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The debate on the submarine canyon origin between the upslope erosion model dominated by retrogressive mass failures and the downslope erosion model controlled by gravity flows has not been fully settled. However, this debate is critical for explaining submarine canyon evolution. This study combines susceptibility mapping and stratigraphic forward modeling (SFM) to examine the origin and evolution of submarine canyons under various fluvial discharge and morphologies. The SFM work consists of dozens of hypothetical numerical experiments based on typical passive margin bathymetry with half bathymetry occupied by an incipient canyon and associated river mouth topography, and another half bathymetry by steep slopes without canyons. Evolution characteristics in both plan and cross-section views are analyzed, and the impacts of fluvial and morphological features on canyon evolution are tested. The results indicate that the submarine canyons retreat landward, tributaries develop on the canyon outer banks, and blind canyons grow landward to capture small gullies and form shelf-incising canyons. The upslope pattern is dominant regardless of changes in fluvial discharge and morphologies. The locations of tiny gullies on steep slopes determine the distribution and growth direction of submarine canyons, whereas fluvial conditions and morphology parameters affect the canyon dimensions. High fluvial discharge and high canyon sidewall slope angle promote tributary development and canyon erosion. High canyon sinuosity leads to an asymmetrical distribution of tributaries on canyon outer banks whereas high regional slope angle increases the canyon length and decreases the canyon spacing. This study settles the debate between the upslope and downslope erosion models. In addition, it refines the upslope model by highlighting the importance of small-scale gullies and testing the influence of fluvial and morphological conditions on canyon evolution. The conclusions could promote the understanding of submarine canyons and assist in reservoir exploration and hazards prevention.

A numerical model has been developed for the simulation of turbidity currents driven by nonuniform, non cohesive sediment and flowing over a complex three dimensional submarine topography. The model is based on an alternative approach known as Cellular Automata paradigm. The model is validated by comparing a simulation with a reported field-scale event. The chosen case is a turbidity current which occurred in Capbreton Canyon and was initiated by a storm in December 1999. Using data from recent oceanographic cruises, the deposit of the event has been precisely described, which constrain values of model parameters. The model simulates the 1999 turbidity current over the actual canyon topography and related turbidite using three different types of particle. The model successfully simulates areas of erosion and deposition in the canyon. It predicts the vertical and longitudinal grain size evolution, and shows that the fining-up sequence can be deposited by several phases of deposition and erosion related to the current energetic variation during its evolution. This result could explain the presence of intrabed contacts or the frequent lack of facies in Bouma sequences.

Cellular automata (CA) represent an interesting approach to the modelling of dynamical systems evolving on the basis of local interactions and internal transformations. The CA model, specially developed for simulating density currents, is described. The objective is to predict the formation and evolution of channels and the structure of deposits associated to the flow path. For simulation purposes, currents are represented as a dynamical system subdivided into elementary parts, whose state evolves as a consequence of local interactions and internal transformations within a spatial discrete domain. The model is developed for unsteady, two-dimensional, depth-averaged, particle-laden turbulent underflows driven by gravity, acting on density gradients created by non-uniform and non-cohesive sediment. CA is defined as a tessellation of finite-state automata (cells). The attributes of each cell (substates) describe physical characteristics. The natural phenomenon is decomposed into a number of elementary processes, with a particular composition that makes up the transition function of the CA. By applying this function to all the cells simultaneously, the evolution of the phenomenon can be simulated in terms of modification of the substates. The transition function includes the effects of water incorporation at the suspension–ambient fluid interface, a transport equation for the particle volume concentration, and a toppling rule for the deposited sediments. Simple and flexible, the obtained model constitutes a first step toward quantitative comprehension of the impact of external parameters on the turbidity current dynamics and on the organisation of the subsequent depositional sequences.