Diagenetic mineral development within the Upper Jurassic Haynesville-Bossier Shale,USA

Despite recent advances, diagenetic processes in fine-grained sediments are still relatively poorly understood. Key questions still to be resolved include the types of diagenetic minerals present in mudstones and the extent of element mobility in these low permeability systems. This study utilizes data from the Haynesville-Bossier Shale, USA, to analyze lithologies, discriminate authigenic phases and identify mobile elements during diagenesis. It has implications for understanding how authigenic minerals develop and the sources of those authigenic minerals in fine-grained sediments. On the basis of grain-size and mineralogy five lithologies are designated: (i) silica-rich argillaceous mudstones; (ii) argillaceous siliceous mudstones; (iii) mixed siliceous mudstones; (iv) mixed mudstones; and (v) authigenically-dominated mudstones. The diagenetic development of the Haynesville-Bossier Shale can be divided into early and late diagenesis. Ferroan and non-ferroan dolomite, framboidal pyrite and bioclast pore-filling kaolinite and calcite grain replacements and cements all formed during early diagenesis. Late diagenetic mineral phases include illite formed by the illitization of smectite, replacive and displacive chlorite, calcite-replacive albite, quartz-replacive calcite and replacive and/or displacive quartz. The presence of extensive late diagenetic mineral precipitates indicates that there was a degree of element mobility on at least the local scale. Aluminium present in albite is most likely to have resulted from the illitization of smectite. Quartz overgrowths probably resulted from illitization and the pressure dissolution at quartz silt grain boundaries. Externally, hydrothermal fluids resulting from regional-scale igneous activity appear to have played a role in the formation of chlorite and possibly albite. The work indicates that extensive mineral development and element mobility occurred during late diagenesis.     

Diagenetic processes in cretaceous sandstones from occidental Brazilian Equatorial Margin

Despite a great interest in Brazilian Equatorial Margin exploration, very little was published on the diagenesis of sandstones from that area. A wide recognition petrographic study was performed to identify the major diagenetic processes that impacted the porosity of Lower Cretaceous sandstones of the Pará-Maranhão, São Luís, Bragança-Viseu and Barreirinhas basins. Arkoses from the Pará-Maranhão Basin show neoformed or infiltrated clay coatings, mica replacement and expansion by kaolinite and vermiculite, and precipitation of grain-replacive and pore-filling quartz, kaolinite, albite, chlorite, calcite, dolomite, siderite, pyrite and titanium oxides. Compaction, quartz and calcite cementation were the main porosity-reducing processes. Barreirinhas Basin lithic arkoses and subarkoses display clay coatings, compaction of metamorphic fragments into pseudomatrix, and precipitation of grain-replacive and pore-filling kaolinite, quartz, albite, chlorite, calcite, dolomite, TiO₂ and pyrite. The main porosity-reducing processes were calcite cementation in the subarkoses, and compaction and quartz cementation in lithic arkoses. Quartzarenites from this basin were early- and pervasively cemented by dolomite. Arkoses and lithic arkoses of the São Luís and Bragança-Viseu basins show clay coatings, pseudomatrix from mud intraclasts compaction, and precipitation of pore-filling and grain-replacive kaolinite, vermiculite, smectite, quartz, albite, chlorite, illite, calcite, dolomite, hematite, TiO₂ and pyrite. Compaction of mud intraclasts and dissolution of feldspars and heavy minerals were the main porosity-modification processes. These preliminary results may contribute to the understanding of the spatial and temporal distribution of the diagenetic processes and their impacts on the porosity of the sandstones from these basins.     

