Review of Palaeobotany and Palynology 193 (2013) 1–14

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Review of Palaeobotany and Palynology

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Research paper Late –early acritarchs from graptolitic shales of the Yinzhubu and Ningkuo formations of Yiyang, South China

Wenhui Wang a,c,⁎, Marco Vecoli b, Thijs R.A. Vandenbroucke b, Hongzhen Feng a, Lixia Li a, Jacques Verniers c a School of Earth Sciences and Engineering, Nanjing University, Hankou Street 22, 210093, Nanjing, China b Géosystèmes, UMR 8217 du CNRS, Université Lille 1, Avenue Paul Langevin, bâtiment SN5, 59655 Villeneuve d'Ascq, France c Research Unit of Paleontology, Department of Geology and Soil Sciences, Ghent University, Krijglsaan 281/S8, Ghent, 9000, Belgium article info abstract

Article history: assemblages are described here for the first time from the Early Yinzhubu and Ningkuo Received 4 May 2012 formations of the Nanba section (Yiyang region, Hunan province, South China). Independent stratigraphical Received in revised form 19 November 2012 control is provided by co-occurring late Tremadocian–early Floian (early ) graptolite and Accepted 19 January 2013 biozones. A very diverse association of 33 species attributed to 23 genera is identified, and three acritarch Available online 8 February 2013 assemblage zones are distinguished. These are comparable to coeval assemblages from several localities

Keywords: worldwide. During the Early Ordovician the Yiyang area was at low latitudes. The acritarch association interestingly Late Tremadocian–early Floian shows a mixed character, comprising typical taxa from both cold-water and warm-water paleobioprovinces. South China © 2013 Elsevier B.V. All rights reserved. acritarch biostratigraphy paleogeography

1. Introduction named the trifidum microflora by Fortey et al. (1991) and dated to the latest Tremadocian, using graptolites. In their detailed investigation of Graptolitic shales of late Tremadocian–early Floian age are ex- the Skiddaw Group, Cooper et al. (1995) redefined the assemblage as posed in the Nanba Section, in the Yiyang region of the Hunan Prov- ‘messaoudii–trifidum’, providing an integrated graptolite and acritarch ince, South China (Fig. 1a,b). The succession comprises two litho- biozonation. Servais and Molyneux (1997) reviewed the taxonomic stratigraphic units: the Yinzhubu and the Ningkuo formations, which composition and stratigraphic occurrence of the assemblage, which occur in the lower and upper parts of the sequence respectively (Fig. 2). was re-named the ‘messaoudensis–trifidum’ assemblage. Molyneux et Previous studies on graptolites and have provided a bio- al. (2007) reviewed the occurrences of the messaoudensis–trifidum stratigraphic framework for the succession (Feng et al., 2009; Wang assemblage in England, , southern Ireland, Belgium, Germany, et al., 2012). Five graptolite biozones (Adelograptus tenellus, Aorograptus Spain, Bohemia, Turkey, and Argentina and suggested that this peri- victoriae, Araneograptus murrayi, Hunnegraptus copiosus and Tetragraptus Gondwanan assemblage is of significant biostratigraphical and paleo- approximatus) and three chitinozoan biozones (Lagenochitina destombesi, geographic importance. Recent Argentinian studies have also referred Lagenochitina esthonica and Euconochitina symmetrica) have been recog- to the assemblage (Rubinstein et al., 2007; de la Puente and Rubinstein, nized, allowing precise and independent stratigraphic control throughout 2009; Toro et al., 2010). The assemblage has been described from middle the section. to high-latitude regions (listed above), that border the Gondwana super- Late Tremadocian–early Floian acritarch assemblages have been continent, as noted by Servais et al. (2003). previously described from many localities across the globe, showing Coeval, low-latitude deposits are characterized by a different their potential for long distance correlation, and eventually for the acritarch suite, the ‘Aryballomorpha–Athabascaella–Lua’ assemblage definition of formal acritarch biozonations. The messaoudensis–trifidum (AAL assemblage), defined by the co-occurrence of the three acritarch assemblage from the Tremadocian–Floian boundary typically occurs taxa. First described by Martin (1984, 1992) in the Tremadocian of in peri-Gondwana localities (Vanguestaine and Servais, 2002; Servais Alberta (Canada), the assemblage was subsequently reported from the et al., 2003). This assemblage was first described in the English Lake Tremadocian–Arenig boundary strata of Northeastern China (Martin District by Molyneux and Rushton (1988). Subsequently, it was re- and Yin, 1988) and from Tremadocian deposits in Texas, USA (Barker and Miller, 1989). Based on the paleogeographical reconstruction of Li and Powell, (2001), Li and Servais (2002) noted that all the known ⁎ Corresponding author at: School of Earth Sciences and Engineering, Nanjing University, Hankou street 22, 210093, Nanjing, China. Tel.: +86 2558611122. occurrences of the three characteristic genera of the AAL assemblage E-mail address: [email protected] (W. Wang). are from low latitude regions. Servais et al. (2003) noted that some of

