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The Permian Fengcheng Formation (P1f.) in the Hashan area, situated on the southwestern margin of the Junggar Basin, has witnessed a remarkable breakthrough in shale oil exploration in recent years with nearly 789 million tons of shale oil resources. As a unique set of mixed sedimentary shales, the Fengcheng Formation in the Hashan area is characterized by mixed sedimentation of terrigenous siliciclastic sediments, authigenic minerals, and tuffaceous materials. However, the understanding of pore characteristics in the mixed sedimentary reservoir still remains limited, prohibiting accurate estimation of the oil content and insights into oil mobility. Scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR), X-Ray Computer Tomography (X-CT), and geochemical analysis were performed to investigate the pore size distribution and main controlling factors of the mixed sedimentary reservoir. Results showed that the main pore types in the mixed sedimentary reservoir are intergranular pores and dissolution pores. The pores of the P1f. mixed shales in the Hashan area were classified into II-micropores (< 25 nm), I-micropores (25–100 nm), mesopores (100–1000 nm) and macropores (> 1000 nm). In general, the mixed sedimentary rocks of P1f. formation feature few macropores but a large number of micropores and mesopores. The CS exhibits the most favourable physical properties among all lithofacies. It is concluded that the abundance and maturity of organic matter, mineral composition, sedimentary structure, and diagenesis of reservoir together impact the pore structure in the mixed sedimentary reservoirs. The maturity of organic matter and the content of tuffaceous minerals are the most significant in influencing the pore structure of P1f. shales. Overall, the pore structure of complex lithologic reservoir formed by mixed deposition and its influence on physical properties are studied, and the characteristics of the microscopic pore-throat system of the dominant lithofacies in the Hashan area are clarified, which is of great significance as a guide for the exploration and development of mixed sedimentary reservoirs in continental shale oil in China. [ABSTRACT FROM AUTHOR]

The Albian–Aptian Goru Formation represents a fluvio-deltaic reservoir in both the Central and Southern Indus Basin, Pakistan. Using high-resolution core data, this study provides comprehensive insights into the depositional environment and its role in influencing reservoir heterogeneities in the studied formation. The sedimentological investigations demonstrate five lithofacies, namely, (i) massive sandstone (Sm), (ii) horizontal to low-angle planar laminated sandstone (Sl), (iii) planar cross-laminated sandstone (Sc), (iv) heterolithic beds (Hw and Hr), and (v) massive mudstone (Mm). Facies associations reflect shallow marine depositional settings varying from deltaic in the NE to strand plain in the SW. The framework grains of the established lithofacies exhibit quartzo-feldspathic petrofabrics, which have been sourced from stable craton-continental block settings. The petrophysical data in the core depth zone show high shale content in Well-A and lower parts of Well-B. In Well-A, the crossover between the density and neutron logs is not observed, which suggests unsaturated sands, while Well-B exhibits a permeable zone as indicated by neutron-density crossover, low gamma ray values, and relatively high porosity. The petrographic analysis and scanning electron microscopy indicate high effective porosities contributed by both primary (intergranular and intercrystalline) and secondary porosity (owing to fracturing and dissolution). The upper part of Well-B shows high porosity values up to 28% due to highly fractured quartz. Porosity values are low in the lower parts of the Well-A and Well-B due to intensive calcite cementation, chlorite recrystallization, proto matrix as well as pseudo matrix. This suggests that both Well-A and Well-B have a common source but the reservoir properties can be attributed to the depositional and post-depositional variations in the petrofabric of the studied lithological units. The Cretaceous Goru Formation in Southern Indus Basin, the Pariwar formations in Jaisalmar Basin, and Bhuj Formation in Kutch Basin share same geological history and sedimentary processes. Thus, these studies can be utilized in the exploration of Cretaceous reservoirs in these basins. [ABSTRACT FROM AUTHOR]

In this study, taking the Jurassic Lianggaoshan Formation (J1l) tight sandstones in the eastern Sichuan Basin as an example, the types and well-logging responses of main sedimentological and diagenetic facies in the lacustrine delta-front are investigated based on summarizing the sedimentary characteristics and reservoir properties. Subsequently, further validation and application are conducted in the study area through machine learning. Research results show that the J1l lacustrine delta-front in the eastern Sichuan Basin mainly develops subaqueous distributary channels and mouth bar sand bodies, exhibiting typical densification reservoirs, with porosity and permeability distributed between 0.48% and 11.24% (av. 3.87%) and 0.0003-0.653 x 10-3 µm² (av. 0.026 x 10-3 µm²), respectively. Strong compaction and strong cementation are the primary factors leading to densification, whereas chlorite coatings and weak dissolution play constructive roles in preserving some primary pores, creating a small amount of dissolution pores, and enhancing permeability. In terms of manifestation, the pore-throat content with a radius greater than 0.006 µm governs the reservoir quality. Furthermore, five types of diagenetic facies are identified in the J1l subaqueous distributary channels and mouth bars: strong compaction facies (Type I), strong cementation facies (Type II), chlorite-coating and intergranular pore facies (Type III), weak dissolution and intragranular pore facies (Type IV), and medium compaction and cementation facies (Type V). Overall, the thick and coarse-grained subaqueous distributary channels can be considered as the preferred exploration targets for tight oil and gas, with type III and type IV diagenetic facies being the most favorable reservoirs, characterized by well-logging responses of high AC and low GR, DEN, and RT. Based on the fine division of sedimentological and diagenetic facies, establishing well-logging interpretation models and then employing machine learning to achieve sweet spot reservoir prediction can provide valuable insights for tight oil and gas exploration in regions lacking core data. [ABSTRACT FROM AUTHOR]

Natural fractures are widely developed and distributed in tight sandstone reservoirs in the western Sichuan Basin, China, influenced by complex tectonic movements and diagenetic processes. These natural fractures serve as the main flow channels and important storage spaces in such reservoirs. Understanding their development characteristics and controlling factors determines the positioning and production efficiency of tight gas wells. This paper first explores the types and characteristics of natural fractures in the second member of the Upper Triassic Xujiahe Formation (T3x2) in the western Sichuan Basin through outcrop investigations, core observations, image log interpretations, and thin section analyses. We study the main influencing factors controlling the development and distribution of tectonic shear fractures by combining the characterization of fracture attributes. The results show that the tight sandstone reservoirs in the T3x2 mainly contain tectonic fractures, diagenetic fractures, and overpressure fractures, among which shear fractures in tectonic fractures are the main types. There are four sets of tectonic shear fractures in the study area, oriented in the E-W, N-S, NE-SW, and NW-SE directions. The dip angles of fractures range from 20° to 80°, with an average dip angle of 53°, predominantly consisting of high-angle fractures. The lengths of fractures are mainly within 100 cm, with a mean value of 47.53 cm, and 76.2% of fractures have lengths less than 50 cm. Fracture apertures range from 2.51 to 163.19 μM, with an average of 30.54 μM. The proportion of effective fractures in tectonic shear fractures reaches 85.7%. The development of tectonic shear fractures is primarily influenced by lithology, rock mechanics stratigraphy, diagenetic processes and facies, and faults. Lithology stands as the fundamental factor influencing the degree of fracture development in tight reservoirs. In rocks with the same composition, as the grain size decreases, the degree of fracture development increases. Simultaneously, with the rise in muddy content, fracture development diminishes in siltstone, argillaceous siltstone, silty mudstone, and mudstone. The formation and distribution of fractures are governed by rock mechanics stratigraphy, primarily manifested as a decrease in fracture density with an increase in rock mechanics layer thickness within a certain range. Diagenetic processes affect the abundance of tectonic shear fractures by influencing the mechanical properties of rocks. The stronger the compaction and cementation, the poorer the physical properties, and the higher the brittleness of the rocks, resulting in a greater abundance of tectonic shear fractures. Rocks with strong compaction and robust cementation facies exhibit high brittleness, rendering them more susceptible to fracturing under identical stress conditions. Fractures are highly prevalent in both the hanging wall and footwall of faults. As the distance from the fault increases, the linear density of fractures significantly decreases, owing to the uneven distribution of stress perturbation caused by fault activity. [ABSTRACT FROM AUTHOR]

Soil biocementation through microbially induced carbonate precipitation (MICP) is a promising technique for improving soil behavior in a nondisruptive manner, particularly for rehabilitation and retrofitting applications. Previous studies characterizing the shear behavior of biocemented soils have concentrated on poorly graded sands, whereas research on well-graded gravelly soils, which are extensively used in shallow geotechnical structures, has been lacking. Mohr–Coulomb strength parameters have been predominately employed to interpret the macromechanical effects of biocementation, but the previously reported findings show significant contradictions. In this study, a well-graded aggregate, representative of commonly used well-graded gravelly soils, was biocemented and subjected to monotonic drained triaxial compression. The test results show remarkable improvements in shear behavior, with the observed changes in stress–strain responses, strength and stiffness development, and stress dilatancy agreeing with those reported for biocemented sands as well as conventional cemented soils. Relatively low cementation levels can effectively rectify the mechanical performance caused by poor compaction to that seen at optimal levels, demonstrating the feasibility and potential of biocementation for improving soils of this type. Detailed analysis of the results reveals the decisive role of cementing bonds and their degradation in causing behavioral changes at different shearing stages. The theories of bonded structure and force-chain evolution are used to explain the preyielding observations, while an analytical approach capable of quantifying the evolution of different strength components is presented for postyielding macromechanical characterization. Conversely to the inference drawn from the strength parameters, the largest improvement is found in the frictional rather than the dilative and cohesive components of strength. Further analysis reveals the commonality of the macromechanical effects of biocementation, density, and confinement, and a unique relationship between macromechanical composition and peak stress ratio emerges. [ABSTRACT FROM AUTHOR]

