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在有相对基准面下降良好约束记录的苏格兰西部的4条河流中,冰后期基岩侵蚀的速率可以通过测量溯源裂点以下侵蚀宽谷阶地原地宇宙成因10Be浓度确定。10Be暴露年龄的沿程坡降显示两个不同的趋势:向上游趋于年轻和一致的年龄,对此我们解释为裂点后退和扩散搬运限制性下切的结果。我们发现,开始基岩河床下切和宽谷阶地的区域发育始于末次冰消期(距今11.5ka)不久,裂点后退速率在早—中全新世达到最大,之后不断下降达两个数量级,在晚全新世降到一个与单位河床面积流能无关的低速率。我们推断这种区域性的冰后期裂点后退变缓是全新世期间冰缘沉积物补给逐渐减少、导致基岩侵蚀缺乏“工具”的结果。我们的研究结果表明,主河流侵蚀时期可能与冰川旋回一致,冰期—间冰期过渡之后沉积物的减少可能是冰川作用区河流基岩侵蚀速率变化的重要原因。
The rates of bedrock bedrock erosion in four rivers in western Scotland with a well-defined, well-constrained down-dip can be determined by measuring the in-situ cosmic 10Be concentration of eroding hilly terrains below the tracing point. The slope of the 10Be exposed age shows two different trends: the upward trend toward younger and the same age, which we interpret as the result of a restrictive undercut of the retreat and diffusion. We found that the regional development of bedrock undercutting and wide-horizons started shortly after the last glacial extinction (11.5 ka ago), and the retreat retreat rate reached the maximum in the early-middle Holocene and then dropped continuously by two orders of magnitude, In Late Holocene it dropped to a low rate unrelated to unit area bed flow energy. We conclude that this regional post-iceback tectonic slowing is the result of a gradual decrease in recharge of periglacial sediments during the Holocene, resulting in a lack of “tooling” for bedrock erosion. Our results show that the main river erosion period may coincide with the glacier cycle, and the decrease of sediments after the glacial-interglacial transition may be the important reason for the change of bedrock erosion rate in glacial-affected areas.