Entangled external and internal controls on submarine fan evolution: an experimental perspective

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1002/dep2.109.

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Authors

Ross Ferguson , Ian A. Kane , Joris Eggenhuisen , Florian Pohl , Mike Tilston, Yvonne Spychala , Rufus Brunt

Abstract

Submarine fans are formed by sediment-laden flows shed from continental margins into ocean basins. Their morphology represents the interplay of external controls such as tectonics, climate, and sea-level with internal processes including channel migration and lobe compensation. However, the nature of this interaction is poorly understood. We used physical modelling to represent the evolution of a natural-scale submarine fan deposited during an externally forced waxing-to-waning sediment supply cycle. This was achieved by running five successive experimental turbidity currents with incrementally increasing then decreasing sediment supply rates. Deposits built upon the deposits of earlier flows and the distribution of erosion and deposition after each flow was recorded using digital elevation models. Initially, increasing sediment supply rate (waxing phase) led to widening and deepening of the slope channel, with basin-floor deposits compensationally stepping forwards into the basin, favouring topographic lows. When sediment supply rate was decreased (waning phase), the slope-channel filled as the bulk of the deposit abruptly back-stepped due to interaction with depositional topography. Therefore, despite flows in the waxing and waning phases of sediment supply having nominally identical input conditions (i.e. sediment concentration, supply rate, grain size etc.), depositional relief led to development of markedly different deposits. This demonstrates how external controls can be preserved in the depositional record through progradation of the basin floor deposits but that internal processes such as compensational stacking progressively obscure this signal through time. This evolution serves as an additional potential mechanism to explain commonly observed coarsening- and thickening-upwards lobe deposits, with abrupt transition to thin fine-grained deposits. Meanwhile within the slope channel, external forcing was more readily detectable through time, with less internally driven reorganisation. This validates many existing conceptual models and outcrop observations that channels are more influenced by external forcing whilst internal processes dominate basin floor lobe deposits in submarine fans.

DOI

https://doi.org/10.31223/osf.io/wcq5a

Subjects

Earth Sciences, Geology, Geomorphology, Physical Sciences and Mathematics, Sedimentology, Stratigraphy

Keywords

experimental modelling, external, internal, sediment gravity flow, submarine fan architecture

Dates

Published: 2020-02-02 17:33

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License

CC BY Attribution 4.0 International

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