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Conceptual geological models based on geophysical data can elucidate aquifer architecture and heterogeneity at meter and smaller scales, which can lead to better predictions of preferential flow pathways. The macrodispersion experiment (MADE) site, with >2000 measurements of hydraulic conductivity obtained and three tracer tests conducted, serves as an ideal natural laboratory for examining relationships between subsurface flow characteristics and geophysical attributes in fluvial aquifers. The spatial variation of hydraulic conductivity measurements indicates a large degree of site heterogeneity. To evaluate the usefulness of geophysical methods for better delineating fluvial aquifer heterogeneities and distribution of preferential flow paths, a surface grid of two-dimensional ground penetrating radar (GPR) and direct current (DC) resistivity data were collected. A geological model was developed from these data that delineate four stratigraphic units with distinct electrical and radar properties including (from top to bottom) (1) a meandering fluvial system (MFS); (2) a braided fluvial system (BFS); (3) fine-grained sands; and (4) a clay-rich interval. A paleochannel, inferred by other authors to affect flow, was mapped in the MFS with both DC resistivity and GPR data. The channel is 2 to 4 m deep and, based on resistivity values, is predominantly filled with clay and silt. Comparing previously collected hydraulic conductivity measurements and tracer-plume migration patterns to the geological model indicates that flow primarily occurs in the BFS and that the channel mapped in the MFS has no influence on plume migration patterns. 相似文献
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按照板块构造的观点 ,地球上存在 3类大陆边缘 :活动大陆边缘、被动大陆边缘和转换大陆边缘。被动大陆边缘主要分布在大西洋两岸 ,因此也叫大西洋型大陆边缘。经区域地质构造研究表明 ,南海是一个小大西洋 ,它在新生代像大西洋在中、新生代一样 ,是经过大陆岩石圈张裂 (rifting)、破裂分离 (break up)和海底扩张而生成的小洋盆。虽然目前对大西洋的诞生过程比较清楚 ,但对诞生过程中大陆岩石圈在张裂、破裂分离期间岩石圈的变形过程及其特征仍不太了解。为了进行这方面的研究 ,科学家将在破裂分离前连在一起的大西洋两岸大陆边缘 (科学家命… 相似文献
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广泛分布在太平洋西北部海岛上的风成堆积物 ,显示了砂被带入附近海区的动力学和在更新世漫长时间内气候变化时沉积物质移动的方向。俄罗斯科学院远东分部太平洋地理研究所利用放射性碳测年以及生物地层学和火山灰地层学的资料研究了白令岛和南千岛群岛上的剖面。将晚更新世和全新世划分为若干个风成年龄段。这些堆积物的产生是由于尘土的进一步迁移 (它们覆盖了全新世前的地形 ) ,也由于附近源头 (海岸沙丘砂 )的移动。由多孔非层状砂质岩和轻砂质粘土组成的盖层 ,很可能是在更新世末至全新世初气候逐渐变暖时形成的。在埋藏土中发现的火山… 相似文献
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日本科学家最近在日本东海发现了一个海底下沉地带.这一地带位于东海纪伊海域的南海海沟东南5070km处.通常被称为“大地震巢”. 相似文献
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俄罗斯北极海白垩纪的沉积主要与地台环境有关.白垩纪的岩石与侏罗纪的沉积一样,占包括陆架的极区面积的70%. 相似文献
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大洋型地壳构成将近三分之二的地球硬质壳层 ,也许这种趋势从地球年轻时候起就保存下来了。至今一般都认为 ,在太古代 (超过2 50 0Ma前 ) ,当地幔的温度是现代的 3倍时 ,在扩张过程中形成的洋壳具有另一种组分。这可以根据保存下来的太古代大洋岩石圈的标本来加以审核。通常岩石圈在俯冲返回地幔时多次被改造 ,但其被命名为蛇绿岩套的个别组分保存在板块碰撞和造山运动区。来自北京和一批美国大学的地球物理学家研究了不久前在北京东北 2 50km的华北克拉通区域发现的蛇绿岩套。华北克拉通包括含有片麻岩、角闪岩、云母片岩、白云石化大理岩… 相似文献