Reconstruction of paleovegetation and paleoclimate in the Early and Middle Eocene, Hainan Island, China

Climatic Change (2009) 92:169–189 DOI 10.1007/s10584-008-9457-2 Reconstruction of paleovegetation and paleoclimate in the Early and Middle Eocene, Hainan Island, China Yi-Feng Yao · Subir Bera · David K. Ferguson · Volker Mosbrugger · Khum N. Paudayal · Jian-Hua Jin · Cheng-Sen Li Received: 3 January 2007 / Accepted: 17 April 2008 / Published online: 16 September 2008 © Springer Science + Business Media B.V. 2008 Abstract The Early–Middle Eocene palynoflora and paleoclimate of Changchang Basin, Hainan Island, South China, is described in the present paper and is compared with that of the Middle–Late Eocene, Hunchun City, Jilin Province, North China. Y.-F. Yao · C.-S. Li (B) State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, People’s Republic of China e-mail: lics@ibcas.ac.cn Y.-F. Yao e-mail: yaoyf@ibcas.ac.cn S. Bera Department of Botany, University of Calcutta, Kolkata 700019, India e-mail: berasubir@yahoo.co.in D. K. Ferguson Department of Paleontology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria e-mail: david.kay.ferguson@univie.ac.at V. Mosbrugger Senckenberg Forschungsinstitut und Naturmuseum, Senckenberganlage 25, 60325 Frankfurt am Main, Germany e-mail: volker.mosbrugger@senckenberg.de K. N. Paudayal Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal e-mail: khum99@gmail.com J.-H. Jin (B) School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, People’s Republic of China e-mail: lssjjh@mail.sysu.edu.cn 170 Climatic Change (2009) 92:169–189 The nearest living relatives (NLRs) of the recovered palynotaxa suggest a subtropical evergreen or deciduous broad-leaved forest at the center of the basin but a temperate evergreen or deciduous broad-leaved forest and needle-leaved forest growing in the peripheral part of the basin. Based on the climatic preferences of the NLRs, the climate in the Changchang Basin during the Early–Middle Eocene was warm and humid subtropical with a mean annual temperature of 14.2–19.8◦ C, a mean temperature of the warmest month of 22.5–29.1◦ C, a mean temperature of the coldest month of 1.7–11.9◦ C, a difference of temperature between coldest and warmest months of 12.1–24.6◦ C, a mean annual precipitation of 784.7–1,113.3 mm, a mean maximum monthly precipitation of 141.5–268.1 mm and a mean minimum monthly precipitation of 6.9–14.1 mm. A comparison of the palynoflora and paleoclimate between the Changchang Basin and Hunchun City, suggests essentially a similar climate in South and North China during Eocene time in contrast to the oceanic tropical climate in South China and cool dry temperate climate in North China as at present. 1 Introduction Hainan Island, 33,920 km2 in area, is the second largest continental island in China and located between 18◦ 10′ –20◦ 10′ N and 108◦ 37′ –111◦ 03′ E. It was separated from the Leizhou Peninsula, China mainland by the Qiongzhou Strait in the Middle Pleistocene as a result of volcanic activity (Fig. 1A, B). From the center to the edge of Hainan Island, the topography gradually changes from mountain to highland and plain. The current climate on the island is of a seasonal and oceanic tropical type with a mean annual temperature of 23.8◦ C and a mean annual precipitation of 1,684.5 mm. The modern vegetation of Hainan Island is represented by tropical seasonal rain forest and rain forest in the mountainous area and mangrove forest along the seashore. The vegetation components are dominated by elements of tropical flora and have a close relationship with the southeast Asiatic flora. The Tertiary strata on Hainan Island are mainly distributed in its northern (Haikou subarea) and southwestern (Sanya subarea) parts (Lei et al. 1992; Jin et al. 2002; Table 1). The Haikou subarea comprises the Fushan- Changpo- JialaiJiaju- and Changchang Basins. The deposits in this subarea range from Paleocene to Pliocene in age. The