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1.
To understand the behavior of trace metals in the salt marsh at Skallingen, Danish Wadden Sea, we investigated a profile from surface to 25?cm depth of the salt marsh sediment, focusing primarily on clay mineralogy and grain size distribution of the sediments and their relationship with trace metals. The clay assembly of the sediment consists of illite, kaolinite and much less chlorite and smectite. The major clay minerals of illite, kaolinite as well as chlorite correlate very poorly with all the trace metals investigated, due probably to the weak competing strength of these clays compared with the other adsorbents and to low availability of the mobile trace metals in the system. Correlation between trace metals and clay minerals may therefore be used as an indicator in environmental assessment. Fine grain fractions of the sediment increased markedly after salt marsh invasion in about 1931 but decreased after 1964. This increase was contributed mainly by the grains finer than 20???m while the fraction of 40?C63???m actually decreased soon after the invasion. The relation between most of the trace metals and grain size distributions is close in general but far from linear. The drastic turning point is observed at about 30???m, around where the correlation coefficient r drops from 0.8 to 0.1. Adsorption is the controlling mechanism for the behavior of trace metals in the salt marsh. Fe/Mn (hydr)oxides and organic matter play the key role.  相似文献   

2.
汪寿松  陈昌明  Irion  G 《沉积学报》1988,6(2):78-96
本文目的在于说明有限区域内潮坪小环境沉积物的矿物学和地球化学特点及沉积过程的改造作用。沉积物样品取自汪额诺格岛与联邦德国的德国湾南岸之间的障壁潮坪。粒度分析表明,障壁潮坪由大体平行于大陆的泥坪、混合坪到砂坪三个带组成。粘土矿物以伊利石为主,其次为蒙脱石、高岭石和绿泥石,与北海粘土矿物组合一致。粘土矿物组成和重金属Fe、Mn、Cu、Pb、Zn含量在潮坪不同部位相差无几,说明沉积物受到潮汐水流反覆侵蚀和再沉积作用的混合作用。近潮口附近有机碳含量增高是潮汐水流从北海通过进潮口携入有机物的结果。  相似文献   

3.
Abstract

The characteristics and distribution of clay minerals and their effects on reservoir quality in the Huagang sandstones in the Xihu Sag, East China Sea Basin were studied by using X-ray diffraction, casting thin-sections, scanning electron microscopy, electron microprobe analysis, fluid inclusion analysis, constant-rate mercury injection and nuclear magnetic resonance. Clay minerals consist of kaolinite, chlorite, illite and illite–smectite mixed layer (I/S); kaolinite forms from dissolved feldspars, chlorite occurs as clay coatings that are transformed from clay precursors owing to the flocculation of suspended detrital clays or the crystallisation of pore fluids, and illite forms from the illitisation of detrital smectite, authigenic kaolinite and K-feldspars. Clay distribution is controlled by sedimentary environments, burial history and lithologies. Typical reservoirs in the western sub-sag are thin and developed in braided river facies at relatively shallow burial depths with clays dominated by kaolinite. However, typical reservoirs in the central inversion tectonic zone are thicker and developed in a braided delta front facies at deeper burial depths with clays mainly consisting of chlorite, illite and I/S. High-quality reservoirs are characterised by coarse granularity, high quartz content and low clay content with widespread development of chlorite coatings that inhibit quartz cements at low temperatures. At higher temperatures, the high-quality reservoirs develop more pores providing growth space for quartz cements and result in the coexistence of chlorite coatings and quartz cements. The high-quality reservoirs are controlled by their lithological characteristics rather than chlorite coatings. Illite and I/S clays create severe damage to reservoirs by reducing the size and connectivity of pore-throats.  相似文献   

