Gypsum Rocks Research Articles

Adsorption of Cadmium from Aqueous Solution onto Untreated Gypsum Rock Material: Equilibrium and Kinetics

The concentration of heavy metals exceeding from certain limit may cause risk and endanger ecosystems and human health. Water receives a considerable concentration of heavy metals from different anthropogenic and natural sources. A study was carried out to investigate the effectiveness of rock materials on the reduction of Cd from contaminated water. For this purpose, gypsum was applied to the contaminated water. The findings of the present study concluded that the adsorption of Cd was higher in finer rock material rather than coarse material due to the surface area. The finer grains contained a greater surface area than coarse grains. The isotherms of adsorption were constructed according to the mathematical linearization. The best-fitting followed the Freundlich and Dubinin–Radushkevich models, describing multilayer adsorption and chemical interaction, also confirmed by the pseudo-second-order kinetic model. The material removed a greater amount of Cd from contaminated water, especially at an increasing application rate.

Mode-I fracture toughness and mechanisms of Salt-Rock gypsum interlayers under real-time high-temperature conditions

In this study, an attempt was made to investigate the influence of temperature on the stability and compactness of gypsum rock. The fracture toughness was tested using a real-time online high temperature system, and the sample was characterized by scanning electron microscopy and X-ray diffraction in order to further investigate the fracture characteristics and mechanisms. The results showed that (1) The change in gypsum fracture toughness (KIC) with temperature can be divided into four stages: a slow decrease with increasing temperature between 20 and 100 °C, a sharp decrease from 100 to 300 °C, a slow decrease from 300 to 600 °C, and a rapid decrease from 600 to 700 °C; (2) When gypsum is at the low-temperature stage (20–300 °C), the fracture surfaces are smooth and flat. The main failure mode is trans-granular fracture. In the high-temperature stage (400–700 °C), the fracture surface is rough. The fracture morphology is complex and diverse, with fibrous stripes and secondary cracks being observed on the fracture surface. Intergranular fracture is the main fracture mode. (3) When the temperature of gypsum is between 100 and 300 °C, weakening occurs by thermal dehydration and calcium sulfate dihydrate is dehydrated to β-calcium sulfate and γ-calcium sulfate. At temperatures ranging from 300 to 700 °C, the weakening mechanisms are thermal fracturing and crystal distortion of calcium sulfate. The results of this study provide theoretical guidance for evaluating the stability and compactness of nuclear waste storage.

Features and Constitutive Model of Gypsum’s Uniaxial Creep Damage considering Acidization

Acidic fluids cause rock erosion and further endanger the safety of rock engineering, especially the corrosion of pillars by acidic or weakly acidic groundwater. In this paper, the rock samples in the gypsum mining area were taken as the research object. Uniaxial compression creep tests were carried out under neutral water,pH=6andpH=5hydrochloric acid solutions, respectively. Meanwhile, the specimens before and after saturation were observed by an electron microscope scanner. The results show that (1) the gypsum specimens withpH=5hydrochloric acid were damaged at the first stress level, while that withpH=6andpH=7were destroyed at the second stress level. The failure modes of the three groups were basically the same, with cleavage and end damage of different degrees. The difference is that the failure time of the former is earlier than that of the latter, which indicates that the stronger acidity causes greater corrosion on the creep of the samples. (2) From the perspective of microstructure, the samples saturated in the neutral aqueous solution and dry state are compact and complete in structure, and the whole is relatively homogeneous. However, after saturating in the acid solution, the samples significantly increased dense pores with large size and loose structure. Due to the rapid increase, the surfaces of the samples are almost like “holes”. (3) A new nonlinear creep constitutive model was established by connecting Burgers model with nonlinear viscoplastic body (NVPB) model in series, which can well describe the creep characteristics of gypsum rocks under acid corrosion.

