Abstract
The experimental data on grain size constitution, which showed distinct grain peaks in both sand and silt-clay fractions, suggested that Esashi Dunes in the Oshima Peninsula, Hokkaido developed in a unique process influenced by reworked tephric materials. The dunes were composed of 4 black humic sand layers (Kurosuna A∼D) and underlied a humic soil (Kuroboku-soil) between Jinya Loam Layer. According to the 14C dating of the Kuroboku soil(5,135±25y.BP), the formation of dunes started in the period of the regression after Jomon Transgression. The dune formation was then interrupted in the period of Kurosuna A (2,425±25y.BP) formation and slowed down in the period from Kurosuna B(1,935±25y.BP) to C(1,140±25y.BP) formations. The properties of Kurosuna A and B were similar to that of Kuroboku soil (pH(NaF)≥9.5, content of total carbon≥4%, Melanic Index≤1.7) except for their large proportion of sand fraction.