Reactive transport modeling (RTM) is an emerging method used to address geological issues in diagenesis research. However, the extrapolation of RTM results to practical reservoir prediction is not sufficiently understood. This paper presents a case study of the Eocene Qaidam Basin that combines RTM results with petrological and mineralogical evidence. The results show that the Eocene Xiaganchaigou Formation is characterized by mixed siliciclastic-carbonate-evaporite sedimentation in a semiclosed saline lacustrine environment. Periodic evaporation and salinization processes during the syngeneticpenecontemporaneous stage gave rise to the replacive genesis of dolomites and the cyclic enrichment of dolomite in the middle-upper parts of the meter-scale depositional sequences. The successive change in mineral paragenesis from terrigenous clastics to carbonates to evaporites was reconstructed using RTM simulations. Parametric uncertainty analyses further suggest that the evaporation intensity (brine salinity) and particle size of sediments (reactive surface area) were important rate-determining factors in the dolomitization, as shown by the relatively higher reaction rates under conditions of higher brine salinity and fine-grained sediments. Combining the simulation results with measured mineralogical and reservoir physical property data indicates that the preservation of original intergranular pores and the generation of porosity via replacive dolomitization were the major formation mechanisms of the distinctive lacustrine dolomite reservoirs (widespread submicron intercrystalline micropores) in the Eocene Qaidam Basin. The results confirm that RTM can be effectively used in geological studies, can provide a better general understanding of the dolomitizing fluid-rock interactions, and can shed light on the spatiotemporal evolution of mineralogy and porosity during dolomitization and the formation of lacustrine dolomite reservoirs. [ABSTRACT FROM AUTHOR]

The exploration level of tight sandstone gas reservoirs in the Denglouku Formation (DF) in the Xujiaweizi Fault Depression is low, and hydrocarbon source and accumulation process remain unclear. Through the analysis of natural gas geochemistry, X-ray diffraction, thin section observation, scanning electron microscope, physical property testing, cathodoluminescence, fluid inclusions, and basin simulation, we examine source of hydrocarbon, the period of hydrocarbon accumulation, and the evolution of physical properties of the tight sandstone gas in the DF. Additionally, the formation process of tight sandstone gas reservoirs in the DF is discussed. The results reveal the following: (1) the tight sandstone gas in the DF is categorized as III kerogen cracking gas, primarily sourced from dark mudstone of the second member of the DF, with some contribution from dark mudstone of the Shahezi Formation. (2) The tight sandstone in the DF is in stage B of middle diagenesis. Based on apparent compaction rate, apparent cementation rate, and apparent dissolution rate, it can be divided into four diagenetic facies: (1) strong compaction–medium cementation–weak dissolution facies; (2) medium compaction–strong cementation–medium dissolution facies; (3) medium compaction–strong cementation–weak dissolution facies; and (4) medium compaction–medium cementation–medium dissolution facies. The predominant diagenetic facies are the medium compaction–strong cementation–medium dissolution facies and medium compaction–medium cementation–medium dissolution facies. (3) The hydrocarbon charging period of the DF in study area ranged from 98 to 67.5 Ma. This period is earlier than the tight period of the strong compaction–medium cementation–weak dissolution facies sandstone and later than the tight period of the medium compaction–strong cementation–medium dissolution facies, medium compaction–strong cementation–weak dissolution facies, and medium compaction–medium cementation–medium dissolution facies sandstone. Consequently, two types of tight sandstone gas reservoirs exist in study area: (1) tight sandstone gas reservoir with tight first and then accumulation type and (2) composite tight sandstone gas reservoirs. Our research offers theoretical instruction for exploration of deep tight sandstone gas in northern Songliao Basin. [ABSTRACT FROM AUTHOR]

Analcime plays a significant role in sandstone reservoirs as an authigenic diagenetic mineral in the Junggar Basin (northwestern China). However, the origin and controls on the reservoirs have received remarkably little attention. This study investigates the formation mechanism of analcime in the Middle Permian strata in the Jinan sag (southern Junggar Basin) through petrography and geochemistry. The results show that analcime is formed through early alkaline hydrolysis of volcanic materials under specific temperature and pressure conditions. The reservoir rocks primarily consist of various lithic sandstones, including volcanic debris such as basalt, andesite, and tuff. Analcime is characterized as rich in aluminium and poor in sodium, classified as low- silica analcime with a low Si-Al ratio (1.98-2.38). Furthermore, various other diagenetic minerals, such as glauconite, chlorite, albite, and calcite have been identified. The primary reservoir space chiefly consists of intragranular dissolved pores of analcime, while secondary pores are formed by intragranular pores of feldspar and lithic, along with some remaining intergranular pores. Cementation of analcime during early diagenesis changes primary pore structures and reduces reservoir properties. The low-silica analcime dissolves due to acidic pore fluids associated with three stages of oil and gas charging, transforming into albite and creating numerous secondary pores, thereby enhancing reservoir quality. [ABSTRACT FROM AUTHOR]

Organic-rich shales from the uppermost Doushantuo Fm. (South China) record one of the most negative carbonate carbon isotopic excursions in Earth's history, known as the Shuram excursion, and contain meter to micro-size spheroids. In this study, we use Raman and energy dispersive spectroscopy to identify and describe the most common diagenetic spheroids to refine our understanding of the profound perturbations of the carbon cycle and the evolution of pore fluid chemistry imprinted in the sedimentary Precambrian record, especially in the late Ediacaran. The presence of 13C-depleted carbonate concretions or organic matter (OM) enclosed by lenticular dolomitic structures within the host shale unit suggests OM remineralisation and anaerobic oxidation, resulting in authigenic carbonate precipitation during the earliest stages of sediment diagenesis. Other mineralogical features, however, point to high levels of primary production, such as apatite bands that host spheroidal microfossils with highly fluorescent quartz and OM within abiotic concretions. These observations highlight the importance of considering co-occurring biotic and abiotic processes in explaining the formation of diagenetic spheroids in ancient sedimentary environments. From an astrobiology perspective, the interplay of biotic and abiotic processes reflects the complexity of early life systems and the environments that may exist on other terrestrial planets. Understanding the signatures of biotic and abiotic interactions in the Doushantuo Fm. is crucial for identifying potential biosignatures in extraterrestrial materials, thereby enhancing our understanding of life's universality and adaptability in diverse and extreme environments. [ABSTRACT FROM AUTHOR]

Carbonate archives record a brief snapshot of the ambient Earth's surface conditions at their deposition. However, the geologically reasonable extraction and interpretation of geochemical proxy data from ancient, diagenetically altered rock archives is fraught with problems. Three issues stand out: the dichotomy between petrographic and geochemical alteration; the lack of quantitative age constraints for specific diagenetic phases resulting in a poorly constrained admixture of local, basin-wide and over-regional (far-field) features; and an often insufficient understanding of the temperatures and compositions of diagenetic fluids. Here, the archive of Devonian marine limestones exposed to multiple far-field diagenetic events is used as an example to explore the above-listed issues. Methods applied include petrography, micro XRF, fluid inclusion data, clumped isotopes, δ13C and δ18O isotopes, 87Sr/86Sr ratios and quartz trace element data. Devonian limestones studied here were overprinted by two cross-cutting regional fault zones (T ≈ 230 °C) by multiple events between the Variscan Orogeny and the late Paleogene. The following processes are recorded: (i) protolith deposition and partial dolomitisation during rapid burial in the Middle/Late Devonian (T ≈ 180 °C); (ii) deep burial to ca 6.5 km and tectonic/hydrothermal overprint during the Variscan Orogeny in the Carboniferous (T ≈ 90–230 °C); (iii) rapid uplift to 1–2 km burial depth at the end of the Variscan Orogeny and hypogene karstification (T ≈ 50 to 100 °C) initiated by regional geology in the Permian/Triassic; (iv) tectonic/hydrothermal overprint during the opening of the Proto-Atlantic Ocean between the Early Jurassic and the Early Cretaceous (T ≈ 50 to 130 °C); (v) tectonic/hydrothermal overprint including renewed hypogene karstification and hydrothermal calcite cement precipitation (T ≈ 50 to 180 °C) during Alpine Orogeny between the Late Cretaceous and late Paleogene. Despite this complex series of diagenetic events, the protolith limestones largely preserved their respective Middle/Late Devonian dissolved inorganic carbon (DIC) and 87Sr/86Sr signatures. This study documents that geochemical proxy data, placed into their petrographic, paleotemperature, and local to over-regional context, significantly increases the ability to extract quantitative information from ancient carbonate rock archives. Research shown here has wider relevance for carbonate archive research in general. [ABSTRACT FROM AUTHOR]

The 6th member of the Triassic Yanchang Formation, hereafter referred to as Chang 6 reservoir, in the Wuqi area of the Ordos Basin presents formidable obstacles for efficient tight oil development. This reservoir is known for its tight lithology, strong heterogeneity, inadequate oil saturation, and abnormally low reservoir pressure, which collectively contribute to the highly differentiated mobility of tight oil within the formation. To overcome these challenges, a comprehensive understanding of the factors influencing oil mobility is essential. This study investigates the occurrence characteristics of movable fluids in different diagenetic facies and the corresponding influential factors by employing various microscopic experiments, including high-pressure mercury intrusion, constant-rate mercury intrusion, nuclear magnetic resonance test, scanning electron microscopy, pore-casted thin section analysis, and X-ray diffraction measurement. There is a weaker correlation between the pore-throat radius ratio and the movable fluid saturation in reservoirs of various diagenetic facies (R2 = 0.6104), whereas there is a stronger correlation between movable fluid saturation and throat radius (R2 = 0.9415). Among the seven types of diagenetic facies, chlorite membrane cementation-intergranular pore facies (Facies I) and chlorite and illite membrane cementation-intergranular pore facies (Facies II) have the best-developed throats and the highest coordination number. Illite cementation-intergranular pore facies (Facies III) and illite and chlorite membrane cementation-dissolution facies (Facies IV) demonstrate smaller pore-throat radii and moderate to poor reservoir connectivity. The other three facies, namely illite cementation-dissolution facies (Facies V), illite cementation facies (Facies VI), and carbonate tight cementation facies (Facies VII) exhibit underdeveloped pore structures and lower recovery rates. Pore-throat radius emerges as the principal factor influencing reservoir permeability and storage capacity. The distribution of favorable diagenetic facies is influenced by depositional environments, diagenetic processes, and microscopic pore-throat characteristics. This study significantly enhances our understanding of the differential occurrence characteristics of fluids in different diagenetic facies in the Chang 6 reservoir, providing valuable insights for future exploration and production endeavors aimed at optimizing oil recovery in tight sandstone reservoirs. [ABSTRACT FROM AUTHOR]

