近畿地方の3地点の黒色土の生成, とくに母材と過去の植生について Genesis of Ando-soils of Three Sites in the Kinki District, Japan, with Special Reference to Parent Materials and Past Vegetation
Ando-soils with a humic and thick A horizon are widely distributed in Japan. These soils are mostly derived from tephra materials, and recent studies make it clear that these humic and thick A horizons have developed upward cumulatively. Several factors, such as continuation of grassland vegetation, topographic stability, and a suitable climate, are considered to be necessary for the genesis of Ando-soils. However, Andosoils are only sparsely distributed in the Kinki district of central Japan. To elucidate the pedogenetic processes of Ando-soils in the Kinki district, with special reference to the origin of parent materials and their deposition mode, and the vegetational environment in the past, we researched three soils, Towano soil (Hyogo Prefecture), Aibano soil (Shiga Prefecture), and Shio-no-misaki soil (Wakayama Prefecture). These soils have black or dark-brown colored A horizons over 40cm thick. That of Towano soil is over 2m thick and has alternating deep black and slightly light black sub-horizons. Judging from these stratified component of sub-horizons, it is presumed that the Towano soil has a cumulative development process. Microscopic mineral analysis for the sand fraction and X-ray diffraction analysis for silt and clay fractions were carried out to investigate the origin of parent materials of these soils and their deposition mode. Plant opal and pollen were analyzed to reveal the past vegetational history.<br>Primary mineral composition of the sand fraction showed a mixture of tephra-origin particles (volcanic glass, etc.) and bedrock-origin particles (groundmass fragment of bedrock, etc.). All the horizons of each soil contained volcanic glasses which were mostly derived from at least two kinds of tephra, but volcanic glass contents had no correlation with carbon contents. Silt and clay fractions were dominated by quartz in all horizons of each soil. Among them, the quartz grains in Towano soil were thought to be derived from foreign materials like eolian dust. A large number of plant opal grains have accumulated in most horizons of each soil; they are more strongly weathered in the deeper horizons. From these results, it is concluded that the studied Ando-soils have developed upward cumulatively under the balanced accumulation of organic matter and mineral materials. The results of plant opal analysis and pollen analysis suggested that open site vegetation like a grassland or sparse forest was maintained on the Andosoils. The results mentioned above were generally in accordance with previous research in north-eastern Japan.
第四紀研究 37(1), 13-24, 1998-02-28
Japan Association for Quaternary Research