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In the paper “Formation mechanism of deep Cambrian dolomite reservoirs in the Tarim basin, northwestern China” ( Zhu et al., 2015 ), we concluded that hydrothermal alteration further enhanced porosity in the deep Cambrian dolomite reservoirs in the Tarim Basin, NW China. Professor Ehrenberg and Bjørlykke made comments that the hydrothermal dolomitization and increase in porosity were not well supported and casted doubt on the exploration potential. We insist the influence of hydrothermal alteration on and large exploration potential in the deep Cambrian dolomite reservoirs due to the unique geological conditions and the recent exploration results. [ABSTRACT FROM AUTHOR]

The Lower Ordovician Tongzi Formation containing abundant shoal sediments is the most promising stratum for the petroleum exploration in the Sichuan Basin. However, the current studies mainly focus on the central part of the Basin, the systematic analysis of the southeastern part with well-developed shoal facies is lacking. This paper aims to clarify the characteristics and genesis of the Tongzi Formation reservoir in Southeastern Sichuan Basin, following an analysis of sedimentary facies within the sequence stratigraphic framework. The research shows that the main types of reservoir rocks are oolitic, intraclastic and bioclastic dolostones. And the reservoir spaces consist mainly of intergranular (dissolved) pores, inter-crystalline (dissolved) pores, intragranular dissolved pores and fractures. Among them, intergranular pores account for the highest proportion, which is followed by intragranular dissolved pores. In addition, most throats are necking and flaky which mainly connect intergranular and inter-crystalline pores, respectively. The diagenetic sequence shows that penecontemporaneous karst well improved the porosity of the reservoir in the early-stage although the cementation and compaction reduced parts of pores. The reservoir formation is associated with the tectonic-depositional settings, diageneses and terrigenous contamination. Paleohighlands and submerged uplifts, forming in the early Ordovician amalgamation between Yangtze and Cathaysia blocks, accumulated shoal sediments as the material basis for the reservoir formation. Penecontemporaneous karst forming intragranular dissolved pores and the dolomitization aiding grainstones to resist the pressure solution are the key to increasing porosity and preserving pores. The absence of terrigenous contamination prevented intergranular pores from being strongly cemented, which resulted in the reservoir difference between the central and southeastern Sichuan Basin. The study can be used as a reference for the further exploration of Ordovician petroleum in the Sichuan Basin and other regions owning similar geological settings. [ABSTRACT FROM AUTHOR]

The Cambrian pre-salt dolomite sequence in the Tarim Basin is a target zone of great strategic significance for hydrocarbon exploration in the basin. Using the results of the interpretation of 3D seismic data from Lunnan and 2D seismic data covering the whole basin, and based on a synthesis of outcrop data, drilling data, well logs, core data, and thin-section data, and the findings from previous studies, this paper studies the characteristics of the facies of the Middle–Lower Cambrian in the platform area in the Tarim Basin, the formation and evolution of platform margins, and the sedimentary characteristics, lithofacies, and paleogeographic characteristics of the Middle–Lower Cambrian series. Based on the types of lithofacies and the seismic facies analysis, the sedimentary facies of the Middle–Lower Cambrian strata can be classified into the five types. From bottom to top, the Middle–Lower Cambrian have experienced several development stages, including the deposition of continental shelf sediments of the Yuertusi Formation, gently sloping non-rimmed platform margin sediments of the Xiaoerbulake Formation, weakly rimmed platform margin sediments of the Wusongger and Shayilike formations, and strongly rimmed platform margin sediments of the Awatage Formation. In each stage, the platform margin shifted further east relative to its location in the previous stage. Based on these results and previous studies, the lithofacies and paleogeography maps of the Middle–Lower Cambrian in the Tarim Basin are modified, and the implications for hydrocarbon exploration in this area are discussed. [ABSTRACT FROM AUTHOR]

Siliceous minerals of the Dengying Formation in the Gaoshiti–Moxi area in the central Sichuan Basin exhibit four types of quartz crystals (cryptocrystalline quartz, chalcedony, microcrystalline quartz, and megacrystalline quartz) and three structural types: cryptocrystalline, microcrystalline, and mosaic (laminated mosaic, window-hole interrupted mosaic, and arc-laminated mosaic). Siliceous minerals have a great influence on the storage performance of the reservoirs in the Dengying Formation. According to the petrophysical parameters of the Dengying Formation and porosity intersection diagrams, the siliceous dolomite and the reservoirs have low impedance characteristics, which makes it difficult to distinguish between them and leads to difficulties in the characterization and prediction of the reservoirs. The transverse wave velocity is favorable for reservoir characterization. Currently, the main method used to estimate the transverse wave velocity is petrophysical modeling, which establishes a relationship between the elastic and physical parameters of the reservoir. In this paper, the siliceous minerals in the dolomite in the study area are regarded as solid inclusions, and the calculation method of the rock matrix modulus is improved by using solid replacement. Then, an improved petrophysical model is constructed by combining the KT (Kuster–Toksöz) model, the DEM (Discrete Element Method) model, the Gassmann equation, and the Wood equation. The transverse wave velocity is estimated using the improved model under the constraint of the longitudinal wave velocity. The shapes of the transverse wave velocity curves obtained by the improved model and the deviations from the measured velocities are significantly better than those of the Xu–Payne model and other models. The results show that the improved model can effectively estimate the transverse wave velocity of the reservoir in this area, which provides a basis for future reservoir predictions in this area. [ABSTRACT FROM AUTHOR]

During weathering and pedogenesis of carbonate rock with poor-uranium (U) and thorium (Th), U and Th present the characteristics of strong leaching (especially U) and significant residual enrichment, the cause of which is still unclear. In this paper, a weathering profile developed by dolomite in karst area of Guizhou province in southwest China was selected, which showed zonation characteristics of bedrock (Y), powdery rock (Yf), and soil layer (T1 to T12) from the bottom to up. Through the determination of the occurrence speciation of U and Th in Y and weathering profile, combined with mineralogical, geochemical characteristics, and element mass balance calculation, the constraints of U and Th speciation on the geochemical behavior of U and Th during the weathering of carbonate rock were revealed. The results proved that U and Th in Y preferentially existed in acid insoluble phase, for example, the contents of U and Th in Y were 0.90 mg·kg−1 and 0.28 mg·kg−1, respectively, while those in acid insoluble matter were 2.34 mg·kg−1 and 2.57 mg·kg−1, respectively, but because the mass percentage of acid insoluble matter was extremely low (0.95%), the mass percentages of U and Th in the acid soluble phase in the whole rock were absolutely superior (96% of U and 86% Th). The U and Th in the acid soluble phase of Y were mainly adsorbed on the crystal surface of carbonate minerals or existed in the cement, and the U and Th in the carbonate lattice only accounted for a small proportion. From Y to Yf with the initial dissolution, U and Th released from the surface of carbonate minerals and cements were in carbonate-rich alkaline environment, and these portions of U and Th were leached out, resulting in strong loss of U and Th in the Yf (the loss rates are 83% of U and 65% of Th, respectively). From the Yf to the overlying soil layer T1, the carbonate components were completely dissolved, and the U and Th released from the carbonate lattice showed different behaviors, where U was completely leached and Th tended to stay in the weathered residue. Thus, in the soil layer T1 formed by Y or Yf , the residual U was the inheritance of the U in the acid insoluble phase of Y; For Th, it not only inherited the Th of acid insoluble phase of Y, but also superimposed the Th from carbonate lattice in Y. On the other hand, during the evolution process from Y to Yf and to soil layer T1, with the dissolution of carbonate, the acid insoluble phase also showed a significant tendency of chemical weathering. However, the U and Th in the Y acid insoluble phase were not leached with the decomposition of the acid insoluble phase but were redistributed among the residual phases. For the geochemical behaviors of U and Th in the evolution of soil profile (T1~T12), they were subjected to the occurrence speciation of U and Th in T1 and the change of U and Th occurrence speciation with the upward direction of soil profile. The U and Th released from the carrier minerals were mainly redistributed among the residual solid phases, which weakened the intensity of their further loss. This study deepens the understanding of the geochemical behavior of radionuclides in karst environment and provides reference for the treatment of radioactive pollution in karst areas. [ABSTRACT FROM AUTHOR]

The Guizhou Province is located in karst mountainous area, so it is very important for the future layout and planning of the city to study the underground geological structure of the city based on seismic detection technology. In this paper, taking the underground active fault detection in the Liupanshui City, Guizhou Province, China as an example, a set of appropriate evaluation techniques for the accurate spatial location, structural characteristics and latest activities of the fault suit for mountainous area are proposed. Through pre-stack noise suppression, amplitude fidelity and consistency processing, and multiple iterative analysis of velocity residual statics, the resolution of the geological structure of the underground rock has been significantly improved. Based on the detailed interpretation of the shallow seismic data and the regional geological analysis, it is concluded that the main fault strike of the Weining – Shuicheng section of the Weining - Shuicheng fault is NW, mainly normal fault, the dip direction is mainly southwest, partly northeast and the dip angle is 60-70°. The strata of the two fault plates are strongly compressed and broken, and the limestone and dolomite are generally recrystallized, and calcite veins and masses can be seen. [ABSTRACT FROM AUTHOR]

