A new classification system for mixed (turbidite-contourite) depositional systems: Examples, conceptual models and diagnostic criteria for modern and ancient records

Interactions between along-slope bottom currents and down-slope turbidity flows can create a myriad of features and deposits. Despite numerous efforts to differentiate contourites from turbidites and mixed features, reliable diagnostic criteria are still lacking from the stratigraphic and sedimentological viewpoints. The main aim of this study is to develop criteria to differentiate mixed, along-slope-, and down-slope-generated elements from other deep-water deposits across bathymetric, seismic and sediment core data.Mixed (turbidite-contourite) systems can be placed in three main groups based on their location, dimensions, elongation, lateral migration, spatial and temporal variability: 1) turbidite-dominated mixed systems, 2) synchro-nous systems, and 3) contourite-dominated mixed systems. The persistence of bottom currents -in addition to their velocity, direction, and hydrodynamic fluctuations- is responsible for entraining and redistributing fine-grained particles, carried in suspension by coeval turbidity flows, and reworking previously deposited sediments. Changes in turbidity current velocity, frequency, and duration condition the provision of sediments and devel-opment of turbidites along mixed systems. Several preliminary models are also being proposed in this study, in order to enhance our understanding of the lateral and vertical distribution of mixed systems across the sedi-mentary record. Interactions between along-and down-slope processes may be synchronous, asynchronous or passive. Syn-chronous interactions typically occur within the same physiographic setting and the two processes interact coevally in space and time. Asynchronous interactions are also common across the modern and ancient sedi-mentary records, as bottom currents sweep across the deep-water environments during breaks of the turbidity flows. Passive interactions occur along the distal margins of mixed systems, or when the two processes occur near each other but do not cross over in time. Further controlling factors are held to be influential in the evolution of mixed systems at the short-to long-term; varying degrees of confinement, sediment supply or climatic fluctua-tions can generate cyclic stacking patterns and affect their overall dimensions. Accordingly, mixed systems feature more complex geometries than previously believed, as interactions may generate new secondary pro-cesses and features. Such systems form potential plays and may become future targets for energy geosciences and other research fields.