Microbial Carbonate Precipitation Research Articles

Bacterial carbonic anhydrase-induced carbonates mitigate soil erosion in biological soil crusts

Soil erosion is a significant environmental issue worldwide, particularly in island regions where land resources are exceedingly scarce. Biological soil crusts play a crucial role in mitigating soil erosion, yet the precise effect and mechanism of biological soil crusts against erosion remain ambiguous. In this study, biological soil crusts at various developmental stages from a tropical coral island in the South China Sea were chosen to investigate the role of carbonic anhydrase in mitigating erosion. A cohesive strength meter, real-time quantitative PCR, and 16S rRNA gene high-throughput sequencing were employed to assess variations in soil antiscouribility as well as bacterial abundance and composition during the formation and development of biological soil crusts. Scanning electron microscopy was utilized to detect carbonates induced by bacterial carbonic anhydrase and elucidate their role in the solidification of sand particles. The findings indicate that the formation and development of biological soil crusts significantly enhance anti-scouribility. Comparison to those of bare coral sand, the shear stress increased from 0.35 to 1.11 N/m2 in the dark biocrusts. Moreover, significantly elevated carbonic anhydrase activity was observed in biological soil crusts, demonstrating a positive correlation with antiscouribility. In addition, there was a significant increase in bacterial abundance within the biological soil crusts. The enrichment of Cyanobacteriales and Chloroflexales potentially contributed to the increased carbonic anhydrase activity and antiscouribility. Furthermore, three cyanobacterial strains with carbonic anhydrase activity were isolated from biological soil crusts and subsequently confirmed to enhance sand solidification through microbial carbonate precipitation. This study presents initial evidence for the role of microbial carbonic anhydrase in enhancing the antiscouribility of biological soil crusts during their formation and development. These findings offer novel insights into the functional and mechanistic dimensions underlying the mitigation of soil erosion facilitated by biological soil crusts, which are valuable for implementing sustainable biorestoration and environmental management technologies to prevent soil erosion.

Non‐ureolytic microbially induced carbonate precipitation: Investigating a cleaner biogeotechnical engineering pathway for soil mechanical improvement

AbstractAs the world's population grows, there is an increasing need for soil improvement techniques to accommodate construction demands. Current methods, most often, suffer from a high CO2 footprint, leading researchers to resort to biological methods of soil improvement through microbially induced carbonate precipitation (MICP). Commonly used ureolytic microbial carbonate precipitation produces ammonium ions, which can be environmentally concerning. The present study, therefore, addresses the use of non‐ureolytic MICP for soil improvement. The process of non‐ureolytic MICP relies on the use of heterotrophic bacteria to catalyze the oxidation reaction of organic compounds, eventually calcium carbonate precipitation. In this study, heterotrophic bacteria, such as Bacillus subtilis and Bacillus amyloliquefaciens, have been investigated as a solution for soil improvement via an ammonium‐free MICP. Calcium formate and calcium acetate are used as both calcium and carbon sources. This study, furthermore, examines the impact of MICP treatment on sandy soil and the effect of compaction level on treated samples. The findings indicate that the non‐ureolytic MICP method is an effective approach for stabilizing sand. The Calcium Formate‐B.Subtilis composition is shown to be the most effective compound for improving the unconfined compressive strength of sandy soils, while the Calcium Acetate‐B.Amyloliquefaciens composition is the least effective.

Molecular fossils in reefal carbonates and sponges of the deep fore reef of Mayotte and Mohéli, Comoro Islands, western Indian Ocean