Lower Cambrian Xiaoerblak Formation is one of the major exploration targets in Cambrian pre-salt Tarim Basin; however, the exploration breakthrough is restricted by insufficient understanding of its sedimentary evolution and reservoir genesis. In this paper, based on a systematic description of the outcrop in the Xiaoerblak section, northwestern Tarim Basin, some samples were selected for tests of stable carbon and oxygen isotopic compositions, strontium isotopic composition, order degree, trace and rare earth elements, U-Pb isotopic age and clumped isotope. It is found that the Xiaoerblak Formation mainly develops nine types of dolomites, i.e., laminated microbial dolomite, thrombolite dolomite, stromatolite dolomite, foamy microbial dolomite, grain dolomite, etc. According to the lithofacies associations, it can be divided into three members: Xi 1, Xi 2, and Xi 3, of which member Xi 2 is subdivided into three submembers. The characteristics of lithofacies assemblage formed bottom to top indicate that it can be described as a third-order sequence. The Xiaoerblak Formation was deposited in a nearshore shallow seawater environment characterized by high water salinity and temperature under a warm and humid climate during the Early Cambrian, giving rise to the sedimentary sequence of inner ramp lagoon, subtidal microbial mound shoal and tidal flat in the carbonate ramp setting from bottom to top. Its dolomitization occurred in the penecontemporaneous–shallow burial period when the temperature was relatively low and high-salinity seawater acted as the main dolomitizaiton fluid. The reservoir space mainly comprises primary microbial framework pores and vugs formed by the atmospheric freshwater dissolution. Reservoirs were controlled by lithofacies, high-frequency sequence boundary and early dolomitization. The research results are of great significance for presalt Cambrian lithofacies paleogeographic mapping and reservoir prediction. [ABSTRACT FROM AUTHOR]

Karst water quality degradation has been a challenge for domestic and industrial water supplies worldwide. To reveal the possible factors response for karst water quality degradation, Baotu karst spring system is studied as an representative example. In this study, a hydrogeochemical investigation and mathematical, statistical, and geochemical modeling was conducted together to identify the major hydrochemical processes involved in the degradation process. It is found that the karst water is normally fresh, neutral-to-slightly alkaline, with calcium and magnesium as the predominant cations, and bicarbonate and sulfate as the predominant anions. The abnormally high chloride (95.05 mg/L) and nitrate concentrations (148.4 mg/L) give clues to the potential source of contamination in some karst water. The main hydrochemical facies of karst water are HCO3-Ca and HCO3 × SO4-Ca, accounting for 76% of water samples. The water hydrochemistry is controlled mainly by the dissolution of carbonate minerals (calcite, dolomite), followed by the dissolution of silicate and gypsum. The dissolution of calcite and dolomite mostly happens in the recharge area. In the discharge area, the karst water is basically in equilibrium with calcite. The negative SI value of gypsum represents that the water–gypsum interaction is dominated by dissolution along the whole flow path. Cation exchange is observed in the karst water in the indirect recharge area. Along the flow path, the contents of chloride, sulfate, nitrate, and TDS (Total dissolved solids, abbreviated TDS, indicates how many milligrams of dissolved solids are dissolved in one liter of water) vary significantly, which is mostly affected by pollution from human industrial and agricultural activities. The concentrations of major ions were maintained at a low level (<20 mg/L) in the 1960s in karst water. The fast elevation of the parameter values has occurred in the past two decades. The temporal elevation of some pollutants in karst water suggest that global changes (acid rain) and human activity (such as overusing fertilizer) are main factors resulting in the degradation of karst water quality in the study area. The results of this paper provide invaluable information for the management and protection of karst water resources in the urban and rural areas. [ABSTRACT FROM AUTHOR]

To characterize the polyphase palaeokarst development of Wumishan formation in Jizhong depression, the data of outcrops, cores, thin sections, SEM, core plugs, drilling relief and leakage, and carbon isotope have been analyzed in this paper. The results reveal that the polyphase palaeokarst was petrography controlled of microbial dolostone and grain dolostone, and was identified as three phases: (1) poly-period eogenetic karst during Wumishan depositional environment, (2) two-period telogenetic karst in Triassic and Cretaceous, and (3) hydrothermal karst in Paleogene. The eogenetic karst was related to high frequent sea level fluctuations with development of vugs and selective dissolution porosities which distributed at the top of microbial dolostone and grain dolostone layers. The origin of the telogenetic karst was related to Indosinian and Yanshan orogeny which formed widespread fold belts and thrust faults, and provided the endokinetic force and a strong topography difference. Each period's telogenetic karst was characteristic of one-period fracture-cave system, and the Cretaceous telogenetic karst was stronger than the Triassic telogenetic karst in karst intensity. Moreover, the karst intensity increased downward in superimposed telogenetic karst zones. Hydrothermal karst was related to volcanic activities and provided the hydrothermal environment for its formation. It was featured by solution-enlarged porosities and new forming porosities. The microbial dolostone and grain dolostone layers with three-phase palaeokarst were the best exploration targets for high-quality reservoirs. This paper rebuilds a suitable karst model to show the palaeokarst evolution process. [ABSTRACT FROM AUTHOR]

The Upper Permian Changhsing Formation is one of the most important gas-bearing formations in the Eastern Sichuan Basin. Nonetheless, the primary factors controlling the reef-shoal gas reservoirs of different regions are diverse. Clarifying the controlling factors for the formation of intra-platform reef-shoal reservoirs will promote the exploration and development process of the Changhsing Formation. By using outcrop data, core observation, thin section identification, scanning electron microscope analysis, physical property study, and logging interpretation, this paper analyse the characteristics and factors controlling the reef-shoal reservoir in Dianjiang area of the Eastern Sichuan Basin. The results show that the reef cap and reef base microfacies fine-to-medium crystalline dolomite reservoir have the best physical properties, and the reservoir spaces are primarily composed of intercrystalline pores, intercrystalline solution pores, karst caves, and fractures. The main lithology of reservoir formation is reef-shoal facies. The results for the carbon and oxygen isotopes show that dolomites of different particle sizes are formed in three environments. Affected by regression in the late Changhsingian Age, the reef-shoal of the Changhsing Formation were subaerially exposed to meteoric water diagenesis environments, resulting in the highly dispersed particles in rocks that formed a honeycomb karst system, which greatly improved the physical properties of the reservoirs. After reflux dolomitization, the honeycomb karst system was well preserved due to strong resistance to pressure and dissolution of dolomite. Therefore, dolomitization in the Changhsing formation contributed to reservoir porosity. Later, tectonic fracturing has adjusted and modified the reef-shoal reservoir. In summary, penecontemporaneous karstification was the key to the formation of the reef-shoal reservoir. [ABSTRACT FROM AUTHOR]

Recently, special attention has been drawn to the high-salt argillaceous dolomite reservoir in Jianghan basin, China due to its abundant oil resources with complex geological conditions. However, the current production methods used to develop this reservoir are not efficient with low throughput. Hence, the purpose of this paper is to explore the main possible reasons affecting the oil well productivity and determine suitable field development method for the target oilfield through experimental and numerical simulation approaches. The mercury injection capillary pressure (MICP) test results indicate that the average pore radius of samples is 0.0144 μm, and pore size distribution (PSD) results from MICP indicate that single peaks appeared in the PSD curves of the pore type samples. Permeability peaks of the samples range from 0.01 to 0.03 μm, and mesopores make most of the permeability contribution of the samples, which also reveals the low-permeability and porosity characteristics of the target oilfield. The results of core stress sensitivity tests show that the largest permeability damage rate is 98.97% with an average permeability damage rate of 98.37% while the maximum porosity damage rate is less than 10% with an average damage rate of 5.57% during the process of depressurization. The results of Non-Darcy percolation experiment indicate that threshold pressure gradient testing by water is about 0.03 MPa/m, which is close to the actual situation of the target oilfield. Numerical simulation method that considers the impact of threshold pressure gradient and stress sensitivity were established to study flooding patterns deployment for the research area. The simulation results show that performing water alternating gas flooding (WAG) by using CO2 is recommended for the development of the high-salt reservoir with inverse five-spot flooding pattern made up of 400 m well spacing in X-direction and 150 m row spacing. [ABSTRACT FROM AUTHOR]

Copyright of Nonferrous Metals (Mineral Processing Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dolomite is the most important component of the prolific reservoirs in the Ma55 to Ma51 submembers of the Ordovician Majiagou Formation in the central Yishan Slope, Ordos Basin. However, the origins of the different types of dolomite are unclear because of the different diagenetic environments and complex diagenetic fluids. This paper mainly focuses on the diagenetic environment and diagenetic fluid associated with the dolomite. The petrographic features of the dolomite were studied on the basis of core observation and thin section identification. Geochemical characteristics were analyzed according to the O, C and Sr stable isotopes and major and trace elements. The results demonstrate that, petrographically, the dolomite can be divided into four types, namely, type 1, type 2, type 3 and type 4. Type 1 is mainly characterized by dolomite with gypsum and salt dissolution as well as breccia structures with no clay minerals filling between breccia clasts. Type 2 is characterized by powder-fine crystalline dolomite with apparent residual textures and residual intergranular and intercrystal pores. Type 3 is characterized by leopard limestone or dolomite with leopard textures and massive bioborings. Finally, type 4 is characterized by karst breccia dolomite with many fractures and caves filled by abundant terrigenous clay minerals. In combination with the petrographic data, analysis of the geochemical data reveals that the type 1 dolomite formed in an early near-surface diagenetic environment and the diagenetic fluid might have been early freshwater. Type 2 and type 3 dolomite formed in a shallow-burial diagenetic environment. The diagenetic fluid of type 2 dolomite might have been hypersaline brine that was influenced by freshwater, but that of type 3 dolomite might have been a mixed fluid consisting of seawater and freshwater, which was less saline than the type 2 dolomite fluid. Type 4 dolomite formed in an epidiagenetic near-surface environment and the diagenetic fluid might have been superficial freshwater carrying abundant terrigenous clay minerals. The study shows that the analysis of the diagenetic environment and fluid of dolomite has great significance for research on dolomite origins. The porosity and permeability values of the four types of dolostone reservoirs indicate that type 1 dolomite reservoirs are the best reservoir, type 2 dolomite reservoirs have good physical properties, type 4 dolomite reservoirs are relatively good reservoirs, and the worst reservoir is the type 3 dolomite reservoirs. [ABSTRACT FROM AUTHOR]

