日本海第四紀堆積物のシーケンス層序学的解析への生層序学の貢献 : 時間面としての暖流系種の消長  [in Japanese] Contribution of biostratigraphy to sequence stratigraphic analysis of Quaternary sediments of the Japan Sea : Intrusion and extinction of warm-water species as time planes  [in Japanese]

暖流系種 (黒潮の影響を受けた表層水や陸棚に分布の中心をもつ生物種) が日本海第四紀の層序記録にたびたび現われる。その層位分布を酸素同位体記録と比較した。その結果は, 第四紀の日本海では暖流系種の移住とその後の死滅そして新たな進出とが間氷期・氷期サイクルに呼応して起きたことを示唆する。これらの現象が日本海スケールで同時に起きたのならば, 暖流系種の出現・消滅層準を時間面に使える。これらの時間面は, 日本海第四系の対比に役立つばかりでなく, 第四紀堆積盆のシーケンス層序学的解析にも大いに貢献する。なぜならば, 暖流系種の出現・消滅層準の層序学的位置は氷河性海水準変動と密接な関係にあるので, シーケンス境界や最大海成氾濫面の層序学的位置の予測に使えるからである。暖流系種の層位分布から設定した時間面と既存の時間面との試験的な対比を提示した。

Warm-water species living in the water mass influenced by the Kuroshio Warm Current occur cyclically in Quaternary sediments of the Japan Sea. I compared the stratigraphic pattern of species distribution with the oxygen isotope record, using biostratigraphic and magnetostratigraphic data as the stratigraphic references. The comparison suggests that warm-water species intruded into the Japan Sea during interglacial periods and were apparently locally extirpated at the following glacial period, possibly killed off by marine climate cooling. If these phenomena were nearly synchronous with in the Japan Sea, it is possible to use the appearance and disappearance datums of the warm-water species as time planes. These time planes can increase the confidence level of sequence and systems-tracts interpretations of Quaternary sedimentary basins of the Japan Sea area. Analysis of existing data shows that at least two appearance and disappearance datums of warm-water species are found in each of the depositional sequences controlled by glacio-eustatic sea-level changes. I present here a tentative correlation of the time planes based on the stratigraphic distribution of warm-water species with other datums from sequence stratigraphy, bio stratigraphy, magnetostratigraphy and tephrostratigraphy.