Environments of the Formation of Dunes at Shiriyazaki in the Shimokita Peninsula, Aomori Prefecture

Abstract

The results of studies on landforms, sandpaleosol sequence, and grain size analysis of Shiriyazaki Dune are as follows:
(1) The main geomorphic surface at Shiriyazaki is Tanabu Terrace (about 20m high a. s. l.), which is composed of marine sand and gravel. The red-brown tephra deposited on that terrace was eroded by the wind. On top of the terrace scarp on the northwest side, many blowouts are formed by the strong winter monsoon wind. Parabolic dunes, seif dunes, and their transformational dunes develop at the back of those blowouts on the terrace.
(2) About 60-80% of the older dunes are composed of silt and clay fractions. As the results of pH (NaF) measurement are over 9.4, it is highly possible that those fine materials originated in the tephra.
(3) The result of the ¹⁴C dating of the buried humic soil just below the dune is 8, 350±165yrs BP. And the dune had five periods of formation: there are four other buried humic soils in the eolian sand.
The above facts show that the material of Shiriyazaki Dune has not been supplied from the sand beach, but from the blowouts on terraces by wind erosion. The fine red-brown tephra deposited on the terrace surface was also abraded and deposited in the dune. Consequently, large amounts of silt and clay fractions exist in the early stages of dune formation.
Moreover, it is interesting that the beginning of dune formation was estimated to have taken place in the same period as the regression, about 8, 200-7, 500yrs BP. There is a possibility that the strong winter monsoon linked to the cool climate during the Hypsithermal caused the wind erosion in this area.