Water In Carbonate Rocks Research Articles

Microscopic occurrence of primary water in carbonate gas reservoirs with fractures and vugs and its effect on water invasion mechanism

The structure of carbonate gas reservoirs has multiple pore-fracture cave media, and the gas–water flow mechanism is complex. Computed tomography (CT) and nuclear magnetic resonance (NMR) were used to explore the pore structure differences and collocation relationships of different small-scale carbonate cores with fractures and holes in the Longwangmiao Formation. Based on the concept of fractal dimensions, a quantitative method for water film occurrence was established, combined with surface wetting physics and mechanics. The formation of primary irreducible water and the influence mechanism of the water film on water invasion flow were clarified, the mechanical control mechanism of gas–water flow was analysed from the microelement structure, and the difference in water invasion in different pore structures was proven. This study showed that the bound water in carbonate rocks is controlled by micromechanics and occurs in the reservoir space through four mechanisms. Under the action of intermolecular forces and linear tension, a small amount of water film is formed as a movable pore surface, a small amount of pore edge space exists in the form of a corner because of the uneven rough pore surface, and a small amount exists in pores with pore diameters less than the critical pore diameter to form filling. Numerous pores occurred in isolated pores coordinated only by pores smaller than the critical pore size. Furthermore, the flow of the intrusive water phase is controlled by micromechanics such as the displacement force, viscous force of the water film layer on the pore wall, and the capillary force, which mainly occurs in connected pores and fractures larger than the “critical pore diameter of water invasion.” The “critical pore diameter” of the Longwangmiao formation ranges from 2.2 μm to 3.4 μm, and only the pores coordinated by small pores below the “critical pore diameter of water invasion” cannot be affected by the intrusive water phase due to the action of “pore resistance.” To form residual gas.

Analysis of the chemical characteristics and causes of high total hardness of groundwater in Jianghan Plain, China.

Familiarity with the chemical characteristics of regional groundwater can provide important guidance and reference for the development of regional groundwater exploitation. Jianghan Plain has been reported to have high groundwater total hardness (TH), resulting in the inability of local groundwater to be directly used as drinking water. In order to explore the causes of high TH, the paper analyzed the hydrochemical characteristics of shallow groundwater in Jianghan Plain combined with software of SPSS, JMP, and PHEEQC. The results showed that the cations in the groundwater in the area were mainly Ca2+, while the anions were mainly HCO3-. 20% of groundwater exceed the China national guideline for TH (i.e., 450mg/L). The groundwater chemistry in the study area was controlled by three main factors of dissolution of carbonate rocks, human activities, and redox conditions, among which the interaction between water and rock had the greatest impact. The water carbonate rock interaction within Jianghan Plain was affected by various factors such as water flow and aquifers and showed a gradually weakening trend from west to east. This work not only strengthened the understanding of the causes of the high TH of groundwater in the region, but also provided reference value for regional groundwater environmental management.

Age, duration, and geochemical signatures of paleo-exposure events in Cenomanian–Santonian sequences (Sarvak and Ilam formations) in SW Iran: Insights from carbon and strontium isotopes chemostratigraphy

This study addresses the timing implications of chemical stratigraphy and chronostratigraphic correlation of unconformity-related shallow water (neritic) carbonate rock units. Cenomanian–Santonian sequences (i.e., Sarvak and Ilam formations) host considerable volumes of hydrocarbon in the Zagros region of SW Iran, which represent good examples of unconformity-related reservoirs worldwide. Geochemical traits including carbon, oxygen, and strontium isotopes of these sequences are measured in three wells from the Abadan Plain and one well from the Dezful Embayment. The altered intervals below the exposed erosional surfaces are characterized by remarkable variations in both elemental and isotopic compositions. These variations are marked by increasing in Mg, Al, Fe, Mn, and Rb elemental contents as well as decreasing in Sr and Ca elemental contents. The altered intervals show a positive shift in 87Sr/86Sr isotopic values and a negative trend in δ13Ccarb and δ18Ocarb isotopic values. The paleontological age that is available from previous studies provide a valuable basis for numerical dating of the studied intervals using the rubidium-corrected 87Sr/86Sr isotopic values. The duration of the stratigraphic hiatuses at the Cenomanian–Turonian and mid-Turonian paleo-exposures are calculated as 0.53 Myr and 2.7 Myr, respectively. The calculated durations corroborate the results of previous studies of these paleo-exposures within the Zagros region of western Iran. The concluded (carbon and Sr-isotope) chemostratigraphic correlation of the Cenomanian–Santonian sequences in the Abadan Plain and other parts of the Zagros region can provide a more reliable chronostratigraphic framework of larger scale. The latter can be used in regional correlation and interpretation of the geological-structural evolution of the Zagros region during Cenomanian–Santonian, particularly in western Iran.