Some aspects of the Krol formation of the Himalaya,India

The Lower Krol sediments consist of intercalations of dolomite with shales in the marginal areas (Solan and Nainital), while limestones are interbedded with marls in the central part of the basin (Massoorie). The Upper Krols are largely composed of dolomites with subordinate limestones and shales.The non-carbonate detrital fraction is dominated by quartz with minor amounts of orthoclase, microcline and plagioclase feldspars. Illite and chlorite constitute the dominant clay minerals, lesser amounts of corrensite and kaolinite are sometimes present. An eastward increase in illite and decrease in chlorite has been ascribed to the supply and distribution of the terrigenum.Zirconium, rubidium, strontium, zinc, nickel and manganese were determined by X-ray fluorescence. Early diagenetic dolomites contain Sr, Zn, Ni and Mn in trace amounts, while the late diagenetic dolomites are characterized by an absence of these elements. The posttectonic dolomites are unusually rich in iron, manganese and sometimes in zinc.Authigenic formation of alkali feldspars, chlorite, illite, quartz and pyrite is not uncommon. The feldspars appear to have formed at early and late diagenetic stages. Potash feldspars dominate over albite in association with dolomite, whereas albite tends to be more common in the limestones.The Krol sedimentation seems to have started in a shallow coastal lagoon behind a barrier beach, upwards changing into tidal-flat deposits.     

Mineralogical and geochemical characteristics of Miocene pelitic sedimentary rocks from the south-western part of the Pannonian Basin System (Croatia): Implications for provenance studies

Fifty-two samples of Miocene pelitic sedimentary rock from outcrops on Medvednica,Moslavacka Gora and Psunj Mts.,and boreholes in the Sava Depression and the Pozega Sub-depression were investigated.These sediments formed in different marine(with normal and reduced salinity),brackish,and freshwater environments,depending on the development stage of the Pannonian Basin System.Carbonate minerals,clay minerals and quartz are the main constituents of all pelitic sedimentary rocks,except in those from Moslavacka Gora Mt in which carbonate minerals are not present.Feldspars,pyrite,opal-CT,and hematite are present as minor constituents in some rocks.Besides calcite,dependent on the sedimentary environment and diagenetic changes,high-magnesium calcite,aragonite,dolomite and ankerite/Cadolomite are also present.Smectite or illite-smectite is the main clay minerals in the samples.Minor constituents,present in almost all samples,are detrital illite and kaolinite.In some samples chlorite is also present in a low amount.Major elements,trace elements and rare earth elements patterns used in provenance analysis show that all analysed samples have a composition similar to the values of the upper continental crust(UCC).The contents of major and trace elements as well as SiO_2/Al_2O_3,K_2O/Al_2O_3,Na_2O/K_2O,Eu/Eu~*,La/Sc,Th/Sc,La/Co Th/Co,Th/Cr,Ce/Ce~* and LREE/HREE ratios,show that the analysed pelitic sedimentary rocks were formed by weathering of different types of mostly acidic(silicic),i.e.felsic rocks.     

A Reconstruction and Discussion of the Effect of Diagenetic Environment on Hydrocarbon Generation Based on Diagenetic Mineral Assemblage in Mudstone

Inorganic minerals in mudstone are composed of clay minerals,carbonate and detrital minerals.Detrital minerals(such as quartz and feldspar)are mainly original deposit.However,clay minerals(kaolinite,illite,and chlorite)and carbonate(calcite and dolomite)are mostly diagenetic minerals.Furthermore,conversion of the four kinds of clay minerals are common.The formation of clay minerals and carbonate is controlled by temperature,pressure,p H,Eh and type of cations during diagenesis.Therefore mineral assemblage can indicate the characteristics and change of diagenetic environment.In addition to inorganic minerals,there are also organic matter of different sources and chemical properties in mudstone.Traditionally,it is considered that evolution of organic matter is controlled by thermal effect.Now studies show that inorganic and organic matter can interact with each other and form clay-organic complexes.This suggest that attention should be paid to the influence of diagenetic mineral assemblage and diagenetic environment on the evolution of organic matter* Samples of mudstone from 1500-4500m of the Palaeogene in the Dongying Depression,China,were collected to investigate the changes of mudstone diagenetic environment.XRD,thin section and SEM were used to detect diagenetic minerals and assemblage characteristics.Results showed that content of detrital minerals,which are floating in mud matrix or preserved as silt laminae,is basically unchanged from shallow to deep strata.Clay minerals which are gathered as argillaceous matrix or preserved as argillaceous laminae have growth and decline relation to carbonate which mainly appear as micropoikilitic ferriferous calcite and ferriferous dolomite.All these characteristics indicate that detrital minerals are exogenetic,whereas carbonate is diagenetic minerals.Based on the SEM analysis of the clay minerals,it was found that smectite present honeycomb and reticulate structure,while illite present filiform and schistose structure and there are growth and decline relationship between them.Nevertheless,hexagonal tabular and stratified kaolinite has the highest content from 2400m to3300m.Rosette and stratified chlorite shows increase trend when the burial depth is deeper than 3300m.These characteristics indicated that clay minerals are diagenetic minerals and there are conversions among the four types.Therefore form shallow to deep,three diagenetic mineral assemblage zones can be divided based on the characteristics of carbonate and clay minerals in mudstone.Namely,smectite+illite/smectite zone in the depth of 2000-2500m;kaolinite+illite/smectite zone in the depth of 2500-3300m and illite+chlorite+carbonate zone below 3300m.Previous studies showed that kaolinite is stable under acidic conditions,while other clay minerals and carbonate are stable under alkaline conditions.Hence according to mineral assemblages feature,it was inferred that diagenetic environment of mudstonehasundergonethechangeof alkaline-acid-alkaline.For the organic matter with different chemical properties in mudstone,the hydrocarbon generation will be different in the acidic and alkaline diagenetic environment even if the conditions of temperature and pressure are the same.Therefore,for hydrocarbon generation we should not only focus on thermal effect,but also pay more attention to the differences of diagenetic environment which have great significance for the understanding of hydrocarbon generation,hydrocarbon expulsion and reservoir formation in mudstone.     

