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1.
The mineralogy and geochemistry of clastic sediments in the 1000 m thick Lower Palaeozoic marine sequence of the Oslo Region is discussed on the basis of 200 chemical (XRF) and mineralogical (X-ray diffractometer) analyses. The composition of these sediments is considered to largely be a function of the relative supply from land of the continental shield (Baltic Shield) and from island are systems to the NW in the Trondheim Region. The relative abundance of chlorite and illite is discussed in light of recent knowledge about their distribution in modern oceans. Middle Cambrian to Lowermost Ordovician black shales contain only illite as the dominant clay mineral and have a high potassium content. These sediments are thought to be derived from land on the continental shield, which during this period probably had a low relief and a warm climate where chlorite is not stable. Chlorite is introduced first in the Arenigan (L. Ordovician) and this is interpreted as evidence for transport of clastic chlorite from a developing island arc system in the Trondheim Region to the west. The highest chlorite/illite ratio in the Middle and Upper Ordovician sediments of the Oslo Region corresponds to a Taconic orogenic phase. The content of clastic chlorite in the Lower Palaeozoic of the Oslo Region is thus shown to be a sensitive indicator of palaeoenvironment and tectonic evolution of the Caledonian geosyncline. This conclusion is also supported by a systematic increase in Mg, Fe, Ni, and Cr from Lower to Middle and Upper Ordovician beds. High Cr values exceeding 0–1 % Cr in the Middle/Upper Ordovician shales are due to small grains of clastic chromite resembling those in the serpentinites of the Trondheim Region. This also suggests transport from exposed island arcs onto the epicontinental shelf.  相似文献   

2.
This paper deals with the REE geochemical characteristics of Permian-Triassic marine carbonate rocks in Guizhou Province.It is found that there are two broad categories of strati-graphic units in the region studied in accordance with their ΣREE contents and REE distribu-tion patterns: one is characterized by LREE enrichment and slight Ce depletion,with the REE distribution patterns similar to those of North American shales,and the other featrures relative HREE enrichment and relatively remarkable Ce depletion,with the REE distribution patterns close to those of pelagic sediments.In terms of their different ΣREE contents,five types of stratigraphic units can be distinguished.Incorporation of detrital minerals,REE complexing ca-pability,oxidation-reduction conditions of the media are the main factors affecting the REE com-position and REE distribution patterns of marine carbonate rocks in the region studied.In the light of REE geochemical characteristics of carbonate rocks,coupled with sedimentary facies analysis,this paper discusses the characteristics of the Permian-Triassic marine sedimentary environment in Guizhou Province and its evolutional rules.  相似文献   

3.
The early Proterozoic metasedimentary sequence of the Alligator Rivers Region (a part of the Pine Creek Geosyncline) in the Northern Territory, Australia, overlies an Archaean granitoid basement. Early Proterozoic sedimentary sequences, in general, record important changes in the composition of the upper continental crust about the Archaean-Proterozoic boundary. However, the geochemistry of only a few of these sequences has been documented. The geochemistry of the early Proterozoic succession in the Alligator Rivers Region is reported here and the results are interpreted in terms of differences between the stratigraphic units, their provenance—particularly in relation to crustal evolution, and their subsequent metamorphism and weathering.Clastic metasedimentary rocks throughout the Alligator Rivers Region have a remarkably uniform major and trace element geochemistry. The Kakadu Group and upper member of the Cahill Formation are relatively more enriched in SiO2 and correspondingly more depleted in Al2O3 than the rest of the sequence, reflecting the greater dominance of metapsammitic assemblages. The lower member of the Cahill Formation, which hosts the major U deposits of the Alligator Rivers Region, and the metasedimentary sequence in general, exhibit no significant enrichment in U above normal background values. Rare earth element (REE) concentrations in the metasedimentary units within the Alligator Rivers Region are uniform, though in detail there are some important differences within and between formations.The composition of the early Proterozoic clastic metasediments in the Alligator Rivers Region is consistent with the composition of similar material of the same age from other areas, and supports current ideas on crustal evolution. The Alligator Rivers metasediments are enriched in Si and K, and depleted in Mg, Ca, and Na relative to the Archaean average for clastic sedimentary rocks, and their REE geochemistry resembles typical post-Archaean sedimentary rocks having a light REE enriched pattern and a distinct Eu/Eu1 depletion compared to typical Archaean sediments. However, the REE data indicate that two compositionally distinct sources are involved in the provenance of the Kakadu Group, and possibly the lower member of the Cahill Formation, where two types of REE patterns can be distinguished on their HREE concentration and Eu/Eu1 anomaly.  相似文献   

