Palynostratigraphy and climatic implications of Neogene deposits in the Himi area of Toyama Prefecture, Central Japan

Review of Palaeobotany and Palynology 117 (2001) 281±295

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Palynostratigraphy and climatic implications of Neogene deposits in the Himi area of Toyama Prefecture, Central Japan Wei-Ming Wang a,*, Takeshi Saito b, Tomio Nakagawa c a

Nanjing Institute of Geology and Palaeontology, Academia Sinica, 39 East Beijing Road, Nanjing 210008, China b Faculty of Science and Technology, Meijo University, Nagoya 468-8502, Japan c Maruoka Senior High School, Fukui 910-0293, Japan Received 1 February 2001; accepted for publication 18 July 2001

Abstract A palynological study on the well-outcropped sections in the Himi area of Central Japan yields new evidence of Neogene ¯oral and climatic changes. Five palynostratigraphical zones recognized from the strata show changes in palyno¯oras from the Middle Miocene to the Pliocene. Major changes in the palyno¯oras are indicated by the ¯uctuating occurrence of some elements such as Taxodiaceae, Tsuga, Picea, evergreen Quercus and now-extinct Tertiary types in Japan, re¯ecting a general trend of climate deterioration from before 13 to 2 Ma. This trend is punctuated by the re-expansion of warm-temperate types in the late Middle Miocene (13±9.2 Ma), and in part of the Early Pliocene (5.5±4 Ma). Our results are largely comparable to pollen data derived from the neighboring areas. The inferred climate is largely consistent with the pattern of Neogene climatic change revealed in marine sediment records of the Ocean Drilling Program and the Deep Sea Drilling Project, implying that the evolution of the Neogene climate in Japan has been primarily consistent with worldwide climatic change since the opening of the Sea of Japan. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Palynostratigraphy; climate implications; Neogene; Himi area; Central Japan

1. Introduction The Neogene of Japan provides an opportunity for investigation both palaeo¯oral and palaeoenvironmental studies in relation to changing geographical patterns. There is evidence that the Japanese Islands and the Asian Continent were connected prior to the opening of the Sea of Japan at about 22 Ma (Kano, 1993). A detailed study of the Neogene pollen ¯oras between Japan and the Asian Continent is anticipated to reveal some interesting features produced by the opening of the Sea of Japan and the Neogene climatic * Corresponding author. E-mail address: [email protected] (W.-M. Wang).

change. Here we take the Neogene palynostratigraphy and climate in the Himi area as a regional case study. The Neogene deposits outcropping in the Himi area, together with those in the Yatsuo area, are considered as standard Neogene sequences in the Hokuriku area of Central Japan (Morozumi and Koizumi, 1981). Many studies have been carried out mainly concerning stratigraphy, and involving some fossil groups including foraminifera (Hasegawa, 1979; Maiya et al., 1976), diatoms (Koizumi, 1985; Koizumi and Tanimura, 1985), and radiolaria (Nakaseko et al., 1972; Nakaseko and Sugano, 1973). As the Neogene deposits contain many tuff layers, the magnetostratigraphy of the strata has already been established (Satoguchi et al., 1999).

0034-6667/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0034-666 7(01)00097-5

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Fig. 1. Map of the Himi area showing the sampling sites.

After correlation of diatom sequences in the middle latitude western North Paci®c, diatom datum levels have been ranked and tied directly to the paleomagnetic reversal record (Itoh and Watanabe, 1997). Although the biostratigraphy of the study area is well established, this paper reports the ®rst pollen studies on the strata. We ®rst establish Neogene palynostratigraphic zones and explore their climatic implications, before evaluating our pollen data with results from some neighboring areas, as well as the marine sediment records of the Ocean Drilling Program and the Deep Sea Drilling Project. 2. Geological settings Neogene deposits outcropping in the Himi area adjacent to the Sea of Japan (Fig. 1) are divided into

the Taniguchi, Nakanami, Sugata, Ao and Yabuta Formations in ascending order (Morozumi and Koizumi, 1981; Watanabe, 1990). Our study focuses on the later three formations because the Taniguchi and the Nakanami Formations are not well represented as outcrops in the ®eld. Geological survey mainly follows cross-sections in the geological map of Watanabe (1990). According to the available geological data, together with our ®eld observations and estimates, the Sugata Formation, over 224 m in thickness, consists of mudstone and diatomaceous mudstone with glauconite developed at the top. The Ao Formation, which is ca. 208 m thick, consists almost entirely of mudstone. The Yabuta Formation, about 240 m in thickness, consists mainly of calcareous sandstone with calcareous nodules. All of the three formations are intercalated with many tuff layers, which are

