Accumulations of fine sediments along continental shelf and deep-sea bathymetric contours, known as contourite drifts, form a sedimentary record that is dependent on oceanographic processes such as ocean–basin-scale circulation. A tool used to aid in interpretation of such deposits is the sortable silt hypothesis, which suggests that the mean size of the sortable silt (silt from 10 to 63 μm) within a deposit can be used as a proxy for current velocity. While the hypothesis has been applied to numerous drift deposits, it has not been extensively explored. Slow deposition rates of contourite drift systems make it difficult to study in the deep ocean, and past laboratory studies have not tested the full range of conditions or mechanisms that could lead to sorting. This study uses flume experiments and theory to examine how the mean sortable silt in a deposit is related to current velocity under the action of advective depositional sorting. Tests were conducted for a fixed amount of time with four suspended sediment mixtures and current velocities typical of deep-sea settings (5 to 25 cm s⁻¹). Developed beds were sampled at fixed locations from the entrance and sized. The deposit grain size fined downstream and coarsened with increasing velocity at a particular distance from the inlet. Simple theory was able to capture the observations. Regardless of bed morphology or source sediment mixture, the mean sortable silt in the deposit was related to velocity at a particular flume location across all sediment mixtures. The slope of the relationship between velocity and size was dependent on the distance between the inlet and location of interest. Despite the simplified nature of the study, and the limitations regarding the presumed variability in natural systems, these findings broadly support the validity of mean sortable as a proxy for palaeocurrent velocity at a distance along a depositing current.

中文翻译：

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水流对淤泥的平流分选：一项实验室研究

沿大陆架和深海等深线堆积细小沉积物，称为等高线漂移，形成依赖于海洋-盆地尺度环流等海洋过程的沉积记录。用于帮助解释此类沉积物的工具是可分选淤泥假设，这表明沉积物中可分选淤泥的平均尺寸（10 到 63 微米的淤泥）可用作当前速度的代表。尽管该假设已被应用于许多漂移矿床，但尚未对其进行广泛探索。等高线漂移系统的缓慢沉积速率使得在深海中进行研究变得困难，而且过去的实验室研究没有测试可能导致分选的所有条件或机制。本研究利用水槽实验和理论研究了在对流沉积分选作用下，矿床中平均可分选粉砂与水流速度之间的关系。使用四种悬浮沉积物混合物和深海环境典型的流速（5 至 25 cm s^-1 )。从入口处的固定位置对开发的床位进行采样并确定尺寸。沉积物晶粒尺寸在下游细化，并在距入口特定距离处随着速度的增加而变粗。简单的理论能够捕捉到这些观察结果。无论床形态或源沉积物混合物如何，沉积物中的平均可分选淤泥与所有沉积物混合物中特定水槽位置的速度有关。速度和尺寸之间关系的斜率取决于入口和感兴趣位置之间的距离。尽管这项研究的性质很简单，并且自然系统中假定的可变性存在局限性，但这些发现广泛支持平均可分类作为沿沉积流一定距离处的古海流速度代理的有效性。