Abstract
AbstractSubmarine 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. Physical modelling was used 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 the progradation of 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 reorganization. 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.
Highlights
Submarine fans, the terminal portion of sedimentary source-to-sink systems, are amongst the largest sedimentary accumulations on the planet (Normark, 1970; Posamentier and Kolla, 2003; Talling et al., 2007)
We ask the question: how is an externally forced sediment supply cycle recorded in the morphology and stratigraphy of a submarine fan? We investigate this question using a series of experimental turbidity currents with incrementally increasing decreasing sediment supply rates (Figure 1B)
A comparison of the slope and basin floor environments revealed that external factors have a stronger influence upon slope channels whilst internal processes dominate basin floor lobe deposits
Summary
The terminal portion of sedimentary source-to-sink systems, are amongst the largest sedimentary accumulations on the planet (Normark, 1970; Posamentier and Kolla, 2003; Talling et al., 2007). Shaped by sediment gravity flows which deliver a range of natural and (more recently) anthropogenic materials to deep-water environments, they provide an invaluable record of Earth’s climatic and tectonic history, and the dispersal of sediment, organic carbon and pollutants in the deep ocean (Emmel and Curray, 1983; Pirmez and Imran, 2003; Deptuck et al, 2008; Gwiazda et al, 2015; Picot et al, 2016, 2019; Rabouille et al, 2019) Both external and internal processes control the morphodynamic evolution and stratigraphic record of submarine fans (Figure 1; Beerbower, 1964; Cecil 2003). Understanding these external and internal controls can aid interpretation of Earth’s geological and climatic record
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