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131.
马家沟灰岩(古)岩溶研究中的若干问题探讨   总被引:4,自引:0,他引:4  
讨论了华北地区奥陶系马家沟组灰岩岩溶研究中的几个问题,包括沉积岩溶,暴露岩溶,埋藏岩溶,现代岩溶及陷落柱等,指出了沉积岩溶和暴露岩溶洞穴不能保存或保存甚少,但对后期的岩溶发育具有重要控制作用,最后,提出了今后奥陶系灰岩岩溶研究的基本思路。  相似文献   
132.
近年来“矿源层”这一概念已被广大地质学家所接受,他们认为矿床中的金是从围岩中萃取的,本文认为矿床中的金来源于岩浆残余热液。在地壳深部,当丰度值高的基性岩或其他岩石,在深熔作用下产生花岗质岩浆时,同时带出许多金,当岩浆侵入到上部地壳冷凝结晶时,其中的大部金进入残余热液,最后富集成矿。  相似文献   
133.
新疆北部中二叠统烃源岩地球化学特征与沉积环境   总被引:9,自引:0,他引:9  
首次对新疆北部准噶尔、吐哈及伊犁盆地中二叠统碳酸盐岩类、泥岩类烃源岩的微量元素、稀土元素和有机地球化学丰度进行了系统分析 ,其主要特征是微量元素含量与同类岩石的克拉克值相比 ,有的较高 ,有的偏低 ;轻稀土富集程度较高 ,重稀土相对较低 ,Ce/ Ce*具有较明显的正异常 ,反映出烃源岩沉积环境总体为还原环境。有机地球化学分析证实 ,烃源岩中微量元素含量对沉积水体中生物的分布有一定的影响 ,部分微量元素丰度与有机质含量呈明显的正相关关系。还原程度强的沉积相带是原始有机质沉积的良好场所 ,沉积有机质能及时沉积、保存 ,烃源岩大多有机质丰度高 ;反之 ,则明显变差  相似文献   
134.
1885~2000年长江中下游梅雨特征量的统计分析   总被引:22,自引:3,他引:22       下载免费PDF全文
该文分析了1885~2000年长江中下游梅雨特征量的基本统计特征及其相互关系,在此基础上研究了梅雨较长时间尺度的变化特征。结果发现:①梅雨量的大小与梅雨期的长短和出梅日期的早晚为显著的正相关;②梅雨的主要周期为3 a、6 a和8 a,它们分别与低纬100 hPa高度场、热带系统以及全球陆地温度的变化有关;③控制入梅、出梅和梅雨期6 a左右周期的气候因素是相同的,而3 a左右的周期可能受到不同气候因素的影响;④长江中下游梅雨在近116年期间,经历了6个不同的气候阶段。  相似文献   
135.
晚太古代Sanukite(赞岐岩)与地球早期演化   总被引:9,自引:12,他引:9  
Shirey and Hanson(1984)将某些太古代的高镁闪长岩套称为sanukite(赞岐岩),类似于日本中新世(11~15Ma)Setouchi火山岩带的高镁安山岩。Sanukitoids由闪长岩-二长闪长岩-花岗闪长岩组成,不同于TTC岩套(奥长花岗岩-英云闪长岩-花岗闪长岩)。Sanukitoids具有下列地球化学特征:富Mg,Mg~#>0.60,Ni和Cr>100μg/g,Sr和Ba>500μg/g,LREE富集(大于球粒陨石100倍),无Eu异常。高镁安山岩在太古代很少见,而其相应的侵入岩高镁闪长岩或sanukitoids,虽然数量也很少,但却是各地晚太古代地体中随处可见的。Sanukitoids的原始岩浆是交代的地幔楔部分熔融形成的,随后可能经历了广泛的分离结晶作用。TTC和sanukitoids岩套可以相伴产出,二者均与板片熔融有关,TTG与其直接有关,sanukitoids可能与其间接有关。全球Sanukitoids主要集中在晚太古代时期,可能暗示板块的消减作用在~3.0Ga以后才起了重要的作用。  相似文献   
136.
晚更新世晚期以来的长江上游古洪水记录   总被引:4,自引:2,他引:4       下载免费PDF全文
长江上游三峡河段主要的古洪水记录有:1)三峡深槽的蚀积变化;2)长江阶地粗粒沉积;3)长江的泛滥沉积;4)长江的古洪水平流沉积。不同时间跨度不同类型古洪水记录的精度有较大的差别。古洪水记录显示,晚更新世晚期的40~30kaB.P.,长江上游大洪水比30kaB.P.以来的长江上游大洪水大得多;全新世以来,以3983aB.P.前后的大洪水为相对最大;公元1870年大洪水为3000aB.P.以来最大洪水;近百年来的实测洪水以公元1981年洪水为最大。  相似文献   
137.
