl waters with high temperatures (>87°C), high Total Dissolved Solid concentrations (TDS >3,452 mg/L), and free gases dominated by CO2 (>90 vol%). Springs located along the regional faults in the Precordillera discharge Ca‐SO4 and Na‐K‐Cl waters with moderate temperatures (27–53°C), intermediate TDS concentrations (464–2,458 mg/L), radiocarbon ages between 1.4 and 7.9 kyr, and free gases dominated by N2 (>95 vol%). The Aruma springs, which are located at the transition between the High and the Precordillera, display intermediate characteristics. Numerical models accurately replicate the locations and temperatures of the fault‐related springs only for permeable faults (>10−14 m2), revealing the creation of 100‐km long thermal plumes along faults, locally rising up the 150°C‐isotherm to about ∼1,000 m below the surface. This approach clearly distinguishes the spring origins, which are volcanic in High Cordillera and tectonic in Precordillera. Moreover, we highlight that steep topographic gradient and permeable reverse faults in the Andean forearc may generate considerable thermal anomalies, opening perspectives for the geothermal exploration.

Mining areas and in particular those containing massive sulfides have left a heavy environmental legacy with soils and hydrographic networks highly contaminated with metals and metalloids as for example in the Iberian Pyrite Belt (Huelva, Spain). Here, we present new data on copper (Cu) isotopic composition of waters and solids collected along a continuum Mine ( Tharsis )—River ( Meca )—Lake ( Sancho ) in the Iberian Pyrite Belt. Our results show that the isotopic signature of pit lakes is spatially variable, but remains stable over the seasons; this signature seems to be controlled by water–rock interaction processes. The data obtained on the Meca River imply a number of attenuation processes such as decrease in the metal concentration by precipitation of secondary minerals. This is accompanied by preferential retention of the heavy isotope ( 65 Cu) with a possibility of living organisms (e.g., algae) participation. The terminal Sancho lake demonstrated constant isotopic signature over the entire depth of the water column despite sizable variations in Cu concentrations, which can be tentatively explained by a superposition of counter-interacting biotic and abiotic processes of Cu fractionation. Overall, the understanding of the isotopic variations along the hydrological continuum is useful for a better understanding of metal element transfer within mining environments and surrounding surface waters.

The southeastern part of New Caledonia main island (Grande Terre) is the location of a large ophiolitic formation that hosts several hyperalkaline springs discharging high pH (∼11) and warm (<40°C) fluids enriched in methane (CH4) and hydrogen (H2). These waters are produced by the serpentinization of the ultrabasic rock formations. Molecular surveys had previously revealed the prokaryotic diversity of some of these New Caledonian springs, especially from the submarine chimneys of Prony Bay hydrothermal field. Here we investigate the microbial community of hyperalkaline waters from on-land springs and their relationships with elevated concentrations of dissolved H2 (21.1–721.3 μmol/L) and CH4 (153.0–376.6 μmol/L). 16S rRNA gene analyses (metabarcoding and qPCR) provided evidence of abundant and diverse prokaryotic communities inhabiting hyperalkaline fluids at all the collected springs. The abundance of prokaryotes was positively correlated to the H2/CH4 ratio. Prokaryotes consisted mainly of bacteria that use H2 as an energy source, such as microaerophilic Hydrogenophaga/Serpentinimonas (detected in all sources on land) or anaerobic sulfate-reducing Desulfonatronum, which were exclusively found in the most reducing (Eh ref H2 ∼ -700 mV) and the most H2-enriched waters discharging at the intertidal spring of the Bain des Japonais. The relative abundance of a specific group of uncultured Methanosarcinales that thrive in serpentinization-driven ecosystems emitting H2, considered potential H2-consuming methanogens, was positively correlated with CH4 concentrations, and negatively correlated to the relative abundance of methylotrophic Gammaproteobacteria. Firmicutes were also numerous in hyperalkaline waters, and their relative abundance (e.g., Gracilibacter or Dethiobacter) was proportional to the dissolved H2 concentrations, but their role in the H2 budget remains to be assessed. The prokaryotic communities thriving in New Caledonia hyperalkaline waters are similar to those found in other serpentinite-hosted high-pH waters worldwide, such as Lost City (North Atlantic) and The Cedars (California).

