Mackinawite (FeS) is the first iron sulfide phase to form in anoxic systems containing ferrous iron and sulfide. It is a major inorganic scale in oil and gas piping and its catalytic properties make it a potential candidate for a variety of industrial applications including energy storage systems and batteries. This, together with Mackinawite’s potential for remediation through the doping of heaving metal cations, makes it an interesting subject of investigation. Since in natural conditions iron and sulfide do not generally occur in alike concentrations, investigating diverging ratios of iron:sulfide activities, improves our knowledge about iron sulfide early formation in natural and geo-engineered settings.

Here, we investigated FeS formation at a saturation index of 1.8 (~63 fold supersaturation), varying {Fe²⁺}:{HS^-} and at pH 10.2. Particle size distribution was explored using Dynamic Light Scattering measurements, surface charge of particles (Zeta potential) was measured with Electrophoretic Light Scattering and samples were imaged using Transmission Electron Microscopy.

Regarding particle charge, we observed particles that were more negatively charged when the solution had an excess of anions (HS^-), compared to solutions with more cation(Fe²⁺) which led to having particles with less negative net surface charge.

Furthermore, preliminary results indicated non-linear evolution of FeS particle size through time. Higher concentrations of iron promoted formation of larger particles, whereas having more sulfide induced the formation of  smaller particles.

Our observations reveal that FeS particle formation is sensitive to the ratio of {Fe²⁺}:{HS^-} in the solution. When there is an excess of iron, growth and/or aggregation of nuclei is enhanced and predominates over nucleation, in contrast to the other conditions(equal activities, or excess HS^-). This behavior may be explained by the zeta potential, which reflects the surface charge of the particles. At pH 10, the FeS particles are negatively charged (Wolthers et al., 2005) and more so at stoichiometric and excess-sulfide conditions. In excess Fe, the particles are less charged and therefore less physically stable and more likely to aggregate, leading to larger particle growth.

How to cite: Karami, A., Koskamp, J., and Wolthers, M.: Investigating the impact of {Fe2+}:{HS-} ratio on FeS formation: preliminary results on particle size and charge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14156, https://doi.org/10.5194/egusphere-egu23-14156, 2023.

Spherulitic crystal growth structures are omnipresent in the sedimentary realm. They occur as allochems, such as ooids, as crystal fans in stromatolites or as botryoids in tufa and speleothems. The spherulitic structure is due to radially arranged crystallographic axes which manifests as round outer shapes and the characteristic extinction cross under cross-polarized light. Often, spherulitic structures are ascribed to some mystic biological effect, however, without providing any further explanation of the underlying mechanism.

While the overall driving force for spherulitic growth arises from the crystals attempting to reduce their surface energy, several pathways have been suggested in the literature by which the crystal structure and shape relaxes to the stress field imposed by the surface energy. Prominent is the concept of auto-deformation, where low-angle branching is introduced by crystallographic rearrangement in the interior of the crystal, due to cascades of discrete fracturing. In contrast, a growth front nucleation model has been suggested, in which case low-angle branching already nucleates as atoms or ions are being attached. In this mechanism, the stress field is dissipated before the atoms are incorporated permanently in the crystal lattice, which has the advantage that no bond-breaking event would be necessary (Meister, in press¹). From a non-classical point of view, the growth front model can be modified in the sense that already existing nano-particles are attaching in an oriented way, so that low-angle boundaries are established.

Ultimately, the prevailing crystal growth mode depends on crystal growth kinetics, as a result of both macroscopic factors – such as the supersaturation ratio of the bulk solution and interfacial energy – and molecular-scale factors that shape the nano-scale energy landscape. The mineralogical and crystallographic structure that can be reached by overcoming the lowest possible kinetic barrier should result, just as predicted by Ostwald’s step rule (Meister, in press²). Inorganic and organic co-solutes may act as modifiers, impacting the interface energy landscape and thereby shifting the boundary between step-flow growth and adhesive growth, facilitating non-crystallographic branching, and, thus, provoking configurations different from idiomorphic crystals.

¹⁾ Meister, P. (in press) Spherulitic mineral growth: auto-deformation, growth front nucleation, or semi-oriented attachment? In P. Meister, C. Fischer and N. Preto (Eds.): “Nucleation and growth of sedimentary minerals”, IAS Special Publications, accepted.

²⁾ Meister, P. (in press) Ostwald’s step rule: a consequence of growth kinetics and nano-scale energy landscape. In P. Meister, C. Fischer and N. Preto (Eds.): “Nucleation and growth of sedimentary minerals”, IAS Special Publications, accepted.