4.
Changes in deformation style and amounts of shortening in the Osen-Røa thrust sheet of the Oslo Region occur vertically and laterally approaching the thrust front in the south. Deformation in the CambroMiddle Ordovician sequence passes laterally from closely spaced imbricates in the north (50–60% shortening), through triangle, pop-up and imbricate zones toward the south (20–37% shortening) to widely spaced zones of deformation (up to 20% shortening) approaching the thrust front. Changes in deformation style are attributed to changing boundary conditions across the Klekken thrust, declining end-of-orogenic forces and an increase in thickness of competent units in the Ordovician rocks to the south. Vertical changes in deformation style are attributed to the increasing percentage of competent units upward in the Cambro-Silurian sedimentary rocks. In the north, the accompanying decrease in shortening upwards requires a structurally necessary upper detachment horizon to separate folded late Middle Ordovician-Silurian sediments from imbricated early Cambro-Middle Ordovician sediments below; while southward in the Oslo area the upper detachment needs to be placed between Silurian and Cambro-Ordovician units. Finally, in Eiker, with less than 20% shortening, the whole CambroSilurian sequence appears to have deformed as a single unit. In the northern Oslo Region, the upper detachment probably has a backthrust sense of motion above an imbricate stack (passive roof duplex). Further south the upper detachment is probably directed toward the foreland.  相似文献   

5.
Boström, K., & Fisher, D. E.: Lateral fluctuations in pelagic sedimentation during the Pleistocene glaciations. Boreas, Vol. 1, pp. 275–288. Oslo, 1st December, 1972.
A total of 308 sediment samples of dated cores from 7 different locations have been analyzed for several major and trace elements. Our results, as well as previously published ones, show that during the Pleistocene the pelagic sediments have high concentrations of Mn, Cu, Co, REE, etc., in deposits of glacial age and low concentrations in corresponding interglacial ones; for hemipelagic sediments the situation is reversed. This shows that the boundary between reducing hemipelagic sediments and well-oxidized pelagic sediments has been migrating laterally back and forth due to climatic variations. Such sediment sequences may be easily confused with deposits where postdepositional migration of Mn and other elements has taken place.  相似文献   

6.
 The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Received, October 1996 Revised, August 1997 Accepted, September 1997  相似文献   

7.
Fossil bones and teeth from terrestrial environments encode unique rare earth and trace element (REE and TE) signatures as a function of redox conditions, pH, concentrations of complexing ligands, and water-colloid interactions. This signature is set early in the fossilization process and serves as a paleoenvironmental and paleoclimatic proxy. These signatures can also be used to interpret temporal and spatial averaging within vertebrate accumulations, and can help relocate displaced fossil bones back into stratigraphic context. Rare earth elements in vertebrate fossils from upper Eocene and Oligocene strata of Toadstool Geologic Park, northwestern Nebraska, record mixing and evolution of Paleogene vadose or groundwaters and variations in paleoenvironments. REE signatures indicate that HREE-enriched alkaline groundwater reacted with LREE- and MREE-enriched sediments to produce 3-component mixtures. REE signatures become increasingly LREE- and MREE-enriched toward the top of the studied section as the paleoenvironment became cooler and drier, suggesting that REE signatures may be climate proxies. Time series analysis suggests that REE ratios are influenced by cycles of ca. 1050, 800, 570, 440, and 225 ka, similar to some previously determined Milankovitch astronomical and climate periodicities.  相似文献   

8.
Bone apatite acts as a natural, timed sampling device, scavenging trace elements from local pore waters over timescales of ca. 1-50 ka. The rare earth element (REE) and U/Th composition of fossil bones reflects associated pore water compositions during the period of recrystallisation. The REE composition of fossil bones is controlled by partitioning of REE between pore waters and particle surfaces, and the REE composition of fossil bones reflects the REE composition of pore waters which vary spatially and temporally. Light REE are preferentially sorped onto particle surfaces, thus the high La/Yb values seen in many bones from coastal marine and aeolian environments are best explained by release of REE from light REE-enriched particles to local pore waters and subsequent immobilisation in recrystallising bones. The REE compositions of bones recovered from pedogenically altered diatomite sediments of the Olorgesailie Formation of southern Kenya vary over spatial scales of less than 10 m. Location accounts for 48% of the observed variation in bone chemistry and bones recovered from eight discrete excavations within the same time-equivalent stratigraphic layer can be assigned to their excavation location with >70% accuracy based on a discriminant analysis of REE, U, and Th composition. Despite this within-layer variation, bones recovered from different stratigraphic horizons within the Olorgesailie Formation can also be distinguished on the basis of their trace element composition. Bones recovered from four stratigraphic horizons spanning ca. 0.5 million years were assigned to their correct stratigraphic layer with >90% accuracy. Where sedimentological conditions are favourable, the trace element composition of fossil bone may be used to test stratigraphic provenance and burial location in excavated bone with a temporal resolution of <10 ka and a spatial resolution of <10 m. The trace element composition of fossil bone may also be used to investigate the accumulation history of vertebrate assemblages and to reconstruct pore water variability across land surfaces.  相似文献   