The northern part of the Sanandaj-Sirjan zone hosts important iron deposits formed during the Mesozoic magmatism. The Baba-Ali and Galali ore deposits occurred on the border of Hamedan, Kermanshah, and Kurdistan provinces. Ores in these deposits include magnetite together with pyrite, pyrrhotite, chalcopyrite, and hematite. The petrographic studies show at least two generations of magnetite and one generation of pyrite in the Baba-Ali, and one generation of magnetite and pyrite in the Galali ore deposits. The supergene processes replaced the magnetite with hematite, goethite, and limonite in the surface parts of the deposits. Field and mineralographic evidence show that the studied ore deposits are of skarn type. The δ34S values of pyrite from the Baba-Ali and Galali deposits range from +6.8 to +13.3‰ and +6.1 to +7.3‰ respectively, and calculated δ34SH2S of the mineralizing fluid range from +7.8 to +14.3 ‰ and +7.1 to +8.3‰, respectively. The δ34S values of the Baba-Ali and Galali ore deposits are higher than the magmatic source values for the skarn deposits. Therefore, these positive values indicate the incorporation of sulfur from both magma and host/wall rocks. The igneous bodies of the studied area are mainly composed of mafic to felsic intrusive rocks, which formed as a result of magmatism resulting from the subduction of the Neo-Tethys oceanic crust beneath the Central Iran Microcontinent (CIM) during the Late Jurassic-Early Cretaceous time. Due to the emplacement of dioritic magmas within the carbonate rocks of the region, iron mineralization (magnetite) of the skarn type has occurred with the metamorphism of the host rocks. Introduction The Sanandaj-Sirjanzone in western Iran contains many iron ore deposits. The Baba-Ali, Galali, Tekyeh-Bala, Chenar, and Khosrow-Abad iron ore deposits are located in the NW Hamedan and SE Songhor provinces (Fig. 1). In the present study mineralography, paragenetic sequence, and field relation of the Baba-Ali and Galali ore deposits are compared and investigated to identify the type of mineralization system. Subsequently, sulfur isotope data for the Baba-Ali and Galali ore deposits are presented and compared to understand the source of sulfur and their probable genetic relationship. Materials and methods Forty-five thin, thin-polished, and polished sections from the ore deposits were studied. Sixpyrite samples from the Baba-Ali and six pyrite samples from the Galali iron ore deposits were analyzed for their sulfur isotope contents using an isotope ratio mass spectrometer (IRMS, IsoPrime100) at Tsukuba University, Japan. The CDT (Canyon Diablo Troilite) standard sample was used to measure sulfur isotopes. Results Petrography The Baba-Ali iron ore deposit is mainly composed of magnetite (two generations). The first-generation magnetite is formed massively and the second-generation is formed as vein. Pyrite is the most abundant sulfide mineral in the Baba-Ali ore deposit which is formed in one generation. Pyrite crystals are often anhedral to subhedral in shape and are usually formed together with magnetite. In some samples, large crystals of pyrite show evidence of crushing resembling the cataclastic fabric. Other sulfide minerals such as pyrrhotite and chalcopyrite are present as anhedral crystals and sometimes have magnetite patches. The mineralography of the Galali ore deposit is similar to the Baba-Ali ore deposit. Magnetite as the main ore mineral occurs in one generation including massively anhedral crystals. There is also one generation of pyrite which mainly includes euhedral and large crystals (up to 2 cm in diameter). Goethite, limonite, and hematite have been formed as a result of supergene processes. Discussion Paragenetic sequence The paragenetic sequences of the studied ore deposits are similar (Fig. 8). Field, mineralographic, and paragenetic similarities of the studied ore deposits may indicate their probably similar genesis. The difference is because of the size of the ore deposits; the Baba Ali is the largest one and has the most diverse mineral assemblage. Sulfur isotopes The δ34Svalues of the pyrite from the Baba-Ali and Galali iron ore deposits are presented in Table 2. Except for two samples (BS-304, BS-303), the δ34S values have a limited range and are similar. The δ34S values of the Baba-Ali and Galali ore deposits range from +6.8 to +13.3‰, and +6.1 to +7.3‰, respectively. According to Ohmoto and Rye (1979), the main composition of sulfur in ore-forming fluids is often in the form of H2S. Therefore, to measure the Δ34SH2S of the fluid in equilibrium with the pyrite, the formula proposed by Ohmoto and Rye (1979) was used. The calculated δ34SH2S values of the ore-forming fluid (T=375 ˚C) in the studied deposits (Baba-Ali and Galali) range from+7.8 to +14.3‰and +7.1 to +8.3‰, respectively. The T=375 ˚C is considered based on the average temperature values of the Baba-Ali formation (Zamanian et al., 2007; Sarjoughian et al., 2020). In the same way, similar temperature conditions (T=375 ˚C) have been assumed for the Galali ore deposit. The sulfur isotopic values compared to the isotopic ranges in the geological systems (Rollinson, 1993) are shown in Fig. 9. Based on the petrographic evidence and the paragenesis sequence, the pyrites formed in the retrograde stage and at a T

Paleoelevation and paleoclimate reconstructions based on carbonate proxies rely on the preservation of syndepositional surface water isotopic signatures. This study investigates the reliability of fine-grained carbonates (micrites) in recording well-preserved isotopic composition. Utilizing a suite of research tools, including petrography, X-ray diffraction mineralogy, stable isotopes, clumped isotope temperatures, isotope mixing, solid-state bond reordering modeling, and trace element concentrations, we examine the diagenetic history of late Oligocene micritic carbonates from the Nima Basin in central Tibet. Our findings reveal that the lacustrine carbonates at deposition were micritic and calcite-dominated. However, they underwent partial dolomitization through cryptic recrystallization during shallow burial at temperatures of ∼34–40 °C, likely influenced by groundwaters with abundant Mg2+ and trace elements distinct from surface waters. Subsequently, during the further burial at temperatures of ∼120–130 °C, vein calcites precipitated from thermal fluids. Concurrently, the calcite component of fluid-adjacent micrites underwent open-system recrystallization, recording temperatures of 100–130 °C, while the associated dolomite component remained minimally altered due to its higher resistance to dissolution. In contrast, micritic calcites unaffected by thermal fluids experienced partial solid-state bond reordering that elevated clumped isotope temperatures to 50–60 °C. This study underscores the complex diagenetic histories that micrites can undergo, emphasizing the need for caution when interpreting carbonate stable oxygen isotopes in paleoclimate and paleoelevation studies, especially in tectonically active regions. Finally, our analysis infers that the stable oxygen isotopic values of the calcitic soil carbonates in the Nima Basin are well-preserved and reflect moderately high paleoelevations of ∼3.3 km at 26–25 Ma. This suggests a >1 km elevation gain during the Neogene, highlighting subsurface geodynamic processes as additional drivers of surface uplift in central Tibet. [ABSTRACT FROM AUTHOR]

Carbonate rocks are susceptible to diagenesis, and the correct identification of diagenetic features and stages are primary tasks in paleoelevation and paleoclimate studies using carbonate proxies. In this study, we apply three key parameters that include stable isotopes, clumped isotope temperatures, and U-Pb ages to identify different diagenetic stages, i.e., eogenesis, mesogenesis, and telogenesis. We then adopt these criteria to explore the diagenetic history of the middle–late Eocene lacustrine carbonates in the Gerze area of western central Tibet, which have yielded contrasting interpretations of diagenetic stages and paleoelevation estimates. Petrographic observations and electron microprobe element mapping permitted the identification of different diagenetic features. The Gerze carbonates (4GZ section) contain distinct phases of micrite and vein/vug-fill calcite (sparite) with different stable oxygen isotope values of −4 to −6 ‰ and −10 to −14 ‰ (VPDB), respectively. The micrites are dominantly dolomite in composition and yield clumped isotope temperatures of 40–50 °C, which are interpreted to be the result of dolomitization during shallow burial. In contrast, the vein/vug-fill calcites exhibit lower clumped isotope temperatures of 20–30 °C and U-Pb ages of 3.0–3.3 Ma, indicating a late-stage telogenetic origin after exhumation to near the Earth's surface. Our documentation of different carbonate diagenetic stages sheds light on existing paleoelevation interpretations. We conclude that existing evidence remains inconclusive as to the paleoelevation of the Gerze area basin floors during the middle–late Eocene. [ABSTRACT FROM AUTHOR]

Feldspar alteration is among the most important processes in clastic rocks during diagenesis, but uncertainty remains about the factors that control feldspar diagenesis under subsurface conditions. Hence, the Upper Triassic Xujiahe formation of the Western Sichuan Basin were examined by an integrated petrographic, mineralogical and geochemical approach to unravel the causes and effects of feldspar diagenesis, with implication for mass transfer and openness of the geochemical system. The sandstones at various depths demonstrate three distinct, separate diagenetic behaviors of detrital feldspar within a single formation including (1) the complete dissolution of both plagioclase and K-feldspar in the upper member; (2) conservation of abundant detrital feldspar grains with minor albitization or overgrowths within the lower member of depths greater than 5 km; and (3) complete disappearance of K-feldspar within the uppermost horizons of the lower member, while plagioclase have survived in significant amounts. The exceptional disappearance of K-feldspar is the result of selective dissolution of K-feldspar during burial, accompanied by illite cementation and substantial K transfer at a scale of tens of meters. It is apparent that the clay diagenesis in the overlying mudstones, rather than porewater chemistry, is the major control of the reactivity of K-feldspar in adjacent deeply buried sandstones. [ABSTRACT FROM AUTHOR]

The origin and depositional setting of dolomites remain a complex and debated topic. In the Indus Basin Pakistan, the dolomites in Jutana Formation form a thick sequence within the Cambrian stratigraphy. The current study investigates the detailed depositional setting as well as the mineralogical composition of dolomites in the Jutana Formation to provide insight into their origin. The study focuses on integrating the microfacies and Scanning Electron Microscopy (SEM) with X-ray diffraction (XRD) data along with Wireline logs of Jutana Formation in Khewra Gorge, Eastern Salt Range. Based on field and petrographic observations, four microfacies were identified including (a) siliciclastic algal laminated dolomitic breccia (MJD-1), (b) burrowed sandy ferroan dolomicrite (MJD-2), (c) in-situ medium-coarse grained dolomicrite-dolosparite (MJD-3), (d) fine grained micaceous dolosparite (MJD-4). The microfacies analysis reveals that the deposition of the Jutana Formation is primary on carbonate platform in peritidal environments, ranging from supratidal to subtidal. Digenesis has obliterated most of the primary depositional features, making the interpretation of the original depositional setting challenging. The XRD analysis suggests that these dolomites are nearly stoichiometric and less ordered, indicating an early diagenetic setting, further supported by the presence of anhydrite seen under the SEM. The original depositional setting on the carbonate platform is also supported by cross plot graph wireline logs. [ABSTRACT FROM AUTHOR]

