Carbonate Cements Research Articles

The secondary pore development model of coarse-grained deposition: A case study of the Xiazijie Formation in the Northwestern Margin of the Junggar Basin

The coarse-grained glutenite rock mass of the proximal fan delta is characterized by the blocky texture, mixing of gravels with varied sizes, high mud content, and low porosity and permeability, leading to difficulties in assessment and exploration of oil and gas enrichment regularities of tight glutenite. The Permian Xiazijie Formation in the northwest margin of Junggar Basin has a set of tight glutenite reservoirs, and the reservoir quality is an important controlling factor for oil and gas enrichment. Based on three-dimensional earthquake, casting thin sections, rock physical property, geochemistry, the sedimentary facies division, petrologic features, physical property regularities, pore types and diagenesis of Xiazijie Formation were analyzed. This research develops the pore evolution model of the coarse-grained deposition via the quantitative analysis of porosity evolution. First, during the rapid compaction, intensive mechanical compaction results in reduction of the original porosity from 29.8% to 15.1%. Secondly, the cement formed during the eodiagenesis destructs the reservoir space and leads to an average porosity loss of 6.5%. Third, dissolution effectively improves reservoir quality. It mainly dissolves the zeolite cement, and the porosity grows to 12.1% from 8.6%. The dissolution occurs during the main hydrocarbon expulsion stage of the source rock, which is in favor of hydrocarbon emplacement. Fourth, during the telodiagenesis with the deepening burial and intensifying pressure solution, siliceous and carbonate cement precipitate, the reservoir physical property is degraded again, the porosity loss is about 3.4%. After a series of complex diagenetic processes, the current tight glutenite reservoir comes into being, with the porosity of about 8.7%. The research results provide theoretical reference for coarse-grained glutenite reservoir prediction.

Study on influencing factors and mechanism of pore compressibility of tight sandstone reservoir—A case study of upper carboniferous in ordos basin

A series of studies were carried out on 11 tight sandstone samples of Upper Carboniferous in Ordos Basin. Firstly, the deposit composition and pore structure characteristics are investigated based on analysis and experiments including cast thin section scanning electron microscope high-pressure mercury intrusion and nuclear magnetic resonance Then, combined with DP-P test, the stress-dependent permeability change and pore compressibility characteristics of sandstone reservoirs were studied to reveal the influencing factors and mechanism of reservoir pore compressibility. The detrital particles of the sandstone reservoir in the study area are mainly quartz (75.8%–89%), followed by fragments (3%–16.1%), and almost no feldspar. The content of interstitial materials is 6.5%–11.2%. The type I reservoirs mainly consist of mesopores and macropores, accounting for 60.57% and 32.84% respectively. Mesopores are dominated in Type II reservoirs, accounting for 78.98% of the total pore volume. There are almost no macropores, while a similar proportion of mesopores, micro mesopores and micropores in the type Ⅲ reservoirs. The study of pore compressibility shows that the pore compressibility coefficient decreases with the increase of effective stress, and the reduction rate shows the two-stage characteristics of rapid in the early stage and slow in the later stage. The pressure turning point is between 3 and 10 MPa. The average pore compressibility coefficient increases from type I to type Ⅲ reservoirs. The compressibility coefficient is directly proportional to the changing rate of the pore volume. The higher the content of rigid detrital particles, quartz and carbonate cement in sandstone, the smaller the pore compressibility coefficient, while the higher the content of ductile components such as soft rock fragments and clay minerals, the greater the pore compression coefficient. The pore-throat structure is closely related to the pore compressibility, reservoirs with low displacement pressure, T2glm value, and large average pore-throat radius show lower compressibility coefficient. In addition, the compressibility coefficient of the reservoir is positively correlated with DL (dimension of large pores such as mesopores and macropores), and negatively correlated with DS (the fractal dimension of micropores and micro mesopores). It is considered the pore compression of sandstone including two stages, viscoplastic destructive deformation of ductile components for the first and then the small-scale non-ideal elastic deformation on rigid particles.

Coupling Relationship between Diagenesis and Hydrocarbon Charging in Middle Permian–Lower Triassic in the Eastern Slope of Mahu Sag in Junggar Basin, Northwest China

In this study, a variety of test and analysis methods, such as cast thin sections, fluorescent thin sections, scanning electron microscopy, fluid inclusions, etc., were comprehensively used and combined with logging data, sedimentary systems, burial history and other research results, to systematically study the diagenesis characteristics of Middle Permian Lower Wuerhe formation–Lower Triassic Baikouquan formation reservoirs and their control on hydrocarbon accumulation. The coupling relationship between the hydrocarbon accumulation process and reservoir secondary pores was established. The result shows that besides the development of primary intergranular pores, the reservoir develops secondary pores, such as particle dissolution pores, cement dissolution pores and fractures. The development of secondary dissolution pores, such as particle dissolution pores, carbonate and zeolite cement dissolution pores, is mainly controlled by the range and scale of organic acids produced by the thermal evolution of source rocks. It is considered that being located in the updip direction of source rocks, being involved in the development of the unconformity surface and the faults connecting source rocks, and being involved in the development of alkaline cements (such as laumontite) are the three dominant conditions for the development of secondary dissolution pores in the study area.