The History of Transgressions during the Late Paleocene-Early Eocene in the Kuqa Depression, Tarim Basin: Constraints from C-O-S-Sr Isotopic Geochemistry

The Tethys Sea extended into the Kuqa Depression from the Paleocene to the late Eocene and provided an abundant provenance for the deposition of evaporite sequences. Until now, detailed research on the history of transgressions during the late Paleocene-early Eocene in the Kuqa Depression has been limited. Therefore, in this study, we took the upper Paleocene Talak section and the lower Eocene Xiaokuzibai section in the western part of the Depression as the research objects and analyzed the petrology, the carbon and oxygen isotopes of carbonate rocks, and the sulfur and strontium isotopes of gypsum rocks to systematically study the above issues. The δ13C, δ18O and δ34S values of the upper Paleocene evaporite sequences were determined to be between 4.2‰ and 5.7‰, between −5.2‰ and 2.4‰, and between 16.5‰ and 17.9‰, respectively. The δ13C, δ18O, δ34S, and 87Sr/86Sr values of the lower Eocene evaporite sequences were determined to be between −6.9‰ and −2.0‰, between −9.0‰ and −4.5‰, between 10.5‰ and 17.0‰, and between 0.708642 and 0.709883, respectively. The analysis results show that the evaporite sequence of the upper Paleocene was formed by transgression. The deposition of the evaporite sequence changed from continental to marine deposition, and then gradually transitioned to continental during the Early Eocene. This paper is of great significance for reconstructing the history of transgressions in the Tethys tectonic realm during this period.

Assessment of Water Quality Using Chemometrics and Multivariate Statistics: A Case Study in Chaobai River Replenished by Reclaimed Water, North China

Dry rivers could be effectively recovered by reclaimed water in North China, while river water quality would be an important issue. Therefore, it is important to understand the spatiotemporal variation and controlling factors of river water. Water samples were collected during March, May, July, September, and November in the year 2010, then 20 parameters were analyzed. The water environment was oxidizing and alkaline, which was beneficial for nitrification. Nitrate was the main nitrogen form. Depleted and enriched isotopes were found in reclaimed water and river water, respectively. Total nitrogen (TN) and total phosphorus (TP) of reclaimed water exceed the threshold of reclaimed water reuse standard and Class V in the surface water quality criteria. Most river water was at the severe eutrophication level. The sodium adsorption ratio indicated a medium harmful level for irrigation purpose. Significant spatial and temporal variation was explored by cluster analysis. Five months and nine stations were both classified into two distinct clusters. It was found that 6 parameters (chloride: Cl−, sulphate: SO42−, potassium: K+, sodium: Na+, magnesium: Mg2+, and total dissolved solids: TDS) had significant upward temporal variation, and 12 parameters (dissolved oxygen: DO, electric conductivity: EC, bicarbonate: HCO3−, K+, Na+, Ca2+, TDS, nitrite-nitrogen: NO2-N, nitrate nitrogen: NO3-N, TN, TP, and chlorophyll a: Chl.a) and 4 parameters (Mg2+, ammonia nitrogen: NH3-N, and the oxygen-18 and hydron-2 stable isotope: δ18O and δ2H) had a significant downward and upward spatial trend, respectively. The Gibbs plot showed that river water chemistry was mainly controlled by a water–rock interaction. The ionic relationship and principal component analysis showed that river water had undergone the dissolution of carbonate, calcite, and silicate minerals, cation exchange, a process of nitrification, photosynthesis of phytoplankton, and stable isotope enrichment. In addition, gypsum and salt rock have a potential dissolution process.