W.-M. Wang et al. / Review of Palaeobotany and Palynology 117 (2001) 281±295

distinguishable for geological correlation. There is a hiatus between the Sugata and the Ao Formations, which is widely recognized in the studied area. As there is no sign of erosion at the top surface of the Sugata Formation, this hiatus was suggested to be formed by non-deposition, while the glauconite bed was formed during the hiatus (Watanabe, 1990). 3. Materials and methods We took samples at an average interval of about 8 m in the ®eld. All together 82 samples were taken, of which 54 samples were analyzed for the current study. Detailed sample localities and stratigraphic horizons of these studied samples are indicated in Figs. 1 and 2. Age control for the intervals analyzed for pollen derives from paleomagnetic measurements and diatom biostratigraphic data (Watanabe, 1990; Yanagisawa and Akiba, 1998). Preparation of the samples in the laboratory ®rst sieving dry powdered samples through a 60 mesh screen, then subjecting them to KOH (10%), HF (47%) and the acetolysis, and ®nally soaking them in ZnCl2 solution with a speci®c gravity of 2. Slides were prepared by mounting the pollen grains in glycerin jelly. Reference collections of modern Japanese and Chinese pollen taxa along with published morphological keys (Shimakura, 1973; Nakamura, 1980a,b; Wang et al., 1995) were used in pollen identi®cation. Pollen grains were identi®ed and counted on four slides for every sample. Counts of at least 250 grains were achieved for all samples, with the exception of several samples where pollen contents were too low. Spores were divided only into monolete and trilete types because of their low occurrence. Dino¯agellate cysts occurred frequently and were counted but not identi®ed further. Both spores and dino¯agellate cysts were excluded from the pollen sum that was used for calculating pollen percentages. However, relative representation of pollen grains, monolete spores, trilete spores and dino¯agellate cysts is shown in Table 1. 4. Results 4.1. Palynostratigraphic zones A total of 64 pollen taxa were identi®ed (Table 1),

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and the major ¯oral components are shown in the pollen diagram and Plates I±III. Pteridophyte spores were limited, making up 0.6±8.2% on average of each zone. Dino¯agellate cysts frequently occurred in the samples, and are especially rich in the upper part of the Sugata Formation, the middle and upper parts of the Ao Formation, and the lower part of the Yabuta Formation. Five palynostratigraphic zones were recognized from the studied beds on the basis of changes in the major pollen components (Fig. 3). Zone I (samples SG01±SG04 from the lower part of the Sugata Formation; Middle Miocene beyond 13 Ma in age). This zone is characterized by the predominance of Pinus-Psudolarix. Other gymnospermous pollen grains include moderate amounts of Tsuga, Taxodiaceae, Picea, along with small amounts of Keteleeria, Abies, Larix-Pseudotsuga, Dacrydium, Ephedra, etc. Angiospermous pollen grains have more consistent and lower representation. Some continuously occurred elements include evergreen Quercus, Carya, Ulmus-Zelkova, Liquidambar, deciduous Quercus, and Juglans-Pterocarya. Zone II (samples SG05±SG13 from the upper part of the Sugta Formation; late Middle Miocene to earliest Late Miocene, ca. 13±9 Ma in age). Angiospermous pollen grains in this zone show an increase in their representation while gymnospermous pollen grains decrease correspondingly. As a whole, there is no distinct change in the gymnospermous pollen component, but Pinus-Psudolarix is lower, and Taxodiaceae is slightly higher. Tsuga, Picea, and small amounts of Keteleeria, Abies, Cathaya, etc. are also present. The rise in angiospermous pollen abundance is mainly due to evergreen Quercus, Carya, Ulmus-Zelkova, Fagus, Deciduous Quercus, Juglans-Pterocarya, and Castanopsis type. Zone III (samples AO01±AO06 from the lower part of the Ao Formation; Late Miocene, ca. 6.4±5.5 Ma in age). This zone is distinguished by marked reductions in representation of evergreen Quercus and Carya. Conversely, both Taxodiaceae and Abies among the gymnospermous pollen, and Fagus among the angiospermous pollen show signi®cantly increased values. Artemisia pollen occurs from this zone onwards. Zone IV (samples AO07±YB06 from the middle and upper parts of the Ao Formation and the lower part of the Yabuta Formation; Early Pliocene, ca.

