Carbonates and Evaporites最新文献

Carbonate rocks hold considerable volumes of hydrocarbons in various basins around the globe. Understanding the complex pore systems is a key factor in unlocking the potential of carbonate rocks. Matrix properties are also a challenge in carbonate reservoirs. Exploration geoscientists include the regional portfolio targeting the sweet spots for every basin. This study defines the reservoir quality and character of carbonate rocks with scope to the complete carbonate succession of north Western Desert and Abu Gharadig basin (AGB) as one of the most prolific basins in Egypt. More than 301 core samples are used in this study to represent all carbonate rock types. The workflow includes core data classification (grouping), petrographical investigation, reservoir mineralogy, and matrix parameters integrated with well logs and elastic properties. The provided work investigates the effect of pore structure and mineralogy on the petrophysical properties of the rock and its impact on elastic properties as well. Carbonate reservoirs in AGB are divided into three main categories: type-I, type-II, and type-III. Reservoirs enhancement by dolomitization and dissolution are controlling the distribution of pores, which are the key factors to delineate their potential. This study defines the characteristics of each group and the attractive formations for future exploration and development. The main differences in rock type, composition, diagenetic processes, and elastic properties were described. The rock brittleness index was calculated from dynamic properties for each carbonate type to get more insights about the rock brittleness and elasticity and predict variations of each group for future consideration in the basin.

The Mahura iron placer deposit is located 55 km northeast of Arak city in the Markazi province, Iran. From a geological point of view, it is located in the Central Iran Zone. In this study, the trace element geochemistry of magnetite is used to determine the origin of placer magnetites in the Mahura deposit. Magnetite is the most important placer mineral that occurs as micrometer-sized grains in the Quaternary alluvium. The alluvium consists of sandy, silty and clayey sediments containing a considerable amount of volcanic rock fragments of various sizes. The results of the petrographic studies and the whole-rock geochemistry indicate that the volcanic rock fragments are mostly andesite and basaltic andesite. These volcanics contain 4 to 10% magnetite as disseminated grains in the groundmass and as inclusions in plagioclase and amphibole phenocrysts. The mineral chemistry of the placer magnetites indicates 2.59–3.33% Ti, so that they can be considered as titanomagnetite or as a solid solution between magnetite and ilmenite. The chemical composition of the magnetites in the volcanic rock fragments also falls within the range of titanomagnetite with a tendency towards magnetite in the TiO₂-Fe₂O₃-FeO system. The composition of the placer magnetites and magnetites in the volcanic rock fragments are plotted in the magmatic field in Ti-Al and Ti versus Ni/Cr diagrams. The diagrams Ti + V versus Ni/(Cr + Mn) and Ti + V versus Ca + Al + Mn indicate that placer magnetites and magnetites in the volcanic rock fragments belong to the Fe-Ti, V deposits. In the V-Ti diagram, all magnetites fall into the range of titaniferous iron ores. The comparison of the trace element composition of placer magnetites and magnetites in the volcanic rock fragments in the elemental diagrams above showed that all magnetites have the same origin, so that the placer magnetites were most likely released from the volcanic rock fragments by erosion over time. On the other hand, the comparison of the chemical composition of the volcanic rock fragments in the alluvium with that of volcanic rocks from the Ashtian area north of the Mahura deposit in the petrogenetic diagrams reveals similar nature for these rocks and that the magnetite-bearing volcanic rock fragments originate from the Ashtian Basin.

Carbonate rocks have been used as a building material for centuries all around the world. Construction and reconstruction projects still commonly employ them, particularly for replacing damaged ashlars in monuments. Unfortunately, Carbonate rocks are highly vulnerable to salt weathering, leading to their eventual breakage. This study focuses on analyzing how dolostones used in the construction of Falak-ol-Aflak castle behave when exposed to salt crystallization weathering. To achieve our goal, we conducted 40 salt crystallization test cycles on the selected dolostones using Na₂SO₄ and MgSO₄ solutions. After every 10 cycles, we assessed the visual changes and physico-mechanical properties of the salt-crystallization samples. We measured the damage rate (DR) of weight (W), P-wave velocity (V_p), porosity (n), and point load index (PLI) to determine these properties. SEM observations were conducted to examine the structural changes of the building stones resulting from the salt crystallization tests. Based on the findings, it can be concluded that saline solutions containing Na₂SO₄ cause more damage to samples than those containing MgSO₄.