4.
Laboratory experiments indicate that clay particles of the <2-üm fraction can be considerably degraded by the bivalve Mytilus edulis: dickite, kaolinite, smectite, chlorite and illite particles are partially dissolved and rounded by the digestive processes. Structural changes and a decrease in crystallinity of kaolinites, dickites and illites are striking. Investigations of clay minerals from tidal flat sediments highly populated by marine invertebrates, from marine suspensions and samples from profiles across Mytilis edulis beds on the North Sea coast of Germany show, however, that these materials have a uniform mineral composition. This uniformity of clay mineralogy can be explained by the hydrodynamic conditions in the nearshore area, where tidal currents and waves cause a periodic resuspension and transport of sediments introduced into the Wadden Sea from different sources (glacial, fluviatile). Processes of bioturbation also redistribute the sedimentary material. These mixing processes effectively erase any evidence of local enrichment of the biogenically degraded clays. However, the disordered clays should react more sensitively (i.e. have higher adsorption capacities for organic substances, hydroxides and metals) in sediments than untreated materials, so that biodegradation is of basic importance for clay diagenesis. During these processes, Pb, V, Ni and Fe are dissolved from the digested particles.  相似文献   

5.
The spatial distribution of clay minerals in sandstones, which may both enhance or degrade reservoir quality, is poorly understood. To address this, clay mineral distribution patterns and host‐sediment properties (grain size, sorting, clay fraction abundance and bioturbation intensity) have, for the first time, been determined and mapped at an unprecedentedly high‐resolution in a modern estuarine setting (Ravenglass Estuary, UK). Results show that the estuary sediment is dominated by illite with subordinate chlorite and kaolinite, although the rivers supply sediment with less illite and significantly more chlorite than found in the estuary. Fluvial‐supplied sediment has been locally diluted by sediment derived from glaciogenic drift deposits on the margins of the estuary. Detailed clay mineral maps and statistical analyses reveal that the estuary has a heterogeneous distribution of illite, chlorite and kaolinite. Chlorite is relatively most abundant on the northern foreshore and backshore and is concentrated in coarse‐grained inner estuary dunes and tidal bars. Illite is relatively most abundant (as well as being most crystalline and most Fe–Mg‐rich) in fine‐grained inner estuary and central basin mud and mixed flats. Kaolinite has the highest abundance in fluvial sediment and is relatively homogenous in tidally‐influenced environments. Clay mineral distribution patterns in the Ravenglass Estuary have been strongly influenced by sediment supply (residence time) and subsequently modified by hydrodynamic processes. There is no relationship between macro‐faunal bioturbation intensity and the abundance of chlorite, illite or kaolinite. Based on this modern‐analogue study, outer estuarine sediments are likely to be heavily quartz cemented in deeply‐buried (burial temperatures exceeding 80 to 100°C) sandstone reservoirs due to a paucity of clay grade material (<0·5%) to form complete grain coats. In contrast, chlorite‐enriched tidal bars and dunes in the inner estuary, with their well‐developed detrital clay coats, are likely to have quartz cement inhibiting authigenic clay coats in deeply‐buried sandstones.  相似文献   

6.
Clay minerals formed through chemical weathering have long been implicated in the burial of organic matter (OM), but because diagenesis and metamorphism commonly obscure the signature of weathering-derived clays in Precambrian rocks, clay mineralogy and its role in OM burial through much of geologic time remains incompletely understood. Here we have analyzed the mineralogy, geochemistry and total organic carbon (TOC) of organic rich shales deposited in late Archean to early Cambrian sedimentary basins. Across all samples we have quantified the contribution of 1M and 1Md illite polytypes, clay minerals formed by diagenetic transformation of smectite and/or kaolinite-rich weathering products. This mineralogical signal, together with corrected paleo-weathering indices, indicates that late Archean and Mesoproterozoic samples were moderately to intensely weathered. However, in late Neoproterozoic basins, 2M1 illite/mica dominates clay mineralogy and paleo-weathering indices sharply decrease, consistent with an influx of chemically immature and relatively unweathered sediment. A late Neoproterozoic switch to micaceous clays is inconsistent with hypotheses for oxygen history that require an increased flux of weathering-derived clays (i.e., smectite or kaolinite) across the Precambrian-Cambrian boundary. Compared to previous studies, our XRD data display the same variation in Schultz Ratio across the late Neoproterozoic, but we show the cause to be micaceous clay and not pedogenic clay; paleo-weathering signals cannot be recovered from bulk mineralogy without this distinction. We find little evidence to support a link between these mineralogical variations and organic carbon in our samples and conclude that modal clay mineralogy cannot by itself explain an Ediacaran increase in atmospheric oxygen driven by enhanced OM burial.  相似文献   

