Calcrete profile development in Quaternary alluvial sequences,southeast Spain: implications for using calcretes as a basis for landform chronologies     

Ian Candy  Stuart Black  Bruce W. Sellwood  John S. Rowan 《地球表面变化过程与地形》2003,28(2):169-185

A detailed study of the morphology and micro‐morphology of Quaternary alluvial calcrete profiles from the Sorbas Basin shows that calcretes may be morphologically simple or complex. The ‘simple’ profiles reflect pedogenesis occurring after alluvial terrace formation and consist of a single pedogenic horizon near the land surface. The ‘complex’ profiles reflect the occurrence of multiple calcrete events during terrace sediment aggradation and further periods of pedogenesis after terrace formation. These ‘complex’ calcrete profiles are consequently described as composite profiles. The exact morphology of the composite profiles depends upon: (1) the number of calcrete‐forming events occurring during terrace sediment aggradation; (2) the amount of sediment accretion that occurs between each period of calcrete formation; and (3) the degree of pedogenesis after terrace formation. Simple calcrete profiles are most useful in establishing landform chronologies because they represent a single phase of pedogenesis after terrace formation. Composite profiles are more problematic. Pedogenic calcretes that form within them may inherit carbonate from calcrete horizons occurring lower down in the terrace sediments. In addition erosion may lead to the exhumation of older calcretes within the terrace sediment. Calcrete ‘inheritance’ may make pedogenic horizons appear more mature than they actually are and produce horizons containing carbonate embracing a range of ages. Calcrete exhumation exposes calcrete horizons whose morphology and radiometric ages are wholly unrelated to terrace surface age. Composite profiles are, therefore, only suitable for chronological studies if the pedogenic horizon capping the terrace sequence can be clearly distinguished from earlier calcrete‐forming events. Thus, a detailed morphological/micro‐morphological study is required before any chronological study is undertaken. This is the only way to establish whether particular calcrete profiles are suitable for dating purposes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Evolution and inheritance of a rock coast: western Galicia,northwestern Spain     

R. Blanco Chao  M. Costa Casais  A. Martínez Cortizas  A. Prez Alberti  A. S. Trenhaile 《地球表面变化过程与地形》2003,28(7):757-775

There is increasing evidence that shore platforms and other elements of rock coasts may be inherited, at least in part, from interglacial stages when sea level was similar to today's. Most of this evidence, which includes ancient beaches and datable terrestrial deposits, has been obtained from areas of resistant, slowly eroding rock, where the platforms often appear to be much too wide to have developed since the sea reached its present level. It is much more dif?cult to demonstrate that inheritance has occurred in areas of weaker rock, which generally lack any datable material. The coast of western Galicia in northwestern Spain has shore platforms in igneous and metamorphic rocks that were deeply weathered during the Tertiary. These platforms are closely associated with ancient beaches from the last interglacial stage, and associated periglacial and ?uvio‐nival deposits that covered and fossilized most of the Eemian platforms and cliffs during the late middle and late Weichselian glacial stage. The sedimentary processes and the thickness and facies of the sediments were determined by the height, aspect and gradient of the coastal mountains, and their distance from the coast. Radiocarbon dating, sedimentary analysis and platform morphology indicate that the shore platforms of Galicia have been inherited from at least the last interglacial stage. They were fossilized in places beneath thick Weichselian deposits and then exhumed during the Holocene transgression. The abundant evidence for inheritance in Galicia has important implications for other coasts in fairly weak rocks where such evidence is generally lacking. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

La vallée d'Ys : un paléoréseau hydrographique immergé en baie de Douarnenez (Finistère,France)     

Gwénaël Jouet  Claude Augris  Bernard Hallegouët  Pascal Le Roy  Joël Rolet 《Comptes Rendus Geoscience》2003,335(5):487-494

Interpretation of the recent high-resolution survey, CANADOU 2000, in the Bay of Douarnenez (Finistère, France) allowed us to restore the morphology of the substratum and the sedimentary filling of the bay. The Brioverian and Palaeozoic substratum reveals a well-defined network of incised valleys as results of successive emergence stages of the Bay during the Quaternary. Valleys join in a westward-widened mean valley, called Ys Valley. The present-day sedimentary fill of the bay of Douarnenez appears mainly controlled by the Holocene rise and the consecutive highstand. It comprises fluvial and estuarine deposits filling up incised valleys and marine sedimentation extending out of the incised valleys. To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003).To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003).  相似文献   

武汉市高层建筑岩土工程问题分析     

谭松林  江权 《水文地质工程地质》2003,(Z1)

武汉市是华中地区最大的城市,改革开放以来,兴建了许多高层建筑。高层建筑尤其是超高层建筑的主要特点是高度大、重心高、基底压力大及基础埋深大等。而武汉地区的地质条件又比较复杂,就第四纪地层而言,从最新沉积的各类软土如人工填土、淤泥类土、软塑状粘性土等,到全新世(Q4)沉积的各类砂土与卵砾石,直至晚更新世(Q3)及其以前沉积的老粘土均有分布。各类土层的厚度、深度及性质均变化较大。因此武汉地区高层建筑的岩土工程问题就显得复杂与多样,在众多复杂的岩土工程问题中,本文主要分析了比较突出的基础持力层与基础类型的确定,深基坑开挖中的边坡滑移、基坑涌水、流砂、突涌以及基坑防护等。通过对这些问题的分析,从中可以得出一些规律,对今后高层建筑的兴建具有一定的指导作用。  相似文献   

Lipid distribution in a subtropical southern China stalagmite as a record of soil ecosystem response to paleoclimate change   总被引：3，自引：0，他引：3  