GYPSUM AND LIMESTONE DISSOLUTION WITHIN FATHA FORMATION (MIDDLE MIOCENE) AT VARIOUS pH SOLUTIONS: A LABORATORY STUDY

The studied rocks (gypsum, limestone, & marl) of Middle Miocene Fatha Formation situated beneath the foundations of the study site in Mosul city. These rocks were obtained from four boreholes, at various depths up to 30 meters. The aim of work is to study the dissolution of rocks at various conditions, and then obtain the effect of the dissolution on their physio-mechanical properties, in addition, to amelioration our understanding of the consequences of the dissolution by acid-sulphate solution which is indisputably linked to sulphur oxidation. Gypsum and limestone rocks (10 samples of each type of rocks) and immersed in three solutions at various pH environmental conditions; acidic (0.0001N H2SO4), neutral (tap water), and alkaline (0.0001N NaOH) solutions. Chemical analysis results of specific elements (Ca2+, Mg2+, Na+, K+, S2-, Cl-) at the acidic, neutral, & alkaline solutions show that: The dissolution (concentration of Ca2+ & S2-) was higher in alkaline solution of gypsum rocks, while the dissolution (concentration of Ca2+) of the limestone rocks was higher in neutral (tap water) solution than other solutions. The physio-mechanical properties of gypsum and limestone rocks samples such as, bulk specific gravity, indirect tensile strength, and unconfined compressive strength were determined. The compressive strength of water-saturated samples of gypsum rocks decreased by 25.56% and of limestone by 23.97% when compared with the dry samples, but the indirect tensile strength of water-saturated samples of gypsum rocks decreased by 36.62% and of limestone by 36.34% compared with the dry samples.

Environmental determinants influencing anthrax distribution in Queen Elizabeth Protected Area, Western Uganda.

Bacillus anthracis, the bacteria that causes anthrax, a disease that primarily affects herbivorous animals, is a soil borne endospore-forming microbe. Environmental distribution of viable spores determines risky landscapes for herbivore exposure and subsequent anthrax outbreaks. Spore survival and longevity depends on suitable conditions in its environment. Anthrax is endemic in Queen Elizabeth Protected Area in western Uganda. Periodic historical outbreaks with significant wildlife losses date to 1950s, but B. anthracis ecological niche in the ecosystem is poorly understood. This study used the Maximum Entropy modeling algorithm method to predict suitable niche and environmental conditions that may support anthrax distribution and spore survival. Model inputs comprised 471 presence-only anthrax occurrence data from park management records of 1956–2010, and 11 predictor variables derived from the World Climatic and Africa Soil Grids online resources, selected considering the ecology of anthrax. The findings revealed predicted suitable niche favoring survival and distribution of anthrax spores as a narrow-restricted corridor within the study area, defined by hot-dry climatic conditions with alkaline soils rich in potassium and calcium. A mean test AUC of 0.94 and predicted probability of 0.93 for anthrax presence were registered. The five most important predictor variables that accounted for 93.8% of model variability were annual precipitation (70.1%), exchangeable potassium (12.6%), annual mean temperature (4.3%), soil pH (3.7%) and calcium (3.1%). The predicted suitable soil properties likely originate from existing sedimentary calcareous gypsum rocks. This has implications for long-term presence of B. anthracis spores and might explain the long history of anthrax experienced in the area. However, occurrence of suitable niche as a restricted hot zone offers opportunities for targeted anthrax surveillance, response and establishment of monitoring strategies in QEPA.

An Assessment of Soil’s Nutrient Deficiencies and Their Influence on the Restoration of Degraded Karst Vegetation in Southwest China

The distribution of karst landscapes over the Earth’s surface, to a large extent, follows the distribution of carbonate (limestone and dolomite) and gypsum rocks and together these make up about 12% of the Earth’s land area, and the largest karst region in to world is in Southwestern China. Characterized by a unique set of landforms, these geographical areas also differ from other geomorphic regions by the presence of cave systems in the subsurface. Unfortunately, due to human disturbances, such as deforestation, agricultural expansion, livestock overgrazing and fire, these regions have been affected by varying degrees of degradation, which could also be worsened if water and soil erosion phenomena typical of these areas are considered. Therefore, there is a need to implement measures and strategies to protect these karst areas and develop plans to restore vegetation in this region. To support local and national authorities to achieve this goal, this study aims to characterize nutrient deficiencies in degraded areas and estimate what could be the thresholds required to facilitate the restoration of vegetation in karst areas in southwest China. The results obtained confirm that the total element concentrations for Soil Organic Carbon (SOC), N, K, Ca, P, S and Mg were relatively high in the study karst area in southwest China. However, the total amounts of soil nutrients stored were very low due to the limited amount of soil identified as a consequence of previous deforestation processes undertaken within this study area and this aspect needs to be taken into consideration if aiming at a positive success of future restoration processes.

