Pliocene and Pleistocene Pollen Stratigraphy in Central and Southwestern Japan

Abstract

The floral change, like as the faunal succession, the paleomagnetic chronology and the absolute age, is one of the most important means for the subdivisions of the Pliocene and Pleistocene time. In Kinki district, the studies of the Plio-Pleistocene flora have been proceeded since the 1930's. And the floral subdivisions in this district have been proposed by several workers (Fig. 3). The writer rearranges these plant fossils into 14 stratigraphic divisions (see Appendix). As the result, it is definitely shown that the following 7 macrofloras, in descending order, have the distinctive features. 7. Yokooji Flora (=Aphananthe flora) 6. Nishinomiya Flora (=Larix gmerinii and Syzygium floras) 5. Nishiyama Flora (=Paliurus nipponicus flora) 4. Ibaraki Flora (=Metasequoia flora) 3. Sennan Flora (=Transitional flora 2) 2. Shimagahara Flora (=Transitional flora 1) 1. Seto Flora (=Pinus trifolia flora) Pollen analysis is carried out on the samples covering almost all horizons of the Pliocene and Pleistocene deposits in Kinki and Tokai districts. Based on the feature of each pollen spectrum, the following 14 pollen assemblages are distinguished (ONISHI, 1975). Judging from the contained taxa and the stratigraphic horizon, some pollen assemblages can be connected with the above-mentioned macrofloras as shown in parenthesis. 1) Cyclobalanopsis-Carya assemblage (Seto Flora) 2) Cyclobalanopsis-Podocarpus assemblage (Syzygium flora) 3) Cyclobalanopsis-Abies assemblage (Yokooji Flora) 4) Quercus-Liquidambar assemblage (Sennan Flora) 5) Quercus-Taxodiaceae assemblage 6) Fagus-Quercus assemblage 7) Taxodiaceae-Zelkova assemblage 8) Metasequoia-Picea A assemblage (Ibaraki Flora) 9) Fagus-Nyssa assemblage (Shimagahara Flora) 10) Fagus-Cryptomeria assemblage 11) Fagus-Tsuga assemblage 12) Diploxylon-Cryptomeria assemblage 13) Picea-Cryptomeria assemblage 14) Picea-Haploxylon assemblage Based on the stratigraphic distribution of these pollen assemblages, 8 pollen zones, K 1 to K 8 in ascending order, are distinguished in these districts (ONISHI, 1975) and are used as the standard for correlation. Pollen analysis is also carried out on the samples from the other 5 districts in central and southwest Japan. As the result, the following pollen assemblages are added. 15) Ulmus-Zelkova assemblage 16) Haploxylon-Abies assemblage 17) Haploxylon-Cryptomeria assemblage 18) Taxodiaceae-Pinaceae assemblage The Pliocene and Pleistocene deposits of each district are divided into the following pollen zones. And each zone is correlated to the standard zone of Kinki and Tokai districts (Fig. 28). A) OITA DISTRICT : In total, 7 pollen assemblages and 4 pollen zones, named O 1 to O 4, are distinguished in the Oita Group and Oka Formation. B) SAN'IN DISTRICT : In the Plio-Pleistocene Tsunozu Group, 4 pollen assemblages and 3 pollen zones, called T 1 to T 3, are recognized. The middle and late Pleistocene deposits, in which 3 pollen assemblages are involved, compose zone S 1. The latest Pleistocene and Holocene deposits which involve 3 pollen assemblages compose zone S 2. C) HOKURIKU DISTRICT : The Omma Formation involves Picea-Haploxylon assemblage and composes zone H 1 and the Utatsuyama Formation has Fagus-Quercus assemblage and composes zone H 2. D) KANTO DISTRICT : In the Plio-Pleistocene Kazusa Group which have been divided into 6 pollen zones, here named B 1 to B 6, 6 pollen assemblages are distinguished. E) NIIGATA DISTRICT : In the Pliocene Chuetsu Group and the Plio-Pleistocene Uonuma Group, 4 pollen assemblages are recognized. Several pollen zones have already been reported. Summarizing these data, 8 pollen zones, named N 1 to N 8, are distinguished. Pollen zones obtained from 6 districts are summarized into the following 7 pollen zones in descending order. Abies Zone, Cryptomeria Zone, Fagus Zone, Metasequoia Zone, Taxodiaceae Zone, Liquidambar Zone, and Carya-Nyssa Zone. The Plio-Pleistocene boundary which have been proposed by ITIHARA in Kinki district approximately agrees with the base of the Metasequoia Zone. The correlation by means of these pollen zones is compared with the correlations based on the other criteria, such as the proboscidean fauna, the paleomagnetism and the absolute age. As the result, these correlations well agree with each other. The relations between pollen zones and the other criteria are as follows. A) Proboscidean Fauna The range of Elephas naumanni is restricted in the upper half of the Cryptomeria Zone and that of Stegodon orientalis is in the lower half of this zone. Stegodon cf. elephantoides occurs within the Liquidambar Zone. The coexistence of Elephas shigensis and Stegodon akashiensis is restricted approximately in the Metasequoia Zone. B) Paleomagnetism The lower boundaries of Brunhes, Matuyama and Gauss Epochs are respectively situated in the upper parts of Fagus, Liquidambar and Carya-Nyssa Zones. C) Absolute Age The boundary between Abies and Cryptomeria Zones is estimated to be about 25, 000 years B. P. based on 14C ages. The lower boundaries of Cryptomeria, Fagus and Metasequoia Zones are respectively estimated to be about 0.5, 1.0 and 2.0 million years based on fission-track ages.