what plate margins do abyssal plains form at
A-C. Abyssal Plain The flat area of the ocean basins between oceanic ridges and trenches or passive margins. Average depth of the abyssal plain is 4km below sea level. Typically the sedimentary rocks forming here are black shales and turbidites.Accretionary Wedge (prism) A zone of deformed sediment made up of thrust slices scraped off a subducting oceanic plate and added onto the over-riding plate.ontinental Crust A collective term for the crust that forming the continents; it has an average thickness of 35 km but can be up to 70 km under mountain ranges. Typically the composition is granitic with a density of 2.7 meaning that it is too buoyant to be subducted at convergent (destructive) plate margins.