100 kyr fluvial cut-and-fill terrace cycles since the Middle Pleistocene in the southern Central Andes, NW Argentina
100 kyr fluvial cut-and-fill terrace cycles since the Middle Pleistocene in the southern Central Andes, NW Argentina
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DOI：
10.1016/j.epsl.2017.06.001
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发表时间：
2017-09
影响因子：
5.3
通讯作者：
Stefanie Tofelde;T. Schildgen;S. Savi;H. Pingel;A. Wickert;B. Bookhagen;H. Wittmann;R. Alonso;J. Cottle;M. Strecker
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文献类型：
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作者：
Stefanie Tofelde;T. Schildgen;S. Savi;H. Pingel;A. Wickert;B. Bookhagen;H. Wittmann;R. Alonso;J. Cottle;M. Strecker
山间盆地河流充填阶地是记录构造和气候驱动的地球表面过程系统变化的宝贵地貌档案。然而，往往是保存填充阶序列是不完整的和/或他们可能会形成远离其源区，复杂的强迫机制和景观响应之间的因果关系的识别，特别是在多千年的时间尺度。安第斯山脉中部南部的山间托罗盆地至少有五代河流阶地，它们被雕刻成几百米厚的第四纪山谷充填砾岩。利用9个宇宙成因10 Be深度剖面进行的新的地表暴露测年显示，这些阶地的连续废弃具有75±7和487±34 ka之间的10万年旋回。根据4个26 Al/10 Be埋藏样品和3个火山灰夹层锆石U-Pb年龄测定，砾岩的沉积年龄范围为18±141 ~ 936±170 ka，反映了多期的充填-切割作用。虽然最初的加积开始于101 Ma，而自大约100 Ma以来的整体净切割。500 ka与狭窄盆地出口处的构造过程有关，叠加的100 kyr周期的加积和下切最好用偏心驱动的气候变化来解释。在这些周期内，河流切口的发病可以与全球寒冷的时期和增强潮湿的阶段记录在邻近的玻利维亚高原的古气候档案，而沉积主要发生在更干旱的阶段高原和全球间冰期。我们认为，增强径流在全球冷相，由于区域降水率增加，减少蒸散，或两者兼而有之，导致在托罗盆地，这超过了任何可能增加的上游泥沙供应，从而引发切口的泥沙输运能力增加。与附近的两个盆地，记录岁差（21-kyr）和长偏心率（400-kyr）迫使沉积和地貌档案相比，记录的周期尺度与流域长度的平方。
Fluvial fill terraces in intermontane basins are valuable geomorphic archives that can record tectonically and/or climatically driven changes of the Earth-surface process system. However, often the preservation of fill terrace sequences is incomplete and/or they may form far away from their source areas, complicating the identification of causal links between forcing mechanisms and landscape response, especially over multi-millennial timescales. The intermontane Toro Basin in the southern Central Andes exhibits at least five generations of fluvial terraces that have been sculpted into several-hundred-meter-thick Quaternary valley-fill conglomerates. New surface-exposure dating using nine cosmogenic 10 Be depth profiles reveals the successive abandonment of these terraces with a 100 kyr cyclicity between 75±7 and 487±34 ka. Depositional ages of the conglomerates, determined by four 26 Al/10 Be burial samples and U–Pb zircon ages of three intercalated volcanic ash beds, range from 18±141 to 936±170 ka, indicating that there were multiple cut-and-fill episodes. Although the initial onset of aggradation at∼ 1 Ma and the overall net incision since ca. 500 ka can be linked to tectonic processes at the narrow basin outlet, the superimposed 100 kyr cycles of aggradation and incision are best explained by eccentricity-driven climate change. Within these cycles, the onset of river incision can be correlated with global cold periods and enhanced humid phases recorded in paleoclimate archives on the adjacent Bolivian Altiplano, whereas deposition occurred mainly during more arid phases on the Altiplano and global interglacial periods. We suggest that enhanced runoff during global cold phases–due to increased regional precipitation rates, reduced evapotranspiration, or both–resulted in an increased sediment-transport capacity in the Toro Basin, which outweighed any possible increases in upstream sediment supply and thus triggered incision. Compared with two nearby basins that record precessional (21-kyr) and long-eccentricity (400-kyr) forcing within sedimentary and geomorphic archives, the recorded cyclicity scales with the square of the drainage basin length.