7.
《Comptes Rendus Geoscience》2008,340(12):779-790
Acoustic P and S wave propagation in the argillaceous sediments is related to the media porosity as well as on clay-mineral composition. The propagation-velocity prediction of these waves thus requires knowledge of these two parameters and their impact on the velocities. Porosity decreasing with effective pressure increasing, due to the burial, follows an exponential law. We will limit our analysis to the three clays: kaolinite, illite and montmorillonite. The variations of porosity between various clays are strongly reduced with the increase in effective pressure, which tends to minimize the impact of mineralogy with the burial. By integrating these equations in a model of Reuss and Voigt, in which we consider an association mineral argillaceous/fluid, we extract a law of evolution for bulk and shear moduli of clay according to the pressure, for each type of clay. By associating clay moduli calculation results to qualitative and quantitative predictions from spectral nuclear-radiations tools and X-ray-diffraction measurements on cores, it is possible to predict sonic velocities in clays with a given effective pressure. An example of P and S velocity modelling is presented on a well in the deep offshore-turbiditic environment.  相似文献   

8.
The Late Cretaceous sedimentary sequence in the Upper Benue Trough consists of seven formations. Outcrop samples from the type localities of these units were analysed by X-ray diffraction for their day mineral content. The composition and distribution of the clay minerals are influenced by tectonics, relief and water depth. Three main depositional phases are recognizable on the basis of clay mineral assemblages, two of which are associated with tectonic movements. The first phase, characterized by the presence of chlorite, illite, kaolinite and mixed-layer clays is common to Albian-Cenomanian sediments. This phase is succeeded by mixed-layer clays and smectite-rich, Turonian-Early Santonian sediments. The re-occurrence of chlorite and illite in association with kaolinite and mixed-layer clays in the Post-Santonian sediments constitutes the third depositional phase. These clay mineral assemblages are indicative of two periods of tectonism (Albian and Late Santonian) and an intervening Turonian-Early Santonian period of quiescence in the Upper Benue Trough.  相似文献   

9.
Burial Metamorphism of the Ordos Basin in Northern Shaanxi   总被引：1，自引：0，他引：1  
Burial metamorphism has been found in the Ordos basin of northern Shaanxi. On the basis of a rather intensive study of burial metamorphism of sandstone, it has been shown that the evolution from diagenesis to metamorphism involves four stages: cementation of clay minerals, regrowth of pressolved quartz and feldspar, cementation of carbonates and formation of laumontite. On that basis it has been put forward that the laumontite is formed by burial metamorphism of clay and carbonate minerals. According to the thermodynamic data of minerals, the conditions under which laumontite is formed are T<250℃ and X_(CO_2)<0.17. High-resolution SEM and TEM studies of clay minerals in mudstone show that there occur a mixed layer assemblage of bertherine and illite/chlorite and transformation from bertherine to chlorite. On that basis coupled by the X-ray diffraction analysis the author suggests the following transformation of clay minerals during burial metamorphism: the earliest smectite-kaolinite assemblage changes into the bertherine-illite mixture with increasing depth, then into the illite/chlorite mixed layer assemblage and finally into dispersed individual illite and chlorite. The reaction of the transformation is:smectite+kaolinite+K~+=illite+chlorite+quartz According to the study of the oxygen isotope thermometry of the coexisting illitequartz pair, the temperature of the above transformation is lower than 180℃.  相似文献   