Mid-Norian to Hettangian record and time-specific oolites during the end-Triassic Mass Extinction at Wadi Milaha, Musandam Peninsula, United Arab Emirates

The end-Triassic Mass Extinction (ETME) is generally regarded as a consequence of the environmental changes associated with the emplacement of the Central Atlantic Magmatic Province (CAMP) and ranks among the ‘big five’ mass extinctions in Earth history. A notable feature of the ETME is a halt in marine carbonate deposition followed by the formation of unusual facies such as carbonate cement fans and oolites in the early aftermath of the event. The ETME time interval has been well studied over the last few decades, in contrast to a few minor extinction events that preceded it, among them the extinctions associated with the Norian-Rhaetian boundary (NRB). This study provides new insights into these extinction events with complete mid-Norian to Hettangian δ18Ocarb and δ13Ccarb record from a key section at Wadi Milaha (Ras Al Khaimah Emirate, United Arab Emirates). Ooids are important proxies for palaeoenvironmental reconstruction. The post ETME oolite horizon is documented providing morphological classification as well as a detailed modal analysis of rock components and different types of coated grains. Through a multi-technique approach, we argue for the stability of the carbon cycle across the NRB extinction event and the existence of a hiatus at the TJB (Triassic-Jurassic Boundary) in Wadi Milaha. Our new morphological classification of post-extinction ooids is compatible with a major role for seawater geochemistry with respect to sedimentological processes, by example in the peculiar way ooids diversify and alternate with other kinds of coated grains.

Towards a Mineral Systems Model for Surficial Uranium Mineralization Based on Deposits in the Erongo District of Namibia

Surficial deposits in Namibia’s Erongo district contain substantial but low-grade resources of uranium and vanadium (nearly 500 Mlb U3O8), hosted in palaeochannels. This review attempts to develop a mineral systems model for the deposit type, but it is emphasised that research into this important class of deposit has been minimal since the nineteen eighties, largely as a result of a limited investment in uranium exploration. The deposits are the result of groundwater movement in aquifers developed within Cenozoic palaeochannels. The source of uranium was probably granitic rocks traversed by these palaeodrainages, particularly black-quartz rich pegmatites similar to those that make up the hard-rock alaskite deposits of the region. Transport of uranium is generally assumed to have occurred in aqueous uranium species after palaeochannels became filled with sediment. U-enriched clasts within the palaeochannels have yet to be investigated as a local source of uranium. The localised deposition of uranium occurred after regionally extensive carbonate cementation of the palaeochannel sediments, which was the result of climate change (aridification). Pre-uranium calcite may have acted as a chemical buffer (pH) and probably influenced palaeochannel hydrology, restricting groundwater flow to the deeper portions. Uranium is paragenetically related to Mg clays and dolomite, suggesting that the groundwater evolved to a more Mg-rich composition during uranium deposition, probably as a result of more extreme evaporation. The controls on the localisation of mineralisation remain unclear and unpredictable, as are the controls on uranium grade—the fundamental determinant of economic viability. There are few absolute age determinations for any of the deposits, but none occur in rocks likely to be older than the Miocene. This reflects low preservation potential. For example, the Langer Heinrich deposit is incised by active drainage with attendant erosion and probable removal of mineralised material.

Diagenetic Facies Controls on Differential Reservoir-Forming Patterns of Mixed Shale Oil Sequences in the Saline Lacustrine Basin

The Permian Lucaogou Formation has developed mixed shale reservoirs, but there are few studies on the diagenetic facies, and the control effect of differential diagenesis on the reservoir capacity of shale oil reservoirs in this area is not clear. Therefore, shale samples of the Lucaogou Formation were systematically selected in this study, and through cast thin sections, field emission scanning electron microscopy, XRD mineral analysis, low-temperature nitrogen adsorption and high-pressure mercury injection experiments, the reservoir capacity of the shale oil reservoirs was evaluated from the perspective of diagenetic evolution. The results show that the shale oil reservoir of the Lucaogou Formation in Jimsar Sag is in the middle diagenetic stage A. The diagenetic evolution sequence is compaction—chlorite cementation—silica cementation—first-stage carbonate cementation—first-stage dissolution of authentic albite—illite/smectite mixed layer cementation—second-stage carbonate cementation—second-stage dissolution. The shale reservoirs are divided into five diagenetic facies: tuffaceous–feldspar dissolution facies, mixed cementation dissolution facies, chlorite thin-membrane facies, carbonate cementation facies and mixed cementation compact facies. Among them, the former two diagenetic facies have strong dissolution and weak cementation and are high-quality diagenetic facies, mainly characterized by large pore volume and good pore connectivity, with relatively low D2 values defined as the fractal dimension of mesopores. On the basis of the above research, three different control models of Lucaogou Formation shale oil reservoirs are proposed, including dissolution to increase pores, chlorite cementation to preserve pores, and strong compaction cementation to reduce pores. The quality of reservoirs developed in this model is successively high, medium, and low. This work can provide guidance for the fine characterization and grading evaluation of mixed shale oil reservoirs in saline lake basins and has important theoretical and practical significance for the prediction of shale oil “sweet spot” distribution.