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Table 1 List of the pollen taxa and their minimum (average) maximum percentages, and percentage representation of total pollen grains, monolete spores, trilete spores and dino¯agellate cysts in the Neogene pollen zones of the Himi area Pollen Zone

Zone I

Zone II

Zone III

Zone IV

Zone V

Gymnospermous pollen Podocarpaceae Dacrydium Podocarpus

0(0.5)1.3 0(0.1)0.3

± 0(0.1)0.4

± ±

0(0.0)0.4 0(0.1)0.7

0(0.1)0.8 ±

19.7(32.0)45.0 0(0.1)0.5 0(1.0)2.2 1.3(2.6)4.0 3.4(5.3)6.7 1.6(2.8)4.9

9.7(14.6)21.9 0(0.5)1.5 0(0.9)2.3 0.4(2.2)4.5 1.4(6.3)13.5 0.7(2.1)3.9

2.8(5.1)7.2 0.3(2.3)3.7 1.9(4.9)7.8 0(0.4)1.9 1.4(8.0)18.1 0.6(1.3)2.0

5.5(14.6)23.2 1.8(10.0)15.3 0.7(2.9)8.6 0(1.3)3.4 3.7(6.7)12.4 0(2.8)4.4

3.8(11.6)19.1 0(4.1)13.7 0.4(1.2)3.3 0(0.7)1.8 0.5(6.9)14.4 0.7(2.2)6.8

0.4(1.1)1.7 7.4(13.3)25.1

0(0.1)0.4 5.3(13.2)21.6

0(0.1)0.4 9.2(13.3)21.9

0(0.1)0.4 6.6(19.7)39.3

0(0.0)0.7 6.7(23.1)35.8

0(0.1)0.3

0(0.0)0.3

0(0.0)0.3

0(0.0)0.4

0(0.1)0.5

± 0(6.8)15.6

0(0.1)1.1 6.5(13.2)26.3

± 16.7(24.3)38.4

± 0(5.9)14.7

0(0.2)1.9 4.1(13.0)31.6

±

0(0.0)0.3

0.2(1.3)3.3

0(0.5)1.7

0(0.4)1.8

Angiospermous pollen Salicaceae Salix

±

0(0.0)0.4

±

±

0(0.0)0.4

Juglandaceae Carya Juglans-Pterocarya Platycarya

3.6(6.1)9.4 0.3(1.0)2.3 ±

4.0(6.6)11.3 0.7(1.6)3.0 0(0.0)0.4

0.9(3.3)9.1 0.3(1.3)3.2 ±

0(1.8)6.3 0(0.9)3.5 0(0.0)0.4

0(0.5)1.6 0(0.4)1.8 ±

Betulaceae Alnus Betula

0(0.4)1.0 0(0.4)1.0

0(0.6)1.8 0(0.8)2.5

0.3(0.9)1.2 0(0.4)1.6

0(0.6)2.5 0(0.2)0.8

0(1.3)2.6 0(0.5)1.5

Corylaceae Corylus Carpinus

± 0(1.0)2.1

0(0.2)0.7 0(1.8)7.0

0(0.1)0.4 0.3(0.9)1.6

0(0.1)0.8 0(0.7)2.8

0(0.1)0.5 0(0.9)3.0

Fagaceae Fagus Deciduous Quercus Evergreen Quercus Castanopsis type

0(5.0)8.1 0.4(1.5)4.2 4.7(7.5)9.9 0(0.8)2.9

2.6(5.1)9.2 0.5(3.9)8.8 4.9(14.8)27.0 0.2(1.2)2.8

12.5(18.3)28.2 1.8(3.0)4.0 1.0(3.0)5.2 0(0.7)2.4

8.5(17.8)37.3 0(2.1)6.2 0.4(3.3)10.0 0(0.8)2.2

10.5(20.8)31.9 0(1.4)2.6 1.1(2.4)4.4 0(0.2)0.8