Differential Analysis of Volumetric Strain Method Characterization in the Context of Phase Change of Water in Carbonate Rocks.

Modernized technological processes or increasing demands on building materials force the scientific community to analyze in more detail the suitability of individual raw materials and deposits. New or modernized research methodologies make it possible to better understand not only the geometrical structure of the pore space of materials but also the processes taking place in them and the interaction of many factors at the same time. Despite the extensive literature in the field of research on capillary-porous materials, scientists still face many challenges because not everything is known. Carbonate rocks are the most common (one-tenth of Earth’s crust) sedimentary rocks. Analysis of the test results obtained with the use of the modernized differentia analysis of volumetric strain (DAVS) methodology allows for a better adjustment of rock deposits to the products that can be produced from them. In this manner, it is possible that it will contribute to a more rational use of exhaustible rock deposits and not only carbonate ones. This research subject is of great importance for modern science, which was also noted in many of science publications.

Application of Inductively Coupled Plasma Spectrometric Techniques and Multivariate Statistical Analysis in the Hydrogeochemical Profiling of Caves-Case Study Cloșani, Romania.

The aim of the study was to develop the hydrogeochemical profiling of caves based on the elemental composition of water and silty soil samples and a multivariate statistical analysis. Major and trace elements, including rare earths, were determined in the water and soil samples. The general characteristics of water, anions content, inorganic and organic carbon fractions and nitrogen species (NO3− and NH4+) were also considered. The ANOVA—principal component analysis (PCA) and two-way joining analysis were applied on samples collected from Cloșani Cave, Romania. The ANOVA-PCA revealed that the hydrogeochemical characteristics of Ca2+-HCO3− water facies were described by five factors, the strongest being associated with water-carbonate rock interactions and the occurrence of Ca, Mg and HCO3− (43.4%). Although organic carbon fractions have a lower influence (20.1%) than inorganic ones on water characteristics, they are involved in the chemical processes of nitrogen and of the elements involved in redox processes (Fe, Mn, Cr and Sn). The seasonal variability of water characteristics, especially during the spring, was observed. The variability of silty soil samples was described by four principal components, the strongest influence being attributed to rare earth elements (52.2%). The ANOVA-PCA provided deeper information compared to Gibbs and Piper diagrams and the correlation analysis.

Integrated assessment of major element geochemistry and geological setting of traditional natural mineral water sources in South Korea at the national scale

Springs and hot spas have been used worldwide since ancient times as sources of potable, medicinal and bathing water, as well as for industrial purposes. They also sustain spring-dependent ecosystems and provide water flow to downstream ecosystems. We investigated the major element hydrogeochemistry of traditional springs, CO2-rich waters, and hot spas in South Korea and their relationships with features of bedrock geology and structural settings at the national scale to classify water types and identify the major factors controlling the occurrence of each water type. Three criteria—mineral content, CO2(aq), and water temperature—defined six major water types. Alkaline mineral water in carbonate rocks and sedimentary rocks result from readily weatherable lithology. The majority of mineralized waters are CO2-rich or thermal waters with a wide range of mineral contents. Their occurrence was found to be mainly concentrated near faults and boundaries between Early to Middle Jurassic granitic rocks and other rocks of much older ages, and this pattern was quantitatively identified through proximity analysis. This finding indicates that younger granitic rocks provide sources of heat and deep-seated CO2, and faults link these deep sources to groundwater flow. Hydrolysis of primary silicate minerals, including feldspar and biotite, is likely to supply major and minor solutes including Mg2+, F-, and Fe to CO2-rich and thermal waters. F- concentration appears to be regulated by the saturation states of calcite and fluorite, and Mg2+ concentration in alkaline thermal water is driven by the formation of Mg-bearing secondary silicates. We demonstrated that natural mineral water in tectonically stable regions has diverse thermal and hydrogeochemical properties that are mainly controlled by their lithological and structural settings at the regional scale. These results may help elucidate the generation processes of natural mineral waters with high cultural and ecological values, leading to their sustainable use and protection.

