Geochemistry of large river suspended sediments:: Silicate weathering or recycling tracer?
Geochemistry of large river suspended sediments:: Silicate weathering or recycling tracer?
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DOI：
10.1016/s0016-7037(99)00307-5
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发表时间：
1999-12-01
影响因子：
5
通讯作者：
Allègre, CJ
中科院分区：
文献类型：
--
作者：
Gaillardet, J;Dupré, B;Allègre, CJ
本研究的重点是世界上最大的河流输送的悬浮沉积物的主要和微量元素组成。它的主要目的是回答；下面的问题是：现代河流颗粒的风化程度是否与硅酸盐风化引起的河流溶解负荷的估计一致？与众所周知的大陆岩石风化过程中元素的流动性一致，我们证实了Na， K， Ba的河流沉积物相对于上大陆地壳是系统的枯竭。对于每一种可移动元素，我们都试图对河载固体的风化指标进行系统分类。发现所有这些指标之间具有全局一致性。重要的是，风化强度存在变化。在主要流经低地的河流中，观察到风化强度与气候的明显依赖关系。然而，风化强度与气候或地形参数之间不存在全球相关性，因为在低地观测到的趋势被流经造山带的河流所掩盖。风化强度与悬浮沉积物浓度呈负相关关系，表明物理剥蚀率最高的地区产生的风化沉积物最少。最后，通过一个简单的稳态模型对化学风化和物理风化进行了比较。我们认为，大型河流悬浮沉积物的风化强度只能与河流的（硅酸盐衍生的）溶解负荷相协调，因为在大型河流盆地中，大多数受风化作用的大陆岩石已经经历了以前的风化循环。提出了一种计算大流域沉积再循环比例的简单图解法。最后，即使造山带产生弱风化的沉积物，我们也强调这样一个事实，即硅酸盐化学风化速率（以及由此产生的CO，硅酸盐风化消耗率）在山区大大增强，这仅仅是因为造山带流域的沉积物产量更高。因此，控制化学风化速率的参数将是控制物理剥蚀速率的参数。版权所有爱思唯尔科学有限公司
This study focuses on the major and trace element composition of suspended sediments transported by the world's largest rivers. Its main purpose is to answer the; following question: is the degree of weathering of modern river-borne particles consistent with the estimated river dissolved loads derived from silicate weathering?In agreement with the well known mobility of elements during weathering of continental rocks, we confirm that river sediments are systematically depleted in Na, K, Ba with respect to the Upper Continental Crust. For each of these mobile elements, a systematics of weathering indexes of river-borne solids is attempted. A global consistency is found between all these indexes. Important-variations in weathering intensities exist. A clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands. However, no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones. An inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments. Finally, chemical and physical weathering are compared through the use of a simple steady state model. We show that the weathering intensities of large river suspended sediments can only be reconciled with the (silicate-derived) dissolved load of rivers, by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles. A simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins. Finally, even if orogenic zones produce weakly weathered sediments, we emphasize the fact that silicate chemical weathering rates (and hence CO, consumption rates by silicate weathering) are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher. Hence, the parameters that control chemical weathering rates would be those that control physical denudation rates. Copyright (C) 1999 Elsevier Science Ltd.