An anaerobic, hydrogenotrophic methane-producing archaeon was isolated from an alkaline thermal spring (42 °C, pH 9.0) in New Caledonia. This methanogen, designated strain CANT, is alkaliphilic, thermotolerant, with Gram-positive staining non-motile cells. Strain CANT grows autotrophically using hydrogen exclusively as an energy source and carbon dioxide as the sole carbon source (without the requirement of yeast extract or other organic compounds). It grows at 20–45 °C (optimum, 45 °C) and pH 7.3–9.7 (optimum, pH 9.0). NaCl is not required for growth (optimum 0 %) but is tolerated up to 1.5 %. It resists novobiocin, streptomycin and vancomycin but is inhibited by ampicillin and penicillin, among other antibiotics. The genome consists of a circular chromosome (2.2 Mb) containing 2126 predicted protein-encoding genes with a G+C content of 36.4 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain CANT is a member of the genus Methanobacterium , most closely related to the alkaliphilic Methanobacterium alcaliphilum WeN4T with 98.5 % 16S rRNA gene sequence identity. The genomes of strain CANT and M. alcaliphilum DSM 3459, sequenced in this study, share 71.6 % average nucleotide identity and 14.0 % digital DNA–DNA hybridization. Therefore, phylogenetic and physiological results indicate that strain CANT represents a novel species, for which the name Methanobacterium alkalithermotolerans sp. nov. is proposed, and strain CANT (=DSM 102889T= JCM 31304T) is assigned as the type strain.

Investigations conducted during the GEOSECS program concluded that radium-226 (T1/2 = 1602 y) and barium are tightly correlated in waters above 2500 m in the Atlantic, Pacific and Antarctic Oceans, with a fairly uniform 226Ra/Ba ratio of 2.3 ± 0.2 dpm µmol-1 (4.6 nmol 226Ra/mol Ba). Here, we report new 226Ra and Ba data obtained at three different stations in the Pacific Ocean: stations K1 and K3 in the North-West Pacific and station old Hale Aloha, off Hawaii Island. The relationship between 226Ra and Ba found at these stations is broadly consistent with that reported during the GEOSECS program. At the three investigated stations, however, we find that the 226Ra/Ba ratios are significantly lower in the upper 500 m of the water column than at greater depths, a pattern that was overlooked during the GEOSECS program, either because of the precision of the measurements or because of the relatively low sampling resolution in the upper 500 m. Although not always apparent in individual GEOSECS profiles, this trend was noted before from the non-zero intercept of the linear regression when plotting the global data set of Ba versus 226Ra seawater concentration and was attributed, at least in part, to the predominance of surface input from rivers for Ba versus bottom input from sediments for 226Ra. Similarly, low 226Ra/Ba ratios in the upper 500 m have been reported in other oceanic basins (e.g. Atlantic Ocean). Parallel to the low 226Ra/Ba ratios in seawater, higher 226Ra/Ba ratios were found in suspended particles collected in the upper 500 m. This suggests that fractionation between the two elements may contribute to the lower 226Ra/Ba ratios found in the upper 500 m, with 226Ra being preferentially removed from surface water, possibly as a result of mass fractionation during celestite formation by acantharians and/or barite precipitation, since both chemical elements have similar ionic radius and the same configuration of valence electrons. This finding has implications for dating of marine carbonates by 226Ra, which requires a constant initial 226Ra/Ba ratio incorporated in the shells and for using 226Ra as an abyssal circulation and mixing tracer.

The Gardanne alumina plant (Marseille region, Southeast France) has disposed its residues as a slurry (red muds) in the Mediterranean Sea up to 2015 when new regulations allowed the sole discharge of a clarified effluent. This reduced the quantity of suspended material from ~300 g/L to less than 10 mg/L. The detailed chemical composition of this clarified effluent has been determined by ICP-OES, ionic chromatography, 1H NMR spectroscopy and carbon analysis. It is a Na–Al–OH aqueous solution at pH 12.5 having a solute load of 1.5 g/L and an organic carbon content of about 100 mg/L, all other elements being in minor or trace amounts. A X-ray diffraction and SEM study showed that the submarine concretions forming at the outfall upon mixing the effluent with seawater are predominantly composed of a Mg–Al–OH double layer hydroxide of the hydrotalcite supergroup that contains Ca and S (wermlandite subgroup), along with minor calcite, bayerite, and rarely brucite and akaganeite (an iron hydroxide). The investigation of the stability of standard hydrotalcite in the marine environment through solubility calculations showed that hydrotalcite minerals are not stable in normal seawater and as such are prone to dissolve and release their components to the environment.