黄骅坳陷三马地区中-深部储层成岩作用及主控因素分析

黄骅坳陷三马地区储集岩样品的显微特征及成岩矿物的组合关系分析结果表明，三马地区下第三系中深层储层主要处于晚成岩A期，成岩现象包括石英、长石的次生加大、碳酸盐矿物胶结作用、矿物交代作用、溶解作用和粘土矿物转化作用等。其中石英次生加大于2700m左右开始出现，随埋深增大，石英增生加强；长石次生加大现象不十分普遍；碳酸盐胶结作用包括早期自生泥晶方解石胶结作用、连晶方解石和晚期白云石(或铁方解石)的胶结作用。在扫描电镜下可见到方解石与含铁方解石集合体充填在粒间孔隙中或与石英、钠长石及粘土矿物共生，白云岩多呈菱形粒状分布于粒间；常见的交代现象主要有方解石交代长石、石英及粘土矿物，粘土矿物交代长石、石英等；溶解作用主要有长石的溶解、碳酸盐颗粒的溶解和方解石胶结物的溶解等，粘土矿物的转化主要为蒙脱石、高岭石向伊利石(或绿泥石)转化。还讨论了储层岩相、岩性特征、孔隙水中有机酸含量、早期方解石的充填、烃类早期注入等因素对储层成岩演化的控制作用。     

金沙江河流悬浮物与沉积物的矿物学特征及其表生地球化学意义

为研究金沙江流域表生风化特征,系统采集了金沙江和岷江流域32件河流悬浮物和河床砂样品,对其进行了矿物组成分析。结果表明,不同江段河流悬浮物、沉积物的矿物组成大致相同,以石英、方解石、斜长石和粘土矿物为主,局部有白云石、钾长石和角闪石等;粘土矿物主要有伊利石、绿泥石、高岭石和蒙脱石。河床沉积物中非粘土矿物碎屑(岩屑)含量明显高于悬浮物。伊利石为铁镁质,Kubler指数在轻微变质范围内,主要来源于三叠系碎屑岩和砂板岩。金沙江、岷江的河流悬浮物矿物组成与流域内出露的碎屑岩、砂板岩、火成岩、碳酸盐岩等的分布有较好的对应关系。河流悬浮物和沉积物的矿物组成及伊利石结晶指数特征表明流域内以物理风化为主。     

酒西盆地碎屑岩胶结物的形成问题

酒西盆地下白垩统陆相碎屑岩胶结物的形成关系到油气储集的重要问题,富铁的洪积扇沉积体系和非富铁的河流一湖泊沉积体系形成两种不同的胶结物组合类型,平面上可分为三带胶结物:混合胶结带、铁镁胶结带和浓聚成岩带。盆地边缘带是以铁、泥、钙为主的混合胶结物,中间为以碳酸铁镁矿物的白云石、铁白云石为主的胶结物,盆中带形成胶结物的浓聚成岩层,事实证明过渡的铁镁胶结带是最富于聚集油气的地带。本文还在纵向上探讨了泥质粘土矿物和碳酸盐胶结物的成岩变化。     