Magnesite (MgCO₃) is a valuable mineral with wide industrial applications; thus, geochemical familiarity and deposit quality are critical for making the best use of these resources. Tanzania is reported to have magnesite deposits in at least 12 different locations; however, four of these were chosen at random for study. This study aimed to examine the mineralogical and elemental composition of rock samples from Chambogo (KL), Muriatata (AR), Lobolosoiti (MN), and Chikaza (DM) using x-ray fluorescence (XRF) and powder x-ray diffraction (XRD). XRF examination revealed that sample KL, AR, MN, and DM, respectively, contain 45.21%, 46.06%, 43.21%, and 43.21% of magnesium oxide. Besides MgO, all samples contained SiO₂, Fe₂O₃, Al₂O₃, CaO and several trace elements as impurities, with only calcium oxide, iron, arsenic, and chromium identified as impurities of concern. However, XRD analysis indicated magnesite as the major mineral phase in rock samples KL, AR, MN, and DM, with percentage concentrations of 65.2, 68.14, 63.87, and 68, respectively. In all rock samples, strong peaks at 2θ ∼ 33^o, 43^o, 54^o and 55^o, confirmed the crystalline nature of magnesite. Calcination of these samples however, resulted in peak shift and phase change, with main diffraction peaks generated at 2θ ∼ 36.9^o, 42.9^o and 62.3^o, confirming the formation of crystalline MgO. Despite considerable contamination levels of CaO, iron, chromium, and arsenic in the samples, all samples had enough magnesite to be mined for industrial use.

The present work deals with the investigation of the mineralogical characteristics of stream sediments, as possible source of economic heavy minerals. Their heavy minerals content was separated and identified, and the most abundant economic heavy minerals are ilmenite, magnetite, garnet, rutile, leucoxene, zircon, monazite, and cassiterite. Besides the identified economic heavy minerals, some radioactive and REE-bearing minerals were found too including: thorite, xenotime, and chernovite. Also, fluorite, apatite and gold occur in the sediments. The studied stream sediments are characterized by moderate concentrations of major oxides and trace elements commonly associated with mafic rocks, and high concentrations of those associated with felsic rocks, suggesting that they were derived from different sources. The existence of some elements was interpreted in terms of their occurrence in the structure of the recorded accessory minerals such as Th, Zr, and Y. The low values of the Cr/V ratio of the stream sediments (Average = 0.48) indicate a negligible contribution from ultrabasic sources. The radioactivity measurements show a predominance of thorium over uranium as these sediments are most likely pronounced natural trap for the thorium minerals such as thorite and monazite. The low values of eU/eTh ratio (average = 0.17) indicate the removal of uranium due to supergene processes.

The carbonate rocks in the eastern part of NE Turkey are situated within the Pontide paleo-magmatic arc and are frequently in contact with granitoid formations, often hosting skarn mineralization in the region. These carbonate rocks, typically found on ridges and hillsides exhibit predominant orientations along east–west, northeast-southwest, and northwest-southeast directions. A part of limestone, named as biomicrite, metamorphosed and display a saccharoidal texture. Comprised mainly of calcite, with less secondary quartz and iron oxide minerals, these carbonate rocks are classified as Fe-poor calcio-carbonate and magnesio-carbonate, having higher CaO and LOI contents. Marble and recrystallized limestone with granoblastic texture mainly comprise of calcite, less quartz, magnetite, and hematite. Marble classification diagrams suggest calcic skarn mineralization, indicated by decreasing CaO (or CO₂) and increasing MgO from limestone to marble (or skarn). Strontium contents deviate slightly from the lithosphere carbonate average, while low Rb contents, attributed to skarn metamorphism, indicate the absence of K-bearing minerals. The high Al₂O₃/SiO₂ in the carbonate rocks can points out hydrothermal activity and carbonate disengagement can indicate to actualize at temperatures that can affect Ce and Al mobilities. The low authigenic U value, low U/Th and Ni/Co ratios in carbonate rocks have been implied that protolith constituents deposited under oxic conditions. Positive Eu anomalies in limestone and marble suggest the influence of hydrothermal fluids. Carbon and oxygen isotope values in marble are similar with those of metamorphic and skarn marbles, indicating a magmatic origin. Overall, mineralogical and geochemical analyses propose a uniform source and/or geological process for all studied marbles.

