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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Neogene rejuvenation of central Appalachian topography: Evidence for differential rock uplift from stream profiles and erosion rates
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Neogene rejuvenation of central Appalachian topography: Evidence for differential rock uplift from stream profiles and erosion rates

机译：阿巴拉契亚中部地形的新近纪复兴：从河流剖面和侵蚀速率看岩石差异抬升的证据

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摘要

The persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution. In the eastern North American Appalachians, this question is manifest in the outstanding problem of whether topographic relief is in a quasi-equilibrium state, decaying slowly over many millennia, or whether relief has increased during the late Cenozoic. Here we present quantitative geomorphic data from the nonglaciated portion of the Susquehanna River drainage basin that provide insight into these end-member models. Analysis of channel profiles draining upland catchments in the northern Valley and Ridge, Appalachian Plateau, Blue Ridge, and Piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300-600m elevation but not systematically associated with transitions from weak to resistant substrate. Cosmogenic ~(10)Be inventories of modern stream sediment indicate that erosion rates are spatially variable, ranging from ~5-30m/Myr above knickpoints to ~50-100m/Myr below knickpoints. Overall, channel gradients, normalized for drainage area, scale linearly with catchment-averaged erosion rates. Collectively, regionally consistent spatial relationships among erosion rate, channel steepness, and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level. Reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with ~100-150m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization. Channel response timescales imply that the onset of relative base level change predates ~3.5Ma and may have begun as early as ~15Ma. We suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of North America during the Neogene.
机译：古代造山带中地形的持久性仍然是景观演化中的突出问题之一。在北美东部的阿巴拉契亚山脉，这个问题表现在一个突出的问题上，即地形起伏是否处于准平衡状态，几千年来缓慢衰减，或者在新生代晚期起伏是否增加。在这里，我们介绍了来自萨斯奎哈纳河流域非冰川部分的定量地貌数据，这些数据为深入研究这些最终成员模型提供了见识。对北部山谷和山脊，阿巴拉契亚高原，蓝岭和皮埃蒙特省的高地集水区的河道剖面进行分析后发现，大量溪流在300-600m高处聚集了清晰的拐点，但与从弱到强的过渡没有系统关联基质。宇宙成因〜（10）Be是现代河流沉积物的清单，表明侵蚀速率在空间上是可变的，范围从高于折点的〜5-30m / Myr至低于折点的〜50-100m / Myr。总体而言，针对流域面积标准化的河道坡度与流域平均侵蚀率成线性比例关系。总的来说，侵蚀速率，河道陡度和拐点之间区域一致的空间关系揭示了持续的一波瞬态河道调整，以适应相对基准面的变化。高于拐点的遗迹通道剖面的重建表明，较高的切开率与伴随表观成因的岩石抬升而来的相对基面下降约100-150m有关，而不是改变为更具侵蚀性的气候或排水结构。通道响应时间尺度暗示相对基准水平变化的发生早于〜3.5Ma，并且可能早于〜15Ma开始。我们认为，在新近纪期间，沿北美洲东部沿海的地幔动力学变化可能推动了航道网络的调整。

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