Claim: West Philippine Basin (also known as the West Philippine Sea Basin), formed during the early Oligocene epoch, is the oceanic crust located underneath the western part of the Philippine Sea; and is deeper and older than the eastern basins and has crustal heat-flow values approaching that of old oceanic crust.
Evidence: The West Philippine Basin, also known as the West Philippine Sea Basin, is the oceanic crust located underneath the western part of the Philippine Sea. It was formed during the early Oligocene epoch. The West Philippine Basin is deeper and older than the eastern basins and has crustal heat-flow values approaching that of old oceanic crust.