Paleogene of this subarea belongs to continental deposits with abundant organic mudstone, while the Neogene is composed of marine deposits dominated by detrital rock. The deposits in the Sanya subarea are exposed in the Yinggehai Basin and are Oligocene in age. The Changchang Basin is a Cenozoic basin (about 34 km2 in area) located in the northeastern part of Hainan Island (Fig. 1A). The Paleocene and Eocene strata of this basin are very well developed, but the Oligocene deposits are missing. The Changchang sequence of the Paleogene is divided into three formations from bottom to top (Table 1). These are the Changtou Formation of Paleocene age and Changchang and Wayao Formations of Eocene age. The Changchang section in Changchang Basin, northeastern Hainan Island (Fig. 1B) consists of two parts: a lower part of multi-colored lacustrine facies and an upper part of dark colored Climatic Change (2009) 92:169–189 171 Fig. 1 Location of Changchang Basin in Hainan Island (A). Detail map around Jiazi Town, Qiongshan City (B) 172 Table 1 Cenozoic strata of Hainan Island (Jin et al. 2002) Geological period Neogene Sedimentary basin Fushan Basin Pliocene Miocene Changpo Basin L Late, M middle, E early; Fm. formation Jialai Basin Jiaju Basin Changchang Basin Yinggehai Basin Pliocene Pliocene Dengloujiao Fm. Changpo Fm. Changpo Fm. Yinggehai Fm. Huangliu Fm. Meishan Fm. Sanya Fm. Wayao Fm. Wenshicun Fm. Haoxian Fm. Changchang Fm. Changtou Fm. Climatic Change (2009) 92:169–189 Wanglougang Fm. Wanglougang Fm. L Dengloujiao Fm. Dengloujiao Fm. M Jiaowei Fm. Changpo Fm. E Xiayang Fm. Paleogene Oligocene L–M Weizhou Fm. E Liushagang Fm. The first member Eocene L The second member M The third member E Paleocene Changliu Fm. Climatic Change (2009) 92:169–189 173 lake-swamp facies, 99.3 m in thickness (Lei et al. 1992) (Fig. 2). This section is assigned to the Changchang Formation of Early–Middle Eocene age (Table 1). Earlier, some paleobotanical and palynological studies had been carried out on the Changchang Formation, Changchang Basin, Hainan Island (Guo 1979; Zhang 1980; Lei et al. 1992). This paper aims to reconstruct the climate of the Changchang Basin Palynomorphs in each palynological zone Lithology Thickness Fig. 2 Stratigraphic section of Changchang Basin and palynomorphs in each palynological zone 174 Climatic Change (2009) 92:169–189 during the Early–Middle Eocene based on the climatic preferences of the nearest living relatives (NLRs) of the recovered palynotaxa. The study also compares the flora and climate of this part of South China with those of Middle–Late Eocene sedimentary strata of Jilin Province, North China to discover whether there was any difference in flora and climate in North and South China during Eocene time. 2 Materials and methods Fifty-five palynological samples were collected from this section in the field. The samples were analyzed following standard techniques (Peck 1974; Moore and Webb 1978; Moore et al. 1991; Li and Du 1999). No pollen grains or spores were found in 20 samples, fewer than 200 grains (5–187) were found in 13 samples, while more than 200 grains (218–2,028) were found in 22 samples. The pollen grains and spores were identified using the palynological literature and monographs (Sun et al. 1981, 1982, 1989; Wu and Yu 1981; Zhang 1981; Yu 1983; Lei 1985; Li 1989; Zhang et al. 1990; Lei et al. 1992; Li and Qing 1994; Song et al. 1999). The reconstruction of the Early–Middle Eocene climate in the Changchang Basin is attempted following the Coexistence Approach (CoA, Mosbrugger and Utescher 1997; Xu et al. 2000). The method is based on the assumption that the climatic tolerance of a fossil taxon is similar to that of its Nearest Living Relative (NLR). The procedure for obtaining the climatic tolerance of a NLR is as follows. Firstly, the climatic parameters of all NLRs (seed plants) in a palynoflora are obtained from the climatic records within their modern distribution area (Wu and