Identification, biochemical composition and phycobiliproteins production of Chroococcidiopsis sp. from arid environment

Molecular and microscopic studies were performed to identify Chroococcidiopsis sp., an endolithic cyanobacterium, isolated from gypsum rocks of Atacama Desert (Chile). It was adapted to grow in mineral liquid medium, with 9 mM nitrate, bubbled with CO2-enriched air (2.5 % v/v), and continuously illuminated with a white light of 70 μmol photons m–2 s–1. The obtained biomass (productivity of 0.21 g L–1 d–1) had a C/N ratio of 6.67, and it contained carbohydrates (45.40 % of dry weight), proteins (36.72 %), lipids (5.60 %) nucleic acids (3.90 %) and ashes (8.28 %). The lipid fraction was particularly rich in palmitic (29.86 % of total fatty acids), linoleic (18.20 %), palmitoleic (12.75 %), linolenic (10.92 %), stearic (9.64 %) and capric acid (6.29 %). Chroococcidiopsis sp. accumulated phycobiliproteins in a light-dependent process and produced 204 mg g–1, under incident light of 10 μmol photons·m–2·s–1, with a relative abundance of 40.9 % for phycocyanin, 23.3 % for phycoerythrin, and 35.8 % for allophycocyanin. The biomass from this cyanobacterium can be a good source of these pigments, especially APC (maximum of 95 mg g dw−1), which are of interest for pharmacological, cosmetic, and food industries.

Finite element analysis of embankments on gypsiferous subgrade soil - stone column strengthened with geogrid

Gypsum and anhydrite rocks are frequently found in numerous countries of the world in extensive deposits, the huge region in middle and west of Iraq is classified as a gypseous soil. Stone columns are non-time dependent foundation technique used to increase the structural stability and to reduce the structural deformations of soil. In the present study, the finite element method is used as a tool to utilized the effect of using stone columns with geogrid as reinforcing material for treatment gypsiferous subgrade soil under embankment during both construction and consolidation conditions. The results show that decreasing the stone column spacing leads to a considerable decrease in the settlement beneath the embankment, especially below the center line, reduction in the settlement of about 60% and when using geosynthetic material the reduction about 75%. Also, increases the excess pore water pressure immediately after the construction of each lift of the embankment and then falls with and without using geosynthetic material. The vertical stress in the gypsiferous subgrade soil increases at a very small rate especially in the early stages and decreases as stone columns spacing decreases.

Damage Analysis of Soaking Gypsum and Safety Evaluation of Goaf: Based on Energy Dissipation Theory

Based on the theory of energy dissipation, the energy dissipation model of gypsum rock was established, and we analyzed the energy dissipation law of four stages (compaction stage, elastic stage, plastic stage, and failure stage) of gypsum rock failure process with different soaking time. The results show that: the energy of the system (total strain energy, releasable elastic strain energy and dissipative strain energy) changes dynamically. The total strain energy and releasable elastic strain energy decrease with the increase of soaking time. The growth rate is also negatively related to soaking time, while the dissipative strain energy is positively related to soaking time. Then, based on the geological characteristics and test data of gypsum mine in Northern Jiangsu Province, FLAC3D software was used to simulate the stability of goaf under natural and saturated conditions respectively. The simulation results show that the plastic area of goaf was not obvious and the stability was good under natural conditions. In the state of water saturation, most of the area was completely penetrated by the plastic area, the pillar was seriously unstable, which endangers the safety of the goaf.

Indications of the sedimentary environments by the sedimentary characteristics and trace elements of Ordovician Majiagou Formation, Northern Shaanxi salt basin

ABSTRACT The abundant geochemical information on elements in the autogenous sedimentary rocks can help reconstruct the paleoenvironment of the stratigraphic sedimentation period. Based on the analysis of sedimentary characteristics of Ordovician Majiagou Formation and the trace elements in limestone, dolomite and gypsum rocks in Northern Shaanxi salt basin, the relationship between the distribution of trace elements of Majiagou Formation and the sedimentary environment is discussed. The results display that Majiagou Formation is mainly composed of the sedimentation of carbonate rocks and evaporites, and the subfacies of open platform and restricted platform are developed. The trace element analysis shows that the deposition period of the Majiagou Formation is dominated by dry hot climate, and there are alternating dry and wet seasons in climate evolution. In middle Ordovician, the sedimentary environment of Majiagou Formation was undergoing the transformation of oxygen enrichment-oxygen deficiency-anoxic environment.

