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The clumped isotope paleo-thermometer has become a valuable proxy for the burial history reconstruction of carbonate formations. To maximise the accuracy of these reconstructions, post-depositional alterations, such as recrystallisation and Δ47 isotope exchange reactions, must be understood. In this study, we examine the isotopic behaviour of calcites and early dolomite samples from the same stratigraphic intervals, and thus with similar burial history. This approach provides additional constraints on the kinetics of Δ47 reordering in dolomite during exhumation. Clumped isotope measurements were performed on 19 calcites and 15 early dolomites from the Permian, Jurassic, and Cretaceous periods from four locations in Oman spanning different burial regimes. The calcite and dolomite samples were collected from the rock matrix, based on the assumption that fine material was more susceptible to recrystallisation. Our results show that calcites and dolomites record different Δ47 values despite being subjected to the same thermal history. The maximum Δ47 temperature recorded in dolomites (181 ± 13 °C) corresponds to the oldest and most deeply buried Permian rock. This value is approximately 35 °C higher than those measured in the co-located and coeval calcite matrix (145 ± 14 °C). This discrepancy suggests that calcite and dolomite have different kinetic parameters. Our data confirm (1) that dolomite Δ47 values are more resistant to alteration during burial and exhumation than Δ47 calcite values, and (2) that dolomite has a higher Δ47 closing temperature than calcite during cooling. The presence of two mineral phases with distinct kinetic parameters in the same stratigraphic unit provides additional constraints on models of burial and uplift. In addition, mineralogical data coupled with Δ47 and burial depths suggest that the progressive development of dolomite cation ordering is driven by temperature elevation, as previously suggested. [ABSTRACT FROM AUTHOR]

The end of the Cryogenian glaciations undoubtedly affected the chemistry of the Neoproterozoic oceans, with potential consequences for the evolution of life; the duration and extent of this influence are poorly constrained. Lithium (Li) isotopes in carbonates can be used to investigate past weathering events and riverine input into the oceans. Here, we report the Li isotope (δ7Li) composition of the Ediacaran cap dolostones (Marinoan) from the Nuccaleena Formation, South Australia and the Doushantuo Formation, South China to investigate changes in weathering during the aftermath of the Marinoan glaciation. The origin of dolomite formation is still hotly debated, and the inability to precipitate dolomite at ambient temperatures (the 'dolomite problem') has not yet been resolved. The dominant hypothesis for the presence of marine dolomite is that it is of secondary origin, owing to diagenetic replacement of calcium carbonate, but a second hypothesis is that it forms as a result of primary marine deposition; both are plausible hypotheses. Using carbon isotopes (δ13C) and ratios of manganese and strontium (Mn/Sr), we suggest that diagenesis may not have significantly altered the δ7Li composition of the primary dolomite, but this cannot be discounted without further diagenetic modelling. As a result, we cannot infer the δ7Li composition of the Ediacaran oceans, as further work must be done to address the impact of diagenesis on the δ7Li values. Nevertheless, this dataset contributes to a Li isotope chemostratigraphic record of the Proterozoic, which is a key element to understanding the emergence of complex life. [ABSTRACT FROM AUTHOR]

Petrographic and geochemical studies were carried out on the Paleocene–Eocene carbonates of the Kolosh Formation in the High Folded Zone to infer the environment of deposition, diagenetic overprints, and their origin. The petrographic study revealed five main microfacies; packstone, wackestone, mudstone, grainstone, and crystalline carbonate. There are different depositional environments from shoal to shallow marine environments (mid-ramp conditions) that are adequate for mixing continental material with seawater. Several evidences of diagenetic processes were observed, such as micritization, neomorphism, and dolomitization. Petrographic and geochemical analyses show the dominance of calcite and dolomite minerals. The contents of major oxides and the concentrations of trace elements were normalized to Post-Archean Australian Shale (PAAS) values. The Paleocene–Eocene carbonates are enriched in CaO, MgO, Cr, and Ni, whereas are highly depleted in Na2O, K2O, TiO2, Al2O3, Rb, Ba, Th, and Zr. The low contents of Al2O3 and SiO2 refer to a low siliciclastic involvement during the deposition of the Paleocene–Eocene carbonate. The REEs average content is lower (15.60 ppm) than that of marine carbonates (28 ppm). The REE patterns (normalized to PAAS) display a seawater-like type, while a slightly lower average Y/Ho value (33.66) relative to that of typical seawater (~ 44 to 74) refers to the alteration of the seawater by the freshwater. The REEs of this study are comparable with the limestone of the Middle Eocene Fulra Formation and Arabian Sea carbonates. Paleocene–Eocene carbonates have δ13CPDB ranging between − 13.31 and 1.25‰PDB, and δ18O from − 6.30 to 0.12‰PDB. The negative values and no correlation between δ13C and δ18O indicate that modification of the primordial composition of the isotopes is not a result of diagenesis only, but other factors, such as temperature, and organic matter have an important role. The negative Ce/Ce*, Th/U ratios, and authigenic U suggest their accompanying the deposition of the carbonates in oxidizing conditions. The paleotemperature of the studied carbonates (~ 12 to 42 °C) is slightly higher than other global records in the Paleocene–Eocene, which may propose the variations in the composition of oxygen isotope and modification in the geochemical characteristics during the post-carbonate deposition time. [ABSTRACT FROM AUTHOR]

The deeply buried Lower Cambrian Longwangmiao Formation and Upper Ediacaran Dengying Formation from the Sichuan Basin, China, have a total natural gas reserve up to 3 × 1012 m³. The complex diagenetic evolution and their impacts on the present-day reservoir quality have not been systematically elucidated, hampering the current exploration. Crucially, the integration and comparation diagenetic study on these two formations, which may be able to shed new lights on reservoir formation mechanism, are yet to be systemically evaluated. By compiling geochemistry data, including carbonate U-Pb ages and petrophysics data, coupled with new petrology, trace elements, and strontium isotope data, of various types of diagenetic carbonates, this study aims to decipher the potential links between diagenesis and reservoir development of both formations. Intriguingly, similar diagenetic sequence, which contains five distinctive dolomite phases, is established in both formations. The matrix dolomite (D1) and early dolomite cement (D2) were likely formed by reflux dolomitization, as inferred by their nearly syn-depositional U-Pb ages and elevated δ18O caused by seawater evaporation. The subsequent moderate burial dolomite cement (D3) was most plausibly the product of burial compaction as indicated by its lighter δ18O and slightly younger U-Pb ages compared with D1 and D2. Whereas deep burial dolomite cements (D4 and D5) yield markedly depleted δ18O, elevated 87Sr/86Sr, along with much younger U-Pb ages and higher precipitation temperatures, suggesting that they were likely linked to hydrothermal fluids. Despite the wide occurrence of meteoric and organic acids leaching and thermochemical sulfate reduction, they may have only played a subsidiary role on these reservoirs development. Instead, superior reservoir quality is tightly linked to tectonics as inferred by higher reservoir quality closely related to the well-developed fractures and faults filled with abundant hydrothermal minerals. Notably, good reservoirs in both formations are mainly attributed to high permeability caused by tectonics. Hence, this new contribution emphasizes the crucial role of tectonics on spatially explicit reservoir prediction of deep to ultra-deep (up to > 8000 m) carbonates in the Sichuan Basin, as well as other sedimentary basin analogues in China. [ABSTRACT FROM AUTHOR]