Microbial carbonates are common components of Quaternary tropical coral reefs. Previous studies revealed that sulfate-reducing bacteria trigger microbial carbonate precipitation in supposedly cryptic reef environments. Here, using petrography, lipid biomarker analysis, and stable isotope data, we aim to understand the formation mechanism of microbial carbonate enclosed in deep fore reef limestones from Mayotte and Mohéli, Comoro Islands, which differ from other reefal microbial carbonates in that they contain less microbial carbonate and are dominated by numerous sponges. To discern sponge-derived lipids from lipids enclosed in microbial carbonate, lipid biomarker inventories of diverse sponges from the Mayotte and Mohéli reef systems were examined. Abundant peloidal, laminated, and clotted textures point to a microbial origin of the authigenic carbonates, which is supported by ample amounts of mono-O-alkyl glycerol monoethers (MAGEs) and terminally branched fatty acids; both groups of compounds are attributed to sulfate-reducing bacteria. Sponges revealed a greater variety of alkyl chains in MAGEs, including new, previously unknown, mid-chain monomethyl- and dimethyl-branched MAGEs, suggesting a diverse community of sulfate reducers different from the sulfate-reducers favoring microbialite formation. Aside from biomarkers specific for sulfate-reducing bacteria, lipids attributed to demosponges (i.e., demospongic acids) are also present in some of the sponges and the reefal carbonates. Fatty acids attributed to demosponges show a higher diversity and a higher proportion in microbial carbonate compared to sponge tissue. Such pattern reflects significant taphonomic bias associated with the preservation of demospongic acids, with preservation apparently favored by carbonate authigenesis.

Irrigation alters biogeochemical processes to increase both inorganic and organic carbon in arid-calcic cropland soils

Irrigation in arid croplands is necessary to sustain crop growth, but with increasing water scarcity and population growth in drylands, irrigation systems may need to shift from flooding to dripping techniques to cope with increased water demand. Therefore, it is important to understand how irrigation drives organic and inorganic carbon dynamics in arid-calcic soils. This study on arid-calcic cropland soils assessed the influence of flood and subsurface drip irrigation on soil organic carbon (SOC) and soil inorganic carbon (SIC) formation as influenced by soil chemical properties and bacterial and fungal biomass. As well, these dynamics were assessed in an unmanaged/unirrigated desert soil. Under drip irrigation, SOC was significantly greater than under flood irrigation, but flood stored more SIC than drip irrigation and no irrigation. The observed SOC–SIC patterns were likely driven by calcium binding. Flood irrigation adds significantly more calcium and bicarbonate to the system, while leaching dissolved organic carbon (DOC). Under flood, calcium is likely more preferentially bound as calcium carbonate. Under drip irrigation, less water was added, calcium and SOC were maintained in the rooting zone where SOC may be stabilized via cation-mediated bridging. Despite higher SOC under drip, more total, and bacterial biomass were detected under flood than drip irrigation, which promoted fungal biomass. Bacterial biomass under flood irrigation may be contributing to microbial carbonate precipitation, supported by the greater presence of common bacterial groups known to contribute to this process, and significant positive relationships with calcium. This research emphasizes the importance of examining SOC and SIC dynamics from abiotic and biotic and particularly microbial perspectives; to optimize soil carbon storage in arid croplands.

Self-assembled silk fibroin cross-linked with genipin supplements microbial carbonate precipitation in building material.

The process of microbially induced carbonate precipitation (MICP) is known to effectively improve engineering properties of building materials and so does silk fibroin (SF). Thus, in this study, an attempt was taken to see the improvement in sand, that is, basic building material coupled with MICP and SF. Urease producing Bacillus megaterium was utilized for MICP in Nutri-Calci medium. To improve the strength of SF itself in bacterial solution, it was cross-linked with genipin at the optimized concentration of 3.12 mg/mL. The Fourier transform infrared (FTIR) spectra confirmed the crosslinking of SF with genipin in bacterial solution. In order to understand how such cross-linking can improve engineering properties, sand moulds of 50 mm3 dimension were prepared that resulted in 35% and 55% more compressive strength than the one prepared with bacterial solution with SF and bacterial solution only, respectively with higher calcite content in former one. The FTIR, SEM, x-ray powder diffraction spectrometry and x-ray photoelectron spectroscopy analyses confirmed higher biomineral precipitation in bacterial solution coupled with genipin cross-linked SF. As the process of MICP is proven to replace cement partially from concrete without negatively influence mechanical properties, SF cross-linked with genipin can provide additional significance in developing low-carbon cement-based composites.

