Abstract Tunnel valleys are subglacial incisions formed mainly by meltwater erosion on soft sediment overridden by glaciers. Despite being common in the Pleistocene and Ordovician glacial record, where their fills constitute excellent aquifers and hydrocarbon traps, tunnel valleys are poorly recognized in late Paleozoic strata. Other types of glacial and non-glacial valleys, on the other hand, have been widely reported from Carboniferous and Permian glacial successions, most cut into the basement or older sedimentary rocks and interpreted as glacial valleys eroded by outlet glaciers draining high-relief settings. The degree of glacial influence on the formation of these valleys has strong implications for the volume of ice during late Paleozoic glaciations. In this paper, we report the Lapa sandstone, an exhumed valley-fill succession encased in Pennsylvanian glacial rocks of eastern Parana Basin, southern Brazil, and its subsurface counterparts. The Lapa sandstone forms a slightly sinuous ribbon several tens of kilometers long, 1500 m wide and 100 m thick composed essentially of glaciofluvial facies. By comparing the external geometry and the sediment fill of the valley with several types of erosive-based, elongated sediment bodies, we conclude that the Lapa formed as the infilling of a tunnel valley cut beneath an ice margin that advanced to the north onto poorly consolidated, mud-rich sediments. Valley fills previously mapped in the subsurface area to the west are considered to have been formed by the same mechanism and during the same glaciation event. The Lapa tunnel valley and its subsurface counterparts are the first example reported from the late Paleozoic glacial record in South America, but similar features are also expected in any formerly glaciated basin, and their recognition may help in estimating the extent of glaciation across the region and guiding exploration for hydrocarbon traps.

中文翻译：

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巴拉那盆地的隧道谷填埋及其对冈瓦纳西南部晚古生代冰川作用范围的影响

摘要 隧道河谷是冰下​​切口，主要由融水侵蚀被冰川覆盖的软沉积物形成。尽管在更新世和奥陶纪冰川记录中很常见，它们的填充物构成了极好的含水层和碳氢化合物圈闭，但在晚古生代地层中很难识别隧道山谷。另一方面，从石炭纪和二叠纪冰川序列中广泛报道了其他类型的冰川和非冰川河谷，大多数切入基底或较老的沉积岩中，并被解释为被出口冰川排出高地貌环境侵蚀的冰川河谷。冰川对这些山谷形成的影响程度对晚古生代冰川期间的冰量有很大的影响。在本文中，我们报告了 Lapa 砂岩，在巴西南部巴拉那盆地东部的宾夕法尼亚冰川岩中挖掘出的山谷填充序列及其地下对应物。拉帕砂岩形成一条长数十公里、宽 1500 m、厚 100 m 的略微弯曲的带状带，主要由冰川河流相组成。通过将山谷的外部几何形状和沉积物填充与几种类型的侵蚀性细长沉积体进行比较，我们得出结论，拉帕形成为隧道山谷的填充物，在冰缘下方切割，向北推进到不牢固的冰缘, 泥质丰富的沉积物。先前在西部地下区域绘制的山谷填充被认为是由相同的机制和在相同的冰川事件中形成的。