Alternating acid and alkaline diagenesis in the Shahejie Formation of E12 structure in the Laizhou Bay Sag, Bohai Bay Basin

The high-quality reservoirs in the Shahejie Formation of the Laizhou Bay Sag, Bohai Bay Basin, Eastern China formed in the Paleogene saline lacustrine environment and show complex diagenetic evolutionary processes caused by alternating acid and alkaline fluids. Through observations under an optical microscope and a scanning electron microscope, casting thin sections, and plane porosity measurements, this study investigated the diagenesis differences in the third member of the Shahejie Formation (Es3 Member) in the root and central portions of a fan delta in the E12 structure in the eastern Laizhou Bay Sag, respectively. The Es3 reservoirs in the well A-1 which have no any hydrocarbon shows, are relatively tight, and have high argillaceous content, poor particle sorting, strong mechanical compaction, and intense carbonate cementation due to long-term activities of alkaline fluids. Moreover, they were not altered by organic acid due to the far lateral distance from source rocks. By contrast, the Es3 reservoirs in the well A-2 with hydrocarbon accumulations, contain an anomalously high porosity zone due to the superimposition of five episodes of alternate acid-alkaline fluids. The diagenetic fluids controlling the formation of the high-quality Es3 reservoirs are sourced from connate saline pore waters, gypsum dehydration, salt diapir, and organic acid. Moreover, chlorite coats in the reservoirs in the well A-2 inhibit secondary overgrowth of quartz and, thus, protect primary pores. The chlorite coats and alkaline-acid dissolution alterations are critical to the formation of the high-quality reservoirs in well A-2.

Super plasticizer assisted bath ultra sonication for dispersion of multi walled carbon nanotubes in cement composites

This paper presents the observations and findings from an experimental study for dispersion of multiwalled carbon nanotubes (MWCNTs) by bath ultra-sonication in the presence of polycarboxylate ether (PCE) based superplasticizer. Commercial brand of superplasticizer (SP) compatible with cement was adopted for exploring its usage as surfactant during aqueous dispersion of MWCNTs. Cement composite pastes were evaluated for variation in compressive strength and fresh property for a fixed addition percentage of MWCNT. Aqueous dispersion of MWCNTs for incorporation to cement pastes was prepared considering three different sonication process variables; time period of sonication, SP to MWCNT dosage during sonication and temperature of sonication medium. A total of 168 experimental variations were evaluated for compressive strength of resulting cement–carbon nanotubes composite pastes at 7 days age to arrive at an optimal process of bath ultra-sonication with governing variables. Results showed that a sonication time period in the range of 4–5 hours with an SP to MWCNT ratio of 2.5–3 was necessary for satisfactory dispersion of MWCNTs over different temperature ranges of sonication bath medium. Further, the temperature of sonication medium in the range of 35–40°C during aqueous dispersion of MWCNTs was observed to induce noticeable enhancement in strength of composite system indicating improvement in dispersion within an optimal range of sonication medium temperature. Microscopic observations for optimal process variables of dispersion during bath ultra sonication showed evidence of physical changes in MWCNTs from an agglomerated state of particles to separated state.

Chlorite characterization and diagenetic evolution as primary controls on Zhuhai Formation sandstone reservoir quality in Zhu-III sag, Pearl River Mouth Basin, south China sea

Zhu-Ⅲ sag in the Pearl River Mouth Basin is rich in hydrocarbon resources. The Oligocene Zhuhai Formation is a key exploration horizon in Zhu-Ⅲ sag. However, the exploration results show that the reservoir is deeply buried, the diagenesis is complex and the reservoir heterogeneity is strong. Therefore, looking for high-quality reservoirs, which are the zones with relatively high porosity and permeability, is a key point of resource exploration. Based on the previous research results, this study analyzed the reservoir characteristics and diagenesis characteristics, established the pore evolution model of the study area, and defined the main controlling factors of reservoir development and used core observation, thin section, scanning electron microscope, X-ray diffraction and so on. The research shows that compaction is the main reason for the reservoir densification of Zhuhai Formation. Chlorite in Zhu-III sag consists of two occurrence states and characteristics. These two kinds of chlorite have a great influence on reservoir quality in three key zones. Pore-lining chlorite can effectively improve the reservoir quality. Another is chlorite cement which can destroy the pore structure. Meanwhile, fluid-controlled carbonate cement also has an obvious effect on the reservoirs in key zones. Fluid in early stage leads to the formation of carbonate cement and that in late stage leads to the dissolution of carbonate cement. In general, we clarify the diagenesis and pore evolution in key zones in Zhu-Ⅲ sag and its reservoir is mainly affected by compaction, dissolution, chlorite and hydrocarbon charging. This study of reservoir diagenetic evolution process and pore characteristics is crucial and helpful in the exploration and development of reservoir in Pearl River Mouth Basin and other basin.