A comparative analysis of the morphological features of horizons affected by paleoearthquakes revealed significant difference of seismites from lithologically different deposits. Powerful earthquakes determine not only the destruction of the sedimentary structure of near-surface deposits and their chaotic mixing, but also actively affect the underlying layers to a depth of several tens of meters; since the degree of diagenetic lithification of rocks in different horizons varies with depth, the nature of their seismogenic transformations also changes. It was found that major seismic events were associated with the time intervals of tectonic and paleogeographic restructuring of sedimentation basins, which consisted in the intensification of the basin floor subsidence and changes in the composition of sediments accumulated in the paleobasin. A special type of seismites was formed during the impact of earthquakes on siliceous deposits, which have been spanned by the diagenetic redistribution of authigenic mineral matter in a gel state. [ABSTRACT FROM AUTHOR]

This study involves microfacies analysis of the Kometan Formation from northeastern Iraq supported by detailed petrographic investigation for the main components and diagenetic processes using a petrographic microscope, scanning electron microscope (SEM), and X-Ray diffraction (XRD). The techniques have revealed that the formation includes two microfacies; lime wackestone and lime packstone microfacies which in turn are subdivided into seven sub-microfacies, that were deposited in the quiet and deep marine environment. Planktonic foraminifera (keeled and globular chamber types) are dominant, along with oligostegina in addition to subordinate benthonic foraminifera and fine-grained bioclasts. Calcite forms the main mineralogical composition in euhedral (rhombohedral), microcrystals, starshaped, and columnar crystals in addition to pyrite and glauconite. All components are embedded in the micritic groundmass. The main diagenetic processes affecting the studied rocks include; chemical compaction (stylolite formation), dissolution, recrystallization, and cementation. [ABSTRACT FROM AUTHOR]

Hemipelagic calcareous ooze is a mixture of biogenic carbonate ooze and detrital terrigenous materials from continental weathering. Understanding its early diagenetic features is critical for geophysical measurement and geo-hazard assessment. However, the early diagenesis of hemipelagic calcareous ooze has rarely been studied due to a lack of samples and in-situ measurement in shallow strata. During IODP Expedition 368, hemipelagic calcareous oozes, up to hundreds of meters thick, were encountered in the shallow subsurface (< 400 m) at two sites (U1501 and U1505) close to the continent-ocean transition zone in the northern South China Sea margin. Here, we use coring and well logging data to perform rock physics diagnostics to characterize early diagenetic processes in hemipelagic calcareous ooze. The calcareous ooze in the study area is primarily chalky marl with the ratio of carbonate to carbonate plus siliciclastic minerals ranging 30% ~ 70%, according to a mineralogy-based lithofaices classification scheme. In the chalky marl interval, pyrite accounts for around 15% of the total mineral composition and this existence may be related to significant post-rift magmatic activity that produced significant amouts of volcanic material. The porosity reduction with depth in the chalky marl interval has three phases and carbonate content is suggested to be the controlling factor affecting porosity reduction. The varying carbonate content in the oozes can result in contrasting mechanical properties and porosities, potentially serving as weak layers for submarine landslides. Additionally, the interface between calcareous ooze and siliciclastic sediment is also a potential failure plane. Therefore, we propose that the development of hemipelagic calcareous ooze has significant implications for seafloor instability on continental margins. [ABSTRACT FROM AUTHOR]

Wetlands store large amounts of C in biomass, sediments and water. A major C fraction is in the dissolved organic matter (DOM) with multiple regulatory functions. Patagonian wetlands undergo changes in the water cycle due to climate warming and lower precipitation, causing shorter hydroperiods and reduced landscape connectivity with effects on C budgets. This study focuses on the optical characterisation of the DOM of an ephemeral wetland of North Patagonia. Along the hydroperiod the DOM showed optical signatures indicating terrestrial inputs, degradation and internal production. Dissolved organic carbon (DOC) concentration ranged between ∼4 and ∼9 mg L−1. The DOM pool displayed high molecular weight/size and aromatic fingerprints. Humic components C1 (microbial and/or vegetation derived) and C2 (soil/sediment) prevailed in the DOM, whereas the non-humic component C3 (from aquatic processes) increased from early spring. Experimental exposure to PAR + UVR produced slight changes in DOC and reduction in DOM molecular weight/size. The components showed distinctive photoreactivity/lability: C1 > C3 > C2. Along the hydroperiod the relative contribution of the humic vs. non-humic components (C1 and C3) determined the reactivity/lability of the DOM. In Fantasma pond, the DOM pool fluctuates in response to hydrology and degradation processes, and the alternance between dry and flooded periods determines C dynamics. [ABSTRACT FROM AUTHOR]

Considering the action mechanisms of overpressure on physical changes in skeletal grains of deep reservoir rocks and the differences in physical changes of skeletal grains under overpressure and hydrostatic pressure, the sandstone of the Jurassic Toutunhe Formation in the southern margin of Junggar Basin was taken as an example for physical modeling experiment to analyze the action mechanisms of overpressure on the physical properties of deep reservoirs. (1) In the simulated ultra-deep layer with a burial depth of 6000–8000 m, the mechanical compaction under overpressure reduces the remaining primary pores by about a half that under hydrostatic pressure. Overpressure can effectively suppress the mechanical compaction to allow the preservation of intergranular primary pores. (2) The linear contact length ratio under overpressure is always smaller than the linear contact length ratio under hydrostatic pressure at the same depth. In deep reservoirs, the difference between the mechanical compaction degree under overpressure and hydrostatic pressure shows a decreasing trend, the effect of abnormally high pressure to resist the increase of effective stress is weakened, and the degree of mechanical compaction is gradually close to that under hydrostatic pressure. (3) The microfractures in skeletal grains of deep reservoirs under overpressure are thin and long, while the microfractures in skeletal grains of deep reservoirs under hydrostatic pressure are short and wide. This difference is attributed to the probable presence of tension fractures in the rocks containing abnormally high pressure fluid. (4) The microfractures in skeletal grains under overpressure were mainly formed later than that under hydrostatic pressure, and the development degree and length of microfractures both extend deeper. (5) The development stages of microfractures under overpressure are mainly controlled by the development stages of abnormally high pressure and the magnitude of effective stress acting on the skeletal grains. Moreover, the development stages of microfractures in skeletal grains are more than those under hydrostatic pressure in deep reservoir. The multi-stage abnormally high pressure plays an important role in improving the physical properties of deep reservoirs. [ABSTRACT FROM AUTHOR]