This study investigates the diagenetic history and timing of hydrocarbon migration in the lower Permian Ingleside Formation as revealed in the Ingleside roadcut at Owl Canyon area, Colorado. Fourteen beds were identified within the studied exposure and are composed of quartz arenite sandstone, limestone, dolomite, or siltstone. Observations from outcrop and thin sections, including calcite veins, carbonate-hosted vugs, and carbonate cement, indicate carbonate mobility throughout the outcrop. Stylolites parallel to bedding were probably formed by pressure solution related to compaction, and pressure solution of carbonates is one possible source of carbonate that could have precipitated in veins or as a cement. The Ingleside Formation was affected by other diagenetic processes, including feldspar dissolution and alteration and several stages of cementation. Hematite, calcite, dolomite, kaolinite, and quartz overgrowth cements are the major types of cements identified within the studied exposure. Hematite cement was determined to have precipitated very early, followed immediately by the precipitation of poikilotopic carbonate cement. Blocky calcite and blocky dolomite cements, the most common cements within the formation, formed after the hematite and poikilotopic cements. Kaolinite cement may have precipitated in association with feldspar dissolution and alteration or occurred with feldspar dissolution during modern weathering. Hydrocarbon migration may have taken place before the of the blocky carbonate cement. The CaO in sandstone samples is due to the occurrence of calcite and dolomite cement. The MgO in sandstone samples is related to dolomite content. Furthermore, the low concentration of K2O in sandstone samples could be attributed to the low proportion of K-feldspar, and other K-rich minerals and possibly reflects loss of K during diagenesis. The relationship fact that S and MgO are both more abundant in samples from the middle and upper parts of the outcrop than in deeper samples suggests that they were added by diagenetic fluids. This study of the Ingleside outcrop provides insights on the diagenesis, possible timing of possible hydrocarbon migration through the Ingleside Formation, and geochemical and mineralogical composition of the exposure, which was used to interpret the diagenetic history throughout the outcrop. Therefore, it adds to the understanding of hydrocarbon migration and hydrocarbon pathways in this part of the Denver Basin.

To determine the diagenesis and evolution of the Cambrian DEPS (dolomite-evaporite paragenetic system) in the eastern Sichuan basin, the isotopic geochemistry characteristics of C, O, and fluid inclusions were studied. Four diagenetic systems were determined in the Cambrian DEPS based upon the hydrological system. These include the pore brine during the penecontemporaneous stage, sealed brine during the early diagenetic stage, compaction hot brine during the middle and late diagenetic stage, and mixed hydrothermal fluids involving deep thermal water during the later tectonic uplift stage. The character and source of fluids of various diagenetic stages and systems have a certain familiarity and inheritance features of development and evolution. However, fluids of various diagenetic stages and systems have different effects on the reservoirs. The diagenetic systems and manner of diagenesis are related to reservoir development closely. These include burial dolomitization and dissolution of sealed brine of the early diagenetic stage, and TSR (thermochemical sulfate reduction) and recrystallization of the mixed hydrothermal fluids involving deep thermal water during the tectonic uplift stage. Analyzing the basin structure indicates that a series of faults caused by the Cambrian detachment layer in the Eastern Sichuan Basin are the dominant factor controlling the spatiotemporal coupling relationship between the diagenetic systems and the reservoir in DEPS. The shoal subfacies control the regional distribution of the reservoir. During the early diagenetic stage, buried dolomitization helped with continued reservoir development, while TSR and recrystallization in the tectonic diagenetic stage improved reservoir quality by enhancing porosity and permeability. The Cambrian DEPS strata and the underlying Qiongzhusi Formation mud shale form a high-quality source-reservoir-caprock assemblage in the eastern Sichuan Basin.

