パラオ諸島の歴史と地質

抄録

Recently we had chance to visit Palau Islands two times in 1986 and 1988. The aim of the present article is to introduce the geology including some new evidences investigated by us, and the human history of the islands is also briefly described.
The Aimeliik volcaniclastic rocks, which have been recognized as in the Eocene Aimeliik (=Aimiriki) Formation by the former scientists, from the quarry at Ngeruluobel located at about 1km west of the Palau International Airport terminal at Airai in southern end of Babelthuap Island, are discussed in Cepter V. Many foraminifers, calcareous algae and some corals were found as individuals in the matrix or in the limestone gravels of the volcaniclastic rocks. Among the determinable species of foraminifers, Biplanispira absurda, B, inflata, B. mirabilis, Pellatispira rutteni, Fabiania saipanensis and Discocyclina dispansa were reported from the Matansa Limestone (Upper Eocene) of Saipan, and Gypsina globulus, Eulepidina formosa from the Tagpochau Limestone (Lower Miocene) of Saipan by HANZAWA (1957). It seems there are at least two groups of foraminiferal fauna showing different ages, namely, the Upper Eocene and Lower Miocene (Aquitanian to Burdegalian). Accordingly, the depositional age of the Aimeliik volcaniclastic rocks should be Late Miocene or later.
In Chapter VI, we introduce our study (SAKAGAMI et al., 1987) on the environmental change in some period of the Miocene to Pliocene by the pollen and spore analyses of the Airai lignite-bearing beds in Babelthuap Island.
Lastly the literatures on geological sciences are comprehensively compiled for the convenience to the future study.