Mechanistic study to investigate the injection of surfactant assisted smart water in carbonate rocks for enhanced oil recovery: An experimental approach

More than half of the world's discovered oil is held in carbonate reservoirs, most of which are naturally oil-wet fractured reservoirs. Oil Recovery efficiency can be improved noticeably if the rock wettability is changed from an oil-wet to a water-wet state. However, what factors control the wettability alteration are not clearly specified. In this study, a comprehensive mechanistic study is performed using different experimental tools to investigate the effects of active ions, non-active ions, CTAB, and different combinations of ions and CTAB on the sample rock's wettability. The results indicate that using CTAB and a smart water solution, in which the sodium and chloride ions are eliminated and the concentration of sulfate ions is increased, (SW-0NaCl-4SO42− + 1CTAB) reduced the contact angle to 43.58°. The zeta potential value of the oil-wet calcite powder increased from −61.12 to −7.6 mV after treatment with SW-0NaCl-4SO42− + 1CTAB. Moreover, the mean roughness value of oil-wet calcite powder increased from 5.02 to 25.89 nm after treatment with SW-0NaCl-4SO42− + 1CTAB. In fact, sulfate ions are capable of removing the strongly adsorbed carboxylic groups from the surface and changing the wettability of the calcite surface to a more water-wet state. Also, the cationic surfactant monomers tend to ionically react with carboxylic groups and separate them from the calcite surface. Moreover, the removal of sodium and chloride ions also leads to significant changes in the wettability. The imbibition results showed that the change of wettability from an oil-wet to a more water-wet state results in a critical increase in oil recovery efficiency during imbibition of distilled water into the calcite rock slice. High oil recovery efficiency can be obtained by optimizing the smart water solution composition and using a proper concentration of surfactant.

Deep carbon degassing in the Matese massif chain (Southern Italy) inferred by geochemical and isotopic data.

The Italian Apennines are among the most important sources of freshwater for several Italian regions. With evidences of deep CO2-rich fluids intruding into aquifers in the nearby central-southern Apennines, a thorough investigation into the geochemistry of groundwater became critical to ensure the water quality in the area. Here, we show the main hydrogeochemical processes occurring in the Matese Massif (MM) aquifer through the investigation of 98 water samples collected from springs and water wells. All waters were classified as HCO3 type with Ca dominance (from 50% up to 97%) and variable amount of Mg (from 1% up to 49%). A multivariate statistical approach through the application of the factor analysis (FA) highlighted three main hydrogeochemical processes: (i) water-carbonate rock interactions mostly enhanced in peripheral areas of the MM by CO2 deep degassing; (ii) addition of NaCl-rich components linked to recharging process and to water mixing processes of the groundwater with a thermal component relatively rich in Cl, Na, and CO2; (iii) anthropogenic activities influencing groundwater composition at the foothills of MM. Furthermore, the first detailed TDIC, pCO2, and δ13C-TDIC distribution maps of the MM area have been created, which track chemical and isotopic anomalies in several peripheral areas (Pratella, Ailano, and Telese) throughout the region. These maps systematically highlight that the greater the amount of dissolved carbon occurs the heavier the C isotope enrichment, especially in the peripheral areas. Conversely, spring waters emerging at higher altitudes within MM are only slightly mineralized and associated with δ13C-TDIC values mainly characterized by recharging processes with the addition of biogenic carbon during the infiltration process through the soil.

Hydrogeochemical features and origin of geothermal water of carbonate rocks in the NE Guanzhong Basin, China

A great number of geothermal waters in carbonate rocks are located in the NE Guanzhong Basin. Hydrogeochemical features and genesis of geothermal waters in carbonate rocks were investigated by hydrogeochemical and statistical methods. The results show that the geothermal water in carbonate rocks is basically fresh water with the dominant water type of Na-HCO3. The hydrogeochemistry of geothermal water is governed by water-rock interaction, and the reservoir environment of geothermal water is open. The origin of geothermal water can be the atmospheric infiltration water. This study is aimed to provide the scientific basis for the sustainable development and utilization of geothermal waters of carbonate rocks in Guanzhong Basin.