0034-6667/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.revpalbo.2013.01.005 2 W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14

Fig. 1. Location map of the Nanba section, Yiyang area. The star represents the position of the studied section. 1. Gaoqiao, Ziyang, Shanxi Province (Hu, 1986); 2. Wangjiazhai, Youyang, Hubei Province (Brocke, 1997); 3. Ercun, Kunming, Yunnan Province (Fang, 1986); 4. Renmingqiao, Wuding, Yunnan Province (Gao, 1991); 5. Yinchunli, Luquan, Yunnan (Fang, 1986); 6. Wannike, Luquan, Hunan Province (Fang, 1986). Modified from Feng et al. (2009).

the elements of the messaoudensis–trifidum assemblage have been and chitinozoan biostratigraphy from the same section provide reliable reported from the following mid latitude areas: southern Baltica biostratigraphic constraints (Feng et al., 2009; Wang et al., 2012). The (Bagnoli et al., 1988; Raevskaya, 1999), the Yangtze Platform, Southwest South China terrane can be subdivided in three main units along an China (Brocke, 1997)andIran(Ghavidel-Syooki, 1995, 2000). Moreover, east–west transect (Fig. 1a): the Yangtze Platform, the Jiangnan Slope isolated elements of the AAL assemblage can also co-occur with the and the Southeast Basin, which are characterized by different facies elements from the high latitude assemblage in mid latitude regions, associations, corresponding to specific sedimentary environments. producing ‘mixed assemblages’ characterized by both ‘cold-water’ and Previous studies concerning Early-Middle Ordovician acritarchs were ‘warm-water’ forms (Servais et al., 2004). Vecoli (2004) even reported carried out in the Jianshan–Changshan–Yushan (JCY) area in the east the occurrence of Athabascaella from the Tremadocian of southern Tunisia, of the Jiangnan Region (Huang, 1991; Huang et al., 1994; Xu and You, located at high paleolatitudes during Ordovician times. 2001; Xu et al., 2002; Yin and Playford, 2003; Yan et al., 2011), and in In their review paper, Li et al. (2002) presented a comprehensive the Sandu area in the south–west of the Jiangnan Region (Li, 1991; Xu, bibliographic list of publications on Chinese Paleozoic acritarchs, 1995, 1996, 1999, 2001; Xu et al., 1995). The Nanba section is located pointing out that papers concerning Ordovician acritarchs occupied in the north of the Jiangnan Region and is characterized by slope facies the largest portion of all the papers. However, palynological data sediments (Figs. 1b, 2). The Nanba section consists of two formations: from late Tremadocian–early Floian strata are still rather scarce in the Yinzhubu Formation and the Ningkuo Formation (Fig. 2). Lithologi- China. In north China, besides the studies mentioned above, there cally, the lowest part of the Yinzhubu Formation is characterized by gray are only two reports from the Hunjiang region (Jilin Province), on micritic limestone, passing into mudstones interbedded with silty mud- the North China Plate (Yin, 1985, 1986). More than 80% of papers on stones higher in the formation. The overlying Ningkuo Formation Chinese Ordovician acritarchs concern South China localities, i.e., the is dominated by grayish or yellowish green mudstones. Sedimentary Ziyang area/Shanxi Province (Hu, 1986); the Kunming-Wuding area/ structures and tube-like trace fossils in the Ningkuo Formation suggest Yunnan Province (Fang, 1986; Gao, 1991), and the Hubei Province a more dynamic sedimentary environment. This paper uses a three- (Brocke, 1997)(Fig. 1b). More specifically, most of the reports concern fold division of the Tremadocian as suggested by Bergström et al. localities in the Yangtze Platform, while there are no acritarch records (2009);alsoseeWang et al. (2012). The time slices (TS) by Webby of late Tremadocian–early Floian strata from the Jiannan Slope of the et al. (2004) are also listed in the correlation charts for comparison. South China terrane. It should be noted that, with few exceptions, precise independent chronostratigraphic control on the published late 3. Graptolite and chitinozoan biozonation Tremadocian–early Floian acritarch assemblages from China, and else- where, is scarce. The Yinzhubu Formation and the Ningkuo Formation are dated In this study, for the first time, acritarch assemblages are recorded using five graptolite biozones: the Adelograptus tenellus; Aorograptus from the Nanba Section of the Jiannan Slope, South China. Their strati- victoriae; Araneograptus murrayi; Hunnegraptus copiosus and Tetragraptus graphic occurrences are calibrated by means of co-occurring chitinozoan approximatus biozones (Feng et al., 2009)(Fig. 2). These five graptolite and graptolite biozones. The three acritarch assemblages form the basis biozones span a late Tremadocian to early Floian age. The boundary be- for an acritarch-based informal local biozonation of the studied section. tween the Tremadocian and Floian stages coincides with the boundary The collated biostratigraphic evidence confirms a Tremadocian–early between the Hunnegraptus copiosus Biozone and the T. approximatus Floian age for the section studied. The biogeographic significance of the Biozone. Chitinozoan biozones are also present in the Nanba section: acritarch suite is also discussed. the Lagenochitina destombesi Biozone, the L. esthonica Biozone and the Euconochitina symmetrica Biozone (Wang et al., 2012). 2. Stratigraphy and geological setting 4. Materials and methods The Nanba section comprises a late Tremadocian–Floian succession along a road cut oriented North–South and located southwest of the Forty-seven samples were processed using standard palynological city of Yiyang in South China (Fig. 1c). Recent studies on graptolite preparation procedures for the recovery of chitinozoans (Paris, 1981) W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14 3