9.
This work presents a clarified stratigraphic scheme of the Miocene sediments of the Fore-Urals and the territory of Bashkortostan. As a result of the work carried out, the regional stratigraphic divisions of the Miocene of the Fore-Urals were described and stratotypes and reference sections were established for the first time. The stratigraphic scheme of the Miocene sediments includes the sequences of the Lower (the upper part of the Tyulganskian Formation, Kuyurgazinskian and Voroshilovskian formations), the Middle-Upper (Ushkatlinskian Formation) and the Upper (the lower sub-formation of the Tchebenkovskian Formation) Miocene. In addition, the stratigraphic scheme developed was correlated with those of the Urals, the Russian Plain and the Lower Volga Region. The scheme is based on the data obtained from study of sediments, analysis of paleontological and lithological data, and summary of literary and library materials, which allowed us to elucidate in detail the Miocene events in the Fore-Urals.  相似文献   

10.
R. J. KORSCH 《Sedimentology》1978,25(2):247-265
The subdivision of thick sequences of turbidite sediments has been problematical because of the monotonous nature of the units. One method, of using detailed detrital petrography for a large number of specimens, has delineated variations with a sequence of Late Palaeozoic age in eastern Australia. The rocks occur within a single structural block and are all members of one sedimentary petrographic province. They have been subdivided into three stratigraphic units (Moombil Beds, Brooklana Beds and Coramba Beds) and greywackes from these units are quartz-poor to quartz-intermediate, feldspathic or volcanolithic types. Dacitic volcanism has provided most of the detritus and the contribution from non-volcanic sources is small. The Coramba Beds are further subdivided into four petrographic units which are parallel to the stratigraphic boundaries. These lithostratigraphic units are based on the presence or absence of detrital hornblende, and the relative ratio of volcanic lithic fragments to feldspar. Vertical petrographic variations within the entire sequence indicate that although the acid volcanic source was predominant throughout the time of deposition, there is a noticeable increase in the contribution from intermediate-volcanic, acid-plutonic, low-grade metamorphic and sedimentary sources towards the top of the sequence. Detrital hornblende is also present in the upper parts of the sequence.  相似文献   

11.
In the Flandrian Fenland sediments of the Nar Valley, Norfolk, an upper clay and thick upper peat overlie lower clay and lower peat units thinning eastwards up the valley. Lithostratigraphic and altitudinal variations in less than thirty metres led to the application of a soil mechanics technique, the oedometer test, to the sediment units in order to estimate amounts of compression and corrections for the altitudinal displacements. The principles and assumptions behind the oedometer test are reviewed and results from compression tests on Flandrian Fenland deposits in the Nar Valley discussed in relation to interpretation of stratigraphic data, especially in terms of reconstruction of former sea levels. Limitations of the technique, particularly with reference to peats, are discussed.  相似文献   

12.
长江与黄河沉积物REE地球化学及示踪作用   总被引：66，自引：4，他引：62  
杨守业  李从先 《地球化学》1999,28(4):374-380
长江与黄河沉积物的稀土元素（ＲＥＥ）组成特征不同。长江沉积物ＲＥＥ含量较高,元素含量变化也大于黄河样品;球粒陨石标准化模式表明长江沉积物的（Ｌａ／Ｌｕ）Ｎ、（Ｌａ／Ｙｂ）Ｎ、（Ｇｄ／Ｙｂ）Ｎ的值也相应地比黄河沉积物中的高１０％左右,分布曲线均呈明显的石倾状,轻重稀土分馏明显,相对富集ＬＲＥＥ。且长江样品比黄河样品更富集ＬＲＥＥ,但Ｅｕ亏损不及黄河样品;两者的北美页岩标准化曲线均呈平坦稍右倾状,具有  相似文献   