This study takes the tight sandstone of the lower sub‐member of the first member of the Eocene Shahejie Formation (Es1x) in the Suning area, Raoyang Sag, Bohai Bay Basin. Furthermore, it determines the rock type of the middle‐deep tight sandstone through lithologic profiling, core observation and log data analysis. The genetic control factors of tight sandstone in the study area are analysed using conventional thin section, pore‐casted thin section and scanning electron microscope, and the characteristics and genetic control factors of tight sandstone reservoirs are summarized. The research results show that the tight sandstones in this area are primarily feldspathic sandstone and feldspathic lithic sandstone, with high quartz contents, around 61.50%. The average porosity of the reservoir in the study area is 4.69%, and the average permeability is 2.92 mD, which are characteristics of low‐porosity and low‐permeability reservoirs. Through research, it has been found that the distribution of sedimentary facies and diagenesis in the study area control the development and distribution of 'sweet spots'. Both compaction and cementation reduce the physical properties of the reservoir, while dissolution can increase porosity, thereby increasing the physical properties of the reservoir; dissolution resulted in an increase of approximately 3.57%–3.69% in the porosity of the tight reservoir in the study area, with an average porosity increase of 3.63%, and is the main controlling factor for the development of 'sweet spots' in the reservoir. The results provide an important basis for guiding the exploration and development of tight sandstone oil and gas in the lower sub‐member of the first member of the Eocene Shahejie Formation (Es1x)in the Suning area. [ABSTRACT FROM AUTHOR]

The main purpose of the study is to identify the thin-bed reservoirs of the Eastern Folded Belt (Sylhet and Bandarban) and characterize them with diligence. A detailed qualitative and quantitative analysis has been carried out. It is based on thin-section petrographic analyses of sandstone samples. These samples are from the reservoir horizons of the Sylhet region and Bandarban region fields. The purpose of this analysis is to characterize the textural and mineralogical properties. Additionally, it aims to evaluate the post-depositional diagenetic changes. The results obtained from the field and laboratory analysis are studied extensively to characterize the thin-bed reservoirs. Samples from the Sylhet area are medium-coarse-grained, fairly sorted, tight packing, submature-mature sublithic characteristics. Contrarily, samples from the Bandarban region are mature-submature sublithic arenites, which are fine-medium-grained, moderately well-sorted, and moderately loosely packed. Despite the similarity of the detrital elements (quartz, feldspar, lithic grains, mica, etc.) in the two areas, silica cementation is more frequent in Sylhet region samples than early carbonate cementation in Bandarban region samples. Comparatively speaking, the sediments in the Sylhet region are more compact than those in the Bandarban region. The most important outcome of this study is that the thin bed of the unconventional reservoir and the conventional reservoir are in close proximity. The Thin-bed reservoir units of the Eastern Folded Belt are found to be medium to fine-grained and well sorted, with frequent alteration of sand-shale with the prevalence of parallel bedded sandstone. Average porosity is 4% to 12%, and pore spaces are interconnected. So, the permeability rate is good enough to flow the hydrocarbon through these pore spaces. Most importantly, the thin bed and tight reservoir (average porosity 4% to 12%, but pore spaces are not interconnected) are not more prominent than 1 meter or 2 meters. Subsequently, though the vertical thickness is not so high, they keep up a momentous tirelessness of horizontal progression. On the contrary, at whatever point it comes to a conventional reservoir, the vertical thickness is higher than that of the unconventional reservoir. But their lateral persistence is not as long as unconventional ones. [ABSTRACT FROM AUTHOR]

The Sirban Limestone Formation (SLFm) dolostones cropping out in the Riasi Allochthon (NW Himalaya, Jammu, India) show a range of δ13C (−1.08 to 0.73‰) and δ18O (−11.50 to −7.82‰) values and the mean values of 0.15‰ and −9.12‰ Pee Dee Belemnite (PDB), respectively. The δ13C values indicate that these dolostones were deposited during Neoproterozoic, and the δ18O values also are very close to the average Mesoproterozoic carbonate values obtained from the coeval carbonates. The characteristic δ13C values have the potential to provide an age constraint for the SLFm, and the mean δ18O value is comparable to the 'best preserved' δ18O mean value (−7.5 ± 2‰) reported for most of the Meso-Neoproterozoic to Early Cambrian carbonates. δ13C vs. δ18O plot for the SLFm suggests normal marine origin with late-stage cementation. In the present study, stable isotope geochemistry of the SLFm dolostones is attempted. Preliminary data on the major-and-minor elemental composition of SLFm has also been presented. In addition, several petrographic facies identified in the SLFm have also been documented here. Diagenesis characterisation of these facies show dolomitization represents an important phase in the early diagenesis process. The subsequent diagenetic stages range from early seafloor cementation to late-stage tectonic stylolitisation, which have obliterated the original textures to dominant diagenetic textures, also reflected in the δ13C and δ18O values. Similar isotope profiles can be potentially significant for the chemostratigraphic correlation of different sections within the Riasi Allochthon and coeval equivalents regionally and globally. [ABSTRACT FROM AUTHOR]

Field and petrographic studies of the Qishn Formation provide insights in to sequence stratigraphic and reservoir attributes of the formation. The reservoir properties are controlled by complex interaction between depositional textures and diagenetic products. The Barremian-Aptian Qishn Formation was deposited between Precambrian basement rocks and marl-dominated Albian Kharfort Formation. The Qishn Formation consists of lower sandstone (Shabon Member), middle unit dominated by lime mudstone (Hinna Member), and upper bioclastic limestone with dolostone interbeds (Hasheer Member). The formation defines a transgressive-regressive sequence with maximum flooding surface (MFS) at the top of the Hinna Member. The petrographic and diagenetic analyses indicate that Shabon and Hasheer members constitute good reservoirs. The Shabon Member is dominated by friable medium- to coarse-grained arkose to lithic arenite with porosity as high as 20%. Despite a burial depth of ~ 5 km, the sandstone maintains most of its intergranular pores. The diagenetic features include early calcite cement followed by burial compaction. However, since most of the pores were already filled by calcite cement, volumetric reduction due to compaction was minimal. Post-compaction dissolution of the early calcite cement resulted in restoration of the intergranular pores. The Hasheer Member consists of extensively cemented bioclastic packstone to rudstone with porosity < 6% and sucrosic dolomite with intercrystalline and vuggy pores reaching up to 15%. The mud-dominated Hinna Member can be considered as potential cap rock for any fluids within the Shabon Member, whereas the marls of the Kharfot Formation constitute potential caprock for the preservation of fluids in the Hasheer Member. [ABSTRACT FROM AUTHOR]

The Early Cretaceous Yamama Formation of X oilfield, deposited in a semi-restricted setting, holds considerable oil reserves. However, the reservoir is extremely heterogeneous and is poorly studied. Integrating outcrops, cores, cast thin sections, regular or special core analysis, wireline logging data from six wells, and seismic data, this study provides an improved understanding of reservoir petrophysical characteristics and geological controlling factors including sedimentation, diagenesis, and sequence. The results showed that eight lithologies are developed in the Yamama Formation, of which packstone and wackstone are dominant. The physical properties span a wide range, with porosity mainly distributed between 10% and 25%, and the permeability mainly distributed between 0.1 mD and 1 mD. Nine types of pores are developed, with moldic pores, micropores, and skeletal pores being the most developed. The reservoir has six types of microstructures, of which the poorly sorted with mega-throat represent the best reservoir. The Yamama Formation was mainly deposited in a lagoon, along with five other facies, such as supratidal flat, patchy reef, back shoal, shoal, and open shelf. Six types of diageneses are developed, with dissolution during the penecontemporaneous stage being the most beneficial to the reservoir and cementation being the most destructive. Three sequences were recognized in the Yamama Formation. It concluded that the hydrodynamics in semi-restricted depositional setting is weak overall and does not have the potential to develop large-scale high-quality reservoirs. A wide range of bioclasts were selectively dissolved to form a large number of secondary pores. Sediments rich in Algae, Bacinella, and peloids tend to form moldic pores, skeletal pores, and intergranular pores, respectively, which are prone to be favorable reservoirs. Controlled by the coupling of sedimentation and diagenesis driven by sequence, the reservoir is extremely heterogenous. [ABSTRACT FROM AUTHOR]

The upper member of the Lower Ganchaigou Formation (UMoLGF) is a highpotential hydrocarbon exploration area in the North margin of the Qaidam Basin (NMoQB). It represents a typical low-permeability sandstone reservoir. The current understanding of reservoir characteristics of the UMoLGF is poor, and the main controlling factors of high-quality reservoir development remaining unclear. This study, for the first time, integrated various factors to investigate the formation mechanism of high-quality reservoirs in the UMoLGF's low-permeability sandstone reservoirs. Results show three provenance systems developed in the study area: northwest, northeast, and east. The northwestern and northeastern areas share similar reservoir characteristics. The rock type is predominantly feldspar, with relatively poor particle sorting and rounding. Pore types are dominated by secondary dissolution pores. However, the northwestern area has more developed fractures and poorer pore structures than the northeastern. Meanwhile, in the eastern area, the rock fragment content was high, the rock type was mainly litharentie and lithic arkose, particles were well-sorted and well-rounded. Residual intergranular pores, with good structures, dominated the pore type. The UMoLGF has entered the eo-diagenesis B stage with minor progression into the meso-diagenesis A stage. Based on quantitive calculations, this study established porosity evolution models for the different study areas. The initial porosities in the northwestern, northeastern, and eastern areas were 30.8%, 30.4%, and 34.8%, respectively. Compaction and cementation are the major factors contributing to porosity reduction in the three areas, with the most significant impact in the northwestern area. Dissolution significantly improved the reservoir properties in the northwestern area, with little effect on the northeastern and eastern areas. The formation of high-quality reservoir in the UMoLGF was affected by provenance, diagenesis, and fractures, with the primary controlling factors varying by area. In the northwestern area, the formation of high-quality reservoirs benefited from strong dissolution and well-developed fractures. In the northeastern area, the high-quality reservoir was relied upon favorable provenance and dissolution. In the eastern area, provenance provided an excellent material basis for developing high-quality reservoirs, with dissolution and chlorite cementation further improving reservoir properties. This study provides a theoretical foundation for further exploration and development of UMoLGF and offers insights for exploring and developing similar low-permeability sandstone reservoirs. [ABSTRACT FROM AUTHOR]