Fig. 2. Stratigraphic section of the Lower Ordovician formations in the Yiyang area, Hunan Province showing lithofacies, sampling levels, graptolite and chitinozoan biozones. Hollow circles=barren sample; solid circles=productive sample; graptolite zones after Feng et al. (2009); chitinozoan zones after Wang et al. (2012). Aorogr.=Aorograptus; Hunnegr.= Hunnegraptus; L.=Lagenochitina; E.=Euconochitina. 4 W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14 and acritarchs (Bagnoli et al., 1988), at the Department of Geology to identify a considerable portion of the acritarchs. In summary, a total and Soil Sciences of Ghent University. The organic residues larger of 33 acritarch taxa could be identified, 14 of which are positively iden- than 53 μm were used for the chitinozoan studies of Wang et al. tified to the species level, ten identified only at the genus level, and the (2012). The organic residues smaller than 53 μm were sieved again, remaining nine left in open nomenclature (Figs. 3, 4). this time through a nylon filter (10 μm mesh), and the remaining The identified acritarch taxa are listed here (in alphabetical order). material was mounted on standard microscopy slides for examina- All these taxa are figured in Plates I–IV. tion. A Zeiss Axioskop 2 Plus microscope was used for observation Annulum sp. cf. A. squamacea (Volkova, 1968) Martin in Martin and and photography. Scanning electron microscope (SEM) micrographs Dean, 1983 were taken following the methods described in Playford and Martin Aryballomorpha grootaertii (Martin, 1984) emend. Martin and Yin, (1984). All the palynological slides and illustrated specimens are de- 1988 posited in the collections of the Paleontology and Stratigraphy labora- Athabascaella playfordii Martin, 1984 emend. Martin and Yin, 1988 tory, School of Earth Sciences and Engineering, Nanjing University, Athabascaella rossii Martin, 1984 emend. Martin and Yin, 1988 China. The collection numbers range from 5YYN4 to 47YR15. Attritasporites messaoudensis Combaz, 1967 Caldariola glabra (Martin, 1972) glabra Servais and Molyneux, 1997 5. Palynological results sp. Cristallinium sp. A total of 35 palynological samples from the Nanba section yielded Cymatiogalea sp. aff. C. messaoudensis Jardiné, Combaz, Magloire, moderate to well preserved acritarchs. The abundance and diversity Péniguel and Vachey, 1974 inconnexa Servais and Molyneux, 1997 of acritarchs fluctuate significantly in the studied samples (Fig. 3), Cymatiogalea sp. although the vertical distribution of acritarchs does not seem to show Dactylofusa velifera Cocchio, 1982 any correlation with changes in lithology, similarly to that of graptolites Dasydiacrodium sp. cf. D. obsonum Martin in Martin and Dean, 1988 (Feng et al., 2009). Acritarch specimens vary in color from black to dark Ferromia pellita (Martin, 1975) emend. Martin, 1996 brown (commonly) and light brown (more rarely) within a single Goniosphaeridium sp. cf. G. tuberatum (Downie, 1958) Martin, 1972 sample, indicating a relatively high thermal alteration, which acted Leiosphaeridia sp. selectively on the different acritarch species. This has made it difficult Micrhystridium sp. cf. M. shinetonense Downie, 1958

Fig. 3. Relative abundances of acritarchs in the studied samples from the Nanba section. All specimens present on the single slides for each productive sample were counted to determine relative abundances of species for each productive sample. A=Abundant (>50 specimens), C=Common (10–50 specimens), and R=Rare (b10 specimens). W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14 5

Fig. 4. Stratigraphic distribution of acritarchs in the Nanba section, Hunan Province, South China.