The complexity of diagenesis and hydrocarbon accumulation in the deep reservoirs in southern Junggar Basin restricts hydrocarbon exploration in the lower reservoir assemblage. The lithofacies and diagenesis of reservoirs in the Cretaceous Qingshuihe Formation in the Gaoquan structure of the Sikeshu Sag, southern Junggar Basin were analyzed. On this basis, the thermal history was calibrated using calcite in-situ U-Pb dating and fluid inclusion analysis to depict the hydrocarbon accumulation process in the Gaoquan structure. The results show that the Qingshuihe reservoir experienced two phases of calcite cementation and three phases of hydrocarbon charging. The calcite cements are dated to be 122.1±6.4 Ma, 14.4±1.0 Ma –14.2±0.3 Ma. The hydrocarbon charging events occurred at around 14.2–30.0 Ma (low-mature oil), 14.2 Ma (mature oil), and 2 Ma (high-mature gas). The latter two phases of hydrocarbon charging contributed dominantly to the formation of reservoir. Due to the S-N compressive thrust activity during the late Himalayan period since 2 Ma, the traps in the Gaoquan structure were reshaped, especially the effective traps which developed in the main reservoir-forming period were decreased significantly in scale, resulting in weak hydrocarbon shows in the middle-lower part of the structure. This indicates that the effective traps in key reservoir-forming period controlled hydrocarbon enrichment and distribution in the lower reservoir assemblage. Calcite U-Pb dating combined with fluid inclusion analysis can help effectively describe the complex diagenesis and hydrocarbon accumulation process in the central-west part of the basin. [ABSTRACT FROM AUTHOR]

Based on the measurements of petrological, petrophysical and elastic properties of the samples of different sedimentary facies in the fourth member of Sinian Dengying Formation (Deng 4 Member) in the Sichuan Basin, the diagenetic processes of reservoirs of different sedimentary facies and their controls on the petrophysical properties were discussed. The results show that cracks and mineral composition jointly control the petrophysical properties, and both are significantly influenced by sedimentary environment and diagenesis. The microbial dolomite of mound-shoal facies mainly experienced multi-stage dolomitization, penecontemporaneous dissolution, tectonic rupture and hydrothermal/organic acid dissolution processes, giving rise to cracks and dissolved pores. The grannular dolomite of inter-mound-shoal bottomland or dolomitic lagoon facies mainly underwent mechanical compaction, burial dolomitization and tectonic-hydrothermal action, creating cracks and intercrystalline pores. The diagenesis related to crack development increases the pressure- and saturation-dependent effects of samples, leading to significant decrease in the compressional wave impedance and Poisson's ratio. Dolomitization changes the properties of mineral particles, resulting in a Poisson's ratio close to dolomite. The muddy, siliceous and calcareous sediments in the low-energy environment lead to the decrease of impedance and the differential change of Poisson's ratio (significantly increased or decreased). The samples with both cracks and dissolved pores show high P-wave velocity dispersion characteristics, and the P-wave velocity dispersion of samples with only fractures or pores is the lowest. [ABSTRACT FROM AUTHOR]

Louedale is the only open-air Middle Stone Age site iii the Free State dated to early Marine Isotope Stage 4. Framing the chronology of this context, especially by taking into account diagenetic processes that may N.(fect nge results, is thus fundamental to understand modern human dynamics in the interior of South Africa. In a recent study, we inuestigated the effect of diagenesis on teeth samples collected for Ucombined electron spin resonance and uranium-series dating at the site. By combining different characterisation niethods, it was shown that the wrimium (U) content of enamel varied in the specimens, and carbonthat it was positively correlated with the degree of crystallinity of carbonate hydroxyapatite, whereby larger amounts of U are associated with highly crystalline enaniet. The large variability in U content was in contrast witli thefact that teethwerefound in the same depositional context. High levels of U in some of the samples limit the accu ract/Of age determiltations, Since seueral 1111-Jertainties remain regarding U uptake and teaching, which both affect dose rate modelling. In stick complex cases, calculating minimum nges is the most cautious option. New samples were collected at the site during the excavation canipitign in 21)11. Enamel was analysed using Fourier transform infrared spectroscopy and scanning electron microscopy coupled with cathodoluminescence iii order to determine its degree Of atomic order and the presence of foreign ions (especially U), and the correlation between the two. We discuss here the contribution of U-uptake modellingon the age calculation, and present new ESR ages calculated assumpassuming an early uptake of U, ranging from 84 + 9 ka to 56 + 5 ka. Together with previous ages obtained on the gravel layer, a weighted inean age of 64 kn can be used as a minimum age estimate for thebase of the seque 11Ce. [ABSTRACT FROM AUTHOR]

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Since most of the petroliferous basins of Pakistan have not been fully explored, the country's energy output falls short of its energy demands. Studies conducted both internationally and domestically show that it has far higher potential for hydrocarbons than its current proven reserves. It has been estimated that there are around 105 trillion cubic feet of natural gas resources that are potentially recoverable from the shale formations of Indus Basin. The Cretaceous shales of the Sembar Formation are one of the major prospects for shale gas exploitation in Central and Southern Indus Basins. An integrated study was conducted to evaluate its conventional and unconventional resource potential in terms of reservoir characteristics, organic richness and clay type. Conventional reservoir potential within the top sand facies of the Sembar Formation exhibited consistent behavior with regards to its porosity and fluid saturation. The lower part of this formation is characterized primarily by the prevalence of shale facies. Empirical log-based techniques were utilized to assess the organic richness of these facies, which showed total organic carbon (TOC) content ranging 1–1.4%. Along with its organic richness, the category of clay minerals is a very important factor in estimating unconventional resource potential. The log-based mineralogical assessment revealed the presence of brittle clay minerals (illite), which are suitable for fracking. The diagenetic changes of clay minerals may increase brittle components, which could lead to an increase in the integral rigidity of these rocks. Moreover, deep feedforward neural network (DFNN) analysis, which is a non-linear neural network regression technique, was used to delineate the spatial and vertical variations of TOC. The impedance sections, combined with the original seismic trace and TOC curve from the well, were utilized as input for training the seismic attributes for predicting seismic-based TOC. The findings of the DFNN analysis on the Duljan Re-Entry-01 well indicate a strong correlation coefficient of 93% between Passey TOC and the predicted TOC curve. Additionally, the root mean square error was found to be a mere 0.09. The TOC prediction based on seismic-based DFNN analysis yielded an average value of approximately 1.1%, with a maximum value of 2.3%. These two-dimensional TOC sections for the Sembar shales provide an extremely positive impact in evaluating its shale gas potential. [ABSTRACT FROM AUTHOR]