Ding 1999). Secondly, the maximum and minimum of each parameter of each NLR are established. Thirdly, the climatic interval of each parameter of all NLRs is overlapped and the coexistence interval of all NLRs is obtained. The modern climatic data recorded by the meteorological stations of China are extracted from the publications of the Information Department of Beijing Meteorological Center (IDBMC 1983a, b, c, 1984a, b, c). Sometimes the distribution area of a genus is likely to extend beyond China. In the case of Quercus, Kou et al. (2006) have been able to show that the climatic data from the rest of its distributional area fall within the range of tolerance of Quercus based on Chinese data. Herein, we give the genus Ephedra as another example. We checked the recent publications which mentioned the genus with the meteorological record in NW Patagonia, Argentina (Jose et al. 1994), Sierra Nevada (Christopher et al. 2007), Sonoran Desert (The Deserts of North America, http://instruct.uwo.ca/biology/320y/namdes.html), Turkey (Deniz and Sümbül 2004), Central Asia (McGinley 2007), Iran (Heshmati 2007) and Saudi Arabia (Karemy and Zayed 1992) (Table 2); These also demonstrate that all the records fall within the range of tolerance of Chinese Ephedra. In the present paper, the following climatic parameters are estimated, viz., the Mean Annual Temperature (MAT), the Mean Temperature of the Warmest Month (MWMT), the Mean Temperature of the Coldest Month (MCMT), difference of temperatures between coldest and warmest months (DT), the Mean Annual Precipitation (MAP), the Mean Maximum monthly Precipitation (MMaP) and the Mean Minimum monthly Precipitation (MMiP). Climatic Change (2009) 92:169–189 Table 2 The MAT and MAP in the distribution area of Ephedra out with China based on recent studies of the genus Place Location Altitude (m.a.s.l.) MAT (◦ C) MAP (mm) References Sonoran desert, N America White Mountains, Sierra Nevada NW Patagonia, Argentina Antalya, Turkey Southern deserts, Central Asia Sand deserts, central plateau, Iran Baha plateau, Saudi Arabia – – – 36◦ N, 29◦ E – – 19◦ 50′ –20◦ 18′ N, 41◦ 38′ –42◦ 10′ E – 150–950 1,250 900–1,400 1,660 – 500–1,200 1,700–2,400 – 13.3 7.4 7.5 ∼ 16 15–18 – ∼ 300 142 304 616.5 70–125 <200 360.1 The Deserts of North America (2007) Christopher et al. (2007) Jose et al. (1994) Deniz and Sümbül (2004) McGinley (2007) Heshmati (2007) Karemy and Zayed (1992) – −4.9 − 19.8 16.4–1,113.3 Present paper The tolerance of Ephedra from Chinese data 175 176 Climatic Change (2009) 92:169–189 Fig. 3 Palynomorphs recovered from the Changchang Basin, Hainan Island, compared with the palynoflora of Hunchun City, Jilin Province Climatic Change (2009) 92:169–189 177 3 Results 3.1 Description of polynological zones Forty-six palynomorphs were identified in the studied geological section (Fig. 3), including 36 angiosperm, four gymnosperm and six pteridophyte taxa. Some selected spores and pollen recovered from the Changchang Basin are shown in Fig. 4. The palynoassemblage is characterized by the dominance of angiosperm pollen (94.5%). Among these, pollen grains of Fagaceae, viz., Faguspollenites Raatz, Fig. 4 A selection of the spores and pollen recovered from the Changchang Basin (all palynomorphs are illustrated at the same magnification. Scale bar = 80 µm) 1–4 Pinuspollenites, 5 Taxodiaceaepollenites, 6–8 Liquidambarpollenites, 9 Ulmipollenites, 10–11 Tricolpopollenites, 12 Unidentified pollen, 13 Gothanipollis, 14 Margocolporites, 15–16 Momipites, 17, 19 Cupuliferoipollenites, 18 Quercoidites, 20 Retimultiporopollenites, 21 Rutaceoipollenites, 23 Pterisisporites, 24–27 Polypodiaceae 178 Climatic Change (2009) 92:169–189 Fig. 5 Pollen percentage diagram of Changchang Basin, Hainan Island Cupuliferoipollenites Potonié, Quercoidites Potonié and Castanopsis (D. Don) Spach, were prevalent in the assemblage, constituting 88.9% of the total pollen and spores. Some representative elements of tropical