Rock composition and origin of the Duwi Formation calcareous rocks, Upper Egypt

Upper Cretaceous phosphorite beds of the Duwi Formation, Upper Egypt, are intercalated with limestone, sandy limestone, marl, calcareous shales, and calcareous sandstone. Calcareous intercalations were subjected to field and detailed petrographic, mineralogical and geochemical investigations in order to constrain their rock composition and origin. Mineralogically, dolomite, calcite, quartz, francolite and feldspars are the non-clay minerals. Smectite, kaolinite and illite represent the clay minerals. Major and trace elements can be classified as the detrital and carbonate fractions based on their sources. The detrital fraction includes the elements that are derived from detrital sources, mainly clay minerals and quartz, such as Si, Al, Fe, Ti, K, Ba, V, Ni, Co, Cr, Zn, Cu, Zr, and Mo. The carbonate fraction includes the elements that are derived from carbonates, maily calcite and dolomite, such as Ca, Mg and Sr. Dolomite occurs as being dense, uniform, mosaic, very fine-to-fine, non-ferroan, and non-stoichiometrical, suggesting its early diagenetic formation in a near-shore oxidizing shallow marine environment. The close association and positive correlation between dolomite and smectite indicates the role of clay minerals in the formation of dolomite as a source of Mg^2＋ -rich solutions. Calcareous rocks were deposited in marine, oxidizing and weakly alkaline conditions, marking a semi-arid climatic period. The calcareous/argillaceous alternations are due to oscillations in clay/carbonate ratio.     

Alteration mineralogy of eocene volcanic and volcaniclastic rocks from Sivas basin in Turkey

The study area covers volcanic-volcanosedimentary units of Eocene age in the Sivas-Ula? area from Turkey. The pyroclastic (tuffaceous claystone/siltsone/sandstone, crystal ash tuff) and volcanic (basalt, basaltic andesite, andesite) rocks of the Karacalar member from the Kaleköy Formation include volcanogenic (plagioclase, augite, hornblende, biotite), diagenetic (K-feldspar, mixed-layered chlorite-smectite/C-S, chlorite, analcime) and post-volcanic (calcite, dolomite, quartz) minerals. The volcanogenic (plagioclase), diagenetic (K-feldspar, C-S, chlorite), postvolcanic (quartz, calcite, dolomite) and detrital (illite) minerals were observed in the epiclastic (shale, siltstone, calcareous siltstone, sandstone, calcareous sandstone) and chemical (limestone, gypsum) rocks of the Yapali member from this formation. C-S + K-feldspar zoning is widely developed by due to the interaction between sea-water and volcanic glass in basic-intermediate composition, on the basis of optic and electron microscopes and also X-rays data. This zone corresponds to the deeper parts of the Sivas basin in the Eocene period and show vertically a transition into zeolite zone in approximately northern parts of the basin (Yavu area).     

兰州市取暖期可吸入颗粒物中单颗粒矿物组成特征

为研究兰州市2005年冬季大气可吸入颗粒物(PM10)中单颗粒的矿物组成,用能谱扫描电镜识别和统计了兰州市区(东方红广场)和郊区(榆中县)两个采样点的单矿物颗粒。结果在市区样品中识别出方解石、伊/蒙混层、石英、斜长石、伊利石、石膏、绿泥石、高岭石、浊沸石和钾长石等21种矿物,前7种占统计总量的75%以上;郊区样品中识别出20种矿物,以方解石、石英、伊利石、绿泥石、斜长石和伊/蒙混层为主(占70%以上),与市区相比缺少钾石膏、金红石和水铝酸钙而增加了硫酸镁和磷灰石。总体来看,大气PM10中的矿物颗粒可分为粘土类、长石类、碳酸盐类、硫酸盐类、氧化物类和其他六类,以粘土类和碳酸盐类矿物为主(约占60%);冬季市区颗粒物表面的“硫化”现象较郊区严重;这些矿物颗粒主要来自地表土,人为排放和大气中二次化学反应生成的矿物的贡献较小。     

