Quaternary tephra layers of suwanose island in the tokara islands, south japan

概要

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A large section exposed in the southern part of Suwanose Island in 1993 provides an excellent sequence of tephra beds that can be used to establish the Quaternary tephrochronology of this island as well as that of the Tokara Islands. In total, more than twenty tephra beds occur at this section, which is approximately 60m high. These tephra beds may be divided into five tephra groups: Suwanose south lower tephra group (Ss-L), Suwanose south lower scoria group (Ss-Ls), Suwanose south upper pumice group (Ss-Up). Suwanose south upper scoria group (Ss-Us), and Bunka, post-Bunka scoria group (Bn-PBs). AT ash, identified by microprobe and refractive index analyses, is found near the top of Ss-Ls, indicating that Ss-Ls, Ss-Up and Ss-Us are younger than 23 ka, that is, of the late Pleistocene age. It should be noted that dacitic and rhyolitic pumice-fall beds and a pyroclastic-flow deposit occur in units Ss-Up and Ss-L, that coarse scoria-fall beds of the late Pleistocene age are present in Ss-Ls, and that Ss-Us is characterized by fine-grained, air-fall scoriaceous sand of the Holocene age.
首都大学東京の論文