10.
Iheya‐North‐Knoll is one of the small knolls covered with thick sediments in the Okinawa Trough back‐arc basin. At the east slope of Iheya‐North‐Knoll, nine hydrothermal vents with sulfide mounds are present. The Integrated Ocean Drilling Program (IODP) Expedition 331 studied Iheya‐North‐Knoll in September 2010. The expedition provided us with the opportunity to study clay minerals in deep sediments in Iheya‐North‐Knoll. To reveal characteristics of clay minerals in the deep sediments, samples from the drilling cores at three sites close to the most active hydrothermal vent were analyzed by X‐ray diffraction, scanning electron microscope and transmission electron microscope. The sediments are classified into Layer 0 (shallow), Layer 1 (deep), Layer 2 (deeper) and Layer 3 (deepest) on the basis of the assemblage of clay minerals. Layer 0 contains no clay minerals. Layer 1 contains smectite, kaolinite and illite/smectite mixed‐layer mineral. Layer 2 contains chlorite, corrensite and chlorite/smectite mixed‐layer mineral. Layer 3 is grouped into three sub‐layers, 3A, 3B and 3C; Sub‐layer 3A contains chlorite and illite/smectite mixed‐layer mineral, sub‐layer 3B contains chlorite/smectite and illite/smectite mixed‐layer minerals, and sub‐layer 3C contains chlorite and illite. Large amounts of di‐octahedral clay minerals such as smectite, kaolinite, illite and illite/smectite mixed‐layer mineral are found in Iheya‐North‐Knoll, which is rarely observed in hydrothermal fields in mid‐ocean ridges. Tri‐octahedral clay minerals such as chlorite, corrensite and chlorite/smectite mixed‐layer mineral in Iheya‐North‐Knoll have low Fe/(Fe + Mg) ratios compared with those in mid‐ocean ridges. In conclusion, the characteristics of clay minerals in Iheya‐North‐Knoll differ from those in mid‐ocean ridges; di‐octahedral clay minerals and Fe‐poor tri‐octahedral clay minerals occur in Iheya‐North‐Knoll but not in mid‐ocean ridges.  相似文献   

11.
The Upper Red Formation (URF) comprises over 1–5 km of late Miocene siliciclastic sediments in the Central Iran Basin. The formation is dominated by volcaniclastic conglomerates and arenites. The prevailing arid conditions during most of the basin's history resulted in deposition of predominantly organic‐poor, red sediments with gypsum and zeolites. This investigation concentrates on the mineralogy and geochemistry of the URF in the southern and northern margins of the basin where the formation was buried to depths of 2.4 and 6.6 km, respectively. Fine fraction mineral separates from the southern margin consist of nearly pure smectite and zeolites at a depth of 400 m and smectite with minor quartz and calcite at 1800 m. Shallow samples (1350 m) from the northern section are rich in smectite, illite/smectite with some discrete illite and chlorite. This assemblage is progressively replaced by discrete illite and chlorite with increasing burial depth so that only these two minerals are found at depths greater than 4300 m. The initial alteration process involved replacement of glass and volcanic lithics by smectite and zeolites in both margins of the basin. Increased depth of burial in the northern margin resulted in the progressive isochemical alteration of smectite to discrete illite and chlorite. Diagenesis of clay assemblages occurred essentially in a closed system. Solute products of glass hydrolysis reactions were retained in highly alkaline, saline ground waters from which zeolites, carbonates and oxides precipitated as cements. It is unlikely that these sediments were ever significantly leached by meteoric waters or by organic acids generated during burial diagenesis. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

12.
The Shurijeh Reservoir Formation of Neocomian age is represented by a sandstone sequence, occasionally interbedded with shale, in the Gonbadli gas field, Kopet-Dagh Basin, Northeastern Iran. In this study X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques were used together to characterize the Shuirjeh clay minerals in 76 core samples collected from two deep Gonbadli wells. The results of XRF analysis showed high percentages of silicon and moderate to low percentages of aluminum, sulfur, calcium, potassium, sodium, magnesium, and iron in both wells. The XRD analysis indicated that the above elements were concentrated in the form of quartz, anhydrite, dolomite, calcite, plagioclase, K-feldspar, hematite, and clay minerals. Further XRD examination of the clay fraction revealed that illite, chlorite, and kaolinite were the major types of clay minerals. Unlike, glauconite, smectite, and a mixed layer clays of both the illite–smectite and chlorite–smectite types were observed only in very few samples. The percentages of individual clay minerals were determined using external standard calibration curves and successfully validated by a system of simultaneous linear equations acquired from detailed elemental information based on the XRF analysis. The error reached ± 5% for the main mineral constituent and ± 15% for minor minerals. A local regression relationship was also derived, based on the XRF elemental information, which can be used to estimate the clay contents of other Shurijeh drilled wells with data of pulsed-neutron spectroscopy tools. According to the proposed quantitative approach, the amount of illite varied considerably, reaching 18.3%. In contrast, the amounts of kaolinite and chlorite were generally small, i.e., less than 8.4%. The amount of total clay minerals changed greatly from a minimum of 5% to a maximum of 32.5%. An increase in illite with increasing burial depth and temperature was an obvious indication of deep burial diagenesis in this formation.  相似文献   

