Genesis of Esashi Dunes in the Oshima Peninsula, Hokkaido, Japan: A Study Based on Physico-chemical Properties of the Dune Components:A Study Based on Physico-chemical Properties of the Dune Components

概要

論文の詳細を見る
The Esashi dunes developed on Ohma Marine Terrace (50-65m high a. s. l.), north of Esashi, Oshima Peninsula, contain 5 buried humic soils within the 20-30m-high profile. Grain size distribution, humus properties, spectrum color, pH value in NaF, and mineral composition were examined for 40 samples taken from the dune profiles to discuss the genesis of these dunes and the Jin-ya Loam layer underlying the dunes. The results are summarized as follows:(1) The grain size distribution of the dune material was characterized by distinct peaks in two fractions: sand (20μm≤) and silt-clay (20μm>). The weight percentage of the silt-clay fraction was about 60%, 20-35%, and 15-20% at the bottom, middle, and top of the dune profile, respectively. The constitution of grain size shifted to finer fractions in deeper layers, and Jin-ya Loam mainly consisted of silt-clay fraction.(2) The carbon content of the dune materials ranged from 1 to 7 wt%; the type of humic acid was defined as A-type, using the values of MI, PI, and ΔlogK. In contrast, the humic acid of Jin-ya Loam was assigned as P-type.(3) Degree of spectrum color (a*, b*, L*-value), measured for organic carbon free samples, showed that dune samples had the same yellowish hue (10YR) as the Jin-ya Loam, the brown loam.(4) pH (NaF) value of samples from both the dune and the Jin-ya Loam layer was≥9.5, which indicated the properties for tephric materials.(5) Mineral composition(63-125μm)of Jin-ya Loam was inferred to be partly originated from volcanic matreials including tephra fall deposit (ex. Nigorigawa-a tephra, ca 12ka).From the above facts, it was suggested that the Esashi dunes have developed in a different process from coastal dunes. Silt-clay fractions in the dune were inferred to be materials from Jin-ya Loam, mainly composed of tephras which were eroded and reworked in the dunes. Accumulation of humus was considered to be associated with the deposition of the fine fractions, which characterized the humus properties of the Esashi dunes to become similar to that of Kuroboku-soil. Such kinds of dunes, in which silt-clay fractions originated from tephra are the important components as well as sand fractions, can be proposed as tephricloess dunes.
日本第四紀学会の論文

Genesis of Esashi Dunes in the Oshima Peninsula, Hokkaido, Japan: A Study Based on Physico-chemical Properties of the Dune Components:A Study Based on Physico-chemical Properties of the Dune Components

スポンサーリンク

概要

著者

関連論文

スポンサーリンク