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1
Yaxley, Gregory M., Bruce A. Kjarsgaard e A. Lynton Jaques. "Evolution of Carbonatite Magmas in the Upper Mantle and Crust". Elements 17, n. 5 (1 ottobre 2021): 315–20. http://dx.doi.org/10.2138/gselements.17.5.315.
Testo completoAbstract (sommario):
Carbonatites are the most silica-poor magmas known and are amongst Earth’s most enigmatic igneous rocks. They crystallise to rocks dominated by the carbonate minerals calcite and dolomite. We review models for carbonatite petrogenesis, including direct partial melting of mantle lithologies, exsolution from silica-undersaturated alkali silicate melts, or direct fractionation of carbonated silicate melts to carbonate-rich residual melts. We also briefly discuss carbonatite–mantle wall-rock reactions and other processes at mid-to upper crustal depths, including fenitisation, overprinting by carbohydrothermal fluids, and reaction between carbonatite melt and crustal lithologies.
2
Korinevsky, V. G., e E. V. Korinevsky. "Isotopic evidences of magmatic nature of the dolomite-calcite bodies of the Ilmeny Mountains and the Plastovsky district of the South Urals". Vestnik of Geosciences 11 (2020): 3–19. http://dx.doi.org/10.19110/geov.2020.11.1.
Testo completoAbstract (sommario):
The data obtained for the first time on the isotopic composition of oxygen and carbon of calcites and graphites of dolomitecalcite rocks of the Ilmeny Mountains and dykes of a similar composition in the Plastovsky district have confirmed their magmatic genesis. The temperature of formation of carbonate bodies (590—1000 °Ñ), determined from the isotopic ratios of C and O in calcite and graphite, corresponds to the temperature range (600—900 °Ñ) of the formation of carbonatite associations. According to the same ratios of isotopes in calcites, the protoliths of carbonate rocks are located within the carbonatite fields of the folded regions and in the transition zone to carbonates of marine origin. This is probably due to the fact that these rocks are a product of carbonate magma during remelting of sedimentary carbonate rocks in subduction zones, or under the influence of the heat of granite intrusions.
3
Bishop, Janice L., Rachel T. Schelble, Christopher P. McKay, Adrian J. Brown e Kaysea A. Perry. "Carbonate rocks in the Mojave Desert as an analogue for Martian carbonates". International Journal of Astrobiology 10, n. 4 (1 luglio 2011): 349–58. http://dx.doi.org/10.1017/s1473550411000206.
Testo completoAbstract (sommario):
AbstractCarbonate rocks in the Mojave Desert are presented as potential analogues for the carbonates on Mars. Rocks collected from the Little Red Hill site contain iron oxide-bearing coatings that greatly suppress the spectral features due to carbonate of the underlying material and impart a spectral slope. The Mojave Desert was formerly a lush pedogenic soil environment that, over time, transformed into the current arid climate with abundant rock varnish. One niche for microbes in the current desolate environment is inside and underneath the rocks where the microbes profit from solar protection by the iron oxide rock coatings. Carbonates were long predicted to be present on Mars and have recently been detected by instruments on Phoenix and MER and using hyperspectral orbiters such as the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), the Planetary Fourier Spectrometer (PFS) and the Thermal Emission Spectrometer (TES). We describe here the results of a study of carbonate rocks from the Little Red Hill site of the Mojave Desert that includes X-ray diffraction (XRD), chemistry and visible-infrared reflectance spectroscopy. Coatings on the carbonate rocks greatly reduced the strength of the carbonate bands and caused changes in the shape of some bands. We compare these data with a carbonate outcrop at Nili Fossae, Mars. If microbes once inhabited Mars, similar carbonate rocks with iron oxide coatings could have provided a UV-protected niche there as well. Thus, analysis of carbonate-bearing regions on Mars by future landers would be useful sites to search for biosignatures.
4
Arman, Hasan, Mahmoud Abu Saima, Osman Abdelghany e Safwan Paramban. "Comparative Study on Degradability Characteristics of Evaporitic and Carbonate Rocks from Al Ain, United Arab Emirates". IOP Conference Series: Earth and Environmental Science 906, n. 1 (1 novembre 2021): 012130. http://dx.doi.org/10.1088/1755-1315/906/1/012130.
Testo completoAbstract (sommario):
Abstract The slake durability index (SDI) test is a well know and extensively used to measure the degradability behaviour of rocks especially for weak rocks like mudstone, shale, evaporites, carbonates, etc. The degradability of rocks plays a critical role in engineering design process either on or in the rock mass for safe and sustainable structures. Evaporitic and carbonate rocks are vulnerable to physical, chemical and mechanical weathering, break down, as result of wetting-drying processes during the SDI test. Evaporites and carbonates are outcropped at the surface and subsurface of the Al Ain city, which is located on the south-eastern of Abu Dhabi, capital city of the United Arab Emirates (UAE) at various level, and it is one of the rapid growing cities in the UAE. However, the detailed comparative data on the slaking behaviour of evaporites and carbonates are not available presently in the study area. Therefore, this paper provides a comparative study on the degradability characteristics of evaporitic and carbonate rocks in the city of Al Ain as well as comprehensive data for the study area. 142 rock blocks (∼ 40×40×40 cm3 in size), which represent evaporitic (48 blocks) and carbonate (94 blocks) rocks were collected from various accessible either surfaces outcrops or excavated areas from the study area. 48 and 94 slake durability test samples of evaporites and carbonates were prepared and slake durability tests were performed according to the American Society for Testing and Materials (ASTM) standards. Furthermore, their compositional and textural characteristics were examined using polarized-light microscope, X-ray diffractometry (XRD), X-ray fluorescence (XRF) and scanning electron microscope (SEM). The degradability data for evaporite and carbonate rocks designate medium to very low and extremely high to very high values based on the classification after multiple cycling, Id1 to Id4, processes, respectively. The weight loss values from the first to the fourth cycles (Id1–Id4) of evaporite and carbonate samples are approximately 24–95 and 0.68-4.22 wt%. Obviously, evaporites are highly vulnerable compare to carbonates because of their differences in chemical and mineralogical structures and their reactions to the slaking fluid of distilled water. Hydration-dehydration effects on the evaporitic rocks may occur within short time compare to the carbonate rocks due to their natural occurrences. Thus, this study provide comparable and details information for the degradability characteristics of evaporitic and carbonate rocks, and likely improve the understanding of the durability of both rock types in the study area and elsewhere. Especially, such a reliable and inclusive information will compromise a practical guideline for engineers and decision makers to overcome difficulties on durability problems associated with evaporites and carbonates in the study area and elsewhere.
5
Nikiforov, Anatoly V., Elena O. Dubinina, Nikolay A. Polyakov, Amina M. Sugorakova e Aylan K. Khertek. "Influence of Host Marble Rocks on the Formation of Intrusive Alkaline Rocks and Carbonatites of Sangilen (E. Siberia, Russia)". Minerals 11, n. 7 (22 giugno 2021): 666. http://dx.doi.org/10.3390/min11070666.
Testo completoAbstract (sommario):
The study of the O and C isotope composition of calcite from nepheline syenites, ijolites and carbonatites of the Chik intrusion and the intrusions of the Erzin–Tarbagatay group of Sangilen (Eastern Siberia, Russia) showed derivation from alkaline melts enriched with a carbonate component from the host marbleized sedimentary rocks. The calculations showed that about 40% of the initial mass of carbonates involved in the interaction with silicate melts have remained after decarbonation. During the assimilation of the carbonate, an oxygen isotope exchange took place between the residual carbonate material and the silicate phase. Crystallization products of such hybrid magmas are carbonatite veins, calcite-rich nepheline rocks and their pegmatites with a calcite core.
6
Adam, Ludmila, Michael Batzle e Ivar Brevik. "Gassmann's fluid substitution and shear modulus variability in carbonates at laboratory seismic and ultrasonic frequencies". GEOPHYSICS 71, n. 6 (novembre 2006): F173—F183. http://dx.doi.org/10.1190/1.2358494.
Testo completoAbstract (sommario):
Carbonates have become important targets for rock property research in recent years because they represent many of the major oil and gas reservoirs in the world. Some are undergoing enhanced oil recovery. Most laboratory studies to understand fluid and pressure effects on reservoir rocks have been performed on sandstones, but applying relations developed for sandstones to carbonates is problematic, at best. We measure in the laboratory nine carbonate samples from the same reservoir at seismic (3–3000 Hz) and ultrasonic [Formula: see text] frequencies. Samples are measured dry (humidified) and saturated with liquid butane and brine. Our carbonate samples showed typical changes in moduli as a function of porosity and fluid saturation. However, we explore the applicability of Gassmann’s theory on limestone and dolomite rocks in the context of shear- and bulk-modulus dispersion and Gassmann’s theory assumptions. For our carbonate set at high differential pressures and seismic frequencies, the bulk modulus of rocks with high-aspect-ratio pores and dolomite mineralogy is predicted by Gassmann’s relation. We also explore in detail some of the assumptions of Gassmann’s relation, especially rock-frame sensitivity to fluid saturation. Our carbonate samples show rock shear-modulus change from dry to brine saturation conditions, and we investigate several rock-fluid mechanisms responsible for this change. To our knowledge, these are the first controlled laboratory experiments on carbonates in the seismic frequency range.
7
Chen, Jun-Qing, Xiong-Qi Pang, Song Wu, Zhuo-Heng Chen, Mei-Ling Hu, Luo-Fu Liu, Kui-You Ma, Bo Pang e Zhi-Peng Huo. "Method for identifying effective carbonate source rocks: a case study from Middle–Upper Ordovician in Tarim Basin, China". Petroleum Science 17, n. 6 (19 settembre 2020): 1491–511. http://dx.doi.org/10.1007/s12182-020-00489-z.
