海成層の上限(marine limit)の認定 (最終氷期以降の海水準変動とそれをめぐる諸問題<特集>)

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This paper deals with the method to determine the upper limit of Holocene marine facies. The example for the Holocene sediments is given by Tamatsu Bed developed in the mouth of the Akashi River, Hyogo Prefecture. The Tamatsu Bed consists chiefly of unconsolidated sand (lower), marine clay (middle) and silt (upper), and the age being from 9, 000y. B. P. to 2, 000y. B. P.We have examined the Tamatsu Bed on marine molluscan fossils, marine diatom assemblages, trace fossils of marine animals and lithofacies especially formation of pyrite crystals. The altitude of the upper limit above the present sea level is as follows:Marine molluscan fossils +0.5mMarine diatom assemblages +2.2mTrace fossils of marine animals +1.6mPyrite crystals formation +2.2mAmong them diatom assemblages, especially Terpsinoe americana which inhabits at the intertidal zone of the mouth of a river may be the best indicator of sea level. It is noticed that the fine crystals of pyrite formed on the surface of the outcrop show the same upper limit as that of diatom assemblage.
日本第四紀学会の論文