Sedimentary cycles of evaporites and their application in sequence division in the upper member of the Xiaganchaigou Formation in Yingxi Area, Southwestern Qaidam Basin, China

The upper member of the Xiaganchaigou Formation in the Yingxi Area of the Southwestern Qaidam Basin is a set of evaporite-bearing lacustrine series. In this study, petrographic analyses of rock thin sections, cores, drillings, logging as well as geochemistry were used to study the characteristics of the sedimentary cycles of the series. Concurrently, this study adopts a transgressive–regressive (T–R) cycle sequence theory, based on lithology, logging curves, the stacking pattern of the subsequences, and unconformity and seismic reflection terminal relations. This approach uses evaporites as the primary marker layer for identifying the initial lake flood surface and dividing the sequence of the evaporite-bearing series in the upper member of the Xiaganchaigou Formation. Results show a zonal distribution of evaporites transitioning laterally from the center to the margin of the basin to mixed carbonate rocks and then to clastic rocks. Vertically, there are two third-order sedimentary cycles and six fourth-order sedimentary cycles. Five types of evaporite lithofacies combinations were identified. Evaporites were formed by evaporative crystallization at a particular depth beneath lake water during a lacustrine regression during an arid paleo-climate and rapid subsidence of the basin basement. It has been established based on the asymmetric sedimentary cycle development model that during the lacustrine transgression stage, the mixed carbonate rocks were transformed into mudstone upward, and during the lacustrine regression stage, the mixed carbonate rocks transformed into gypsum rocks, glauberite, and halite, upward, while a delta and reef flat limestones developed at the edge of the basin. There is a one-to-one correspondence between the T–R cycle sequence division and the sedimentary cycle division.

Model test and DEM investigations into effects of cavities on a single pile in weak rock

The purpose of this study is to examine the effects of different cavity locations on the bearing capacity of pile foundations. To accomplish the purpose, a series of model tests was carried out on a small-scale single pile embedded in gypsum rock with predetermined cavities, thereafter, the numerical analysis was conducted. The studied model was simulated by the discrete-element method (DEM) using the two-dimensional discontinuous program PFC2D. The reduction factor was calculated to quantify the impact of cavities on the bearing capacity of pile foundations. The experimental and analytical results clearly show that the reduction factor decreased with an increase in the depth from the pile tip to the cavity, and the pile capacity is significantly reduced when cavities are located close to the pile tip. The two-dimensional DEM results visualised the cracks appeared inside the rock mass and the collapse of the cavity roof area, which cannot be seen in the experiment. The study also indicated a critical distance from the pile tip to the cavity that the influence of cavities to the pile is negligible.

Provenance and salt structures of gypsum formations in Pb-Zn ore-bearing Lanping basin, Southwest China

Large-scale gypsum rocks associated with world-class Pb-Zn ore formations are widely distributed in the Lanping Basin, Sowthwest China. Geochemical studies alongside field investigations were conducted in this study to determine the source and evolutionary processes of the gypsum rocks in this area. The gypsum sequences in the Lanping Basin developed in two formations: the Triassic Sanhedong Formation and the Paleogene Yunlong Formation. The gypsum hosted in the former displays a primary thick-banded structure with δ34SV-CDT values in the range of 14.5‰–14.8‰. Combined with the 87Sr/86Sr values (0.707737–0.707783) of limestone, it can be suggested that the Sanhedong Formation is of marine origin. In contrast, the gypsum from the Paleogene Yunlong Formation is characterized by the dome, bead and diapiric salt structures, wider range of both 87Sr/86Sr (0.707695–0.708629) and δ34SV-CDT values (9.6‰–17‰), thus indicating a marine source but with the input of continental materials. The initial layered salt formations were formed by chemical deposition in a basin and were later intensely deformed by collisional orogeny during the Himalaya period. As a result, variable salt structures were formed. We hereby propose an evolutionary model to elucidate the genesis of the gypsum formations in the Lanping Basin.

