Cosmogenic exposure dating of late Pleistocene moraine stabilization in Alaska
Cosmogenic exposure dating of late Pleistocene moraine stabilization in Alaska
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DOI：
10.1130/b25649.1
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发表时间：
2005-07
影响因子：
4.9
通讯作者：
J. Briner;D. Kaufman;W. Manley;R. Finkel;M. Caffee
中科院分区：
文献类型：
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作者：
J. Briner;D. Kaufman;W. Manley;R. Finkel;M. Caffee
73个新的1 0 Be/ 2 6铝年龄从57个冰碛石和2个tors，连同43个先前公布的宇宙成因暴露年龄从41冰碛石，让我们批评使用宇宙成因暴露（CE）测年的冰碛石在阿拉斯加。在冰碛退化过程中，巨石的挖掘可能会引起最大的不确定性，在限制冰退缩后的初始冰碛稳定的时间。同位素遗传似乎是最重要的冰碛物沉积接近他们的冰斗端壁。巨石表面（基岩）的侵蚀速率可以大致限制，并导致一个范围内的冰碛稳定年龄。积雪的历史是很难约束，但它的影响被认为是轻微的高卵石采样。尽管有这些复杂的情况，CE年龄提供了关于阿拉斯加最后一次和倒数第二次冰期时间的重要新信息。三个倒数第二的冰碛物产生的CE年龄与海洋同位素阶段（MIS）4/早期MIS 3（45-65 ka）重叠，而不是MIS 6（约100万年）。140 ka）。基于我们新的CE年表和现有的14 C年龄从六个研究领域的组合，冰川退缩从当地晚威斯康星州最大：约。24-27 ka，Kokrines Hills（west-interior Alaska）; ca. 24-26 ka，东北部布鲁克斯岭（东北阿拉斯加）;约。21-23 ka，育空地区Tanana高地（东内陆阿拉斯加）;约. 22 ka，Ahklun Mountains（SW Alaska）;约. 20 ka，阿拉斯加山脉西部（阿拉斯加中部）;约。16-18 ka，Chuilnuk山脉（阿拉斯加西南部）。总体而言，冰川退缩是同时与最后一次全球最大冰川的高峰，可能是有限的水分供应。
Seventy-three new 1 0 Be/ 2 6 Al ages from 57 moraine boulders and 2 tors, together with 43 previously published cosmogenic exposure ages from 41 moraine boulders, allow us to critique the use of cosmogenic exposure (CE) dating of moraine boulders in Alaska. Boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat. Isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls. Boulder-surface (bedrock) erosion rate can be roughly constrained and leads to a range in moraine stabilization ages. Snow-cover history is difficult to constrain, but its effect is thought to be minor for the tall boulders sampled. Despite these complications, the CE ages provide important new information regarding the timing of the last and penultimate glaciations in Alaska. Three penultimate moraines yielded CE ages that overlap with marine isotope stage (MIS) 4/early MIS 3 (45-65 ka) rather than MIS 6 (ca. 140 ka). Based on a combination of our new CE chronologies and existing 1 4 C ages from six study areas, glaciers retreated from their local late Wisconsin maxima: ca. 24-27 ka, Kokrines Hills (west-interior Alaska); ca. 24-26 ka, northeastern Brooks Range (NE Alaska); ca. 21-23 ka, Yukon Tanana Upland (east-interior Alaska); ca. 22 ka, Ahklun Mountains (SW Alaska); ca. 20 ka, western Alaska Range (central Alaska); ca. 16-18 ka, Chuilnuk Mountains (SW Alaska). Overall, glacier retreat was concurrent with the peak of the last global glacial maximum, probably in response to limited moisture availability.