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Steady Autogenic Model for Multiscale Growth Patterns, Avulsion, and Evolution of Submarine Fans up to the Basin-Scale


Channels on many submarine fans oscillate in Densimetric Froude Number as the flow path steepens by avulsion and is lowered by channel extension. Here we consider the influence of oscillating Froude number conditions on submarine fan organization based on theory, field data, and experimental observations. We conclude that many architectural properties including: stratal pattern, lobe stacking, channel fill style, fan extension/bypass, and channel network organization are influenced by cyclic changes in Froude number and may be more predictable than is currently thought. An investigation of avulsion scaling and fan organization based on the fluid mechanics indicates that stratigraphic length and thickness scales are: (1) rooted in the fluid mechanics, (2) inherited by the morphodynamics, (3) and reflected in the stratigraphy, forming the basis for nested feedback cycles across multiple scales. The effect of downstream control and variability in the propagation of information (gravity waves) through the distributary channel network has generally been underestimated (i.e. non-normal flow). Multiple scales of fan hierarchical organization, from beds to sequence sets, develop under non-equilibrium conditions and are strongly influenced by along channel (i.e. 1-D) hydraulics. A small change in slope or another flow/fluid property (e.g. h, ?, ??) induces sudden changes in stratal pattern (Fr’) or facies/texture (Re) by crossing boundaries (thresholds) between flow regimes. For example, variations in channel network pattern and channel fill style attributed to slope change in the literature can be explained by the inhibition of channel extension under supercritical conditions and by different modes of morphodynamic feedback in different flow regimes. Slope change may be depositional or tectonic or a combination of both depending on scale. These ideas challenge conventional sequence stratigraphic concepts because they account for typical stratal cycles like progradation, aggradation, and retrogradation (PAR) over substantial length and time scales (up to the largest lobe-scale) by autogenic mechanisms.