(1) Background: The geothermal spring of La Crouen (New Caledonia) discharges warm (42 °C) alkaline water (pH~9) enriched in dissolved nitrogen with traces of methane, but its microbial diversity has not yet been studied. (2) Methods: Cultivation-dependent and -independent methods (e.g., Illumina sequencing and quantitative PCR based on 16S rRNA gene) were used to describe the prokaryotic diversity of this spring. (3) Results: Prokaryotes were mainly represented by Proteobacteria (57% on average), followed by Cyanobacteria, Chlorofexi, and Candidatus Gracilibacteria (GN02/BD1-5) (each > 5%). Both potential aerobes and anaerobes, as well as mesophilic and thermophilic microorganisms, were identified. Some of them had previously been detected in continental hyperalkaline springs found in serpentinizing environments (The Cedars, Samail, Voltri, and Zambales ophiolites). Gammaproteobacteria, Ca. Gracilibacteria and Thermotogae were significantly more abundant in spring water than in sediments. Potential chemolithotrophs mainly included beta- and gammaproteobacterial genera of sulfate-reducers (Ca. Desulfobacillus), methylotrophs (Methyloversatilis), sulfur-oxidizers (Thiofaba, Thiovirga), or hydrogen-oxidizers (Hydrogenophaga). Methanogens (Methanobacteriales and Methanosarcinales) were the dominant Archaea, as found in serpentinization-driven and deep subsurface ecosystems. A novel alkaliphilic hydrogenotrophic methanogen (strain CAN) belonging to the genus Methanobacterium was isolated, suggesting that hydrogenotrophic methanogenesis occurs at La Crouen.

A novel anaerobic, alkaliphilic, mesophilic, Gram-stain-positive, endospore-forming bacterium was isolated from an alkaline thermal spring (42 °C, pH 9.0) in New Caledonia. This bacterium, designated strain LB2T, grew at 25-50 °C (optimum, 37 °C) and pH 8.2-10.8 (optimum, pH 9.5). Added NaCl was not required for growth (optimum, 0-1 %) but was tolerated up to 7 %. Strain LB2T utilized a limited range of substrates, such as peptone, pyruvate, yeast extract and xylose. End products detected from pyruvate fermentation were acetate and formate. Both ferric citrate and thiosulfate were used as electron acceptors. Elemental sulphur, nitrate, nitrite, fumarate, sulphate, sulfite and DMSO were not used as terminal electron acceptors. The two major cellular fatty acids were iso-C15 : 0 and C16 : 0. The genome consists of a circular chromosome (3.7 Mb) containing 3626 predicted protein-encoding genes with a G+C content of 36.2 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the isolate is a member of the family Proteinivoraceae, order Clostridiales within the phylum Firmicutes. Strain LB2T was most closely related to the thermophilic Anaerobranca gottschalkii LBS3T (93.2 % 16S rRNA gene sequence identity). Genome-based analysis of average nucleotide identity and digital DNA-DNA hybridization of strain LB2T with A. gottschalkii LBS3T showed respective values of 70.8 and 13.4 %. Based on phylogenetic, genomic, chemotaxonomic and physiological properties, strain LB2T is proposed to represent the first species of a novel genus, for which the name Alkalicella caledoniensis gen. nov., sp. nov. is proposed (type strain LB2T=DSM 100588T=JCM 30958T).

The very alkaline waters produced by low temperature serpentinization of ultramafic rocks may contain elevated concentrations of dissolved organic carbon likely to act as a substrate for microbial life. High-pH (up to 11.7) waters collected at on-land sites (Oman, Liguria, New Caledonia, Portugal) and porewaters (pH up to 12.5) collected in boreholes drilled during IODP Exp 366 in three Marianna forearc mud volcanoes (Yinazao, Fantangisña and Asùt Tesoru) have been analyzed for organic compounds using 1 H NMR spectroscopy. Whereas the waters collected at continental sites are devoid of organics, very high concentrations of acetate (up 80 µmol/L), formate (up to 250 µmol/L), ethanol (up to 700 µmol/L), methanol (up to 300 µmol/L) and acetonitrile (up to 40 µmol/L) are found in porewaters