Analysis of stacked Permo‐Pennsylvanian palaeosols from north‐central Texas documents the influence of palaeolandscape position on pedogenesis in aggradational depositional settings. Palaeosols of the Eastern shelf of the Midland basin exhibit stratigraphic trends in the distribution of soil horizons, structure, rooting density, clay mineralogy and colour that record long‐term changes in soil‐forming conditions driven by both local processes and regional climate. Palaeosols similar to modern histosols, ultisols, vertisols, inceptisols and entisols, all bearing morphological, mineralogical and chemical characteristics consistent with a tropical, humid climate, represent the Late Pennsylvanian suite of palaeosol orders. Palaeosols similar to modern alfisols, vertisols, inceptisols, aridisols and entisols preserve characteristics indicative of a drier and seasonal tropical climate throughout the Lower Permian strata. The changes in palaeosol morphology are interpreted as being a result of an overall climatic trend from relatively humid and tropical, moist conditions characterized by high rainfall in the Late Pennsylvanian to progressively drier, semi‐arid to arid tropical climate characterized by seasonal rainfall in Early Permian time. Based on known Late Palaeozoic palaeogeography and current hypotheses for atmospheric circulation over western equatorial Pangea, the Pennsylvanian palaeosols in this study may be recording a climate that is the result of an orographic control over regional‐scale atmospheric circulation. The trend towards a drier climate interpreted from the Permian palaeosols may be recording the breakdown of this pre‐existing orographic effect and the onset of a monsoonal atmospheric circulation system over this region.  相似文献   
138.
The morphology of the horn-core structure and section shape of the Bos galerianus type specimen, as well as the general anatomy of the frontal and occipital areas of the skull, suggest that the skull is better attributed to the Indian genus Hemibos. This finding contributes to our understanding of faunal dispersal patterns into Europe at the Early–Middle Pleistocene transition.  相似文献   
139.
The global climate changings at the end of Pleistocene led to extinction of the typical representatives of Mammoth fauna–mammoth, woolly rhinoceros, wild horse, bison, muskox, cave lion, etc.–on the huge territories of Northern Eurasia. Undoubtedly the Mammoth fauna underwent pressure from the Upper Paleolithic Man, whose hunting activity also could play the role in decreasing the number of mammoths and other representatives of megafauna (large mammals). Archaeological data testify that the typical representatives of Mammoth fauna were the Man's hunting objects only till the end of the Pleistocene. Their bone remains are not usually found on the settlements of Mesolithic Man. Formerly it was supposed that the megafauna of ‘Mammoth complex’ was extinct by the beginning of Holocene. Nevertheless the latest data testify that the global extinction of the Mammoth fauna was sufficiently delayed in the north of Eastern Siberia. In the 1990s some radiocarbon data testified that the mammoths on the Wrangel Island existed for a long time during the Holocene from 8000 till 3700 y. BP. The present radiocarbon data show that wild horses inhabited the north of Eastern Siberia (the lower stream of the Enissey river, the Novosibirskie Islands, the East Siberian sea-shore) 3000–2000 y. BP. Musk-oxen lived on the Taimyr Peninsula and the Lena River delta about 3000 y. BP. Some bison remains from Eastern Siberia belong to the Holocene. The following circumstances could promote the process of preservation of the Mammoth fauna representatives. The cool and dry climate of this region promotes the maintenance of steppe associations – habitats of those mammals. The Late Paleolithic and Mesolithic settlements are not found in the Arctic zone of Eastern Siberia from the Taimyr Peninsula to a lower stream of the Yana River; they are very rare in the basins of the Indigirka and Kolyma Rivers. So, the small number of the Stone Age hunting tribes on the North of Eastern Siberia was another factor in the long-term preservation of some Mammoth fauna representatives.  相似文献   
140.
The South Kerala Sedimentary Basin (SKSB) constitutes one of the most significant landward extensions of the southwest offshore sedimentary basins of India, and is situated between 8o45' and 10o15' N latitudes. With a maximum width of about 20 km and incorporating a 700 m thick sedimentary succession ranging in age from Early Miocene to Holocene, this belt lies almost entirely under water or alluvium-covered coastal plains. In this study, we use two continuously cored bore holes at Eruva (7.25m deep) and Muthukulam (3m deep) separated by a distance of about 7km to investigate the depositional environment as well as paleo ecology of the depocentre and climatic aspects during the Late Pleistocene and Holocene. Results from C14 dating of shell fragments from Eruva (depth zone: 2.10–6.64m) yielded ages in the range of 36.2 to 42.5 kyBP corresponding to the late Pleistocene. Wood fragments in the Muthukulam core sample (depth zone: 1.27–3.00m) gave C14 ages in the range of 3.7 to 7.2 kyBP indicating a Holocene history. The lower half of the Eruva bore hole indicates a marginal marine environment with an abundant supply of terrestrial carbonaceous debris probably corresponding to a period of abnormally high rainfall recorded in many parts of the globe covered by the Asian summer monsoon. The sediments in the upper part of this bore hole indicate a continuation of this environment but with much less input of terrestrial organic carbon. The lower part of the bore hole from this locality, corresponding to the Holocene transgression, is similar to the lower part of Eruva bore hole in the case of TOC. Deposition took place in water bodies with considerable marine influence but receiving high amounts of terrestrial plant debris-mostly in the form of finely divided particles mixed with mud. This transgressive sequence was also deposited during a time when the Asian summer monsoon was abnormally high in intensity as indicated by many examples in India, Africa, Madagascar and elsewhere. It is significant that during the deposition of this part, the sea level was probably the same as present or higher suggesting possible lowering of the stream velocities and resultant deposition of only muddy sediments laden with terrestrial organic material along the coast. The upper part of the section shows a progressively reduced rainfall pattern culminating in a period of very low precipitation with the development of a paleosol, which is traceable all over the SKSB where Late Holocene sediments are available. This period also witnessed aeolian activity modifying the sand ridges in the ridge-runnel systems formed by the Holocene regression.  相似文献   
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