Post-depositional history of the lower Palaeocene interval using petrographic, CL and geochemical data in the East Tethys: Kopet-Dagh Basin, northeast Iran

AbstractThis study investigates the Danian siliciclastic successions in the East Tethys in the Kopet-Dagh Basin, NE Iran, which are composed of conglomerates, sandstones, shales and mudstones. The studied interval includes significant changes in sedimentary environments from alluvial to fluvial systems. The Danian siliciclastic formation is sandwiched between two marine carbonate sequences. The effects of the late Palaeocene sea transgression can be traced back to the precipitation of several types of carbonate cement in the studied siliciclastic formation. Several diagenetic features have been identified in the studied successions. The most observed features comprise physical and chemical compaction, cementation, alteration, dissolution, fractures and fillings. Some of the mentioned diagenetic processes, such as cementation, may be seen in a range of diagenetic environments and phases, such as early meteoric, low depth and deep burial, and late meteoric after the tectonic uplifting. The calcite cements considered in this study have been subdivided into four types. Some of the calcite cements, such as the rim, gravity pendant and meniscus, are classified as type one. They have formed around the rock grains and show no luminescence. The blocky and poikilotopic types have been grouped in type two. They are deposited between grains and exhibit dark luminescence. Type three cement consists of some of the blocky and poikilotopic cements that have formed amid grains and present a bright luminescence. Finally, type four comprises filled fractures which display a dark luminescence (blocky cement). Geochemical data revealed that the categorized cement types were precipitated in three diagenetic environments: early meteoric; burial; and late meteoric after the uplifting. The meteoric diagenetic environment is subdivided into vadose and phreatic meteoric. The burial diagenetic environment is subdivided into shallow burial and deeper burial. The qualitative petrographic method contributed to the initial recognition of the diagenetic features. The semi-quantitative cathodoluminescence method, the quantitative major and trace elements, and oxygen and carbon stable isotope analysis were utilized to evaluate the exact diagenetic processes and environments. Finally, the diagenetic sequence was reconstructed and depicted as diagenetic models and a paragenesis sequence. The data of this study can lay the foundation for future studies on the siliciclastic diagenesis in the studied basin.

A Review of Self-Sensing in Carbon Fiber Structural Composite Materials

Sensing is a basic ability of smart structures. Self-sensing involves the structural material sensing itself. No device incorporation is needed, thus resulting in cost reduction, durability enhancement, sensing volume increase and absence of mechanical property diminution. Carbon fiber renders electrical conductivity to a composite material. The effect of strain/damage on the electrical conductivity enables self-sensing. This review addresses self-sensing in structural composite materials that contain carbon fiber reinforcement. The composites include polymer-matrix composites with continuous carbon fiber reinforcement (relevant to aircraft and other lightweight structures) and cement–matrix composites with short carbon fiber reinforcement (relevant to the civil infrastructure). The sensing mechanisms differ for these two types of composite materials, due to the difference in structures, which affects the electrical and electromechanical behaviors. For the polymer–matrix composites with continuous carbon fiber reinforcement, the longitudinal resistivity in the fiber direction decreases upon uniaxial tension, due to the fiber residual compressive stress reduction, while the through-thickness resistivity increases, due to the fiber waviness reduction; upon flexure, the tension surface resistance increases, because of the reduction in the current penetration from the surface, while the compression surface resistance decreases. These strain effects are reversible. The through-thickness resistance, oblique resistance and interlaminar interfacial resistivity increase irreversibly upon fiber fracture, delamination or subtle irreversible change in the microstructure. For the cement–matrix composites with short carbon fiber reinforcement, the resistivity increases upon tension, due to the fiber–matrix interface weakening, and decreases upon compression; upon flexure, the tension surface resistance increases, while the compression surface resistance decreases. Strain and damage cause reversible and irreversible resistance changes, respectively. The incorporation of carbon nanofiber or nanotube to these composites adds to the costs, while the sensing performance is improved marginally, if any. The self-sensing involves resistance or capacitance measurement. Strain and damage cause reversible and irreversible capacitance changes, respectively. The fringing electric field that bows out of the coplanar electrodes serves as a probe, with the capacitance decreased when the fringing field encounters an imperfection. For the cement-based materials, a conductive admixture is not required for capacitance-based self-sensing.

