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21.
新元古代晚期盖帽碳酸盐岩的成因与“雪球地球”的终结机制 总被引:5,自引:3,他引:5
新元古代晚期约635 Ma的地球发育了到达赤道附近的冰川作用,地质记录上表现为代表寒冷气候的冰期沉积杂砾岩,直接被代表温暖环境的碳酸盐岩层(常称盖帽碳酸盐岩)覆盖。由于盖帽碳酸盐岩奇特的岩石学和地球化学特征,引起了对其成因认识的巨大争论,提出了“雪球地球”和“甲烷渗漏”等假说。“雪球地球”假设可以解释一些令人困惑的地学现象,如低纬度和低海拔冰川沉积、盖帽碳酸盐岩、碳酸盐δ13C负漂移和条带状铁矿层等,但许多科学家对此提出了质疑。最近对盖帽碳酸盐岩的δ13C分析结果(最低达-41‰)、盖帽碳酸盐岩发育的类似现代冷泉碳酸盐岩沉积组构等似乎支持“甲烷渗漏”假说。 相似文献
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Methanesulphonate was investigated as a potential contributor to the sulphur budget based on the analysis on Antarctic snow/ice from Coffins Ice Cap, King George Island (62°10' S, 58°50,W). The anion was found to be present at a mean concentration of 0. 17 μeq. L-1 with a maximum of 0.73 μeq. L-1. A distinct seasonal variation exists in the top 10 m of the core, equivalent to more than two years of deposition. Dating resulted from δ18O profile suggests that the principal peaks of methanesulphonate are associated with snow deposited in autumn and secondary peaks in spring. The seasonal patterns of methanesulphonate in the subantarctic snow displays a phase difference from that observed in marine air from low and middle latitudes. 相似文献
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研究南海礁栖腔节藻Coelarthrum sp.共附生真菌Pestalotiopsis neglecta SCSIO41403的次级代谢产物。采用中压正相柱层析色谱法和半制备高效液相色谱法, 对真菌发酵产物进行分离纯化, 制备获得6个次级代谢产物单体化合物, 使用核磁共振、质谱等波谱学方法, 结合其理化性质以及文献数据对比, 分别鉴定为: gamahorin (1)、microsporaline C (2)、7-hydroxy-5-methoxy-4,6-dimethylphthalidc (3)、demethyl nectriapyrone A (4)、4-hydroxybenzaldehyde (5)和4-hydroxyphenethyl acetate (6)。这6个化合物均为首次从该菌株发现, 其中化合物1、2、5和6是首次从海洋动植物共附生真菌中发现。抗菌活性筛选显示其中化合物3对白色念珠菌有明显抑制活性。 相似文献
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???????г????????????????????????????????????????????г????????????32°N~34°N??102°E~104°E?????????????EGM2008?????????????????????г?????????????????????????????????????????????????????г???????????????????С??0.5×10-5 ms-2??????????????????0.71°????????????????±4.65×10-5 ms-2?? 相似文献
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The influence of vertical loads on the lateral response of group piles installed in sandy soil and connected together by a concrete cap is studied through finite elements analyses. The analyses focus on the five piles in the middle row of 3 × 5 pile groups. The vertical load is applied by enforcing a vertical displacement equivalent to 2% of the pile diameter through the pile cap prior to the application of the lateral loads. The results have shown that the lateral resistance of the leading pile (pile 1) does not appear to vary considerably with the vertical load. However, the vertical load leads to 23%, 36%, 64%, and 82% increase in the lateral resistance of piles 2–5, respectively. The increase in the lateral pressures in the sand deposit is the major driving factor to contribute the change in the lateral resistance of piles, depending on the position of the pile in the group. The distribution of lateral loads among piles in the group tends to be more uniform when vertical loads were considered leading to a more economical pile foundation design. 相似文献
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2005年5月~8月在雷州市覃斗镇海威水产种苗基地的室内水池进行方斑东风螺亲螺培育,对亲螺不同批次产出的卵囊、卵、及其幼虫进行比较。结果表明:随着亲螺产卵批次的增加,亲螺产卵囊数、卵囊含卵数、产卵量逐次减少;卵囊长、宽逐次变小,厚逐次增加,形状由葵花子片状的比例大变为棒状的比例大;幼虫浮游期逐次延长;变态期幼虫壳长逐次变小;各批次之间的变态率逐次降低;卵径、孵化率、出囊幼虫大小差异不显著。 相似文献
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Lúcia Carvalho Coelho Antonio Claudio Soares Nelson Francisco F. Ebecken Jos Luis Drummond Alves Luiz Landau 《国际地质力学数值与分析法杂志》2006,30(14):1477-1500
High porosity and low permeability limestone has presented pore collapse. As fluid is withdrawn from these reservoirs, the effective stresses acting on the rock increase. If the strength of the rock is overcome, pore collapse may occur, leading to irreversible compaction of porous media with permeability and porosity reduction. It impacts on fluid withdrawal. Most of reservoirs have been discovered in weak formations, which are susceptible to this phenomenon. This work presents a study on the mechanical behaviour of a porous limestone from a reservoir located in Campos Basin, offshore Brazil. An experimental program was undergone in order to define its elastic plastic behaviour. The tests reproduced the loading path conditions expected in a reservoir under production. Parameters of the cap model were fitted to these tests and numerical simulations were run. The numerical simulations presented a good agreement with the experimental tests. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
30.
Bao Yang Achim Bruning Jingjing Liu Mary E. Davis Shao Yajun 《Global and Planetary Change》2009,69(1-2):71-78
The climatological signal of δ18O variations preserved in ice cores recovered from Puruogangri ice field in the central Tibetan Plateau (TP) was calibrated with regional meteorological data for the past 50 years. For the period AD 1860–2000, 5-yearly averaged ice core δ18O and a summer temperature reconstruction derived from pollen data from the same ice core were compared. The statistical results provide compelling evidence that Puruogangri ice core δ18O variations represent summer temperature changes for the central TP, and hence regional temperature history during the past 600 years was revealed. A comparison of Puruogangri ice core δ18О with several other temperature reconstructions shows that broad-scale climate anomalies since the Little Ice Age occurred synchronously across the eastern and southern TP, and the Himalayas. Common cold periods were identified in the 15th century, 1625–1645 AD, 1660–1700 AD, 1725–1775 AD, 1795–1830 AD, 1850–1870 AD, 1890–1920 AD, 1940–1950 AD, and 1975–1985 AD. The period 1725–1775 AD was one of the most prolonged cool periods during the past 400 years and corresponded to maximum Little Ice Age glacier advance of monsoonal temperate glaciers of the TP. 相似文献