The paper shows that the formation of orthogonal systems of open macrofractures (cleavages) of sedimentary basins can occur at the stage of diagenesis during the first hundreds of years for a small range of shelf depths (up to 100 m) during sedimentation. During this period, sediments are compacted and the excess water is slowly squeezed out, which determines the decrease in the Poisson’s ratio from values close to 0.5 to values 0.3–0.2. Because of this, in sediments, the stress state of which is almost completely determined only by the gravity of the overlying rocks, is reduced by 50 % or more of the horizontal compression stress level from the initial lithostatic pressure level. On the other hand, if the limit of pseudoplastic flow is reached in the rock, vertical compaction occurs, accompanied by an increase in horizontal compression. These two competing processes together with the factor of fluid pressure in fractures and pores determine the possibility of brittle fracture formation. It is shown that for rocks with a low level of yield strength (clay), compaction leads to an increase in the level of horizontal compression stresses, which makes brittle fracture in such rocks at the stage of diagenesis impossible. In rocks with a high level of strength (sandstone, limestone), brittle fracture due to excess water pressure in the sub­vertical microcracks starts earlier than the shear yield limit is reached.

Objective To clarify the causes of the vertical difference of pore structure in low permeability-tight sandstone reservoirs. Methods Taking the WL area of the Ordos Basin as an example, using physical property tests, casting thin sections, scanning electron microscopy and high-pressure mercury injection, through the division of diagenetic facies and the analysis of vertical distribution differences of different diagenetic facies the characteristics, differences and causes of pore structure in different layers of the Yanchang Formation were discussed. Results The study showed that there were five types of pore structures in the main strata of the Yanchang Formation in the study area, and there were great differences in the pore structures between the same strata and different strata. The Chang 2 and Chang 3 oil layers of the upper combination mainly developed Ⅲa- and Ⅲb-type pore structures, the Chang 4+5 and Chang 6 oil layers of the middle combination mainly developed Ⅳa- and Ⅳb-type pore structures, andthe Chang 7, Chang 8 and Chang 9 oil layers of the lower combination mainly developed Ⅳb- and Ⅴ-type pore structures. With the increasing of burial depth, the pore structure and the porosity and permeability conditions in the reservoir gradually deteriorated overall. There were four types of diagenetic facies types in the reservoir of the Yanchang Formation in the study area. The vertical difference of pore structure was mainly controlled by the difference distribution of diagenetic facies types. The dissolution dominated by atmospheric water leaching in the upper combination was strong. The diagenetic facies types dominated by unstable component dissolution facies and chlorite cementation were developed, and the pore structure formed was dominated by relatively good types. The middle combination had strong cementation, and the diagenetic facies types dominated by chlorite cementation facies and carbonate cementation facies were developed, and the pore structure formed was mainly medium type.The lower combination had strong compaction and cementation, and the diagenetic facies types dominated by carbonate cementation facies and soft-rich compaction filling facies were developed, and the pore structure formed by them was mainly relatively poor. Conclusion The research results can provide favorable guidance for oil and gas exploration and development of the Triassic Yanchang Formation in the Ordos Basin.

The results of integrated sedimentology, petrography, and petrophysical study of the Upper Devonian (Middle Famennian) Dankovo-Lebedyansky carbonates from Southeast Tatarstan of the Volga-Ural Basin revealed a variety of microfacies and diagenetic events that impacted the reservoir quality. Although our earlier study documented microfacies analysis and depositional environments, none of the studies focused on diagenesis, microfacies interaction, and their controls on the studied sediment's reservoir quality. Based on petrographic and microfacies analyses, the seven identified microfacies types are peloidal grainstone MF 1, cemented bioclastic peloidal grainstone MF 2, echinoderm-concentrated packstone MF 3, algae packstone MF 4, bioclastic wackestone MF 5, whole-fossil wackestone MF 6, and dolomite MF 7. For the investigated sediments, a gently deepening carbonate ramp depositional model with an inner, middle, and outer ramp setting is proposed. The observed diagenetic events in this study include micritization, calcite cementation (six cement types), dolomitization (six dolomite types), dissolution (fabric and non-fabric-selective dissolution), compaction, and microfracturing. The identified microfacies were classified into three distinct classes based on their petrophysical characteristics. MF 1 and MF 7 are microfacies types with the best reservoir quality. MF 3 and MF 4 are microfacies types of moderate reservoir quality. MF 2, MF 5, and MF 6 are microfacies types with poor or non-reservoir quality. Calcite cementation, micritization, and compaction are the primary diagenetic modifications responsible for porosity reduction. Moldic pores created by dissolution are a significant porosity-improving process. Porosity is locally enhanced by stylolite and microfractures. Dolomitization improved reservoir quality by creating intercrystalline and vuggy porosity. Understanding the impact of microfacies and diagenesis on reservoir quality is crucial for understanding reservoir properties in nearby fields with similar settings.

Nutrient release from sediment is considered a significant source for overlying water. Given that nutrient release mechanisms in sediment are complex and difficult to simulate, traditional approaches commonly use assigned parameter values to simulate these processes. In this study, a nitrogen flux model was developed and coupled with the water quality model of an urban lake. After parameter sensitivity analyses and model calibration and validation, this model was used to simulate nitrogen exchange at the sediment–water interface in eight scenarios. The results showed that sediment acted as a buffer in the sediment–water system. It could store or release nitrogen at any time, regulate the distribution of nitrogen between sediment and the water column, and provide algae with nitrogen. The most effective way to reduce nitrogen levels in urban lakes within a short time is to reduce external nitrogen loadings. However, sediment release might continue to contribute to the water column until a new balance is achieved. Therefore, effective measures for reducing sediment nitrogen should be developed as supplementary measures. Furthermore, model parameter sensitivity should be individually examined for different research subjects.