13.
The clay mineralogy of the clay intervals interbedded with siliceous mudstones across the Permian-Triassic boundary (PTB) in Pengda, Guiyang, Guizhou province, was investigated by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The clay mineral assemblages of the sediments are mainly I/S clays and minor smectite, kaolinite, and illite as reveled by XRD analyses. The peak-shape parameters BB1 and BB2 of I/S clays of the representative clay bed PL-01 are 4.7° and 4.4°, and the peak position of the low angle reflection is at 6.8° 2θ (13.6 ), suggesting that the I/S clays has a IS type of ordering. However, the presence of multi-order reflections and their intensities are different from those of completely ordered 1∶1 mixed-layer I/S clay rectorite, indicating that I/S clays of the Pengda section have partially ordered IS structures. HRTEM observations show that most of the I/S clays exhibit an IS stacking ordering. However, in some areas within a IS particle, smectite layer is observed in doublets, triplets, and quartets, which are interstratified by various amounts of illite layers, suggesting the presence of other irregular stacking in addition to the major 1∶1 IS ordered stacking. Transformation of smectite layer into illite layers is also observed in the I/S clays, suggesting that the Pengda I/S clays are derived from smectite illitization, in good agreement with the clay mineral assemblage. The I/S clays of the Pengda section contain up to 45% to 95% smectite layer, the notably higher contents of smectite layer relative to those of other PTB stratigraphic sets in south China can be attributed to difference in alteration and smectite illitization processes due to different sedimentary environments.  相似文献   

14.
Mineralogical and chemical investigations (<2μm clay separates) of shale samples from the Neogene-age Surma Group obtained from four wells (Habiganj-11, Shahbazpur-1, Titas-11, Titas-15) in the Bengal basin, Bangladesh, were carried out in order to reveal the clay mineral composition as reservoir exploration and exploitation requires a good understanding of the clay minerals. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-Ray fluorescence spectrometry (XRF). Mineralogically, the sub-surface Surma Group shales comprise predominantly quartz, plagioclase, illite, chlorite, kaolinite, with lesser amounts of K-feldspar, dolomite and smectite, and minor to trace amounts of calcite, siderite and pyrite. The chemical composition of the <2 μm clay separates also suggests an illite and chlorite-rich composition. With increasing burial depth, the Surma Group shales are enriched in illite. The gradual decreasing of the smectite clays with depth and ultimate disappearance at greater depths (≥ 3000 m) may have been responsible for the presence of the diagenetic illite. Based on the mineralogical composition it is most likely that the illite-chlorite associations together with quartz and feldspar were predominantly detrital in origin and thus reflect the presence of a rapidly-rising source terrain not subjected to intense weathering.  相似文献   

15.
Natural radionuclides in the uranium and thorium series were measured in solid tidal phases (suspended particles, bottom sediment, surface microlayer colloids) of a salt marsh in lower Delaware. The purpose was to identify potential processes responsible for trace element cycling (sources, redistribution and exchange) in salt water marshes and with their coastal waters. Generally, concentrations of U, Th,210Pb, and210Po on the tidal solid phases suggest a general mechanism by which tidal marshes appear to be trapping the nuclides into their interiors. The processes may include transport of enriched fine particles into the marsh, capture by salt marsh grass and chemical fixation by redox processes at the sediment surface. Specifically, the uranium contents of most of the samples are similar with activity ratios234U238U≧1, indicating a mixture of detrital and nondetrital (authigenic) uranium inputs such as seawater or ground water. Since the230Th daughter is generally deficient by about 50%, the authigenic enrichment process appears to favor uranium and is potentially linked to the extensive diagenetic sulfur redox cycle of salt marsh sediments. The210Po/210Pb activity ratio is less than one on Spartina adsorbed solids, and could suggest a general process in salt marshes which favors210Pb enrichment by atmospheric fallout over enrichment of210Po on time scales of weeks which correspond to complete tide marsh exchange. A228Th/232Th activity ratio of less than unity on the solids adsorbed onto marsh grass suggests a net process whereby diffusive loss of the intermediate daughter228Ra from the adsorbed solids to tidal waters dominates over potential228Th scavenging by suspended sediment.  相似文献   