Ordovicidium yangtazeense Tongiorgi, Yin and Di Milia, 1995 Stelliferidium ? sp. 2 Petaloferidium bulliferum Yin, Di Milia and Tongiorgi, 1998 Vavrdovella ? areniga (Vavrdová, 1973)emend.Loeblich and Tappan, Petaloferidium sp. 1976 areniga Molyneux in Molyneux and Rushton, 1988 Peteinosphaeridium angustilaminensis Playford, Ribecai and Tongiorgi, 1995 6. Composition and stratigraphic occurrence of Peteinosphaeridium sp. aff. P. dissimile Górka, 1969 contractum acritarch assemblages Tongiorgi, Yin and Di Milia, 2003 Peteinosphaeridium sp. The vertical distribution of the acritarch taxa (Figs. 3, 4), allows Polygonium gracile Vavrdová, 1966 for the assignment of three informal local assemblage zones through- Polygonium ? sp. out the studied stratigraphical interval of the Nanba section (late Polygonium spp. Tremadocian–early Floian). The three assemblage zones are discussed Pterospermella sp. below in ascending stratigraphical order. Rhopaliophora palmata (Combaz and Peniguel, 1972)emend.Playford and Martin, 1984 6.1. Assemblage zone A Rhopaliophora pilata (Combaz and Peniguel, 1972) emend. Playford and Martin, 1984 Occurrence: Lowermost part of the Yinzhubu Formation, sample Stellechinatum uncinatum (Downie, 1958) Molyneux, 1987 levels 5YYN4–25YYR16 (Fig. 4), in the Adelograptus tenellus, Aorograptus Stelliferidium trifidum (Rasul, 1974) Fensome, Williams, Barss, Freeman victoriae and lowermost part of Araneograptus murrayi graptolite and Hill, 1990 biozones; and in the Lagenochitina destombesi chitinozoan Biozone Stelliferidium? sp. 1 (Feng et al., 2009; Wang et al., 2012). 6 W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14

Acritarch assemblage: The acritarch assemblage is characterized first occur at the base of the zone and whose ranges are entirely con- by the occurrence of Athabascaella playfordii and A. rossii from the fined within the zone, such as: Cymatiogalea sp. aff. C. messaoudensis base of the zone, and by the progressive stratigraphic appearance of inconnexa, Dactylofusa velifera, Dasydiacrodium sp. cf. D. obsonum, Goniosphaeridium sp. cf. G. tuberatum, Polygonium spp., Vavrdovella ? Petaloferidium sp. and Pterospermella sp.. The second group comprises areniga areniga and Ferromia pellita. species that first occur at the base of this zone, and range throughout This assemblage shows a “mixed” paleobiogeographical character, part of, or the entire, overlying zone C; these are: Aryballomorpha containing taxa which are considered typical for the “messaoudensis– grootaertii, Annulum sp. cf. A. squamacea, Cristallinium sp., Leiosphaeridia trifidum” cold-water assemblages (i.e., Vavrdovella), together with sp., Micrhystridium sp. cf. M. shinetonense, Ordovicidium yangtazeense, taxa which are common in the “AAL”, warm-water assemblages Petaloferidium bulliferum, Peteinosphaeridium angustilaminensis, such as Athabascaella. Peteinosphaeridium sp., Polygonium gracile, Polygonium ?sp.,Rhopaliophora The top of Assemblage zone A is taken to coincide with the base of pilata and Stellechinatum uncinatum. The three following species first the succeeding Assemblage zone B. occur within zone B and range into zone C: Caldariola glabra glabra, Cymatiogalea sp. and Rhopaliophora palmata. 6.2. Assemblage zone B In addition, Assemblage zone B also includes all the species char- acteristic of the previous Assemblage zone A. The top of Assemblage Occurrence: Upper part of Yinzhubu to lowermost part of Ningkuo zone B is taken to coincide with the base of the succeeding Assem- formations, sample levels 26YYR17–31YYR22 (Fig. 4), in the blage zone C. Araneograptus murrayi graptolite Biozone; and in the Lagenochitina destombesi and L. esthonica chitinozoan biozones (Feng et al., 2009; Wang et al., 2012). 6.3. Assemblage zone C Acritarch assemblage: The base of this assemblage zone is well- defined by the first stratigraphic occurrence of several species, which Occurrence: Ningkuo Formation, sample levels 32YYR23–45YR14 can be divided in two groups: the first group consists of species that (Fig. 4), in the Araneograptus murrayi, Hunnegraptus copiosus and

Plate I. Late Tremadocian–early Floian acritarchs from the Yinzhubu and the Ningkuo formations (Yiyang area, China). Scale bar represents 10 μm. (see on page 7)

1. Goniosphaeridium sp. cf. G. tuberatum (Downie, 1958) Martin, 1972. 1: 110115 sample: 15YYR8, C65. 2–3. Aryballomorpha grootaertii (Martin, 1984) emend. Martin and Yin, 1988. 2: 1101353 sample: 35YYR26, J54/2; 3:110132 sample: 32YYR23, A58/4. 4–6. Athabascaella playfordii Martin, 1984 emend. Martin and Yin, 1988. 4: 1101351 sample: 35YYR26, W32/4; 5: 26YYR17-15; 6: 35YYR26-13. 7–8. Athabascaella rossii Martin, 1984 emend. Martin and Yin, 1988. 7: 26YYR17-20; 8: 1101362 sample: 36YYR27, B47/1. 9. Attritasporites messaoudensis Combaz, 1967. 9:1101423 sample: 42YYN, H63/2. 10–11. Caldariola glabra (Martin, 1972) emend. Molyneux in Molyneux and Rushton, 1988 glabra Servais and Molyneux, 1997. 10:1101283 sample: 28YYR19, E33/1; 11: 1101352 sample: 35YYR26, L32/2. 12. Coryphidium sp. 12. 110144 sample: 44YYN15.5, Y38/2. 13–15. Cristallinium sp. 13: 110132 sample: 32YYR23, Y40/1; 14: 1101351 sample: 35YYR26, U48; 15: 33YYR24-4. 16–17. Cymatiogalea sp. aff. C. messaoudensis Jardiné, Combaz, Magloire, Péniguel and Vachey, 1974 inconnexa Servais and Molyneux, 1997. 16: 1101282 sample: 28YYR19, P55/4; 17: 1101263 sample: 26YYR17, W46/4.

