第三系の層序と古地理  [in Japanese] Tertiary biostratigraphy and paleogeography in Japan  [in Japanese]

Our review of scientific activities in Japan in the field of Tertiary biostratigraphy and paleogeography during the 1970's reveals that a tremendous upsurge of activities occurred in the zonation of Tertiary strata by means of planktonic microfossils and geomagnetic reversal sequences, and also in the reconstruction of paleogeography. Two circumstances helped maintain this upward trend in these fields of research during the last decade. One is the initiation of two international research projects to deal with problems of pan-Pacific stratigraphic correlation, both of which were headed by Dr. Nobuo IKEBE. These projects include Committeeon Pacific Neogene Stratigraphy (CPNS) organized in affiliation with IUGS in 1972 and IGCP (International Geological Correlation Programme) Project 114 "Bio stratigraphic datum-planes of the Pacific Neogene" established in 1975. Under the aegis of CPNS, its inaugural congress was held in Tokyo from 16th to 21st of May 1976 with 45 overseas and 167 domestic attendants. The IGCP Project 114 also entertained a meeting entitled "International Workshop on Pacific Neogene Biostratigraphy" in Osaka between 25th and 29th of November 1982, attended by 21 overseas and 70 domestic participants. Three publications resulted from the discussion exchanged at these two meetings: i.e., SAITO and UJIIE, eds., 1977; TSUCHI, ed., 1982; IKEBE and TSUCHI, eds., 1984. The other circumstance was the availability of research funds nearly continuously throughout the decade. These research funds largely came from the Ministry of Education, Science and Culture of the Government of Japan as grants-in-aid. These funds helped organize several national working group projects aimed at improving the chronology and correlation of Japanese Cenozoic as well as Cretaceous sediments through the evaluation and integration of data gained from the fields of planktonic biostratigraphy, magnetostratigraphy and radiochronology. The thrust of Neogene research in Japan during the last decade was directed towards two fronts. One was to establish correlation between low and high latitudinal regions of Japan and the other was to draw reliable correlation lines between sedimentary basins on the Pacific Ocean side and those on the Sea of Japan side of the Japanese Islands. Initially, planktonic foraminifera and calcareous nannoplankton which had commonly been used in planktonic biostratigraphy received greater attention. However, a few years beginning from 1973 saw the development of zonation of Japanese Neogene strata by marine planktonic diatoms. The resulted diatom zonation soon received a world-wide acceptance as an indispensable means to correlate marine Neogene sediments of high latitudinal regions of the North Pacific. The advancement of biostratigraphic correlation of the Neogene deposits has given an increased incentive to the study of paleogeography. Preciseness in correlation by means of planktonic microfossils gave the basis for detailed discussions on regional paleogeography and paleoceanography. The main trend in paleogeographic studies in Japan during the last decade was towards the reconstruction of marine biogeography and changes in marine climate based on paleoecologic analyses of benthic mega- and micro fossils by incorporating increasingly available knowledges of ecology of living organisms. Considerable progresses have been made in our paleoceanographic and paleobiogeographic understanding of the Sea of Japan area during the Neogene.