In 1988, a thin volcanic ash layer was found in the peat layer from nine survey areas of the Choda and Matsukawado archaeological sites, Kasugai City, Aichi prefecture. This layer, about 4mm thick, is composed of light reddish brown to pinkish white and fine to medium-grained ash. It consists chiefly of glass (mainly C-type shards with refractive index of 1.499-1.504; mode 1.501-1.502), which small amounts of plagioclase, orthopyroxene (γ=1.703-1.705), amphibole, biotite and clinopyroxene. The 14C age of the peat layer from the horizon immediately beneath the ash layer is 3, 120±120y.B.P.; this ash layer was found above a bed containing late Jomon potsherds and below a bed containing final Jomon potsherds. So it can be said that this volcanic ash fell around the fine of the boundary between the late and final Jomon Period. This is probably the first time in the lowland Kinki and Chubu district that the ash layer of this period has been recognized as a visible stratum. The authors named the ash the “Matsukawado Volcanic Ash Layer” (MT) after the layer was discovered.
This paper reviews studies conducted between 1980 and 1988 on relative sea level changes and coastal evolution during the Holocene in Japan. The Japanese Working Group of IGCP Project 200, on “late Quaternary sea level changes, ” compiled the two-volume “Atlas of Sea Level Records in the late Quarternary in Japan” in 1987, which included materials related to this topic, based on papers published since 1980. The group also compiled the “Middle Holocene Shoreline Map of Japan (1:200, 000), which demonstrated the location of the middle Holocene shoreline with numerous data on height and radiocarbon age representing the sea level of that stage, and with 15 insets, considered to be typical examples of various types of study. Numbers of papers by year in terms of research field and study area are summarized in Figs. 1 and 2. Several review papers on sea level study have been also published in the last several years, in addition to local studies. Relative sea level curves published in the past 10 years are shown in Fig. 3. The curve patterns show noticeable local or regional differences, reflecting tectonic factors with a different amount and character in each area. Some areas characterized by a rather late culmination age of the postglacial transgression contrast with most of the Japanese coast, which has a culmination age of ca. 6, 000 to 6, 500y.B.P. Two minor fluctuations of Holocene sea level which were pointed out by OTA et al. (1982), have been recognized in several areas; a eustatic origin for such fluctuation is most likely, judging by the nearly coincident occurrence of climatic fluctuation revealed by pollen analyses, molluscan assemblage analyses and submarine core data. The following topics are discussed in particular detail in this paper: 1) Progress of excavation on the Holocene lowland and coral reefs, in order to obtain systematic samples for identification of marine limits and samples for analyses of various fossils and for dating. 2) Holocene marine terrace study with special reference to coseismic uplift and volcanic activity. 3) Identification of the former sea level on the rocky coast. Barnacles and tube worms (Pomatoleios kraussii) as sea level indicators are discussed, including problems with accuracy of radiocarbon dating. 4) Problems concerning the recognition and accuracy of former shorelines in the large alluvial plain. 5) The significance of small drowned valleys as a suitable field for the reconstruction of sea level change. 6) Climatic fluctuation during the Holocene, with relation to sea level fluctuation. 7) Increased overseas studies on Holocene sea level change by Japanese scientists.