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51.
《Sedimentary Geology》2006,183(1-2):15-30
Carbonate concretions in the Miocene sedimentary rocks of the Yeonil Group in the Pohang Basin (Korea) were investigated in terms of stable oxygen and carbon isotope composition to delineate the origin and associated diagenetic environment for their formation. Carbonate concretions are widely distributed in all the sedimentary rocks in the Pohang Basin, showing that the calcitic concretions are preserved within the mass-flow deposits and the dolomitic ones mostly in the hemipelagic siliceous rocks (diatomites). Concretions can be classified into four different types, on the basis of the stable isotopic signatures, each of which represents its own geochemical range.Type I concretions are calcitic and are composed of micrite to microspar. They occur in the conglomerates and sandstones which were deposited by mass flows (debris flow to turbidity current). It shows relatively lower δ18O (− 14.0 to − 9.3‰) and δ13C (− 19.6 to − 8.4‰) values. These concretions grew in a sulfate reducing zone under the influence of residual ambient seawater which had been significantly modified by volcanogenic sediments. Type II concretions are also calcitic, composed mostly of micrite with minor microspar and found in the sandstones. These concretions are characterized by relatively high δ18O (+ 1.8 to + 2.4‰) and variable δ13C (− 17.3 to − 0.4‰) values. These isotopic signatures reflect that Type II concretions formed from just beneath the sediment/water interface down to the sulfate reducing zone through the early stage of methanogenesis. Type III concretions are also calcitic, and composed largely of micrite with a minor contribution of microspar. They are observed in hemipelagic mudrocks which were deposited under the influence of mass flows. They are characterized by intermediate to high δ18O (− 4.6 to + 1.6‰) and high δ13C (− 1.3 to + 8.8‰) values. These concretions grew in a methanogenic zone by residual ambient seawater and/or seawater slightly modified by reaction with volcanogenic sediments. Type IV concretions are dolomite with calcite inclusion, and occur in hemipelagic siliceous rocks. These concretions are mostly composed of micrite and characterized by variable δ18O (− 9.1 to + 0.7‰) and high δ13C (+ 3.1 to + 17.9‰) values, suggesting formation in the methanogenic zone, although the residual ambient seawater is slightly modified by volcanogenic sediments.The same type of the concretions is widely distributed throughout the basin and always shows its own distinctive stable isotopic signature. This means that the formation of the given type depends upon the lithology and composition of host sediments that are closely related to the depositional process of the fan-delta systems regardless of their localities. Further, the different types of concretions are also found at the different, but closely spaced stratigraphic levels in the same locality, displaying the distinctive diagenetic conditions for each type. Such preservation of the unique diagenetic signatures in individual type of concretion suggests that the concretions formed in a completely closed diagenetic system. Therefore, caution should be made to simplify and generalize the diagenetic condition for the formation of any concretions in a large sedimentary basin. 相似文献
52.
用于湿地气候效应模拟的三江平原下垫面数据获取 总被引：1，自引：0，他引：1
三江平原是我国沼泽湿地的重要分布区。在20世纪的后50 a中,三江平原在经过几次大规模的开荒后,其下垫面发生了明显的阶段性变化,湿地大面积消失,农田面积不断增加。为了认识20世纪下半叶不同时期三江平原湿地的气候效应,拟采用第三代区域气候模式(RegCM3)来开展研究。而目前被广泛用于RegCM3的GL-CC数据,所反映的研究区下垫面几乎不存在沼泽湿地,这与事实严重不符,所以必须获取三江平原有沼泽湿地存在的真实的下垫面数据,才能得到可靠的湿地气候效应的模拟结果。分别选择了4期(1954年、1985年、1996年和2000年)有阶段代表性的航片、TM影像数据为主要数据源,利用ERDAS8.7和Arcview3.2等软件,首先得到4期研究区的土地利用数据,然后通过土地利用数据类型向模式数据类型的转换,从4期研究区土地利用数据中提取出了三江平原下垫面的模式数据。经过误差分析,认为获取的4期三江平原下垫面模式数据准确的反映出研究区几个时期的湿地下垫面实况,可以作为三江平原湿地气候效应模拟的基础数据。 相似文献
53.
