Wave Ripples in the Pleistocene Paleo-Tokyo Bay

Abstract

Abundant wave ripples are found in the Pleistocene Shimosa Group distributed in Chiba and Ibaraki Prefectures, central Japan. Wave ripples in the Shimosa Group, which were deposited in the Paleo-Tokyo Bay, are intercalated in the following facies : the upper part of the point bar deposit of fluvial channel facies, distributary bay or lagoonal facies, tidal flat facies, tidal inlet facies, beach facies, shoreface to offshore facies, and deltaic facies.In this paper, it is introduced wave ripples in the distributary bay facies, tidal inlet facies, beach facies, and shoreface facies, which especially contain many typical wave ripples; and their paleo-environmental settings.Most of wave ripples were constructed under several meters deep in the Pleistocene Paleo-Tokyo Bay. Wave ripples in the distributary bay facies were constructed under the 'post-storm condition '. These in the shoreface facies were under both of the fair weather ' and post-storm ' conditions. These in the tidal inlet facies were mainly under the fair weather condition ' and in part under the post-storm condition '. Wave ripples are generally preserved by deposition of the overlying clay. Clay was supplied by floodwater of rivers running into the Paleo-Tokyo Bay.