A Review of Dating Methods now used in Japan
Naotune WATANABE · ScholarSpace (University of Hawaii at Manoa) · 1961
In the last decade or so, marked progress has been made in the geological study of the Pleistocene formation.During the Pleistocene epoch many volcanoes in the Japanese islands were so active that a vast amount of volcanic ash covered a large part of the islands.In 1949 preceramic stone implements were found for the first time in such a volcanic ash layer, and since then many similar discoveries have been reported from various regions of Japan.Owing partly to these discoveries, the Pleistocene formation drew the attention of geologists and geomorphologists, and in 1953 a research group was organized by these specialists and included archreologists.This group has carried out intensive studies on the volcanic ash layers especially in central Japan, and successfully established their stratigraphy which covers the whole range of the Quaternary period.The term 'Tephrochronology' (tephro means volcanic ash) was given to this sort of chronology.In Hokkaido lying north of the main island of Japan, many volcanoes erupted in the Holocene epoch, and the eruptive materials from these volcanoes formed layers in the superficial subsoil.Shinobu Yamada, a pedologist, studied the stratigraphy of these layers and determined the absolute date of each layer by studying old records on volcanic eruptions, the estimated accumulation rate of peat formation, and so on.He classified fifty-four different layers derived from twelve volcanoes in the southern part of Hokkaido.The date of these layers goes back to more than 5,000 years.The stratigraphy thus established serves to date the potsherds and other remains which are often found in those layers.Even before these intensive geological or pedological studies were done, the change in ancient coast line had long been noticed by archreologists in relation to the location of prehistoric shell-mounds around Tokyo Bay.The first attempt at dating a prehistoric site in Japan was performed by John Miln about 80 years ago.Based on the accumulation rate of alluvial soil, Miln obtained the age of 3,000 years for a shell-mound located at the ancient coast.In the 1930's members of the Ohyama Institute of Prehistory carried out a systematic study to compare the chronological sequence of pottery types with the regression of the ancient coast line.It is evident from the distribution of shell-mounds that the Bay of Tokyo once intruded into the alluvial plain as far as 80 km.from the present coast line.This seems to have been the case about 5,000 years ago.The sea-level of those times must have been 5 metres or so higher than the present.Assuming the shell-mounds of sea shells were made near the coast line and those of fresh water shells were made after the coast line had receded, the pottery types found in these shell-mounds were consistently connected with the gradual regression of the ancient shore line.The pollen sequence in the peat formation in Japan has become clear rather recently.Jun Nakamura, Shoichi Hori and Matsuo Tsukada analysed the peat from bogs in central Japan and obtained similar results with respect to the tendency of