Effect of polypropylene fibre and lime admixture on engineering properties of clayey soil 总被引：2，自引：0，他引：2
In order to reduce the brittleness of soil stabilized by lime only, a recent study of a newly proposed mixture of polypropylene fibre and lime for ground improvement is described and reported in the paper. To investigate and understand the influence of the mixture of polypropylene fibre and lime on the engineering properties of a clayey soil, nine groups of treated soil specimens were prepared and tested at three different percentages of fibre content (i.e. 0.05%, 0.15%, 0.25% by weight of the parent soil) and three different percentages of lime (i.e. 2%, 5%, 8% by weight of the parent soil). These treated specimens were subjected to unconfined compression, direct shear, swelling and shrinkage tests. Through scanning electron microscopy (SEM) analysis of the specimens after shearing, the improving mechanisms of polypropylene fibre and lime in the soil were discussed and the observed test results were explained. It was found that fibre content, lime content and curing duration had significant influence on the engineering properties of the fibre–lime treated soil. An increase in lime content resulted in an initial increase followed by a slight decrease in unconfined compressive strength, cohesion and angle of internal friction of the clayey soil. On the other hand, an increase in lime content led to a reduction of swelling and shrinkage potential. However, an increase in fibre content caused an increase in strength and shrinkage potential but brought on the reduction of swelling potential. An increase in curing duration improved the unconfined compressive strength and shear strength parameters of the stabilized soil significantly. Based on the SEM analysis, it was found that the presence of fibre contributed to physical interaction between fibre and soil whereas the use of lime produced chemical reaction between lime and soil and changed soil fabric significantly. 相似文献
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探地雷达(GPR)在海南岛东北部海岸带调查中的应用 * 总被引：2，自引：0，他引：2
对海南岛东北部海岸带调查采用了探地雷达(GPR)研究海岸带沙体的结构、展布和沉积序列,取得了很好的效果。文章通过和有限的露头资料对比以及对反射波形态、结构的研究,确定了海滩脊、海岸沙丘的反射特征以及潜水面的位置。雷达图像显示五龙港古海滩脊由亚水平、不连续、高振幅和透镜状反射波组成;木兰头海岸沙丘已受到人类活动的扰动,短的、陡倾斜反射可能代表未受扰动的海岸风成沙的前积层。研究表明探地雷达是一种可靠、快速和经济的地球物理方法,在砂砾质海岸可产生高质量、高分辨率和连续的反射剖面,值得加以推广。 相似文献
56.
本文提出了人为土的工程概念,从其成因的角度给出了人为土明确的科学定义,归纳和总结了人为土的基本特征,为人为土的工程分类体系建立、合理评价、工程利用和环境整治提供科学依据。 相似文献
57.
甘肃灵台黄土-红粘土序列中坡缕石的分布及其古气候意义 总被引：8，自引：0，他引：8
坡缕石是典型的干旱、强蒸发环境的指示矿物,黄土-红粘土序列中坡缕石的分布对古气候和古环境重建具有重要的指示意义。本文对灵台任家坡剖面中黄土、古土壤和红粘土代表性样品进行了场发射扫描电镜和高分辨透射电镜观察,结果发现,在3.6Ma以前沉积的红粘土中存有大量的自生坡缕石,而在3.2Ma以来沉积的红粘土及其上覆黄土古土壤序列没有坡缕石。剖面样品扫描电镜原位观察形貌特征和微观结构显示,坡缕石属于成壤作用自生矿物,系由伊蒙矿物在富镁孔隙液作用下转化形成。灵台剖面中坡缕石消失的层位与红粘土磁化率升高和粉尘通量及沉积速率增加的层位相一致。坡缕石在剖面中的分布指示3.6～3.2Ma前后是东亚季风的重要转型期,东亚古气候格局发生改变,由连续干暖的夏季风占主导向干冷冬季风和暖湿夏季风高频强波动交替环境演化。 相似文献
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