Testo completoAbstract (sommario):
AbstractHydrocarbon expulsion occurs only when pore fluid pressure due to hydrocarbon generation in source rock exceeds the force against migration in the adjacent carrier beds. Taking the Middle–Upper Ordovician carbonate source rock of Tarim Basin in China as an example, this paper proposes a method that identifies effective carbonate source rock based on the principles of mass balance. Data from the Well YW2 indicate that the Middle Ordovician Yijianfang Formation contains effective carbonate source rocks with low present-day TOC. Geological and geochemical analysis suggests that the hydrocarbons in the carbonate interval are likely self-generated and retained. Regular steranes from GC–MS analysis of oil extracts in this interval display similar features to those of the crude oil samples in Tabei area, indicating that the crude oil probably was migrated from the effective source rocks. By applying to other wells in the basin, the identified effective carbonate source rocks and non-source rock carbonates can be effectively identified and consistent with the actual exploration results, validating the method. Considering the contribution from the identified effective source rocks with low present-day TOC (TOCpd) is considered, the long-standing puzzle between the proved 3P oil reserves and estimated resources in the basin can be reasonably explained.
8
Xu, Hengchao, Xiaotong Peng, Shun Chen, Jiwei Li, Shamik Dasgupta, Kaiwen Ta e Mengran Du. "Macrofaunal burrowing enhances deep-sea carbonate lithification on the Southwest Indian Ridge". Biogeosciences 15, n. 21 (30 ottobre 2018): 6387–97. http://dx.doi.org/10.5194/bg-15-6387-2018.
Testo completoAbstract (sommario):
Abstract. Deep-sea carbonates represent an important type of sedimentary rock due to their effect on the composition of the upper oceanic crust and their contribution to deep-sea geochemical cycles. However, the role of deep-sea macrofauna in carbonate lithification remains poorly understood. A large lithified carbonate area, characterized by thriving benthic faunas and a tremendous amount of burrows, was discovered in 2008, blanketing the seafloor of the ultraslowly spreading Southwest Indian Ridge (SWIR). Benthic inhabitants – including echinoids, polychaetes, gastropods and crustaceans – are abundant in this carbonate lithified area. The burrowing features within these carbonate rocks, as well as the factors that may influence deep-sea carbonate lithification, were examined. We suggest that burrowing in these carbonate rocks enhances deep-sea carbonate lithification. We propose that active bioturbation may trigger the dissolution of the original calcite and thus accelerate deep-sea carbonate lithification on mid-ocean ridges. Macrofaunal burrowing provides a novel driving force for deep-sea carbonate lithification at the seafloor, illuminating the geological and biological importance of bioturbation in global deep-sea carbonate rocks.
9
Kuang, Hong Hai. "Pattern Recognition of Carbonate Rocks in Rs Image". Key Engineering Materials 500 (gennaio 2012): 37–39. http://dx.doi.org/10.4028/www.scientific.net/kem.500.37.
Testo completoAbstract (sommario):
Pattern recognition of carbonate rocks in RS image have been studied in the paper. Samples of carbonate rocks were scanned into rock images.By analysing these samples of carbonate rocks,a new arithmetic was chosed and a standard curve of carbonate rocks by the arithmetic can be gotten.Rs images were divided into grids.There are curves by the arithmetic in grids. The standard curve of carbonate rocks and curves in grids were compared.If both of curves look very similar,the grid is carbonate rocks area.
10
Ehlmann, Bethany L., John F. Mustard, Scott L. Murchie, Francois Poulet, Janice L. Bishop, Adrian J. Brown, Wendy M. Calvin et al. "Orbital Identification of Carbonate-Bearing Rocks on Mars". Science 322, n. 5909 (19 dicembre 2008): 1828–32. http://dx.doi.org/10.1126/science.1164759.
Testo completoAbstract (sommario):
Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering, proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.
11
Aderhold, M., C. Disselkamp, R. Formanski, M. Grimberg, A. M. Grineisen, L. M. Kroenert, M. S. Ogan et al. "Comparison of different methods to characterise the abrasivity potential and mechanical properties of carbonates with respect to its relevance for practical purposes in excavation technologies". IOP Conference Series: Earth and Environmental Science 1124, n. 1 (1 gennaio 2023): 012044. http://dx.doi.org/10.1088/1755-1315/1124/1/012044.
Testo completoAbstract (sommario):
Abstract The characterisation of the abrasivity potential of carbonates plays an important role for drilling-based excavation technologies, for example in tunneling or geothermal exploration. Although carbonates are known to have a rather low abrasivity, they have been associated with severe excavation performance reductions. We compared different methods to characterise the abrasivity potential of carbonates with respect to its applicability for practical purposes in excavation technologies. In this study, seven carbonate rocks were investigated which differ with respect to their microstructural properties and degrees of dolomitisation. These carbonate rock samples were selected from different lithological units in Germany (Jurassic: Kelheimer limestone, Wachenzell dolomite, Solnhofen limestone, Pappenheim limestone, Treuchtlingen limestone; Devonian: Wülfrath limestone, Brilon limestone). Rock samples were characterised with respect to basic physical properties (density, ultrasound velocity), microstructure (thin section analysis, XRD), mechanical properties (uniaxial compressive strength UCS, splitting tensile strength STS) and commonly applied abrasivity indices (Cerchar abrasivity index test CAI, LCPC test) as well as derived indices (equivalent quartz content eQu). Our results confirm that the tested carbonate rocks show low abrasivity indices in terms of CAI, LCPC and eQu with an increase in abrasivity potential with increasing dolomite content. The microstructural properties play an important role for the abrasiveness of purely calcitic carbonates. Uniaxial compressive strength and splitting tensile strength were high and can additionally be, as has been shown before, particularly sensitive to sample preparation. We conclude that carefully determining the mechanical properties of carbonate rock samples in combination with common approaches to determine the abrasivity potential is key to properly predict tool wear, and required to derive information on performance in carbonate rocks. This study is the outcome of a research-oriented teaching program at Ruhr-University Bochum within the Geoscience curriculum for students with focus on Engineering Geology. Student authors are listed in alphabetical order (Aderhold to Zinke).
12
Yin, Gongming, Chunru Liu, Renmao Yuan, Fei Han, Rui Ding e Jean-Jacques Bahain. "ESR Chronology of Bedrock Fault Activity in Carbonate Area: Preliminary Results from the Study of the Lijiang-Xiaojinhe Fault, Southeastern Tibet, China". Geochronometria 48, n. 1 (1 gennaio 2021): 215–21. http://dx.doi.org/10.2478/geochr-2020-0033.
Testo completoAbstract (sommario):
Abstract Carbonated rocks constitute one of the main lithologies of the southeastern Tibet area, China, a tectonically very active zone. However, due to the lack of suitable dating materials, it is difficult to carry out chronological studies of the local tectonic evolution in such carbonate areas. In the present study, electron spin resonance (ESR) method had been applied on the dating of carbonates heated during fault activity of the Lijiang-Xiaojinhe (LX) Fault, an important active fault located in the northwest of Yunnan Province. Clear displaced landforms show that the fault has undergone strong late-Quaternary activity. During the fault activity, the heat produced by friction lead to the melting of the frictional surface of the rocks, and the melting can attenuate or zero the ESR dating signal of carbonate. The aim of the present paper was to check the ability of carbonate use to chronologically identify fault activity using electron spin resonance (ESR) method. The results showed the last fault activity of the LX fault was dated by ESR about 2.0±0.2 ka ago, in agreement with historical and radiocarbon data. Hence ESR can be if necessary a practicable dating alternative method for the study of fault activity chronology in carbonate rock area.
13
Shan, Zhi Gang, Hong Hai Kuang, Ming Sheng Kuang e Chun Hong Zhou. "Porous Materials of Carbonate Rocks under the Condition of Low Temperature and High Pressure". Key Engineering Materials 500 (gennaio 2012): 34–36. http://dx.doi.org/10.4028/www.scientific.net/kem.500.34.
Testo completoAbstract (sommario):
There are significant impacts on the safty of tunnels because of porous materials.In order to avoid serious accidents of tunnels, Porous materials of carbonate rocks under the condition of low temperature and high pressure have been studied in the paper. Samples of local carbonate rocks have been collected from carbonate rock formation. Special machine was designed to simulate the condition of low temperature (10°C-20°C ) and high pressure (1-30Mpa) undergroud 4000M in jinping.Samples of local carbonate rocks have been tested in the machine. Spectrographs and scanners have been used to observed the change of porous materials of carbonate rocks.Results of the technological measurements show that the change of porous materials of carbonate rocks is affected by low temperature and high pressure.With the change of low temperature and high pressure, surface chemistry is affected throughout the surface of carbonate rocks. When the temperature of carbonate rocks exceed 15°C and pressure less than 18Mpa,there will be new compounds on the surface of carbonate rocks. These new compounds will change the porosity and thesaturated permeability of carbonate rocks.The change may led to serious accidents of tunnels.If we want to avoid these serious accidents,we must keep the temperature of carbonate rock formation less than 15°C and pressure exceed 18Mpa.
14
Mudarisova, Raushania A., Yuri V. Volkov, Nailya M. Khasanova e Boris V. Uspensky. "Carbonate reservoir rocks characterization of the Kazanian Stage of the Gorsky ultraviscous oil field by electron paramagnetic resonance method". Georesursy 24, n. 2 (30 settembre 2022): 90–98. http://dx.doi.org/10.18599/grs.2022.3.8.