16.
Industrial uranium orebodies have recently been found through in-depth uranium exploration in the Luohe Formation in the southwestern Ordos Basin, which is an important breakthrough in deep prospecting for sandstone-type uranium deposits. The composition, content and characteristics of clay minerals in the Luohe Formation in the Zhenyuan area were systematically studied by means of thin section identification, scanning electron microscopy, X-ray diffraction and altered mineral spectral scanning. Unlike the most important uranium-bearing rock series in the Zhiluo Formation in the northeast and southwest of the basin, the ore-bearing Luohe Formation sandstone has low contents of clay minerals while the clay mineral assemblages vary in different sand bodies. Among them, the main types of mudstone, oxidized sandstone, calcareous sandstone and mineralized sandstone are illite-smectite mixed-layer mineral and illite, followed by kaolinite and chlorite, the main types uranium-rich sandstone and gray-green sandstone are kaolinite and illite-smectite mixed-layer mineral, followed by illite and chlorite. Even though adsorption of clay minerals, such as chlorite, illite-smectite mixed-layer mineral, kaolinite, and illite may contribute to U enrichment and uranium mineral precipitation, no correlation between clays and uranium minerals have been observed, indicating that clay minerals are not the main factor affecting uranium enrichment during the deep metallogenic process. The study of clay minerals in the Luohe Formation sandstone demonstrated that there are at least two phases of chlorite and one phase of kaolinite in the study area, which respectively represent two phases of alkaline fluid and one phase of acid fluid activities, revealing a fluid phase transition of alkaline-acidic-alkaline. Therefore, the clay minerals can be used as an important indicator for uranium mineralization. © 2020, Science Press. All right reserved.  相似文献   

17.
以储层敏感性流动实验为基础,结合X射线衍射、扫描电镜、铸体薄片等方法,对松辽盆地扶新隆起带北部扶余油层超低渗储层粘土矿物特征及其对储层敏感性的影响进行了研究,结果表明:扶余油层主要含有绿泥石、伊利石、高岭石和伊/蒙混层等4种矿物,其中伊利石含量最多,绿泥石和伊/蒙混层次之,高岭石最少。储层速敏性和碱敏性相对较弱,水敏性和盐敏性较强,对储层影响较大,勘探开发时应重点关注。粘土矿物对储层水敏性的影响主要有3个方面,其中粘土矿物绝对总量是扶余油层水敏性强弱的主控因素。  相似文献   

18.
粘土矿物组合和绿泥石成分常被用来讨论盆地沉积物的成岩作用和埋藏古温度。许多沉积盆地的研究结果显示,泥 岩和页岩中的粘土矿物组合和绿泥石的成分与埋藏深度/温度有关。但也见有例外的现象存在。文中主要探讨了新疆塔北隆 起泥岩中的粘土矿物组合和绿泥石成分的特征,以及与盆地古盐度的关系。研究结果表明：（1）在塔北隆起泥岩中,埋藏 深度2777.37~4604.41m,地层单位为J1-N2的粘土矿物组合为I+Chl和I+Chl+Ka; 埋藏深度5071.52~5299.37m,地层单位为 T1的粘土矿物组合为R0I/S+I+Chl和R0I/S+Chl。（2）研究区的成岩绿泥石为Ⅱb型铁镁绿泥石,其成分特征主要表现为： ①配位八面体中阳离子的占位数为11.532(总平均值);②ⅥAl含量明显大于ⅣAl含量;③（Fe+Mg）为4.016（总平均值）;④ Si/Al比值>1。（3）根据研究区盐类矿物的分布范围以及古盐度的数据,讨论了古盐度对该区粘土矿物组合和绿泥石成分的 影响,指出古盐度是影响本区粘土矿物组合和绿泥石成分变化的主要因素。用古盐度解释了<5000m深度的粘土矿物组合 中不含无序伊/蒙混层（R0I/S）矿物,而>5000m深度粘土矿物组合中含有无序伊/蒙混层（R0I/S）矿物的异常现象。揭示了 在一定的深度范围（2777.37~4405.27m）,一定的古盐度条件下（Sr/Ba比值≥0.4,并有盐类矿物出现）,绿泥石成分受到 古盐度的制约,并且随着古盐度的增高,绿泥石成分中的Al、ⅣAl、Na、Na2O、Al/Si随之增高,而Si/Al则随之降低。由 绿泥石成分温度计获得的温度值也伴随着古盐度的增高而增高。因此,由绿泥石成分温度计所计算的温度不能代表本区实 际埋藏的古温度。（4）研究区内绿泥石成分中的SiO2和FeO与母岩的对应成分之间有一定的相关性,其SiO2绿泥石与SiO2岩石、 FeO绿泥石与FeO岩石呈负相关的线性关系,并且这种关系在古盐度的干扰下也未受到影响。  相似文献   