In our original article we evaluated diagenetic changes to rat cortical bone osteocyte lacunae over increasing post-mortem intervals. We suggested that with further, more intensive research, it may be possible to exploit these changes for the purposes of post-mortem interval estimation of skeletal remains. In their comment to our paper, Miszkiewicz et al. (in press) raise concerns about the project design and interpretation of the results. Here, we reply to their comments and offer answers to their concerns. [ABSTRACT FROM AUTHOR]

This document is an editorial for a special issue of the Minerals journal focused on the deposition, diagenesis, and geochemistry of carbonate sequences. The editorial highlights the importance of studying carbonate formations, which serve as archives of past climates, tectonic events, and biological evolution. It emphasizes the significance of understanding depositional characteristics, diagenetic alterations, and geochemical variations within carbonate sequences for unraveling their geological significance and economic potential. The editorial invites readers to explore the collection of articles in the special issue, which cover diverse topics and methodologies, and contribute to our understanding of carbonate systems worldwide. [Extracted from the article]

The reservoir quality of tight sandstone is usually affected by pore throat structures, and understanding pore throat structures and their fractal characteristics is crucial for the exploration and development of tight sandstone gas. In this study, fractal dimensions of pore throat structures and the effect of diagenesis on the fractal dimension of tight sandstone sweet spot in Huagang Formation, Jiaxing area, East China Sea Basin were studied by means of thin sections, scanning electron microscopes, X-ray diffraction analysis, scanning electron microscope quantitative mineral evaluation, and high pressure mercury injection experiments. The results show that the total fractal dimension ranges of type I, type II, and type III sweet spots were 2.62–2.87, 2.22–2.56, and 2.71–2.77, respectively. The negative correlation between total fractal dimensions, porosity, and permeability of type I sweet spots was different from those of type II and type III sweet spots. The negative correlation between total fractal dimensions of type II and type III sweet spots and maximum mercury saturation, average pore throat radius, and skewness were significant, whereas the correlation between total fractal dimensions of type I sweet spots, and maximum mercury saturation, average pore throat radius and skewness were not significant. The positive correlation between the total fractal dimensions of type II and type III sweet spots and the relative sorting coefficient, displacement pressure, and efficiency of mercury withdrawal were significant, whereas the correlation between the total fractal dimension of type I sweet spots and relative sorting coefficients, displacement pressures and efficiency of mercury withdrawal were not significant. The effect of diagenesis on fractal dimensions was investigated. Compaction reduced the pore space of tight sandstone and increased fractal dimensions. Quartz cementation and calcite cementation blocked pores and throats, reduced pore space, and increased fractal dimensions. Chlorite coat can inhibit compaction, protect pore throat structures, and maintain fractal dimensions. Most clay minerals filled primary pores and secondary pores and increased fractal dimensions. Dissolution increased the pore space of tight sandstone and decreased the fractal dimensions of the pore throat structures. The pore throat structures of type I sweet spots were mainly composed of macropores, mesopores, transitional pores, and micropores, and the fractal dimension of type I sweet spots was chiefly controlled by chlorite coat formation, dissolution, and a small amount of compaction. This study provides a reference for pore throat structure and fractal dimension analysis of tight sandstone sweet spots.

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.

The present work aimed at evaluating indicators of hydrocarbon sources to sediments from the Solimões River region, in the central Amazon. The 16PAH, the alkylated homologs and molecular markers were investigated. The entire series of alkylated PAH were present and, in some cases, with a distribution observed when oil residues dominate. Nevertheless, hopanes characterizing immature environments undergoing diagenetic transformation were identified in samples from the Solimões River and in surface as well as in core sediment samples from Preto Lake, in the Coari-Manaus stretch. Investigation suggests early diagenesis of the organic matter confirmed by identifying biogenic markers produced during organic matter transformation. Some of these markers derive from incomplete combustion of biomass and are contained in particulate matter formed during forest burning. In the sediments of an industrial area near the city of Manaus, the entire series of mature hopanes was present indicating anthropogenic source of hydrocarbons. The results so far obtained point out the complexity of PAH source appraisal.

The Qingshuihe Formation in the western section of the southern margin of the Junggar Basin has excellent oil and gas exploration prospects. The systematic study of its diagenesis characteristics and pore evolution process will provide guidance for the later fine exploration and evaluation of oil and gas. Therefore, based on the analysis of ordinary thin sections, cast thin sections, whole rock X-ray diffraction, grain size, scanning electron microscopy, carbon and oxygen isotopes of carbonate cements and fluid inclusions, the diagenesis characteristics and pore evolution process of the Qingshuihe Formation in the western section of the southern margin of the Junggar Basin were systematically studied, and the differences of reservoir pore evolution process between different diagenetic facies were further discussed. The study shows that: (1)The reservoir of the Qingshuihe Formation in the studied area is dominated by glutenite. The content of rock debris is high, with an average of 65.97%, mainly tuff rock debris. The cement is mainly calcite. The average porosity of the reservoir is 6.2%, and the average permeability is 7.45×10-3 μm2. It is generally a tight reservoir of low porosity and low permeability, but high-quality reservoirs are still developed locally; (2)The reservoir burial mode of the Qingshuihe Formation in the southern margin of the Junggar Basin is characterized by long-term shallow burial and late rapid deep burial, and can be further divided into four evolutionary stages: long-term shallow burial, tectonic uplift to near surface, normal deep burial, and rapid deep burial. The diagenetic evolution of the reservoir was in early diagenetic stage A in the long-term shallow burial, tectonic uplift to near surface, and normal deep burial stages, while in the rapid deep burial stage, the reservoir was in early diagenetic stage B to middle diagenetic stage A; (3)The reservoir of the Qingshuihe Formation can be divided into four typical diagenetic facies types, namely, strong compaction facies, calcareous/iron argillaceous strong cementation facies, tuffaceous filling weak dissolution facies, and weak compaction pore development facies. The pore evolution model of the clastic rock reservoir of the Qingshuihe Formation in the southern margin of the Junggar Basin was established based on the constraints of diagenetic facies. The weak compaction pore development facies are high-quality reservoir diagenetic facies, followed by tuffaceous filling weak dissolution facies.