Growing concern over the combustion cost and environment has made road engineers and scientists to explore the possible use of locally available materials for the construction of roads. The present study evaluated the strength and durability characteristics of five sites having locally available silty soils using lime and cement–sand stabilization technique. The test results showed that the cement–sand stabilization technique using 6% cement and 5% local sand resulted in higher strength and durability as compared to lime stabilization. There is also a significant increase in the value of the soaked California bearing ratio (CBR). As unconfined compressive strength (UCS) attained the threshold strength as prescribed by IRC SP 72 2015 for the granular sub-base (GSB) layer, by the use of sand cement stabilization, this technique of stabilization for local silty soils could be used for GSB for low volume road (LVR) construction. As observed from microstructural results which were performed by analysing SEM images, sand cement stabilisation leads to CSH gel and agglomerate formation thereby increasing strength and durability properties. The cost analysis for the replaced stabilized GSB layer showed that using sand–cement stabilization, the estimated cost can be reduced by 56% of the total cost as compared to the conventional method. [ABSTRACT FROM AUTHOR]

In the BM-C-33 area, divided into the Raia Manta and Raia Pintada development areas, reservoirs are arranged into three structural highs: Gávea, Seat, and Pão de Açúcar. These reservoirs consist of pre-salt limestones deposited on volcanic sequences and underwent complex diagenetic evolution. Successive post-depositional processes, including silicification, affected original mineral assemblage, modified pore textures, and caused intense fracturing. Based on borehole image logs (BHI), wireline data from four wells, and 2D and 3D seismic data, this study details natural fracture acoustic and resistivity properties. It also discusses the relationship of faults, fractures, and vugs with diagenetic and tectonic processes. The authors used the data to divide the pre-salt section (Cabiúnas and Macabu formations) into three informal stratigraphic units. The analysis of interpreted fractures within these units suggests that major fracturing occurred due to regional tectonic stress, with local aspects like structural positioning interfering. The results of the fracture analysis imply a direct relationship between fracturing and silicification. Additionally, fracture density, vug volume distribution, and the presence of dissolution features like enlarged fractures limited to specific units imply stratigraphic control on fluid percolation. Finally, the study examines structural particularities in BM-C-33 area that potentially impacted intensity and extension of diagenetic alterations. [ABSTRACT FROM AUTHOR]

The article discusses the development of a proposed mapping system called Process-Landform-Material (PLM) for engineering geology field mapping. The PLM system aims to provide consistent and objective information for mapping purposes related to Earth-related hazards, geotechnical materials, and ground responses. It incorporates modifications to a previously published system and includes categories for surficial deposits, underlying materials, and various process and landform types. The PLM system is flexible and can be expanded to accommodate specific user needs. [Extracted from the article]

The active tectonics of northern Central Mongolia is studied between two largest W–E-trending left lateral fault zones: the Khangai Fault and the Tunka–Mondy. These strike-slip zones are part of a single ensemble of active faults in the Mongol–Baikal region, formed under conditions of maximum northeastern compression and maximum northwestern extension. Their ENE-trending Erzin–Agardag and Tsetserleg faults with a dominant sinistral component extend between these zones. A series of the N-trending graben basins (Busiyngol, Darkhat, and Khubsugul) are located between the eastern end of the Erzin–Agardag strike-slip fault and the western part of the Tunka–Mondy strike-slip zone. The basins form a sinistral deformation zone, which is kinematically similar with the strike-slip faults, which follow the latter. In contrast to the largest boundary strike-slip faults, this structural paragenesis formed under conditions of N–S-trending relative compression and N–S-trending extension. A change in the orientation of the axes of the principal normal stress may be caused by the rotation of the block between the boundary faults. The area of graben-shaped basins is located above the top of a vast volume of low-velocity mantle, which we have identified as the Khangai plume. The lithospheric mantle above this rise is reduced; the remaining part of the lithosphere is heated and softened. The large active strike-slip faults are located above areas of subsidence of the low-velocity top of the mantle. Our trenching of the active faults showed that strong earthquakes repeated in the area of graben-shaped basins more often than in the large strike-slip zones, but they were characterized by lower magnitudes. [ABSTRACT FROM AUTHOR]

An integrated study of several methods to characterize a carbonate reservoir provides a comprehensive result on carbonate facies and diagenesis. Therefore, a study on the Tertiary carbonate reservoir at the East Arm of Sulawesi area, Banggai - Sula Basin, is intended to determine the Salodik Group carbonate reservoir facies and diagenesis. Moreover, the purpose of this study is to determine the intensity and implication of syn-depositional or post-depositional processes, and to provide the reservoir final properties values, such as porosity and permeability to classify the reservoir quality. The methods of the study are based on carbonate fieldwork mapping to obtain samples on distributed traverses. Further analyses are the laboratory works to determine facies and diagenesis features on a more detailed scale. This study shows several facies, dominantly classified into reefal packstone, planktonic foraminifera packstone-wackestone, large foram packstone-mudstone, skeletal packstone-wackestone, planktonic-large foraminifera packstone-wackestone, and large foraminifera-red algae packstone. The dominant diagenesis processes are cementation and dissolution. Moreover, meteoric vadose and meteoric phreatic are predominantly the main diagenesis environment of Salodik Group formations. Furthermore, the dominant diagenesis stage is Eogenetic. The post-depositional process or the diagenetic processes, provides a more significant impact on carbonate reservoir properties than the syn-depositional process as shown on lithofacies texture. However, in general, from the younger to the oldest formation of Salodik Group, this shows a decreasing trend of reservoir properties due to the dominant cementation process in the oldest formation. Overall, the reservoir quality referring to porosity value is classified as negligible to excellent. While, based on permeability data, it is classified as the tight to good reservoir. [ABSTRACT FROM AUTHOR]

The study focused on the influence of geological genesis and degree of crystallinity on the quantification of mineral phases and amorphous content in Cuban clays. Two clay deposits with different geological genesis were taken and the samples were characterized using X-ray diffraction and techniques for analyzing the clay fraction. Dominant paragenesis were established for each deposit, dominated by kaolinite, and useful relationships were found between structural and particle size differences with geological genesis, which can affect proper quantification. It was determined that the level of weathering conditions the degree of crystallinity, which in turn has a strong relationship with factors that affect proper quantification. Finally, the fundamental elements for formulating a comprehensive methodology for the proper characterization and quantification of clay phases were established. [ABSTRACT FROM AUTHOR]

Pressure solution processes taking place during diagenesis deeply modify the hydraulic properties of carbonates, affecting their mechanical layering and hence the dimension, distribution, and connectivity of high-angle fractures. The formation of stylolites is controlled by the texture of the host rock and therefore by the depositional environment and the diagenetic processes that involve it. This study reports the results of a multidisciplinary study carried out on a Jurassic–Cretaceous carbonate platform in southern Italy. The goal is to unravel the control exerted by single carbonate textures and specific diagenetic processes on the formation of bed-parallel stylolites. Microfacies analyses of thin sections are aimed at obtaining information regarding the composition and texture of the carbonates. Petrographic observations coupled with CL analyses are key to deciphering their diagenetic history. Results are consistent with carbonates originally deposited in a shallow-water realm in which carbonate mud is occasionally abundant. In this environment, early cementation inhibits their chemical compaction. In grain-supported facies, pressure solution is only localized at the grain contacts. During shallow burial diagenesis, precipitation of blocky calcite predates the formation of bed-parallel stylolites in the grain-supported facies. Contrarily, mud-supported facies favor chemical compaction, which results in stylolites showing a good lateral extension and thick sediment infill. A classification of different types of stylolite morphology is attempted in relation to facies texture. In detail, rougher morphology (sharp-peak) characterizes the stylolites nucleated in grain-supported facies, while smoother morphology (rectangular to wave-like) is observed in stylolites on mud-supported facies. Application of this knowledge can be helpful in constraining the diagenetic history of carbonate rocks cored from depth, and therefore predict the fracture stratigraphy properties of carbonates buried at depth. [ABSTRACT FROM AUTHOR]