Ulmaceae Celtis-Aphananthe Hemiptelea Ulmus-Zelkova Ulmoideipites krempii

0(0.1)0.4 0(0.1)0.5 1.3(3.3)7.6 0(0.2)0.8

0(0.0)0.2 0(0.2)0.7 0.8(3.2)5.0 ±

0(0.0)0.2 0(0.1)0.3 1.2(2.1)3.2 ±

0(0.1)0.4 0(0.0)0.4 0(1.6)6.2 0(0.0)0.4

0(0.0)0.4 0(0.0)0.8 0.4(1.7)3.9 ±

Hamamelidaceae Liquidambar

2.2(2.7)3.4

0(1.3)3.0

0(1.2)2.4

0(2.1)4.1

0(0.2)0.8

Eucommiaceae Eucommia?

±

0(0.0)0.4

±

±

±

Pinaceae Pinus-Pseudolarix Cathaya Abies Keteleeria Picea Pinaceae gen. indet. (bissacate type) Larix-Pseudotsuga Tsuga Ephedraceae Ephedra Cupressaceae? Taxodiaceae Sciadopityaceae Sciadopitys

Fig. 2. Neogene geological column in relation to the diatom zonation (Yanagisawa and Akiba, 1998), and the sampling horizons of the Himi area.

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Table 1 (continued) Pollen Zone

Zone I

Zone II

Zone III

Zone IV

Zone V

Euphorbiaceae Sapium

±

±

±

±

0(0.0)0.4

Rutaceae?

±

0(0.0)0.3

±

±

±

Meliaceae Melia

0(0.1)0.3

±

±

±

±

Aceracea Acer

0(0.9)2.3

0(0.9)1.8

0(0.6)1.2

0(0.1)1.1

0(0.1)0.5

Hippocastanaceae Aesculus

±

±

±

0(0.0)0.4

±

Aquifoliaceae Ilex

0(0.2)0.4

0(0.1)0.7

0(0.2)0.5

0(0.0)0.4

0(0.9)14.6

Tiliaceae Tilia

0(1.0)2.2

0(0.8)2.2

0(0.2)0.6

0(0.4)1.6

0(0.5)3.9

Malvaceae Hibiscus

±

±

±

±

0(0.0)0.5

Elaeagnaceae Elaeagnus

0(0.1)0.3

0(0.0)0.3

±

0(0.0)0.7

0(0.1)0.5

Lythraceae Lagerstroemia

±

±

±

±

0(0.0)0.5

Alangiaceae Alangium

±

±

±

±

0(0.0)0.5

Nyssaceae Nyssa

0(0.2)0.7

0(0.0)0.2

0(0.2)0.5

0(0.1)1.1

0(0.3)1.1

Ericaceae

0(0.1)0.4

0(0.0)0.2

±

0(0.0)0.4

0(0.1)0.7

Styracaceae cf. Styrax

0(0.1)0.4

0(0.0)0.4

±

±

±

Symplocaceae Symplocos

±

0(0.1)0.4

0(0.1)0.3

±

0(0.0)0.4

Oleaceae Fraxinus Other Oleaceae

0(0.2)0.4 ±

0(0.2)0.7 ±

0(0.2)0.6 ±

0(0.2)0.8 0(0.0)0.4

0(0.1)0.4 0(0.0)0.4

Caprifoliaceae Lonicera

±

±

0(0.0)0.3

0(0.1)0.4

± 0(0.0)0.4

Liliaceae

±

±

±

±

Cyperaceae

±

0(0.1)0.4

0(0.2)0.6

0(0.0)0.4

±

Gramineae

0(0.3)0.7

0(0.4)1.3

0(0.3)0.6

0(0.2)1.1

0(0.5)2.3

Polygonaceae Polygonum Persicaria Fagopyrum ?