Abstract Reservoir quality in carbonate reservoirs is significantly influenced by diagenetic processes. Although diagenesis is studied as a common reservoir quality damaging/enhancing process in many previous studies, literature is limited about the spatial modeling of diagenesis processes using advanced geostatistical algorithms. In the current study, 3D models of the main diagenetic processes which affect the reservoir quality of the Sarvak reservoir in an Iranian oilfield located in the north Dezful Embayment were constructed using geostatistics. According to the petrographic studies, a total of 10 microfacies were identified. In addition, the significant diagenetic processes in this reservoir include dolomitization, cementation, dissolution, and compaction. In this study, diagenetic electrofacies were determined using the “multi-resolution graph clustering” method based on the quantitative results of the petrographic studies. The results of spatial modeling and provided average maps were used to investigate the lateral variation of those properties and their relationship with effective porosity. It shows that trends of the secondary porosity and velocity deviation log (VDL) maps are generally correlatable with the effective porosity maps confirming the impact of dissolution as a main significant diagenetic process on reservoir quality enhancement. The most impact of the dissolution on porosity is observed in Lower Sarvak-E2 zone where the correlation coefficient is 0.75. The correlation coefficient between porosity and VDL in some zones is high indicating the effect of diagenesis on reservoir quality as it exceeds 0.61 in Lower Sarvak-A1 zone. In the occurrence of dolomitization, it has dual constructive and destructive effects on the reservoir quality. The most constructive and destructive effects of dolomitization were observed in Lower Sarvak-E1 and Lower Sarvak-F zones in which the correlation coefficients were 0.476 and − 0.456, respectively. In addition, low porosity zones are correlatable with developing cementation, stylolites, and solution seams.

The Lower Jurassic Reservoir (LJR) in the Lenghu area on the northern margin of the Qaidam Basin (NMoQB) has become the most promising target for hydrocarbon exploration. The reservoir has experienced complex diagenesis; however, the porosity evolution and the influence of different diagenesis events on reservoir densification remains unclear. In this study, various analytical methods was first used to clarify the diagenetic stage and sequence, establish a porosity evolution model, quantitatively analyze the time and influence of different diagenesis events on reservoir densification, and illustrate the densification mechanism of tight sandstone reservoir in the Lenghu area. The results showed that the dominant rock types in the LJR were feldspathic litharenite, followed by litharenite, lithic arkose, and a small amount of subarkose and sublitharenite. The reservoir is a typical tight sandstone reservoir (TSR), with average porosity and permeability of 5.5% and 0.08 mD, respectively. The pore types were primarily secondary pores, followed by residual intergranular pores and occasional fractures. Diagenesis of LJR has entered the meso-diagenetic stage A, with minor progression into meso-diagenetic stage B. Quantitative calculation showed that the initial porosity of LJR is 32.2%. In eo-diagenetic stage A, compaction is the main factor for porosity reduction. In eo-diagenetic stage B, the porosity loss rates caused by compaction and cementation were 81.5% and 11.8%, respectively. In this stage, the LJR in the Lenghu area has almost been densified, mainly affected by compaction, calcite cementation and clay minerals cementation. Additionally, cementation is an important factor causing reservoir heterogeneity and is dominated by calcite and clay mineral cementation. After entering the meso-diagenetic stage A, dissolution is the main diagenesis event, which can increase porosity by 6.0%. This stage is the critical period for forming high-quality reservoir of LJR in the Lenghu area, mainly in the 4,400 m depth. In meso-diagenetic stage B, the influence of dissolution gradually decreased. Simultaneously, in this stage, the cementation of iron-bearing calcite further strengthened the densification of the LJR in the Lenghu area.

Diagenetic albitization has been observed in sedimentary basins around the world. This process significantly changes the original composition of sandstones and the chemistry of the formation waters under the influence of partial pressure of CO2. The transformation of detrital feldspars into albite is considered a crucial diagenetic process in the Gulf Coast and North Sea reservoirs. Earlier studies suggest that plagioclase albitization typically happens before that of K-feldspar. In the Gulf Coast's Frio Sandstone, located in the Upper Oligocene at depths between 900 and 2400 m, detrital plagioclase is often dissolved and replaced by albite, while K-feldspar mostly dissolves without much substitution. Similarly, in the North Sea reservoirs, especially in the upper section of the Upper Triassic Lunde Formation at depths beyond 2900 m, plagioclase tends to undergo albitization, whereas K-feldspar remains largely unaffected or experiences minimal transformation. This research focuses on analyzing the differences in the albitization patterns of detrital and K-feldspar plagioclase through the KINDISP and Geochemist's Workbench (GWB) geochemical modeling tools, aiming to compare them. These diagenetic processes are crucial for reservoir geology, as they influence the concentration of silica in water, which, in turn, affects quartz cementation. This study aims to explore the variations in the albitization behavior of detrital and K-feldspar plagioclase using the KINDISP and Geochemist's Workbench (GWB) geochemical models and conduct a comparative analysis between them. Understanding these diagenetic reactions becomes relevant for reservoir geology analysis, as such phenomena control the aqueous silica concentration to some extent, which is consequently reflected in the quartz cementation. The dissolution of plagioclase and K-feldspar releases silica into the pore fluids. As the concentration of silica in the fluid increases, it leads to the precipitation of quartz as overgrowths on detrital quartz grains, a process known as quartz cementation. This was observed particularly in simulations involving temperature increases up to 150 °C, where the equilibrium between albite and anorthite was closely linked to the stability of quartz (Ben et al., 1993). The removal of feldspar through albitization reduces porosity and permeability but contributes silica to the system, which promotes quartz cementation. This, in turn, decreases the reservoir quality by filling pore spaces with secondary quartz, reducing the rock's ability to store and transmit fluids. Thus, the study highlights the importance of these diagenetic processes in reservoir evaluation, as the balance between feldspar dissolution and quartz cementation ultimately controls reservoir properties.

The upper Paleozoic gas reservoir in the Daniudi gas field, Ordos Basin, is one of the typical tight sandstone gas reservoirs in China. Research into the sequential order of reservoir densification and gas accumulation is the key to revealing the formation mechanism of tight sandstone gas reservoirs. However, this scientific issue is still a subject of debate in the Daniudi gas field. Based on a series of reservoir experiments and in combination with stratigraphic burial and thermal maturity history, a comprehensive study is conducted on the formation and natural gas accumulation processes of the upper Paleozoic sandstone reservoir in the Daniudi gas field. Study results indicate that the main causes of sandstone reservoir densification of the study area include long-term compaction, multistage quartz cementation and carbonate cementation. In accordance with the time order of reservoir densification and gas accumulation, the formation of tight gas reservoirs can be divided into two types: self-sourced and near-source accumulations. In the former, before sandstone reservoir densification occurs, low-maturity natural gas generated from coal rocks and dark mudstones enter the reservoir quickly, migrate towards structural highs as driven by buoyancy, and then accumulate and form gas reservoir in favourable lithologic traps. In the latter, after tight sandstone reservoirs are formed, high-maturity gas migrates along fractures formed in the Late Cretaceous and accumulate in the nearby reservoir with micro-fractures. The study results provide a new understanding of the formation process of tight sandstone gas reservoirs and provides a reference for the exploration and development of the same type gas reservoirs.

