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281.
A. P. Dykes 《Landslides》2007,4(3):279-290
The West Mouth of the Great Cave at Niah in Sarawak, northwest Borneo and the North Passage that leads to the West Mouth contain
large deposits of guano. The main deposit, several metres thick in places, forms the sloping floor of the entire North Passage.
A mass movement deposit identified in the West Mouth, having a volume of 600 m3, originated as a guano mudflow up the North Passage in the order of 40,000 years ago. This failure of the guano slope was
investigated to determine whether particular conditions or events could be identified as the most likely causes. The physical,
hydrological and geotechnical properties of samples of the material were determined so that the stability of the slope could
be assessed. Stability analyses showed that shearing failure of the slope would require inputs of water to the slope in quantities
for which no feasible explanation can be suggested. However, the properties of the guano are similar to those of loess, indicating
a high susceptibility to ‘hydrocollapse’. Very shallow failure of the slope, possibly as several smaller mudflows, could therefore
have occurred due to additional water in quantities that could realistically be supplied as rainwater spray, possibly with
a seismic trigger. The climate must therefore have been wetter than it is at present. These findings have implications for
the interpretation of sediment deposits in other relict caves. 相似文献
282.
283.
Brent B. Wolfe Matthew D. Falcone Ken P. Clogg-Wright Cherie L. Mongeon Yi Yi Bronwyn E. Brock Natalie A. St. Amour William A. Mark Thomas W. D. Edwards 《Journal of Paleolimnology》2007,37(2):221-231
Recent advances in sample preparation techniques and mass spectrometry have fostered more routine oxygen isotope analysis
of aquatic cellulose in lake sediment cores, a proxy for lake water oxygen isotope history. These methodological developments
have significantly increased the feasibility of incorporating this approach into high-resolution, multi-site, and multi-proxy
studies, which are frequently necessary to answer complex hydrological, hydroecological and hydroclimatic questions requiring
a paleoenvironmental perspective. Direct translation of lake sediment aquatic cellulose oxygen isotope composition into lake
water oxygen isotope composition offers appreciable opportunity for quantitative paleohydrological reconstructions, as evidenced
by studies conducted over the past 15 years that span Holocene and pre-historical timescales. 相似文献
284.
Diatoms were identified and enumerated from a surface sediment calibration set of 50 lakes in northwestern Québec. The relationship
between species composition and environmental variables was examined using canonical correspondence analysis (CCA). Forward
selection and Monte Carlo permutation tests in CCA indicated that diatom species distributions in the data set are most strongly
correlated to lakewater pH. A strong (r
2
boot = 0.83) weighted averaging calibration model, that includes bootstrapped error estimates, was developed for inferring past
lakewater pH. Using this model, temporal changes in pH were reconstructed for two kettle lakes, Lac de la Pépinière and Lac
Perron. Based on limnological data, both the study lakes were expected to have recently acidified due to increased acidic
precipitation and increases in anthropogenic metal loading. However, our long-term pH inference data indicate that these lakes
were naturally acidic during pre-industrial times. Nonetheless, the rate of acidification, particularly in Lac de la Pépinière,
has accelerated in the last ∼75 years. These long-term pH records developed for the dilute lakes in northwestern Québec suggest
that the region has received increased atmospheric pollutants from the nearby Horne smelter in Rouyn-Noranda. The pH inference
profiles are markedly different from many other paleolimnological studies in acid-sensitive regions of Canada that have become
acidic primarily as a result of industrial activities.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
285.
威连滩冲沟砂黄土的风蚀与降雨侵蚀模拟实验 总被引:3,自引:0,他引:3
通过风洞与模拟降雨实验,研究了风力与降雨对青海省贵南县威连滩冲沟砂黄土的复合侵蚀作用。实验得出:①风蚀后的降雨使砂黄土表面在风干过程中形成了一层较为坚硬的结壳,增大了土壤的抗蚀性,降低了第二次风洞实验后期的风蚀率;②土壤水分与人为扰动是影响土壤风蚀的两个重要因素。当土壤水分较小时,风蚀率受人为扰动影响巨大;当土壤水分较大时,人为扰动对土壤风蚀的影响较小;③在持续降雨的实验条件下,砂黄土的产流、产沙量随着雨强的变化而改变。这种变化与表土的侵蚀率、可蚀性物质的多少、土壤水分以及土壤的入渗率等都有很大的关系。 相似文献
286.
287.
288.
289.
铼—锇同位素分析中试样化学预处理方法进展 总被引:4,自引:0,他引:4
评述了用于Re-Os同位素体系分析的化学前处理技术的发展。简要介绍了卡洛斯管熔样法、Os的CCl4提取、溴提取和微蒸馏方法。卡洛斯管封闭熔样方法,有效地防止了Os的挥发损失和保证了Os同位素平衡,是一种很有发展前景的熔样方法。蒸馏法仍是分离和纯化Os的有效方法,溶剂(CCl4)提取和溴提取法在许多实验室里应用,而微蒸馏则是Os的二次纯化的主要方法。Re的化学分离和纯化仍是离子交换和萃取法。引用主要文献29篇。 相似文献
290.
非线性最小二乘参数平差迭代算法 总被引:7,自引:1,他引:7
在非线性最小二乘问题现有的3类主要算法--高斯-牛顿法、阻尼最小二乘法和最小二乘的拟牛顿法的基础上,引入了综合性能更优的非线性规划的SQPM(序列二次规划法)算法,并且为进一步提高SQPM算法迭代的收敛性,对其步长策略进行了改进。改进的SQPM算法成为无需精确计算参数概略值的非线性最小二乘参数平差的实用和有效算法。 相似文献