Most of the phosphate ore in southern China is contained within siliceous dolomite phosphate rock, and more than 90% of it is medium and low‐grade collophane. Reverse flotation of carbonate gangue minerals (dolomite) from phosphate in acidic media is still the most economical method for the reduction of carbonate in collophane concentrates. It has been recognized that the collophane and dolomite in acidic media affect the surface properties of minerals, thereby affecting their flotation properties. In this paper, HCl and H3PO4 were used as regulators or inhibitors to study the flotation behaviour of collophane and dolomite. The inhibition mechanism of collophane and dolomite in two acid media was studied by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) and X‐ray photoelectron spectroscopy (XPS) analyses. It was found that the addition of an inhibiting acid can partially depress the collophane and improve the flotation of dolomite, thus achieving their flotation separation, and the inhibition effect of H3PO4 on collophane is better than that of HCl. And it was found by TOF‐SIMS analysis that the increase in acid concentration did not reduce the adsorption concentration of the collector, and the main reason for the inhibition was not the decrease in the adsorption concentration of the collector. The adsorption capacity of collector on dolomite surface with H3PO4 is greater than that with HCl. The XPS test indicated that metaphosphate (PO3−1) is the pivotal ion for depressing collophane under acid conditions. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Carbonate rocks are one of major geothermal reservoir types around the world. Understanding the thermal properties of carbonate rocks is of significance to the assessment and utilization of deep geothermal reservoirs. Different from conventional test methods, this paper introduced a new approach, molecular dynamics calculation (MDC), to studying the thermal properties of carbonate rocks. By means of MDC, the thermal properties including specific heat, thermal conductivity and thermal diffusivity of four types of carbonate rocks including calcite, dolomite, magnesite, and smithsonite were investigated. The intrinsic relationship among the Debye temperature, elastic and thermal properties of carbonate rocks was revealed. The variations of the thermal properties with the average atom weight and temperature (300–800K) were obtained and regressed as functional formulas for applications. Further, taking carbonate rock samples from North China as an example, the specific heat and thermal conductivity were tested and compared with the MDC results based on actual lattice parameters by using X-ray diffraction method (XRD). The results showed that there was a good agreement between the test and calculation results. Finally, the thermal properties of ferroan dolomite samples were predicted. The present method can provide a promising extension tool for analyzing other crystalline rocks for geothermal applications. [ABSTRACT FROM AUTHOR]

It is beneficial in terms of the theoretical significance and application prospects to define the structure and reservoir development model of the lower Paleozoic unconformity in the Jiyang Depression of Bohai Bay Basin, China, for oil and gas exploration of unconformity in carbonate strata. Geological and geochemical evidence shows that a regional unconformity formed during the Huaiyuan Movement in the lower Paleozoic strata of the Jiyang Depression. Along the top of the regional unconformity between the Yeli Liangjiashan Formation and Fengshan Formation, various types of karst breccia have developed, showing prominent characteristics of development and vertical karst zonation. The paleokarst zone can be divided into the vadose zone and the underflow zone, and there are apparent differences between the two zones in terms of the mode of karst activity and type of reservoir space. Primitive sedimentary microfacies, dolomitization, and supergene karstification controlled the reservoirs of the Fengshan Formation and Yeli-Liangjiashan Formation. There are significant differences in the original physical properties due to the differences in the original sedimentary microfacies. The pore development of granular dolomite of high-energy beach facies has the best reservoir performance. In the later period, the superposition of dolomitization and supergene karstification resulted in apparent differences in karst development mode, development intensity, reservoir type, and reservoir physical properties. Among them, the granular dolomite reservoir has the best physical properties and has developed a cavity-type reservoir that has a planar distribution along an unconformity surface. [ABSTRACT FROM AUTHOR]

The pore structure and connectivity in petroleum reservoirs are controlled in part by their petrological properties. Mixed siliciclastic-carbonate rocks have complex compositions and heterogeneous spatial distributions of the various minerals. As a result, the study of the pore structure and connectivity of mixed siliciclastic-carbonate tight reservoirs has been limited. In this study, methods such as thin section microscopy, X-ray diffraction, X-ray computed tomography, low pressure N2 adsorption, and spontaneous imbibition were adopted to comprehensively analyze the petrological properties, pore structure, and connectivity of the mixed siliciclastic-carbonate tight reservoirs in the upper member of the Xiaganchaigou Formation in the Yingxi Area, Qaidam Basin. The results showed that micrometer-sized pores in mixed siliciclastic-carbonate tight reservoirs are mainly dissolution pores, and that the spatial distribution of the pores is highly heterogeneous. The average pore radius range, average throat radius range, and average coordination number range of micronmeter-sized pores are 2.09~3.42 μm, 1.32~2.19 μm, and 0.48~1.49, respectively. Restricted by the concentrated distribution of local anhydrite, the connectivity of micronmeter-sized pores develops well only in the anhydrite, showing negligible contribution to the overall reservoir connectivity. In contrast, nanometer-sized pores in the mixed siliciclastic-carbonate tight reservoirs are mainly intercrystalline pores in dolomite. The range of nanometer-sized pores diameters is mainly distributed in 1.73-31.47 nm. The pores have a smooth surface, simple structure, and relatively homogeneous spatial distribution. The dissolution of dolomite intercrystalline pores by acidic fluids increases the connectivity of the nanometer-sized pores. This paper presents genetic models for microscopic pore structures and connectivity of mixed siliciclastic-carbonate rocks, making possible the evaluation on the quality of the mixed siliciclastic-carbonate tight reservoirs. [ABSTRACT FROM AUTHOR]

The Zhe-Min Uplift (ZMU) has undergone tectonic subsidence, which has been associated with a notable transgression in the northern marginal seas of China since the middle Pleistocene. However, its uplift history during the late Quaternary is still inadequate. The Old Red Sand (ORS) is a late Pleistocene deposit that is widely distributed along the southeastern coast of China. The ORS consists of partially-cemented fine- to medium-grained sand. In this paper, we focus on mud-rich ORS deposits of the Liushui area, Pingtan Island, Fujian Province, and report optically stimulated luminescence (OSL) ages, and new datasets of grain size, mineralogy (detrital zircon, clay and detrital minerals) and organic carbon and nitrogen isotope profiles to improve understanding of chronology, provenance, palaeoenvironmental evolution and tectonic infuence. Based on the OSL data, we hypothesize that the development of the ORS was associated with lower sea levels, with most deposition occurring within MIS4. Based on comparison of detrital zircon U Pb ages, the coarse fraction of the Liushui ORS was mainly derived from the Minjiang River, with modest input from weathering of coastal granites. The East Asian Winter Monsoon contributed some materials from the East China Sea shelf during the last glacial period, as indicated by the fine-grained nature of the Liushui ORS, low K-feldspar/plagioclase ratios, high dolomite content and the frequency of Neoproterozoic and Palaeoproterozoic detrital zircons. The deposition of the ORS was influenced by both the East Asian Winter Monsoon and sea level changes. The clay minerals in the mud layers of the Liushui ORS were dominated by kaolinite and illite, with little chlorite and no smectite, indicating that they originated from the Minjiang River. The TOC/TN ratios of the mud layers, as well as their isotope characteristics, indicate the organic matter was derived from marine sources, presumably during the transgression event in MIS5. The average uplift rate of the ORS was about 0.03 mm/yr. The uplift of the ORS provided new insights into the geological records of the ZMU, which differed from the subsidence observed in the northern region of the Minjiang River during the late Pleistocene. • The formation of the ORS was association with lower sea level, and the MIS4 was primarily the deposition stage. • During the last glacial, the more sediments from the East China Sea shelf were transported to the ORS by EAWM. • The mud layer was the transgression records during MIS5. • The distribution of the ORS was influenced by tectonic activity. [ABSTRACT FROM AUTHOR]