Testo completoAbstract (sommario):
The use of the electron paramagnetic resonance (EPR) method for studying carbonate rocks is widespread. EPR makes it possible to reconstruct lithological and geochemical environments of ancient sedimentation, including redox conditions and paleo-radioactivity of sedimentation basins. The paper considers the heterogeneous structure of carbonate reservoir rocks of the Kazanian Stage of the Gorsky ultraviscous oil field by paramagnetic marks: manganese ions Mn2+, radical ions SO3–, SO2–, РO22-(РO20) in carbonate minerals and radical С600 in the remains of organic matter in the rock. The carbonate reservoirs of the Gorsky structure, tectonically confined to the eastern side of the Melekess Depression, are represented by two main lithotypes: dolomitic boundstones and dolomitic oolitic packstones, which have various post-sedimentary alterations. EPR data were obtained for 28 samples with a step of 0.5-1.5 m along the section. The EPR spectra are characterized by narrow lines that indicate the marine origin of carbonates. Based on the EPR spectra of the ions Mn2+ and its content in carbonate minerals, the lagoonal-marine genesis of the Gorsky structure rocks was revealed. The dominant dolomite mineralization of the section was established. The absence of dolomite radicals and low values of the degree of population of the magnesium and calcium positions of dolomites are due to the secondary nature of carbonates. The distribution of manganese ions, organic and inorganic radicals in the rock along the section is shown simultaneously with its reservoir properties and the conditions for the formation of two dolomite lithotypes.
15
Dubinina, E. O., L. G. Filimonova e S. A. Kossova. "Isotopic (δ34s, δ13c, δ18o) properties of the disseminated mineralization of plutonic rocks in the Dukat ore field (Northeast of Russia)". Геология рудных месторождений 61, n. 1 (15 gennaio 2019): 39–51. http://dx.doi.org/10.31857/s0016-777061139-51.
Testo completoAbstract (sommario):
The variations in the δ34S, δ13C, and δ18O values of the disseminated sulfides and carbonate phase, which occurred in trace amounts in the plutonic rocks controlling the position of the unique Dukat Au-Ag field (Northeast of Russia), were examined. These properties were compared with similar isotopic parameters of the ore associations in the field. The δ34S values of sulfides and jarosite obtained from plutonic rocks were in a relatively narrow range (from -3.4 to +3.6‰) when compared with the range of variation of the δ34S values of sulfides obtained from the ore bodies (from 4.5 to +2.0 ‰). Pyrite sulfur obtained from the early mineralization of K-Na-leucogranite and pyrite obtained from the ore bodies were observed to have the same source. Pyrite formed during the later magmatic stages is characterized by a small amount of lighting based on the sulfur isotopic signature. The carbonate phases of the plutonic ore in the Dukat ore field are characterized by the δ13С values (from 12.8 to 8.8‰). The carbonates are split into groups according to the oxygen isotopic signature: carbonate balanced with the rock silicate matrix at high temperatures and carbonate with abnormally low δ18О values (from -0.8 to +0.9 ‰). The obtained data can be described using the model that assumes that the formation of the isotopic parameters of sulfide sulfur and carbonate carbon occurs during the process of sulfate recovery using organic carbon oxidation (TSR). Further, the calculations revealed that the observed δ34S and δ13С values in the rocks and ore associations in the Dukat field can be obtained during the abiogenic recovery of marine sulfate in a temperature range of 300 °C–450 °C. The comparison of the isotopic parameters of the rock carbonate with those of the ore association carbonate demonstrated that the surrounding/base rocks and fluid that separated during the cooling of the K-Na-leucogranite intrusion bodies, which resulted in a loss of approximately 80% CO2, could serve as the source of the carbonates of the ore bodies.
16
Mousavi, Maryam, Maša Prodanovic e David Jacobi. "New Classification of Carbonate Rocks for Process-Based Pore-Scale Modeling". SPE Journal 18, n. 02 (14 dicembre 2012): 243–63. http://dx.doi.org/10.2118/163073-pa.
Testo completoAbstract (sommario):
Summary Carbonate rocks are complex in structure and pore geometry and display heterogeneity on all length scales. In this paper, carbonate rocks are described on the basis of their contents and pore geometry for use in pore-scale modeling. Definitions of grains and porosities are based on other carbonate-rock classifications; we did not invent new concepts. On the basis of carbonate content (grain, mud, and cement), carbonate rocks were divided into three types: muddy, grainy, and mixed. Each type was divided into subtypes on the basis of pore geometries defined by other researchers. Pore-size distribution of Lønøy (2006) was used for each subtype. We review existing carbonate-rock models and suggest approaches, and show preliminary flow-simulation results, for pore-scale modeling of different grains, cement, and pore geometry in these complex rocks.
17
Harbar, Vladyslav, e Andriy Lisovskiy. "Carbonations and carbonate profile forming processes of rendzinas of the Podilski Tovtry". Visnyk of the Lviv University. Series Geography, n. 51 (27 dicembre 2017): 88–97. http://dx.doi.org/10.30970/vgg.2017.51.8741.
Testo completoAbstract (sommario):
The peculiarities of content and profile distribution of carbonates in rendzinas and soil-forming rocks of the Podilski Tovtry are investigated. It has been determined that the predominant process of weathering of carbonate rocks is a chemical dissolution, in which carbonates are converted into bicarbonates and, in the case of washing water regime, are applied from the soil (the process of decarbonization) and mechanical grinding and destruction of the remaining carbonate inclusions in the process of soil cultivation. The dissolution of carbonate rocks causes accumulation in the soil profile of an insoluble residue, the intensity of which depends on the composition of carbonate rocks, the rate of filtration of aqueous solutions, their aggressiveness and the concentration of destructive substances. The most intensive such accumulation occurs in acidic medium, at a low rate of infiltration of solutions and at high concentrations of CO2. It was established that the highest proportion of CaCO3 is characterized by lithotamium limestone (up to 90–93 %), and the lowest – carbonate polygenetic loams (up to 35–40 %). The feature of the profile distribution of the content of carbonates in rendzinas is its gradual growth in the upper part of the soil profile and rapid in the middle and lower parts. It is determined that the rendzinas of the Podilski Tovtry carbonates are represented predominantly in the form of wreckage of initial soil-forming rocks of different sizes and shapes, as well as amorphous solid-phase crude and finely dispersed products of weathering in the form of powdery and powdery carbonate dusting. It is established that in dense crystallized lithotamium limestones of the main strand, the carbonate mass weakly passes moisture, and the main process of weathering occurs due to surface corrosion. The accumulation of secondary carbonates in the form of mycelium and veins is characteristic on the slopes of the Tovtry (mostly in brown rendzinas and pararendzinas), due to the vertical and lateral migration flows of the dissolved forms of CaCO3. Key words: rendzinas, Podilski Tovtry, carbonates, carbonate profile.
18
Zhang, Tong. "Geological and geochemical characteristics and genesis of carbonate rocks in a certain area". E3S Web of Conferences 358 (2022): 02034. http://dx.doi.org/10.1051/e3sconf/202235802034.
Testo completoAbstract (sommario):
Carbonate rock is a general term for the rock composed of carbonate minerals, which is mainly composed of carbonate sediments, with calcite (limestone) and dolomite (dolomite) as the main forms. Carbonate rocks are important oil storage rocks, storing more than half of the world's natural gas and oil, and co-existing with various types of solid sedimentary deposits. They are themselves a kind of mineral that can be used in construction, chemical industry, metallurgy and other processes, so they have very important economic value. This paper analyzes the geological and geochemical characteristics and genesis of carbonate rocks in a certain area in order to provide theoretical support for related work.
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Banerjee, Amlan, Sarbani Patranabis-Deb, Dilip Saha e M. Santosh. "Inorganic silicification of ancient carbonate rocks". Journal of Sedimentary Research 91, n. 2 (28 febbraio 2021): 186–96. http://dx.doi.org/10.2110/jsr.2020.099.
Testo completoAbstract (sommario):
ABSTRACT Mechanisms of inorganic silicification of early Precambrian (older than 750 Ma) carbonate rocks remain equivocal. A quantitative model is presented here that captures the essence of ancient inorganic silicification of the carbonate rocks and is based on the hypotheses that carbonate silicification, a volume-conservative replacive process, is driven by crystallization stress induced by the growth of the guest mineral. Results of the quantitative model for silicification of calcitic limestone and dolostone are compared and validated against available independent observations and are found to be geologically reasonable. The quantitative model suggests that silicification of carbonate rocks is dependent on the host-rock composition and that calcitic limestones will be readily silicified compared to dolostone and/or aragonitic limestone. Results also show that silicification rate of carbonate rocks—irrespective of their composition—increases with increase in silica supersaturation and reactive surface area. Porosity and permeability of the host rock also increases the silicification rate of the carbonate rocks. Results also predict that substantial volume of silica-saturated fluids is required for inorganic silicification of a one-meter cube of carbonate rock. The quantitative model presented here has its limitations and should not be viewed as a unique and truly realistic representation of the carbonate silicification mechanism. The quantitative model presented here is unable to explain the formation of porosity and subsequent volume reduction of the parent material during the replacement process as observed in replacement experiments. Also, the effect of pH on silicification of carbonate rocks cannot be quantitatively estimated in this study. The quantitative model presented here should be viewed as one of the possible mechanisms of carbonate silicification that has to be tested further with experimental data and by model refinement.
20
Verwer, Klaas, Hendrik Braaksma e Jeroen A. Kenter. "Acoustic properties of carbonates: Effects of rock texture and implications for fluid substitution". GEOPHYSICS 73, n. 2 (marzo 2008): B51—B65. http://dx.doi.org/10.1190/1.2831935.