Mineral and chemical composition of Karak mudstone, Kohat Plateau, Pakistan: implications for smectite-illitization and provenance

The Karak mudstone interbedded in an Eocene evaporite sequence, is dominated by R-1 ordered illite-smectite with a 20 to 30% expandable component. Minor phases include kaolinite, chlorite, illite/muscovite, plagioclase, potash feldspar, quartz, dolomite and pyrite. The present illite-smectite was probably originally smectite or highly expandable illite-smectite which underwent conversion to illite-smectite with a low expandable component in a comparatively low-temperature (ca. 100°C) closed-system sedimentary basinal diagenetic environment at a depth of ca. 5 km. Al³⁺ and K⁺ necessary for the conversion reaction were provided through the breakdown of potash feldspar. Burial under a 5 km thick pile of sediments produced some of the observed structures. Whole-rock chemistry presented here suggests that the mudstone formed by severe weathering of acidic source rocks. The influx of freshwater probably flushed out Ba, Rb, Ca and Mn from the restricted basin.     

Effect of diagenesis on clay mineralogy and organic matter in the Tunisian southern subsurface

This study aims to follow the effect of the diagenetic transformations on the clayey fraction and the organic matter of the Tunisian southern sub-surface. 61 samples from oil well named NWA-1 were recuperated for series of analyses. This study follows a comparative approach between the mineralogical, geochemical and petrographic studies. To discuss results from a statistical viewpoint, the Principal Component Analysis (PCA) was applied in order to find out any correlation between different components. The associated minerals quartz, feldspar, calcite, pyrite, anhydrite, gypsum, dolomite and olivine are also detected. These associated minerals remove by-products by the illitization reaction. The Index of Crystallinity (IC) of illite shows that, except some anomalies, the studied samples are between the epizone and the anchizone. Downward, samples show the effect of diagenetic processes and weak signs of low-grade metamorphism. As regards to the organic matter, values of Tmax range between 333°C and 463°C. On the other hand, potential hydrocarbon compounds (S2) show low values compared to those of (S1); but they maintain a similar variability from 0.63 to 21.12. SEM observations and X-ray microanalyses supported the formation of authigenic micro-quartz. The PCA of clay minerals, chemical components, and the depth shows three different populations. Feldspar, chlorite and quartz make up a population positively correlated with the depth. The second population seems to be indifferent to depth variation; it is made up of two sub-populations: the population of illite, gypsum and anhydrite, which is obtained by a counter clock rotation of depth population; and the population of pyrite, kaolinite, olivine phyllosilicate, which is obtained by an anticlockwise rotation of depth population. Third, the population of smectite, calcite and dolomite is inversely proportional to the depth variation. On the other hand, the PCA of TOC, Tmax, HI, S1, S2 and the depth make up a homogenous statistical population following the depth evolution.     

Diagenetisch gebildeter Magnesit und Dolomit in den Grödener Schichten des Dobratsch im Gailtal,Kärnten — österreich

Dolomite, magnesite, calcite and aragonite are described from sandstones and conglomerates of the Grödener Schichten of the Dobratsch in the Gailtal Alps, Carinthia — Austria. The carbonates occur as early and late diagenetic cements, as recrystallized matrix of more or less laminated carbonate layers (up to 0.5 m thick), as concretions, as fillings of early diagenetic shrinkage cracks and late diagenetic fissures and as crystals in open cavities and clefts. The formation of dolomite and magnesite may have been caused by pore solutions highly enriched in magnesium, which are likely to have formed by evaporation in a hypersaline environment. Magnesite and dolomite most probably have been formed diagenetically from aragonite and/or calcite during progressive evaporation cycles. Because of magnesite is a common constituent in Permo-Scythian sediments of the Eastern Alps, its presence is of importance for the evaluation of the environment. Additionally the wide-spread occurrence of magnesite within these post variscian sediments has important implications regarding the paleogeographical reconstruction and the evaluation of diagenetic processes.     