How to cite: Meister, P.: Surface stress dissipation during growth front nucleation as mechanism for spherulitic crystal growth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3946, https://doi.org/10.5194/egusphere-egu23-3946, 2023.

It has been well known that the activity of bacteria causes a promoting crystallization in the natural environment. On the other hand, it has been pointed out that bacteria activity also plays a role in the dissolution of crystals, and the microscopic observation showed that the inhibition of the bacteria affects the pit formation to promote the dissolution of calcite[1]. The authors found a grope of bacteria, which promotes the dissolution process of calcite. We isolated bacteria from calcite-enriched soil and examined their calcite-degrading activity.

To understand the role of bacteria in the dissolution process, In the experiments, the cleavage surface of the calcite was exposed to the culture fluid of the bacteria for 4 days to investigate the effect of bacteria on the calcite dissolution. The surface morphology of the calcite was investigated using an optical microscope and scanning electron microscope after the dissolution experiment in the culture fluid with bacteria.

The calcium ion concentration in the culture fluid of Streptomyces was one-third of control, Escherichia coli DH5a, indicating the promoting the dissolution process of calcite. The surface observation of the calcite surface, which has been exposed in the culture fluid of bacteria shows the etch pits, which were formed during the dissolution process.

Differing from the previous study, [1] the shape of the etch pits showed a rounded and asymmetric shape and deviated from the rectangular, which reflects the symmetry of the surface. These etch pits were formed accompanied by the bacteria colony. And the bacteria colony was formed along the cleavage step on the calcite surface. These observations infer that the inhabitation of the bacteria and the dissolution of the calcite are related to each other and the effect of the surface activity of calcite in the dissolution process could be larger by the biological activity.

Reference

[1] A. Luettge and P.G. Conrad, Direct observation of microbial inhibition of calcite dissolution, App. Env. Micr (70) 2004

How to cite: Kobatake, H. and Inoue, H.: Selective dissolution of calcite in a bacterial habitat environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17414, https://doi.org/10.5194/egusphere-egu23-17414, 2023.

Iron (oxyhydr)oxide concretions are cemented mineral masses formed via authigenic cements in sedimentary rocks at any time during diagenesis (syndepositional, burial, and late-stage). These features are common in porous and permeable sandstone and even present on Mars in at least two different locations and formations. One notable study area for the spherules is within the Navajo Sandstone in the Grand Staircase Escalante National Monument (GSENM) in southern Utah. Diagenetic concretions, particularly iron (oxyhydr)oxide mineralogies, are thought to form via a two-fluid mixing model where one fluid has the reactants in solution, then another fluid meets and mixes with the reactant-bearing fluid, and the concretions precipitate. These two fluids could be a reducing fluid that mobilizes iron as Fe²⁺ and then mixes with an oxidizing fluid to precipitate iron oxyhydr(oxide), but an acidic fluid could mobilize iron as Fe³⁺ and then interact with a neutral fluid for the same result.  Another proposed model for iron (oxyhydr)oxide concretions calls for calcium carbonate precursor concretions and mobilization of iron by acidic fluids. The acidic, iron-bearing fluid then dissolves the carbonate concretion, which buffers the solution enough to precipitate iron oxyhydr(oxide) in the same morphology as the original calcite concretion. Our research shows that in GSENM, iron concretions and calcite concretions are present within the same stratigraphic horizon and in close proximity. Another field observation is the presence of calcite concretions in clusters along paleo water tables, rather than dispersed in a self-organized spacing within three dimensions like the iron features. Also present within the region are concretions with manganese oxide phases and the iron concretions tend to include manganese oxide, but not calcite. Calcite concretions do commonly contain some iron (oxyhydr)oxides, particularly as rims around grains. In the Entrada Sandstone, also in southern Utah, iron concretions are precipitated from fluid brought in with an igneous intrusion that mobilized the iron within the host rock. Structures in the area acted as baffles keeping the fluid stagnant and iron (oxyhydr)oxide concretions are only present between the igneous dike and the nearest baffle. Calcite concretions in the area are dispersed throughout the host rock (both within and outside of the baffles), suggested that mineral precipitation rates control concretion formation and that iron (oxyhydr)oxide concretions need a longer period of fluid stagnation for formation than do calcite concretions. Understanding the complex formation mechanisms can help to unravel the history of diagenetic fluids of varying chemistries and therefore, the habitability of subsurface environments on both Earth and Mars.