± ± ±

± 0(0.1)0.5 ±

± 0(0.0)0.3 ±

± 0(0.3)1.4 ±

0(0.0)0.5 0(0.1)1.4 0(0.0)0.4

Caryophyllaceae

±

±

0(0.1)0.4

±

±

Chenopidaceae

0(0.1)0.3

0(0.3)0.7

0(0.3)0.8

0(0.2)0.7

0(0.2)1.2

Ranunculaceae

±

0(0.1)0.7

±

0(0.0)0.8

±

Hydrocaryaceae Trapa

±

±

±

±

0(0.1)0.8

W.-M. Wang et al. / Review of Palaeobotany and Palynology 117 (2001) 281±295

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Table 1 (continued) Pollen Zone

Zone I

Zone II

Zone III

Zone IV

Zone V

Compositae Artemisia Other Compositae

± ±

± 0(0.2)0.4

0(0.9)1.9 0(0.1)0.6

0(1.1)2.9 0(0.2)0.8

0(1.4)4.2 0(0.3)1.4

Unknown Af®nities Fupingopollenites Indeterminable Types

0(0.1)0.4 0.3(0.6)1.0

0(0.0)0.4 0.7(1.7)4.0

± 0(0.4)0.9

0(0.0)0.4 0(0.3)1.2

0(0.0)0.4 0(0.8)4.2

Total Pollen Grains Total Monolete Spores Total Trilete Spores Total Dino¯agellate Cysts

81.7(90.3)96.5 0.8(6.4)14.3 0.3(1.8)2.9 1.1(1.6)2.5

61.7(80.6)93.5 0.3(1.4)3.8 0.3(0.6)0.9 2.0(17.4)37.0

82.4(89.9)95.5 0(0.6)1.3 ± 3.9(9.5)17.0

50.5(79.0)93.5 0(3.3)8.3 0(0.6)1.5 2.0(17.1)48.5

80.1(91.1)97.5 1.4(3.7)9.2 0(0.7)2.1 0(4.5)15.9

Fig. 3. Pollen diagram showing percentage representation of major ¯oral components in samples. Castanopsis type in the ®gure includes Castanopsis, Castanea, Pasania, and Lithocarpus.

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5.5±4 Ma in age). Taxodiaceae has declined substantially, while Cathaya has greatly increased values. Tsuga, Pinus-Psudolarix, Picea and Abies are also conspicuous among the gymnospermous pollen taxa. Angiospermous pollen is best represented by Fagus, with a partial recovery of evergreen Quercus, Liquidambar, Carya, and others in the lower-middle spectra of the zone. Zone V (samples YB07±YB23 from the middle and upper parts of the Yabuta Formation; latest Early Pliocene to Late Pliocene, ca. 4±2 Ma in age). This zone is characterized by increased and highly variable values of Taxodiaceae. Other gymnospermous pollen grains such as Pinus-Psudolarix, Cathaya, Tsuga, and Picea also display some ¯uctuations. Angiospermous pollen grains apart from Fagus have low values. There is a slight increase in the representation of some herbaceous types, such as Artemisia and Gramineae. 4.2. Major ¯oral patterns Palynostratigraphic zones show clearly ¯oral changes in the Neogene of the Himi area. The ¯ora may be divided into major ¯oral elements, such as warm types including now-extinct Tertiary plants, gymnosperms with the exception of Cathaya and some other now-extinct types, herbaceous plants, and others. Among the warm types, evergreen Quercus is most distinct in the upper Middle Miocene to the lowest Upper Miocene (Zone II). It declines in the Upper Miocene (Zone III) and partly recovers in the Lower Pliocene (lower part of Zone IV). The Upper Pliocene shows some ¯uctuation in the occurPlate I. All ®gures £ 400. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Pinus-Pseudolarix (Pinus type). AO06. Pinus-Pseudolarix (Pseudolarix type). SG06. Cathaya. AO05. Cathaya. AO06. Larix-Pseudotsuga. SG02. Keteleeria. SG09. Abies. SG09. Picea. SG09. Abies. AO03. Picea. AO02. Tsuga. AO03. Dacrydium. SG02.

