Late Quaternary Sea-level change Recorded on the Topographic Features of Several Straits around the Okinawa Islands

Abstract

In this paper, some problems of the late Quaternary sea-level change are discussed, based upon the following topographical data of five straits around the Okinawa Islands.
The breadth to depth ratio of the straits (Figure 2) seems to reflect still-standing sea-levels; -110±10m, -80±5m and -50±5m. According to the radiocarbon ages of shallow-water shells and peat obtained from the continental shelf and the coastal plains in the Japanese Islands (Figure 4), it is supposed that the sea-level at the maximum Würm (17, 000 to 20, 000y.B.P.) was about 80m below the present level. Therefore, the result agrees with the evidence from the strait topography around the Okinawa Islands.
Even though the sea-level was down to about -80m at the maximum Würm, any land bridge between the Okinawa Islands and other lands can not be expected. Thereby it is inevitable to consider that the immigration of Minatogawa-jin (a paleolithic man) into the Okinawa Islands about 30, 000y.B.P. was made by means of primitive boat or raft.