Chronology and Palaeoenvironmental Condition for the Formation of the Buried Humus Soils of the Coastal Sand Dune Area in the Hokuriku District, Central Japan

Abstract

Palynological, stratigraphical and chronological investigations were made on the Holocene buried humus soils intercalated in the coastal sand dunes developed along the Japan Sea in the Hokuriku district, Central Japan.The purpose of the present investigations is to determine a definite age of the formation of the humus soils, palaeoclimatic condition under which they were formed, their topographical environments and the relationship between the formation of their humus soils and coastal sand dune and the cahnge of sea-level.Most of the studied humus soils and peat deposits are considered to have formed during the close of the Middle Jomonian to the Early Old Tomb periods. The conclusion are based on 14C dating, the stratigraphy, topographical setting and archaeological remains found in the humus soils.The palaeoclimatic condition at those periods was cool temperate, judging from such macroplant remains as erect tree stumps, leaves and seeds, and microplants as pollen grains and spores. The annual mean temperature was estimated at some 11°C, and the flora which was developed on the Inner and Middle or Old sand dunes was composed mainly of either a riparian or a mixedslope type, being closely similar to the present lowland vegetation in the northern Honshu.A relative minor rise of the sea-level and migration of the coastal sand dunes seem to have caused the formation of most of the buried humus soils and peat which is called Sotan in Japanese, and submerged and buried forests in the coastal areas of the Japan Sea, Hokuriku district, Central Japan.