13.
长江口晚新生代沉积物的物源研究: REE和Nd同位素制约*   总被引：14，自引：19，他引：14  
长江三角洲地区第四纪以来堆积了200多米厚的碎屑沉积物,主要由河湖相和滨浅海相组成,构成了多个沉积旋回。选择长江口地区一个320m深的PD钻孔,运用多通道等离子体质谱MC ICP-MS方法,开展沉积物中的REE和Nd同位素组成分析,研究了上新世以来三角洲地区沉积物物源的变化。沉积物中REE和Nd同位素组成具有明显的变化规律,Ce呈弱的负异常,介于0.83~0.99之间,而Eu呈现中等亏损,在0.53~0.73之间变化。岩芯中上新统沉积物中Ce异常变化大,而Eu亏损相对第四系沉积物更显著。143 Nd/144 Nd比值在钻孔中变化较小,介于0.511975~0.5122367之间,平均值为0.512062。相关分析揭示粒度和化学风化对Nd同位素组成影响小。REE和Nd同位素判别图解揭示河口地区上新统沉积物主要来自长江流域中、下游的近源物源区,而第四系沉积物的物源虽然存在一定的变化,但是总体上与上新统沉积物来源明显不同,主要来自更广泛的流域物源区,尤其是长江上游的风化物质被大量输运到河口三角洲地区。在第四纪构造和气候因素控制下,古长江水系具有不同的演化阶段,流域源岩经历的风化作用强度也不同,因此河流沉积物的源汇过程也相应地发生变化。  相似文献   

14.
华南热水沉积硅质岩建造及其成矿效应   总被引：15，自引：0，他引：15  
华南地区热水沉积建造发育。文中介绍该地区热水沉积建造 ,特别是震旦系顶部、泥盆系榴江组和二叠系当冲组 3个重要层位的硅质岩建造 ,分析它们的地质地球化学特征。研究表明 ,华南三层位沉积硅质岩的共同特征是TiO2 、Al2 O3 和K2 O含量一致偏低 ,大部分微量元素含量偏低 (与地壳克拉克值相比 ) ,但Ba、As、Sb富集 ,具有较为典型的热水沉积成因特点。多元统计分析显示 ,大部分微量元素在第一个主因子上均有显著因子载荷 ,与它们在基底的富集或亏损无关 ,代表了古地热系热水循环中的淋滤因子。华南三层位热水成因硅质岩具有相似的REE地球化学特征。REE总量低 ,稀土配分模式落在典型热水沉积物的上、下限之间 ,多数样品呈现δCe和δEu负异常。正常沉积的混入使部分硅质岩的REE配分模式复杂化。最后 ,讨论了与热水沉积建造相关的成矿效应 ,为金属矿床成因和评价提供约束条件  相似文献   

15.
Six graywackes from the Archean greenstone belt in the Wind River of Wyoming and 11 graywackes and three shales from the Archean Fig Tree Group, South Africa, were analyzed for the rare earth elements (REE). There are real deviations beyond analytical uncertainty among sediments from the same formation. The absolute abundance of the REE (∑REE) is somewhat lower than that of the North American shale composite (NASC) which is representative of younger sedimentary rocks. Still, the results confirm previous suggestions that the RE pattern in Precambrian sediments is the same as the NASC but that, relative to the heavy REE, graywackes are slightly enriched in the light REE, shales are depleted, and there is a slight enrichment in Eu relative to the NASC. The average abundance of Eu relative to the other REE for all the Precambrian sediments is the same as that in chondritic meteorites. Attesting to the complexity of graywacke genesis, there is no correlation between the variations in the REE parameters and the variations in major or minor element concentrations. In particular, there is no obvious correlation between the excess Eu and Sr abundance. The total amount of REE, the LaYb ratio, and the Eu enrichment factor, however, all increase in the graywackes with the amount granite-gneiss detritus in the rocks. In general, the REE distributions in Archean graywackes and shales appear to be related to the relative amounts of clastic feldspar, mica, and minor phases which concentrate the REE.  相似文献   

16.
Iron formations probably formed as chemical sediments when an Fe-rich solution entered the sedimentary environment. The REE patterns of such sediments are affected by the amount and type of precipitating and detrital phases, the REE pattern of the iron source solution, the REE pattern of the sea water into which the solution flows, and the mixing which takes place between input solution and sea water. What is known about the different types of iron formation suggests that all of these factors may vary from one type to another. Therefore, variations in REE patterns cannot be attributed solely to changes in sea water REE patterns. Comparison of the REE patterns of Archean and Ordovician iron formations of the Algoma type shows that similar iron formations have similar REE patterns regardless of age. This implies similar genetic histories.  相似文献   

