RHEOLOGICAL COMPLEXITY IN SEDIMENT GRAVITY FLOWS FORCED TO DECELERATE AGAINST A CONFINING SLOPE, BRAUX, SE FRANCE

Hybrid event beds are now recognized as an important component of many deep-sea fan and sheet systems. They are interpreted to record the passage of rheologically complex sediment gravity currents (hybrid flows) that comprise turbulent, transitional, and/or laminar zones. Hitherto, the development of hybrid flow character has mainly been recognized in system fringes and attributed to distal and lateral flow transformations and/or declining turbulence energy expressed over lateral scales of several kilometers or more. However, new field data show that deposition from hybrid flows can occur relatively proximally, where flows meet confining topography. Turbidity currents primed to transform to hybrid flows by up-dip erosion and incorporation of clay may be forced to do so by rapid, slope-induced decelerations within 1 km of the slope. Local flow transformation and deposition of hybrid event-beds offer an alternative explanation for unusual facies developed at the foot of flow-confining seafloor slopes.