Karst biogeochemistry in China: past, present and future

The dissolution and deposition processes of carbonate rock, called CO2–water–carbonate rock interaction, are controlled by complex interactions among the biosphere, pedosphere, atmosphere, and lithosphere. The interactions between biogenic activity and the CO2–water–carbonate rock system (dissolution and precipitation of carbonate rocks, element cycles and so forth) had been named karst biogeochemistry. In order to reveal their internal control mechanism over space and time, Chinese researchers undertook an in-depth exploration of their interrelationships. The main results of karst biogeochemistry in China can be summarized as follows: (i) biogenic activity plays an important role in regulating dissolution and precipitation of carbonate rocks; (ii) biogenic metabolic effects are involved in the positive or negative modulation of δ13C, δ15N and the cycling of other elements; (iii) CO2 exchange during carbonate rock dissolution and precipitation, which is mainly due to photosynthesis, results in the accumulation of organic matter; and (iv) primary karst biogeochemistry models have been established to evaluate carbon and nitrogen cycling. In addition to these findings, future studies should increasingly focus on the following topics: (i) the apparent stability and transformation of dissolved organic carbon caused by microbial activities need to be clarified; (ii) the temporal-spatial scales of microbial biomineralization and the accompanying variances of karst biogeochemical cycles should be investigated to comprehensively understand the transformations and transport of substrates from biological activity in the CO2–water–carbonate rock system; (iii) regional-global scale models on karst biogeochemical cycles should be developed for the study of large/small-scale spatial and temporal variance on karst biogeochemical cycles; (iv) new advanced techniques and methods are required and should be applied for the karst studies involving mathematics, hydrochemistry, isotope chemistry, geology, biology and so forth.

Structurally-controlled hydrothermal fluid flow in an extensional tectonic regime: A case study of Cretaceous Qamchuqa Formation, Zagros Basin, Kurdistan Iraq

Shallow water carbonate rocks of the Lower Cretaceous Qamchuqa Formation host a significant reserve of oil in the NNE Arabian plate-Southwestern Zagros Sutured Belt in the Kurdistan Region, Iraq. Such carbonates consist of several dolostone bodies with unique and complex arrays of saddle and zebra dolomite textures especially in fractured intervals. Integration of field, core description, microstructural analysis, petrographic, stable C, O and Sr isotopes, and fluid inclusion analyses reveals two main phases of multiple fluxes of hydrothermal fluid circulation during the Zagros Orogeny at the end of Cretaceous and Cenozoic times. An early regional non-focused hydrothermal dolomitization and a subsequent fault- and fracture- controlled hydrothermal fluid flow, which led to replacement and cementation by a range of saddle dolomite and zebra textures. Several generations of matrix dolomite, saddle dolomite and calcite cement were identified. The host dolostone has been affected by shortening, folding, fracturing, and thrust faulting. Saddle dolomite pipes, in particular, were found to be associated with en-échelon folding. The morphology and areal extent of the zebra dolomite are controlled by the pore geometry of the host dolostone in relationship to fracturing and faulting.Both matrix and saddle dolomite cements have comparable, overlapping stable isotopic values ranging from 0.39‰ to 3.57‰ and −0.12 to 3.11‰ VPDB, respectively for δ13C and δ18O values range from −10.53‰ to −4.47‰ and −12.87 to −7.79‰ VPDB, respectively. 87Sr/86Sr ratios of pervasive matrix dolomite range from 0.707702 to 0.707839, fall close to late Cretaceous seawater values. Slightly more radiogenic values of saddle dolomites ranging from 0.707759 to 0.708024 resulted from mixing of basinal brines with connate waters. Isotopic signatures of later calcite cements show more radiogenic Sr ratios from 0.707755 to 0.708198 and negative δ13C values 1.76 to −7.45‰, possibly related to late diagenetic processes due to incursion of meteoric waters during subaerial exposure.Fluid inclusion data of pervasive matrix dolomite and saddle dolomites show homogenization temperatures (Th) with a wide range from 71.3 to 169.7 °C and 82.3 to 188.2 °C, and salinity between 14.4 to 25.4 and 15.6 to 27.9 wt% NaCl eq., respectively. These values demonstrate the effect of hydrothermal fluid flow of the alteration of host dolomite and formation of saddle dolomite in fractures and faults.