Akaganeite and jarosite were detected in two mudstone drill samples from Vera Rubin ridge (VRR), Gale crater by Chemistry & Mineralogy X‐Ray Diffraction (CheMin). The co‐occurrence of these two minerals is quite rare in both terrestrial and Martian aqueous environments. In order to confine the chemical conditions of paragenetic akaganeite and jarosite, and provide insight into late‐stage diagenetic alterations at VRR, we synthesized akaganeite and jarosite with varying SO42− concentrations and initial pH levels. Synthetic samples were characterized using Field Emission Scanning Electron Microscopy, X‐ray powder diffraction and Raman spectroscopy. Our study reveals that akaganeite and jarosite exist in equilibrium in the solution with 0.011–0.028 M SO42− with respect to 0.6 M Cl− and an initial pH of 1.3–2.2. In combination with the CheMin detection results, the chemistry and pH values of the fluids at VRR can be further constrained. Considering the absence of goethite and the relative higher portion of akaganeite than jarosite in the drill samples, the pH values should be 1.4–2 and the S/Cl molar ratio should be within the range of 0.018–0.042. Based on our laboratory results, we hypothesize that the presence of akaganeite and jarosite at VRR represents an individual episode of acidic groundwater activity. During the late‐stage diagenetic process at VRR, upwelled acidic groundwater dissolved the local chlorides to form the Cl−‐dominated fluids. Subsequent evaporation further concentrated the acid saline fluids and therefore resulted in an extremely acidic environment (1.4 ≤ pH＜2 with S/Cl molar ratio of 0.018–0.042), which produced akaganeite and jarosite. Plain Language Summary: Akaganeite and jarosite have been detected in drill samples of Gale crater. But their co‐occurrence has only been found in two drill samples Stoer and Rock Hall at VRR. The formation conditions of akaganeite and jarosite at VRR remain unknown. To solve this issue, we conducted synthesis experiments under different SO42− concentrations and initial pH levels. We found that akaganeite and jarosite coprecipitate in the solution with 0.011–0.028 M SO42− with respect to 0.6 M Cl− and an initial pH of 1.3–2.2. In conjunction with the CheMin data and our experimental results, the chemistry and pH values of the fluids at VRR can be further constrained. The formation of akaganeite and jarosite at VRR likely occurred in a Cl−‐dominating and SO42−‐bearing solution (S/Cl molar ratio of 0.018–0.042) under extremely acidic conditions (pH range of 1.4–2). We hypothesize that the coprecipitation of akaganeite and jarosite represents an individual episode of acidic groundwater activity at VRR. The upwelling acidic groundwater possibly dissolved the local chlorides to form a Cl‐dominated fluid with trace amounts of SO42−. Evaporation further concentrated the fluid to extreme acidic and thus formed akaganeite and jarosite. Key Points: Akaganeite and jarosite at Vera Rubin ridge (VRR) formed in a Cl‐dominated solution with trace amounts of SO42− under extremely acidic conditionThe formation of akaganeite and jarosite at VRR represents an individual episode of acidic groundwater activityThe abundant Cl in the fluids is possibly of local origin while the extreme acidity is accomplished by evaporation [ABSTRACT FROM AUTHOR]

Loose desert sand poses a constraint for geotechnical engineers to construct tunnels without a lining, which is typically steel, concrete, or slurry shield. Many desert mammals, however, can construct tunnels in loose sand, and the tunnels can remain stable over extended periods of time in harsh desert environments. This study presents the state of knowledge on mammal burrows in loose desert sand and provides insights from a geotechnical engineering perspective with the aim of understanding how desert mammals tackle a geotechnical challenge. The study presents these desert mammals as biogeotechnical engineers and explains their burrow stability using three fundamental soil mechanics principles: (i) unsaturated soil mechanics, (ii) compaction, and (iii) soil cementation. Damara mole-rats, kangaroo rats, pocket gophers, and round-tailed ground squirrels are presented as the desert biogeotechnical engineers. Proof-of-concept experiments conducted with a poorly graded fine sand demonstrate the effects of the fundamental soil mechanics principles used by the animals on soil strength. A limit equilibrium tunnel stability analysis performed using sand from a kangaroo rat habitat in the Sonoran Desert also demonstrated the link between tunnel stability of desert mammals and the three geotechnical principles. [ABSTRACT FROM AUTHOR]

Alluvial glutenite reservoirs have obviously stronger heterogeneous and more complex control factors than sandstone reservoirs. Taking the Binxian Uplift area in the Boahi Bay Basin as an example, the aim of this study is to clarify the characteristics and control factors of the alluvial glutenite reservoir quality and the influence of reservoir properties on hydrocarbon accumulation. Pore types in the study area mainly include residual intergranular pores, intergranular dissolved pores, intragranular dissolved pores, and mold pores. The residual intergranular pores and intergranular dissolved pores are the main pore types. Most samples have porosity greater than 15% and permeability is mainly concentrated between 50 mD and 500 mD. It is shown that lithology type, microfacies, and diagenesis have significant impact on the reservoir quality. The reservoir qualities of very fine sandstone and fine sandstone are better than those of conglomerate and gravel-bearing sandstone. Instead of grain size, sorting affects the alluvial glutenite reservoir quality significantly. Oil-bearing samples commonly have sorting coefficient less than 2 while non-oil-bearing samples have sorting coefficient larger than 2. There are significant differences in reservoir physical properties of different sedimentary microfacies. The stream flow in mid-alluvial fan (SFMA) and braided channels outside alluvial fans (BCOA) have relatively weaker compaction and better reservoir quality than the overflow sand body (OFSB) and debris-flow in proximal alluvial fan (DFPA). Calcite cementation, the main cement in the study area, commonly developed at the base of SFMA and BCOA and near the sandstone-mudrock contacts. The source of calcium carbonate for calcite cement mainly came from around mudstone. High calcite cement content commonly results in low porosity and permeability. Individual glutenite thickness is also an important influencing factor on reservoir quality. Reservoirs with large thickness (>4 m) have high porosity and permeability. Dissolution occurred in the reservoir, forming secondary dissolution pores and improving reservoir quality. The dissolution fluid for formation of secondary pores is mainly meteoric waters instead of organic acid. The reservoir property has an important influence on hydrocarbon accumulation. The lower limit of physical properties of an effective reservoir is a porosity of 27% and permeability of 225 mD. The findings of this study can be utilized to predict the reservoir quality of alluvial glutenite reservoirs effectively in the Bohai Bay Basin and other similar basins. [ABSTRACT FROM AUTHOR]

The Benxi-Taiyuan Formation in the southern region of the Ordos Basin represents a typical mixed sedimentary system, which has witnessed recent breakthroughs in the exploration of tight sandstone gas within the Benxi Formation. However, the development patterns of reservoirs in this mixed sedimentary area remain unclear, influenced by the sedimentary model and the distribution scale of sedimentary sandstone bodies. This study investigates the paleogeomorphology, sedimentary model, sandstone body type, petrological characteristics, and pore structure of the Benxi Formation. Field profiles, drilling core observations, microscopic section analysis, scanning electron microscopy (SEM), high-pressure mercury injection (HPMI), and physical property analysis are employed. The findings indicate that the paleogeomorphology before the deposition of the Benxi Formation exhibits a west-to-east high-to-low trend, with a steeper gradient in the north and a gentler gradient in the south. This paleogeomorphology influences paleocurrent direction and the distribution of sandstone bodies. The sedimentary system, consisting of clastic tidal flats, mixed tidal flats, and mixed lagoons, develops from west to east on a plane, with the mixed lagoon being more prominent in the northeast of the study area. The sedimentary model determines the initial composition and structure of the reservoir, as well as subsequent diagenesis processes. Diagenetic reconstruction plays a crucial role in assessing the development degree of reservoir. Compaction and cementation result in the densification of the Benxi Formation sandstone. Dissolution and preservation of primary pores are critical for high-quality reservoir development. Among the various depositional models, the sand flat facies in the clastic tidal flat area of the Ben 2 Member and the tidal channel facies in the mixed tidal flat areas of the Ben 1 and Ben 2 members exhibit a high degree of pore development within the sandstone body, making them favorable locations for high-quality reservoir development. In summary, this study highlights the importance of paleogeomorphology, sedimentary models, and diagenetic reconstruction in understanding the controlling factors for efficient reservoir development in the mixed sedimentary system of the Benxi-Taiyuan Formation. Knowledge of these factors aids in the exploration of high-quality reservoirs within concealed and dispersed sandstone formations in the Ordos Basin. [ABSTRACT FROM AUTHOR]

This study provides for the first time details of the mineralogy, petrography and mineral paragenetic relationships of manganese ores of the Avontuur deposit, a prominent northern outlier of the Kalahari Manganese Field in the Northern Cape Province of South Africa. Using a combination of light and electron microscopy and X-ray powder diffractometry on an extensive suite of exploration drill core samples, it is shown that the manganese ores comprise an exceptionally fine-grained assemblage of Mn2+-silicates (friedelite, tephroite, gageite), Mn2+/Mn3+-oxides (jacobsite, hausmannite) and Mn2+-carbonates (rhodochrosite, kutnahorite, Mn-dolomite and Mn-calcite). This mineral assemblage is a product of diagenesis and very low-grade regional metamorphism. Locally, this assemblage is overprinted by contact metamorphism or supergene alteration. Despite close geochemical and textural similarities, the manganese ores of the Avontuur deposit are surprisingly different in their mineralogy compared to the carbonate- and braunite-dominated mangano-lutites of the main Kalahari deposit. Distinctly higher concentrations of both SiO2 and Fe2O3 in the manganolutites of the Avontuur deposit as compared to the main Kalahari Deposit provide the reason for the markedly different mineralogy. Such marked differences in bulk chemistry are tentatively attributed to systematic lateral variations in the physicochemical conditions of mineral precipitation during the deposition of the Hotazel Formation. [ABSTRACT FROM AUTHOR]

Strong winds, particularly in the absence of disaster-resistant designs, significantly impact the stability of greenhouse foundations and eventually lead to structural damage and potential harm to crops. As a countermeasure, rebar stakes are commonly used to reinforce the foundations of non-disaster-resistant greenhouses. This study evaluates the pull-out resistance (Rpull-out) of rebar stakes considering various factors like soil compaction, embedded length, installation duration and angle, and changes in soil water content against uplift pressure by strong winds. A combination of field (i.e., the cone penetration test and rebar stake pull-out test) and laboratory (i.e., the compaction test, soil compaction meter test, and soil box test) tests are performed for the assessment of Rpull-out. The results indicate that Rpull-out increases with higher soil compaction, greater embedded length, longer installation duration, and an inclined installation angle. The soil compaction exerts the most significant impact; 90% to 100% of the soil compaction rate has approximately 10 folds higher Rpull-out than the 60–70% compaction rate. If the embedded length is increased from 20 cm to 40 cm, there is a two-fold increase in the average of Rpull-out. Inclined installation of rebar stakes increases Rpull-out by 250% to 350% compared to vertical installation, and rebar stakes installed prior to the uplift event have 1.5 to 6.4 fold increases in Rpull-out than those with instant installation. Additionally, we observed variations in the surface soil moisture due to climatic changes introducing variability in Rpull-out. These findings lead to the proposition of efficient rebar stake installation methods, contributing to the enhanced stability of a greenhouse. [ABSTRACT FROM AUTHOR]