Sandy Dolomite is a kind of widely distributed rock. The uniaxial compressive strength (UCS) of Sandy Dolomite is an important metric in the application in civil engineering, geotechnical engineering, and underground engineering. Direct measurement of UCS is costly, time-consuming, and even infeasible in some cases. To address this problem, we establish an indirect measuring method based on the convolutional neural network (CNN) and regression analysis (RA). The new method is straightforward and effective for UCS prediction, and has significant practical implications. To evaluate the performance of the new method, 158 dolomite samples of different sandification grades are collected for testing their UCS along and near the Yuxi section of the Central Yunnan Water Diversion (CYWD) Project in Yunnan Province, Southwest of China. Two regression equations with high correlation coefficients are established according to the RA results, to predict the UCS of Sandy Dolomites. Moreover, the minimum thickness of Sandy Dolomite was determined by the Schmidt hammer rebound test. Results show that CNN outperforms RA in terms of prediction the precision of Sandy Dolomite UCS. In addition, CNN can effectively deal with uncertainty in test results, making it one of the most effective tools for predicting the UCS of Sandy Dolomite. [ABSTRACT FROM AUTHOR]

The organic-rich mudstones and dolostones of the Permian Fengcheng Formation (Fm.) are typically alkaline lacustrine source rocks, which are typified by impressively abundant β-carotane. Abundant bcarotane has been well acknowledged as an effective indicator of biological sources or depositional environments. However, the specific biological sources of β-carotane and the coupling control of biological sources and environmental factors on the enrichment of β-carotane in the Fengcheng Fm. remains obscure. Based on a comprehensive investigation of the bulk, molecular geochemistry, and organic petrology of sedimentary rocks and the biochemistry of phytoplankton in modern alkaline lakes, we proposed a new understanding of the biological precursors of β-carotane and elucidated the enrichment mechanism of β-carotane in the Fengcheng Fm. The results show that the biological precursors crucially control the enrichment of β-carotane in the Fengcheng Fm. The haloalkaliphilic cyanobacteria are the primary biological sources of β-carotane, which is suggested by a good positive correlation between the 2-methylhopane index, 7- + 8-methyl heptadecanes/Cmax, C29%, and β-carotane/Cmax in sedimentary rocks and the predominance of cyanobacteria with abundant β-carotene in modern alkaline lakes. The enrichment of β-carotane requires the reducing condition, and the paleoredox state that affects the enrichment of β-carotane appears to have a threshold. The paleoclimate conditions do not considerably impact the enrichment of β-carotane, but they have some influence on the water's paleosalinity by affecting evaporation and precipitation. While it does not directly affect the enrichment of β-carotane in the Fengcheng Fm., paleosalinity does have an impact on the cyanobacterial precursor supply and the preservation conditions. [ABSTRACT FROM AUTHOR]

A total of 18 samples of shallow groundwater around the Hancheng mining area in the Guanzhong Basin were collected from 1–4 May 2018. According to the analysis of hydrochemical data, the Gibbs semi-logarithmic diagram and Piper diagram were used to research the hydrogeochemical behavior of shallow groundwater around the Hancheng mining area in the Guanzhong Basin. The results of the groundwater hydrochemical analyses shown on the Gibbs and Piper plots are as follows: The chemical composition analysis showed that the main cation components were Mg2+, Ca2+, Na+, and K+, the anion components were HCO3−, Cl−, and SO42−. A measure of 89% of the groundwater samples in this area were freshwater, the HCO3− were mainly dolomite, calcite, and gypsum dissolved precipitation resulted. Na+ and Cl− came from the dissolution of halite. Most of the groundwater was of the SO4·Cl-Ca·Mg type, accounting for 61.1%. The main ion chemistry of the shallow groundwater in this area is controlled by rock weathering, and pyrite oxidation is a significant factor affecting the SO42− concentration. These research results will help analyze the formation mechanism of chemical components and provide some basic data for the evolution of mine water in this area in the future. [ABSTRACT FROM AUTHOR]

Xianxian geothermal exploitation area is one of the areas with the best occurrence conditions of geothermal resource in North China, rich in medium and low temperature geothermal resource, and is a typical carbonate geothermal field. However, its hydrogeochemical evolution process is not clear, and no complete conceptual model of geothermal genesis has been established to guide the exploration, development and utilization of geothermal resource in the area. It restricts the sustainable development of regional geothermal resource and the realization of carbon emission reduction targets. In this study, geothermal fluids in the area were collected for testing and analysis in terms of hydrochemical characteristics and stable isotopes. Based on systematic geochemical research, the formation mechanism of geothermal fluids was analyzed, and a conceptual model of geothermal genetic in the study area was established. The main understanding is as follows: the hydrochemical type of geothermal water in the study area is Cl-Na type, and the water-rock interaction is not balanced. The formation of geothermal water in the area is affected by the infiltration of atmospheric precipitation, and it is terrestrial leached water. The flow path of geothermal water is long, the water circulation is slow, and the metamorphism is deep. Dolomite, calcite and gypsum dissolution are the main sources of Mg2+, Ca2+, , and in geothermal water, besides, other minerals containing calcium and magnesium are also part of their sources. The source of geothermal water recharge is atmospheric precipitation, and the recharge elevation of geothermal water is about 619–1069 m. The age of the geothermal water is between 16 000 and 18 000 years. The sulfur in geothermal water mainly comes from the leaching of sedimentary layer. [ABSTRACT FROM AUTHOR]

The dolomite in the Yuntai Mountain, Shibing, Guizhou, China constitutes the gentle stratum, affected by several weathering processes. It is coupled with a vertical joint development, which makes it easy to form the collapse and stone peaks corroded by running water. The aim of this paper is to study the effects of weathering processes of dolomite outcropping in the Yuntai Mountain (Shibing, Guizhou, China). This work shows the dolomite's physical and mechanical characteristics, microscopic characteristics of rock and pore structure based on chemical and minero-petrographic analyses. The findings indicate that the dolomite in this region is gray, pure quality and hard-packed superfine grain to fine grain. Mass surface voids suggest that the dolomite's pass is small and has more pore throat. Its grain cementation is relatively poor. The degree of rock weathering is relatively high. The mechanical strength is lower than that of the surrounding limestone. This work shows how the macro-micro characteristics of the dolomite affect the formation of collapse and stone peaks. This work further focuses on the study of the cone-shaped peak cluster basement and the upper tower-shaped stone peaks, which are the most important features of this region. [ABSTRACT FROM AUTHOR]

【Objective】The objective of the paper is to provide a reference for soil nutrient management and sustainable operation in Karst areas.【Method】The soil samples were collected from woodland and dry land in Baiduo Village(dolomite areas) and Shiqiao Village(limestone areas) in Shibing County,Guizhou Province,and then the soil nutrient was analyzed.【Result】The soil developed from dolomite was featured with higher organic matters,total N,available P,available K and hydrolysable N.The soil developed from limestone was featured with higher total P and total K.Total N was positively and very significantly related to hydrolysable N and organic carbon in soil developed from limestone and dolomite.Hydrolysable N was positively and significantly related to organic carbon in limestone areas.Hydrolysable N was positively and very significantly related to organic carbon in dolomite areas.Land use patterns had obvious effects on nutrient content in soil developed from limestone and dolomite.Soil total K,total N,hydrolysable N and organic carbon content in limestone woodland was higher than dry land,and available K,total P,available P and pH was lower than dry land.Soil total P and available P in dolomite woodland are lower than dry land,and other indexes are higher than dry land.The organic matter,total N,total P and total K content in dolomite-developed soil was Grade II,Grade I,Grade VI and Grade III respectively.The organic matter,total N,total P and total K content in limestone-developed soil was Grade II,Grade I,Grade V and Grade I separately.【Conclusion】Soil nutrient was not only affected by soil forming rock,but also affected by land use pattern. [ABSTRACT FROM AUTHOR]

The Fengcheng Formation in the Mahu sag of the Junggar Basin was primarily composed of detritus, pyroclastic material, carbonates, and evaporites. In order to establish the diagenesis pathways of the Fengcheng Formation, some methods of polarized light microscope, SEM, CL, EPMA, LR, and fluid inclusion analysis were applied to discuss the diagenesis process. The results showed the following: (a) The formation of an alkaline lake was the result of the influence of a high concentration of sodium-rich sources, and it led to the preservation of alkaline minerals in the stratum. (b) After the sediments were buried, three mineral assemblages were formed in the Fengcheng Formation, which are carbonate mineral assemblages (i.e., calcite + ferreous dolomite), reedmergnerite and carbonate mineral assemblages (i.e., reedmergnerite + calcite + ferreous dolomite), and reedmergnerite and alkaline mineral assemblages (i.e., reedmergnerite + shortite + trona), respectively. (c) According to the homogenization temperature of reedmergnerite primary fluid inclusions, the alkaline diagenesis of Fengcheng Formation was divided into an early stage (≤100 °C) and a middle stage (>100 °C), respectively. The earlier stage is marked by the formation of ferrous saddle dolomite, quartz dissolution, and the agglutination of laumontite. These processes occurred under normal burial conditions. The latter is marked by the reedmergnerite's appearance, which is correlated with the deep hydrothermal activity controlled by faults. (d) Based on sedimentary and diagenetic factors, including climate, provenance, diagenetic surroundings, and the action of subsurface fluid, the alkaline deposition-diagenesis model for shale series in four stages of the Fengcheng Formation was established. [ABSTRACT FROM AUTHOR]