FUNDAMENTAL STUDY ON CO<sub>2</sub> MINERALIZATION TECHNOLOGY FOR CONCRETE USING CEMENT SLURY

For the purpose of fixing CO2 to concrete, a method for manufacturing concrete using carbonated cement slurry was examined. In the process of injecting CO2 into the cement slurry, more than 90% of the injected CO2 is fixed as fine calcium carbonate particles. Concrete using carbonated cement slurry did not cause a decrease in fluidity due to two-stage mixing method and showed the same level of strength development and durability as blanks. The amount of CO2 in concrete exceeded 20 kg per ton of cement. In addition, it was possible to manufacture concrete with CO2 fixed in the actual plant.

A indústria do cimento de acordo com os Objetivos de Desenvolvimento Sustentável da ONU através da tecnologia das sementes C-S-H - Uma análise crítica

The United Nations (UN) has stablished several goals and actions in order to mitigate climate change and reduce its consequences. As one of the main responsible of global anthropogenic carbon emissions, cement industry has a great potential on collaboration to achieve such goal. New solutions are studied to decrease the environmental impact caused by cement production. Clinker content replacement by Supplementary Cementitious Materials (SCM) is indicated as the more feasible one. Despite the environmental benefit offered by the action, the composition modification of the binder leads to initial performance issues. Cementitious materials with lower clinker content and presence of SCM presents higher setting time and lower early strength, which limits the application of the measure regardless of its environment advantage. The use of C-S-H (calcium silicate hydrate) seeds additive can overcome such effect, since it accelerates cement hydration, improving its initial performance. Therefore, such additional input enables the vaster application of low carbon cements. Nonetheless, the manufacture of C-S-H seeds also emits greenhouse gases with environmental impacts comparable to cement production. Hence, the objective of this study is to analyse and discuss the contribution of the use of C-S-H seeds on the potential carbon footprint reduction of cementitious materials and if this measure could help to achieve the goals stablished by the UN. The reviewed papers pointed the additive as a feasible solution to low carbon cements production which allays technical and environmental requirements. Therefore, it was concluded that C-S-H seeds can effectively contribute to achieve the UN stablished goals towards climate change mitigation.

Літогенез верхньоюрських відкладів Зовнішньої зони Передкарпатського прогину

Geological- and biological-paleogeographical conditions of sedimentogenesis within the Carpathian segment of Tethys ocean during Tithonian were considered. The rock-forming organisms with calcic function (flora and fauna), which compose main lithological types of carbonate rocks were identified. On the base of biological-paleoceanographical and lithological investigation of different genetic types of Upper Jurassic carbonate rocks of the Outer zone of the Carpathian Foredeep and analysis of literature data on modern carbonate sediments, the structural classification of Late Jurassis epipelagic sediments of the Carpathian segment of the Meso-Tethys was made. In that classification pelitic, aleuritic, psammitic and ruditic fractions of sediments were distingnished. Geological-paleogeographical model of occurrence of the Tithonian sediments within the Carpathian segment of the Meso-Tethys (the Outer zone of the Carpathian Foredeep) was built by the author. That model presents areals of biogenic and abiogenic epipelagic sediments and depicts their facial variations. Geological-paleogeographical study of Upper Jurassic sediment complexes of epipelagic part of the Meso-Tethys has shown that they were formed within widespread interior shelf, probably, with small inclination of the sea bottom. In Upper Jurassic there was abundant growth of the benthos with calcic function and avalanchecal sedimentation of their skeletal remains took place with forming of biogenic carbonate sediments. The coral-algae biocoenosis there were biological indicators of considered parts of Tethys region. In modern basins of the World ocean analogous processes take place at the depths of about 50 m, in temperature conditions about 23–25 °C and the salinity of the sea waters about 2.7–3.8 ‰. The manifestations of diagenetic and katagenetic processes in the Upper Jurassic carbonate rocks of Outer zone of the Carpathian Foredeep have been investigated and their influence of the formation of the reservoir properties of rocks has been found out. During the diagenesis, the rocks were recrystallized, micritizated and cemented. From the mineralogical point of view, the changes consisted in the transformation of primary aragonite and magnesium-calcite skeletal remains of organisms into calcite, as well as processes of dolomitization, ferruginization and silicification. At the stage of diagenesis, Fe-containing minerals ̶ glauconite and pyrite ̶ has been formed. The dolomitization of Jurassic organogenic limestones of Outer zone of the Carpathian Foredeep has been caused by the mixing of the fresh meteoric waters with buried marine pore waters in the underground phreatic zone adjacent to the ancient coastline. Silicification is a consequence of the metasomatic substitution of the carbonate substance by silicate, which has been caused by decrease of the pH occurred after dolomitization. Katagenetic transformation of the rocks are manifested in the dissolution of the remains of organisms, grains of carbonate cement and the late cementation of pores and microfractures. Changes of carbonate rocks are associated with the bringing of certain substances in the sediment (sulphatization, celestinization) or their removal (dedolomitization, decementation). Neoplasm minerals of the katagenesis stages are represented by anhydrite and celestine. The proceses of recrystallization of carbonate rocks at different stages of katagenesis contributed to the selective leaching of limestones and dolomites and led to formation of secondary cavities and caverns, different in shape and size. The predominance of cavities of certain types determines the type of reservoir, among which are distinguished pores, pore-caverns and joint caverns. The processes of diagenesis and katagenesis are associated with the dissolution of carbonate material, which differently affects the reservoir properties of sediments. Authigenous mineral formation, with the exception of dolomitization, impairs the reservoir properties of the Upper Jurassic carbonate rocks, and recrystallization improves. Burial of carbonate rocks at depth contributes to the preservation and even improvement of their reservoir properties both due to dissolution and textural heterogeneity (jointing develops at the boundary of the elements of textural heterogeneity). Observations show that the most favourable in this respect are organogenic and detrital varieties of carbonate rocks. The presence of clay minerals in the composition of their cement increases the textural heterogeneity and, as a consequence, the ability to formation of joints.

