Post-Little Ice Age record of coarse and fine clastic sedimentation in an Alaskan proglacial lake
Post-Little Ice Age record of coarse and fine clastic sedimentation in an Alaskan proglacial lake
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阿拉斯加前冰川湖中小冰期后粗碎屑和细碎屑沉积的记录
DOI：
10.1130/g20839.1
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发表时间：
2004
期刊：
影响因子：
5.8
通讯作者：
S. P. Anderson
中科院分区：
文献类型：
--
作者：
M. Loso;R. Anderson;S. P. Anderson
许多对冰川沉积物产量的评估仅仅依赖于细粒悬浮沉积物的测量。我们发现，在阿拉斯加前冰湖冰山湖中，悬垂沉积物占碎屑沉积物总量的20%。1999年，这个湖的排水暴露出了破碎的湖泊沉积物的露头，记录了悬浮沉积物的沉积。自两个世纪前的小冰期高点以来，湖泊水位在四次突然的溢洪道控制事件中下降，这些事件在地层学上被记录为盆地范围内异常细粒度沉积物沉积的短暂增加。Varve计数限制了这些事件的年龄，因此也限制了每个废弃海岸线和相关三角洲的年龄。从公元1825年到1999年，三角洲和湖底沉积物的体积限制了四个多年代际的具体产量。总产沙量在3.8 ~ 4.9 t·km ~ 22·yr ~ 21之间，泥沙以沙砾为主（81% ~ 86%）。一系列证据表明，在这个面积小（66平方公里）且高度玻璃化的盆地中，产沙量忠实地记录了上游产沙量，这意味着有效的冰下侵蚀速率为1.6毫米/年。这些数据表明，仅基于悬浮沉积物的总产量估计存在很大误差，并表明采石占该系统中冰川侵蚀的很大一部分。
Many assessments of glacial sediment yield rely solely on mea- surements of fine-grained suspended sediment. We show that sus- pended sediment contributes ,20% of the total clastic sediment discharge into Iceberg Lake, an Alaskan proglacial lake. Drainage of this lake in 1999 exposed outcrops of varved lacustrine sediment that record suspended sediment deposition. Since a Little Ice Age highstand two centuries ago, lake level has dropped in four abrupt spillway-controlled events that are recorded stratigraphically as transient increases in the basinwide deposition of unusually fine grained sediments. Varve counting constrains ages of these events and, hence, of each abandoned shoreline and associated delta. Vol- umes of deltaic and lake-floor sediments constrain specific yields from four multidecadal intervals between A.D. 1825 and 1999. To- tal yield ranges from 3.8 to 4.9 3 10 3 t·km 22 ·yr 21 , and most of the sediment (81%-86%) is sand and gravel now in the deltas. A range of evidence suggests that sediment yield faithfully records up- stream sediment production in this small (66 km 2 ) and heavily gla- cierized basin, implying an effective subglacial erosion rate of 1.6 mm/yr. These data show that estimates of total yield based upon suspended sediment alone are subject to large errors and suggest that quarrying accounts for a large fraction of the glacial erosion in this system.