Significant volumes of hydrocarbons have been produced from karstified Infracambrian dolomites in a 'buried hill' structure at depths of 5860m to 6027m and reservoir temperatures of 190-201°C in well Niudong-1 in the Baxian depression, Bohai Bay Basin. This is the deepest oil and gas discovery made in eastern China so far and structures at similar depths are targets for exploration elsewhere in the Bohai Bay Basin. However the origin and accumulation of the hydrocarbons at Niudong-1 is not clear: they may have been generated from highly mature lacustrine source rocks in the Sha-4 Member of the Eocene Shahejie Formation; or they may have been derived from thermal cracking of previously-accumulated oil. This paper investigates the organic geochemistry of the Sha-4 Member source rocks and the crude oils produced from well Niudong-1. Analyses of molecular parameters show that the hydrocarbons originated from the pyrolysis of organic matter in Sha-4 Member source rocks, rather than from cracking of previously accumulated oil. Infracambrian dolomites at the Niudong-1 location may have been charged with low-maturity oil around 34 Ma ago, when the Sha-4 Member source rocks were buried to depths of about 3500m and first entered the oil window. During further rapid burial to more than 5500m starting at about 15Ma, these source rocks became highly mature and generated significant volumes of light oil and gas. Overpressures in the source rock interval forced these hydrocarbons to migrate into unconformably-underlying Infracambrian dolomite reservoir rocks at the Niudong-1 structure. Significant risks are associated with future exploration of deep 'buried hill' structures in the Bohai Bay Basin. Not all the structures were charged with oil, and accumulations were not necessarily preserved during Neogene burial as the reservoirs may have been breached by faulting. [ABSTRACT FROM AUTHOR]

Pre-stack simultaneous inversion is a seismic exploration technology which is widely applied to recognize lithology and detect oil and gas by analyzing the feature of amplitude variation versus offset (AVO). A gas-bearing reservoir can cause an obvious change in P-impedance and density. To effectively discriminate gas-bearing dolomite within Longwangmiao Fm. in Sichuan Basin of China, the pre-stack inversion method is employed by strict quality procedures. These procedures mainly include rock physics analysis, AVO modeling and pre-stack simultaneous inversion. Using the technology, P-impedance, S-impedance and density are obtained simultaneously. The distribution of gas-bearing dolomite is identified by P-impedance versus density cross-plotting from well data. The final prediction result indicates the existence of gas-bearing dolomite in the upper part of Longwangmiao Fm. in the study area, which is consistent with well data. Generally, pre-stack simultaneous inversion represents an effective method to predict gas-bearing dolomite reservoir and should be applicable in other study areas. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ore-hosting dolomites from the Bayan Obo REE deposit, China, are mostly porphyritic in texture. • REE ores are hosted in hypabyssal carbonatite intrusions. • Fractionation of carbonatite magmas may have produced evolved melts rich in alkali, REE, Fe and volatile components, which facilitated the formation of REE ore. Abstract The Bayan Obo deposit is the largest rare-earth element (REE) deposit in the world. In this deposit, ore bodies are hosted in fine-grained ore-bearing dolomite marbles, known as the H8 dolomite marble. The H8 dolomite marble has been considered as part of the Bayan Obo Group composed Paleoproterozoic sedimentary rocks. However, the H8 dolomite marble can be younger than the Bayan Obo Group, and thus, the genesis of the dolomite marble should be re-examined. In this paper, we describe petrography and compositions of the H8 dolomite marble. The dolomite marbles generally have high FeO, MnO and SrO contents, different from sedimentary limestone or dolostone but similar to dolomite carbonatites. In composition, they can be grouped into magnesio-carbonatite and ferro-carbonatite. Texturally they are porphyritic and comprise originally hypabyssal intrusions. It is thus proposed that carbonatitic magmas injected slowly into a magma chamber where they have undergone fractionation to produce evolved dolomite-carbonatite magmas rich in alkali, REE, Fe and volatile components. Such evolved, metal-rich magmas were consequently injected along the contact zone between the early dolomite carbonatite sill and other layer of the Bayan Obo Group, and produced an large fenitization aureole enclosing ores rich in Fe, Nb, REE, F and alkali metals. Changes in CO 2 /H 2 O ratios, oxygen fugacity and halogen content of fluids were responsible for the formation of different types of ore, including massive magnetite-rich, aegirine-rich and Na-amphibole-rich ores. Considering the fact that the ore bodies are located at the place where dolomite carbonatites are relatively thick and the fenitization is relatively extensive, we speculate that the ore formation was genetically related to extensive fenitization involving exsolution of large amounts of fluids and subsequently extensive metasomatism. It is concluded that carbonatitic magmas played a major role in the formation of the REE mineralization in the Bayan Obo deposit. [ABSTRACT FROM AUTHOR]

Compared to other marine-shale gas reservoirs in South China, the shale that developed in faulted basins in East China possesses peculiar characteristics regarding the mineral types and their evolution. The diagenesis of inorganic minerals, generation of hydrocarbons, and evolution of organic matter control the final features and quality of these shale reservoirs. Therefore, we must analyze this diagenesis based on the essential characteristics of the representative reservoir and discuss the influence of the diagenesis' evolution stage on the shale reservoir. This topic is also of practical value for contemporary shale-oil exploration and development. In this paper, we observe diagenesis, study its essential characteristics (such as the structure of the reservoir and pores), determine the key factors that control the reservoir's storage capacity, and analyze the role of diagenesis (organic and inorganic) in the evolution of pores and the reservoir's storage capacity. The mineral types are diverse, and the content of calcite and other carbonate minerals is generally very high. Organic matter is abundant, thermal evolution is low, and the hydrocarbon generation capacity is strong. Because of their high variability, some pores are hard to differentiate from microfractures. Dissolved pores, which are generated by intercrystalline pores and the dissolution of calcite, dolomite, and other carbonate mineral grains, are the major component of a macroporous matrix. The large proportion of hydrocarbons that are generated by solid organic matter leads to the accumulation of pressure. The shale generates a high number of microfractures, which form a reservoir space network system that increases the porosity of the reservoir. Dolomite has a unique supporting role for the matrix pores, leading to the development of a matrix pore-seam system. The reservoir's mineral composition, pore diameter, porosity, and organic-matter content determine the reservoir properties and oil saturation. Organic-rich laminated shale has the best physical properties, dominated by macro-pores and easily connected and merged pore seams. The massive shale has the poorest reservoir property. The development and evolution of pores are mainly controlled by the transformation of clay minerals, the content of carbonate minerals, the sedimentary structure and the intensity of diagenesis. Dissolution depends on the intensity of hydrocarbon generation, the expulsion of acid by organic matter, the state of the carbonate minerals and organic matter, and the smooth depression of the fluid environment. Organic diagenesis is closely related to the diagenesis and evolution of inorganic matter and is typically reflected in the recrystallization of calcite, abundance of organic matter, and hydrocarbon generation by organic matter. A local alkaline diagenetic fluid environment and reduction in the degree of hydrocarbon generation transform incremental porosity to pore reduction. Favorable lithofacies and advantageous layer sections should be selected by considering the stage of diagenesis evolution. • Depicting the shale reservoir pores by a variety of methods and technologies. • Explaining the effects of shale diagenesis (inorganic mineral diagenesis and organic hydrocarbon generation) on reservoir characteristics. • Contrasting the storage capacity of different shale lithfaices, determing the favorable lithofacies and target interval. [ABSTRACT FROM AUTHOR]

The Daniudi gas field in China's Ordos Basin is located in the transitional zone between palaeo‐topographic highs and slopes, whereby dissolution‐collapse breccias are widespread within the palaeokarstic reservoir. Abundant cores, well logs and thin sections were used to study palaeo‐topography, palaeokarstic breccia types, diagenesis and reservoir pore characteristics. The results indicated that reservoir quality is controlled by lithology, palaeo‐topography and diagenesis. The extent of palaeokarstic reservoir dissolution was shown to be determined by lithologic differences, whilst only gypsiferous dolostones and finely crystalline dolostones emerged in reservoir formation. Palaeo‐topography was also found to regulate reservoir development. The reservoirs are primarily located 20 m below the Ordovician unconformity in palaeo‐topographic hills and palaeo‐topographic slopes, whilst their depth is palaeo‐topography dependent. Lithology and palaeo‐topography also coordinate the distribution of palaeokarst breccia facies. Clast‐supported and matrix‐supported chaotic breccias were found in argillaceous dolostone strata. However, crackle–mosaic breccias occurred in gypsiferous dolostones and crystalline dolostones, located in palaeogeomorphic residual hills and slopes. Reservoirs generally develop in crackle–mosaic breccias of Ma51 and Ma52 sub‐Members, the quality of such reservoirs is dependent on the development and distribution of palaeokarst breccia facies and diagenesis. Dissolution of dolomite and anhydrite nodules was found to result in moldic pores and dissolution‐enlarged pores. Overall, the most damaging effect on reservoir quality resulted from calcite cement infilling moldic pores, enlarged pores and fractures. [ABSTRACT FROM AUTHOR]