Organic petrology, mineralogy and depositional environment of the Kipra lignite seam, Maritza-West basin, Bulgaria

The aim of the present study is to provide additional information about the properties and depositional environment of the Kipra lignite seam, which was deposited during the regressive stage of development of the Maritza-West basin. Petrographical and mineralogical data, along with ash yields and sulphur contents of 24 samples from a seam profile, have been used to study the vertical variation of the depositional settings during peat accumulation and subsequent coalification.The Kipra lignite is characterized by high ash yields and sulphur contents. It formed in a rheotrophic, low-lying mire with alkaline pH value. Vegetation with low preservation potential dominated within the palaeomire. During peat formation, frequent changes of the water level controlled the depositional environment. During the deposition of units 1 and 2, high water energy caused the transportation of high amounts of inorganic material into the mire, resulting in the formation of weakly gelified mineral-rich lignite. The organic matter from units 3 and 4 is characterized by enhanced gelification, which probably reflects the decreasing energy of the system. Good positive correlation between sulphur contents and the GI values was established in units 4, indicating that the gelification of the tissues was probably mainly controlled by the bacterial activity. In contrast, the gelification of the samples from unit 3 of the Kipra seam was probably governed by the redox conditions. The organic matter deposited under relatively wet conditions, in which the thermal and oxidative destruction of the tissues, was limited.A variety of major, minor and accessory minerals are present in Maritza-West lignite. The mineral composition is dominated mainly by pyrite, gypsum and calcite, and to a lesser extent limonite, quartz, kaolinite, montmorillonite, illite, chlorite and plagioclase. Jarosite, hematite, halloysite, mica, K-feldspar, aragonite, siderite, and dolomite were also determined in very low concentrations. These minerals formed syngenetically and epigenetically. The syngenetic stage is characterized mainly by the formation of pyrite, carbonates, silicates and sulphates, whereas the Fe-oxyhydroxides, partially the carbonates and almost all silicates are of detrital origin. During the epigenetic stage, carbonates, sulphates, clay minerals, pyrite, and Fe-oxyhydroxides were formed. Alteration products like gypsum, jarosite, limonite, chlorite, kaolinite, illite, mica, and calcite were generated due to the transformation of detrital and authigenic minerals.     

大港滩海区第三系湖相混积岩的成因与成岩作用特征

大港滩海第三系沙河街组一段下部分布的混积岩主要为陆源碎屑质-碳酸盐混积岩, 其次为碳酸盐质-陆源碎屑混积岩和含碳酸盐-陆源碎屑混积岩.其中白水头地区的混积岩发育于辫状河-扇三角洲前缘水下分流河道沉积体系之中,为相缘渐变混合沉积的产物;而马东-马东东地区的混积岩发育于重力流沉积体系之中,为浊流沉积的产物.本区混积岩主要经历了压实作用、胶结作用和溶蚀溶解作用.孔隙流体的化学性质经历了由碱性到酸性,最后又回到碱性的变化历程.其中海绿石、微晶方解石、部分石英溶蚀和连生方解石为碱性流体条件下的共生组合;次生加大石英、油气侵位、溶蚀溶解、高岭石为酸性条件下的共生组合;伊利石、绿泥石、钠长石化、孔隙充填方解石和白云石为碱性流体条件下的共生组合.     

Diagenetic evolution of the volcaniclastic deposits: an example from Neoproterozoic Dokhan Volcanics in Wadi Queih basin,central Eastern Desert,Egypt

Wadi Queih basin hosts a ～2,500-m thick Neoproterozoic volcanoclastic successions that unconformably lie over the oldest Precambrian basement. These successions were deposited in alluvial fan, fluviatile, lacustrine, and aeolian depositional environments. Diagenetic minerals from these volcaniclastic successions were studied by X-ray diffractometry, scanning electron microscopy, and analytical electron microscopy. The diagenetic processes recognized include mechanical compaction, cementation, and dissolution. Based on the framework grain–cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-filling clay cements. Secondary porosity development occurred due to partial to complete dissolution of early calcite cement and feldspar grains. In addition to calcite, several different clay minerals including kaolinite, illite, and chlorite with minor smectite occur as pore-filling and pore-lining cements. Chlorite coating grains helps to retain primary porosity by retarding the envelopment of quartz overgrowths. Clay minerals and their diagenetic assemblages has been distinguished between primary volcaniclastics directly produced by pyroclastic eruptions and epiclastic volcaniclastics derived from erosion of the pre-existing volcanic rocks. Phyllosilicates of the epiclastic rocks display wider compositional variations owing to wide variations in the mineralogical and chemical compositions of the parent material. Most of the phyllosilicates (kaolinite, illite, chlorite, mica, and smectite) are inherited minerals derived from the erosion of the volcanic basement complex, which had undergone hydrothermal alteration. Smectites of the epiclastic rocks are beidellite–montmorillonite derived from the altered volcanic materials of the sedimentary environment. Conversely, phyllosilicate minerals of the pyroclastic rocks are dominated by kaolinite, illite, and mica, which were formed by pedogenetic processes through the hydrothermal influence.     