Plate II. Tremadocian acritarchs from the Yinzhubu and the Ningkuo formations (Yiyang area, China). Scale bar represents 10 μm. (see on page 8)

1–2. Cymatiogalea sp. 1: 110130 sample: 30YYR21, A41/2; 2: 1101352 sample: 35YYR26, H39/1. 3–5. Polygonium ? sp. 3: 1101361 36YYR27, X37/1; 4: 110140 sample: 40YYN14.1, C61/1; 5: 1101262 sample: 26YYR17, S39. 6–8. Dactylofusa velifera Cocchio, 1982. 6: 1101262 sample: 26YYR17, P35/1; 7: 1101262 sample: 26YYR17, U49/3; 8: 1101263 sample: 26YYR17, A49/4. 9. Dasydiacrodium sp. cf. D. obsonum Martin in Martin and Dean, 1988. 9: 1101261 sample: 26YYR17, V49/4. 10–13. Ferromia pellita (Martin, 1975) emend. Martin, 1996. 10: 1101262 sample: 26YYR17, Z44; 11: 1101261 sample: 26YYR17, Q58/1; 12: 1101352 sample: 35YYR26, M59; 13: 1101262 sample: 26YYR17, U42. 14–16. Stellechinatum uncinatum (Downie, 1958) Molyneux, 1987. 14: 26YYR17-7; 15: 1101261 sample: 26YYR17, K59/4; 16: 26YYR17-11. 17. Annulum sp. cf. A. squamacea (Volkova, 1968) Martin in Martin and Dean, 1983. 17: 1101351 sample: 35YYR26, G53/4.

Plate III. Late Tremadocian–early Floian acritarchs from the Yinzhubu and the Ningkuo formations (Yiyang area, China). Scale bar in 7a represents 5 μm, others represent 10 μm. (see on page 9)

1–3. Leiosphaeridia sp. 1: 110132 sample: 32YYR23, X56; 2: 1101423 sample: 42YYN, X35/3; 3: 1101263 sample: 26YYR17, B48. 4–5. Micrhystridium sp. cf. M. shinetonense Downie, 1958. 4: 1101262 sample: 26YYR17, S39/1; 5: 1101262 sample: 26YYR17, V41/2. 6–7, 7a, 8. Petaloferidium bulliferum Yin, Di Milia and Tongiorgi, 1998. 6: 26YYR17-9; 7: 110132 sample: 32YYR23, B58/2; 7a: details of processes in fig. 7; 8: 1101262 26YYR17, V39. 9–10. Petaloferidium sp. 9: 1101261 sample: 26YYR17, D35; 10:1101262 sample: 26YYR17, C43/2. 11. Peteinosphaeridium sp. 11: 1101263 sample: 26YYR17, Q38/3. 12–13. Peteinosphaeridium angustilaminensis Playford, Ribecai and Tongiorgi, 1995. 12:1101302 sample: 30YYR21, G29/1; 13: 1101302 sample: 30YYR21, U31/4. 14. Ordovicidium yangtazeense Tongiorgi, Yin and Di Milia, 1995. 14: 1101262 sample: 26YYR17, S38/3. 15–16. Peteinosphaeridium sp. aff. P. dissimile Górka, 1969 contractum Tongiorgi, Yin and Di Milia, 2003. 15: 36YYR27-10; 16: 35YYR26-3. 17–18. Polygonium gracile Vavrdová, 1966. 17: 1101352 sample: 35YYR26, N40; 18: 1101421 sample: 42YYN, T37.

