Bulletin of the Mizunami Fossil Museum

Monograph of the Mizunami Fossil Museum No. 7

Well-developed sedimentary sequences are exposed in Northeast Japan. Many sequencs were selected from the Japan Sea side region of Northeast Japan for palynologiacal analyses. The main studied localities are shown in Fig. l. As a result of these studies, five pollen zones recognized on the basis of floral change.

The Np-1 zone consists mainly of cool-temperate flora which is correlated to the Aniai type flora of mega-fossil plant. The NP-2 zone is characterized by the abundance of warm flora and corresponds to the Daijima type flora of mega-fossil plant. The NP-3 zone consists of warm flora continued from the previous time, but a little cool elements are increasing. The NP-4 zone is composed mainly of cool-temperate plants. The characteristics of the NP-5 zone is similar to the NP-4 zone. However, some warm elememts are revived in many horizones in this zone. Therefore, the tell1perature is a little warll1er than that of the present.

The NP-2 zone has most abundant warm elements among the five pollen zones. The pollen fossils of mangrove plants occur in the NP-2 zone of Toyama district, Central Japan. This palynogical data indicate that the winter season in Toyama district during the middle Miocene was nearly 16℃ higher than the condition existing today. This warm event can be considered as a time of the tropical spike which is called for paleo-temperature rising like a quick pulse (Itoigawa, 1989).

The drilling tip of the ODP (Leg. 127, Site 797) reached 903m below the sea floor of Japan Sea. As a result of pollen analysis of the core samples, the palyno-stratigraphy from the NP-1 to NP-3 zones are clarified continuously. Especially, it becomes clear that the warm temperature of the NP-2 zone was not evenly, but a little lower temperature zone was inserted in the middle part of this zone.