In-situ cosmogenic 10Be production rate at Lago Argentino, Patagonia: Implications for late-glacial climate chronology
In-situ cosmogenic 10Be production rate at Lago Argentino, Patagonia: Implications for late-glacial climate chronology
复制标题
DOI：
10.1016/j.epsl.2011.06.018
复制
发表时间：
2011-09-01
影响因子：
5.3
通讯作者：
Travis, Scott G.
中科院分区：
文献类型：
--
作者：
Kaplan, Michael R.;Strelin, Jorge A.;Travis, Scott G.
当按照普遍接受的北半球平均生产率计算时，巴塔哥尼亚阿根廷湖地区冰碛表面巨石的 Be-10 年龄比相同地貌的最低限制 C-14 年龄更年轻。这种分歧可能是由于缺乏区域性 Be-10 生产率校准站点造成的。为了评估这种可能性，我们在此对从埃尔米尼塔和班德拉港冰碛复合体表面巨石收集的样品中的 Be-10 进行了高精度测量，这些冰碛复合体沉积在巴塔哥尼亚南纬 50 度的安第斯山脉东侧阿根廷湖沿岸。结合两个冰碛系统的最大和最小限制 C-14 年龄，当使用包含高分辨率地磁模型的时间相关标度方法时，这些测量将局部 Be-10 生产率限制在 3.60 和 3.82 原子/克/年之间（中点 = 3.71 +/- 0.11 原子/克/年）。该范围包括来自 Herminita 和 Puerto Bandera 地点的可接受生产率的上限和下限。该范围的上限比北半球平均生产率低 12% 以上，这是使用 Balco 等人给出的相同缩放方法计算得出的。 [四。 Geochron 3 (2008) 174-195]。其他缩放模型产生的生产率与 Balco 等人的生产率具有类似的大偏移。 （2008）率。另一方面，巴塔哥尼亚确定的可接受生产率值的范围与最近在新西兰南阿尔卑斯山麦考利谷得出的生产率有 1 sigma 重叠并包含其中[A.普特南等人，Quat。地质年代学。 5（2010a）392-4091。在不确定性范围内（即 1 西格玛重叠），巴塔哥尼亚的这一生产率范围也与最近确定的北美东北部和挪威北部低海拔地点的生产率一致。当使用麦考利生产率计算巴塔哥尼亚暴露日期时，对于晚冰期冰碛系统，C-14 和 Be-10 年表是相互兼容的。这两份年表都表明，南巴塔哥尼亚冰原的出口冰川在阿根廷湖西段达到了晚冰期最大值，温度为 13,000 卡。南极冷逆转结束时的 BP（14,500-12,900 cal.yr BP）。随后，在新仙女木期（距今 12,900-11,700 年）期间，出口冰川退缩至接近现今的冰缘。这次大撤退在大约 12,200 cal 时中断。一年前，乌普萨拉冰川在埃尔米尼塔半岛上形成了一个由冰碛脊组成的叶间复合体。南太平洋两岸巴塔哥尼亚和新西兰的山地冰川表现出晚冰期冰缘波动的连贯模式。 (C) 2011 Elsevier B.V. 保留所有权利。
When calculated with the commonly accepted average Northern Hemisphere production rate, Be-10 dates of surface boulders on moraines in the Lago Argentino area of Patagonia are younger than minimum-limiting C-14 ages for the same landforms. This disagreement could result from the lack of a regional Be-10 production-rate calibration site. To assess this possibility, we here present high-precision measurements of Be-10 in samples collected from surface boulders on the Herminita and Puerto Bandera moraine complexes deposited alongside Lago Argentino on the eastern flank of the Andes at 50 degrees S in Patagonia. Together with maximum- and minimum-limiting C-14 ages for the two moraine systems, these measurements confine the local Be-10 production rate to between 3.60 and 3.82 atoms/g/yr (midpoint = 3.71 +/- 0.11 atoms/g/yr) when using a time-dependent scaling method that incorporates a high-resolution geomagnetic model. This range includes upper and lower error bounds of acceptable production rates derived from both the Herminita and the Puerto Bandera sites. The upper limit of this range is more than 12% below the average Northern Hemisphere production rate, as calculated using the same scaling method, given in Balco et al. [Quat. Geochron 3 (2008) 174-195]. Other scaling models yield production rates with similarly large offsets from the Balco et al. (2008) rate. On the other hand, the range of acceptable production rate values determined from Patagonia overlaps at 1 sigma with, and encompasses, the production rate recently derived in Macaulay valley in the Southern Alps of New Zealand [A. Putnam et al., Quat. Geochron. 5 (2010a) 392-4091. Within uncertainties (i.e., overlap at 1 sigma) this Patagonian production rate range also agrees with a recently determined production rate from low-elevation sites in northeastern North America and northern Norway. When the Macaulay production rate is used to calculate Patagonian exposure dates, C-14 and Be-10 chronologies are mutually compatible for late-glacial moraine systems. Both chronologies then indicate that outlet glaciers of the Southern Patagonian Icefield achieved a late-glacial maximum in the western reaches of Lago Argentino at 13,000 cal. yr BP at the end of the Antarctic Cold Reversal (14,500-12,900 cal. yr BP). Outlet glaciers subsequently receded to near present-day ice margins during the Younger Dryas stadial (12,900-11,700 cal. yr BP). This general retreat was interrupted about 12,200 cal. yr BP when Upsala Glacier constructed an interlobate complex of moraine ridges on Herminita Peninsula. Mountain glaciers in Patagonia and New Zealand, on both sides of the South Pacific Ocean, exhibited a coherent pattern of late-glacial ice-margin fluctuations. (C) 2011 Elsevier B.V. All rights reserved.