Facies Implication of GERCUS Formation with The Bathymetry and Tectonic Activity of Van-Pyrenean Phases in Haibat-Sultan Mountain, Iraqi Kurdistan Region

The Eocene red clastic strata are represented by molasses facies of Gercus Formation and well exposed at Haibat-Sultan Mountain . A sequence of about 88m thick of the formation is located in the middle part of the Mountain. Detailed investigations including field, petrographic investigations which are linked  between bathymetric fluctuation and depositional environment.  The sequence is generally found to be a shallowing upward facies which start from deep marine (Kolosh Formation) to continental environment passing through shallow marine. Petrographic studies revealed the presence of a high rate of terrigenous grains; the most abundant clasts are sedimentary rock fragments such as limestone and chert. There are less abundant clasts derived from igneous and metamorphic rocks like quartz, feldspar, and micain addition to  authigenic  grains of glauconite are also represented. The pore space between grains are filled by  red clay with carbonate cement. The provenance consisted mainly of  Balambo,Tanjiro,Shiranish,and Aqra Formations while the Igneous and metamorphic grains are reworked from ophiolte and metamorphic ource areas that cropped out on the Hinterland near Iraq-Iran border. Gercus Formation in this area is deposited in four  depositional environments: fluviatile environments( river environment ), alluvial fan (shore line) , delta, and shore face environments. The deposition and fluctuation  influenced by  paleo-slope and regional tectonism of Van–Pyrenean phases. The Middle Part of this Formation interfingers with the Avanah Formation (Carbonate Rocks)  which was deposited during the rising of sea level.

Paragenesis of an Ediacaran carbonate-platform phosphorite: Constraints from optical petrography and texture-specific clumped isotope paleothermometry

The Salitre Formation is comprised of several hundred meters of primarily carbonate rocks, representing sedimentation in an intracratonic foreland basin during the Ediacaran Period (c. 600–550 Ma). The lowermost member of the Salitre Formation contains sedimentary phosphorite deposits, in which the dominant phosphate-bearing phase is cryptocrystalline carbonate-rich fluorapatite (CFA) cement. These CFA cements occur exclusively associated with digitate stromatolite buildups, decimeters to meters in vertical and lateral scale, which interfinger with cross-stratified grainstone. Notably, there are also non-phosphatic stromatolite buildups in close proximity to the phosphatic, in the same depositional facies. This implies that the mechanisms that control the distribution of phosphate cement development versus carbonate cement development are not driven by the location of depositional facies within the architecture of the Salitre paleobasin. Other models which could explain the distribution and style of phosphate mineralization there include: (1) differential diagenesis involving diagenetic fluids which infiltrate one lithofacies more pervasively than another to effect the replacement of primary cement mineralogies according to microtextural differences, and (2) differences in primary porewater chemistries over minute spatial scales which result in the formation of different primary cement phases. In this study, we present paired petrographic thin sections and novel measurements of ∆47, δ13Cmineral, and δ18Omineral. We provide a paragenetic framework for phosphatic and non-phosphatic lithofacies of the Salitre Formation which constrains the thermal and chemical alteration history of CFA, calcite, and dolomite cements. Structural carbonate in the CFA and calcite cements co-occurring in partially phosphatic digitate stromatolite buildups and adjacent carbonate grainstone generally yield similar δ13Cmineral values (0–5 ‰ VPDB), δ18Omineral values (−5–0 ‰ VPDB), as well as similar ∆47 temperatures (90–115 °C) and calculated δ18Owater (10–19 ‰ VSMOW), supporting a scenario in which CFA and calcite formed and then both recrystallized in equilibrium with the same diagenetic fluids under low water–rock ratio conditions at depth. Dolomite cements yielded similar δ18Omineral values to CFA and calcite, and similar to slightly higher temperatures (85–150 °C) — supporting a scenario in which dolomite cements were recrystallized in equilibrium with a different, and isotopically lighter, generation of fluids. Given the general absence of pervasive, fabric-destructive replacement is scarce, these geochemical data do not support later stage, differential diagenesis as a mechanism for controlling the distribution of phosphatic versus non-phosphatic cements. Rather, primary differences in porewater biogeochemistry seem the likeliest explanation. This is important, as it implies that the ecology of the Ediacaran seafloor controlled the style and quality of mineralization observed today, and that the presence of CFA cements in these rocks represents a unique taphonomic window for select microbial communities.