Plate IV. Late Tremadocian–early Floian acritarchs from the Yinzhubu and the Ningkuo formations (Yiyang area, China). Scale bar represents 10 μm. (see on page 10)

1. Polygonium spp. 1: 110134 sample: 34YYR25, A48/3. 2–3. Pterospermella sp. 2: 1101262 sample: 26YYR17, F55/1; 3: 1101262 sample: 26YYR17, S59A. 4. Transitional form between Rhopaliophora palmate and R. pilata. 4: 1101262 sample: 26YYR17, F55/3; 5. Rhopaliophora palmata (Combaz and Peniguel, 1972) emend. Playford and Martin, 1984. 5: 110133 sample: 33YYR24, P34/3. 6–7. Rhopaliophora pilata (Combaz and Peniguel, 1972) emend. Playford and Martin, 1984. 6: 26YYR17-16; 7: 1101353 sample: 35YYR26, G51/3. 8–10. Stelliferidium trifidum (Rasul, 1974) Fensome, Williams, Barss, Freeman and Hill, 1990. 8: 1101361 sample: 36YYR27, E52/3; 9: 1101362 sample: 36YYR27, X49/3; 10: 36YYR27-9. 11–12. Stelliferidium ? sp. 1. 11: 33YYR24-8; 12: 110132 sample: 32YYR23, Y67. 13–14. Vavrdovella ? areniga (Vavrdová, 1973) emend. Loeblich and Tappan, 1976 areniga Molyneux in Molyneux and Rushton, 1988. 13: 1101282 sample: 28YYR19, R48; 14: 1101351 sample: 35YYR26, E53. 15–16. Stelliferidium ? sp. 2. 15: 33YYR24-18; 16:1101351 sample: 35YYR26, O53/3. W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14 7

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Tetragraptus approximatus graptolite biozones; and in the Euconochitina 3ofCooper et al. (1995) as defined in the English Lake district. Further symmetrica chitinozoan Biozone (Feng et al., 2009; Wang et al., 2012). comparison between the South Chinese and British biozonations can be Acritarch assemblage: The base of Assemblage zone C is defined by made on the basis of co-occurring graptolites. In the English Lake Dis- the first stratigraphic occurrences of Coryphidium sp. and Stelliferidium? trict, Sub-assemblage 1 was correlated to the Araneograptus murrayi sp. 1. The following species first occur within the zone, listed in order of Biozone of the British Isles and Sub-assemblages 2 to 3 were regarded their occurrence in successively higher stratigraphic levels: Stelliferidium as equivalent to the Hunnegraptus copiosus Biozone of Britain and Baltica sp. 2, Peteinosphaeridium sp. aff. P. dissimile contractum, Stelliferidium (Cooper et al., 1995, fig. 4). Here, in South China (see Sections 6.1, trifidum and Attritasporites messaoudensis. All the characteristic species 6.2, 6.3), the three assemblage zones (A, B and C) are associated with of Assemblage zone A and the majority of those of Assemblage zone B graptolites indicating the Adelograptus tenellus, Aorograptus victoriae, also range through Assemblage zone C. The top of zone C is currently Araneograptus murrayi and Hunnegraptus copiosus biozones. The recorded not defined. graptolites generally confirm the correlation between the present acri- tarch assemblages in the present study and those reported from the 7. Comparison with previously described coeval English Lake District (Fig. 5). acritarch assemblages Integrated studies of graptolites and acritarchs were carried out on the Barriga Formation in the Sierra Morena of Spain. The Spanish Molyneux et al. (2007) give a detailed review of the stratigraphic and messaoudensis–trifidum assemblage was reported to correspond to paleogeographic occurrences of the messaoudensis–trifidum assemblage the Araneograptus murrayi Biozone or to the Araneograptus murrayi around the world. Here we compare the acritarch assemblages from Biozone plus potentially the lower part of the Hunnegraptus copiosus graptolite-bearing sections in the English Lake District, Britain, Spain Biozone, which represents a clear pre-approximatus age (Servais and and Argentina, as well as with previously reported Chinese assemblages. Mette, 2000). The messaoudensis–trifidum assemblage in Spain there- The acritarch assemblages described in this paper contain several fore spans an equivalent time interval as do our three assemblage taxa that are characteristic for the messaoudensis–trifidum assem- zones (A, B and C). However, although the acritarch assemblages blage. In particular, Caldariola glabra glabra, Coryphidium, Cymatiogalea described herein contain some characteristic acritarch taxa for the messaoudensis, Stelliferidium trifidum,andVavrdovella ? areniga areniga messaoudensis–trifidum assemblage, there is a difference in the num- have been previously described from several peri-Gondwana localities. ber of characteristic acritarchs as well as in their abundance, between In the English Lake District, Cooper et al. (1995) split Molyneux and the acritarch assemblages of these two areas. Rushton (1988)'s messaoudensis–trifidum assemblage into five sub- The Early Ordovician succession of Argentina (e.g., the Pascha- assemblages. Sub-assemblages 1–3 are of pre-phyllograptoides and Incamayo section, Cordillera Oriental, northwestern Argentina) yielded pre-approximatus age. All the characteristic taxa of the messaoudensis– well preserved microflora assemblages with good age-control provided trifidum assemblage mentioned above make their first occurrence with- by graptolites and chitinozoans (Waisfeld et al., 2006; Rubinstein et al., in sub-assemblage 1. The overlying sub-assemblage 2 is characterized 2007). Recent study of chitinozoans and acritarchs recovered from by the appearance of Rhopaliophora palmata and Striatotheca sp.; Tremadocian graptolitic strata from the same section revealed the pres- while the appearance of Coryphidium, Striatotheca and Veryhachium ence of a typical messaoudensis–trifidum acritarch assemblage (de La characterize sub-assemblage 3. The comparison with the three assem- Puente and Rubinstein, 2009). In the upper section of the Saladillo blage zones defined here (A, B and C), is based on the appearances Formation, Stellechinatum cf. uncinatum (Downie) Molyneux, 1987 and of Vavrdovella ? areniga areniga in acritarch Assemblage zone A; Stelliferidium cf. trifidum (Rasul) Fensome et al., 1990 were recovered Dactylofusa velifera and Rhopaliophora palmata in Assemblage zone B in levels with graptolites of Kiaerograptus Biozone; in the uppermost and Coryphidium sp. in Assemblage zone C. It indicates that the assem- Saladillo Formation and the lower section of the overlying Parcha blage zones A, B, C show a correspondence with sub-assemblages 1 to Formation, Vavrdovella areniga (Vavrdova) Loeblich and Tappan, 1976,

