Relations quantitatives entre les craies à silex et les formations résiduelles à silex de l’ouest du bassin de Paris     

Benoît Laignel  Florence Quesnel  Robert Meyer  Jean-Jacques Macaire 《Geodinamica Acta》2013,26(4):171-181

Résumé

Depuis plus d’un siècle, l’origine autochtone ou allochtone des formations résiduelles à silex (en abrégé RS : résidus à silex) par rapport aux craies a fait l’objet de multiples discussions. Pour répondre à ce problème, un bilan d’altération entre ces deux formations a été effectué. Il repose sur une connaissance précise des âges des craies-mères des RS et sur des comparaisons granulométrique et chimique entre craie et RS. Ces comparaisons s’appuient sur les quantités de silex contenues dans les craies et les RS, sachant que les silex sont reconnus comme autochtones et que leur degré de dissolution est calculé. Les résultats apportent des informations sur l’évolution crétacée du Bassin anglo-parisien, avec la mise en évidence de la craie du Maastrichtien dans le bassin de Paris et la reconstitution des épaisseurs de craie dissoutes. De plus, ils indiquent que la stratigraphie des craies est conservée dans les profils de RS. Ils montrent également que les silex, éléments autochtones des RS, sont faiblement altérés. Les matrices des RS sont, quant à elles, en grande partie allochtones, notamment dans les dix mètres supérieurs de la formation. L’allochtonie diminue avec la profondeur, avec des RS pouvant être considérés comme des résidus d’altération de la craie au sens strict à partir de 20 mètres de profondeur. © Elsevier, Paris  相似文献   

Ordovician backarc‐basin metadolerite and metabasalt of the South Kitakami Terrane,Northeast Japan          下载免费PDF全文

Takayuki Uchino  Makoto Kawamura 《Island Arc》2016,25(4):274-286

Basement rocks that occur along the northern margin of the South Kitakami Terrane in Japan consist of Ordovician ultramafic rocks (Hayachine ultramafic complex), gneissose amphibolite (Kuromoriyama amphibolite), and mafic rocks (Kagura igneous rocks, KIR). The KIR are composed of metagabbro, metadolerite, metabasalt, and minor felsic–intermediate dikes. Although the KIR contain green hornblende due to metamorphism of greenschist to epidote–amphibolite facies, they rarely retain primary brown hornblende. Approximately 30% of the metabasalt shows porphyritic textures, with phenocrysts of saussuritized plagioclase and/or altered mafic minerals. The geochemistry of the common metadolerite and metabasalt of the KIR shows a tholeiite trend, a low TiO₂ content, and high Th/Nb and Ti/V ratios. The KIR are therefore indicative of a supra‐subduction zone tectonic setting, which implies a backarc origin (as also indicated by discrimination diagrams). Trace element patterns of the KIR resemble those of the backarc‐basin basalt of the Japan and Yamato basins in the Japan Sea. We propose that the KIR formed during backarc spreading from the Ordovician to Early Silurian. This view is supported by the geochemical data, the tectonic setting of the Hayachine ultramafic rocks, and the provenance of clastics within Silurian sedimentary rocks.  相似文献   

Late Holocene record of environmental changes,cyclones and tsunamis in a coastal lake,Mangaia, Cook Islands          下载免费PDF全文

Catherine Chagué‐Goff  Jordan Chi Hang Chan  James Goff  Patricia Gadd 《Island Arc》2016,25(5):333-349

A 4.3 m‐long peat sequence from the shore of Lake Tiriara, Mangaia, Cook Islands, was analyzed using an ITRAX core scanner equipped with a magnetic susceptibility meter. Variations in the elemental profiles, providing insights into long‐ and short‐term environmental changes over the last 3500 years, are supported by grain size data and diatom assemblages. The scattering ratio (Mo Inc/Mo Coh) was evaluated and found to represent a good proxy for organic matter in peat. X‐Ray Fluorescence (XRF) data were processed by principal component analysis that confirmed the distinction of biogenic and detrital phases, organic matter and elements of marine origin. The record preserved in the peat sequence includes a peatland infilling stage followed by alternating drier and wetter periods. A notable steady increase in clay associated with high counts of detrital elements from 2000–1700 cal yr BP is attributed to increased erosion, which is most probably linked with human colonization and/or more intense chemical weathering linked with a wetter climate. Freshwater gastropods (Melanoides sp.), which were possibly introduced by humans, or are native, occupied the wetland during a period of lower water level about 1000–1100 cal yr BP. Short‐term changes in the elemental profiles are often linked with slight coarsening of the inorganic fraction that is, however, only revealed after grain size analysis. Peaks in marine indicators (Br, Cl, S, and/or Ca) associated with marine‐dominated diatom assemblages most probably represent marine incursions through the underground tunnel in the makatea, a fossilized, uplifted coral limestone rim. While none of the marine event units present characteristics typical of cyclone or tsunami deposits, the concurrent or absent peak of detrital elements (Fe, Si, Rb, Ti, K) attributed to increased erosion of the volcanic cone associated with a cyclone is used to distinguish both types of events, as also suggested by principal component analysis.  相似文献   

