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1.
A. P. M. Vaughan L. A. Dowling F. J. G. Mitchell S.‐E. Lauritzen A. M. McCabe P. Coxon 《第四纪科学杂志》2004,19(6):577-590
Organic‐rich deposits, uncovered during overburden removal from mantled gypsum karst at Knocknacran opencast gypsum mine, Co. Monaghan, are the best candidate to date for a last interglacial record in Ireland. The two till and organic‐rich deposits (preserved at different quarry elevations) were emplaced on to a Tertiary dolerite surface during high‐energy flood events and subsequently folded and faulted by movement towards sinkholes in underlying gypsum. Uranium–thorium disequilibrium dating suggests that the organic‐rich deposits in the upper section were hydrologically isolated at ca. 41 ka and those in the lower section at ca. 86 ka. Interpretation of the pollen content, although tentative because of the depositional and post‐depositional history of the material, suggests that the organic material originated in a warm stage possibly warmer than the post‐Eemian interstadials. The unusual setting of preservation may indicate that in situ, last interglacial deposits have generally been removed by erosion in Ireland. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Thaw modification is the general process whereby frost-fissure wedges are modified during thaw, and by which frost-fissure pseudomorphs may develop. Specific processes of thaw modification are inferred from ice-wedge pseudomorphs, composite-wedge pseudomorphs and deformed sand wedges in the Pleistocene Mackenzie Delta: i.e. thermal erosion, collapse, subsidence, refreezing, loading, buoyancy, spreading, folding and shearing. Thaw modification is believed to result in selective preservation of pseudomorphs and wedges. Sand wedges are more likely to be preserved than are ice-wedge pseudomorphs or compositewedge pseudomorphs, because only those sand wedges that penetrate massive ice or icy sediments are prone to thaw modification. Furthermore, whereas ice wedges preferentially develop in ice-rich, fine-grained sediments (thaw-sensitive), their pseudomorphs appear to be selectively preserved in ice-poor, coarse-grained sediments (thaw-stable). 相似文献
4.
Houyi ZHENG Congqiang LIU Zhongliang WANG 《中国地球化学学报》2006,25(B08):174-174
Bedrock weathering and atmospheric deposition are the two primary sources of base cations (K^+, Na^+, Ca^2+ and Mg^2+) to forest ecosystems. Therefore, the key problem is to understand the relative inputs from these two sources and the cycling in the ecosystem. This study focuses on the effects of acid deposition on cation cycling in a small-forested karstic catchment in Guizhou Province. Sr isotope ratios were used as a tracer for understanding the transport process between the different cation pools: rock, soil, surface water, atmospheric deposition and plant. The samples of wet deposition, total deposition, throughfall, surface and ground waters, vegetation, and soil were monthly collected. The exchangeable Sr^2+ and Ca^2+ in soil samples were extracted by using 1 M ammonium acetate. The leaf-tissue samples were ashed at 550℃, and the residue was digested in ultrapure HClO4 and HNO3. All water samples were filtrated through 0.45 μm aperture filter paper. Base cation concentrations and Sr isotopic composition were analyzed for all the samples. The results show that acid deposition (average pH 4.9) frequently occurred in the studied region. Cation abundance follows an increasing manner from rainwater, throughfall, to surface water or ground water samples, suggesting that acid deposition at first eiuviates Ca^2+ , Mg^2+ and Sr^2+ from leaf, then the exchangeable cations from soil, and at last cations accumulate in surface water or ground water. 相似文献
5.
David W. Kelley Stefanie A. Brachfeld Edward A. Nater Herbert E. Wright Jr. 《Journal of Paleolimnology》2006,35(1):193-206
Sediments from Lake Pepin on the Mississippi River, southeastern Minnesota, are used as provenance tracers to assess variations
in hydrology and sediment-transport during the middle Holocene. Three rivers contribute sediment to Lake Pepin, and each catchment
is characterized by a distinctly different geologic terrain. The geochemical fingerprint for each drainage basin was determined
from the elemental composition of heavy minerals in the silt-sized fraction of modern sediment samples. Down-core elemental
abundances were compared with these fingerprints by use of a chemical-mass-balance model that apportions sediment to the source
areas. We observed a decreased contribution from the Minnesota River during the interval ~6700–5500 14C yr BP, which we attribute to decreased discharge of the Minnesota River, likely controlled by a combination of precipitation,
snow melt, and groundwater input to the river. This hydrologic condition coincides with the mid-Holocene prairie period recorded
by fossil pollen data. The occurrence of this feature in a proxy record for hydrologic variations supports the hypothesis
that the mid-Holocene prairie period reflects drier conditions than before or after in midwestern North America. 相似文献
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Based on cross-dating tree rings from the Tianmu Mountain, Zhejiang Province, the tree rings α-cellulose δ 13C time series was measured. By spectrum analysis, the variation of tree-ring δ13C sequence shows a quasi periodicity of 4.4 years, which is coincident with the standard cycle of El Nino. After removing the long-term decrease trend of the δ13C variation related to atmospheric CO2 concentration, the response of the δ13C to climate elements was analyzed using meteorology data from a nearby weather station. The results suggest that there is a distinct relativity between high-frequency variation of tree ring δ 13C series and seasonal climate parameters, e.g. Temperature and precipitation, with a significant time-lag effect. In addition, the high frequency also reflects the strength change of the East Asian Monsoon. The multiple regression method was employed to reconstruct the historical climate, and to analyze the climate change and trend in the last 160 years in the northern Zhejiang Province. 相似文献
7.
Jean-Paul Vicat Hubert Mvondo Luc Willems André Pouclet 《Comptes Rendus Geoscience》2002,334(8):545-550
Numerous karstic features have been recognised in the non-carbonaceous micaschists and gneisses of the Yaoundé Pan-African nappe, south of Cameroon. It is shown that their formation was controlled by the structural features of the rocks. The wells and the pipes in the bedrock outcrops point out a current karstification process, resulting from the plagioclase dissolution by the acid rain waters. Hill wall alveoli and caves, of pre-Miocene age, are exhumed features that were done by dissolution in the aquiferous underground. To cite this article: J.-P. Vicat et al., C. R. Geoscience 334 (2002) 545–550. 相似文献
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高密度电法勘探在岩溶查找中的应用 总被引:10,自引:0,他引:10
介绍了武汉市汤逊湖污水处理厂厂址的地质概况和地球物理特征,以及高密度电法勘探的施工方案,分析了视电阻率异常特征,并说明了其异常验证情况。高密度电法勘探结果表明该区存在溶洞,为施工提供了决策依据,建议在有溶洞的地段采取相应措施,以防止工程建设后发生地质灾害。 相似文献
10.
井间电阻率层析成象的某些进展 总被引:7,自引:2,他引:7
用有限元法作电阻率层析成象的核心问题是Jacobi矩阵的求取和反演成象算法的研究。本文主要论述了这两方面的最新进展,即求取Jacobi矩阵的格林函数法,用于反演成象计算的平滑度约束反演。文中通过理论模型的成象计算,比较了两种反演算法的成象效果。 相似文献