秋田県北部峰浜地域に分布する上部鮮新統〜下部更新統の浮遊性有孔虫化石層序

• Main Authors: 山﨑 誠, 小松 優子, 福永 里実, 佐藤 時幸, YAMASAKI Makoto, KOMATSU Yuko, FUKUNAGA Satomi, SATO Tokiyuki
• Format: Report
• Language: Japanese
• Published: 秋田大学大学院工学資源学研究科 2015
• Subjects: Neogloboquadrina pachyderma
• Online Access: http://hdl.handle.net/10295/2990; https://air.repo.nii.ac.jp/?action=repository_uri&item_id=2644; https://air.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2644&item_no=1&attribute_id=48&file_no=1

Planktic foraminiferal biostratigraphy of the upper Pliocene to lower Pleistocene Tentokuji and Sasaoka Formations distributed in the Minehana area located in the northern part of Akita Prefecture, Japan, is described in detail. Totally 44 samples were analyzed for this study. Based on calcareous nannofossil and planktic foraminiferal assemblages, the studied section includes the horizon of global cooling that was resulted from Northern hemisphere galaciation in the latest Pliocene. Globigerina bulloides and Globigerina quinqueloba occurred throughout the studied section. Cold-water planktic foraminifera were generally observed in the middle to upper part of studied section. Especially, a polar to subpolar dweller, Neogloboquadrina pachyderma (sinistral coiling variety), was found commonly just after global cooling at latest Pliocene while dextral coiling variety of this species, which thrived in warmer water, were rare in the middle to upper part of the studied section. On the other hand, tropical to subtropical species such as Globigerinoides ruber were also found at the upper part of the studied section. It indicates that the studied area seems to be covered by warm water in the early Pleistocene.