Petrographical characterization and field observations were caried out to evaluate Kamlial Formation in Bagh district, Azad Jammu and Kashmir. Based on detailed petrography, the lithic arenite consisted of quartz (20–25%), feldspar (7–11%), rock fragments (20–37%), cementing materials (11–21%), and accessory minerals. Grains are mostly angular to subrounded and poorly to moderately sorted. The analysis revealed that the lithic arenite is mineralogically immature; also, the current activity during the time of deposition was low. Polycrystalline quartz indicates that the sandstone was derived from metamorphic source, while monocrystalline quartz indicates a granitic origin. Quartz having an angular shape suggests the source rock was near the depositional site, while quartz having a rounded shape represents long transportation. The presence of feldspar in the lithic arenite suggests the rocks were deposited at high relief or cold temperatures. Primary porosity in sandstone was reduced by calcite cements around the grain, while secondary porosity was developed by fracturing of quartz and feldspar. Tectonic uplift in the study area was demonstrated by fractured quartz and mica in thin sections. Field observations of various sedimentary structures were observed such as load casts, ripple marks, and mud cracks, etc. The presence of conglomerates and load casts in the study area indicates that the Kamlial sandstone was deposited by fluvial and shallow marine environment. Furthermore, the ripple marks indicate that the tidal flat environment controlled the deposition of the sediments.

Petrographic and diagenetic analysis of the Middle-Upper Jurassic successions (Sargelu, Naokelekan, and Barsarin) formations and boundaries between them in the Sargelu area, Kurdistan region, N.E. Iraq was conducted based on the lithologic description, thin section analysis, and scanning electron microscopy. The study aims to define the petrographic components and diagenetic processes that affect the carbonate rocks of Jurassic succession in the studied section. Thirty-eight thin sections have been prepared, with five samples selected using the S.E.M. technique to reveal the petrographic components and diagenetic processes. The Jurassic succession is composed mainly of carbonates (limestone and dolostone) interbedded with shale units. Petrographically, the Sargelu, Naokelekan, and Barsarin formations are composed of skeletal grains (pelagic pelecypods, radiolaria, calcispheres, planktonic and benthonic foraminifera such as miliolid, ostracods, bioclasts, and stromatolites) which are the most common, in addition, non-skeletal grains such as poloids, micritic groundmass, and recrystallized micro spars, Many diagenetic processes affected the studied carbonate rocks such as micritization, dolomitization compaction and stylolite formation, authigenic minerals (pyrite), cementation, neomorphism, dissolution and porosity formation as represented by moldic, vuggy, channel and fracture porosity.

The presence of authigenic Na-feldspars in sedimentary carbonate rocks is unusual and its origin is controversial in terms of genesis and timing. The use of optical microscopy, cathodoluminescence and in situ semi-quantitative EDX analysis techniques, has allowed the identification and characterization of authigenic albite crystals in the Mesozoic pre- and syn-rift carbonates of the northwestern margin of the Bortziriak-Cinco Villas Massif, in the northeastern Basque-Cantabrian Basin (western Pyrenees). The euhedral habit, crystal size, spatial distribution and crosscutting relationships, together with the pure albitic composition, suggest a relatively early replacement origin. Compaction of sediments during burial, besides possible fluid migration linked to the intense syn-rift halokinetic activity, may have been decisive for the mobilisation of cations, and hence, for the albitization of the carbonate rocks.

The foreland Claromecó Basin, located in the south-western sector of Buenos Aires province, Argentina, has a relevant economic and energetic interest due to the presence of coal layers contained in the Permian Tunas Formation, which might be considered effective source rock for gas resource generation. This study aims to reconstruct the diagenetic evolution of the Tunas Formation at the Claromecó Basin (PANG 0001 and PANG 0003 wells) and determine how the diagenesis affected the reservoir quality. To this purpose, core samples of the Tunas Formation were analysed using a combination of micro petrographic analyses (transmitted light, QEMSCAN, cathodoluminescence), fluid inclusions studies, and petrophysical methods (conventional core analysis, CCA). The analysed sedimentary successions are composed of sandstones interbedded with mudrocks, carbonaceous mudrocks, tuffs, and coals. Sandstones are medium- to fine-grained, framework-supported, and moderate-to-well-sorted. Authigenic minerals are calcite and laumontite, with minor proportions of quartz and feldspar overgrowths and clay minerals (illite, muscovite, and chlorite). Porosity is of secondary type, generated by fracturing and dissolution of feldspars and carbonate cement. Porosity determined by optical, QEMSCAN, and CCA analyses ranges from 0.1 to 4 %, with a permeability varying between 10-3 and 10-6 millidarcies. Fluid inclusion studies were performed in sandstone cements and calcite and quartz veins. Primary, pseudo-secondary, and secondary aqueous and organic fluid inclusions were recognized. Organic fluid inclusions show green and light blue fluorescence, which indicates the presence of hydrocarbons. Homogenization temperatures of fluid inclusions obtained from microthermometry studies range from 124 to 200 °C in cements and 110 to 230 °C in veins. These temperatures confirm a metagenesis stage for the Tunas Formation, within the wet to dry gas window. Given the petrophysical characteristics of the analyzed levels, sandstones could be considered unconventional tight gas sandstone reservoirs. Obtained results point out that during early diagenesis, physical compaction and precipitation of carbonate cement are the principal factors that significantly reduce the primary porosity. Furthermore, in the mesogenesis stage, chemical compaction, calcite and zeolite cements precipitation, and quartz overgrowths further contribute to porosity loss. However, secondary porosity was produced during mesogenesis due to the dissolution of unstable grains and calcite cements caused by the action of acid fluids generated during the decomposition and maturity of organic matter. Additionally, secondary porosity was also generated by fracturing due to burial and tectonic stress and by the increased pore pressure during hydrocarbon generation and migration. The reservoir properties of the Claromecó Basin have been controlled mainly by diagenetic and tectonic processes that acted during the burial history of the basin. Clasts and cements composition also influenced diagenesis together with the presence of organic-rich rocks, which could generate hydrocarbons.