Fig. 5. Correlation between the Nanba Section, Yiyang area, based on the data of the present study, and other areas in the Yangtze Platform, e.g. South China, according to Brocke (1997); the English Lake District, UK, according to Cooper et al. (1995). The thick line in the middle represents the base of the graptolite Tetragraptus approximatus Biozone con- curring with the base of the Floian . 1). Cooper (1999); 2). Webby et al.(2004); 3). Bergström et al. (2009). Ao.=Aorograptus; H.=Hunnegraptus; Ar.=Araneograptus; Ad.=Adelo.=Adelograptus; R.=Rhabdinopora; Ac.=Acanthograptus; D.=Dictyonema; Kiaerogr.=Kiaerograptus; T.=Tetragraptus; L.=Lagenochitina; E.=Euconochitina. 12 W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14

Caldariola glabra var. glabra (Martin) Molyneux and Rushton, 1988, between the two terranes during Ordovician times (Li and Powell, Rhopaliophora palmata (Combaz and Peniguel) Playford and Martin, 2001). The present palynological study provides some improvements 1984, Coryphidium? sp., Peteinosphaeridium sp. and Polygonium spp. in the precision of the paleogeographical reconstruction of the two were recovered from the Araneograptus murrayi graptolite Biozone; terranes. For example, Torsvik and Cocks (2009) have tentatively Coryphidium sp. was recovered from the A. murrayi and Hunnegraptus pointed out that the South China terrane was separated from the copiosus biozones of the upper section of the Parcha Formation. These core Gondwana, while the North China terrane was considered as occurrences indicate the high similarity of the acritarch assemblage welded to Gondwana, near Australia, during Early Paleozoic. In the from Argentina with those presented here from South China (Assem- present study, a gradual increase of cold-water elements and the blage zones A–C). decrease in warm-water elements can be observed in the acritarch In the Kunming-Luquan area of the Yunnan province near the south- assemblages from lower to upper beds of the Nanba section. This west margin of the Yangtze Platform from South China, an acritarch kind of variation might be interpreted as reflecting the movement assemblage dominated by small forms attributed to Micrhystridium of South China terrane from lower paleolatitudes towards the spp. was recovered from the Tangchi Formation (Fang, 1986). Much circumpolar regions of Gondwana, as also suggested by previously more abundant and diverse acritarch associations were recovered published paleomagnetic data (Yang et al., 2004). from the overlying Hongshiya Formation. Similarities between the assemblages described herein and those from the Kunming-Luquan 9. Conclusions area are noted in the occurrence of Polygonium and Pterospermella.In the Ziyang area of Shanxi province, north–west of the Yangtze Platform, (1) Three acritarch assemblage zones are identified from the Yinzhubu Hu (1986) recognized three acritarch assemblages. The lowest Assem- and the Ningkuo formations in the Nanba section, South China. blage I in the Gaoqiao Formation is characterized by the occurrence (2) The acritarch-bearing part of the Nanba section is of a late of species in Buedingiisphaeridium, Micrhystridium and Polygonium,the Tremadocian–early Floian age. The age is biostratigraphically latter two taxa indicate some broad similarities between our assem- controlled by graptolite and chitinozoan biozones. Integrated blages and the acritarch assemblage from the Ziyang area. Brocke acritarch–chitinozoan–graptolite biostratigraphy is available for (1997) recognized three Tremadocian acritarch assemblages from the the first time in the Jiangnan Slope environment of South China. Yangtze platform of southwest China. Based on the distribution of (3) The three informal acritarch biozones defined here will help to Athabascaella playfordii, Dactylofusa velifera, Rhopaliophora pilata and refine the biostratigraphic correlation of the Late Tremadocian– Stellechinatum uncinatum, it is possible to propose a correlation of early Floian stratal sequences on Gondwana, especially in the Brocke's Assemblage I, Assemblage II and Assemblage III with our absence of graptolites or chitinozoans. Assemblage zone A, Assemblage zone B and Assemblage zone C, respec- (4) The progressive occurrence of acritarch taxa usually considered tively (Fig. 5). In the Hunjiang region of North China, well-preserved as characteristic of “cold water” paleobiogeographical realms acritarchs were reported from the graptolite Adelograptus–Clonograptus throughout the studied section supports the paleogeographic biozones (Martin and Yin, 1988; Yin, 1995). The occurrence of reconstruction in which the South China Terrane experienced a Aryballomorpha grootaertii, Athabascaella playfordii, A. rossii, Rhopaliophora northward movement during the Early Paleozoic, away from a palmata and R. pilata strongly supports a connection between the low latitude position, towards higher latitudes. Hunjiang area and the Nanba section.