Chemostratigraphy of Late Sinemurian – Early Pliensbachian shallow-to deep-water deposits of the Central High Atlas Basin: Paleoenvironmental implications

Shallow water carbonate rocks are especially prone to diagenetic alteration. As such they are sometimes problematic archives of past carbon cycle perturbations, casting doubt on the reliability of shallow-water carbonates carbon isotopes analyses for chemostratigraphic purposes. In this paper, bulk organic carbon isotopes (δ13Corg) is used as a robust replacement of the more sensitive carbonate carbon isotope systems for the establishment of a refined chronostatigraphic framework for the evolution of Sinemurian-Pliensbachian neritic carbonate systems in the Central High Atlas Basin of Morocco. These data show very similar patterns and characteristics in the organic carbon isotope curves of basinal and platform sections and thus illustrate the reliability of these archives. Simultaneously, we explore the expression of the global carbon isotope excursion at the Sinemurian-Pliensbachian boundary (SP event) in the study area in Morocco. This event has been previously described as a negative carbon isotope excursion of ∼2‰ associated with a large transgression in numerous basins. In Morocco and other neritic carbonate records, the SP event is better described as a return to previous values after a positive carbon isotope excursion coinciding with a major latest Sinemurian regression recognised on a global scale. Similar patterns are also found in other sections, although sometimes poorly expressed. However, it shows, that the SP event has ambiguous characteristics and questions the conventional hypothesis of it being linked to the massive injection of 13C-depleted carbon into the atmosphere-ocean system.

An experimental investigation into the spontaneous imbibition of surfactant assisted low salinity water in carbonate rocks

Surfactant assisted smart water injection is one of the areas of research interests in enhanced oil recovery. Simultaneous use of smart water and surfactants has drawn great attention in last decades. Majority of studies highlight co-injection of cationic surfactant and sea water/low salinity water. Therefore, this paper opens a new approach by examining the effect of diluted sea water, termed as dSW, containing Sodium Dodecyl Sulfate (SDS) on spontaneous imbibition in carbonate media. Reservoir core plugs and oil samples were provided, saline waters were synthesized in laboratory and different tests were accomplished. It was observed that the brine spiked in Mg2+ is able to improve water wetness of calcite by reducing contact angle from 114° to 42° and reduction in interfacial tension (IFT) from 34.2 to 13.9 mN/m. Measurement of oil properties before and after imbibition, showed that Mg2+ plays the main role in increasing microscopic sweep efficiency and improving ultimate oil recovery. Moreover, faster imbibition rate and higher capillary number was gained by increasing Mg2+ concentration. Ca2+ was found to be a disturbing ion as it led to incompatible condition in the fluid system. We confirmed that in the presence of excess Ca2+, SDS molecules not only aggregate in the bulk of solution, but also another form of incompatibility, known as salt bridge, was occurred. It was also demonstrated that activity of SO42- was concealed in the presence of SDS.

Effects of low salinity water on calcite/brine interface: A molecular dynamics simulation study

Calcite is among the most abundant minerals organizing the oil reservoir formation and therefore its surface properties play a central role in the increase of the oil recovery efficiency. The effect of low-salinity water in carbonate rocks reveals that brine composition and salinity can improve the oil recovery in carbonates through wettability alteration. However, the specific mechanism for wettability changes that leads to improved oil recovery in calcite is not well understood. To obtain deeper insights at atomic level into the understanding the characteristics of the calcite-water interface, we performed classical molecular dynamics simulations in the presence of different ions in brine solutions in the oil reservoirs. The results showed highly ordered water layer in the vicinity of calcite surface, followed by subsequent layers rich in ions of brine. These layers form an electric double layer, with monovalent Na+ ions in the Stern layer and anions in the diffuse layer. The results also indicated that divalent cations do not appear in the electric double layer. The appearance of ions at calcite/brine interface is more effective in wettability alteration for low saline brines such as seawater than high saline ones like formation water validating the applicability of low saline water injection method to improve oil recovery efficiency.

Nitrate fate and origin in epikarst springs in Jinfo Mountain area, Southwest China

