Neogene planktonic foraminiferal biostratigraphy of the northern coast of Suruga Bay and Izu Peninsula

本文对骏河湾北方海岸和伊豆半岛新近纪地层进行了浮游有孔虫生物地层学研究。骏河湾北方海岸的地层受到了大窝新构造运动的强烈影响，因此，我们尝试了各种硬岩样品的方法，如Kalibor法、氯化钠法和真空烘箱法。结果表明，骏河湾北部海岸的地层中存在浮游有孔虫。可以获得关于该区域层序的浮游有孔虫年龄确定的以下新数据。根据时代鉴定种的出现，将静冈群、和田岛群和川野群归属于晚中新世的N.17。这三个组包含在相同的间隔中。小越地群相当于中新世晚期至上新世早期的N. 17 b-18，成研寺群相当于上新世的N. 19，滨石岳群相当于上新世的N. 21，在伊豆半岛获得了一些新的浮游有孔虫生物地层资料。根据汤岛温泉附近露头中年龄诊断种的出现，汤岛群的一部分被分配到最新的早中新世的N.8。在伊豆半岛中部海拔400- 500 m的山顶上发现了一些上新统白滨群层序，表明半岛自上新世以来曾发生过隆起。

In this study, planktonic foraminiferal biostratigraphy of Neogene sequences on the northern coast of Suruga Bay and Izu Peninsula is examined.As the strata on the northern coast of Suruga Bay have strongly been affected by neotectnics of the Fossa Magna, various methods for hard rock samples utilizing Kalibor, Sodium chloride and vacuum oven were tried to examination of planktonic foraminifera.As a result, following new data on planktonic foraminiferal age-assignments of sequences of the area could be obtained. From occurrences of age-diagnostic species, the Shizuoka, Wadajima and the Kawaino Groups are assigned to N.17 of late Miocene age. These three groups are included in a same interval. The Kogochi Group corresponds to N.17b-18 of late Miocene to early Pliocene age, the Seikenji Group to N.19 of Pliocene age, and the Hamaishidake Group to N.21 of Pliocene age.In Izu Peninsula, some new data on planktonic foraminiferal biostratigraphy could be obtained. Based upon occurrences of age-diagnostic species in an outcrop near the Yugashima Spa, a part of the Yugashima Group is assigned to N.8 of the latest Early Miocene age. Some Pliocene sequences of the Shirahama Group are found exposed on hill tops of about 400-500m above sea level in the central part of Izu Peninsula, which suggest an upwarping of the peninsula sinc Pliocene time.