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431.
电感耦合等离子体质谱法测定生物样品中超痕量稀土时氧化物干扰的研究 总被引:11,自引:10,他引:11
试验了100~700ug/LBa的氧化物对Eu产生的干扰,干扰程度与Ba量呈线性,其相关系数r在0.9986~0.9995。用模拟样品溶液对不同含量的Ba对Eu的干扰采取了简单的数学方法校正,校正后的结果在误差允许范围之内。.对小麦和人发标准物质中Ba氧化物对Eu的干扰及校正效果进行了比较。结果表明,在所使用的仪器条件下,这两个标准物质中的Ba对Eu的干扰必须校正。研究了ug/L水平的轻稀土氧化物对重稀 相似文献
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Neil F. Glasser Krister N. Jansson Bradley W. Goodfellow Hernan de Angelis Helena Rodnight Dylan H. Rood 《Quaternary Research》2011,75(3):636-646
At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49°S, 72°W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide (10Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ± 1.7 ka, 22.4 ± 2.3 ka, 34.4 ± 3.4 ka to 37.6 ± 3.4 ka (and possibly 60 ± 3.5 ka), and 99 ± 11 ka (1σ). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on 14C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought. 相似文献
435.
Timing and duration of North American glacial lake discharges and the Younger Dryas climate reversal
John A. Rayburn Thomas M. Cronin David A. Franzi Peter L.K. Knuepfer Debra A. Willard 《Quaternary Research》2011,75(3):541-551
Radiocarbon-dated sediment cores from the Champlain Valley (northeastern USA) contain stratigraphic and micropaleontologic evidence for multiple, high-magnitude, freshwater discharges from North American proglacial lakes to the North Atlantic. Of particular interest are two large, closely spaced outflows that entered the North Atlantic Ocean via the St. Lawrence estuary about 13,200–12,900 cal yr BP, near the beginning of the Younger Dryas cold event. We estimate from varve chronology, sedimentation rates and proglacial lake volumes that the duration of the first outflow was less than 1 yr and its discharge was approximately 0.1 Sv (1 Sverdrup = 106 m3 s−1). The second outflow lasted about a century with a sustained discharge sufficient to keep the Champlain Sea relatively fresh for its duration. According to climate models, both outflows may have had sufficient discharge, duration and timing to affect meridional ocean circulation and climate. In this report we compare the proglacial lake discharge record in the Champlain and St. Lawrence valleys to paleoclimate records from Greenland Ice cores and Cariaco Basin and discuss the two-step nature of the inception of the Younger Dryas. 相似文献
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大庸市四都坪震旦系南沱组岩石特征及成因探讨 总被引:2,自引:0,他引:2
文中提出以砾、砂、泥作三端员成分进行陆源沉积岩结构分类的三角图解方案,并用于四都坪南沱组岩石的划分,将其划分为杂屑岩、角砾岩、杂砂岩、粉砂质泥岩等。杂屑岩在南沱组剖面中占82%,其中的砾石成分复杂,有砂岩、板岩、大理岩、花岗岩等,大砾石表面有冰川擦痕和磨光面。角砾岩中角砾成分单一,无大漂砾,具颗粒支撑,并见夹有塑性变形的含锰灰岩。杂砾岩中发育砂纹层理及冲刷构造。因此,认为南沱组在成因上与冰川活动有关,在冰浅海环境中堆积,同沉积断裂的存在提供斜坡条件,冰川重力及埋藏冰消融等引发重力流,使冰川沉积不时受颗粒流、碎屑流干扰,而在冰期末又遭冰水及海水的改造。 相似文献
439.
The fact that the cross-profile of the glacial valley could be well approximated by parabolas (Y = aXb, b = 2.0) is explained by the variation principle, assuming that the glacier erosion works towards minimizing thefriction between ice and bedrock. The variation principle proves that the ideal or fully-developed morphology of the glacial valley should be a catenary, the curve which a chain hanging from two fixed points forms. Maclaurin's series expansion of the catenary equation shows that a parabola is a very good approximation of the catenary; hence, the good approximation of the cross-profile by parabolas. Different catenaries are generated by changing the form ratio (depth/rim width) and are then approximated by Y = aXb by the method of last-squares. The b values obtained become only fractionally larger than 2.0 with invreasing form ratios of up to 1.0, indicating that b values would range, in practice, between 1.0 and about 2.0 Two types of trend in the relationship between b values and the form ratio were obtained from several glaciers. For one type the b value becomes larger with increasing form ratios, and for the other the opposite. The first type is called the Rocky Mountain model after its source of data and represents overdeepening of the glacial valley development. The second type is caalled the Patagonia-Antarctica model, representing a widening, instead of a deepening, process of development. These differences are attributed to the nature of the glaciers which produced these valleys, i.e. alpine glaciers and continental ice sheets. 相似文献
440.
基于野外沉积物调查、已报道的风成沉积物年代和重建的湖泊水位波动曲线,初步绘制了末次冰期冰盛期和全新世早期青海湖东岸的沙漠范围。初步认为,末次冰期冰盛期时青海湖大幅度萎缩,湖底沉积物暴露并遭受风蚀,在偏西风的搬运下,近岸粗颗粒砂堆积在日月山西侧和倒淌河河谷,形成流动沙丘,细颗粒沉积物被向东搬运沉积至河湟谷地和黄土高原。倒淌河源头的沙丘最晚是在末次冰期盛冰期(23~16ka BP)沙漠扩张时形成并残留至今的;青海湖东部日月山西侧山麓地带和倒淌河河谷中、晚全新世黄土、古土壤下部普遍沉积的风成砂是末次冰期冰盛期和全新世早期(11~9 ka BP)青海湖东岸地区大范围沙化的证据。 相似文献