Concentration of dissolved nitrate (NO3−) and stable nitrogen isotopic composition of nitrate in water samples from 19 epikarst springs in the Jinfo Mountain area were analysed in order to understand the temporal–spatial distribution of nitrate in karst spring waters and trace nitrogen sources for the springs that have suffered from nitrate contamination. The results show that hydrochemistry of epikarst spring water is Ca·Mg–HCO3 facies, reflecting the control of water–carbonate rock interaction. NO3− concentrations in water of springs within the national nature reserve (NNR) in the Jinfo Mountain area range from 0 to 8.16 mg/L, suggesting that these springs within the NNR have good water quality. However, most springs outside the NNR have high NO3 concentrations (c: 10.5–46.18 mg/L) that have exceeded the value of Chinese national drinking water quality standard (NO3–N ≤10 mg/L), revealing that these springs have suffered from nitrate contamination to a significant degree. δ15N–NO3 values of these contaminated springs outside the NNR range from −1.2 ‰ to 11.27 ‰, higher than those of unpolluted springs within NNR (−5.2 ‰ –8.6 ‰). Two main sources of nitrate in these contaminated springs have been identified, including animal manure/sewage and chemical nitrogen fertilisers that are from anthropogenic activities. Our study also shows that the nitrate fate and origin are associated with the land use in the recharge catchment of individual epikarst springs, and the establishment of national nature reserve can protect the water quality of epikarst spring.

Lithofacies palaeogeography of the Late Permian Wujiaping Age in the Middle and Upper Yangtze Region, China

The lithofacies palaeogeography of the Late Permian Wujiaping Age in Middle and Upper Yangtze Region was studied based on petrography and the “single factor analysis and multifactor comprehensive mapping” method. The Upper Permian Wujiaping Stage in the Middle and Upper Yangtze Region is mainly composed of carbonate rocks and clastic rocks, with lesser amounts of siliceous rocks, pyroclastic rocks, volcanic rocks and coal. The rocks can be divided into three types, including clastic rock, clastic rock–limestone and limestone–siliceous rock, and four fundamental ecological types and four fossil assemblages are recognized in the Wujiaping Stage. Based on a petrological and palaeoecological study, six single factors were selected, namely, thickness (m), content (%) of marine rocks, content (%) of shallow water carbonate rocks, content (%) of biograins with limemud, content (%) of thin-bedded siliceous rocks and content (%) of deep water sedimentary rocks. Six single factors maps of the Wujiaping Stage and one lithofacies palaeogeography map of the Wujiaping Age were composed. Palaeogeographic units from west to east include an eroded area, an alluvial plain, a clastic rock platform, a carbonate rock platform where biocrowds developed, a slope and a basin. In addition, a clastic rock platform exists in the southeast of the study area. Hydrocarbon source rock and reservoir conditions were preliminarily analyzed based on lithofacies palaeogeography. Sedimentary environments have obvious controls over the development of the resource rocks. With regard to the abundance of organic matter, the hydrocarbon potential of the coastal swamp environment is the best, followed by the basin environment and the carbonate rock platform. The gas reservoir types of the Wujiaping Stage can be classified as conventional and unconventional gas reservoirs, like coal bed gas and shale gas; all of them have well exploration prospects.

The carbon isotope fractionation in the atmosphere–soil–spring system associated with CO2-fixation bacteria at Yaji karst experimental site in Guilin, SW China

In the epikarst-diffusing infiltration layer, the water–carbonate rock–CO2 gas interaction takes place under the driving force of biotic/abiotic CO2. Therefore, it is necessary to study the changes of carbon isotopic composition relating to biotic/abiotic CO2 in the karst system. This paper presents some hydrogeochemical and biological characterization in the Yaji karst experimental site of SW China. Based on the hydrogeochemical studies, it was found that spring 31 (S31) mainly flowing out from doline 1, was primarily characterized as a HCO3 −–Ca type, with a mean magnesium/calcium ratio of only 0.87 %, and a positive relationship (R 2 = 0.9591) existed between calculated PCO2 and SI C in S31 which generally originates from the complex water–carbonate rock–CO2 gas interactions. The difference of soil CO2–δ13C in two soil layers (0 to −10 and −20 to −30 cm) from doline 1 is 6.6 ‰ and the CO2-fixation bacteria has the significant positive correlation with soil organic carbon (SOC) in doline 1(P < 0.0003). Moreover, the difference between soil CO2–δ13C in doline 1 and δ13CDIC in S31 is 10.93 and 76 % CO2 in S31 comes from soil biotic CO2 based on O’Neil equation. The above results indicate that when atmospheric CO2 transfers through the epikarst-diffusing infiltration layer, 12CO2 will be requested by the CO2-fixation bacteria with high priority, and soil CO2 probably originates from heterotrophic microbial respiration in the bulk soil. Then, under the intervention of CO2-fixation bacteria, the epikarst-diffusing infiltration layer will produce the “placenta” function to spur the stable isotopic equilibrium fractionation between soil CO2 and spring DIC, which could be used to predict the value of soil CO2–δ13C or δ13CDIC when we only have one aspect result of the samples, especially for monitoring drip water in the cave. Moreover, the future research on the isotopic fractionation of CO2-fixation bacteria could provide more surprising information to explain the function of epikarst-diffusing infiltration layer.