and subtropical plants such as Proteacidites Cookson and Myrtaceidites Cookson et Pike, also appeared in the flora. Gymnosperm pollen was rare and represented by less than 3%. Pinuspollenites Raatz with 2.7% dominates among gymnosperms. Tsugaepollenites Potonié et Venitz, Ephedripites Bolchovitina and Taxodiaceaepollenites Kremp were sporadically present (0.1%). Pteridophytes spores were also low in frequency (2.7%), being represented by Polypodiaceaesporites Thiergart (2.5%), Pterisisporites Sung et Zheng (0.09%), Triletes Reinsch (0.05%), Lygodiumsporites Thiergart (0.04%), Hymenophyllumsporites Rouse (negligible) and Cyathidites Couper (negligible). Three palynological assemblages of the Changchang section could be recognized from top to bottom (Fig. 5), as follows: Zone 1 (0–63.8 m in depth) This palynological assemblage is barren of any pollen or spores from 0 to 46 m, while 30 types of palynomorphs were identified in the deposits from 46 to 63.8 m, including 22 angiosperm, four gymnosperm and four pteridophyte taxa. Angiosperm pollen dominates and reaches 96.9%, with mostly deciduous broad-leaved trees now growing in the temperate and subtropical regions. Fagaceae pollen are very frequent (94.36%) in this zone and are represented by Faguspollenites, Cupuliferoipollenites, Quercoidites and Castanopsis. Myrtaceidites, Proteacidites and Hamamelidaceae are among the tropical and subtropical taxa present in the assemblage. Gymnosperm taxa (2.6%) are represented by Pinuspollenites, Tsugaepollenites, Ephedripites and Taxodiaceaepollenites. Pteridophytes are uncommon (0.5%), being represented by Polypodiaceaesporites, Pterisisporites, Triletes and Cyathidites. Zone 2 (63.8–79.8 m in depth) Only 18 types of palynomorphs are found in this zone, comprising 14 angiosperm, two gymnosperm and two pteridophyte taxa. Like zone 1, angiosperm pollen dominates the palynoassemblage of this zone (97.9%) and is represented mostly by Fagaceae pollen. Few tropical and subtropical taxa of Monocolpopollenites Pflug et Thomson and Hamamelidaceae are present along with some temperate deciduous broadleaved tree taxa such as Betulaepollenites Potonié, Alnipollenites Potonié, Momipites Wodehouse and Ulmipollenites Wolff. The total percentage of gymnosperm taxa accounts for 2.0%. Pinuspollenites and Taxodiaceaepollenites are recorded with 0–3.9% and 0–2.6%, respectively. Two types of ferns, viz., Polypodiaceaesporites (0–0.2%) and Pterisisporites (0–0.1%) are also present sporadically in this zone. Zone 3 (79.8–99.3 m in depth) Forty-two types of palynotaxa were identified from this zone, of which 34 are angiosperm, three gymnosperm and five pteridophyte taxa. Angiosperm pollen ◮ Climatic Change (2009) 92:169–189 179 180 Climatic Change (2009) 92:169–189 occurs in a lower frequency than that in zones 1 and 2, but remains predominant and reaches 92.4% of the pollen sum. Faguspollenites, Momipites,Betulaepollenites and Juglanspollenites Raatz represent deciduous broad-leaved tree taxa. Few herbaceous taxa (Cucurbitaceaepollenites, Corsinipollenites Nakoman, Cruciferaeipites Zheng and Chenopodipollis Krutzsch) are also present at low frequency (0.1–0.2%). The pollen types of tropical and subtropical taxa Myrtaceidites, Palmaepollenites, Proteacidites, Gothanipollis Krutzsch, Symplocoipollenites Potonié, Margocolporites Ramanujam ex Srivastava and Hamamelidaceae increase in this zone. Gymnosperm taxa (3.0%) are represented by Pinuspollenites, Ephedripites and Taxodiaceaepollenites. A comparatively higher percentage of pteridophyte spores (4.6%) with Polypodiaceaesporites, Pterisisporites, Triletes, Lygodiumsporites and Hymenophyllumsporites are recorded in this zone. 3.2 Coexistence analysis on the whole palynoassemblage and each of the palynological zones Thirty-six fossil palynomorph taxa used in our CoA approach are shown in Table 3. The seven climate parameters (MAT, MWMT, MCMT, DT, MAP, MMaP and MMiP) from the CoA approach on