Serpentinization is a natural process that transforms ferromagnesian minerals such as olivine into serpentine and that produces waters at very high pH and gases enriched in methane (CH 4 ) and hydrogen (H 2 ). We report the composition of gases venting at two springs (Bain des Japonais and Rivière des Kaoris) of the serpentinizing environment of the Prony Bay (New Caledonia) collected eight times between 2011 and 2014, along with in situ measurements (temperature, pH, oxydo‐reduction potential, dissolved oxygen content) of on‐land alkaline springs of the Southern New Caledonia ophiolite. Venting gases are mainly composed of H 2 , CH 4 , and N 2 and their composition has slightly varied during the 4‐year field survey. An elevated oxygen (O 2 ) content in a high‐pH water sample is due to air uptake during surface flow. O 2 ‐corrected gas compositions along with those published for gas data obtained at similar serpentinizing environments (Italy, Turkey, Philippines, and Oman) show that the H 2 and CH 4 concentrations display a linear correlation with a slope close to the value corresponding to the CH 4 production from carbon dioxide rather from a less oxidized carbon such as carbon monoxide. Although these data are consistent with the stoichiometry of the Sabatier reaction, as such in the gas phase, it is also possible that microbial hydrogenotrophic methanogenesis takes place in the aqueous phase followed by degassing. A diagram is proposed that outlines the partitioning of H 2 and CH 4 between the gaseous and aqueous phases and the need to consider a two‐phase flow in the hydrology of these hyperalkaline environments.

As a shelf-dominated basin, the Arctic Ocean and its biogeochemistry are heavily influenced by continental and riverine sources. Radium isotopes (226Ra, 228Ra, 224Ra, and 223Ra), are transferred from the sediments to seawater, making them ideal tracers of sediment–water exchange processes and ocean mixing. As the two long-lived isotopes of the radium quartet, 226Ra and 228Ra (226Ra with a t1∕2 of 1600 years and 228Ra with a t1∕2 of 5.8 years) can provide insight into the water mass compositions, distribution patterns, as well as mixing processes and their associated timescales throughout the Canadian Arctic Archipelago (CAA). The wide range of 226Ra and 228Ra activities, as well as of the 228Ra∕226Ra, measured in water samples collected during the 2015 GEOTRACES cruise, complemented by additional chemical tracers – dissolved inorganic carbon (DIC), total alkalinity (AT), barium (Ba), and the stable oxygen isotope composition of water (δ18O) – highlight the dominant biogeochemical, hydrographic, and bathymetric features of the CAA. Bathymetric features, such as the continental shelf and shallow coastal sills, are critical in modulating circulation patterns within the CAA, including the bulk flow of Pacific waters and the inhibited eastward flow of denser Atlantic waters through the CAA. Using a principal component analysis, we unravel the dominant mechanisms and apparent water mass end-members that shape the tracer distributions. We identify two distinct water masses located above and below the upper halocline layer throughout the CAA and distinctly differentiate surface waters in the eastern and western CAA. Furthermore, we highlight water exchange across 80∘ W, inferring a draw of Atlantic water (originating from Baffin Bay) into the CAA. This underscores the presence of an Atlantic water “U-turn” located at Barrow Strait, where the same water mass is seen along the northernmost edge at 80∘ W as well as along the southeasternmost confines of Lancaster Sound. Overall, this study provides a stepping stone for future research initiatives within the Canadian Arctic Archipelago, revealing how quantifying disparities in the distributions of radioactive tracers can provide valuable information on water mass distributions, flow patterns, and mixing within vulnerable areas such as the CAA.

The submarine discharge of the high pH clarified Bayer effluent of the Gardanne alumina plant (Marseille region, France) leads to the formation of concretions at the outfall 324 m underwater and to a plume of white particles. The bulk chemical composition of the concretions has been determined by SF-ICP-MS. Mg and Al are the major elements measured with concentrations of a few hundred mg g-1. Ca and S are also found at concentrations in the range of mg g-1. Among the measured trace elements there is a specific interest in As and V because of environmental concerns pointed out by regulation authorities. Their concentrations are of tens to thousands μg g-1, respectively. Concentrations of the other elements are in the range of a few ng g-1 to few hundreds μg g-1. In order to constrain the dispersion of particles in the environment and to understand how chemical elements can be scavenged from or released to seawater, the size distribution of particles composing the concretions has been measured by settling rate experiments and, for each size class of particles, their chemical composition has been determined. For example, As and V are mainly associated to particles with mean diameters between 15.6 and 63 μm and settling rates around 96 m d-1. Overall, all the main elements (Mg, Al, Ca, S) composing concretions are associated to this size class of particles which represents 53-60% of the total concretion mass.