8. Paleobiogeographic implications Acknowledgments

After the first attempt to model Ordovician acritarch biogeography Financial support from the National Natural Science Foundation of by Cramer and Díez (1972, 1974, 1977), numerous other biogeograph- China (No. 40972009 and No. 41172012) is acknowledged. The lead ical models of acritarch distribution have been proposed (Vavrdová, author thanks the EMECW Lisum project for provided scholarship. 1974; Martin, 1982; Martin and Dean, 1988; Albani, 1989; Li, 1989; Carys Bennett is thanked for English language editing of the manuscript. Li and Servais, 2002; Servais et al., 2003; Molyneux et al., 2007). Late We thank Sabine Van Cauwenberghe and Jan Mortier for technical Tremadocian to early Floian acritarch assemblages have been described assistance in sample preparation and SEM work. We thank Thomas J. worldwide from localities located at high and low paleolatitudes. Verleye and Koen Verhoeven for assistance with photography. We are In summary, the messaoudensis–trifidum assemblage is regarded as grateful to Dr. Thomas Servais (France) and Dr. Claudia V. Rubinstein representing a typical cold-water province, at middle to high (Argentina) for their critical review and valuable comments that im- paleolatitudes (Martin, 1984; Martin and Yin, 1988; Martin, 1992; proved the manuscript. This is a contribution to IGCP 591. Volkova, 1997; Li and Servais, 2002; Servais et al., 2003; de La Puente and Rubinstein, 2009) while the AAL assemblage is regarded as a typical References warm-water province at low paleolatitudes. However, the distinction Albani, R., 1989. Ordovician (Arenigian) acritarchs from the Solanas Sandstone Formation, between these two assemblages might not be so straightforward, as Central Sardinia, Italy. Bollettino della Societa Paleontologica Italiana 28, 3–37. some elements of the AAL assemblage also occur in high latitudes Bagnoli, G., Stouge, S., Tongiorgi, M., 1988. Acritarchs and from the Cambro- (Vecoli, 2004; Breuer and Vanguestaine, 2004 and the authors' personal Ordovician Furuhäll (Köpingsklint) section (Öland, ). Rivista Italiana di fi “ ” Paleontologia e Stratigrafia 94 (2), 163–248. observation). Acritarch associations displaying signi cant mixing of Barker, G.W., Miller, M.A., 1989. Tremadocian (lower Ordovician) acritarchs from the typical elements of the two assemblages have been reported from subsurface of West Texas. 22nd Ann. Meeting Amer. Ass. Stratigr. Palynologists, South China and Baltica, and have been interpreted as indicating a Tulsa, Oct. 18–21, 1989. Program and Abstracts, Dallas, p. 14. paleogeographical position at mid paleolatitudes (Bagnoli et al., 1988; Bergström, S.T., Chen, X., Gutiérrez-Marco, J.C., Dronov, A., 2009. The new chrono- stratigraphic classification of the Ordovician System and its relations to major Yin, 1995; Brocke, 1997; Servais and Fatka, 1997; Brocke and Fatka, regional series and stages and to δ13C chemostratigraphy. Lethaia 42, 97–107. 1999; Webby et al., 2004). Breuer, P., Vanguestaine, M., 2004. The latest Tremadocian messaoudensis–trifidum There are significant compositional differences between Early acritarch assemblage from the upper part of the Lierneux Member (Salm Group, Stavelot Inlier, Belgium). Review of Palaeobotany and Palynology 130, 41–58. Ordovician acritarch suites from the South China and those from Brocke, R., 1997. First results of Tremadoc to lower Arenig acritarchs from the Yangtze North Chinese terranes (Yin, 2006). In Yin (2006)'s review paper, Platform, Southwest China. In: Fatka, O., Servais, T. (Eds.), Acritarcha in Praha, acritarch assemblages from South China show a “mixed” character, Proceeding of International Meeting and Workshop: Acta Universitatis Carolinae, Geologica, 40, pp. 337–355. while North Chinese assemblages completely lack typical Gondwanan, Brocke, R., Fatka, O., 1999. Acritarch assemblages at the ‘Tremadocian’–‘Arenigian’ cold-water taxa. This corroborates the paleogeographical separation boundary. Acta Universitatis Carolinae, Geologica 43, 45–47. W. Wang et al. / Review of Palaeobotany and Palynology 193 (2013) 1–14 13

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