The origin of highly permeable flow paths in carbonate-siliciclastic rocks, such as large-aperture fractures in aquifers in the Eastern Bohemian Cretaceous Basin (EBCB), is poorly understood. The karst potential was assessed from the rock carbonate content and the degree of disintegration after leaching in HCl. Surprisingly, dissolution of calcite in EBCB usually did not lead to rock disintegration until calcite > 78%. Instead, porosity increased significantly. High-porosity rock is held together by microns-thick secondary silica cement with a foam-like structure and considerable tensile strength. Three types of conduits occur in the EBCB: (i) bedding-parallel conduits associated with calcite-rich layers, (ii) subvertical fracture swarm conduits that develop on damaged zones of fracture swarms, and (iii) conduits formed by dissolution of calcite veins by groundwater flow. These are ghost-rock karst features where calcite is leached from the rock in the first phase and the residue is washed out by conduits under steep hydraulic gradients in the second phase. Very similar features have been described in Minnesota and Wisconsin, USA. Research has shown that fractures with sharp-edged walls that give the impression of an extensional tectonics origin may actually be ghost-rock karst features in which dissolution and piping have played an important role in their enlargement. [ABSTRACT FROM AUTHOR]

Enhanced continental phosphorus input into the ocean has been suggested as a potential trigger for the transient oxygenation events during the mid‐Proterozoic; however, the response of phosphorus cycling to these marine oxygenations remains unclear. Here, we report the changes in phosphorus cycling associated with a ∼1.7 Ga transient oxygenation. Abundant authigenic aluminum phosphate–sulfate mineral svanbergite (SrAl3(PO4) (SO4) (OH)6; 8.02 ± 4.92 wt%) is identified within the ∼1.7 Ga Yunmengshan ironstones from the Xiong'er Basin, North China and other contemporaneous basins. This observation provides new evidence to support the suggestion that early diagenetic aluminum phosphate‐sulfate minerals could have represented a critical sink of marine phosphorus during the Proterozoic. We suggest that atmospheric oxygenation and concomitant changes in porewater redox chemistry may have enhanced the formation of early diagenetic phosphates, leading to a negative feedback on the oceanic phosphorus reservoir and atmospheric oxygen levels. Plain Language Summary: It becomes increasingly clear that multiple transient oxygenation events likely punctuated the low background oxygen world during the mid‐Proterozoic. This may imply that a negative feedback could have inhibited a secular rise in atmospheric oxygen, though the deoxygenation mechanisms remain unclear. Phosphorus (P) availability regulated primary production and therefore controlled the atmospheric oxygen levels during this time, and oxygenation would in turn affect phosphorus cycling. Here we investigate the P cycling during a ca. 1.7 Ga transient oxygenation using mineralogical and geochemical methods. The results show an enhanced phosphorus burial during this transient oxygenation. The elevated phosphorus and sulfate inputs from the enhanced continental weathering and oxygenation may have promoted the formation of aluminum phosphate‐sulfate minerals. This, in turn, reduced the bio‐availability of phosphorus in the marine environment, ultimately limiting marine productivity and leading to a negative feedback on the oxygenation event. This study highlights that phosphorus cycling pathway, which was previously overlooked, may have played a role in the deoxygenation during the intermittent oxygenation events in the mid‐Proterozoic. Key Points: Abundant phosphorus and sulfur precipitation as authigenic svanbergite is associated with the ∼1.7 Ga transient oxygenationThe oxygenation resulted in suboxic and acidic porewater conditions rich in P‐ and sulfate, facilitating the authigenesis of svanbergiteThe enhanced P and S burial as svanbergite represents a significant but overlooked negative feedback during the transient oxygenation [ABSTRACT FROM AUTHOR]

Deep tight gas reservoirs are considered important hydrocarbon exploration targets. High-quality reservoir prediction is critical for successfully exploring and developing deeply buried tight sandstone gas. Previous research has found that the reservoir quality of deeply buried tight sandstones is controlled by diagenesis and sedimentary facies. However, the variation of diagenetic alterations in different facies is still poorly studied on deltaic tight gas sandstone. In this study, core analysis, wireline log data, and 3D seismic were studied for the characterization of diagenetic alterations and sedimentary facies. The tight sandstones were formed in braided river delta deposits. Gravel- bearing coarse-grained sandstone facies and cross-bedded sandstone facies developed in tight sandstones. The Gravel-bearing coarse-grained sandstone is formed in the mid-channel bar of deltaic distributary channels. The major diagenetic processes developed in the tight sandstone include compaction, cementation, and dissolution. Constructive diagenesis can generate secondary pores, mainly including dissolution and kaolinite metasomatism, which can effectively improve reservoir physical properties. Through the diagenesis alterations linked to different lithofacies in cored wells, there are obvious diagenesis variations in different lithofacies. Despite strong compaction, the reservoirs in coarse sandstone facies have developed internal dissolution. After compaction, cementation, and dissolution to increase porosity, the reservoir retains intergranular and secondary pores and forms relatively high- quality reservoirs. The fine sandstone facies with cross-bedding are strongly compacted, with internal ductile particles being compacted and deformed, and the particle orientation is clearly arranged. The reservoir is tight, and the development of dissolution in the reservoir is weak, resulting in poor reservoir quality. In addition, reservoirs located at the interface between sandstone and mudstone are often affected by diagenesis, resulting in the development of calcareous cementation, leading to poor reservoir quality. Therefore, high-quality reservoirs are mostly distributed in coarse sand lithofacies, mainly distributed in the mid-channel bar of distributary channel deposits. Sedimentary facies control the original physical properties of the reservoir with different content and texture; the quality of the original reservoir is subject to diagenetic alteration in different ways. The points in this study could offer insights better to predict deep tight reservoir quality in continental basins. [ABSTRACT FROM AUTHOR]

In current energy structure adjustments, the prominence of unconventional oil and gas resources continues to grow, with increasing attention being paid to tight gas, a major component of natural gas production. The Xujiahe Formation gas reservoir in the Western Sichuan Depression represents a typical tight gas reservoir and the study of its reservoir characteristics is a key focus for current and future exploration and development efforts. This review employs the PRISMA method to screen and integrate the primary findings of 26 documents spanning the period from 2008 to 2023, with the aim of providing a comprehensive overview of the progress and outcomes of research on the tight gas reservoir characteristics of the Xujiahe Formation in the Western Sichuan Depression. The selected research documents summarize the characteristics of the Xujiahe Formation tight gas reservoir in the Western Sichuan Depression from four perspectives: lithology, physical properties, reservoir space, and the main factors influencing reservoir quality. Through a review of these previous studies, it is evident that existing research has predominantly focused on the relationship between diagenesis and reservoir densification, indicating certain limitations. We also delve into the characteristics of tight gas sandstone reservoirs in the study area, considering their depositional systems, fracture development, cementation, and impact on the exploration and development of tight gas reservoirs. Additionally, we propose measures to stabilize and enhance tight gas production in the Xujiahe Formation in the Western Sichuan Depression. Moreover, we outline the next steps for further research and exploration. [ABSTRACT FROM AUTHOR]

Arroyo Verde epithermal deposit, in the North Patagonia region of Argentina, is located within the Lower Chon Aike volcanism and is developed between 192.6 ± 2.5 Ma (mineralization host rock) and 189.5 ± 2.6 Ma (overlying lava). Marifil volcanic complex is the host rock for these veins, veinlets and breccias. This particular small deposit has developed low to intermediate sulphidation characteristics, with gangue mineral textures associated with several ore minerals. Electron probe microanalysis determines electrum, silver minerals such as acanthite, and tetrahedrite, related Ag-Cu minerals like jalpaite, mckinstryite, stromeyerite, and base metals like chalcopyrite, sphalerite, galena and pyrite. Fluid inclusions in quartz of two out of five events indicate that these Low Jurassic veins were formed due to subtle boiling and dilution mechanisms and by low-salinity (3.4 wt.% to 6.7 wt.% NaCl Eq) magmatic-hydrothermal fluid at 225 to 310 °C. The fluid inclusion measurements that indicate boiling (Event 3) were plotted, and based on this data, we interpret that the Arroyo Verde deposit has been eroded between 550 and 700 m. This particular character has not been previously recorded for other sectors of the eastern north Patagonian region. [ABSTRACT FROM AUTHOR]

The content of sediment-forming minerals in two cores from the eastern (ANS45-37) and western (ANS45-48) parts of the valley of the Vema Fracture Zone is studied using semiquantitative XRD analysis of bulk powder sediment samples. The mineral composition of deep-sea sediments from the Amazone Cone is also analyzed for comparison. It appeared that the average composition of the terrigenous component of both cores (according to prevailing quartz, secondary mica, plagioclase and potassium feldspar, as well as smectite, chlorite, kaolinite, illite) is quite similar and approximately corresponds to the composition of sediments from the Amazon Cone. The ratio of four clay minerals suggests supply of terrigenous material to the Amazon and Orinoco due to erosion of the Andes and humid tropical weathering in the lower courses of the rivers with further transport of the suspended load to the ocean. This material was transported to the valley of the Vema Fracture Zone due to interplay between gravitational flows from the South American continental slope and current of Antarctic Bottom Water. In addition, data on biogenic calcite (planktic foraminiferal tests, nannofossils) and opal A (radiolarians, sponge spicules) have been obtained. In the study area, several authigenic (diagenetic) minerals are identified. In particular, siderite and greigite are first found in the sediments from the Vema valley and Amazon Cone, respectively. [ABSTRACT FROM AUTHOR]

The two main parameters of grouting volume and grouting pressure are the keys to ensuring the quality of postgrouting. However, there is no equation for predicting the main grouting parameters of long and large-diameter postgrouting drilled shafts. In this paper, field data of 708 shafts in 128 projects were systematically investigated utilizing mathematical statistics, and equations for predicting the grouting volume and grouting termination pressure of long and large-diameter drilled shafts suitable for various soil layers were proposed. The range of coefficients of the grouting volume classified by soil types was defined. When establishing the equation for predicting the grouting termination pressure for a long drilled shaft, the influences of the cement grout weight in the grout pipe and the height difference between the pressure sensor and the grout valve on the grouting pressure were considered. Taking the grouting pressure and grouting volume as the control conditions of postgrouting operation, the criteria conditions for terminating postgrouting were proposed.The proposed equations for predicting the grouting volume and grouting termination pressure were verified based on a project case study. The factors affecting the grouting termination pressure were analyzed in detail. These research results were of great significance to the design of postgrouting drilled shafts. [ABSTRACT FROM AUTHOR]

