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首页> 外文期刊>Geomorphology >Fluvial terrace formation along Wyoming's Laramie Range as a response to increased late Pleistocene flood magnitudes
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Fluvial terrace formation along Wyoming's Laramie Range as a response to increased late Pleistocene flood magnitudes

机译：怀俄明州拉勒米山脉沿河阶地的形成，是对晚更新世洪水强度增加的反应

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This study evaluates the potential climatic mechanisms involved in fluvial terrace genesis along Wyoming's Laramie Range. We used optical dating methods to determine depositional ages for fluvial fills, and to calculate incision rates for terrace suites along two of the region's larger rivers. Optical ages were determined for the five lowest terrace levels (T5-T1) which were deposited at ～59.6, 39.2, 26.3, 22.7, and 18.5 ka, and incision rates calculated for the two rivers were ～0.29-0.34 m/kyr over the last ～60 kyr. The formation of fluvial terraces in the central Rocky Mountains is commonly attributed to climatically induced changes in sediment input. According to most studies, relatively low incision rates existed during the colder periods of the Pleistocene due to high stream sediment loads, but terraces were formed during warmer interglacial periods when reduced sediment availability facilitated higher incision rates. However, this conceptual model cannot explain the incision records presented here, which show that the streams incised 9-10 m in two to three events during Oxygen Isotope Stage 2, but only 1-2 m during the warmer climates of the last ～18.5 ka. The stream power model we adapted to this setting suggests that late Quaternary streams operated under two basic states. During the colder conditions of the Pleistocene, higher flood magnitudes resulted in higher lateral erosion and incision rates. However, the lower stream discharge common to the warmer interglacial periods resulted in relatively inactive streams when both lateral erosion and incision rates were lowered. This model can explain the high incision rates during the cold conditions of Oxygen Isotope Stage 2, the occurrence of terrace fill ages near cold to warm transitions, and the apparent acceleration in incision rates toward the end of the last glacial cycle. Finally; this study suggests that terrace fill ages and incision rates are similar for the distally glaciated Laramie River, nonglaciated Sybille Creek, and the proximally glaciated streams that drain the Wind River Range. This implies that rivers responded synchronously to late Quaternary climate changes regardless of their influence by alpine glaciation.
机译：这项研究评估了怀俄明州拉勒米山脉沿河阶地发生的潜在气候机制。我们使用光学测年方法确定河流填充物的沉积年龄，并计算沿该地区两条较大河流的露台套房的切开率。确定了五个最低阶地水平（T5-T1）的光学年龄，分别沉积在〜59.6、39.2、26.3、22.7和18.5 ka，两条河流上的切入速率计算为〜0.29-0.34 m / kyr。最后〜60吉尔。落基山脉中部河流阶地的形成通常归因于气候导致的泥沙输入变化。根据大多数研究，由于较高的河流沉积物负荷，在更新世的较冷时期存在较低的切开速率，但在较温暖的冰期间形成梯田，这是因为减少的泥沙可利用性促进了较高的切开速率。但是，该概念模型无法解释此处给出的切口记录，该记录表明，在氧气同位素第2阶段中，溪流在2至3个事件中切入9-10 m，而在最后一个〜18.5 ka的较暖气候中只有1-2 m 。我们适应此设置的流功率模型表明，晚期第四纪流在两种基本状态下运行。在更新世较冷的条件下，较高的洪水幅度导致较高的横向侵蚀和切割速率。但是，当横向侵蚀和切开率均降低时，较暖的冰期间期较低的水流排放导致水流相对不活跃。该模型可以解释在氧同位素第2阶段寒冷条件下的高切开率，在从冷到暖转变之间的阶地充填年龄的发生以及到最后一个冰川周期结束时切开率的明显加速。最后;这项研究表明，向远方冰川化的拉勒米河，未冰川化的Sybille Creek和向风河山脉排干的向近方冰川化的河流，梯田的填满年龄和切开率相似。这意味着，河流不受第四纪晚期冰川变化的影响而同步响应。

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