Mitigating alkali-silica reaction in cement mortars through microbial carbonate precipitation technique

Alkali-Silica Reaction (ASR) is a major cause of durability reduction in cement mixtures. This reaction takes place between the reactive silica contained in aggregates and the alkaline elements contained in cement (sodium and potassium), producing a hydrophilic gel known as glass water. This gel swells upon absorbing water, causing a damaging internal pressure in the mortar. This study aimed to investigate the impact of Microbial-Induced Calcite Precipitation (MICP) with Sporosarcina pasteurii on the progress of ASR in cement mortars. The mortars were made using the accelerated mortar bar method (ASTM C1260) by substituting 0, 25, 50, 75, and 100 % of aggregates with waste glass, as the extreme material causing ASR. The glass was treated by two methods named Wet Calcite Precipitation (WCP) and Fixed Calcite Precipitation (FCP), which both involved spraying 0.5 ml/cm2 of bacterial suspension on the glass. After 28 days of exposure to alkaline conditions, the mortars were examined by Scanning Electron Microscopy, X-ray Diffraction spectroscopy, and Energy-dispersive X-ray spectroscopy to verify the occurrence of ASR. The mortars were subjected to the expansion test, the ultrasonic pulse velocity (UPV) test, and the compressive strength test to measure their physical and mechanical properties. Both MCP treatments managed to significantly reduce the adverse effects of ASR (compared to the control) at the 95 % confidence level. Between WCP and FCP, WCP was more effective in improving the results of UPV and expansion tests, and FCP was more effective in improving compressive strength. The findings showed that MICP can effectively inhibit the adverse effects of ASR in cement mortars.

Dual eco-friendly application of silica fume and scoria in cement-based materials through the enhancement of microbially-induced carbonate precipitation

The partial replacement of cement or natural aggregates with industrial wastes and using microbially-induced carbonate precipitation to heal cracks are two developing methods to make more sustainable concrete. In this study, a combination of these two methods was used for the first time: Partial replacement of cement with silica fume to economically create a more favorable pH for bacterial activity and substituting natural sands partially with scoria aggregates as a novel carrier and protector for bacterial spores against the harsh and alkaline conditions of cement mortar. Preliminary investigations identified scoria as a suitable carrier since the activity of immobilized cells did not decrease considerably. Thermogravimetric and X-ray diffraction analyses confirmed that spores immobilized in scoria are capable of precipitating calcium carbonate. Different mortar mixtures were made with and without scoria immobilized healing agents and silica fume. In the absence of silica fume, adding biological healing agents to mortar mixture enhanced flexural and compressive strengths by 13% and 10%, respectively, and by 18% and 15% in the silica fume amended mortars. Healing agents lowered sorptivity coefficients by 49% when samples lacked silica fume and 63% when specimens included it. The presence of silica fume resulted in a more favorable pH environment for bacterial activity and increased precipitation of calcium carbonate, as confirmed by the scanning electron microscope. Replacing a part of cement with silica fume -as an industrial byproduct- has multiple ecological benefits: protecting the environment via waste reuse, reducing demand for energy and natural resources, decreasing greenhouse gas emissions, lowering cement manufacturing costs, and finally improving the performance of microbial carbonate precipitation leads to the production of more sustainable concrete.

Urea supply control in microbial carbonate precipitation to effectively fill pores of concrete

In cement-based cementitious materials, high-porosity areas tend to expand microcracks. To counter this problem, microbially induced calcite precipitation (MICP) was suggested to fill the pores. However, it is unclear how to control the supply of urea to increase the MICP efficiency of Bacillus sp. Therefore, in this study, the microbial growth rate, urease activity, and urea-to-carbonate conversion efficiency were determined under different urea concentrations. When the urea concentration was 0.15 mol/L, the growth rate was 0.22 h−1, the cell number reached 4 × 109 colony-forming units (CFUs) mL−1, and the urease activity was approximately 0.12 mg g-1h−1. Additionally, the conversion efficiency reached 40%, following the rule of 0.51 + 0.08 e0.5x. The electron-transfer rate of MICP measured via cyclic voltammetry was 6.6 × 10-6 cm s−1. It is based on nutrients, Bacillus sp., and urea and aims to develop a self-healing coating by reducing the porosity and improving its apparent impermeability.

