最終間氷期以降の海成段丘の年代と分布に関する諸外国の研究の紹介

抄録

The purpose of this paper is to review work on the about age and distribution of marine terraces since the last interglacial in 22 areas (excluding Japan) of the world (Fig. 1 and Table 1).
The results are as follows. 1) Distribution and uplift rate: There are a number of marine terraces lower than the last interglacial terrace (S terrace) in 12 areas; where the height of the S terrace is over 30m and the uplift rate since the formation of the S terrace is 0.3m/1000yrs. This uplift rate is the minimum rate required to expose all terraces between the S terrace and 60KA terrace, assuming that (1) tectonic uplift continues at a constant rate, and (2) the sea-level curve of MACHIDA (1975) is correct. Especially, in the areas adjacent to the trenches of plate boundary, the height of the S terrace attains 300-400m, and the uplift rate since the formation of the S terrace range between 1.5 and 3.1m/1000yrs. The difference in the uplift rate of each area is perhaps due to differences in the character of the mobile belts (OTA and NARUSE, 1977). The marine terraces younger than the S terrace are found in the “zone of plate convergence” or “zone of plate transformation”. Especially, in the “zone of plate convergence” where the uplift rate is great, many marine terraces are developed.
2) Age of terraces: The marine terraces dated ca. 100KA, 85KA and 60KA are recognized in many places of the world (Fig. 2). These ages agree well with relatively warmer episodes (Stages 3 and 5) in the oxygen-isotope stages founded in a tropical Pacific deep-sea core (SHACKELTON and OPDYKE, 1973). It is obvious that the formation of these terraces is essentially affected by sea-level fluctuations due to glacial eustasy, as has alreadly been proposed. Dates of samples mostly concentrate at 85KA then around 100KA and 60KA. This suggests the magnitude of transgressions.
Marine terraces between 50KA and 30KA have been reported in California, New Guinea, New Hebrides, India, Mediterranean and South Africa. As a result of the combined effect of crustal movement and eustatic sea level change (BLOOM et al., 1974), the uplift rate since the formation of the S terrace requires more than 1.5m/1000yrs. mento expose the former shorelines above present sea level. In the former three areas tioned above, the uplift rate is higher than this value, but in other areas, it is less. Further studies concerning the acceleration of uplift rate towards the present, modification of the paleo sea level and cross checking of dates are necessary.