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rence of the pollen grains (Zone V). Liquidambar, which diminishes through the Neogene, partly regains its representation in the Lower Pliocene (Zone IV). Both Carya and Keteleeria more or less decline upwards. Cathaya shows its lowest occurrence in the Middle Miocene (Zones I, II). It ¯ourishes in the Lower Pliocene (Zone IV), and declines with some ¯uctuations in the Upper Pliocene (Zone V) (Saito et al. 2000). Among the other gymnospermous plants, Taxodiaceae is well represented in most of the studied beds, and becomes especially distinct in the Upper Miocene (Zone III) and then ¯uctuates from the latest Lower Pliocene (Zone V). Pinus-Psudolarix has constant representation through the studied sediments, and is especially rich in the Middle Miocene (Zone I). Both Tsuga and Picea more or less increase their percentages through the sequence. Fagus among the others thrives from the Upper Miocene (Zone III). Herbs are not an important ¯oral component in the pollen ¯oras, but become more frequent in the Upper Pliocene (Zone V). Artemisia makes its appearance in the Upper Miocene (Zone III).

5. Discussion 5.1. Climatic implications Pollen ¯oras from the Neogene Himi area suggest a general tendency towards climatic deterioration from before 13 to 2 Ma. It is mainly indicated by a decrease in the warm-temperate evergreen taxon Quercus and by an increase in the cool-temperate genus Fagus and

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the cool-temperate or boreal taxon Tsuga. This trend is punctuated by re-expansions of warm-temperate types. A ®rst climatic reversal is recognized in the late Middle Miocene to the earliest Late Miocene ¯oras (Zone II, ca. 13±9.2 Ma), by the recovery of some major warm-temperate taxa such as evergreen Quercus and Tertiary taxa such as Carya. A cooling in the Late Miocene at about 6.4±5.5 Ma follows, when Taxodiaceae and Fagus increased signi®cantly and the warm-temperate and Tertiary types fell sharply (Zone III). There are no data between 9.2±6.4 Ma because of the stratigraphic hiatus. A decline in Taxodiaceae, a ¯ourish of Cathaya, and a partial recovery of the warm-temperate and Tertiary types in the Early Pliocene (Zone IV) imply another smaller climatic amelioration. The climate then cools in the Late Pliocene, as indicated by the abundance of Tsuga and Fagus (Zone V). Fluctuations in pollen taxa within this Zone might re¯ect climatic variations such as glacial-interglacial cycles. However, our sampling intervals are too coarse to examine any cyclicity in detail. Evidence from the Neogene of central and western Japan displays a climatic optimum around 16 Ma. It is revealed by evidence for mangrove pollen (Yamanoi, 1984; Saito et al., 1995), mangrove swamp mollusks, limestone of coral reef condition, etc. (Itoigawa and Yamanoi, 1990). This warm climate is followed by an abrupt cooling that begun at 15 Ma as re¯ected by a change in the marine fauna from the tropicalsubtropical Kadonosawa type to the cold-water Shiobara-Yama type in central and northern Japan (Tsuchi, 1991). This cooling event was also recognized in the pollen ¯oras of the Oga Peninsula,

Plate II. All ®gures £ 1000. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Ephedra. SG09. Taxodiaceae. AO03. Taxodiaceae. SG09. Sciadopitys.AO02. Carya. SG09. Juglans-Pterocarya (Pterocarya type). SG13. Juglans-Pterocarya (Juglans type). SG09. Corylus. SG13. Carpinus. AO02. Fagus. AO08. Fagus. AO04. Alnus. SG06.

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Northeast Honshu of Japan (Wang and Yamanoi, 1996). Our current data just cover this period of climatic deterioration. To sum up, pollen ¯oras from the Neogene of the Himi area show an overall trend towards climatic deterioration from the Middle Miocene, but this process was punctuated by the climatic reversals mainly in the late Middle Miocene, and part of the Early Pliocene. 5.2. Pollen comparison with the neighboring areas Yamanoi (1978, 1992, 1998) divided the Neogene pollen ¯oral record of Japan into zones NP-1 to NP-6 mainly based on the pollen data of ODP Leg 127 and the sediments along the coast of the Sea of Japan. Pollen zones of this study are correlated with Yamanoi's NP-3 to NP-6. Zones I and II are correlated with NP-3 (13±6.5 Ma) characterized by a high proportion of Carya and Liquidambar. Zones III and IV are comparable with NP-4 (6.5±4 Ma) characterized by high abundance of Taxodiaceae and Fagus. We here propose to subdivide zone NP-4 into NP-4a and NP-4b because of the abundance of Cathaya in Zone IV. Zone V may be correlated with NP-5 (4±2.5 Ma), characterized by scarce occurrence of Carya and Liquidambar. Pollen analyses of cores taken on ODP Legs 127 and 128 in the Sea of Japan exhibit a Late Miocene decline in deciduous and Tertiary types, and a subsequence rise in boreal components, a mid-Pliocene reversal of these trends centered on 4 Ma, followed by Late Pliocene/Pleistocene high-frequency, highamplitude ¯uctuations of temperate and boreal pollen