19.
Clay mineralogy and whole-rock stable isotopes (δ18O and δ13C) of Upper Cretaceous marly sediments on the Basque-Cantabrian Basin have been integrated to determine the main effects of diagenesis, palaeoclimate and tectono-sedimentary factors in sections belonging to deep- (Barrika) and platform-marine (Isla de Castro, Villamartín and Olazagutía) settings.The mean values for the clay assemblages and δ18O exhibit notable differences among the sections, partially explainable by the influence of diagenesis. The Barrika sediments, with more diagenetically advanced illite-smectite (I-S) mixed-layer (R1, 70% illite), authigenic chlorite, and low δ18O (−4.05‰ PDB), experienced higher diagenetic grade than Isla de Castro and Olazagutía, which have R0 I-S (20% illite) and heavier δ18O. Villamartín was also affected by higher diagenesis than Isla de Castro and Olazagutía, given the occurrence of R1 I-S (60% illite) and low δ18O (−4.11‰ PDB). However, the absence of other clays in Villamartín (e.g. authigenic chlorite) is indicative of less diagenetic grade than Barrika. These results show the useful integration of clay mineralogy and stable isotopes to detect different diagenetic grades in distinct marine successions of the same basin.Despite being influenced by diagenesis, the clay mineralogy partially preserves its inherited signature. This allows detection of major contents of I-S and mica, and minor kaolinite, interpreted as indicative of warm palaeoclimatic conditions. High kaolinite content in Villamartín and absence of kaolinite in Isla de Castro, though, are considered to be a product of neither diagenesis nor palaeoclimatic influences. Instead, tectono-sedimentary causes, related to unsuitable conditions for clay formation and transport from the local source areas, contributed to original clay differences. The inferred effects of diagenesis, palaeoclimate and tectono-sedimentary factors make this work important to show the potentially great variety of controls on the clay mineralogy of marine sections, which are often uncritically treated in studies concerning the Late Cretaceous.  相似文献   

20.
A continuous shallow marine 10 m thick succession within the Langpar Formation in the Um Sohryngkew river section of Meghalaya, containing late Maastrichtian through early Danian planktonic foraminiferal zones – CF4, CF3, CF2, CF1, P0, Pα and P1a and the K/Pg boundary (between CF1 and P0) that makes unique of its kind. The section has been re-studied and sampled for clay mineralogy to understand the palaeoenvironmental conditions prevalent in the region and to assess the K/Pg transition. The relative abundances of the clay mineral phases permitted a threefold sub-division of the studied section with a illite, illite/ smectite dominated lower part, illite, kaolinite and abundance of montmorillonite dominated middle part and kaolinite–montmorillonite dominated upper part. Enriched HREEs in the lower part of the succession suggest variations in the pH of alteration solutions. Most of the samples show positive cerium (δCe) and europium (δEu) anomalies, the former reflecting oxidizing conditions at the time of clay formation. Illite dominated clays present a positive Eu anomaly, formed at relatively higher temperatures than the clays with less illite and without Eu anomalies, whereas clays occurring in the lower and upper parts exhibit a prominent negative Eu anomaly. Shifts in the redox condition found in this section are more or less similar to the foraminiferal changes and Au, Pt, Pd anomalies. Clay mineralogical attributes and REE patterns, comparable to those of the known K/Pg boundaries, appeared within the CF3 and CF2 zones in the Um Sohryngkew river section. The sample at the boundary between CF3 and CF2 is marked by a negative <delta>Ce anomaly, high La/Yb and TOC values, suggesting that sea level rise during the upper part of CF3 was caused by tectonism rather than warming. The similar characteristics of clay minerals and REE patterns, attributed to the initiation of tectonic events during the CF3 zone, indicate environmental changes that affected the shelf area and the provenance of these sediments.  相似文献   

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