An experimental approach to microbial carbonate precipitation in improving the engineering properties of sandy soils

PurposeStabilization of weak soil can be achieved through different methods, some of which include jet column, cement stabilization and fly ash stabilization. Unfortunately, the use of the aforementioned methods of soil improvement affects the environment negatively thereby leading to environmental degradation. With the aforesaid impediment in mind, the need for devising methods of weak soil improvement becomes pertinent.MethodsBacillus sp. — a non-pathogenic organism found abundantly in soil — was investigated in this study as a potential agent of soil improvement. The usability of Bacillus sp. in soil improvement was investigated with direct shear tests and permeability tests under optimum conditions in this study.ResultTime-dependent study on the effect of the ureolytic bacteria Bacillus sp.-induced calcium carbonate precipitation shows reduction in permeability and increase in the strength of the soil under study. On exhaustion of the available nutrients in the soil, however, the strength of the soil is not negatively impacted.ConclusionMicrobially induced calcium precipitation by Bacillus sp. is effective in soil improvement as such it may serve as substitute for conventional soil stabilization techniques. The ability of the bacteria to precipitate calcium carbonate in the soil leads to reduction in the permeability and increase in the shear strength of the soil.

Biochemical composite material using corncob powder as a carrier material for ureolytic bacteria in soil cadmium immobilization

Corncob powder possessing its superiority in environmental sustainability and cost, was approved with strong capability of being a replacement of biochar in facilitating the microbial carbonate precipitation process. In this study, the ureolytic bacterial strain Bacillus sp. WA isolated from a pre-acquired metal contaminated soil in Guiyu, China, was showed to be well attached on the surfaces of corncob powder, indicating the carrier's role as a durable shelter for bacterial cells. The efficient immobilization helped develop biochemical composite material (BCM) and proven to function better the calcite precipitation. Afterwards, the mechanism and multi-directional benefits of BCM in edaphic cadmium remediation were examined through pot experiment and compared with corncob powder/bacterial strain/nutrient media as control groups. Integrated lab-scale analyses emphasized the advantages of BCM by the maximum soil urease activity (up to 3.440 U/mg and increased by 214% in 28 days), maximal bacterial propagation (most abundant population in fluorescence microscopy), richest surface functional group (most remarkable OC bond and CO bond in FTIR result), notable calcite precipitation (clear calcite crystals on the surface of BCM compared to control group under SEM-EDS), and highest Cd immobilization rate (exchangeable Cd decreased by 68.54%), among all treatments. The pH and electroconductivity measurements additionally led to the mechanism of corncob powder and NBU promoting pre-existed ureolytic bacteria in soil, which demonstrated the added value of corncob to be fine carbon source and residence shelter for soil microorganism, revealing its potential in developing agricultural materials.

Effect of Hydrocarbon Contamination on Biostabilization of Soil Contaminated with Motor Oil and Gasoline

Environmental problems caused by soil contamination can cause changes in the physical, chemical and geotechnical properties of the soil. Research on a suitable method for soil improvement has focused on the use of biological methods for soil improvement and remediation. Microbial calcium carbonate precipitation has been applied to solve many geotechnical problems. In this study, sandy soil was mixed with two conventional hydrocarbon pollutants and classic soil mechanics tests (compaction, direct shear, uniaxial and permeability tests) were implemented. The use of two bacterial solutions, two-phase injection and bacterial flocculation with injection of cementation solution, produced favorable results. Considering the lower inhibition of gasoline in low dilution, it was possible to improve with both methods. In the case of soil contaminated with motor oil, limitations on the use of microbial calcium carbonate precipitation were improved with the use of bacterial flocculation. The results of this approach were more suitable because the bacteria stabilized between the soil grains. XRD, SEM, EDS and wet chemical analysis were carried out to help confirm and interpret the results.

