Pleistocene Periglacial Eolian Deposits in Southwestern Alaska: Sedimentary Facies and Depositional Processes
Pleistocene Periglacial Eolian Deposits in Southwestern Alaska: Sedimentary Facies and Depositional Processes
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阿拉斯加西南部更新世冰缘风成沉积物：沉积相和沉积过程
DOI：
10.1306/212f91f1-2b24-11d7-8648000102c1865d
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发表时间：
1990
影响因子：
2
通讯作者：
P. D. Lea
中科院分区：
文献类型：
--
作者：
P. D. Lea
摘要更新世冰缘风尘沉积广泛分布于阿拉斯加西南部的努沙加克、霍利特纳和上库什科维姆低地。这些沉积物主要由砂席沉积和砂黄土夹层组成，其次为沙丘沉积和黄土。沙板沉积的范围从1)由移动的风浪形成的清晰、平行的小角度纹层到2)不规则的亚水平地层，这些地层反映了分离不佳的风浪的迁移、在稀疏的植被表面上的聚集、在准平面床上的附着和/或新风沙沉积。砂土-黄土界面层表现为交替的推移质和悬浮沉积，主要与原有风系的随机和季节变化有关。在阿拉斯加西南部的更新世风沙记录中，沙席沉积的优势超过了结构良好的沙丘沉积，反映了在这个以前的冰缘环境中，松散、干燥的沙子的可获得性有限。由于冰胶结、稀疏的植被、高水位和积雪的季节性组合，沉积后的沙子被固定为低起伏的垫层。
ABSTRACT Pleistocene periglacial eolian sediments are widespread in the Nushagak, Holitna, and Upper Kuskokwim lowlands of southwestern Alaska. These sediments comprise mainly sand-sheet deposits and sand-loess intergrades, with subordinate sand-dune deposits and loess. Sand-sheet deposits range from 1) sharply defined, parallel, low-angle laminae formed by migrating wind ripples to 2) irregular subhorizontal strata which reflect migration of poorly segregated wind ripples, accumulation on a sparsely vegetated surface, adhesion on a quasi-planar bed, and/or niveo-eolian deposition. Sand-loess intergrades represent alternating bed-load and suspension deposition related mainly to the stochastic and seasonal variability of former wind systems. The dominance of sand-sheet deposits over deposits of well-formed dunes in the Pleistocene eolian record of southwestern Alaska reflects the limited availability of loose, dry sand in this former periglacial environment. Immobilization of sand after deposition as low-relief sheets resulted from a seasonally variable combination of ice cementation, sparse vegetation, high water tables, and snow cover.