| Research Abstract |
The Kazusa and the Shimousa Groups in the Boso Peninsula are stratotypes of Japanese marine Pleistocene deposits. The Shimousa Group comprises several cyclothems controlled by glacial eustasy. One of conclusions of this study is that the basal formation of the Group is the Nagahama Formation composed of gravel bed overlying the Ichijuku Formation, which belongs to the Kazusa Group with clear boundary named the Nagahama Unconformity. Recent studies had cleared that the unconformity was formed at marine isotope stage 16.
An obvious geological succession of marine Pleistocene in Wanganui Basin, New Zealand, have been researched by many workers and the correlation for marine stratigraphy and terraces had been proposed by Pillans(1990). A question arose, however, about the correlation by my field survey at 1993. I found some thin black colored tuff layers interbedded Upper Westmere Siltstone at the coast and the Marorau terrace deposits at the hilly district, and there is a great possibility that they are the same layers.
If my observation is correct, Pillans's correlation between the succession at Castlecliff coast and the flight of terraces will be obliged to revise. As the Ararata terrace is fixed stratigraphically with Rangitawa Pumice, some terraces higher than the Rangitatau terrace must be shifted their stratigraphic horizons to older stages, respectively. One of the merits of new version is dissolution of a contradiction, which the Rangitatau terrace was formed during marine isotope stage 12, namely, low sea-level stage. Moreover, if the Ball terrace corresponds to isotope stage 15, inferred obvious low sea-level at just before the terrace corresponds to stage 16 which is said as extreme low sea-level. The basal surface of the Nagahama formation of the Boso is correlated to the one of the Sea field Sand of the Wanganui district by remarkable lowstand of sea-level.
|