the whole palynoassemblage are shown in Table 4 and Fig. 6. The climatic parameters have also been determined for each of the three palynological zones (Table 4, Fig. 7). Coexistence analysis of the palynological zones 1 and 3 gives exactly the same result as that obtained from the whole palynoassemblage (The coexistence intervals of 14.2–19.8◦ C for MAT, 22.5– 29.1◦ C for MWMT, 1.7–11.9◦ C for MCMT, 12.1–24.6◦ C for DT, 784.7–1,113.3 mm for MAP, 141.5–268.1 mm for MMaP, and 6.9–14.1 mm for MMiP) (Table 4). However, palynological zone 2 gives slightly wider coexistence intervals but still overlapping Table 3 Palynomorph taxa used in CoA (Song et al. 1999) Fossil palynomorph taxa NLRs Fossil palynomorph taxa NLRs Pinuspollenites Tsugaepollenites Taxodiaceaepollenites Ephedripites Faguspollenites Pinus L. Tsuga Carr. Taxodiaceae Ephedra Tourn. ex Linn. Fagus L., Castanopsis (D. Don) Spach Castaneae Mill. Quercus L. Anacardiaceae, Rhus (Tourn.) L. Ilex L. Liquidambar L. Rutaceae Betula L. Alnus Mill. Loranthaceae Juglandaceae Cruciferae Chenopodiaceae Proteacidites Juglanspollenites Multiporopollenites Caryapollenites Magnolipollis Proteaceae Juglans L. Juglans L. Carya Nutt. Magnolia L. Salixipollenites Euphorbiacites Fraxinoipollenites Salix L. Euphorbiaceae Oleaceae Hamamelidaceae Cucurbitaceaepollenites Monocolpopollenites Palmaepollenites Triatriopollenites Margocolporites Ulmipollenites Corsinipollenites Tiliaepollenites Hamamelidaceae Cucurbitaceae Palmae Palmae Myricaceae Caesalpiniaceae Ulmus L. Onagraceae Tilia L. Cupuliferoipollenites Quercoidites Rhoipites Ilexpollenites Liquidambarpollenites Rutaceoipollenites Betulaceoipollenites Alnipollenites Gothanipollis Momipites Cruciferaeipites Chenopodipollis Climatic Change (2009) 92:169–189 Table 4 Coexistence intervals of the whole palynoassemblage and each of the three palynological zones Palynological zone Number of taxa MAT (◦ C) MWMT (◦ C) MCMT (◦ C) DT (◦ C) MAP (mm) MMaP (mm) MMiP (mm) Whole palynoassemblage 3 2 1 36 34 15 24 14.2–19.8 14.2–19.8 13.3–22.6 14.2–19.8 22.5–29.1 22.5–29.1 22.5–29.1 22.5–29.1 1.7–11.9 1.7–11.9 1.7–15.3 1.7–11.9 12.1–24.6 12.1–24.6 10.7–26.0 12.1–24.6 784.7–1,113.3 784.7–1,113.3 613.9–1,900.3 784.7–1,113.3 141.5–268.1 141.5–268.1 137.3–387.9 141.5–268.1 6.9–14.1 6.9–14.1 2.0–54.0 6.9–14.1 181 182 Climatic Change (2009) 92:169–189 Fig. 6 Climate data of the coexistence area of 36 extant taxa of seed plants in China. 1 Pinus, 2 Taxodiaceae, 3 Tsuga, 4 Ephedra, 5 Juglans, 6 Carya, 7 Fagus, 8 Castanea, 9 Castanopsis, 10 Corylus, 11 Alnus, 12 Betula, 13 Quecus, 14 Tilia, 15 Liquidambar, 16 Myrtaceae, 17 Rhus, 18 Anacardiaceae, 19 Protaceae, 20 Euphorbiaceae, 21 Caesalpiniaceae, 22 Ilex, 23 Rutaceae, 24 Onagraceae, 25 Salix, 26 Ulmus, 27 Magnoliaceae, 28 Loranthaceae, 29 Chenopodiaceae, 30 Cruciferae, 31 Cucurbitaceae, 32 Symplocaceae, 33 Palmae, 34 Oleaceae, 35 Hamamelidaceae, 36. Myrtaceae Climatic Change (2009) 92:169–189 Fig. 7 Coexistence intervals of the whole palynoassemblage and each of the three palynological zones. A zone 1, B zone 2, C zone 3, D whole palynoassemblage 183 184 Climatic Change (2009) 92:169–189 with the other results. There is no evidence of climatic change during the overall period of deposition. 4 Discussion 4.1 The paleovegetation and paleoclimate in Changchang Basin The palynoflora found in the Changchang Basin includes temperate plants, viz., Pinus L., Betula L., Alnus Mill., Corylus L., Ulmus L., Tilia L., Juglans L., Salix L., Castanea Mill., temperate and subtropical plants, viz., Carya Nutt., Magnolia L., Liquidambar L., and subtropical and tropical plants, viz., Taxodiaceae, Ilex L., Myrtaceae, Proteaceae, Anacardiaceae, Rutaceae, Symplocaceae, Palmae, Caesalpiniaceae. Based on the climatic preferences of the nearest living relatives of recovered palynotaxa, paleovegetation vis-à-vis paleoclimate of the basin is suggested. For instance, plants of the genera Salix and Betula are commonly