不同类型煤矸石中微量元素含量的探讨

通过采集山东省兖济滕煤炭基地不同类别煤矸石（砂质矸、泥质矸、新鲜矸、风化矸、自燃矸）样品,对其矿物组成及微量元素含量进行分析测试。结果显示：矸石样品矿物组成主体均为高岭石、石英、伊利石／蒙脱石混层、蒙脱石、长石、方解石、白云石及黄铁矿等矿物,所测样品中未发现绿泥石。各种类型煤矸石样品中微量元素含量差别较大,砂、泥质含量不同的矸石样品中微量元素含量不同。砂质矸中微量元素含量低,泥质矸含量相对高。自燃矸大部分微量元素含量高于新鲜矸和未自燃风化矸,Co、Ni、Cu、Mo、Cd元素在自燃矸、风化矸中均显示富集的性质,但自燃矸比风化矸对元素的富集作用更为明显,因此泥质矸、风化矸、自燃矸可以释放出更多的有害微量元素,综合利用中应予以注意。     

塔中地区志留系沥青砂岩成岩作用及其对储层性质的影响

运用沉积学原理对塔中地区志留系经历复杂成岩演化的沥青砂岩进行研究分析,了解到该岩石主要经过压实作用、胶结作用和溶蚀作用等成岩作用。其胶结物的主要类型有绿泥石、伊利石、高岭石、伊-蒙混层等粘土矿物以及碳酸盐矿物、石英、长石、黄铁矿等。孔隙类型以粒间孔隙、粒内孔、铸模孔、特大孔、裂缝孔隙等为主,其中以粒间孔隙最为发育,低地温梯度有利于在深层形成次生孔隙。志留系沥青砂岩储层物性受沉积和成岩双重因素的影响,成岩演化阶段处于晚成岩A期。根据影响储层物性的储层成岩作用,可将成岩相类型划分为不稳定碎屑溶蚀成岩相、压实-弱溶蚀成岩相、压实充填成岩相、压实压溶成岩相、碳酸盐胶结成岩相等几种主要类型,成岩相类型决定了储层性质,不稳定碎屑溶蚀成岩相和压实-弱溶蚀成岩相是本区较好的油气储层。     

'Forbidden zone' subduction of sediments to 150 km depth— the reaction of dolomite to magnesite + aragonite in the UHPM metapelites from western Tianshan, China

The solid‐state reaction magnesite (MgCO₃) + calcite (aragonite) (CaCO₃) = dolomite (CaMg(CO₃)₂) has been identified in metapelites from western Tianshan, China. Petrological studies show that two metamorphic stages are recorded in the metapelites: (1) the peak mineral assemblage of magnesite and calcite pseudomorphs after aragonite which is only preserved as inclusions within dolomite; and (2) the retrograde glaucophane‐chloritoid facies mineral assemblage of glaucophane, chloritoid, dolomite, garnet, paragonite, chlorite and quartz. The peak metamorphic temperatures and pressures are calculated to be 560–600 °C, 4.95–5.07 GPa based on the calcite–dolomite geothermometer and the equilibrium calculation of the reaction dolomite = magnesite + aragonite, respectively. These give direct evidence in UHP metamorphic rocks from Tianshan, China, that carbonate sediments were subducted to greater than 150 km depth. This UHP metamorphism represents a geotherm lower than any previously estimated for subduction metamorphism (< 3.7 °C km^?1) and is within what was previously considered a ‘forbidden’ condition within Earth. In terms of the carbon cycle, this demonstrates that carbonate sediments can be subducted to at least 150 km depth without releasing significant CO₂ to the overlying mantle wedge.