The depositional period of the early Miaolingian Maozhuang Formation in the North China Platform (NCP) is characterized by sediments of a restricted tidal-flat facies zone, i.e., transgressive red bed (sabkha facies) and highstand dolostone, and by sediments of an open tidal-flat facies zone, i.e., transgressive red bed and highstand limestone. The Maozhuang Formation at the Jinzhouwan section is composed of sediments of an open tidal-flat facies in which highstand limestone is marked by a set of bioherms that represent rare examples of microbial carbonates in the NCP. They consist of stromatolites and leiolites with intercalations of oolitic grainstones that can be categorized into four units: Unit [1] encompasses large-scale columnar stromatolites, small quartz grains and trilobite fragments; Unit [2] consists of structureless leiolites that contain trilobite fragments, quartz grains, and few dark and dense clumps of micrite dominated by calcified sheaths of filamentous cyanobacteria which probably grew in relatively thick cyanobacterial mats; Unit [3] comprises radial ooids that contain abundant fossils of calcified sheaths of filamentous cyanobacteria that might be genetically involved in the formation of ooids; Unit [4] contains small columnar stromatolites and small-scale micritic clumps dominated by filamentous cyanobacteria. The filamentous fossils in units [3] and [4] provide useful information regarding the origin of radial ooids and stromatolites in normal marine environment. Further, the large and small columnar stromatolites of early Miaolingian age in units [1] and [4] represent a unique example because they belong to the first episode of cyanbacterial calcification at the base of Phanerozoic. [ABSTRACT FROM AUTHOR]

In recent years, "Jin Gao Yu" that has been traded as a kind of jade has appeared in areas of the Luonan and Shangnan counties, Shangluo City, Shaanxi Province, attracting the attention of scholars and consumers for its delicate texture and warm color. In this study, infrared spectroscopy, Raman spectroscopy, X-ray diffraction analysis, and electron microprobe analysis were used to conduct a systematic gemmological test and an analysis of "Jin Gao Yu". The results show that "Jin Gao Yu" is a compact mineral aggregate dominated by dolomite, which contains quartz mineral inclusions. The color of "Jin Gao Yu" is grayish-white to earthy-yellow, the refractive index is about 1.54, and the relative density is about 2.86. Its crystal structure is basically the same as that of dolomite, both of which are trigonal systems with granular crystalloblastic textures. It has good crystallinity. The recrystallization phenomenon can be seen under a polarizing microscope. This study determined the species of "Jin Gao Yu", improved its gemological basic data, provided a theoretical basis for the identification of "Jin Gao Yu" in the future, and, also, provided a new direction for the use of dolomite. [ABSTRACT FROM AUTHOR]

The chemical weathering of carbonate rocks is the main form of interaction between earth spheres in the karst critical zone. The karst weathering cover, which is composed by residua from carbonate rocks weathering, contains important information about the climate environment and material cycle. We present the chemical composition of weathering covers in karst area of Guilin, Guangxi province, analyze their weathering process and strength, and compare them with the other weathering covers in other karst area in China, including Yunnan, Guizhou, Hunan, and Qinghai Tibet Plateau. The results showed: (1) the chemical composition of Guilin weathering covers were similar to that of carbonate weathering covers in other areas of China, and had the common characteristics of uniform distribution of chemical composition in the profile and obvious enrichment of Fe, Al and trace elements. During the formation of carbonate weathering cover and the residua, the rapid dissolution of Ca and Mg had an important impact on the migration and enrichment of other elements. (2) The chemical index of alteration (CIA) of carbonate weathering covers in Guilin and other karst areas of China was much larger than that in the upper crust (UCC) (60.13), which showed strong chemical weathering characteristics of the humid and hot climate. (3) The weathering process of carbonate rock was different from that of silicate and loess. In the early stage of carbonate rock weathering, soluble components (calcite and dolomite) had been rapidly dissolved and leached. All the carbonate weathering residua was measured to be in the stage of K2O weathering and Al2O3 increasing. Therefore, the weathering degree of carbonate weathering cover was mainly determined by the leaching of K2O and the increase of Al2O3. As a result, there was no correlation between CIA and Na/K (molar ratio), but was a significant negative correlation between CIA and K/Al (molar ratio) in the carbonate weathering cover. (4) The CIA values of weathering residua and carbonate weathering cover in southern China were negatively correlated with latitude, reflecting the influence of climate factors. From the influence of lithology, the chemical compositions of parent rock can affect the CIA of weathering cover, and the content of insoluble matter in carbonate rock was negatively correlated with CIA. From the influence of topography, the CIA value of weathering residua decreased from the high to the low position and from the shallow to the deep part of the profile. [ABSTRACT FROM AUTHOR]

In this paper, the genesis of dolomite in Longwangmiao Formation is analysed through field investigation and geochemical methods, and dolomization model is established, which is very important for the next reservoir prediction in Longwangmiao Formation. According to the crystal size, the Longwangmiao Formation dolomite can be divided into two types: microcrystalline dolomite (MID) and macrocrystalline dolomite (MAD). Both types of dolomite have higher Al content than lime mudstone, indicating that during the deposition process of the Longwangmiao Formation, terrigenous materials are continuously mixed into the sediment, which significantly affects the geochemical characteristics of the Longwangmiao Formation. The rare earth element (REE) composition of the two types of dolomite is consistent with that of lime mudstone (LM), with an obvious δCe positive anomaly and no δEu anomaly, which is a typical distribution pattern of marine carbonate sediments. The microcrystalline dolomite has a higher Na element content, lower δ13C value, and higher δ18O value, suggesting that it is formed in a highly saline evaporation environment. Most of the macrocrystalline dolomite has a residual grain texture. The elements, as well as the isotopic geochemical characteristics of the dolomite, are consistent with those of lime mudstone, indicating that macrocrystalline dolomite is formed early and inherits the geochemical characteristics of the precursor limestone. We believe that the dolomitization model of the Longwangmiao Formation is an evaporative concentration + reflux seepage model. In the late sedimentary period of the Longwangmiao Formation, the sea level declined and a large area of lagoon appeared in the restricted and semi-restricted platform. As the evaporation and concentration continued, precursor minerals such as high-magnesium calcite and aragonite mud experienced chemical precipitation. In this process, a large amount of Ca2+ was consumed, resulting in an increase in the Mg2+/Ca2+ ratio. Then, the precursor minerals underwent dolomitization, and microcrystalline dolomite began to form. At the same time, owing to the difference in density between the high-salinity concentrated seawater and the pore water existing in the early limestone, the concentrated seawater flowed back and penetrated downward, causing the dolomitization of the underlying strata, and then the formation of macrocrystalline dolomite. The degree of dolomitization was mainly affected by the development degree of the granule beach and the thickness of the strata. • The highlights of this article are as follows: • This paper provides a case study of terrigenous clastic dolomite. • This paper analyses the genesis of the dolomites of Longwangmiao Formation and establishes a dolomitization model. • We analysed a large number of samples and provided basic geochemical data for Longwangmiao Formation. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs), as important geochemical tracers, can well reflect the information carried by diagenetic fluids. In this paper, petrological and REE characteristics are studied to investigate diagenetic fluid information and dolomite petrogenesis using samples from the fifth member of Ordovician Majiagou Formation (Ma5) in the Ordos Basin based on the comprehensive analysis of C, O, and Sr isotopes. Three types of dolomites are identified in the study area, namely the dolomicrite, micrite-silty dolomite, and silty dolomite. Different types of dolomites have distinct total REE contents, among which the dolomicrite has the highest average total REE content and that could be possibly attributed to the abundant algal and argillaceous materials. All the three types of dolomites are featured by lower total contents of REEs than marine micrite, enriched light rare earth elements (LREEs) and deficit heavy rare earth elements (HREEs), which could result from the constant diffusion of REEs in the late diagenetic environment as well as the stronger complexing capacity of HREEs than LREEs. REE partition patterns in three types of dolomites are similar to those in marine micrite, which indicate the dolomitization fluids to be seawater or marine-origin fluids. In the dolomicrite, an obvious negative Eu anomaly (average value 0.63) and a faint negative Ce anomaly (average value 0.94) suggest that the sedimentary environment should be featured by low temperature and weak oxidation. Meanwhile, negative δ 13 C excursion (average value - 1.23‰), positive δ 18 O excursion (average value −7.59‰), and high mean 87 Sr/ 86 Sr ratios (average value 0.70992) along with petrological characteristics demonstrate the dolomicrite to originate from penecontemporaneous dolomitization. In the micrite-silty dolomite, the obvious negative Eu anomaly (average value 0.69) and the medium negative Ce anomaly (average value 0.72) indicate such kind of dolomites should be formed in the sedimentary environment characterized by low temperature and weak oxidation-weak reduction. The negative δ 13 C excursion (average value −0.43‰), positive δ 18 O excursion (average value −7.29‰), and relatively low mean 87 Sr/ 86 Sr ratios (average value 0.70955) identify the micrite-silty dolomite to be product of seepage reflux dolomitization in the supratidal zone. In the silty dolomite, the weakened negative Eu anomaly (average value 0.75) indicates relatively high temperature, and the obvious negative Ce anomaly (average value 0.66) implies reducing environment. Based on analysis of values of δ 13 C (average value −0.65‰) and δ 18 O (average value −6.46‰) as well as ratios of 87 Sr/ 86 Sr (average value 0.70958), silty dolomite is regarded to form due to burial dolomitization. [ABSTRACT FROM AUTHOR]