distributed in the north temperate zone. The plants of the genus Ilex are mostly distributed in the tropics and subtropics, while some species extend into the temperate regions. The genus Liquidambar is discontinuous between the temperate and subtropical zones of the East Asia, S.W. Asia and North America. The Palmae is a pantropical family, which is widely distributed in the tropical and subtropical regions of the world (Wu 1991; Mabberley 1997; Wu et al. 2003). Based on the palynoassemblage, it is assumed that the vegetation in the central part of the Changchang Basin was evergreen or deciduous broad-leaved forest and the vegetation on the surrounding mountain was needle-leaved forest and deciduous broad-leaved forest. During the Early–Middle Eocene of the Changchang Basin, it is thought that a subtropical climatic regime, very similar to the present climate (MAT: 17.0◦ C; MAP: 1,013.1 mm) of Xichang City (27◦ 54′ N, 102◦ 16′ E), Sichuan Province, southwestern China, existed (Table 5). The modern climate in Hainan Island is of an oceanic tropical type (MAT 23.8◦ C; MAP 1,684.5 mm) with tropical seasonal rain forest in the mountains area and mangrove forest fringing the coastal plain. 4.2 Comparison of palynoflora and paleoclimate with Hunchun City An Eocene palynoflora and paleoclimatic estimates are available from Hunchun City, Jilin Province, (42◦ 51′ 13′′ N, 130◦ 20′ 98′′ E) North China (Kou 2005), enabling us to compare it with those of the Changchang Basin, South China (19◦ 37′ 73 N, 110◦ 27′ 12 E). Although these two sites are geographically widely separated (Fig. 8), the palynoflora and paleoclimate are close to each other. Angiosperm taxa dominate both the Changchang and Hunchun City palynoassemblages, represented by 94.5% and 50.8–84.55%, respectively. Forty-six taxa of palynomorphs from the Changchang Basin, compared to 52 types from Hunchun City, have been recovered among which 27 taxa appeared common to both (Fig. 3). More temperate elements are encountered in Hunchun City (42.3% of total palynomorphs) than in Changchang Basin (26.0%); in contrast, there are more tropical and subtropical elements among the Changchang Basin palynotaxa (41.3%) than in the Hunchun City assemblage Climate parameters Changchang Basin, Hainan Island Xichang City, Sichuan Province Hunchun City, Jilin Province Xuyi County, Jiangsu Province (19◦ 37′ 73 N, 110◦ 27′ 12 E) (27◦ 54′ N, 102◦ 16′ E) (42◦ 51′ 13 N, 130◦ 20′ 98 E) (33◦ 01′ N, 118◦ 30′ E) a b b c d (Eocene climate) (Recent climate) (Recent climate) (Eocene climate) (Recent climate) (Recent climate)e MAT (◦ C) MWMT (◦ C) MCMT (◦ C) DT (◦ C) MAP (mm) MMaP (mm) MMiP (mm) 14.2–19.8 (17) 22.5–29.1 (25.8) 1.7–11.9 (6.8) 12.1–24.6 (18.4) 784.7–1,113.3 (949) 141.5–268.1 (204.8) 6.9–14.1 (10.5) 23.8 – – – 1,684.5 – – 17 22.6 9.5 13.1 1,013.1 215.5 4.8 14.3–14.9 (14.6) 25–26.3 (25.7) 1.9–3.7 (2.8) 21.7–23 (22.4) 797.5–1,344 (1,070.8) 185.3–209.8 (197.6) 14.2–16.4 (15.3) 5 – – – 504 – – 14.6 27.6 0.7 26.9 958.3 246 21.8 Climatic Change (2009) 92:169–189 Table 5 Comparison of Eocene and recent climate in Changchang Basin, South China and Hunchun City, North China, and comparison of the Eocene climate in Changchang Basin and Hunchun City with the recent climate of Xichang City, Sichuan Province and Xuyi County, Jiangsu Province Number in bracket is the median MAT mean annual temperature, MWMT mean temperature of the warmest month, MCMT mean temperature of the coldest month, DT difference of temperatures between coldest and warmest months, MAP mean annual precipitation, MMaP mean maximum monthly precipitation, MMiP mean minimum monthly precipitation a Data from present paper b Data c Data d Data e Data from IDBMC (1984b) from Kou (2005) from IDBMC (1983a) from IDBMC (1984a) 185 186 Climatic Change (2009) 92:169–189 Fig. 8 Location of Changchang Basin, Hainan Island and Hunchun, Jilin Province in China (26.9%). Taken as a whole, these palynological data suggest that the two