Testo completoAbstract (sommario):
More than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of Miocene (Tortonian) age were quantitatively analyzed for texture, mineralogy, and acoustic properties. We measured the P- and S-waves of carbonate rocks under dry (humidified) and brine-saturated conditions at [Formula: see text] effective pressure with an ultrasonic pulse transmission technique [Formula: see text]. The data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences. Two major textural groups were distinguished on the basis of trends in plots of compressional-wave velocity versus Poisson’s ratio (a specific ratio of P-wave over S-wave velocity). In granular rocks, the framework of depositional grains is the main medium for acoustic-wave propagation; in crystalline rocks, this medium is provided by a framework of interlocking crystals formed during diagenesis. Rock textures are connected to primary depositionalparameters and a diagenetic overprint through the specific effects on Poisson’s ratio. Calculating acoustic velocities using Gassmann fluid substitution modeling approximates measured saturated velocities for 55% of the samples (3% error tolerance); however, it shows considerable errors because shear modulus changes with saturation. Introducing brine into the pore space may decrease the shear modulus of the rock by approximately [Formula: see text] or, alternatively, increase it by approximately [Formula: see text]. This change in shear modulus is coupled with the texture of the rock. In granular carbonates, the shear modulus decreases; in crystalline and cemented carbonates, it increases with saturation. The results demonstrate the intimate relationship between elastic behavior and the depositional and diagenetic properties of carbonate sedimentary rocks. The results potentially allow the direct extraction of granular and crystalline rock texture from acoustic data alone and may help predict rock types from seismic data and in wells.
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Saberi, Mohammad Reza. "Fluid detection in carbonate rocks by integrating well logs and seismic attributes". Interpretation 8, n. 1 (1 febbraio 2020): SA1—SA10. http://dx.doi.org/10.1190/int-2019-0054.1.
Testo completoAbstract (sommario):
Prestack seismic attributes are efficient tools for hydrocarbon exploration and pore fluid detection with the help of various techniques, such as amplitude variation with offset analysis. Such studies focus mainly on siliciclastics rather than carbonates because detection of fluid effects in carbonate rocks can be masked by their complex pore structure and heterogeneity. Current fluid detection methods from seismic attributes usually rely on a linear background model for P- and S-wave velocities of the water-saturated rocks, and any deviation from this trend is assigned to possible pore fluid changes. This means that the false (or even missed) effect of fluids can be detected in carbonate rocks if inappropriate fluid detection attributes (such as the ones designed for siliciclastics) are used. This is mainly due to the varying pore structure in carbonates, which can make their background model (the model for fully water-saturated rock) mainly nonlinear. I observed that this nonlinearity in the carbonates background model becomes more linear by using P-velocity squared versus the product of the P- and S-velocities crossplot instead of P-velocity versus S-velocity crossplot. Furthermore, I used this proposed crossplot to define a more appropriate background model for my carbonate sequence containing some percentages of gas. I derived a new seismic fluid attribute based on the proposed background model, and I compared the results with various other fluid factors. My results highlight fluid changes more brightly and consistently than existing alternatives for carbonate environments.
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Larson, Erik B., e Ronald V. Emmons. "Dissolution of Carbonate Rocks in a Laboratory Setting: Rates and Textures". Minerals 11, n. 6 (5 giugno 2021): 605. http://dx.doi.org/10.3390/min11060605.
Testo completoAbstract (sommario):
Determining the dissolution rates of carbonate rocks is vital to advancing our understanding of cave, karst, and landscape processes. Furthermore, the role of carbonate dissolution is important for the global carbon budget and climate change. A laboratory experiment was setup to calculate the dissolution rates of two whole rock carbonate samples with different petrographic makeup (ooids and brachiopods). The carbonate rock samples were also explored under a scanning electron microscope to evaluate the textures that developed after dissolution The oolitic limestone dissolved at a rate of 1579 cm yr−1, and the pentamerous limestone (dolostone) dissolved at a rate of 799 cm yr−1. Both rocks did not dissolve evenly across their surface as indicated by scanning electron microscopy, it appears the allochems dissolved preferentially to the matrix/cement of the rocks and that some mechanical weathering happened as well. This work reports that the petrography and mineralogy of carbonate rocks is important to consider when exploring the cave, karst, and landscape evolution and that attention should be paid to the petrography of carbonate rocks when considering the global carbon budget.
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Winarno, Tri, Jenian Marin, Ilham Hani Pratama e Anis Kurniasih. "The analysis of volcanic activity influences at the lower and middle part of Sentolo Formation, Kulon Progo using petrographic method". MATEC Web of Conferences 159 (2018): 01040. http://dx.doi.org/10.1051/matecconf/201815901040.
Testo completoAbstract (sommario):
The research area is a part of South Serayu Mountain zone, specifically Bregada Kulon Progo. The Bregada Kulon Progo is a product of volcanic activity in the past, which can be seen by the volcanic rock called Old Andesite Formation. The end of the volcanic activity is characterized by the deposition of carbonate rocks which were part of Jonggrangan Formation and Sentolo Formation. The lower part of Sentolo Formation is composed by the mix of carbonate and volcanic materials. The research is carried out by two methods. The first is field method, which is implemented by geological mapping and rock sampling. The second is laboratory method, which is implemented by petrographic method. The petrographic method is implemented by making thin section of the rocks, then observing the thin section with polarization microscope to determine the composition of the rocks. The rock samples are mainly from the lower and middle part of Sentolo Formation, which probably still got the influence of volcanic activity. The benefit of the research is knowing the influence of volcanic activity in the carbonate rocks of Sentolo Formation. The presence of volcanic materials in the lower part of Sentolo Formation, can be predicted by two processes. First, the volcanic activity supplied those materials directly, and second, from the rework of the volcanic materials then mixed with carbonat materials of Sentolo Formation.
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Safira, Amanda, Dina Yulianita e Widya Utama. "Fluid Substitution Analysis Using Gassmann’s Equation Modification on Carbonate Environment". Pakistan Journal of Scientific Research 1, n. 2 (30 dicembre 2021): 8–12. http://dx.doi.org/10.57041/pjosr.v1i2.6.
Testo completoAbstract (sommario):
Gassmann’s equation can be used to determine the velocity of compressional waves that pass through rocks with various pore fluid contents, using fluid substitution concept, but is generally applied to certain conditions only (physical rock properties). Carbonate rock has properties in contrary of Gassmann’s assumption; is a heterogenic, anisotropic rock and does not have a well-interconnected pores. In this research, secondary data from laboratory measurements are used, consisting of carbonate rocks (limestone and dolomite) to test modified Gassmann’s equation on carbonate rocks. Two approaches of Gassmann’s equation are used by using k-dry and k-1 components, which are the value of compressional modulus bulk of saturated rocks. The result of both approaches shows that the usage of k-1 component is more optimal to be applied to carbonate rocks because it does not use k-dry component, which should only be used on field measurements, as there is a difference in the environment condition (air, temperature, and pressure) on reservoir and laboratory.
25
Winkler, Erhard M. "Cleaning Carbonate Rocks". APT Bulletin 19, n. 4 (1987): 2. http://dx.doi.org/10.2307/1494140.
Testo completo
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Arthur, Michael A. "Carbonate rocks deconstructed". Nature 460, n. 7256 (agosto 2009): 698–99. http://dx.doi.org/10.1038/460698a.
Testo completo
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Ghosh, Ranjana, e Mrinal K. Sen. "Predicting subsurface CO2 movement: From laboratory to field scale". GEOPHYSICS 77, n. 3 (1 maggio 2012): M27—M37. http://dx.doi.org/10.1190/geo2011-0224.1.
Testo completoAbstract (sommario):
Finding an appropriate model for time-lapse seismic monitoring of [Formula: see text]-sequestered carbonate reservoir poses a great challenge because carbonate-rocks have varying textures and highly reactive rock-fluid system. We introduced a frequency-dependent model based on Eshelby’s inclusion and differential effective medium (DEM) theory that can account for heterogeneity in microstructure of rocks and squirt flow. We showed that the estimated velocities from the modified DEM theory match well with the laboratory measurements (ultrasonic) of velocities of carbonate rocks saturated with [Formula: see text]-rich water. The theory predicts significant decrease in saturated P- and S-wave velocities in the seismic frequency band as a consequence of porosity and permeability enhancement by the process of chemical dissolution of carbonates with the saturating fluid. The study also showed the combined effect of chemical reaction and free [Formula: see text] saturation on the elastic properties of rock. We observed that the velocity dispersion and attenuation increased from complete gas saturation to water saturation. The proposed model can be used to invert geophysical measurements to detect changes in elastic properties of a carbonate reservoir and interpret the extent of [Formula: see text] movement with time. These are the key elements to ensure that sequestration will not damage underground geologic formation and [Formula: see text] storage is secure and environmentally acceptable.
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Ali, Salahalddin Saeed. "Geotechnical Properties of Certain Iraqi Carbonate Rocks". Journal of Zankoy Sulaimani - Part A 4, n. 1 (23 settembre 2000): 69–85. http://dx.doi.org/10.17656/jzs.10066.
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Castro, Dayse Daltro de, e Paula Lucia Ferrucio da Rocha. "QUANTITATIVE PARAMETERS OF PORE TYPES IN CARBONATE ROCKS". Revista Brasileira de Geofísica 31, n. 1 (1 marzo 2013): 125. http://dx.doi.org/10.22564/rbgf.v31i1.251.
