Clinoform development by advection-diffusion of suspended sediment: Modeling and comparison to natural systems
Clinoform development by advection-diffusion of suspended sediment: Modeling and comparison to natural systems
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DOI：
10.1029/98jb01516
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发表时间：
1998-10
影响因子：
--
通讯作者：
C. Pirmez;L. Pratson;M. Steckler
中科院分区：
文献类型：
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作者：
C. Pirmez;L. Pratson;M. Steckler
斜坡是构造层序的基本单元。在现代的三角洲上，可以发现今天形成的这些双曲线形的表面。这些三角洲的斜坡状表面的沉积速率剖面显示，沉积物积累的顶置和底置区域的速度较低，最大的积累速率上的前积区。我们提出了一个斜坡形成的模型，该模型依赖于对现代斜坡沉积的解释，作为河口剪切应力分布的结果。模型斜形面是用悬浮泥沙浓度守恒方程和简单时均流速场的流体守恒方程生成的。在该模型中，悬浮泥沙水平平流进入一个盆地，泥沙颗粒的重力沉降抵消垂直湍流扩散。在浅水区，剪切应力太大，不允许沉积，沉积物绕过顶置区。随着水深的增加，近床剪切应力降低，沉积物被允许在前积区存款，逐渐减少的速度向深水。这种沉积模式导致斜坡表面随时间推移而变薄。由模型产生的斜坡表面捕捉自然斜坡的基本形态特征。这些措施包括在顶置和底置，陡峭的前积坡，粒度增加，并通过时间的斜坡进入深水增加前积坡逐渐翻转。由于控制模型斜坡的参数与自然系统中可以测量的物理量有直接关系，因此该模型是解开与这些沉积物相关的物理过程的重要一步。
Clinoforms are the building blocks of prograding stratigraphic sequences. These sig- moid-shaped surfaces can be found forming today on modem deltas. Sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions, with a maximum accumulation rate on the upper foreset region. We pres- ent a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river. Model clino- form surfaces are generated using an equation for the conservation of suspended sediment concentration, together with a conservation of fluid equation for simple time-averaged flow velocity fields. In the model, suspended sediment is advected horizontally into a basin, and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion. In shallow water, shear stresses are too large to allow deposition, and sediment bypasses the topset region. With increasing water depth, near-bed shear stresses decrease, and sediment is allowed to deposit at the foreset region, with gradually decreasing rates toward deeper water. This sedimentation pattern leads to progradation of the clinoform surfaces through time. The clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms. These include the gradual slope rollover at the topset and bottomset, steeper foreset slopes with increased grain size, and an increase in foreset slope through time as clinoforms prograde into deeper water. Because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems, the model is an important step toward unraveling the physical processes associated with these deposits.