Impact of sedimentation and diagenesis on deeply buried sandy conglomerate reservoirs quality in nearshore sublacustrine fan: A case study of lower Member of the Eocene Shahejie Formation in Dongying Sag, Bohai Bay Basin (East China)

The sandy conglomerates of the lower member of Shahejie (Es4x) in the north of Dongying Sag, Bohai Bay Basin, were investigated to understand the formation mechanism of the good reservoir and controlling factors in deeply buried strata. This research is based on seismic, logging, and core data and comprehensively utilizes methods such as core description, petrographic analysis, cathodoluminescence image analysis, SEM-EDS analysis, and mercury intrusion. The sandy conglomerates are predominantly lithic arkose and litharenite. The reservoirs in the Es4x have experienced three diagenetic processes, compaction, dissolution, and cementation. Compaction remains the major factor affecting the reservoir quality, mainly in the progradation sequence, and cementation has a destructive effect on reservoirs, principally in the retrogradation sequence. The quantification of the compaction by the compaction index revealed that mechanical compaction is higher in the progradation sequence (0.68) than in the retrogradation sequences (0.59). Compaction is suppressed by carbonate cementation, but the extensive cementation significantly degrades the reservoir quality, especially in the retrogradation sequence. Dissolution of different rock fragments, feldspar, and the whole dissolution, in general, enhance the reservoir's quality in both intervals but more in the progradation sequence. Three types of reservoirs representing type I, type II, and Type III mercury intrusion capillary pressure curves were encountered in the Es4x. The braided channels in the progradation and retrogradation sets encompass the greatest reservoir quality and are characterized by type I and II reservoirs with good petrophysical properties. The preeminent reservoirs appear in the braided channels of the progradation set. The development of high-quality reservoirs is governed by the depositional subfacies, compaction, and dissolution in the Es4x. This study will contribute to comprehending the origin of the genesis mechanism of high-quality in deep sublacustrine sandy conglomerate and will help the exploration and pre-drill for favorable reservoirs in similar basins around the world.

Carbonate cementing minerals in rhizoliths from Badain Jaran Desert: Implication for pedo-diagenesis and environment of dune soil

Pedogenic carbonates are a good proxy of soil formation and functioning because the morphology of minerals is directly related with the processes of dissolution–precipitation. Carbonate rhizolith is one type of pedogenetic carbonate forming in modern soils of dunes and loess. The calcite micro-morphology with the sedimentary hydrogeochemical conditions prevailing during their formation remains open. Electron microscopy with an X-ray energy dispersive spectrometer and X-ray diffraction were used to investigate in detail the micro-morphology of carbonate cements of the rhizoliths and obtain paleoenvironmental information in the dune soil of Badain Jaran Desert in Northwest China. Two types of carbonates rhizoliths, primary rhizoliths (PR) and reworked rhizoliths (RR), were found. The PRs are present in situ within dune soils. The RRs are being eroded out from soil, potentially dislocated or transferred, and weathered at the soil surface. PRs displayed homogeneous micritic mass of calcite crystals, with pores, cavities and voids among the mass. RRs displayed various morphologies of calcite crystals (polyhedral, euhedral rhombic, tooth-like, prismatic and pillar), rosettes, short rods, and calcified fungal hyphae. The diagenesis differences at soil depth and surface affected the crystal morphologies. The homogeneous micritic mass of calcite crystals of the PRs were formed during the early diagenesis, preferentially in wet soils with semi-closed and semi-redox conditions. In contrast, the cementing minerals of the RRs became bigger and clearer in the late diagenesis than during early diagenesis due to recrystallization in open, dry and oxidative conditions at the soil surface. Therefore, the cement crystal morphologies of the rhizoliths can reflect the local environmental and climatic conditions. These objects can be used as environmental and pedo-diagenesis proxies in dune soil or sediments, recording the associated conditions of moisture, temperature, wind, erosion, weathering, solar radiation at the soil surface or at depth. Therefore, assessing the micromorphology of pedogenic carbonates has important implications for soil ecology and evolution as well as plant root physiology in deserts.

