Chronology of anthropedogenesis in the Omiya tableland, Japan, based on a ^<14>C age profile of humic acid(Soil genesis, classification and survey)

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概要

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• Volcanic ash soils along the western edge of the Omiya tableland, Japan, are covered with thick anthropogenic soil horizons. The formation of anthropogenic soil horizons occurs because of the soil dressing practice known as "Dorotsuke," where alluvial soil materials are deposited on fields and mixed with volcanic ash topsoil by tillage over the years. To clarify the chronology of this anthropedogenesis, carbon-14 (^<14>C) age profiles were estimated using humic acid fractions from three pedons: an anthropogenic soil, an undressed Andosol, and a Fluvisol. Soil charcoal fragments were also dated to estimate maximum burial age. Charcoal fragments displayed vertically random age distributions, indicating that the fragments may have had multiple origins. However, the age of charcoal in the lower part of the anthropogenic soil horizons indicated that the initiation of anthropedogenesis occurred later than the late 13th century. The ^<14>C age profile of humic acid in the Andosol exhibited little variation in age with depth in the subsoil. The ^<14>C age profile of humic acid in the Fluvisol suggested that the humic acid fraction included allochthonous old carbon (C), although the soil itself had been formed from recent sediments. The ^<14>C age profile of humic acid in the anthropogenic soil showed features of its two component soils. The ^<14>C ages in the volcanic ash subsoil matched with those in the Andosol, whereas the ages increased in the anthropogenic soil horizons because of supplementation with old C from alluvial soil materials. However, the peak ^<14>C ages occurred in the lower part of the anthropogenic horizons, whereas the middle part on the peak position displayed a gradual age-depth gradient. This feature was interpreted as a sign of ^<14>C activity equilibrium throughout anthropedogenesis. On the basis of this postulated ^<14>C activity equilibrium, the linear age-depth gradient at the peak position was derived from differences in burial time, and burial ages were calculated by estimating steady-state ^<14>C. The calculated ages were lower than the charcoal ages. These age estimates suggest that anthropedogenesis was initiated in the Middle Ages and reached an intermediate stage before or during the first half of the Edo period.

• 2012-12-00

著者

• Tamura Kenji

  Graduate School Of Life And Environmental Sciences University Of Tsukuba

• MATSUZAKI Hiroyuki

  School of Engineering, The University of Tokyo

• WAKABAYASHI Shokichi

  National Institute for Agro-Environmental Sciences

• MIYAIRI Yosuke

  Atmosphere and Ocean Research Institute, The University of Tokyo

• ASANO Maki

  National Institute for Agro-Environmental Sciences

• TAMURA Kenji

  Graduate School of Life and Environmental Science, University of Tsukuba

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