Testo completoAbstract (sommario):
Carbonate rocks are controlled by variable depositional systems and diagenetic process and have a wide variety of pore and grain shapes/sizes. Those characteristics imprint different petrophysical properties in carbonates, which are more difficult to predict than in siliciclastic rocks. Measurements on carbonates reveal that pore/rock type parameters are function of total porosity and play an important role in the relationship between porosity and P-wave velocity. In this research, thedatabase consists of carbonate rock samples with a wide range of bulk porosities, pore types and rock textures, from different Brazilian areas in Southeast Continental Margin. We investigated the hypothesis that scatter values observed in velocity at a given porosity can be explained by pore types and pore shape characteristics. The quantification of pore shape/size distribution in each sample was based on four geometrical parameters from thin sections measurements – pore size, aspect-ratio,tortuosity and pore complexity. By multivariate analysis, those parameters were applied in the correlation between porosity and P-wave velocities in order to reducescatter values normally observed. RESUMO: As rochas carbonáticas são compostas por calcários e dolomitos de diversos tipos. Além da deposição, os processos de cimentação, dissolução e recristalização transformam essas rochas, produzindo uma grande variedade de tamanhos de grãos, formas e estruturas de poros, criando ou reduzindo porosidade e permeabilidade. Estas características dos carbonatos imprimem grande peculiaridade às propriedades físicas tornando-as mais difíceis de predizer do que em rochas siliciclásticas. As formas dos poros também afetam as propriedades físicas das rochas carbonáticas, produzindo um efeito específico nas propriedades acústicas devido às relações geométricas com a fase sólida das rochas. Por tudo que foi exposto, a compreensão do sistema de poros leva ao melhor entendimento e quantificação das propriedades petrofísicas das rochas carbonáticas. Nesta pesquisa foram utilizadas rochas carbonáticas com diferentes texturas, porosidades e tipos de poros de diferentes áreas da Margem Continental Sudeste Brasileira e o principal objetivo foi melhorar a correlação entre a porosidade e a velocidade das ondas P obtidas de plugues de rochas secas e úmidas. Para tal, foi realizada a avaliação e a quantificação do sistema poroso utilizando a análise multivariada de parâmetros geométricos (tamanho, forma, tortuosidade e complexidade do poro) obtidos de fotografias digitais de lâminas delgadas, para auxiliar na redução da dispersão normalmente observada nas relações entre velocidade e porosidade.Palavras-chave: propriedades petrofísicas, lâminas delgadas; porosidade; velocidade das ondas P
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Zakaria, A. S. S., H. A. A. Nasr-El-Din e M. Ziauddin. "Predicting the Performance of the Acid-Stimulation Treatments in Carbonate Reservoirs With Nondestructive Tracer Tests". SPE Journal 20, n. 06 (18 dicembre 2015): 1238–53. http://dx.doi.org/10.2118/174084-pa.
Testo completoAbstract (sommario):
Summary Carbonate formations are very complex in their pore structure and exhibit a wide variety of pore classes, such as interparticle porosity, moldic porosity, vuggy porosity, and microporosity. Geologists have defined carbonate pore classes on the basis of sedimentology, thin sections, and porosity/permeability relationships, but the question remains concerning how these pore classes govern the acid flow through porous media. Core samples from six different carbonates, mainly limestone, were selected for the study. The samples were first investigated with thin-section analysis, high-pressure mercury-injection tests, and nuclear-magnetic-resonance measurements for pore-structure characterization, and X-ray diffraction for mineralogy examination. Next, tracer experiments were conducted, and the tracer-concentration profiles were analyzed to quantify the carbonate pore-scale heterogeneity. The heterogeneity is expressed with a parameter f—the available fraction of pore structure contributing to the flow. The data were used to study the flow of acid through carbonate rocks and correlate the pore classes to the acid response. More than 30 acid-coreflood experiments were conducted at 150°F and a hydrochloric acid concentration of 15 wt% on 1.5 × 6-in. core samples at different injection rates on each carbonate rock type. The objective of these sets of experiments is to determine the acid pore volume to breakthrough for each carbonate pore class. The findings of this study help us to connect the results from different characterization methods to the acid flow through the porous media of carbonate rocks. It was also found that the response of the acid depends on the carbonate pore classes. Application to the design of matrix acid treatments in carbonate rocks is discussed.
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Eder, Vika G., Elena A. Kostyreva, Anna Yu Yurchenko, Natalia S. Balushkina, Inga S. Sotnich, Elena V. Kozlova, Alvina G. Zamiraylova e Natalia I. Savchenko. "New data on lithology, organic geochemistry and accumulation conditions of the Bazhenov formation in Western Siberia". Georesursy 21, n. 2 (maggio 2019): 129–42. http://dx.doi.org/10.18599/grs.2019.2.129-142.
Testo completoAbstract (sommario):
This paper presents data on lithological composition, distribution, reservoir properties, geochemistry of organic matter and genesis of carbonate rocks of the Bazhenov formation within the central part of Western Siberia (the region of the Khantei hemianteclise). The following types of carbonates are distinguished: a) primary biogenic – shell rock interlayers and residues of coccolith; b) dia- and catagenetic – in varying degrees, recrystallized rocks with coccoliths, nodules and aporadiolarites; c) catagenetic – cracks healed with calcite in limestone of the foot of the Bazhenov formation. It was determined that the crystallization of the carbonate material of nodules took place in various conditions: in the bottom part of the sediments and in the later stages of diagenesis. The source of calcite for nodules was calcareous nanoplankton or bivalve shells. The carbonate content of the cuts decreases in the following sequence: Yuzhno-Yagunsky → Povkhovsky → Novortyagunsky → Druzhny areas, which are associated both with facial features and various physicochemical conditions of diagenesis and catagenesis. Transformation of organic matter increases in the northeast direction from South Yagunsky to Povkhovsky area, which is confirmed by molecular parameters of catagenesis. The carbonate rocks of the bottom part of the Bazhenov formation in the South Yagunsky area are similar in structure to the main oil-bearing reservoirs of the Salym and Krasnoleninsky fields.
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Stennikov, A. V., I. A. Bugaev, A. G. Kalmykov, A. Yu Bychkov, E. V. Kozlova e G. A. Kalmykov. "Experimental study of gydrotermal production of oil from Domanik Formation rocks". Moscow University Bulletin. Series 4. Geology, n. 6 (28 dicembre 2017): 64–69. http://dx.doi.org/10.33623/0579-9406-2017-6-64-69.
Testo completoAbstract (sommario):
The experimental results on the synthetic oil production from Domanik Formation rocks under hydrothermal conditions are given. Oil fractions extracting potential of the rocks under hydrothermal was shown to be up to 60 mg/g or 6,0 wt.%. Inorganic additives (sodium carbonate or silica) incorporation does not influence on the oil recovery factor. Meanwhile the amount of recoverable oil products depends on the mineral composition of the rock. The dependence between the percentage of hydrocarbons emission and mineral composition of the rocks was determined. Clay minerals and silica increase the yield of synthetic oil, carbonates, conversely, inhibit the process.
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Leger, Marie, e Linda Luquot. "Importance of Microstructure in Carbonate Rocks: Laboratory and 3D-Imaging Petrophysical Characterization". Applied Sciences 11, n. 9 (22 aprile 2021): 3784. http://dx.doi.org/10.3390/app11093784.
Testo completoAbstract (sommario):
Carbonate rocks are considered to be essential reservoirs for human development, but are known to be highly heterogeneous and difficult to fully characterize. To better understand carbonate systems, studying pore-scale is needed. For this purpose, three blocks of carbonate rocks (chalk, enthrocal limestone, and dolomite) were cored into 30 samples with diameters of 18 mm and lengths of 25 mm. They were characterized from pore to core scale with laboratory tools. These techniques, coupled with X-ray micro-tomography, enable us to quantify hydrodynamic properties (porosity, permeability), elastic and structural properties (by acoustic and electrical measurements), pore distribution (by centrifugation and calculations). The three rocks have similar properties to typical homogeneous carbonate rocks but have specific characteristics depending on the rock type. In the same rock family, sample properties are different and similarities were established between certain measured properties. For example, samples with the same hydrodynamic (porosity, permeability) and structural (formation factor, electrical tortuosity) characteristics may have different elastic properties, due to their cohesion, which itself depends on pore size distributions. Microstructure is understood as one of the essential properties of a rock and thus must be taken into account to better understand the initial characteristics of rocks.
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Eder, Vika G., Alvina G. Zamiraylova e Georgii A. Kalmykov. "Evidence of carbonate rocks formation on geochemical barriers in black shale on the example of the Bazhenov formation of the Western Siberia". Georesursy 21, n. 2 (maggio 2019): 143–52. http://dx.doi.org/10.18599/grs.2019.2.143-152.
Testo completoAbstract (sommario):
A comprehensive lithological-geochemical study of rocks of the Upper Jurassic-Lower Cretaceous blackshale Bazhenov formation showed that most of its carbonatized interlayers to the boundaries of packs of different composition differing in carbonate content, degree of siliceousness or clayiness. At the same time, at the boundaries of the Bazhenov formation with host sediments, where carbonate rocks are often found in association with “pyrite” low carbon rocks according to geochemical parameters (degree of pyritization, Mn/Al, Ua), a change in the redox regime is recorded. In the most studied stratum at intervals of occurrence of carbonates, a change in the redox regime is not observed. It is assumed that they existed alkaline barriers, as evidenced by the change in the composition of rocks. The following geochemical barriers (bottom-up along the section) were identified in the Bazhenov formation and its transition to the enclosing sediments, on which evidence of localization of carbonate minerals was found: redox barrier 1 (lower BF boundary), alkaline barrier 1 (border of mixes of kerogen - clay-siliceous low-carbonate and silicites), alkaline barrier 2 (border of kerogen-clay-siliceous low-carbonate and siliceous-carbonate “coccolith” packs); Redox barrier 2 (the upper limit of the BF).