Use of DC voltage fluctuation method to investigate real-time Mode I and Mode II subcritical crack growth behavior in gypsum rock

Subcritical crack growth strongly influences the mechanical behavior of rock and the precursory phase of geohazards and catastrophic failure. In earlier studies, indirect measuring methods were used to investigate the subcritical crack growth behavior of rock materials. However, these methods cannot fully reflect the whole process of subcritical crack growth of geomaterials. Therefore, in this study, a new method (DC voltage fluctuation method) was developed which can monitor the whole process of crack growth and measure the crack growth rate in real time. This method is based on the monitoring principle of change in voltage caused by the change in resistance. Then, the whole processes of Mode I and Mode II subcritical crack growth of gypsum specimen were monitored in real time by the self-designed fracture strain gauge, which consists of 10 breakable resistance wires, and a DC voltage signal monitor. Furthermore, using the measured crack growth rates and the stress intensity factors of varying crack path lengths, the parameters of the modified Charles model were fitted. The results show that: (1) the subcritical crack growth process mainly includes three stages: cracking latent period (primary stage), steady-state crack growth stage (secondary stage), and accelerated crack growth stage (tertiary stage). The cracking latent period lasts for the largest proportion of the entire fracture process duration. The duration of each stage decreases gradually with increasing applied load. (2) In the steady-state crack growth stage, both Mode I and Mode II crack growth rates increase with increasing applied load. However, the crack growth rates in the accelerated stage are basically the same with increasing applied load. When a specimen is subjected to a given constant applied load, the subcritical crack growth rate of Mode II is higher than that of Mode I in the secondary and tertiary stages. (3) The parameters A and n of the subcritical crack growth model (modified Charles model) (secondary stage) increase with increasing external applied load. The parameters are closely associated with the size of fracture process zone at the crack tip. The results of this study can provide a deeper insight into the macroscopic failure of rock, and also provide the parameters for the time-dependent damage evolutional process of underground constructions.

A STUDY OF SPRING WATER QUALITY AND ITS SUITABILITY FOR DIFFERENT USES IN THE AREA OF BARTELLA – EASTERN MOSUL

The water of the three springs in the village of Tarjla (located in the area of Bartala, eastern Mosul) is characterized by different physical and chemical properties depending on the results of the laboratory tests of (NTU, EC, TDS, TH, PH) and major ions (Na+, Ca+2, Mg+2, Cl-, ) for six selected water samples for the study area. This difference did not remain constant, but changed with the flow of water to the neighboring villages (Sheikh Amir, Shaquli, Karemlesh), where the percentages of physical and chemical concentrations have changed in terms of the increase and decrease of some water samples. This is due to the time factor and the water contact of some of the soils and rocks that encountered their flow as well as exposure to the sun. The purpose of the research is to study the quality of springs water to determine its suitability for different uses. Using the Piper and Stiff classifications, the water quality is calcium-bicarbonate, the calcium ion predominates over the rest of the positive ions and the bicarbonate ion prevails over the rest of the negative ions, this indicates that spring number (1) and spring number (3) are derived from the Fat'ha formation deposits, which contain limestone and gypsum rocks that contain high concentrations of sulphates. The spring number (2) is derived from the Injana formation and modern sediments that is hydraulically connected with each other and can be considered one reservoir. By comparing the results of laboratory tests with the international standards, it was found that the water of spring number (2) is suitable for human use, and that the water of spring’s number (1) and (3) are not suitable for human use because they contain a high proportion of sulfur ions. All water samples are suitable for agricultural and animal use and very good to excellent

Sedimentary and Diagenetic Features and Their Impacts on Microbial Carbonate Reservoirs in the Fourth Member of the Middle Triassic Leikoupo Formation, Western Sichuan Basin, China