Surface water is extensively used for irrigation and industrial purposes in the Wei River Plain. However, the surface water shows different characteristics in the southern and northern zones of the Wei River Plain. This study aims to investigate the differences in surface water quality between the southern and northern zones of the Wei River Plain and their influencing factors. To ascertain the hydrochemistry and its governing factors, graphical methods, ion plots, and multivariate statistical analyses were employed. The quality of the irrigation water was assessed using various irrigation water quality indices. In addition, water foaming, corrosion, scaling, and incrustation risks were determined to evaluate water quality for industrial uses. The spatial distribution of water quality was done using GIS models. This research revealed that the concentrations of EC, TH, TDS, HCO3−, Na+, Mg2+, SO42− and Cl− on the north side of the plain were twice as high as those on the south side. On both sides of the Wei River Plain, water‒rock interactions, ion exchange, and considerable evaporation were observed. Gypsum, halite, calcite, and dolomite all dissolve to produce significant anions and cations in the water, according to ion correlation analysis. However, additional sources of contaminants led to higher concentrations in the surface water on the north side than on the south side. Surface water in the south of the Wei River Plain has superior quality to that in the north, according to the overall findings of irrigation water and industrial water quality assessments. The findings of this study will boost better water resource management policies for the plain. [ABSTRACT FROM AUTHOR]

The Chigbrak Formation in the Upper Ediacaran is one of the important exploration targets in the Tarim Basin, NW China. However, no significant discoveries have been made in this field, and unclear reservoir genesis is one of the important factors restricting exploration breakthrough. This study examined the outcrops of the Aksu area in northwestern Tarim Basin by using systematic descriptions of petrologic features in the Upper Ediacaran Chigbrak Formation. Samples were selected for tests of stable carbon and oxygen isotopic compositions, strontium isotopic compositions, rare earth elements, LA–ICP–MS element mapping and U–Pb dating. It was found that (1) the Chigbrak Formation is mainly composed of dolomitic microbialite, with average values of δ13C (PDB), δ18O (PDB) and 87Sr/86Sr of 3.50‰, 2.95‰ and 0.709457, and has similar geochemical characteristics to the coeval seawater. The dolomites have also been characterized by a medium degree of cation ordering (avg. 0.68), a low content of ΣREEs (avg. 9.03 ppm) and a chondrite standardized curve of REEs showing enrichment of LREE and depletion of HREE. The U–Pb ages range from 538 to 618 Ma, corresponding to the age of Ediacaran period. (2) Dolomitization occurred in a marine diagenetic environment during the penecontemporaneous period, with seawater as the dolomitization fluid. (3) Vugs are the dominant pore type of Chigbrak Formation, and they are the products of the dissolution of meteoric water in penecontemporaneous period. (4) The main controlling factors of reservoir were lithofacies, meteoric water dissolution controlled by fourth– or fifth–order sequences and tectonic movement, and early dolomitization. The research results are of great significance to the dolomite reservoir prediction of the Upper Ediacaran Chigbrak Formation of the Tarim Basin. [ABSTRACT FROM AUTHOR]

Microbialite textures, such as microbial mats and biofilms, were observed in the Middle Triassic dolomite in the Sichuan Basin, western China, using core examination, thin section petrography, scanning electron microscopy (SEM), and geochemical analyses. The dolomite texture, consisting of fibrous and spherulitic structures, is similar in morphology and size distribution to those observed in microbial culture experiments. Extracellular polymeric substances (EPS) were identified based on the occurrence of fibers forming a reticular pattern and nanometer-sized spheroids. The rare earth element (REE) and stable isotope (C, O, and Sr) compositions of the Middle Triassic dolomite were measured to determine their geochemical characteristics. Using seawater as a standard, the dolomitic microbialites (MD) exhibited significantly positive La and Eu anomalies and higher REE concentrations and (Nd/Yb)sn values than associated limestones, and these patterns are inferred to be related to initial complexation on organic ligands in the biofilm, as proposed by previous researchers. The ambient temperature during dolomite precipitation was estimated to be within the 23 °C to 50 °C range, as indicated by the δ18O values of the dolomite. This study suggests that various microbial effects can significantly affect diagenetic processes in the Middle Triassic dolomite. [ABSTRACT FROM AUTHOR]

• The frictional law under seven complex contact condition has been analyzed. • The contact property of the pipe under has been studied in ADINA systematically. • The cause of the pipe stuck during jacking has been verified in the study area. • The proposed solution for pipe stuck has been successfully verified in the project. The first rock pipe jacking project of China in Chongqing Guanjingkou encountered a pipe sticking problem soon following the abrupt increase of jacking force. It was essential for the direct shear test results and stresses acting normal to the outer periphery of the pipe strings to be relevant in the understanding of jacking forces for the pipe stuck. In this paper, direct shear tests were performed on the frictional characteristic between a dolomite and concrete specimen using the same test method in the earlier companion paper. The normal stresses of the pipe string were obtained through plane strain finite element modeling of the pipe-jacking under different engineering geological conditions, contact characteristics, overburden and contact areas, the threshold values of the normal contact stresses increased dramatically have also been achieved, simultaneously. Then the jacking force needed for stuck pipe strings has been predicted based on the frictional test results and the normal stress simulation in order to determine where the temporary intermediate jacking stations (TIJSs) should be installed. Finally, the pipe stuck problem is solved successfully using the TIJS method, this result provides excellent reference data for the similar engineering problems in the future. [ABSTRACT FROM AUTHOR]

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In this paper, heavy metals (i.e., V, Cr, Co, Cu, Zn, Cd, Pb, and Sb) in soils from a tannery waste lagoon, Hebei, north China were investigated. Element concentrates were determined by a portable X-ray fluorescence in situ and an inductively coupled plasma mass spectrometry in the lab. Two sets of indexes, including geological accumulation index, contamination factor, and pollution load index, and hazard quotient and total carcinogenic risk were adopted to evaluate the pollution and health-risk of heavy metals. A scanning electron microscopy in conjunction with an energy dispersive X-ray spectroscopy and an X-ray photoelectron spectroscopy was used to observe chromium occurrence and speciation. With an average of 6493.11 mg/kg, chromium contents in the lagoon soils reached up to 12971.19 mg/kg, 211-times higher than the threshold of Chinese soils (61.00 mg/kg). Elevated Cr contents resulted in significantly high pollution and noncarcinogenic and carcinogenic risks in the studied area. Chromium in most soils occurred predominately as Cr3+ (60–74%), and to a lesser extent, Cr6+. The mechanism responsible for decreasing Cr6+ percentages in soils with increasing depth was summarized: Cr6+ favors aqueous environment; soil moisture decreased with increasing depth; in soils especially in the lower portion, Cr6+ was reduced by Fe0 and Fe2, transforming into Cr3+ and Fe3+. In addition, the alkaline condition promoted Cr3+ to precipitate, resulting more Cr3+ absorbing in soils. The intimate association of Cr and Fe in soils (i.e., Cr mainly occurred in Fe oxides and dolomite) further confirmed our assumptions. A combined application of microorganism (e.g., Aeromonas hydrophila) and biochar (prepared from maize stalk or peanut shells) were recommended to alleviate Cr pollution in the soils. [Display omitted] • Chromium contents in lagoon soils are much higher than those of soils from the leather tanning districts worldwide. • The average I geo of Cr from studied soils is 7.59, higher than the threshold (>5) for significant pollution. • The Cr3+ percentages ranged from 60 to 74% in most soils, except for 42% in soils kb2 1–10 and kb3 1–10. • Chromium contents and Cr3+ percentages increased with the increasing depth. • Chromium occurs mainly in dolomite and Fe oxides; while no Cr was found in calcite. [ABSTRACT FROM AUTHOR]

Clumped isotope thermometry is an effective tool which allows to understand the post-depositional alteration, including recrystallization and solid-state reordering, of carbonate rocks. However, as both processes are controlled by elevated temperatures, it is frequently a challenge to distinguish between the relative importance of these two processes in deeply buried carbonate successions (depth > 5000 m or formation temperature > 150°C). In this paper, we have established a clumped isotopic framework of paired dolomite and calcite in order to decipher the relative influence of solid-state reordering versus recrystallization and consequently offer an improved understanding of the mechanisms involved. The material studied was derived from two deeply buried successions (Jurassic-Ediacaran) drilled in the central Sichuan Basin of South China. The calcite and dolomite minerals from these cores were separated using buffered acetic acid, and based on a two-component mixing model, the carbon, oxygen and clumped isotopic (Δ 47) compositions of the two endmembers were determined. Based on an evaluation of solid-state reordering models, we conclude that micritic carbonates (dolomite and calcite) from the Jurassic to the Cambrian have been altered during burial by the geothermal gradient as determined by vitrinite reflectance. The Ediacaran micritic dolomite records a hydrothermal event in the transition between the Ediacaran and Cambrian. In contrast, the clumped isotopic temperature of Ediacaran saddle dolomites reflects subsequent hydrothermal activity during the Silurian and Devonian and shows compositional variations controlled by cooling rates. This study highlights the utility of the theoretical framework based on paired dolomite and calcite records to untangle overprinted signals of clumped isotopes in ancient carbonate rocks and gives insight to better understand the complexity of alteration processes in deeply burial carbonate successions. [ABSTRACT FROM AUTHOR]