Hydrochemical characteristics of hot spring waters in the Kangding district related to the Lushan &amp;lt;i&amp;gt;M&amp;lt;/i&amp;gt;&amp;lt;sub&amp;gt;S&amp;lt;/sub&amp;gt; = 7.0 earthquake in Sichuan, China

Abstract. Hydrogeochemistry of 10 hot springs in the Kangding district was investigated by analyzing cation and anion concentrations in the spring water. The water samples were collected in the 5 days after the Lushan MS = 7.0 earthquake, which occurred on 20 April 2013. The spring waters are classified into seven chemical types based on their hydrochemical compositions. Compared with hydrochemical data before the Lushan earthquake, concentrations of Ca2+, HCO3- and total dissolved solid (TDS) in water samples from the Guanding, Erdaoqiao, Gonghe, Erhaoying, Tianwanhe and Caoke springs significantly increased, which may be the result of a greater increase in groundwater from carbonate rocks, and water–carbonate rock interactions, enhanced by the increment of CO2. Concentrations of Na+, Cl- and SO42- in water samples from the Guanding, Zheduotang, Xinxing and Gonghe springs decreased, indicating a dilution of shallow waters. Concentrations of Na+ and SO42- in water samples from the Erhaoying spring water increased, which may be attributed to water–granite interactions enhanced by H2S. The results indicated that hydrochemical components of spring water could be used as an effective indicator for earthquakes.

Upper Maastrichtian to Lutetian nannofossil biostratigraphy, United Arab Emirates, west of the Northern Oman Mountains

The latest Cretaceous (Maastrichtian) to Middle Eocene (Lutetian) interval of shallow water carbonate rocks in the NE part of the Arabian Pensinsula (Oman Mountains) includes important regional oil reservoir units. These carbonates are richly fossiliferous in foraminifera, which have been useful in correlating sequences and formations. Previous foraminiferal studies have indicated the existence of several hiatuses or lacunae related to sea level changes or due to erosion. Subsequent studies of the abundant calcareous nannofossils have permitted definition of these hiatuses via high resolution biostratigraphy. However, these previous studies were of limited extent. In this study a total of 103 nannofossil species were identified from the upper Maastrichtian–Lutetian successions at Jabal Qarn El Barr, El Faiyah Range Mountains (Jabal Thanays and western side of Jabal Buhays), United Arab Emirates, as well as Jabal El Rawdah, west of the Northern Oman Mountains, Oman.

Responses of water yield and dissolved inorganic carbon export to forest recovery in the Houzhai karst basin, southwest China

AbstractKarst terrain (carbonate rocks) covers a vast land of 0.446 million km2 in southwest China. Water yield and carbonate rocks weathering in this region have been receiving increased attention due to a large‐scale forest recovery. Using both hydrological measurements and forest inventories from 1986 to 2007 in the Houzhai karst basin (HKB), we analyzed the responses of water yield and dissolved inorganic carbon (DIC) export to forest recovery in southwest China. With implementation of both the Natural Forest Conservation Program (NFCP) and the Conversion of Farmland to Forests Program (CFFP), the fraction of forest area in HKB was increased from near zero to 18.9% during the study period, but the ratio of total water yield (surface and underground) to precipitation varied very little over the annual period, neither in wet season nor in dry season. By contrast, the concentration of DIC in water, especially in the surface water had a pronounced increase during the study period, with an increase of 0.53 and 0.25 g C m−3 yr−1 for surface water and underground water, respectively. As a result, total annual DIC export at mean annual rainfall significantly increased from the low to high forest area stage. This increase was largely driven by surface water during the wet season, presumably being related to biological activity. It was concluded that forest recovery in HKB had no significant effect on water yield, but resulted in more carbon dioxide (CO2) dissolved in karst water accompanying with carbon uptake by forests. Our results suggested that implementations of both NFCP and CFFP had no shifted water yield regimes in southwest China; instead, they might have alleviated global climate change by increasing carbon uptake through combined biological processes and carbonate rocks weathering. Copyright © 2013 John Wiley &amp; Sons, Ltd.