In recent years, the discovery of two gas fields in the fourth member of the Leikoupo Formation in the Western Sichuan Basin of SW China confirmed the exploration potential of microbial carbonates. The aim of the present study is to clarify the formation mechanism of the microbial reservoirs in the Leikoupo Formation. For this purpose, lithofacies, depositional environments, and diagenesis analyses were performed in samples collected from cores of 12 wells. The climate of study area was arid during Anisian time, and the water body was restricted. In such a climate, an evaporitic environment was developed, where ten types of lithofacies, dominated by microbial carbonates and gypsum rocks, were recognized. Thrombolites and stromatolites are the main high-quality reservoirs rock types in the fourth member of the Leikoupo Formation in the Western Sichuan Basin of SW China, which developed as microbial mounds, with reservoir space of microbial inter-clot pores, intra-clot pores, fenestral pores, inter-crystalline pores, and cracks. The microbial inter-clot pores are the main reservoir space, formed by trapping and binding of marls by benthic microbial communities. These pores were partially filled with evaporites because of the arid climate, which were subsequently dissolved (mainly gypsum) in the syn-depositional period, thus greatly improving the quality of reservoirs. Although some pores were occluded by multi-stage cements during the burial stage, major pores were well preserved own to the early dolomitization, rapid burial of the Leikoupo Formation, and early charging of hydrocarbon. The early dolomitization enhanced the anti-compaction ability of microbial carbonates during the burial stage. Rapid burial of the Leikoupo succession slowed down early cementation, and it also accelerated the maturation and expulsion process source rock to promote early charging of hydrocarbon in pores, which created a closed system, inhibiting strong burial cementation.

Mechanism of water extraction from gypsum rock by desert colonizing microorganisms

Microorganisms, in the most hyperarid deserts around the world, inhabit the inside of rocks as a survival strategy. Water is essential for life, and the ability of a rock substrate to retain water is essential for its habitability. Here we report the mechanism by which gypsum rocks from the Atacama Desert, Chile, provide water for its colonizing microorganisms. We show that the microorganisms can extract water of crystallization (i.e., structurally ordered) from the rock, inducing a phase transformation from gypsum (CaSO4·2H2O) to anhydrite (CaSO4). To investigate and validate the water extraction and phase transformation mechanisms found in the natural geological environment, we cultivated a cyanobacterium isolate on gypsum rock samples under controlled conditions. We found that the cyanobacteria attached onto high surface energy crystal planes ({011}) of gypsum samples generate a thin biofilm that induced mineral dissolution accompanied by water extraction. This process led to a phase transformation to an anhydrous calcium sulfate, anhydrite, which was formed via reprecipitation and subsequent attachment and alignment of nanocrystals. Results in this work not only shed light on how microorganisms can obtain water under severe xeric conditions but also provide insights into potential life in even more extreme environments, such as Mars, as well as offering strategies for advanced water storage methods.

Effects of chemical composition on the solubility and geomechanical characteristics of gypsum rocks from Gachsaran Formation, Iran

Evaporite rocks of the Gachsaran Formation make the reservoirs and foundations of several important dam site in southwest Iran. The solubility of these rocks is the main cause of instability and leakage problems usually observed in these dam sites. Therefore, investigation and consideration of engineering geological characteristics of these rocks, including their solubility, is crucial. In the present study, 10 gypsum rocks of the Gachsaran Formation were selected from Masjed-Soleyman, Haftkel, and Ramhormoz areas in southwest Iran. The chemical and mineralogical compositions of the samples were determined through optical microscopy, XRD, and XRF analyses. Different characteristics of samples including physical and mechanical properties, solubility, and solution rate were determined. Then, the effects of the chemical composition of gypsum rocks on geomechanical characteristics, solubility, and solution rate were assessed. Results showed that the proportion of two main gypsum components of CaO and SO3 and the CaO/SO3 ratio has a significant effect on gypsum strength and solubility. Also, an increase in the abundance of minor oxides of Al2O3, Fe2O3, SiO2, and K2O leads to a decrease in the solution rate.