How to cite: Potter-McIntyre, S.: Iron (oxyhydr)oxide concretion formation: New insights from southern Utah, USA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9263, https://doi.org/10.5194/egusphere-egu23-9263, 2023.

Marine iron-manganese concretions are metal-containing biogeochemical precipitates abundantly encountered in the seafloors of the world ocean. Their importance in paleoenvironmental reconstructions as well as a source for critical metals has been recently realized. Diagenetic and hydrogenetic concretions, however, have different compositions and subsequently can have differing capacities for recording oceanographic processes and for economic utilization. Therefore, their genetic classification can provide crucial information for both environmental and economic applications. Traditionally discrimination of different marine iron-manganese concretion origins has been achieved with geochemical methods, such as investigating their rare earth element content. It is now evident that iron-manganese concretions also host magnetic minerals that are likely formed by facilitation by microbial processes. Currently it is unknown if the different genetic backgrounds of iron-manganese concretions are reflected in their magnetic properties.  

We compared the geochemical and magnetic properties of diagenetic iron-manganese concretions from the Baltic Sea to hydrogenetic concretions from the Pacific. While the commonly utilized geochemical indicators differentiate the concretions found from the two localities as diagenetic and hydrogenetic, it also appears that concentration dependent magnetic parameters such as saturation magnetization and anhysteretic remanent magnetization effectively discriminate between the different types of concretions. Mineral magnetic methods are fast and cost-effective and may provide an alternative tool to quickly screen out diagenetic from hydrogenetic precipitates.

This research is part of the Fermaid project, funded by the Academy of Finland grant 332249.

How to cite: Wasiljeff, J., Salminen, J., Lahaye, Y., and Virtasalo, J.: Mineral magnetic discrimination between diagenetic and hydrogenetic iron-manganese concretions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11426, https://doi.org/10.5194/egusphere-egu23-11426, 2023.

Typically thick aeration zones of topographic groundwater recharge areas are hardly investigated parts of subsurface ecosystems and the subsurface water/matter cycles (Lehmann and Totsche 2020). In fractured bedrock settings, here, mineral surfaces and assemblages, exposed to major flow-paths, can largely differ from the bulk rock-forming compositions. Representing highly diverse and likely important reaction spaces for subsurface matter cycling and groundwater quality, yet, their compositional and morphological diversity, their provided habitat structure and endolithic dwellers, and their matter sources and dynamics are scarcely known. In drill core samples of Triassic limestone-mudstone alternations from the Hainich Critical Zone Exploratory (Collaborative Research Center AquaDiva), we characterized and classified alteration features across regolith down to the phreatic zone. Besides analysis of fracture/pore fillings and rock matrices by digital microscopy, SEM(-EDX), among others, we investigated possible controlling factors like lithofacies associations, depth, water saturation, groundwater flow patterns and oxicity. Generally, strong weathering features with up to 1 mm thick fillings and up to several centimeters thick zones of alteration in rock of the aeration zone contrast with minor features in the phreatic zone. In the limestones and mudstones, major classes of fracture surface coatings, are taken by secondary Fe-oxides and/or clay laminae. Our results highlight the typical presence of diverse and likely dynamic reaction spaces, providing highly diverse microbial habitats. We suggest to carefully consider and explore the diversity and dynamics of mineral fractures surfaces of the aeration zone, and their contributions to element cycling and groundwater quality evolution.

References:

Lehmann, R., Totsche, K. U. (2020). Multi-directional flow dynamics shape groundwater quality in sloping bedrock strata. Journal of Hydrology 580. https://doi.org/10.1016/j.jhydrol.2019.124291

How to cite: Lehmann, R., Eshvara Arachchige, D., Aehnelt, M., and Totsche, K. U.: Diversity and patterns of fracture-exposed alteration features in thick recharge-area regolith, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12008, https://doi.org/10.5194/egusphere-egu23-12008, 2023.

Saline lakes are known to be sensitive to changes in environmental conditions on a broad temporal scale. Therefore, variations in the mineralogical, geochemical, and sedimentological characteristics of these settings have often been interpreted to reflect oscillations in climatic conditions. However, recent work has shown that microbial communities can also influence the formation of carbonate and evaporite minerals in saline lake environments, especially in the salars of South America. Here, both abiotic and organomineralization pathways can be found to exist within the same salar environments, indicating a high degree of spatial heterogeneity of mineralization processes in such settings. Thus, the drivers of the resulting mineral assemblage can be complicated to disentangle through space and time. A process-level understanding of first-order controls on mineral assemblages can provide new insights into sedimentological dynamics of salar environments.