Shucheng Xie  Yi Yi  Junhua Huang  Chaoyong Hu  Yanjun Cai  Matthew Collins  Andy Baker 《Quaternary Research》2003,60(3):340-347

Lipid extracts from a 61.7-cm-long subtropical stalagmite in southern China, spanning the period of ca. 10,000–21,000 yr ago as constrained by U–Th dating, were analyzed using gas chromatography–mass spectrometry. The higher plants and microorganisms in the overlying soils contribute a proportion of n-alkanes identified in the stalagmite. The occurrence of LMW (lower molecular weight) n-alkanols and n-alkan-2-ones in the stalagmite was mainly related to the soil microorganisms. We suggest that HMW (higher molecular weight) n-alkanols and n-alkan-2-ones identified in the stalagmite originate from soil organics and reflect input from contemporary vegetation. Shifts in the ratio of LMW to HMW n-alkanols or n-alkan-2-ones indicative of the variation of soil ecosystems (e.g., microbial degradation of organic matter and/or the relative abundance of soil microorganisms to higher plants) are comparable with the subtropical alkenone-SST (sea surface temperature) record of the same period. The similar trends seen in the δ¹³C data and the lipid parameters in this stalagmite imply that the overlying soil ecosystem response to climate might be responsible for the variation of δ¹³C values.  相似文献   

Secondary ferrimagnetic minerals in Welsh soils: a comparison of mineral magnetic detection methods and implications for mineral formation   总被引：20，自引：0，他引：20  

J. A. Dearing  P. M. Bird  R. J. L. Dann  S. F. Benjamin 《Geophysical Journal International》1997,130(3):727-736

A study of mineral magnetic parameters was carried out on a Late Pleistocene and Holocene sedimentary sequence (of nearly 18 m) from Lake Bledowo (central Poland). Sediments of Lake Bledowo have already been analysed for bulk sediment mineralogy and biogenic materials. The mineral magnetic stratigraphy confirms the major changes in palaeo-environmental conditions that have been deduced from other methods. The most important mineral magnetic change results from the authigenetic formation of ferrimagnetic greigite, Fe₃S₄, during the beginning of lacustrine conditions (± 12 000 yr BP). Our data also indicate a detrital origin of overlying ferrimagnetic iron oxides. It is suggested that they originate from brown soils developed on the boulder clay constituting the west side of the lake shore. Variations of ferrimagnetic iron oxide size are related to the early diagenetic processes in the sediment. Larger particles are present in periods with early diagenesis of organic matter in anoxic conditions. This indicates the dissolution of fine magnetic particles by iron-oxide-reducing bacteria and results in homogeneous magnetic grain sizes, despite their origin from soils, characterized by a multimodal grain-size distribution.  相似文献   

黄汲清院士与第四纪冰川研究     

施雅风 《冰川冻土》1996,18(4):289-295

黄汲清院士是在多方面作出重大贡献的地质学大师，也是第四纪冰川研究的先驱者。他于１９３２￣１９３５年在瑞士完成博士论文期间，受到良好的冰川地质学训练。于１９４３￣１９４４年与合作者对天山南麓台兰河谷中游地质调查中，对冰碛与非冰碛沉积物进行仔细的正确的调查和精美的地质制图，撰写出高水平的论文，由此对中国第四纪冰川研究作出了重要贡献。他关注中国东部第四纪冰川研究的进展，指出忽视古气候研究是工作中的重要缺  相似文献   

欧洲中部地区晚更新世及全新世的泉华沉积     

杨小平 《第四纪研究》1996,16(4):338-344

在中欧地区的河谷、洪积扇、山坡坡麓及湖底常零星分布着更新世及全新世的碳酸盐沉积物。不少学者把碳酸盐沉积当作气候变化的产物并划分出其在中欧沉积的若干时期。笔者通过德国中部Leine河流域新老石灰泉华的详细研究对泉华沉积与气候直接联系的观点提出了新的见解。运用不同方法测年验证，得知研究区的石灰泉华沉积始于11000aB.P,随后石灰泉华在研究区不同地点连续沉积。岩芯上沉积的变化和石灰泉华层的消失应是由地貌过程所引起的泉水出露位置改变所致。  相似文献   

中国北部边疆第四系地下水研究     

李国安  韩朝平 《第四纪研究》1996,16(2):105-114

在中国北部边疆西起天山东端的北山，东至大兴安岭北段的４２００ｋｍ地域内，气候干旱少雨，水资源贫乏，第四系地下水是主要供水源之一。本文首次比较系统地研究了该区第四纪堆积物的分布和地下水的赋存规律。文中依据不同地貌单元、地层岩性及气候条件诸因素将本区第四系地下水划分为枝状沟谷砂砾石层孔隙水、河谷冲积平原砂砾石层孔隙水两种主要类型，并着重对有重要供水意义的河谷冲积平原砂砾石层孔隙水的分布、埋藏条件、富水性及水化学特征进行了论述。  相似文献   

祁连山西段及酒西盆地区第四纪构造运动的阶段划分   总被引：25，自引：6，他引：25  

陈杰  卢演俦  丁国瑜 《第四纪研究》1996,16(3):263-271

通过沉积地层、地貌、构造形变等的综合研究，对祁连山西段及酒西盆地区第四纪构造运动的期次和阶段进行了划分。上新世晚期以来，这一地区至少经历过６次显著的构造变动或构造事件，其中以玉门、酒泉和白杨河运动最为强烈。针对上述构造事件进行了古地磁、孢粉、红外释光和热释光等方法的综合研究和年龄测定，论述了各阶段构造运动的方式、性质和其它有关特征。  相似文献