Inner gorge–slot canyon system produced by repeated stream incision (eastern Alps): Significance for development of bedrock canyons
Inner gorge–slot canyon system produced by repeated stream incision (eastern Alps): Significance for development of bedrock canyons
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反复溪流切割形成的内峡谷-狭缝型峡谷系统（东阿尔卑斯山）：对基岩峡谷发育的意义
DOI：
10.1016/j.geomorph.2014.03.007
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发表时间：
2014
期刊：
影响因子：
3.9
通讯作者：
M. Ostermann
中科院分区：
文献类型：
--
作者：
D. Sanders;Lukas Wischounig;A. Gruber;M. Ostermann
由于狭缝峡谷的后生切割，阿尔卑斯山的许多内基岩峡谷在下游的峡谷宽度、河道类型和梯度方面都表现出突变。许多狭缝峡谷还与充满第四纪沉积物的古老峡谷有关。然而，狭缝峡谷和内部基岩峡谷的年龄通常很难确定。对于斯坦伯格阿什流域（阿尔卑斯山东部）的内基岩峡谷系统，活跃的狭缝峡谷以及充满上乌尔米亚前冰川沉积物的古老废弃峡谷记录了峡谷发育和狭缝峡谷切割的三个阶段。内峡谷侧翼的河流砾岩中的 A234U/230Th 水泥年龄为 29.7 ± 1.8 ka，符合晚冰河条件前不久的晚乌尔米亚谷底加积；此外，年龄表明至少相应的峡谷河段必须更古老。在末次盛冰期（LGM）形成过程中，冰流前进时，流域被堵塞，并形成了前冰川湖。淹没在该湖中的基岩峡谷充满了河湖沉积物。在末次盛冰期期间，整个流域都被冰覆盖。在冰期后重新切割期间，溪流很大程度上再次发现了它们先前存在的内部基岩峡谷。然而，在某些地区，以前的河道被“错过”，形成了狭缝峡谷。然而，更新世沉积物的分布、峡谷切割的模式以及提到的 U/Th 胶结年龄共同记录了末次盛冰期之前的基准面上升和溪流切割的进一步离散阶段。斯坦伯格阿什河及其支流目前的走向是由以下几个部分拼凑而成的：(1) 冰期后切割期间切开的狭缝峡谷； (2) 狭缝峡谷的遗迹切入了早期（乌尔米期中晚期？）基准面升降周期； (3) 重新激活的范围达目前分水岭内基岩峡谷宽度约 200 米，年龄至少超过约 30 ka； (4) 废弃的、充满沉积物的基岩峡谷河段，其历史也必须超过 30ka，并且暴露在活跃溪流旁边。由年龄明显不同的河段组成的“多循环”基岩峡谷系统在遭受冰川作用和/或大规模浪费的山脉中可能很常见。
Many inner bedrock gorges of the Alps show abrupt downstream changes in gorge width, as well as channel type and gradient, as a result of epigenetic incision of slot canyons. Many slot canyons also are associated with older gorge reaches filled with Quaternary deposits. The age of slot canyons and inner bedrock gorges, however, commonly is difficult to constrain. For the inner-bedrock gorge system of the Steinberger Ache catchment (eastern Alps), active slot canyons as well as older, abandoned gorge reaches filled with upper Würmian proglacial deposits record three phases of gorge development and slot–canyon incision. A234U/230Th age of cement of 29.7 ± 1.8 ka in fluvial conglomerates onlapping the flank of an inner gorge fits with late Würmian valley-bottom aggradation shortly before pleniglacial conditions; in addition, the age indicates that at least the corresponding canyon reach must be older. During advance of ice streams in the buildup of the Last Glacial Maximum (LGM), the catchment was blocked, and a proglacial lake formed. Bedrock gorges submerged in that lake were filled with fluviolacustrine deposits. During the LGM, the entire catchment was overridden by ice.During post-glacial reincision, streams largely found again their preexisting inner bedrock canyons. In some areas, however, the former stream course was ‘missed’, and a slot canyon formed. The distribution of Pleistocene deposits, the patterns of canyon incision, and the mentioned U/Th cementation age, however, together record a further discrete phase of base-level rise and stream incision well before the LGM. The present course of Steinberger Ache and its tributaries is a patchwork of (1) slot canyons incised during post-glacial incision; (2) vestiges of slot canyons cut upon an earlier (middle to late Würmian?) cycle of base-level rise and fall; (3) reactivated reaches up to ~ 200 m in width of inner bedrock gorge that are watershed at present, and more than at least ~ 30 ka in age; and (4) abandoned, sediment-filled reaches of bedrock canyons that also must be older than 30 ka and that are exposed alongside the active streams. ‘Multi-cyclic’ bedrock canyon systems composed of reaches of markedly different ages may be common in mountain ranges subject to glaciations and/or mass wasting.