Pyrotechnological activities leave many traces in the archaeological record, most notably ash, which is the powdery residue of the combustion of organics such as wood. These traces have provided important insights into the biological and cultural evolution of humans. Given the common occurrence of ash layers at archaeological sites, the charred remains embedded within these features have been regularly targeted for radiocarbon dating. However, often charcoal does not preserve in sediments, and only the mineral fraction of ash is left. The latter is composed of calcium carbonate derived from the thermal decomposition of calcium oxalates produced by the plants used as fuel, and in principle can be dated using radiocarbon. Past attempts have shown that pyrogenic calcium carbonate in the form of calcite does not always preserve the radiocarbon content of the original plant, and that it is prone to recrystallization. Recently, pyrogenic aragonite (a metastable polymorph of calcium carbonate) in archaeological ash has produced accurate radiocarbon age determinations because its crystals did not recrystallize over time. In this paper, we report on the radiocarbon dating of an ash layer rich in aragonite identified at Tell es-Safi/Gath (Israel). Using a combination of infrared spectroscopy and micro-spectroscopy, X-ray diffraction, scanning electron microscopy, phytolith analysis, micromorphology, and radiocarbon dating, we reconstructed the formation processes of the combustion feature and showed that most of the pyrogenic aragonite crystals in the ash layer exchanged carbon with the environment, and thus cannot be considered a closed system suitable for dating. Therefore, we proposed an improved extraction method to isolate the smallest crystals of pyrogenic aragonite and calcite, which are more likely to keep their original isotopic composition based on independent age controls from the same depositional context. [ABSTRACT FROM AUTHOR]

Diagenesis and pore structure are essential factors for reservoir evaluation. marine-continental transitional facies shale is a new shale gas reservoir of concern in the Sichuan Basin. The research on its diagenesis pore evolution model has important guiding significance in its later exploration and development. However, the current research on pore structure changes, diagenesis, and the evolution of marine-continental transitional facies shale is not sufficient and systematic. In order to reveal the internal relationship between pore structure changes and diagenesis, the evolution of marine-continental transitional facies shale was tested by X-ray diffraction, field emission scanning electron microscopy, low-pressure gas adsorption, nuclear magnetic resonance, and the diagenetic evolution sequence and nanopore system evolution of Longtan Formation shale was systematically studied. The results show that the Longtan Formation shale underwent short-term shallow after sedimentation, followed by long-term deep burial. The main diagenetic mechanisms of the Longtan Formation shale include compaction, dissolution, cementation, thermal maturation of organic matter, and transformation of clay minerals, which are generally in the middle-late diagenetic stage. The pore structure undergoes significant changes with increasing maturity, with the pore volumes of both micropores and mesopores reaching their minimum values at Ro = 1.43% and subsequently increasing. The change process of a specific surface area is similar to that of pore volumes. Finally, the diagenetic pore evolution model of Longtan Formation MCFS in Southeastern Sichuan was established. [ABSTRACT FROM AUTHOR]

Over the lifetime of an animal, metabolic processes in the body maintain bone tissues in a dynamic state of equilibrium. After the death of the organism, bone tissues undergo diagenesis, an intense transformation that affects its physicochemical constitution. Although many recent works have greatly contributed to the understanding of the processes surrounding diagenesis, there is still much yet to be understood about this multifaceted phenomena. In this work, XRF and microCT were used to characterize the specimen elemental configuration and investigate the fossilization process of a recovered Puma concolor (cranium, mandible and teeth elements), found submerged in a lake in the Impossível‐Ioiô Cave System (Bahia, Brazil). MicroCT enabled the identification of the density distribution throughout the specimens, which were used as reference to XRF analyses. The XRF spectra of the analyzed specimen showed the presence of 11 elements: P, Cl, Ca, Mn, Fe, Cu, Zn, Br, Sr, Y and Hg. Yttrium counts proved to be regular throughout the specimen surface and decreased in the interface between bone surface and interior, evidencing their correspondence to sample environmental exposure. Furthermore, a correlation between fossil surface coloration, element configuration and density is presented. The relatively low presence of Fe and Y in the enamel elicits its elementary and structural preservation. The combined results contribute to the understanding of the physicochemical process of paleomastozoological fossilization, further enriching the comprehension of the process of fossilization in a submerged environment. [ABSTRACT FROM AUTHOR]

On the basis of the observation of rock cores and cuttings, combining the information from thin section identification, physical properties analysis, scanning electron microscopy, X-ray diffraction, etc., the characteristics and controlling factors of the tight reservoir in the Permian Lucaogou Formation of the Yongfeng sub-sag of the Chaiwopu sag have been studied. Based on the analysis, the Lucaogou Formation in the study area can be divided into two lithological sections. The tight sandstone reservoir, characterized by low porosity and low permeability, is mainly developed in the upper section of the Lucaogou Formation. The lithology of the tight reservoirs is mainly lithic sandstone with low compositional and structural maturity. The reservoir space types mainly consist of secondary pores, including intergranular dissolution pores, intragranular dissolution pores and fractures, and the primary pores are severely destroyed. The main controlling factors of reservoirs include sedimentary facies, lithology, diagenesis, later tectonic movements and fractures, and the latter two factors have a significant impact on improving reservoir physical properties and seepage capacity. The tight reservoir has high brittleness and low water sensitivity, which is very conducive to large-scale hydraulic fracturing to transform the reservoir and improve oil and gas production capacity. [ABSTRACT FROM AUTHOR]

The West and Central African Rift System (WCARS) hosts all the sedimentary basins of West and Central Africa, and constitutes a priority target for sedimentological studies in the area. Numerous basins in this area, notably the Koum Basin, remain poorly known greenfields, owing to a dearth of studies associated with poor accessibility, security limitations, and accrued exploration focus on hydrocarbon-producing oceanic basins in the area. The present study seeks to reduce the knowledge gap by providing new data on the diagenesis, petroleum system, and paleoenvironments of the Koum Basin. NNW–SSE traverse mapping across the basin aided in the identification of conglomerates, sandstones, and shales/mudstones, hosting dinosaur tracks, plant matter and are intercalated by siltstones and bivalve-rich carbonates. Lithofacies analyses, petrography, scanning electron microscopy, and X-ray diffractometry were applied. The studied facies form three facies associations reflecting fluvio-lacustrine paleoenvironments. Petrography exposed concavo-convex to sutured mineral margins, presenting silicate overgrowths plus calcite, silica, hematite, and clay cements. Albite, quartz, calcite, and microcline dominate bulk mineralogy, with analcime, goethite, and hematite as minors, while chlorite-smectite, illite, and smectite dominate clay mineralogy, all pointing to the pre-eminence of mesodiagenesis within the Koum Basin. Studied shales and siltstones present traces of oil/oil migration paths in organic pores, whereas sandstones and carbonates are devoid of mature organic matter and interconnected porosity. Consequently, a source-rock petroleum system with shales and siltstones playing the dual roles of hydrocarbon source and reservoir is inferred for this basin that can be considered a potential unconventional hydrocarbon reserve. [ABSTRACT FROM AUTHOR]