Zircon U–Pb ages of plutonic rocks in the southern Abukuma Mountains: Implications for Cretaceous geotectonic evolution of the Abukuma Belt          下载免费PDF全文

Yutaka Takahashi  Masumi Mikoshiba  Kazuya Kubo  Hideki Iwano  Tohru Danhara  Takafumi Hirata 《Island Arc》2016,25(2):154-188

Plutonic rocks in the southern Abukuma Mountains include gabbro and diorite, fine‐grained diorite, hornblende–biotite granodiorite (Ishikawa, Samegawa, main part of Miyamoto and Tabito, Kamikimita and Irishiken Plutons), biotite granodiorite (the main part of Hanawa Pluton and the Torisone Pluton), medium‐ to coarse‐grained biotite granodiorite and leucogranite, based on the lithologies and geological relations. Zircon U–Pb ages of gabbroic rocks are 112.4 ±1.0 Ma (hornblende gabbro, Miyamoto Pluton), 109.0 ±1.1 Ma (hornblende gabbro, the Hanawa Pluton), 102.7 ±0.8 Ma (gabbronorite, Tabito Pluton) and 101.0 ±0.6 Ma (fine‐grained diorite). As for the hornblende–biotite granodiorite, zircon U–Pb ages are 104.2 ±0.7 Ma (Ishikawa Pluton), 112.6 ±1.0 Ma (Tabito Pluton), 105.2 ±0.8 Ma (Kamikimita Pluton) and 105.3±0.8 Ma (Irishiken Pluton). Also for the medium‐ to fine‐grained biotite granodiorite, zircon U–Pb ages are 106.5±0.9 Ma (Miyamoto Pluton), 105.1 ±1.0 Ma (Hanawa Pluton) and the medium‐ to coarse‐grained biotite granodiorite has zircon U–Pb age of 104.5 ±0.8 Ma. In the case of the leucogranite, U–Pb age of zircon is 100.6 ±0.9 Ma. These data indicate that the intrusion ages of gabbroic rocks and surrounding granitic rocks ranges from 113 to 101 Ma. Furthermore, K–Ar ages of biotite and or hornblende in the same rock samples were dated. Accordingly, it is clear that these rocks cooled down rapidly to 300 °C (Ar blocking temperature of biotite for K–Ar system) after their intrusion. These chronological data suggest that the Abukuma plutonic rocks in the southern Abukuma Mountains region uplifted rapidly around 107 to 100 Ma after their intrusion.  相似文献   

SHRIMP U–Pb zircon dating of the Kinshozan Quartz Diorite from the Kanto Mountains,Japan: Implications for late Paleozoic granitic activity in Japanese Islands          下载免费PDF全文

Masatsugu Ogasawara  Mayuko Fukuyama  Kenji Horie 《Island Arc》2016,25(1):28-42

The new result of SHRIMP U–Pb zircon dating of the Kinshozan Quartz Diorite from the Kanto Mountains, Japan, provides 281.5 ± 1.8 Ma. The age is 30 m.y. older than the available age of the Kinshozan Quartz Diorite obtained by hornblende K–Ar method. The new U–Pb zircon age represents the time of crystallization of the Kinshozan Quartz Diorite. The hornblende K–Ar age indicates the time that the Kinshozan Quartz Diorite cooled down to 500 °C which is the closure temperature of the systematics. Permian granites are found in small exposures in Japan, and frequently referred to as 250 Ma granites. The Kinshozan Quartz Diorite is considered as a type of the 250 Ma granites, and the age was influential in establishing a model of Paleozoic tectonic evolution for the Japanese Islands. The new age of the Kinshozan Quartz Diorite provides the opportunity to re‐examine the model. The Kinshozan Quartz Diorite and other Permian granites in the south of the Median Tectonic Line of Japan were constituents of the Paleo‐Ryoke Belt. The geochemical characteristics of the granitic rocks in the Paleo‐Ryoke Belt indicated that the granitic rocks were formed in a primitive island arc environment, and the new trace element data also support this interpretation. Examination of the available data and results of the present study suggests the late Paleozoic granitic activity in Japan as follows. At about 310–290 Ma, arc magmatism generated adakitic granites and other granites in the South Kitakami Belt. Quartz diorite and tonalites of primitive characteristic, such as the Kinshozan Quartz Diorite and granites in the Maizuru Belt appear to have been formed at the immature island arc, and accreted to the Japanese Islands at the end of Paleozoic or early Mesozoic era. During 260–240 Ma, granitic activity took place in the Hida and Maizuru Belts as a part of the Asian continent.  相似文献   

Tsunami deposit associated with the 2011 Tohoku‐oki tsunami in the Hasunuma site of the Kujukuri coastal plain,Japan          下载免费PDF全文

Dan Matsumoto  Yuki Sawai  Koichiro Tanigawa  Osamu Fujiwara  Yuichi Namegaya  Masanobu Shishikura  Kyoko Kagohara  Haruo Kimura 《Island Arc》2016,25(5):369-385

