Holocene deposits and Jomon-age shell mounds in northeastern part of Yokosuka City, south-central Japan
Yanai, H.; Kanie, Y.
Science Report of the Yokosuka City Museum 1991(39): 77-83
The northeastern part of Yokosuka City is situated on a land reclaimed since 1869. The subsurface topography of the area comprises narrow buried valleys extending SW-NE and wave-cut benches, as judged from the boring data. The Holocene deposits at three localities of the area were studied, and the paleogeography was reconstructed. Then, the changes of paleoenvironment were revealed by analyzed the pollen fossils and molluscan fauna collected from Ohtaki-machi. In the buried valleys of 9000-8000 yBP, a dry beach appeared following the transgression. Around 6600 yBP the beach was under water of a few meters deep with muddy bottom, and about 5500 yBP the area changed to a shallow coastal sea with sand and gravel bottom. The molluscan fossil assemblage in the Holocene marine environment is harmonious with the molluscan fauna excavated at the Jomon-age shell mounds. The pollen analysis shows that the vegetation of the surrounding area in 9000-8000 yBP was a temperate deciduous broad-leaved forest, and around 6600 yBP it has already turned to a warm-temperate laurel forest.