Origin of carbonate cements in Ben Nevis sandstones of Jeanne d’Arc Basin: Insights from geochemistry

The Ben Nevis sandstones in the Jeanne d’Arc Basin in offshore eastern Newfoundland have abundant carbonate cements, and are the primary hydrocarbon reservoirs of the White Rose Oilfield. A multiapproach of petrographic, carbon and oxygen isotopic, and in situ geochemical analyses were applied to investigate the origin of the carbonate cements in the Ben Nevis sandstones (quartzose to litho-quartzose, Well F-04). Petrographic examinations reveal five generations of cements that occur in concretions, which are (from earliest to latest), siderite, early calcite cement (C1), recrystallized fossil (Crf), sparry fossil-filling calcite (Cf), and late calcite cement (C2). The comparable carbon (3.6‰ VPDB) and oxygen isotopic (−1.3‰ VPDB) compositions of siderite to those of the bivalve shells (δ13C = 3.6 ± 0.6‰ VPDB and δ18O = −1.7 ± 0.5‰ VPDB, respectively) indicate an early precipitation from suboxic water near the sediment-seawater interface. The well-preserved intergranular volumes (IGVs up to 41%) and low δ18O (−3.3 ± 1.1‰ VPDB) as well as comparable δ13C values (3.6 ± 0.6‰ VPDB) of the early poikilotopic calcite (C1) argue for a pre-compaction precipitation at a shallow burial setting with carbon derived mainly from the dissolution of bioclasts. The later calcite cement (C2) precipitated during progressive burial with involvement of organic carbon as indicated by its depleted δ18O (−6.7 ± 2.0‰ VPDB) and δ13C (1.8 ± 1.3‰ VPDB) values, and the reduced IGVs (28.2%), as well as the consistent depletion of Sr with enrichment of Mn. The dissolution of aragonitic bioclasts, was likely the main source of Ca for calcite, which is consistent with the high Sr content of C1 (1369 ± 597 ppm), Crf (2005 ± 472 ppm), Cf (1354 ± 48 ppm) and C2 (1831 ± 696 ppm). The parallel shale normalized (REESN) patterns of the cements and the way they mimic, to some extent, that both of seawater and meteoric water, suggest that the diagenetic fluid is bracketed by those of the early Cretaceous marine and meteoric waters, as reflected by the estimated δ18OSW composition of parent fluid for C1. The consistent Eu anomalies of carbonate cements and the increasing δ18OSW composition of pore water during C2 precipitation reflect the evolution of the diagenetic fluids in siliciclastic intervals during progressive burial.The secondary porosity development as the main contributor to the present reservoir porosity seem to be closely related to the dissolution of calcite cements, especially in the lower part of the Ben Nevis interval. The meteoric water influx from the overlying unconformities may have induced the dissolution of calcite concretions.

Characteristics and genesis of deeply buried under-compacted sandstone and its comparison with normal Sandstone-A case in the lenghu tectonic belt, northern Qaidam Basin

Based on recovered core observations and thin section identifications combined with scanning electron microscopy images and statistics for physical properties, XRD analysis, and data for trace elements and carbon and oxygen isotopes, the genesis of under-compacted sandstone in the Lower Ganchaigou Formation of the Paleogene in the Lenghu VII structure in the northern Qaidam Basin has been confirmed through a detailed comparison with normal intervals for petrology, sedimentary environments and diagenetic characteristics. The results showed that under-compacted sandstone, developing in underwater distributary channels, was characterized by abnormal high porosity and large amount of intergranular pores. The genesis of intergranular pores is the intrusion of organic acid fluids, dissolution of calcite cements and restoration of primary pores. Conclusions could be drawn from the comprehensive comparison with normal interval. First, honeycomb-like chlorite grain coatings were much abundant (33%–58% in total clays) in the under-compacted sandstone comparing to it in normal interval and sandstone in adjacent area (<30%), indicating an intrusion of Mg-rich fluid leading to transformation from I/S to chlorite. Second, the carbonate cements content of the under-compacted sandstone (5.7%–17.3%) and the normal range (4.1%–20.3%) were both dominated by micrite calcite, and large amounts of early calcite residues resulting from dissolution were only found in the under-compacted sandstone. The δ18O value (17.36‰ ∼ −10.54‰) and the δ13C values (−5.12 to −3.51‰) indicated inorganic carbon dominated in carbonate cements; however, the small negative bias for δ13C in the under-compacted sandstone indicated that more organic carbon was contained than is typical. Third, the minor changes in the V/Zr, Ni/Zr, Co/Zr, Sr/Zr and Mo/Zr values suggested similar and stable paleoenvironments in both intervals. The weaker correlations among U/Zr, Ni/Zr and V/Zr indicated that U/Zr was affected by both the environment and fluid intrusion in the under-compacted sandstone. However, U/Zr was much larger (3.6–23.9) in the under-compacted sandstone than it is in normal sandstones (0.83–3.69), which indicated the invasion of acidic fluids originating from source rock.