Wave conditions estimated from wave ripples in the Pleistocene Osaka Group

Abstract

Paleo-wave conditions were estimated from wave ripples in the shallow marine sediments of the Pleistocene Osaka Group. Using new method by Takeda (1992), we can subdivide ancient ripples into four types, based on the relationship between orbital diameters and ripple spacings. Four types of wave ripples are discriminated in the group. Wave ripples in Neyagawa City are “anorbital vortex ripples” and “anorbital planar ripples”. Waves of 0.7-1.5m high in wave height and 2-4sec in wave period are calculated from those ripples. Wave ripples in Toyonaka City are “suborbital vortex ripples”, and 0.2-0.4m in wave height and 0.5-1sec in wave period are obtained. Wave ripples in Izumi City are “orbital vortex ripples”, and 0.1-0.9m in wave height, 2-4sec in wave period are calculated. Those wave conditions are similar to modern waves in the Sennan region, southern part of Osaka Bay. The minimum lengths of fetches for each reconstructed wave are also estimated.