Environmental implications of the use of bio-cement treated recycled aggregate in concrete

Use of aggregates from recycled construction and demolition wastes in concretes alleviates the disposal problem and reduces the cost of concrete significantly. However, excessive water absorption, weak interfacial transition zone, and high porosity are its shortcomings. This study explores a bacterial cement and conventional cement slurry coating treatment on recycled coarse aggregates (RCA) for overcoming these shortcomings. In the first method, microbial carbonate precipitation (MCP) through bio-mineralization treatment has been utilized. Four different concretes were made using both control and treated aggregates. Once the performance of these concrete mixes was found adequate, a life cycle assessment was conducted using ISO14040–44 guideline to determine their environmental impacts. The experimental results confirmed that concrete with MCP treated aggregate offered better material performance than the untreated recycled aggregate based concrete mixes and possessed similar properties as natural aggregate concrete. While MCP process avoided the use of energy intensive cement, this research discovers that concrete with MCP treated aggregates was found to produce marginally higher environmental impacts than other concrete mixes mainly due to additional emissions associated with the bio-cement treatment of RCA. Further environmental mitigation strategies for concrete with MCP treated aggregates has considered to improve its environmental performance in terms of global warming impact and cumulative energy demand. This study demonstrates that the use of 100% RCA delivers significant environmental benefits in terms of ecological footprints, land conservation and biodiversity in a densely populated region like India.

RETRACTED: Simulation of microbial enhanced recycled aggregate preparation system based on artificial intelligence and embedded processor

Construction waste recycling is prevented by its high water absorption rate and the weak bond of the new cement paste. This problem is exacerbated by the fact that Requirements for Accreditation Scheme (RFAS) recycled porridge production. To explore the possibility of repeated use of the RFAS system, it is proposed in the integrated study of Microbial Carbonate Precipitation (MCP) derived from RFAS. Due to its rapid construction, the demand for concrete raw materials, especially coarse aggregates, increases the risk of premature erosion of natural resources. Alternative energy sources for raw materials delay the possibility of this initial exhaustion. Recycled Coarse Aggregate (RCA) played an important role as a ready-mixed concrete substitute. Natural Coarse Aggregate (NCA) changes. Previous studies have shown that RCA's special reinforcing concrete lags behind NCA. I hope that may be due to the microstructure of the calcium carbonate hailstone. Recycling aggregate has high water absorption and crushing indicators. In recent years, the integrated cycle has changed the new treatment model biopsy. Degradation-enhanced protocols have been implemented to change the nature of the motor in circulation. Famous for using the information protocol learning machine based on extracting and source information, it comes on a hardware platform provided that vendors compete between the FPGA and the GPU to run intensive computational learning algorithms quickly and efficiently. Deep learning, which is considered to be the key point by which drivers compare the most advanced machine learning applications.

Recycled aggregate mortar enhanced by microbial calcite precipitation

The reuse of construction and demolition waste (CDW) is hampered by its high water absorption and weak bonds with new cement paste. This problem is more severe for recycled fine aggregates (RFAs) that are involuntarily generated during the production of recycled coarse aggregates. To explore the feasibility of reusing RFAs in construction, microbial carbonate precipitation (MCP) is presented in this study to consolidate the RFAs derived from CDW. The effects of calcium sources on bacterially induced MCP were investigated, and the efficiency of MCP for improving RFAs was evaluated in terms of physical and mechanical properties. Results show calcium chloride is an optimal calcium supplement that is useful for generating calcium carbonate, as compared with the effect of calcium nitrate. MCP treatment has improved the quality of RFAs, with decreases in water absorption, crushing value and the powder content. Furthermore, mortars containing 100% treated RFAs exhibited better workability and improved compressive strength, with a maximum increment of 32% after 28 d of curing. The pore structures of mortars containing modified RFAs were densified, with decreased porosities detected by the mercury intrusion porosity method. X-ray diffraction and scanning electron microscopy revealed the precipitation of calcium carbonate on the RFAs.