17.
Geochemical and mineralogical data from a Pliocene to Pleistocene alluvial sequence are integrated to access the factors that control rare earth elements (REE) geochemistry and the evolution and spatial differences in provenance. The studied alluvial system is situated in a tectonic active setting at the contact between the Variscan Massif, with several Paleozoic and Precambrian units that support a coastal range, and the Atlantic margin. REE and HREE abundances are generally higher in swamp-lake than in floodplain sediments. The majority of the REE in floodplain sediments is hosted by Y and Th-bearing minerals and illite; in swamp-lake sediments is also probable an association with organic matter. The high Gd/Yb, Eu/Eu* and kaolinite content in older sediments suggest that during the earlier phases provenance was mainly from the hinterland (weathered granitic rocks and its sediment cover). The subsequent illite (Mg-rich) clay assemblages and REE patterns indicate mainly lateral input from the eastern basin edge (Palaeozoic and Precambrian metapelitic rocks). These sediments tend to have lower Gd/Yb and La/Sm than their source rocks. The analysis of the chemical index of alteration (CIA) indicates that although a north-directed fluvial axis existed at that time the “mature” basin edge units found to the south (Silurian) had a limited role in supplying sediments. This shift in provenance is attributed to the uplift of the coastal range. Afterwards, the contribution of recycled Cretaceous and Cenozoic sedimentary units increased progressively. This is demonstrated by the increase is SiO2/TiO2, CIA and kaolinite/illite when the climatic conditions are expected to have become less chemically aggressive.  相似文献   

18.
张志  廖群安 《地质通报》2000,19(1):38-42
以现代地层学理论为指导,应用砾石成分的旋回变化、沉积物地球化学元素变化和岩浆活动类型变化的综合信息,论述了江西信江白垩纪陆相盆地的地层划分和中生代晚期的构造演化。  相似文献   

19.
The Belt-Purcell Supergroup comprises dolomite-rich stratigraphic units in a dominantly siliciclastic succession, where sedimentation spans 1400-1470 Ma. Dolomitic units are variable mixtures of co-sedimented argillite and primary carbonate post-depositionally converted to secondary dolomite. Based on rare earth element (REE) relationships three distinct REE patterns are identified in the dolomite-rich units: Type 1 (T1d; d = dolomitic sample) with REE patterns parallel to post-Archean Upper Continental Crust (PA-UCC), albeit at lower absolute abundances due to dilution by carbonate content; Type 2 (T2d) with Heavy REE (HREE) enrichment but Light REE (LREE) depletion relative to T1d; and Type 3 (T3d) with enrichment in LREE and HREE relative to T1d, but erratic Middle REE (MREE) patterns. There is a progressive increase of ΣREE from T1d through T2d to T3d, whereas for ΣLREE/ΣHREE T2d < T1d < T3d. T1d-T2d and T3d represent three different “snapshots” of a continuous process.In terms of timing, dolomitization of calcite primary sediment in all samples likely took place broadly during burial diagenesis, as inferred for most Proterozoic dolomites. T1d is easily explained by provenance: however, T2d and T3d cannot be related to provenance, weathering or sedimentary sorting processes to explain higher concentrations of HREE referenced to PA-UCC and consequently developed in the sediment from a T1d precursor. The same three REE signatures have been described in previous studies in counterpart siliciclastic counterparts throughout the Belt-Purcell Supergroup at three different locations. Mobility of normally stable REE is accompanied by mobility of normally isochemical high field strength elements (HFSE) in T2d and T3d to give REE/REE, HFSE/HFSE, REE/HFSE and Y/HREE fractionations. No specific REE-HFSE signatures are apparent in the carbonate-rich units as compared to their non-dolomitic siliciclastic counterparts. This unusual mobility of REE and HFSE reflected in T2d and T3d is attributed to alkaline oxidizing post-depositional brines. Salinity was derived from seawater-sediment reactions, dissolution of evaporite minerals, and the smectite-illite transformation, whereas alkaline oxidizing conditions were promoted by groundwater interaction with mafic units in the basin, CO2 introduced into the system during episodic rifting with mantle degassing, and interaction of syn-sedimentary mafic intrusions with carbonate units at early stages of BPS deposition. Intermittent brine activity, inducing T2d and T3d patterns, spanned >1 Ga as recorded by secondary monazite grains with age distributions that correspond to large scale tectono-thermal events in Laurentia.Post-depositional processes and redistribution of carbonate can have an impact on transitional stratigraphic contacts between dolomitic and siliciclastic units which may have been incorrectly described as primary due to sedimentary environment changes.  相似文献   

20.
Fauna in the Semibalki locality (Azov Region), its stratigraphic position, and its age were considered. The rocks composing sediments with fossil theriofauna were subject to petrochemical analysis. Taking into account the lithological features of the sediments containing this fauna, it is possible to make the conclusion that the fossil fauna remains are allochthons and their age range is somewhat broader than was considered before.  相似文献   

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