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Ali Abro, Waheed, Abdul Majeed Shar, Kun Sang Lee e Asad Ali Narejo. "An integrated analysis of mineralogical and microstructural characteristics and petrophysical properties of carbonate rocks in the lower Indus Basin, Pakistan". Open Geosciences 11, n. 1 (31 dicembre 2019): 1151–67. http://dx.doi.org/10.1515/geo-2019-0088.
Testo completoAbstract (sommario):
Abstract Carbonate rocks are believed to be proven hydrocarbon reservoirs and are found in various basins of Pakistan including Lower Indus Basin. The carbonate rock intervals of the Jakkher Group from Paleocene to Oligocene age are distributed in south-western part of Lower Indus Basin of Pakistan. However, there are limited published petrophysical data sets on these carbonate rocks and are essential for field development and risk reduction. To fill this knowledge gap, this study is mainly established to collect the comprehensive high quality data sets on petrophysical properties of carbonate rocks along with their mineralogy and microstructure. Additionally, the study assesses the impact of diagenesis on quality of the unconventional tight carbonate resources. Experimental techniques include Scanning Electronic Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray diffraction (XRD), photomicrography, Helium porosity and steady state gas permeability. Results revealed that the porosity was in range of 2.12 to 8.5% with an average value of 4.5% and the permeability was ranging from 0.013 to 5.8mD. Thin section study, SEM-EDS, and XRD analyses revealed that the samples mostly contain carbon (C), calcium (Ca), and magnesium (Mg) as dominant elemental components.The main carbonate components observed were calcite, dolomite, micrite, Ferron mud, bioclasts and intermixes of clay minerals and cementing materials. The analysis shows that: 1) the permeability and porosity cross plot, the permeability and slippage factor values cross plots appears to be scattered, which showed weaker correlation that was the reflection of carbonate rock heterogeneity. 2) The permeability and clay mineralogy cross plots have resulted in poor correlation in these carbonate samples. 3) Several diagenetic processes had influenced the quality of carbonates of Jakkher Group, such as pore dissolution, calcification, cementation, and compaction. 4) Reservoir quality was mainly affected by inter-mixing of clay, cementation, presence of micrite muds, grain compactions, and overburden stresses that all lead these carbonate reservoirs to ultra-tight reservoirs and are considered to be of very poor quality. 5) SEM and thin section observations shows incidence of micro-fractures and pore dissolution tended to improve reservoir quality.
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Pękala, Agnieszka. "Silification of the Mesozoic Rocks Accompanying the Bełchatów Lignite Deposit, Central Poland". Geosciences 10, n. 4 (12 aprile 2020): 141. http://dx.doi.org/10.3390/geosciences10040141.
Testo completoAbstract (sommario):
Fieldwork and exploratory study of Poland’s Bełchatów lignite deposit reveals that the Jurassic and Cretaceous sediments with overlying Neogene clays include rocks of greater hardness than the primary composition would indicate. Mineralogical and petrographic tests show the impact of secondary mineralization involving silification in particular. Transitional and carbonate rocks observed microscopically and subjected to X-ray examination show numerous polymorphic forms of silica replacing carbonate minerals. Opal types A and CT, chalcedony, quartz and microcrystalline quartz are all present. The process of silification observed is a selective and multistage one, with selective activity entailing the displacement and replacement of carbonates from older rocks, mainly Cretaceous opoka-rocks and marls, and Jurassic limestones. The opal fills tectonic fractures and has cemented cracked grains. Cathodoluminescence analysis identifies several generations of silica. The rocks have undergone advanced diagenesis as is evidenced by the recorded metasomatic reactions between minerals. They can further be assumed to be in the locomorphic stage. Such observations are relevant to efforts to reconstruct the origin of the rock matrix, and to the study of its textural features. In addition, the tests run on rocks of the lignite series would seem to be of significant value in identifying and developing associated rocks.
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Brusnitsyn, A. I., E. V. Starikova, M. V. Ignatova e V. N. Kuleshov. "The Nadeiyakha Ore occurrence (Pai-Khoi, Russia): an example of ferromanganese metasediments in carbonaceous dolomitic shales". Литология и полезные ископаемые, n. 2 (28 marzo 2019): 165–92. http://dx.doi.org/10.31857/s0024-497x20192165-192.
Testo completoAbstract (sommario):
The paper presents the results of study of metalliferous (ferromanganese and manganese) rocks at the Nadeiyakha ore occurrence (Pai-Khoi) discovered in 2010. The metalliferous deposit represents a stratiform body lying conformably in the Upper Devonian carbonaceous siliceous and clayey–carbonate–siliceous shales. The ore bed occurs 180 m below the regional Famennian manganiferous rock association in Pai-Khoi. Discovery of the Nadeiyakha ore occurrence suggests the existence of an additional age interval of Mn accumulation within the Devonian sequence of this region. The studied metalliferous rocks display structures and textures typical of the metasedimentary rocks. In terms of composition, they are divided into two varieties: (i) ferromanganese (quartz–carbonate) rocks composed of quartz, dolomite, kutnahorite, rhodochrosite, siderite, and calcite; (ii) manganiferous (quartz–rhodochrosite–silicate) rocks composed of quartz, rhodochrosite, tephroite, sonolite, and pyroxmangite. The Nadeiyakha ore occurrence is marked by the abundance of dolomite in the ferromanganese rocks and host shales. In terms of the relationship of indicator elements (Al, Ti, Fe, and Mn), ferromanganese and manganese rocks are comparable with the recent metalliferous and ore-bearing sediments. The carbon isotope composition in carbonates (δ13C from –16.4 to –7.8‰ PDB) corresponds to authigenic carbonates related to the involvement of carbon dioxide produced during the microbial decomposition of organic matter at the stage of dia- and/or catagenesis. Geological and petrographic observations show that the ferruginous and manganiferous sediments were deposited synchronously with the terrigenous–carbonate–siliceous sediments. Fe and Mn could be sourced from hydrothermal solutions or interstitial diagenetic waters. The latter version seems to be more probable. Metals were accumulated in a depression-trap characterized by a periodic stagnation of bottom waters. Such sedimentation setting promoted the formation of paragenetic association of ferruginous and manganiferous sediments with the carbonaceous sediments and fostered reductive conditions during the postsedimentary mineral formation. Calcium carbonates contained in the primary rocks were subjected to dolomitization during the dia- or catagenesis. This process was promoted by the mobilization of Mg released during the transformation of clay minerals owing to the montmorillonite–illite transition. Iron and manganese carbonates were formed during the later replacement of oxides of Mn3+, Mn4+, and Fe3+. Crystallization of manganese silicates also started at early stages of lithogenesis and terminated during the regional metamorphism of metalliferous rocks.
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Wang, Mengqi, Jun Xie, Fajun Guo, Yawei Zhou, Xudong Yang e Ziang Meng. "Determination of NMR T2 Cutoff and CT Scanning for Pore Structure Evaluation in Mixed Siliciclastic–Carbonate Rocks before and after Acidification". Energies 13, n. 6 (13 marzo 2020): 1338. http://dx.doi.org/10.3390/en13061338.
Testo completoAbstract (sommario):
Nuclear magnetic resonance (NMR) is used widely to characterize petrophysical properties of siliciclastic and carbonate rocks but rarely to study those of mixed siliciclastic–carbonate rocks. In this study, 13 different core samples and eight acidified core samples selected amongst those 13 from the Paleogene Shahejie Formation in Southern Laizhouwan Sag, Bohai Bay Basin, were tested by scanning electron microscopy (SEM), micro-nano-computed tomography (CT), and NMR. SEM and CT results revealed a complex pore structure diversity, pore distribution, and pore-throat connectivity in mixed reservoirs. Sixteen groups of NMR experiments addressed changes in these properties and permeabilities of mixed siliciclastic–carbonate rocks before and after acidification to determine its effects on such reservoirs. NMR experimental results showed no “diffusion coupling” effect in mixed siliciclastic–carbonate rocks. Distributions of NMR T2 cutoff values (T2C) are closely related to the pore structure and lithologic characteristics before and after acidification. The T2C index separates irreducible and movable fluids in porous rocks and is a key factor in permeability prediction. Centrifugation experiments showed that, before acidification, the T2C of mixed siliciclastic–carbonate rocks with 60–90% siliciclastic content (MSR) ranged widely from 1.5 to 9.8 ms; the T2C of mixed siliciclastic–carbonate rocks with 60–90% carbonate content (MCR) ranged from 1.8 to 5.6 ms. After acidification, the T2C of MSR ranged widely from 2.6 to 11.6 ms, the T2C of MCR ranged from 1.5 to 5.6 ms, and no significant difference was observed between MCR reservoirs. Based on an analysis of the morphology of NMR T2 spectra, we propose a new T2 cutoff value prediction method for mixed siliciclastic–carbonate rocks based on a normal distribution function to predict various T2C values from morphological differences in NMR T2 spectra and to calculate the irreducible water saturation (Swir), i.e., the ratio of irreducible total fluid volume to effective porosity. The reliability of the proposed method is verified by comparing predicted T2C and Swir values with those from NMR experimental results. New experiments and modeling demonstrate the applicability of NMR for the petrophysical characterization of mixed siliciclastic–carbonate rock reservoirs. Our results have potential applications for identification and evaluation of mixed siliciclastic–carbonate rock reservoirs using NMR logging.
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Waqas, Umer, Hafiz Muhammad Awais Rashid, Muhammad Farooq Ahmed, Ali Murtaza Rasool e Mohamed Ezzat Al-Atroush. "Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review". Applied Sciences 12, n. 5 (7 marzo 2022): 2752. http://dx.doi.org/10.3390/app12052752.