Babel (2004) published a conceptual model based on marine-fed systems that established links between salinity and the style of gypsum mineral deposition. Based on field and laboratory analyses conducted on sediments in the Salar de Llamara, we adapted this model for a continental saline lake setting (Reid et al., 2021). In the present study, we aimed to test whether our salar-scale conceptual model was applicable more generally to continental saline lake environments. To accomplish this goal, we investigated a 15-year time series of electrical conductivity, a proxy for salinity, collected in five saline lake/wetland systems situated along the margin of the Salar de Atacama. Based on this dataset, we predicted the style and mineralogy of mineral deposition in each setting using our salar-scale conceptual model. Next, we compared our predictions with published field descriptions of the occurrences of biofilms, microbial mats, microbialites, and evaporite deposits in these lakes. Through a principal component analysis, we evaluated environmental characteristics such as electrical conductivity, pH, and dissolved oxygen as controls on mineral morphology and mineralogy.

Results indicate that salinity is a first-order control on sedimentological expression in the lakes of the Salar de Atacama, although the transition between organomineralization pathways and physicochemical precipitation may occur at different salinity values than observed in other saline lake settings. Broadly in agreement with our model from the Salar de Llamara, granular precipitates of carbonate minerals formed within microbial mats were associated with environments characterized by low salinity, while microbial mats with laminated precipitates were found in settings with moderate salinity in the Salar de Atacama. High salinity environments contained crystalline bottom types characterized by selenitic morphology. Because some South American salars have been cited as living laboratories analogous to the ancient conditions that fostered the evolution of terrestrial and Martian life, these insights into mineralization are important. Improved constraints on the controls of carbonate and evaporite mineral deposition in saline lake environments will elucidate the definition of habitable environments, and provide a testing ground for the production and preservation of chemical and morphological biosignatures through time.

How to cite: Oehlert, A. M., Piggot, A. M., Suosaari, E. P., Palma, A. T., Daza, L. R., Kong, T., Pollier, C. G. L., Demergasso, C., Chong, G., and Reid, R. P.: Environmental controls on sedimentary deposits in saline lake environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16421, https://doi.org/10.5194/egusphere-egu23-16421, 2023.

Although thought to be high-resolution archives of paleoenvironmental changes, subsurface sediments deposited in saline lakes situated in salar environments have rarely been studied. To address this knowledge gap, sediment cores of varying depths ranging from 0.42 to 2.2 meters were collected from four saline lakes along the eastern margin of the Salar de Atacama, Chile. Characterization included sedimentological descriptions of lithification, sedimentary structures (microbial mats and microbialites), and color, as well as discrete measurements of total organic carbon content. Radiocarbon analysis was conducted on organic matter in the sediments.  The recovered subsurface lithologies were heterogenous in color, stratigraphic features, and age dates, especially when compared between the lakes. Intervals of coarser sediment in the Soncor system lakes Chaxa, Burros Muertos and Barros Negros, appeared to be crystalline and were likely precipitated during periods characterized by higher salinity lake waters. Sediment cores collected from the Soncor system were broadly characterized by low total organic carbon content and punctuated intervals of coarse grained material deeper in the core. In the core collected from Aguas de Quelana, variations in lithology and hardgrounds were commonly observed. In concert, these results suggest that the eastern periphery of the salar was impacted by changes in salinity and water depth as these wetland area experienced changes in extent as a result of changes in wet and dry periods. Radiocarbon dating conducted on organic matter sampled at 4 intervals from each core revealed ages that were significantly older than expected, possibly due to local reservoir effects and subsurface hydrological dynamics. There were five age reversals documented in the transect of cores suggesting that the sources of radiocarbon may have changed over time. Results indicate that the geologic records of saline lake environments are as heterogeneous through time as they are in space.

How to cite: Piggot, A. M., Reid, R. P., and Oehlert, A. M.: Sedimentological characterization of geological cores from marginal lakes in the Salar de Atacama, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15767, https://doi.org/10.5194/egusphere-egu23-15767, 2023.