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types (Heusser, 1992a,b). These results are also comparable with our data, but the re-expansion of Tertiary and warm-temperate types in the Pliocene of the Himi area is not as distinct as those described by Heusser that are comparable to or greater than Middle-Late Miocene levels. In addition, herbs in the Late Pliocene sequence at ODP Legs 127 and 128 increased remarkably, while they are not so distinct in our data. This may be partly due to the pollen source in the Sea of Japan including vegetation of the Asia Continent. 5.3. Regional and global Climatic comparison Tanai (1992); Uemura (1993) produced a climatic change curve on the basis of foliar physiognomy. The overall deterioration tendency since Late Miocene is broadly comparable with our data. However, detailed comparison is impossible because mega-fossil plants are scarcely distributed constantly in outcrops, and age control on the mega-fossil data is not always suf®cient. Ozawa et al. (1995) summarized the marine climate on the basis of molluscan fauna since the Early Miocene in Japan. They recognized six warm events. Of them, the fourth warm event (ca. 11.5±10 Ma) may be correlated with the uppermost part of the Zone II, when evergreen Quercus percentages were highest. The ®fth warm event (ca. 7±4.5 Ma) is not consistent with our data. However, our data shows a small warming represented by an increase of warm types such as evergreen Quercus and Liquidambar and high percentage of Cathaya in the Zone IV (ca.

Plate III. All ®gures £ 1000. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Deciduous Quercus. AO03. Evergreen Quercus. AO06. Evergreen Quercus. SG09. Castanopsis type. SG13. Ulmus-Zelkova. SG09. Ulmus-Zelkova. AO03. Liquidambar. AO04. Tilia. SG09. Acer. AO02. Ilex. YB22. Chenopodiaceae. AO02. Polygonum. YB13. Artemisia. AO03.

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5.5±4 Ma). The sixth warm event (3±0.8 Ma) is dif®cult to compare because our data indicate clear climatic ¯uctuations at that time. This comparison shows that there are some differences between marine and land climatic records in the Neogene of Japan. Leroy et al. (1999) summarized the global climatic events of the Pliocene mainly based on pollen data and oxygen isotope curves. The early Pliocene climate shows generally warm conditions with the ®rst Pliocene cooling at 4.5 Ma, and the beginning of a sustained temperature decline at 3.6 Ma (Leroy et al., 1999). The warm conditions are comparable with the increase in warm elements and development of Cathaya in our Zone IV. However, our data do not show clear cooling around 4.5 Ma. After 3.6 Ma climate deteriorated with a warming around 3.3±3.15 Ma and cooling leading to Late Pliocene glaciations from 3.15 Ma, and glacial-interglacial cycles from 2.6 Ma (Leroy et al., 1999). This climatic pattern is concordant with the ¯uctuations in the pollen ¯ora of the Zone V, but it is dif®cult to correlate in detail. Kennett (1996) reviewed polar climatic evolution during the Neogene, and considered that cooling and cryospheric development did not proceed uniformly but were punctuated by periods that represent more rapid transitions from one climatic state to another. It is believed that polar climatic, oceanographic and cryospheric processes have had great in¯uence on global environmental history (Kennett, 1977). Important Neogene cooling steps occurred during the Middle Miocene (ca. 14.5±14 Ma), the Late Miocene (ca. 6.5±5 Ma), and the Late Pliocene

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(3.2±2.7 Ma). These cooling steps represent cooling at the high latitudes and in the deep ocean, major expansion of the polar ice sheet, and important changes in the deep-water circulation (Kennett, 1996). The major cooling periods re¯ected by the Neogene pollen data of the Himi area are largely comparable with the polar climatic evolution, implying that the evolution of the Neogene climate in Japan has been mostly consistent with the worldwide climatic pattern since the opening of the Sea of Japan.

and T. Tanai's constructive criticisms greatly improved the manuscript. This project is supported by the Japan Society for the Promotion of Science, the Daiko Foundation (Nagoya), and partly by the Major Basic Research Projects of Ministry of Science and Technology, China (G2000077700) and the National Science Foundation of China (39930020).