Testo completoAbstract (sommario):
This review paper summarizes the recent and past experimental findings to evaluate the damage characteristics of carbonate rocks subjected to thermal treatment (20–1500 °C). The outcomes of published studies show that the degree of thermal damage in the post-heated carbonate rocks is attributed to their rock fabric, microstructural patterns, mineral composition, texture, grain cementations, particle orientations, and grain contact surface area. The expressive variations in the engineering properties of these rocks subjected to the temperature (>500 °C) are the results of chemical processes (hydration, dehydration, deionization, melting, mineral phase transformation, etc.), intercrystalline and intergranular thermal cracking, the separation between cemented particles, removal of bonding agents, and internal defects. Thermally deteriorated carbonate rocks experience a significant reduction in their fracture toughness, static–dynamic strength, static–dynamic elastic moduli, wave velocities, and thermal transport properties, whereas their porous network properties appreciate with the temperature. The stress–strain curves illustrate that post-heated carbonate rocks show brittleness below a temperature of 400 °C, brittle–ductile transformation at a temperature range of 400 to 500 °C, and ductile behavior beyond this critical temperature. The aspects discussed in this review comprehensively describe the damage mechanism of thermally exploited carbonate rocks that can be used as a reference in rock mass classification, sub-surface investigation, and geotechnical site characterization.
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Seiedi, Omolbanin, Mohammad Zahedzadeh, Emad Roayaei, Morteza Aminnaji e Hossein Fazeli. "Experimental and modeling study of wettability alteration through seawater injection in limestone: a case study". Petroleum Science 17, n. 3 (9 gennaio 2020): 749–58. http://dx.doi.org/10.1007/s12182-019-00407-y.
Testo completoAbstract (sommario):
AbstractWater flooding is widely applied for pressure maintenance or increasing the oil recovery of reservoirs. The heterogeneity and wettability of formation rocks strongly affect the oil recovery efficiency in carbonate reservoirs. During seawater injection in carbonate formations, the interactions between potential seawater ions and the carbonate rock at a high temperature can alter the wettability to a more water-wet condition. This paper studies the wettability of one of the Iranian carbonate reservoirs which has been under Persian Gulf seawater injection for more than 10 years. The wettability of the rock is determined by indirect contact angle measurement using Rise in Core technique. Further, the characterization of the rock surface is evaluated by molecular kinetic theory (MKT) modeling. The data obtained from experiments show that rocks are undergoing neutral wetting after the aging process. While the wettability of low permeable samples changes to be slightly water-wet, the wettability of the samples with higher permeability remains unchanged after soaking in seawater. Experimental data and MKT analysis indicate that wettability alteration of these carbonate rocks through prolonged seawater injection might be insignificant.
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Mack, Greg H., e T. Jerzykiewicz. "Provenance of post-Wapiabi sandstones and its implications for Campanian to Paleocene tectonic history of the southern Canadian Cordillera". Canadian Journal of Earth Sciences 26, n. 4 (1 aprile 1989): 665–76. http://dx.doi.org/10.1139/e89-057.
Testo completoAbstract (sommario):
Late Campanian to Early Paleocene sandstones of the Alberta Foothills were derived from three types of rocks: (i) andesitic–dacitic volcanic rocks that were presumably comagmatic with middle to late Mesozoic plutons in the Omineca Crystalline Belt; (ii) low-grade metamorphic rocks in the suprastructure of the Omineca Crystalline Belt; and (iii) sedimentary rocks in die Rocky Mountain Thrust Belt, principally pelitic rocks in the western Main Ranges and carbonates and chert-arenites in the eastern Main and Front ranges. A paucity of quartzo-feldspathic rocks fragments and potassium feldspar indicates that the core of the Omineca Crystalline Belt was not extensively exposed at that time.Vertical trends in composition of the sandstones reveal five petrographic stages. Stage I is dominated by volcanic rock fragments and plagioclase, suggesting that initial progradation of the sediment was largely a response to coeval volcanism or tectonic emplacement of older volcanic rocks. Stages III and V are characterized by a significant decrease in the relative proportion of metamorphic detritus and an increase in the proportion of carbonate and chert detritus. These stages may represent periods of thrusting in the eastern Main Ranges or Front Ranges. In contrast, stages II and IV display increases in metamorphic detritus and stage II shows a concomitant decrease in carbonate and chert detritus, trends that indicate wearing down of the eastern Main Ranges or Front Ranges thrust sheet(s) and reintegration of the Omineca Crystalline belt and the western Main Ranges into the drainage basin. The compositional stages indicative of thrust events are associated with coarse facies, including the Entrance and High Divide Ridge conglomerates, whereas those stages indicative of tectonic quiescence are associated with fine-grained facies including coal.
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Fahrudin, Eka Sainyakit, Ahmad Syauqi Hidayatillah, Purnaning Tuwuh Triwigati e Muhajir. "Facies Development of Carbonate Rock and System Tract Influence Based on Fullbore Formation Microimager (FMI) and Well Log Analysis on Carbonate Reservoir Tuban Formation, North East Java Basin". E3S Web of Conferences 73 (2018): 02021. http://dx.doi.org/10.1051/e3sconf/20187302021.
Testo completoAbstract (sommario):
The North East Java Basin is known to be one of the basins that consist of Miocene carbonate rocks, like the reef carbonate of Tuban Formation. It has the potential hydrocarbons that can be explored. Therefore, the FMI log analysis is very important to identify carbonate rocks of Tuban Formation to know facies and characteristics of that carbonate rocks. The method used descriptive and analysis process of FMI and Gamma Ray log to determine facies of the carbonate rock and the system tract. Based on the result of FMI log analysis, there are variations lithofasies include mudstone, wackestone, packstone, grainstone, floatstone, rudstone and claystone. A collection of rock associations can interpret the reef facies. It involves back reef facies, reef core facies, and fore reef facies. The changes of lithofasies and reef facies are caused by sea level fluctuations and subsidence resulting in the system tract. The system tracts generated in the research area include transgressive and highstand system tract.
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Christiansen, F. G., H. Nøhr-Hansen e O. Nykjær. "The Cambrian Henson Gletscher Formation: a mature to postmature hydrocarbon source rock sequence from North Greenland". Rapport Grønlands Geologiske Undersøgelse 133 (31 dicembre 1987): 141–57. http://dx.doi.org/10.34194/rapggu.v133.7984.
Testo completoAbstract (sommario):
During the 1985 field season the Cambrian Henson Gletscher Formation in central North Greenland was studied in detail with the aim of evaluating its potential as a hydrocarbon source rock. The formation contains organic rich shale and carbonate mudstone which are considered to be potential source rocks. These are sedimentologically coupled with a sequence of sandstones and coarse carbonates which might be potential reservoir rocks or migration conduits. Most of the rocks exposed on the surface are, however, thermally mature to postrnature with respect to hydrocarbon generation, leaving only few chances of finding trapped oil in the subsurface of the area studied in detail.
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Stoppa, F., A. R. Woolley e A. Cundari. "Extension of the melilite-carbonatite province in the Apennines of Italy: the kamafugite of Grotta del Cervo, Abruzzo". Mineralogical Magazine 66, n. 4 (agosto 2002): 555–74. http://dx.doi.org/10.1180/0026461026640049.
Testo completoAbstract (sommario):
AbstractA new occurrence of a rare kamafugite near L'Aquila, Abruzzo, is described in detail to characterize its paragenesis and to establish possible genetic links with similar alkaline mafic igneous rocks from the Oricola-Camerata Nuova (OC) volcanic field, ˜20 km to the west. Both occurrences belong to the Umbria-Latium-Ultralkaline-District (ULUD), an igneous district represented by rare kamafugites and carbonatites and distinct from the much more voluminous Roman Region (RR) rocks. The new kamafugite was found in a cave known as Grotta del Cervo (GC), associated with epiclastic and pyroclastic rocks. In the latter, lapilli ash tuff, welded lapilli, ultramafic xenoliths, cognate lithics and pelletal lapilli have been identified. The mineralogy of the welded lapilli comprises, in order of decreasing abundance, diopside, leucite, haüyne, Mg-mica, andraditic garnet, apatite, magnetite, kalsilite and olivine. The rock is carbonate-free. Based on bulk-rock chemistry it is classified as a kamafugite, closely approaching the composition of ULUD kamafugites, according to Sahama's (1974) criteria. Separate lapilli ash tuff, characterized by the same silicate mineralogy as that of the welded lapilli, plus modal carbonate exceeding 10 wt.%, is classified as a carbonatitic kamafugite. Bulk-rock and trace-element compositions confirm that the Grotta del Cervo rocks closely approach the ULUD analogues.The Grotta del Cervo occurrence partially fills the geographical and compositional gap between ULUD rocks and the rocks from the Vulture Complex, also a carbonatite and melilitite locality ˜200 km south of GC, and adds considerably to the bulk of kamafugitic and related rocks lying along the Italian Apennines. The petrogenesis of these kamafugites rocks is discussed and possible mineralogical similarities with the Roman Region rocks are highlighted.
45
Zhao, Hongyu, e Junhua Huang. "Characteristics of Calcium Isotopes at Different Water Depths and Their Palaeoenvironmental Significance for Carbonate Rocks of the Permian-Triassic Boundary in Chibi, Southern China". Minerals 12, n. 11 (14 novembre 2022): 1440. http://dx.doi.org/10.3390/min12111440.