We describe the detailed sedimentary characteristics of a tsunami deposit associated with the 2011 Tohoku‐oki tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick tsunami deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The tsunami deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging and grain‐size analysis. The deposit covers the pre‐existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well‐sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the tsunami deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the tsunami‐related sedimentation.  相似文献   

建设经济带是经济发展布局的最佳选择——长江经济带经济发展的巨大潜力     

陆大道 《地理科学》2014,34(7):769-772

自1984年, “点-轴开发”理论和中国国土开发、经济布局的“T”字型宏观战略提出以来,“T”字型空间结构战略在20世纪80~90年代得到大规模实施。海岸经济带和长江经济带2个一级重点经济带构成“T”字型,长江经济带将内地2个最发达的核心地区（成渝地区和武汉地区）与海岸经济带联系起来,其腹地几乎包括半个中国,其范围内资源丰富,农业、经济和技术基础雄厚,已经形成世界上最大的以水运为主的、包括铁路、高速公路、管道以及超高压输电等组成的具有超大能力的综合运输通道,其巨大的发展潜力是除海岸经济带以外的其他经济带所不能比拟的。“点-轴开发”理论和中国国土开发、经济布局的“T”字型宏观战略（海岸带和长江沿线作为全国的一级发展轴线）已经得到国内诸多知名学者和有关部门领导的认同,符合中国国土开发和经济布局合理化的要求,以海岸地带和长江沿岸作为今后几十年中国国土开发和经济布局的一级轴线的战略将是长期的。  相似文献   

Cambrian wave‐dominated tidal‐flat deposits,central Wisconsin,USA     

Robert B. MacNaughton  James W. Hagadorn  Robert H. Dott 《Sedimentology》2019,66(5):1643-1672

In central Wisconsin, Cambrian strata of the Elk Mound Group record deposition on open‐coast, wave‐dominated tidal flats. Mature, medium‐grained quartz arenite is dominated by parallel‐bedding with upper‐flow regime parallel‐lamination, deposited during high‐energy storms that also produced three‐dimensional bedforms on the flats. Abundant wave ripples were produced as storms waned or during fair weather, in water depths ≤2 m. Indicators of variably shallow water (washout structures and stranded cnidarian medusae) and subaerial exposure (adhesion marks, rain‐drop impressions and desiccation cracks, including cracked medusae) are abundant. Parallel‐bedded facies preserve a Cruziana ichnofacies, similar to other Cambrian tidal‐flat deposits. Flats were dissected by small, mainly straight channels, the floors of which were grazed intensely by molluscs. Most channels were ephemeral but some developed low levées, point bars and cut‐banks, probably reflecting stabilization by abundant microbial mats and biofilms. Channels were filled with trough cross‐bedding that is interpreted to have been produced mainly during storm runoff. The strata resemble deposits of open‐coast, wave‐dominated tidal flats on the east coast of India and west coast of Korea. Ancient wave‐dominated and open‐coast tidal flats documented to date appear to have been limited to mud‐rich strata with ‘classic’ tidal indicators such as flaser bedding and tidal bundles. The Cambrian (Miaolingian to early Furongian) Elk Mound Group demonstrates that sandy, wave‐dominated tidal flats also can be recognized in the stratigraphic record.  相似文献   

绿色地质勘查综合技术应用分析          下载免费PDF全文

贾占宏  高元宏  梁俭  刘海声  陈佰辉 《探矿工程》2017,44(4):1-4

绿色地质勘查是青海省乃至我国地质找矿发展的必然趋势。开展绿色地质勘查需要了解地质勘查工程影响生态环境的范围及形式,在此基础上综合多种先进的勘探技术手段,以最大程度降低扰动地表生态环境为基础满足预查、普查等阶段的地质找矿目的。其方法包括结合环保型冲洗液、浅层取样钻探、便携钻探设备浅孔钻探、重型钻探设备深部钻探与多向分支定向钻探取样方法等,并综合资料探索三维地质建模的方法开展绿色地质勘查。  相似文献   

大断面黄土隧道初期支护适应性研究   总被引：1，自引：0，他引：1  

扈世民  张顶立  李鹏飞  陈峰宾  张翾 《岩土力学》2011,32(Z2):660-665

以兰渝铁路大断面黄土隧道为工程背景,采用三维数值模拟结合现场监测实验对现有初期支护设计参数的适应性进行研究,对大断面黄土隧道初期支护的受力与变形特性进行综合分析。通过三维数值模拟得到黄土隧道开挖扰动后初期支护的受力与变形状态,将数值计算结果与现场监控量测对比获得典型断面围岩的应力和位移发展规律并对初期支护安全性进行评价;通过FLAC3D的FISH语言开发程序分析混凝土硬化特性对初期支护受力与变形的影响;现场跟踪量测与数值模拟的计算结果基本吻合,结论可为黄土地区隧道初期支护的设计和施工提供一定的借鉴和参考,积累有益的经验  相似文献