6. Conclusion

Hasegawa, S., 1979. Foraminifera of the Himi Group, Hukuriku Province, Central Japan. Tohuku University Science Report, Series 2 (Geology) 49 (2), 89±163. Heusser, L.E., 1992a. Neogene palynology of Holes 794A, 795A, and 797B in the Sea of Japan: stratigraphic and paleoenvironmental implications of the preliminary results. Proceedings of the Ocean Drilling Program, Scienti®c Results 127/128, 325±339. Heusser, L.E., 1992b. Stratigraphic and paleoenvironment implications of Neogene palynology of ODP sites 794, and 797 in the Sea of Japan. In: Tsuchi, R., Ingle, J.C. (Eds.), Paci®c Neogene: Environment, Evolution and Events. University of Tokyo Press, Tokyo, pp. 3±13. Itoh, Y., Watanabe, M., 1997. Magnetostratigraphy of Neogene rocks around the Himi area in Toyama Prefecture, Japan (in Japanese with English abstract). Bulletin of Geological Survey in Japan 48, 339±346. Itoigawa, J., Yamanoi, T., 1990. Climatic optimum in the MidNeogene of the Japanese Islands. In: Tsuchi, R. (Ed.), Paci®c Neogene Events, Their Timing, Nature and Interrelationship. University of Tokyo Press, Tokyo, pp. 3±14. Kano, K., 1993. Cenozoic history of the Japanese Islands (in Japanese with English abstract). Hokuriku Geology Institute 3, 33±50. Kennett, J.P., 1977. Cenozoic evolution of Antarctic glaciation, the Circum-Antarctic Ocean, and their impact on global paleoceanography. Journal of Geophysics Research 82 (27), 3843±3860. Kennett, J.P., 1996. A review of polar climatic evolution during the Neogene, based on the marine sediment record. In: Vrba, E.S., Denton, G.H., Partridge, T.C., Burckle, L.H. (Eds.), Paleoclimate and Evolution, with Emphasis on Human Origins. Yale University Press, New Haven and London, pp. 49±64. Koizumi, I., 1985. Diatom biochronology for late Cenozoic northwest Paci®c. The Journal of the Geological Society of Japan 91, 195±211. Koizumi, I., Tanimura, Y., 1985. Neogene diatom biostratigraphy of the middle latitude western North Paci®c. Initial Reports DSDP 86, 269±300. Leroy, S.A.G., Wrenn, J.H., Suc, J.-P., 1999. Global setting to comparative charts of regional events. In: Wrenn, J.H., Suc, J.-P., Leroy, S.A.G. (Eds.). The Pliocene: Time of Change. American Association of Stratigraphic Palynologists Foundation, Texas, pp. 1±12.

Five palynostratigraphical zones recognized from the Middle Miocene to the Upper Pliocene show changes in the palyno¯oras, which are comparable to the pollen results from the neighboring areas of Northeast Honshu and the Sea of Japan. Their re¯ected climate is largely consistent with the Neogene climatic evolution revealed by the marine sediment records of the Ocean Drilling Program and the Deep Sea Drilling Project. Major changes in the palyno¯oras are indicated by ¯uctuations in occurrence of some elements such as Taxodiaceae, Tsuga, Picea, evergreen Quercus and now-extinct Tertiary types in Japan, which mostly implicate variation in climate. Pollen ¯oras in the studied area show an overall climatic deterioration, but this tendency is punctuated as warm-temperate types re-expanded in the late Middle Miocene and part of the Early Pliocene. There are interesting features in pollen representation. Taxodiaceae is well represented in most of the studied beds, and becomes especially distinct in the Late Miocene and from the latest Early Pliocene. Cathaya shows its major occurrence in the Middle Miocene. It ¯ourished in the Early Pliocene, and gradually declined in the Late Pliocene. Fagus has been thriving since the Late Miocene. Herbs were not an important component of the pollen ¯oras, but Artemisia made its appearance in the Late Miocene. Acknowledgements We thank M. Yoshino in the Faculty of Science and Technology, Meijo University (Nagoya) for his kind encouragement and help in the work. A. P. Kershaw

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