Primary phases in iron-rich chemical sedimentary rocks are important archives of seawater geochemistry throughout the Precambrian. The record of seawater chemistry, however, is obscured by post-depositional changes that occur during diagenesis, metamorphism, and modern weathering. Recent studies have identified silica-cemented horizons in some Archean and Paleoproterozoic iron formation that may preserve reduced, texturally early mineral phases, which may inform interpretations of oxygen dynamics preceding atmospheric oxygen accumulation before the ~2.3 Ga Great Oxidation Event (GOE). However, fewer investigations focus on silica-cemented horizons in Paleoproterozoic iron formation deposited after the GOE, a period where oxygen levels are poorly constrained. Here, we present petrographic observations, scanning electron microscopy, electron microprobe analysis, and Raman spectroscopy of iron mineral phases preserved within silica-cemented horizons of the ~1.9 Ga Biwabik Iron Formation (Minnesota, U.S.A.) to constrain texturally early iron formation mineralogy from this crucial post-GOE interval. Based on textural relationships, the iron silicate greenalite is identified as the earliest-forming iron silicate mineral preserved within silica-cemented horizons. The magnesium- and aluminum-rich iron silicates chamosite and stilpnomelane are preserved proximal to fine-grained, non-silicified horizons, suggesting local geochemical exchange during early diagenesis. The presence of well preserved, early-forming silicates containing predominantly ferrous iron may indicate reducing conditions at the sediment-water interface during deposition of the Biwabik Iron Formation. More definitively, future studies using iron silicate mineralogy as seawater geochemistry proxies should consider preservation by silica cementation, in addition to the efects of local geochemical exchange during diagenesis. [ABSTRACT FROM AUTHOR]

This work investigates how peatlands can be used as archives of past environmental conditions to record changes in atmospheric deposition of some (especially lithophile and chalcophile) elements and any water–rock–organic matter interactions followed by the sedimentation or leaching of others. We have provided a detailed description of both the distribution of various groups of elements and their chemical species in the entire depth of peat deposits. The study analyzes the features of the peat sediment formation and element distribution in the 0–310 cm depth core sample of peat deposits of the Ubinskoye peat bog located in the forest-steppe zone of Western Siberia. The study reveals a profound diagenetic transformation of water and peat chemical composition. Element speciation investigated using the modified Tessier sequential extraction procedure showed the vertical transition of an oxidative geochemical environment to a reducing one with the formation of geochemical barriers for variably valent elements. Computer modeling calculations of saturation indices of pore solutions in relation to a number of minerals allowed us to estimate the degree of equilibrium of the system and the direction of its transformation. Early diagenetic processes lead to the deposition of authigenic minerals. Therefore, barite forms on the redox line, while pyrite is found in the reducing environment. With depth, the content of Ca, Mg and Sr increases, which leads to the formation of authigenic carbonates. [ABSTRACT FROM AUTHOR]

The Bahamian Archipelago has been the subject of extensive studies of stratigraphy, carbonate island morphology and diagenetic overprinting for many decades. A recently‐acquired dataset comprised of high‐resolution light detection and ranging, tightly spaced cored boreholes with image logs, thin sections, porosity and permeability measurements, and isotopic geochemical analyses provides a unique opportunity to perform detailed sequence stratigraphic analysis. This multi‐faceted study first establishes a new high‐resolution sequence stratigraphic framework for the Sandy Point area of San Salvador Island, encompassing six unconformity bound sequences (exposure surfaces) representing varying lengths of missing time. The stratigraphically lowest sequence is Late Pliocene in age and is dominated by reef facies capped by an extensive laminar caliche that represents 1.5 million years of exposure. The overlying Early Pleistocene is split into two sequences, EP1 and EP2, which are both dominated by low‐energy subtidal facies. The upper three sequences are tied to the Marine Isotope Stage 11, 9 and 5e interglacials, and are distinctly different in facies composition and architecture, being dominated by higher energy facies distributed in a more complex mosaic. The new stratigraphic framework highlights significant changes in depositional style and facies architecture that can be linked to increasing sea‐level amplitude oscillations and greater climate gradient at the Mid Pleistocene Transition. The well‐constrained framework is then used to provide key context for observed complex diagenetic evolution through repeated sea‐level inundation and subaerial exposure. These results suggest that well‐developed subaerial exposure surfaces drive increases in non‐matrix features in the subsequent stratigraphic package following exposure as the well‐cemented exposure surface acts to concentrate fluid flow and dissolution. Integration of non‐matrix features within this framework highlights the importance of dissolution/cementation patterns on formation of these modified unconformity surfaces for focusing later meteoric diagenesis and creating enhanced fluid flow pathways for continued multicyclic diagenetic events. [ABSTRACT FROM AUTHOR]

The mineralogy and chemistry of Upper Cretaceous-Lower Paleocene claystone sediments from Mardin and Batman, southeastern Turkey, were analyzed. The main mineral paragenesis in the Upper Cretaceous member formed chlorite-smectite (C-S) and illite, while the Lower Paleocene member occurred of chlorite-vermiculite (C-V) and vermiculite minerals. The clays were silica-poor but indicated high values of Al, Fe, Mg, Cr, Ni, V, and Zr. Lower contents of the alkali elements (Na, Ca, Mg, K) of the clayey sediments suggests a relatively denser weathering of the source area. The mineralogical compositions, major element ratios, trace, and rare earth element (REE) contents of the sediments show that the Upper Cretaceous member consists of materials with a mainly felsic source lithology, while relatively contributions from basic sources are found in the Lower Paleocene unit. A comparison of the major and trace element contents of the phyllosilicate/clay minerals with the members revealed that the patterns of the clays were different from each other, although the enrichments/decreases varied depending on the origin (basement rocks or detrital) of the derived rocks, minerals, and elements. REE content of clays increased from detrital to phyllosilicate/clay minerals of chemical/diagenetic/neoformation origin during the Lower Paleocene. During the Cretaceous and Tertiary periods, local or regional geodynamic and diagenetic events largely governed the rock sedimentation processes and provenance variations amongst Germav Formation members. [ABSTRACT FROM AUTHOR]

Exploration in the Lishui West Sag of the East China Sea Basin is limited by the scarcity of offshore drilling sites, and the prediction of deep, high-quality reservoirs is challenging using only geophysical methods. This study introduces a quantitative approach to diagenetic facies division in individual wells based on logging data, providing a new method and perspective for the prediction of deep, high-quality reservoirs. We employed comprehensive data from core, logging, thin-section casting, cathodoluminescence, scanning electron microscopy, and X-ray diffraction analyses from five wells to study the petrology, physical properties, diagenetic types and strength, and diagenetic minerals of the Paleocene sandstone reservoirs in the Lishui West Sag. Apparent compaction rate, apparent cementation rate, and other quantitative characterization parameters were used to calculate the comprehensive diagenetic coefficient (Cg), and the diagenetic facies were divided into compaction, cementation, and dissolution facies. A logging calculation model for the comprehensive diagenetic coefficient (Cg) and a quantitative identification method for diagenetic facies in individual well reservoirs were established through a fitting analysis between Cg and logging curve parameters. Continuous quantitative identification of vertical diagenetic facies in the five wells in the study area showed that the high-quality reservoirs in wells L1, L2, and L3 within the L1 gas field are characterized by extensive development of dissolution facies, while wells L4 and L5 are dominated by compaction and cementation facies, with poor reservoir properties and no industrial gas flow output. The results demonstrate the reliability of the model method. The establishment of this quantitative characterization method for diagenetic facies using logging data provides guidance for the prediction of favorable reservoirs. [ABSTRACT FROM AUTHOR]

Characterization of pore systems is a key to better understand the heterogeneity of reservoir quality. However, the complicated pore types and pore facies of carbonates in the Hartha Formation of X Oilfield remain poorly understood. In this study, we recognized pore types and explored the impact of depositional environment and diagenetic alterations on pore facies and reservoir heterogeneity. Six types and nine subtypes of pore facies displaying various physical properties and fossils are classified based on the proportion of depositional pores, fabric‐ and non‐fabric‐selective pores. The distribution of pore facies are controlled by the interaction between depositional environment and diagenesis: (i) the depositional environment has an impact on the primary pore types mainly through different lithology and fossils. Micro‐interparticle pores and intraparticle pores of foraminifera are dominated in lagoon, middle ramp and outer ramp, while interparticle pores between grains are dominated in rudist shoal. Rocks deposited in medium‐ to low‐energy shoal contain interparticle pores between grains, micro‐interparticle pores and intraparticle pores of foraminifera. (ii) Major diagenetic events that modify pore types include micritization, fabric‐selective dissolution, cementation, compaction and non‐fabric‐selective dissolution. Micritization facilitates the development of micro‐interparticle pores, while compaction can cause the loss of interparticle pores between grains and micro‐interparticle pores. Cementation destroys not only interparticle pores between grains but also intraparticle pores of foraminifera. Fabric‐ and non‐fabric‐selective dissolution are the main causes for increasing the volume of pores. (iii) The intensity of the diagenetic event is linked to rock composition, rock fabric and palaeotopography that are controlled by depositional environment. Thus, the distribution of pore facies related to the environment is established, which can provide insights for areas lacking cores and adjacent fields with similar settings. [ABSTRACT FROM AUTHOR]

The gravity flow sedimentation of lakes is characterized by diversity and can vary greatly on a small spatial scale, leading to extremely complex diagenesis. This complexity makes it difficult to accurately classify them using conventional diagenetic methods. This paper focuses on the study of gravity flow sedimentary units in the Dongying, the diagenetic facies were classified into five different types by using a novel principal component analysis method. Based on this, the diagenetic evolution of rocks was characterized, and the reservoir quality influence factors were clarified. First, detailed characterizations were conducted on the compositional characteristics of the two main reservoir types (feldspathic sandstone and lithic feldspathic sandstone), along with their diagenetic processes, including compaction, cementation, dissolution, and metasomatism. Then, the diagenetic control factors of gravity flow sandstone were clarified. It was found that the compaction and cementation had the greatest impact on rock porosity, had the presence of a large amount of clay cement leading to pore deterioration. Finally, a principal component analysis model was used to identify five types of diagenetic facies in the study area and characterize their distribution patterns, providing evidence for a deeper understanding of the sedimentary evolutionary sequence. [ABSTRACT FROM AUTHOR]