Induction of microbial carbonate precipitation as a sustainable strategy for post-improvement and remediation of cold mix asphalt

Cold Mix Asphalt (CMA) is highly susceptible to moisture damage, manifesting itself in stripping, raveling, rutting, and cracking faults. This study aimed to tackle this concern with bio-treatment. In doing so, this effort investigates the efficacy of microbial calcium carbonate precipitation in (i) the post-bio-strengthening (PBS) of mechanical properties and (ii) bio-remediation (BR) of moisture damage in cold-mix asphalt emulsion mixtures. To study the post-bio-strengthening potential, a set of cold-mix asphalt specimens was sprayed and injected with bacterial culture medium and nutrient solution to induce calcium carbonate precipitation for the purpose of post-strengthening. Then, the effect of curing times of 7, 14, 28, and 56 days on the fixation of precipitates in the mixtures was examined. To study the bio-remediation potential, another set of cold-mix asphalt specimens was subjected to a freeze-thaw cycle (modified Lottman test) intended to cause moisture damage and bacterial culture medium and nutrient solution were injected, afterward. For these specimens, the appropriate curing time of the fixation process for the bio-remediation was determined. All specimens were subjected to the destructive and non-destructive tests of mechanical properties, semi-circular bending (SCB), moisture susceptibility and also Cantabro test to assess indirect tensile strength (ITS), Tensile strength ratio, Indirect tensile fracture energy ratio, percent of toughness loss, crack propagation by SCB fracture energy, ultrasonic pulse velocity ratio, electrical resistivity, as well as the abrasion resistance. The Analysis of Variance (ANOVA) of the results was performed at 95% confidence level. A Field Emission Scanning Electron Microscope (FESEM) examination was also performed to study the microstructure and precipitates formed in the mixtures. The results showed that the post-bio-strengthened specimens had significantly better mechanical and resistance to moisture damage properties than those of control. The moisture-damaged specimens that underwent the bio-remediation also showed significant improvements in mechanical properties, and in some cases were similar to the undamaged control specimens. The results indicate that microbial calcium carbonate precipitation (MCP) can serve as an effective and sustainable method for both post-strengthening and remediation of cold mix asphalt mixtures.

Effect of simulated acid rain on the stability of calcium carbonate immobilized by microbial carbonate precipitation

The stability of carbonate products resulting from microbially induced carbonate precipitation (MICP) under acid rain is under question. The present study investigated the stability of CaCO3 precipitated by MICP in soil under simulated acid rain (SAR). Soils were treated continuously for two months with four SAR pH levels: 3.5, 4.5, 5.5, and 7.0. During SAR, biostimulation using nutrient broth containing urea and calcium chloride was adopted to ensure CaCO3 precipitation. At the end of treatments, soil samples from top and bottom layers were analyzed for bacterial diversity by Illumina MiSeq sequencing, Fourier transform infrared (FTIR) spectroscopy for identification of chemical functional groups related to calcite precipitation, and X-ray diffraction (XRD) for identification of the main crystalline phases. The analysis identified several ureolytic bacteria mainly from Arthrobacter and Sporosarcina genera in SAR-treated soils accelerated with biostimulation, and urease quantities of greater than 300 mg NH4+ per kg soil at all pH levels. The precipitation of CaCO3 was pronounced and its stability was maintained even when the pH was as low as 3.5. The results obtained in this study are helpful to the scientific community to ensure the immobilization of heavy metals with microbial carbonate precipitation in soil under acid rain.