Testo completoAbstract (sommario):
Calcium isotopes of carbonate rocks can trace calcium cycles and record changes in the marine environment. As published calcium isotope profiles of carbonate rocks at the Permian-Triassic boundary are rare, comparative studies on deep-water profiles were lacking for the major extinction event that occurred during this time. We present sections of different water depths in the Chibi area of southern China that we have selected for a comparative study. We analyzed carbon isotopes, calcium isotopes, as well as major and trace elements of carbonates from two sections (Chibi North and Chibi West) to obtain information on the volcanic activity, ocean acidification, as well as sea level rise and fall in the Chibi area during the mass extinction period. All carbon and calcium isotopes of carbonates from both sections are all negative after the mass extinction boundary. Carbonates from the Chibi North section have higher δ44/40Ca values and lower Sr/Ca ratios than the rocks from the Chibi West section. We propose that the negative bias of the calcium isotopes in the two sections result from diagenesis. Diagenesis transforms primary aragonite into calcite, showing the characteristics of high δ44/40Ca value and low Sr/Ca. By comparing our data with three published profiles of shallow-water carbonate rock, we recognize that calcium isotopes record gradients at different water depths. In the slope environment, the enhancement of pore fluid action near the coast caused an increase of the fluid buffer alteration, and we propose that a regression event occurred in the Chibi region during the Late Permian.
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Torabi, A., M. U. Johannessen e T. S. S. Ellingsen. "Fault Core Thickness: Insights from Siliciclastic and Carbonate Rocks". Geofluids 2019 (2 giugno 2019): 1–24. http://dx.doi.org/10.1155/2019/2918673.
Testo completoAbstract (sommario):
Fault core accommodates intense deformation in the form of slip surfaces and fault rocks such as fault gouge, cataclasite, breccia, lenses, shale smear, and diagenetic features. The complexity and variation in fault core geometry and thickness affect fluid flow both along and across the fault. In this study, we have investigated a total of 99 faults in siliciclastic and carbonate rocks. This has resulted in two large datasets that include 871 fault core thickness measurements T in siliciclastic rocks and 693 measurements in carbonates, conducted at regular intervals along fault elevations (fault height) on the outcrop or photos of the outcrop. Many of these measurements have been analyzed with respect to fault displacement measurements D in order to study the relationship between displacement and fault core thickness and to further uncover the fault growth process. We found that the fault type and geometry, displacement, type of fault rocks, lithology, and competency contrasts between faulted layers lead to significant variations in the fault core internal structure and thickness. Analysis of average values of fault core thickness-displacement data of this study and of previously published studies shows that the core thickness-displacement relationship follows an overall power law, in which its exponent and intercept change depending on the lithology of the faulted rocks. In general, small faults in carbonate and siliciclastic rocks (D≤5 m) show comparable T/D ratios, with a slightly higher ratio in carbonate rocks. The outcomes of this study contribute to the understanding of the fault core internal structure and variation in fault core thickness as a result of the interplay between fault displacement and host rock in different lithologies. These outcomes have significant implication for characterizing the sealing and conductivity potential of faulted rocks, which is relevant to different applications such as petroleum exploration and development of existing fields, hydrogeology, geothermal energy storage and extraction, and CO2 sequestration.
47
Nie, Xin, Chi Zhang, Chenchen Wang, Shichang Nie, Jie Zhang e Chaomo Zhang. "Variable secondary porosity modeling of carbonate rocks based on μ-CT images". Open Geosciences 11, n. 1 (25 ottobre 2019): 617–26. http://dx.doi.org/10.1515/geo-2019-0049.
Testo completoAbstract (sommario):
Abstract As an essential carbonate reservoir parameter, porosity is closely related to rock properties. Digital rock physics (DRP) technology can help us to build forward models and find out the relationship between porosity and physical properties. In order to prepare models for the rock physical simulations of carbonate rocks, digital rock models with different porosities and fractures are needed. Based on a three-dimensional carbonate digital rock image obtained by X-ray microtomography (μ-CT), we used erosion and dilation in mathematical morphology to modify the pores, and fractional Brownian motion model (FBM) to create fractures with different width and angles. The pores become larger after the erosion operation and become smaller after the dilation operation. Therefore, a series of models with different porosities are obtained. From the analysis of the rock models, we found out that the erosion operation is similar to the corrosion process in carbonate rocks. The dilation operation can be used to restore the matrix of the late stages. In both processes, the pore numbers decrease because of the pore surface area decreases. The porosity-permeability relation of the models is a power exponential function similar to the experimental results. The structuring element B’s radius can affect the operation results. The FBM fracturing method has been proved reliable in sandstones, and because it is based on mathematics, the usage of it can also be workable in carbonate rocks. We can also use the processes and workflows introduced in this paper in carbonate digital rocks reconstructed in other ways. The models we built in this research lay the foundation of the next step physical simulations.
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Cooke, Andy P., Quentin J. Fisher, Emma A. H. Michie e Graham Yielding. "Permeability of carbonate fault rocks: a case study from Malta". Petroleum Geoscience 26, n. 3 (12 agosto 2019): 418–33. http://dx.doi.org/10.1144/petgeo2019-055.
Testo completoAbstract (sommario):
The inherent heterogeneity of carbonate rocks suggests that carbonate-hosted fault zones are also likely to be heterogeneous. Coupled with a lack of host–fault petrophysical relationships, this makes the hydraulic behaviour of carbonate-hosted fault zones difficult to predict. Here we investigate the link between host rock and fault rock porosity, permeability and texture, by presenting data from series of host rock, damage zone and fault rock samples from normally faulted, shallowly buried limestones from Malta. Core plug X-ray tomography indicates that texturally heterogeneous host rocks lead to greater variability in the porosity and permeability of fault rocks. Fault rocks derived from moderate- to high-porosity (>20%) formations experience permeability reductions of up to six orders of magnitude relative to the host; >30% of these fault rocks could act as baffles or barriers to fluid flow over production timescales. Fault rocks derived from lower-porosity (<20%) algal packstones have permeabilities that are lower than their hosts by up to three orders of magnitude, which is unlikely to impact fluid flow on production timescales. The variability of fault rock permeability is controlled by a number of factors, including the initial host rock texture and porosity, the magnitude of strain localization, and the extent of post-deformation diagenetic alteration. Fault displacement has no obvious control over fault rock permeability. The results enable better predictions of fault rock permeability in similar lithotypes and tectonic regimes. This may enable predictions of across-fault fluid flow potential when combined with data on fault zone architecture.
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Lacalamita, M., G. Balassone, E. Schingaro, E. Mesto, A. Mormone, M. Piochi, G. Ventruti e M. Joachimski. "Fluorophlogopite-bearing and carbonate metamorphosed xenoliths from theCampanian Ignimbrite (Fiano, southern Italy): crystal chemical, geochemical and volcanological insights". Mineralogical Magazine 81, n. 5 (ottobre 2017): 1165–89. http://dx.doi.org/10.1180/minmag.2016.080.155.
Testo completoAbstract (sommario):
AbstractFluorine-, boron- and magnesium-rich metamorphosed xenoliths occur in the Campanian Ignimbrite deposits at Fiano (southern Italy), at ∼50 km northeast of the sourced volcanic area. These rocks originated from Mesozoic limestones of the Campanian Apennines, embedded in a fluid flow. The Fiano xenoliths studied consist of ten fluorophlogopite-bearing calc-silicate rocks and five carbonate xenoliths, characterized by combining mineralogical analyses with whole-rock and stable isotope data. The micaceous xenoliths are composed of abundant idiomorphic fluorophlogopite, widespread fluorite, F-rich chondrodite, fluoborite, diopside, Fe(Mg)-oxides, calcite, humite, K-bearing fluoro-richterite and grossular. Of the five mica-free xenoliths, two are calcite marbles, containing subordinate fluorite and hematite, and three are weakly metamorphosed carbonates, composed only of calcite. The crystal structure and composition of fluorophlogopite approach that of the end-member. The Fiano xenoliths are enriched in trace elements with respect to the primary limestones. Comparisons between the rare-earth element (REE) patterns of the Fiano xenoliths and those of both Campanian Ignimbrite and Somma-Vesuvius marble and carbonate xenoliths showthat the Fiano pattern overlaps that of Somma-Vesuvius marble and carbonate xenoliths, and reproduces the trend of Campanian Ignimbrite rocks. Values of δ13C and δ18O depict the same trend of depletion in the heavy isotopes observed in the Somma-Vesuvius nodules, and is related to thermometamorphism. Trace-element distribution, paragenesis, stable isotope geochemistry and data modelling point to infiltration of steam enriched in F, B,Mg and As into carbonate rocks at a temperature of ∼300–450°C during the emplacement of the Campanian Ignimbrite.
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Bhat, Ashaq Hussain, S. K. Pandita, H. N. Sinha, Bindra Thusu e Ahsan Ul Haq. "Provenance, Depositional and Diagenetic Reconstruction of the Early Palaeozoic Succession in Kupwara District, Kashmir, North-western Himalaya". Journal of The Indian Association of Sedimentologists 38, n. 2 (31 dicembre 2021): 101–14. http://dx.doi.org/10.51710/jias.v38i2.192.
Testo completoAbstract (sommario):
Early Palaeozoic succession in Kupwara district of Jammu and Kashmir, North-western Himalaya comprise of sandstone, shale, carbonates and slate. The petrological properties of these rocks were used to work out the provenance, depositional environment and their diagenetic history. The siliciclastic sediments with interbedded carbonate rocks indicate shifts in sea level and consequent changes in energy conditions of the basin as well as biogenic interferences leading to carbonate precipitation in a shallow marine depositional environment. Provenance of these rocks has been of mixed nature with monocrystalline quartz dominant in sandstones indicating greater contribution from igneous sources.