Collaborative Research: Sediment Dynamics in Large Drainage Basins

9628283 德里大型流域是一个复杂的系统，沉积物在其中产生、运输、储存，经过不同的时间，要么被掩埋在改造的深度之外，要么被输出到世界的海洋中。 在这些流域中产生沉积物的速率以及沉积物在河流运输系统中逐粒移动时的停留时间，人们知之甚少;然而，测量这些速率是了解固体地球与水圈之间动态相互作用的先决条件。 在过去的十年中，质谱技术的进步使得人们能够可靠地测量极其稀有的核素，例如宇宙射线与岩石相互作用产生的核素。由于宇宙成因的核素丰度（当暴露位置标准化时）反映了地球表面最上层几米内物质的停留时间，简单的分析模型（依赖于各种假设）已被用于估计基岩露头和巨石的“宇宙成因”暴露年龄和侵蚀速率。 在过去的两年中，我们得到了水文科学的资助，以测试一个解释模型（Bierman和Steig，1992年，1995年; Brown等人，一九九五年;格兰杰et 1994 a，B），这表明测量沉积物中的宇宙成因10 Be和26 A1可用于估计流域侵蚀和限制运输系统以及流出流域的速率。因为我们的初始数据（Bierman et apt，1995，综述）和其他人的数据（Brown et al.，1995;格兰杰等人，1994 a，B），表明宇宙成因核素确实是研究中小流域水文过程的有用工具，我们寻求资金将我们目前的研究扩展到更大的尺度和更长的时间框架。 我们提出的研究的总体目标是确定在什么规模和在什么样的河流制度，宇宙成因核素仍然是有用的工具，1）确定流域规模，空间平均侵蚀速率和2）限制沉积物储存的持续时间。为了实现这一目标，我们寻求资金用于同位素和其他必然测量，以确定从四个构造和气候不同的河流系统的排水网络中收集的大约80个样本中10 Be和26 A1丰度的空间变化。恒河（喜马拉雅山脉）、阿普雷（安第斯山脉）、萨加瓦尼托克（阿拉斯加，北坡）和东鳄鱼（澳大利亚北方）。 测试的空间和时间变化的10 He和26 A1丰度在沉积物中的一些世界上的主要河流将限制现有的解释模型，在同位素地球化学的一个显着进步的适用性的规模。我们所产生的关于沉积物储存的相对持续时间和盆地尺度剥蚀的模型速率的数据将在沉积学、水文学和地貌学领域具有根本意义。在我们无法预测测量结果的意义上，有些人可能会认为我们的建议是“高风险科学"。鉴于我们和其他人已经成功地使用10 Be和26 A1来估计侵蚀速率并限制较小流域的沉积物储存时间（Biermam等人，1995，综述; Brown等人，1995;格兰杰等人，1994 a，B），而且由于我们所处理的问题的根本性质，我们认为这样的“风险”是最小的，值得承担。

9628283 Derry Large drainage basins are complex systems in which sediment is generated, transported, stored, and, after varying amounts of time, either buried beyond the depth of reworking or exported to the World's oceans. The rate at which sediment is generated in such drainage basins and the residence time of that sediment as it moves, grain by grain, down the fluvial transport system are poorly known; yet measuring these rate is prerequisites to understanding dynamic interactions between the solid Earth and the hydrosphere. Over the past decade, advances in mass spectrometry have allowed reliable measurement of extremely rare nuclides such as those produced as cosmic rays interact with rock. Because cosmogenic nuclide abundances (when normalized for exposure location) reflect the residence time of material within the uppermost several meters of Earth's surface, simple analytical models (beholden to a variety of assumptions) have been used to estimate "cosmogenic" exposure ages and erosion rates of bedrock outcrops and boulders. During the past two years, we have been funded by Hydrologic Sciences to test an interpretive model (Bierman and Steig, 1992, 1995; Brown et al., 1995; Granger et 1994a,b) which suggests that measurement of cosnogenic 10Be and 26A1 in sediments can be used to estimate the rate at which drainage basins erode and constrain the transport system, and out of the basin. Because our initial data (Bierman et apt, 1995, in review) and the data of others (Brown et al., 1995; Granger et al., l994a,b), suggest that cosmogenic nuclides are indeed useful tools by which to study hydrologic processes in small end moderate size drainage basins, we seek funding to expand our current research to larger scales and over longer tine frames. The overall objective of our proposed research is to determine at what scale and in what fluvial regimes, cosmogenic nuclides remain useful tools for 1) determining basin-scale, spatially-averaged erosion rates and 2) placing limits on the duration of sediment storage. In order to meet this objective, we seek funding for isotopic and other corollary measurements needed to determine the spatial variation in 10Be and 26A1 abundances in approximately 80 samples collected from locations throughout the drainage networks of four tectonically and climatically distinct fluvial systems.: the Ganges (Himalayas), the Apure (Andean Mountains), the Sagavanirktok (Alaska, North Slope) and the East Alligator (northern Australia). Testing the spatial and temporal variation of 10He and 26A1 abundance in sediments of some of the World's major rivers will constrain the scale of applicability of existing interpretive models, a significant advance in Isotope Geochemistry. The data we generate regarding the relative duration of sediment storage and model rates of basin scale denudation will be of fundamental significance in the fields of Sedinentology, Hydrology, end Geomorphology. In the sense that we cannot anticipate the outcome of our measurements, some might consider our proposal "high risk science In light of the success we and others have had using 10Be and 26A1 to estimate erosion rates and constrain sediment storage times in smaller catchments (Biermam et al., 1995, in review; Brown at al., 1995; Granger et el., 1994a,b), and because of the fundamental nature of the questions we are addressing, we feel such a "risk" is minimal and worth taking.