Table4_Hints on the Late Miocene Evolution of the Tonale-Adamello-Brenta Region (Alps, Italy) Based on Allochtonous Sediments From Raponzolo Cave.XLS

Raponzolo is a paleo-phreatic cave explored in 2011 in the Brenta Dolomites (Trentino, Italy), at the remarkable altitude of 2,560 m a.s.l. Differently to all other caves of the area, it hosts well-cemented fine to medium sands of granitic-metamorphic composition. The composition suggests a sediment source from the Adamello and Tonale Unit, separated from the Brenta by one of the most important tectonic lineaments of the Alps (Giudicarie Line). The fine-sand sediment was sampled to determine burial time and thus a minimum age of the cave. Cosmogenic isotopes (26Al and 10Be) in quartz grains allowed to estimate a minimum burial age of 5.25 Ma based on the mean sediment transport time at the surface and infer original altitude of the catchment area. Detrital apatite fission-track (AFT) and U-Pb dating on zircons provide information on the source, both from a regional and altitude (exhumation) perspective. Two populations of detrital AFT ages center at 17 (−2.3 + 2.6) Ma and 23 (−3.3 + 3.9) Ma, whereas the main detrital zircon U-Pb age populations are younger than 40 Ma. These correspond to intrusive and metamorphic sources nowadays outcropping exclusively above 2,200–2,300 m a.s.l. in Northern Adamello and Tonale. The results point to a late Miocene erosion and infilling of the cave by allochtonous sediments, with important implications on the timing of cave speleogenesis, as well as the paleogeographical connection, tectonic evolution and uplift of different structural units of the Alps. The roundness and the well sorted size of the quartz grains suggest a fluvial or aeolian origin, possibly recycled by glacial activity related to cold events reported in high latitude areas of the world at 5.75 and 5.51 Ma. These glacial phases have never been documented before in the Alps. This information confirms that the valleys dividing these geological units were not yet deeply entrenched during the onset of the Messinian Salinity Crisis (5.6–5.5 Ma), allowing an efficient transport of sediments across major tectonic lineaments of the Alps. This study shows the potential of cave sediments to provide information not only on the age of speleogenesis but also on the paleogeography of a wide area of the Alps during the late Miocene.

Raponzolo为一座于2011年在意大利特伦蒂诺的布伦塔多洛米蒂山脉（海拔2,560米）进行考察的古潜穴。与其他区域的所有洞穴不同，它容纳了由花岗岩-变质岩成分构成的紧密固结的细至中粒沙。其成分表明沉积物源自亚当埃洛和托纳莱单元，通过阿尔卑斯山脉最重要的构造线之一（Giudicarie线）与布伦塔相隔。对细沙沉积物进行采样以确定埋藏时间，从而确定洞穴的最小年龄。石英颗粒中的宇宙成因同位素（26Al和10Be）允许根据地表的平均沉积物运输时间估计最小埋藏年龄为5.25百万年，并推断出集水区的原始海拔。碎屑磷灰石裂变轨迹（AFT）和锆石的U-Pb测年提供了关于来源的信息，从区域和海拔（剥露）的角度来看。两个碎屑AFT年龄群体分别集中在17（-2.3 + 2.6）百万年和23（-3.3 + 3.9）百万年，而主要的碎屑锆石U-Pb年龄群体则小于40百万年。这些对应于现今仅在北部亚当埃洛和托纳莱海拔2,200-2,300米以上出露的侵入性和变质岩源。这些结果指向了上新世晚期的侵蚀和外来沉积物填充洞穴，对洞穴洞穴成因的时间、古地理联系、构造演化和阿尔卑斯山脉不同结构单元的抬升具有重要意义。石英颗粒的圆润度和良好的分选性表明其起源于河流或风成，可能被与世界上高纬度地区报道的5.75和5.51百万年的冷事件相关的冰川活动所循环。这些冰川阶段在阿尔卑斯山脉中前所未有。这些信息证实，在墨西拿盐度危机（5.6-5.5百万年前）开始时，分隔这些地质单元的山谷尚未深陷，从而允许沉积物在阿尔卑斯山脉的主要构造线之间高效运输。这项研究展示了洞穴沉积物不仅能够提供洞穴成因的年龄信息，还能够揭示上新世晚期阿尔卑斯山脉广大区域的古地理信息。