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41.
Detailed soil erosion studies bene?t from the ability to quantify the magnitude of erosion over time scales appropriate to the process. An inventory balance for 7Be was used to calculate sediment erosion in a 30·73 m2 plot during a series of runoff‐producing thunderstorms occurring over three days at the Deep Loess Research Station in Treynor, Iowa, USA. The inventory balance included determination of the pre‐ and post‐storm 7Be inventories in the soil, the atmospheric in?ux of 7Be during the event, and pro?les of the 7Be activity in the soil following the atmospheric deposition. The erosion calculated in the plot using the 7Be inventory balance was 0·058 g cm?2, which is 23 per cent of the annual average erosion determined using 137Cs inventories. The calculated erosion from the mass balance is similar to the 0·059 g cm?2 of erosion estimated from the amount of sediment collected at the outlet of the 6 ha ?eld during the study period and the delivery ratio (0·64). The inventory balance of 7Be provides a new means for evaluating soil erosion over the time period most relevant to quantifying the prediction of erosion from runoff. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
42.
G. Chi P. S. Giles M. A. Williamson D. Lavoie R. Bertrand 《Journal of Geochemical Exploration》2003,80(2-3):171-191
Eighty-two core samples were collected from the Spring Valley #1 well which penetrates the Upper Carboniferous strata in the Late Devonian–Early Permian Maritimes Basin. The strata consist of alternating sandstones and mudstones deposited in a continental environment. The objective of this study is to characterize the relationship of sandstone porosity with depth, and to investigate the diagenetic processes related to the porosity evolution. Porosity values estimated from point counting range from 0% to 27.8%, but are mostly between 5% and 20%. Except samples that are significantly cemented by calcite, porosity values clearly decrease with depth. Two phases of calcite cement were distinguished based on Cathodoluminescence, with the early phase being largely dissolved and preserved as minor relicts in the later phase. Feldspar dissolution was extensive and contributed significantly to the development of secondary porosity. Quartz cementation was widespread and increased with depth. Fluid inclusions recorded in calcite and quartz cements indicate that interstitial fluids in the upper part of the stratigraphic column were dominated by waters with salinity lower than that of seawater, the middle part was first dominated by low-salinity waters, then invaded by brines, and the lower part was dominated by brines. Homogenization temperatures of fluid inclusions generally increase with depth and suggest a paleogeothermal gradient of 25 °C/km, which is broadly consistent with that indicated by vitrinite reflectance data. An erosion of 1.1–2.4 (mean 1.75) km of strata is inferred to have taken place above the stratigraphic column. δ18O values of calcite cements (mainly from the late phase) decrease with depth, implying increasing temperatures of formation, as also suggested by fluid-inclusion data. δ13C values of calcite cements range from −13.4‰ to −5.7‰, suggesting that organic matter was an important carbon source for calcite cements. A comparison of the porosity data with a theoretical compaction curve indicates that the upper and middle parts of the stratigraphic column show higher-than-normal porosity values, which are related to significant calcite and feldspar dissolution. Meteoric incursion and carboxylic acids generated from organic maturation were probably responsible for the abundant dissolution events. 相似文献
43.
Charles E Schweger 《Quaternary Research》2003,60(1):44-49
Pollen analysis at two sites, correlated by the presence of the 190,000 yr-old Sheep Creek tephra, documents fluctuations in vegetation and climate consistent with this date and indicates that the records span marine oxygen isotope stage 7 and the stage 6/7 transition. Dawson Cut, near Fairbanks, Alaska, provides a 5.2-m-long pollen record of interglacial boreal forest succeeded by shrub tundra and then forest/tundra. Ash Bend, Stewart River, central Yukon, provides a 9.5-m-long record of interglacial boreal forest succeeded by forest/tundra, shrub tundra, and herbaceous tundra. The replacement of forest at both sites by more open or tundra vegetation indicates warm interglacial conditions giving way to cold and arid climate. It is not clear whether stage 7 was warmer than the present. The warm-cool-warm climate oscillation evident at both sites may correlate to Lake Baikal substages 7a, 7b, and 7c. Sheep Creek tephra fell on forest/tundra vegetation. 相似文献
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46.
丽江7.0级地震地下流体异常特征 总被引:1,自引:3,他引:1
通过对1996年2月3日云南丽江Ms7.0地震前震中周围水位、水氡、水汞、泉点宏观等地下流体共71个台项观测资料的异常及综合特征分析,初步认为震前异常数量较多,异常时间分布具有整体性、同步性、集中性的特点,但异常主要集中在短期阶段,临震异常不突出;突间分布具有集中性和非均匀性,孕震区至远场影响区的异常比例最高,震源区内为相对“盲区”,且突出而肯定的宏观异常极少;异常的时空演变特征复杂,总体没有规律 相似文献
47.
丽江大研镇震灾分布和地脉动测量结果之间的相关性 总被引:4,自引:2,他引:4
丽江7.0级地震后,大研镇被毁建筑物的地理分布呈显4条条带,伤亡人员的地理分布和上述条带重合。91个短周期地脉动测点的观测资料表明,分布在上述条带内的大多数测点,其卓越周期大于0.3S;条带外的测点,其卓越周期一般在0.1S左右。作认为卓越周期和烈度异常之间良好的相关性,是因为地脉动卓越周期和地方震的频谱之间存在良好的相关性。 相似文献
48.
丽江7.0级地震前地震分形异常 总被引:2,自引:2,他引:2
本提供了丽江7.0级地震前滇西北地震活动空间容量维、关联维、信息熵十分显的异常图像;这些异常是在大震孕震区形成、应变释放加速阶段之后出现的,恰好揭示了源区、近源区大释放前的非线性变化过程。这与1965年以来云南及邻区8组大震前地震分形研究的结论完全一致;进一步说明地震活动分形异常对地震孕育的短临阶段具有重要的指示意义。 相似文献
49.
禾青井动水位对断层蠕动与慢地震过程的响应初析 总被引:3,自引:1,他引:3
以湖南禾青井深井水位观测的异常图象为例进行定性分析,发现动水位观测有可能直接反映出断层的滑动或断层的慢地震过程,前者可能为地下水物理参量的观测与研究提供亲折思路,后者则可能对震源物理学的发展和地震预报水平的提高具有特殊的意义。 相似文献
50.
着重介绍了北京顺义4.0级地震前后板桥井水位的异常特征,并通过对板桥井二次异常的对比分析研究,提出井水位异常时间尺度与震级之间的可能关系。 相似文献