The origin of dolostones from the Lei 4 Member (T2l4) of the Middle Triassic Leikoupo Formation in the Western Sichuan Depression is unclear. The occurrence and genetic evolution of dolostones in T2l4 were analysed by polarised thin-sections and cathodoluminescence, major- and trace-element, scanning electron microscope, and carbon, oxygen and strontium isotope analyses. The study results are summarised as follows. (1) The dolostones were mainly precipitated in three stages of <40 °C, 40–60 °C and 60–80 °C, corresponding with three paleodepth ranges of 167–300 m, 433–1000 m and 1067–1433 m. The micritic dolostones and the fabric-retentive dolostones (algal dolostone, granular dolostone) mainly formed in a near-surface–shallow-burial environment, and the crystalline dolostones were mainly formed under intermediate burial conditions. (2) 87Sr/86Sr ratios are equivalent to that of the Middle Triassic seawater, Sr/Ba and V/Ni ratios >1, Na notably higher than that in coexisting limestones of T2l4, and the dolostones always coexist with evaporative minerals such as gypsum, indicating that dolomitisation fluids mainly originated from evaporative concentrated seawater. (3) The dolostones mainly inherit materials from precursor limestones based on trace-element distribution patterns, and carbon and oxygen isotope values that are consistent with coexisting limestones of T2l4. (4) Mediated by micro-organisms during the syngenetic period, micritic dolostones and some algal dolostones were formed by replacing aragonites and calcites. During shallow burial, concentrated seawater rich in Mg2+ from the supratidal–intertidal zone flowed downward owing to gravity along the platform and replaced the underlying carbonate rocks, promoting continuous growth of the early dolomites. In the intermediate burial period, the Mg2+-depleted dolomitisation fluid caused the early micritic and silt-crystalline dolostones to recrystallise into silt- or fine-crystalline dolostones with larger crystals and altered the fabric-retentive dolostones into crystalline dolostones. (5) The evaporative dolostones deposited in the near-surface environment are characterised by maximal enrichment of Fe, Sr and Na, the highest δ18O values, the lowest order degree and the highest Ca/Mg ratios. The reflux dolostones formed in a shallow-burial environment characterised by the lowest Fe, medium δ18O values and the lowest order degree. The burial dolostones that developed in the intermediate burial environment are characterised by relative enrichment of Fe and Mn, minimal Na, the lowest δ18O values, the highest order degree and medium Ca/Mg ratios. The fabric-retentive dolostones mainly formed in a near-surface–shallow-burial environment, and the crystalline dolostones mainly formed under intermediate burial conditions. Dolomitisation fluids mainly originated from the evaporative concentrated seawater, and the dolostones inherit materials from the precursor limestones. Micritic dolostones were formed by evaporative dolomitisation; algal dolostone and granular dolostone were formed by evaporative dolomitisation and reflux dolomitisation; and silt-crystalline dolostone were formed by reflux dolomitisation and burial dolomitisation. [ABSTRACT FROM AUTHOR]

Dendrite, a typical geological pattern, is developed along the bedding plane in limestone and dolomite strata in Jinzigou area, Zhoukoudian, Beijing, China, with a self-similar dendritic morphology. In order to reveal the dynamic mechanism of its formation, the diffusion-limited aggregation method, a model of fractal growth, was selected to simulate the microscopic dynamic mechanism of its formation. Take an L × L square lattice, with L = 200 lattices, 20,000 particles, and L = 250 lattices, 30,000 particles, for simulation. Obtain the simulation results of the dendritic pattern and the intermediate results with 8057 and 10,827 random particles released in the simulation process with 20,000 particles. The results show that the pattern is a typical fractal pattern formed in the process of fractal growth, with a fractal dimension of about 1.6. Its morphology is characterized by fractal geometry, and the dynamic mechanism of its formation is the fractal growth phenomenon generated by self-organizing criticality. The growth process is a nonlinear and non-equilibrium evolutionary process, which is dynamic and far from equilibrium. It is consistent with the fractal dimension of Zhoukoudian dendrite (1.52–1.78). Diffusion-limited aggregation (DLA) is a typical growth process in fractal growth. It leads to the growth of randomly branching structures that closely resemble various important systems in the earth sciences, providing a theoretical basis for revealing the nature of complex geological processes. [ABSTRACT FROM AUTHOR]

While Ediacaran cap dolostones research is a hot topic, detailed sedimentological analysis of barite‐bearing cap dolostones remains scarce. Here, new data are presented from Xiangerwan in northern Three Gorges, South China, to illustrate the sedimentary characteristics, depositional environment and formation mechanism of the barite‐bearing cap dolostone. In ascending order, the succession is divided into: (i) pebbly dolostone; (ii) dolostone with unusual sedimentary structures (for example, sheet cracks and tepee structures); and (iii) barite‐bearing facies. The gravels of the pebbly dolostone record the slow relative sea‐level rise during post‐glacial transgression, with a local terrestrial influence. Sheet cracks and tepee structures represent water escape structures in the supratidal and upper intertidal zone, and gently wavy stromatolites in barite‐bearing facies are deposits typical of the upper intertidal zone. In addition, primary radial length‐slow dolomite cements were originally precipitated at the seafloor. In general, the cap dolostone was formed in a shallow‐water ramp environment. The form and sedimentary characteristics of barites indicate a primary (syngenetic) origin and help to divide the barites into bladed (Type I) and needle‐like (Type II) variants. With the ongoing melting of the Marinoan glacier and water density stratification, the cap dolostone was gradually precipitated, accompanied by exotic gravels input. The stratification persisted, and special sedimentary structures were widely developed. Phosphorus and barium ions were brought up from the deep basin by upwelling, indicated by the flourishing stromatolites and barite fan deposition. Above the sediment–water interface, the Type I barite first grew upward from substrates, then the Type II barite could grow either in the reverse 'V‐shape' cavities between and within the Type I barite clusters, forming rhythm layers with bedded dolomite, or scattered in the laminae of stromatolites or surrounding dolomite. Finally, the formation of barite fans indicates the end of cap dolostone deposition and deeper water sedimentation. [ABSTRACT FROM AUTHOR]

Significant amounts of petroleum are found in the deeply buried Cambrian Xiaoerbulake Formation in the Tarim Basin. However, limited understanding of origin of diagenetic fluids hampers petroleum exploration. In this study, petrological and high-resolution geochemical methods have been performed to understand the origin and evolution of diagenetic fluids, and their effects on the formation of dolostone reservoir. The Xiaoerbulake Formation is characterised by microbialites. The matrix is characterised by modern seawater-like rare earth element and yttrium (REY) patterns and δ18O values of −6.02 ± 2.11‰ Vienna Pee Dee Belemnite (VPDB). Fine-crystalline dolomite cements have similar δ13C values and heavy rare earth element enrichment patterns to that of matrix dolomite, yet with lower δ18O values of −7.47 ± 1.2‰ VPDB. In the deep-burial regimes, medium- to coarse-crystalline dolomite cements and saddle dolomites were precipitated at temperatures of 90–120 and 130–190 °C, respectively, lower δ18O values, distinct middle rare earth element enrichment, and high Fe and Mn contents compared with matrix and fine-crystalline dolomite cements. These imply thermochemical reduction of Fe- or Mn-rich oxides and/or hydrothermal fluids. Compared with other types of dolomite cements, calcite cements are characterised by low δ13C values (as low as −6‰ VPDB), light rare earth elements enrichment and significantly elevated Y/Ho ratios (86 ± 59.3), likely related to the oxidation of organic matter during thermochemical sulfate reduction (TSR). Consequently, diagenetic fluid may have evolved from: Cambrian seawater, meteoric water, shallow-buried seawater-dominated pore water, medium-deep-buried ferrous-rich pore water, lately high-salinity hydrothermal fluid-dominated pore water and finally to acidic fluids related to TSR dissolution. Reservoir quality is enhanced by hydrothermal pulses and TSR in deep-burial settings. This study is significant for those concerned with the formation of deep-buried carbonate reservoirs. [ABSTRACT FROM AUTHOR]

Lacustrine dolomite nucleation commonly occurs in modern and Neogene evaporitic alkaline lakes. As a result, ancient lacustrine microcrystalline dolomite has been conventionally interpreted to be formed in evaporitic environments. This study, however, suggests a non‐evaporitic origin of dolomite precipitated in a volcanic–hydrothermal lake, where hydrothermal and volcanic processes interacted. The dolomite occurs in lacustrine fine‐grained sedimentary rocks in the middle Permian Lucaogou Formation in the Santanghu intracontinental rift basin, north‐west China. Dolostones are composed mainly of nano‐sized to micron‐sized dolomite with a euhedral to subhedral shape and a low degree of cation ordering, and are interlaminated and intercalated with tuffaceous shale. Non‐dolomite minerals, including quartz, alkaline feldspars, smectite and magnesite mix with the dolomite in various proportions. The 87Sr/86Sr ratios (0.704528 to 0.705372, average = 0.705004) and δ26Mg values (−0.89 to −0.24‰, average = −0.55‰) of dolostones are similar to those of mantle rocks, indicating that the precipitates mainly originated from fluids that migrated upward from the mantle and were subject to water–rock reactions at a great depth. The δ18O values (−3.1 to −22.7‰, average = −14.0‰) of the dolostones indicate hydrothermal influence. The trace and rare earth element concentrations suggest a saline, anoxic and volcanic–hydrothermally‐influenced subaqueous environment. In this subaqueous environment of Lucaogou lake, locally high temperatures and a supply of abundant Mg2+ from a deep source induced by volcanic–hydrothermal activity formed favourable chemical conditions for direct precipitation of primary dolomite. This study's findings deepen the understanding of the origin and processes of lacustrine primary dolomite formation and provide an alternative possibility for environmental interpretations of ancient dolostones. [ABSTRACT FROM AUTHOR]