How is a turbidite actually deposited?

Zhiyuan Ge,Rob L Gawthorpe,Age J Vellinga,Wojciech Nemec

doi:10.1126/sciadv.abl9124

Zhiyuan Ge, Rob L Gawthorpe + Show 2 more

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https://doi.org/10.1126/sciadv.abl9124

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Abstract

The deposition of a classic turbidite by a surge-type turbidity current, as envisaged by conceptual models, is widely considered a discrete event of continuous sediment accumulation at a falling rate by the gradually waning density flow. Here, we demonstrate, on the basis of a high-resolution advanced numerical CFD (computational fluid dynamics) simulation and rock-record examples, that the depositional event in reality involves many brief episodes of nondeposition. The reason is inherent hydraulic fluctuations of turbidity current energy driven by interfacial Kelvin-Helmholtz waves. The experimental turbidity current, with realistic grain-size composition of a natural turbidite, used only 26 to 33% of its in-place flow time for deposition, while the remaining time went to the numerous episodes of sediment bypass and transient erosion. The general stratigraphic notion of a gross incompleteness of sedimentary record may then extend down to the deposition time scale of a single turbidite.

Highlights

Turbidity currents are subaqueous turbulent sediment-gravity flows that deliver huge volumes of sand and other clastic sediment to the deep-sea floor [1,2,3]
Can the deposition of sediment by a uniformly fed continuous flow be in reality discontinuous?. We address this contentious issue by a high-resolution advanced computational fluid dynamics (CFD) simulation of a natural-scale, average surge-type turbidity current
The K-H waves in turbidity currents have long been considered as important for the interfacial entrainment of ambient water, but with no obvious direct impact predicted for the bedload transport [7, 27]

Summary

Introduction

Turbidity currents are subaqueous turbulent sediment-gravity flows that deliver huge volumes of sand and other clastic sediment to the deep-sea floor [1,2,3]. There is probably no other coarse-clastic depositional system on Earth that would accumulate hundreds to thousands of meters of sediment by a simple repetition of one and the same discrete rare event—a turbidity current. These systems vary enormously in their dimensions and morphodynamics [3, 14], partly because the turbidity currents differ considerably in their hydraulic properties and behavior [10, 15], the great interest in turbidites and their internal vertical succession of grain size and sedimentary structures, interpreted as the in-place record of flow behavior and evolving bedform pattern [15,16,17,18,19,20,21,22]

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