能登半島珠洲地域の新第三系の岩相および放散虫化石層序
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概要
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Siliceous (diatomaceous) sediments of Miocene age are widely distributed in the Suzu area of the Noto Peninsula. The sediments yield plenty of well-preserved microfossils such as radiolaria, diatom, planktonic foraminifera and calcareous nannoplankton. The Miocene strata in the Suzu area is divided into the following four radiolarian zones in upward sequence : the Calocycletta costata, Eucyrtidium asanoi, Eucyrtidium inflatum, Lychnocanoma nipponica magnacornuta Zones, by using the first appearance datums of E. asanoi, E. inflatum and L. nipponica magnacornuta. Other datum levels such as last appearance, acme, rapid increase and rapid decrease are situated in each zone. Lithopera renzae spiculosa is described as a stratigraphically important new subspecies. Miocene radiolarian biostratigraphy proposed here is applicable to onland sequences both on the Pacific and Japan Sea sides of central and northeast Honshu. This radiolarian stratigraphy is combined with the diatom biostratigraphy proposed by Maruyama (1984) using the same samples in the hope that an integrated siliceous biostratigraphy improves stratigraphic resolution. Each lithostratigraphic unit is positioned by this integrated siliceous biostratigraphy. The Miocene strata in the Suzu area cover four radiolarian zones and nine diatom zones, respectively. A characteristic glauconite bed in this area is used as a key marker. This glauconite bed extends over three radiolarian zones and four diatom zones, respectively. The upper limit of the glauconite bed in terms of the siliceous microbiostratigraphy is uniform from section to section in this area. On the other hand, its lower limit differs from section to section. It is suggested, therefore, that intervals at which samples are taken are fundamentally important in revealing such local differences in timing of the deposition of glauconite.
- 東北大学の論文
- 1988-03-10