Mathematical modelling and simulation of microbial carbonate precipitation: the urea hydrolysis reaction

Microbial carbonate precipitation is expected to play a major role in next-generation soil improvement technologies. To date, research into this method has relied on experimental and/or observational approaches. However, in order to understand the long-term effects of microbial carbonate precipitation and apply these to real environments, it is necessary to employ a predictive approach to determine the future state of the soil when using this soil improvement method. In this work, a mathematical model and numerical simulations based on the reaction–diffusion system for the microbial urea hydrolysis reaction are proposed. These techniques may be used to provide the spatiotemporal precipitation patterns of carbonates between soil particles and the particle surfaces. The simulation results revealed that the characteristic precipitation patterns depend on the diffusion of carbonates caused by the microbial urea hydrolysis reaction, and there was a significant shift in the amount of carbonate from a dissipated state into an equilibrium state.

Using microbial carbonate precipitation to improve the properties of recycled fine aggregate and mortar

This study investigates the use of microbial carbonate precipitation (MCP) by Sporosarcina pasteurii (S. pasteurii) to improve the properties of recycled fine aggregate (RFA). The factors influencing MCP are experimentally investigated. The recommended precipitation conditions for the pH, bacteria concentration, and calcium concentration are determined to be 9.5, 108 cells/mL, and 0.55 mol/L, respectively. Under these proposed conditions, the effects of MCP modification on RFA are also investigated and found the weight of modified RFA increases and the water absorption of modified RFA decreases. The flexural strength and compressive strength of mortar specimens cast by modified aggregate are improved. The result confirms the positive effects of MCP for improving the properties of RFA.

Using microbial carbonate precipitation to improve the properties of recycled aggregate

This paper attempts to find an efficient precipitation method to modify recycled aggregates (RAs) with microbial carbonate precipitation and investigate the modification effect of RAs on the properties of the recycled aggregate concrete (RAC). Firstly, laboratory prepared concrete cubes were prepared as model RAs to compare the effectiveness of different precipitation methods, considering calcium-source addition methods and ways of rotation treatment. Based on the tested results, an efficient precipitation method was proposed. Secondly, the industrial sourced RAs were modified by the proposed precipitation method, and cast into concrete. The bio-modified RAC showed higher compressive strength because of the enhancement of the microhardness of the interfacial transition zones after modification.

Short-term variation of ooid mineralogy in the Triassic-Jurassic boundary interval and its environmental implications: Evidence from the equatorial Ghalilah Formation, United Arab Emirates

Abstract In the Triassic-Jurassic (T-J) interval, only a few continuous carbonate sections have been reported, and detailed studies about ooids and their significance are scarce. This study focuses on abundant ooids in potentially continuous T-J carbonate sections representing equatorial, shallow marine environments. Mineralogical changes of ooids are proposed as a marker for transitional marine chemistry including carbonate saturation after ocean acidification and provide information about crisis and recovery scenarios for the initial CIE (carbon isotope excursion) and subsequent positive CIE. In the Ghalilah Formation, United Arab Emirates (UAE), the Sakhra Member is deposited immediately above the T-J boundary. Based on field work and thin section observation, the Sakhra Member can be divided into three coarsening-upward cycles (in ascending order, named C1–C3), each of which consists of peloidal mudstone/wackestone in the lower part and oolitic packstone/grainstone in the upper part. Petrological observation (thin section, SEM), stable isotope (inorganic carbon and oxygen) and elemental analysis suggest temporal change of original mineralogy from C1 to C3 ooids: from high-Mg calcite in C1 ooids to aragonite in C2 and C3 ooids. The mineralogical change of ooids is possibly related to variations in seawater carbonate saturation. The lower carbonate saturation indicated by C1 ooids reflects a transitional period before recovery from ocean acidification due to massive and rapid release of acidic gases (CO2 and SO2) by CAMP eruptions. Subsequently, from C1 to C3 ooids, seawater gradually experienced increasing carbonate saturation and increasing microbial carbonate precipitation. Increased microbial activities combined with elevated terrestrial influx may have significantly reduced the atmospheric CO2 concentration and restored carbonate saturation, which laid the foundation for full biotic recovery.