We used the textures and chemical composition of authigenic cements in Paleogene sandstones from DN2 Gas Field of Kuqa Foreland Basin (KFB) and evidence of associated fluids from fluid inclusions and formation water measurements to infer timing of fluid migration and discuss link between fluids and tectonics. Eodiagenesis occurred with the participation of meteoric waters and connate waters. Mesodiagenesis operated in the context of high salinity fluids, which were interpreted to originate from overlying Neogene evaporite. Halite, anhydrite, glauberite, carnallite and thenardite are major minerals for the evaporite. Homogenization temperatures measured in this study and K-Ar dating performed on authigenetic illites by previous study indicate that initial migration of high salinity fluid occurred during the late Miocene (12.4–9.2 Ma). The period is consistent with the crucial phase (13–10 Ma) witnessing the rapid development of southern Tianshan and the stage when calcite and anhydrite veins formed in the studied strata. These results suggest that diagenesis related to high salinity fluids probably occurred as a response to Tianshan’s rapid uplift and related tectonic processes. The flow of high salinity fluids was probably driven by density gradient and channeled and focused by fractures formed contemporaneously.

How to cite: Yu, G., Yuan, J., and Liu, K.: Diagenesis of Paleogene sandstones and its response to tectonics in Kuqa Foreland Basin, western China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3769, https://doi.org/10.5194/egusphere-egu23-3769, 2023.

Abstract:As a typical representative of unconventional gas reservoirs, tight sandstone gas reservoirs have the characteristics of large reserves and rich oil and gas resources, and have become an important exploration and development target for the government and enterprises. As one of the large oil-bearing basins in China, Ordos Basin contains many sets of oil-bearing strata, which are rich in oil and gas resources and have obvious characteristics of source-reservoir-cap assemblage. Longdong area in the southwest of the basin, under the influence of sedimentary environment and tectonic factors, continuously deposited a set of relatively complete tight thick sandstone, and the multi-layer system is generally rich in oil and gas. With the deepening of the exploration of tight sandstone oil and gas, the area has gradually become a new oil and gas development replacement area.The physical properties, lithology, pore structure and other parameters of the reservoir in the study area were studied by using casting thin section, scanning electron microscope, high pressure mercury injection, physical property analysis and gas testing data. The results show that the main rock types of He 8 member in the study area are lithic quartz sandstone ( 61.6 % ) and lithic sandstone ( 15.06 % ). The grain size of the reservoir is coarse and the sorting is medium. The pore types are mainly intragranular dissolved pores, followed by intergranular pores and intercrystalline micropores.The reservoir thickness range and lithology in the study area vary greatly and the heterogeneity is strong. Reservoir properties are controlled by sedimentary facies and diagenesis. Sedimentary facies fundamentally control the reservoir physical conditions, sand body structure has an important influence on reservoir physical properties, cutting type single sand body reservoir physical properties is relatively good, splicing type sand body reservoir physical properties, poor isolated single sand body.Compaction is the main reason for the densification of reservoir physical properties. Water mica is the primary factor for the densification of reservoir caused by cementation. The dissolution degree of reservoir is low, and the effect of improving reservoir quality is limited. The research results can provide reliable geological basis and scientific basis for further exploration and development of the lower section of He 8 in Longdong area.

How to cite: cui, G., xu, S., and wei, Q.: Influence of diagenesis on reservoir in He 8 member of the Permian Shihezi Formation in Longdong Area, Ordos Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1034, https://doi.org/10.5194/egusphere-egu23-1034, 2023.

Mechanical compaction is an important diagenesis of sandstone. Particle breakage commonly occurs during mechanical compaction, and plays a significant role in controlling the physical properties of the sandstone reservoir. However, existing experimental and numerical simulation methods have limitations in simulating mechanical compaction when considering particle breakage. In this study, a discrete element method (DEM) is purposed, which takes the maximum contact stress as the criterion of particle breakage and realizes particle breakage by particle cutting. Nine sets of numerical simulations were carried out with different breakage thresholds of reference particle (diameter = 6mm) and Weibull modulus. The parameters were calibrated according to the experimental data in published literature. On this basis, the compaction simulations of coarse sand with and without particle breakage were carried out, and the simulated vertical stress was 50Mpa. The results show that particle breakage caused by mechanical compaction significantly controls the porosity and pore structure. When the vertical stress reached 50 MPa, compared to the simulation results without considering particle breakage, the porosity difference rate caused by particle breakage was 4.63%; the radius difference rates of pores and throats were 2.78% and 6.8%, and the number difference rates of pores and throats were 4.95% and 8.74%, respectively. The simulation method can be used as an important technique in the study of sandstone diagenesis and is significant for revealing the formation process and mechanism of oil and gas reservoirs.

How to cite: Jia, T., Zhang, L., Xu, Z., Chen, C., and Yan, Y.: Effect of particle breakage caused by mechanical compaction on pore characteristics of sandstone: A DEM numerical simulation study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7275, https://doi.org/10.5194/egusphere-egu23-7275, 2023.