The Jurassic–Cretaceous East Vardar Zone (EVZ) is a NNW–SSE-directed NeoTethyan back-arc crustal amalgamation that passes through Romania, Serbia, Bulgaria, North Macedonia, and Greece. This somewhat elongated Jurassic back-arc ocean underwent early compression, “docking” and nappe-stacking in the latest Jurassic–earliest Cretaceous. The Tithonian(Berriasian) limestones, which stratigraphically overlie the Middle Jurassic oceanic crust, are not only crucial markers of the latest Jurassic contraction and exhumation but also bear significant implications for the NeoTethyan Vardar developments (evidence of paleokarstification). During the latest Jurassic–earliest Cretaceous compressional event, the oceanic crust belonging to the EVZ interacted with the Dacia Mega-Unit and its Serbo-Macedonian continental margin. By introducing new structural observations, this study covers the interference character between the EVZ periphery and the western Serbo-Macedonian Unit. Supported by previous mapping results, new structural data are extracted from several key outcrops distributed across central Serbia (Dobroljupci, Kuršumlija, Jastrebac Mt.). The analyses of geodynamic implications related to the NeoTethyan Vardar contraction have outlined the latest Jurassic-earliest Cretaceous accretionary-type deformation embedded in the peripheral units (Tithonian-Berriasian limestones, mélanges, Serbo-Macedonian gneiss). These findings are significant as they provide a deeper understanding of the geological processes that shaped this region during the mid-Mesozoic. Despite Late Alpine overprinting, the latest Jurassic arc-type “soft collision” or “docking” (no evidence of significant crustal thickening with a very limited obduction) produced the newly observed NNE-SW oriented folds. The folds are observed within the Jurassic carbonate rocks and greenschist-facies rocks of likely similar age and origin (train of steeply plunging synforms, D₁). The tectonic resetting and initiation of post-collisional progressive subduction remobilized the stalled remnant of the Vardar marine corridor after the short-term Berriasian exposure and palaeokarstification. Such tectonic developments triggered a foreland-type subsidence and accumulation of the clastic-carbonate Lower Cretaceous “paraflysch” on top of the EVZ ophiolites/mélange/Tithonian limestones. However, the new depositional cycle and the oldest Lower Cretaceous paraflysch sequence remain devoid of ophiolite inclusions.

The chlorite group of minerals (chlorites) are well-known phyllosilicates, which have been described from magmatic, metamorphic and sedimentary rocks. Chlorites often appear in the cement of sandstones and can affect their reservoir properties. Here, we present the results of a study on the distribution and composition of chloritized mixed siliciclastic-carbonate rocks from the Middle Ordovician of the Gydan Peninsula, northern Siberia, Russia. This study is based on the first deep well in the area to penetrate the entire 4500-meter-thick sedimentary succession. A number of different carbonate rock textures are found in this area, including rudstone-floatstone (composed almost entirely of calcite), wackestone and packstone (composed of calcite bioclasts and clayey micrite matrix), marl (containing calcite bioclasts, dolomite / ankerite, illite / muscovite, quartz, feldspar and chlorites), and dolomitic marl (composed of illite / muscovite and dolomite / ankerite). Chlorite is represented by chamosite and contains up to 33.5 wt% FeO and up to 0.7 wt% TiO₂. Chlorite content positively correlates with illite / muscovite content, reaching a maximum in marls and dolomitic marls (up to 13 vol%). Chlorite crystals are micron-sized and appear as authigenic grains, where they can be distributed in the matrix or form secondary rims around calcite bioclasts and dolomite / ankerite grains. The two main processes leading to chloritization in the studied rocks include illite / muscovite replacement by chlorite and a reaction between illite / muscovite and dolomite / ankerite resulted in chlorite crystallization. Paleotemperatures during chlorite crystallization reached as high as 295–318 °C. Chloritization of the studied carbonate rocks resulted in a porosity reduction, as chlorite rims filled micropores at the contacts with the siliciclastic matrix.