New cosmogenic nuclide burial-dating model indicates onset of major glaciations in the Alps during Middle Pleistocene Transition
New cosmogenic nuclide burial-dating model indicates onset of major glaciations in the Alps during Middle Pleistocene Transition
复制标题
新的宇宙成因核素埋藏测年模型表明阿尔卑斯山在中更新世过渡期间发生了主要冰川作用
DOI：
10.1016/j.epsl.2020.116491
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发表时间：
2020
影响因子：
5.3
通讯作者：
J. Jansen
中科院分区：
文献类型：
--
作者：
M. Knudsen;Jesper Nørgaard;R. Grischott;F. Kober;D. Egholm;T. Hansen;J. Jansen
北方阿尔卑斯前陆的一组四个冰水沉积阶地激发了彭克和布吕克纳关于阿尔卑斯山四个大冰期的经典方案：冈茨、明德尔、里斯和乌尔姆。虽然现在已经确定，Würm对应于海洋同位素阶段（MIS）5d-2（距今117-14 ka），Riss类型的地点对应于MIS 6（距今191-130 ka），但对于更老的冰川的年龄没有达成共识。两个最古老的阶地，在瑞士和邻国德国被称为Höhere Deckenschotter（HDS）和Tiefere Deckenschotter（TDS），包含夹层冰碛，直接表明冰川首次到达北方阿尔卑斯山前陆。在这里，我们开始限制HDS的时间，这标志着阿尔卑斯山的第一次主要冰川。为了实现这一目标，我们设计了一个新的埋葬定年模型定制的冰川沉积物：P-PINI（核素目录的粒子路径反演）。该方法适用于一个cosmogenic 10 Be-26 Al反演模型占变量宇宙射线暴露和非稳态侵蚀的源到汇的框架。从五个HDS站点获取10 Be-26 Al的数据（Feusi，Tromsberg，Siglistorf，Irchel Steig和Irchel Hütz）和一个TDS站点（Iberig），我们获得了Feusi特别受约束的年龄分布（±1σ）（0.93 ± 0.13 Ma），伊比利亚（0.93 ± 0.17 Ma）和Tromsberg（0.88 ± 0.14 Ma），Irchel Steig的约束较弱（0.69 ± 0.25 Ma）和Siglistorf（0.94 ± 0.27 Ma），Irchel Hütz（1.39 ± 0.56 Ma）的约束非常差。与形态地层学一致，它表明TDS晚于HDS，我们实施了贝叶斯建模框架，得出Iberig（TDS）的年龄为0.69 ± 0.12 Ma，HDS站点的组合年龄为0.95 ± 0.07 Ma。基于P-PINI埋藏年龄以及组合的贝叶斯埋藏年龄，我们提出了一个年龄约1.0-0.9 Ma的大型阿尔卑斯山冰川的开始，引发了积累的HDS冰水沉积物。这大致符合更新世的第一次长冰期（MIS 24-22），确定为一个步骤的变化，更冷的气候和更大的冰川接近中更新世过渡结束。虽然我们的研究结果挑战了先前报道的瑞士HDS的102 Ma或更长的年龄，但它们证实了南部阿尔卑斯山后前陆的证据，并为G. J. Kukla的早期假设提供了定量支持，他将北方阿尔卑斯山前陆最古老的冰川沉积物归因于MIS 22。最后，我们认为，源到汇的方法P-PINI提供了一个可行的替代既定的等时埋葬定年方法的情况下，涉及非稳定暴露和侵蚀。
A set of four outwash terraces in the northern Alpine Foreland motivated Penck and Brückner's classical scheme of four great Alpine ice ages: Günz, Mindel, Riss, and Würm. While it is now established that the Würm corresponds to marine isotope stages (MIS) 5d–2 (∼117–14 ka) and the Riss type locality to MIS 6 (∼191–130 ka), there is no consensus regarding the age of the older glaciations. The two oldest terraces, known asHöhere Deckenschotter(HDS) andTiefere Deckenschotter(TDS) in Switzerland and neighbouring Germany, contain interbedded tills that directly indicate the first arrival of glaciers into the northern Alpine Foreland. Here, we set out to constrain the timing of the HDS, which signal the first major glaciations in the Alps. To achieve this goal, we devised a new burial-dating model tailored to glaciogenic sediments: P-PINI (Particle Pathway Inversion of Nuclide Inventories). The method applies a source-to-sink framework to a cosmogenic10Be-26Al inversion model accounting for variable cosmic-ray exposure and non-steady erosion. Taking published10Be-26Al data from five HDS sites (Feusi, Tromsberg, Siglistorf, Irchel Steig, and Irchel Hütz) and one TDS site (Iberig), we obtain age distributions (±1σ) that are especially well constrained for Feusi (0.93 ± 0.13 Ma), Iberig (0.93 ± 0.17 Ma), and Tromsberg (0.88 ± 0.14 Ma), less well-constrained for Irchel Steig (0.69 ± 0.25 Ma) and Siglistorf (0.94 ± 0.27 Ma), and very poorly constrained for Irchel Hütz (1.39 ± 0.56 Ma). Consistent with the morphostratigraphy, which dictates that the TDS postdates the HDS, we implemented a Bayesian modelling framework, yielding an age of 0.69 ± 0.12 Ma for Iberig (TDS) and a combined age of 0.95 ± 0.07 Ma for the HDS sites. Based on the P-PINI burial ages as well as the combined, Bayesian burial age, we propose an age around 1.0–0.9 Ma for the onset of the large Alpine glaciations that triggered the accumulation of the HDS outwash sediments. This roughly accords with the first long glaciation of the Pleistocene (MIS 24–22), identified as a step-change to colder climate and larger glaciations towards the end of the Middle Pleistocene Transition. While our results challenge previously reported ages of ∼2 Ma or more for the HDS in Switzerland, they corroborate evidence from the southern Alpine retroforeland and provide quantitative support for the early hypothesis by G.J. Kukla, who ascribed the oldest glacial deposits in the northern Alpine Foreland to around MIS 22. Finally, we suggest that the source-to-sink approach of P-PINI offers a viable alternative to the established isochron burial-dating method in cases involving non-steady exposure and erosion.