Abstract Flume experiments were performed to study the flow properties and depositional characteristics of high‐density turbidity currents that were depletive and quasi‐steady to waning for periods of several tens of seconds. Such currents may serve as an analogue for rapidly expanding flows at the mouth of submarine channels. The turbidity currents carried up to 35 vol.% of fine‐grained natural sand, very fine sand‐sized glass beads or coarse silt‐sized glass beads. Data analysis focused on: (1) depositional processes related to flow expansion; (2) geometry of sediment bodies generated by the depletive flows; (3) vertical and horizontal sequences of sedimentary structures within the sediment bodies; and (4) spatial trends in grain‐size distribution within the deposits. The experimental turbidity currents formed distinct fan‐shaped sediment bodies within a wide basin. Most fans consisted of a proximal channel‐levee system connected in the downstream direction to a lobe. This basic geometry was independent of flow density, flow velocity, flow volume and sediment type, in spite of the fact that the turbidity currents of relatively high density were different from those of relatively low density in that they exhibited two‐layer flow, with a low‐density turbulent layer moving on top of a dense layer with visibly suppressed large‐scale turbulence. Yet, the geometry of individual morphological elements appeared to relate closely to initial flow conditions and grain size of suspended sediment. Notably, the fans changed from circular to elongate, and lobe and levee thickness increased with increasing grain size and flow velocity. Erosion was confined to the proximal part of the leveed channel. Erosive capacity increased with increasing flow velocity, but appeared to be constant for turbidity currents of different grain size and similar density. Structureless sediment filled the channel during the waning stages of the turbidity currents laden with fine sand. The adjacent levee sands were laminated. The massive character of the channel fills is attributed to rapid settling of suspension load and associated suppression of tractional transport. Sediment bypassing prevailed in fan channels composed of very fine sand and coarse silt, because channel floors remained fully exposed until the end of the experiments. Lobe deposits, formed by the fine sand‐laden, high‐density turbidity currents, contained massive sand in the central part grading to plane parallel‐laminated sand towards the fringes. The depletive flows produced a radial decrease in mean grain size in the lobe deposits of all fans. Vertical trends in grain size comprised inverse‐to‐normal grading in the levees and in the thickest part of the lobes, and normal grading in the channel and fringes of the fine sandy fans. The inverse grading is attributed to a process involving headward‐directed transport of relatively fine‐grained and low‐concentrated fluid at the level of the velocity maximum of the turbidity current. The normal grading is inferred to denote the waning stage of turbidity‐current transport.

Jaco H. Baas

Wessel Van Kesteren

George Postma

Sedimentology

作为该领域的国际领导者，SEDIMENTOLOGY 发表了跨越沉积学、沉积地质学和沉积地球化学的开创性研究。涵盖的领域包括：实验和理论谷物运输；沉积物通量；现代和古代沉积环境；层序地层沉积物-生物相互作用；古土壤；成岩作用；稳定同位素地球化学；环境沉积学

As a leading international journal in the field of sedimentology, Sedimentology publishes pioneering research that spans sedimentology, sedimentary geology, and sedimentary geochemistry. The covered areas include experimental and theoretical grain transport, sediment flux, modern and ancient sedimentary environments, sediment-biota interactions in sequence stratigraphy, paleosols, diagenesis, stable isotope geochemistry, and environmental sedimentology.

作为沉积学领域的国际领导者，Sedimentology 发表了跨越沉积学、沉积地质学和沉积地球化学的开创性研究。涵盖的领域包括实验和理论的颗粒运输、沉积物通量、现代和古代沉积环境、层序地层中的沉积物与生物相互作用、古土壤、成岩作用、稳定同位素地球化学以及环境沉积学。

Category	Quartile
地球科学	2
地球科学, 地质学	1

Deposits of depletive high‐density turbidity currents: a flume analogue of bed geometry, structure and texture

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