floras grew essentially under a subtropical climatic regime. The Hunchun climate during the Middle to Late Eocene was quantitatively reconstructed using the Coexistence Approach by Kou (2005). The MAT and MAP of Hunchun during Eocene time were 14.3–14.9◦ C (14.6◦ C) and 797.5–1,344 mm (1,071.8 mm), respectively, which are close to the modern climate of Xuyi (33◦ 01′ Climatic Change (2009) 92:169–189 187 N, 118◦ 30′ E), Jiangsu Province, China (MAT: 14.6◦ C; MAP: 985.3 mm), and also close to those of the Changchang Basin during the Early to Middle Eocene (MAT: 14.2–19.8◦ C (17.0◦ C), MAP: 784.7–1,113.3 mm (949 mm)) (Table 5). The similarity of these climatic parameters in the Changchang Basin and Hunchun City suggests that the Eocene climates in South China and North China were not so different, both warm and humid. The reason behind the similarity of the paleoclimates in the two areas, which are quite far apart (about 23 degrees in latitude) may be explained in two ways. Firstly, from the paleogeographical point of view, the landmass of China during the Paleogene was possibly located at the southeastern part of Eurasia and its landform was relatively flat, as the Indian Plate commenced to collide with the Eurasian Plate in the Eocene (ca. 50 Ma). Late Cretaceous–Paleogene marine deposits have been found in southern Tibet, which indicates that at least some of the region was at sea level around the time of collision (Zhang et al. 1998; Harris 2006). It is suggested that the Tibetan Plateau was not uplifted much during this period. The thickness and density of the troposphere in China was almost uniform everywhere, which could conserve the heat equally (CCPGCCAS 1984; CCVC 1995). Secondly, the eastern part of China, including South and North China, was influenced by the warm oceanic current around Eurasia which caused the temperature of the landmass to increase (CCPGCCAS 1984). Spjeldnaes (1973) suggested that the atmospheric- and oceanic circulation were not too strong in the Paleogene and climatic zones were not as distinct as at the present day, thereby supporting a similar climatic regime throughout the northern and southern part of the Chinese landmass. Furthermore, the Early Eocene was one of the warmest intervals of the Cenozoic, with little or no polar ice (Rea et al. 1990; Sloan and Barron 1992; Sloan and Rea 1995; Sloan et al. 2001), which possibly led to little change in temperature across latitudes at that time. 5 Conclusions 1) The palynoflora of the Changchang Basin in the Early–Middle Eocene is characterized by the dominance of angiosperm pollen (94.5%), followed by gymnosperm pollen (2.8%) and pteridophyte spores (2.7%). 2) The vegetation in the central part of the Changchang Basin in Early–Middle Eocene time was evergreen or deciduous broad-leaved forest surrounded by evergreen or deciduous broad-leaved forest and needle-leaved forest on the nearby highlands. 3) The climate in the Changchang Basin in the Early–Middle Eocene is supposed to have been of a subtropical type. The MAT in Eocene time is estimated as 14.2–19.8◦ C, with a MWMT of 22.5–29.1◦ C, MCMT of 1.7–11.9◦ C, DT of 12.1– 24.6◦ C, MAP of 784.7–1,113.3 mm, MMaP of 141.5–268.1 mm, and a MMiP of 6.9–14.1 mm. 4) A comparison of paleoclimatic parameters between the Changchang Basin (MAT: 14.2–19.8◦ C, MAP: 784.7–1,113.3 mm in Early–Middle Eocene) and Hunchun City (MAT: 14.3–14.9◦ C, MAP: 797.5–1,344 mm in Middle–Late Eocene) suggests that the climate of South China and North China was similar, both warm and humid. 188 Climatic Change (2009) 92:169–189 Acknowledgements We thank Professor Nai-Qiu Du and Dr. Qi-Gao Sun from the Institute of Botany, Chinese Academy of Sciences and Professor Wen-Bo Liao from Sun Yat-sen University for their help with this study. We also thank Dr. Xiang-Yu Kou for providing the data of the Eocene palynoflora and paleoclimate of Hunchun City, Jilin Province. 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