Late Tremadocian–Early Floian Acritarchs from Graptolitic Shales of the Yinzhubu and Ningkuo Formations of Yiyang, South China
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Review of Palaeobotany and Palynology 193 (2013) 1–14 Contents lists available at SciVerse ScienceDirect Review of Palaeobotany and Palynology journal homepage: www.elsevier.com/locate/revpalbo Research paper Late Tremadocian–early Floian 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: Acritarch assemblages are described here for the first time from the Early Ordovician 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 Arenig) graptolite and chitinozoan 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 chitinozoans 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, Wales, 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