Late Ordovician to earliest Silurian graptolite and brachiopod … · 2016-06-21 · 1. Introduction Latest Ordovician to earliest Silurian strata and fossils, mainly the strata of

1. Introduction

Latest Ordovician to earliest Silurian strata and fossils,mainly the strata of the Wufeng Formation,Kuanyinchiao Formation, and the lowest LungmachiFormation, are widely distributed on the Yangtze plat-form (Fig. 1). Graptolites and brachiopods occurcommonly in these rocks throughout the region.Thirty-seven sections from the Yangtze region (Locs1–4, 6–38 in Fig. 1) have been measured and collectedby the authors and other Chinese colleagues in thepast 30 years (Mu et al. 1993). One section atBajiaokou, Ziyang (Loc. 5) was recorded from theSouth Qinling mobile belt, along the north slope ofthe Yangtze platform. Five (Locs 39–43) are from theXiangwan basin, the successor of the Zhujiang pre-Ashgill basin. Localities 39 to 41, along the formerJiangnan belt, occur along the slope of the Xiangwanbasin. Cathaysian Land experienced uplift beginningin the Ashgill and merged with Dianqian Land

(Central Guizhou Land). Moreover, Cathaysian Landbecame more prominent northwestwards during thelate Ashgill. Thus, the Yangtze platform was sur-rounded by Cathaysian Land, Dianqian Land and theChengdu uplift, forming a semi-enclosed bay thatopened northwards during late Ashgill time (Chen,Xiao & Chen, 1987).

Lee & Chao (1924) and Grabau (1924) were the firstto collect and identify the latest Ordovician to earliestSilurian fossils when they erected the Lungma Shalefrom the Yangtze Gorges. Sun (1931) identified thegraptolites collected by Hsieh and Liu fromYuyangguan, Wufeng County, southern Hubei, asAshgill in age and then named the strata the WufengFormation. Sun (1933) subsequently described theWufeng graptolites. Despite this work, the Ashgill ageof the Wufeng Formation was still not commonlyaccepted by palaeontologists in China. It was Mu(1954), when he re-studied the Wufeng graptolite faunaand correlated the Wufeng Formation with otherrelated strata within South China, who firmly estab-lished the age of the formation, which was then used as

Geol. Mag. 137 (6), 2000, pp. 623–650. Printed in the United Kingdom © 2000 Cambridge University Press 623

Late Ordovician to earliest Silurian graptolite and brachiopodbiozonation from the Yangtze region, South China, with a

global correlation

CHEN XU*§, RONG JIAYU*, CHARLES E. MITCHELL†, DAVID A. T. HARPER‡,FAN JUNXUAN*,

ZHAN RENBIN*, ZHANG YUANDONG*, LI RONGYU* & WANG YI*

*Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, 210008,the People’s Republic of China

†Department of Geology, State University of New York at Buffalo, Buffalo, NY 14260, USA‡Geological Museum, University of Copenhagen, Oster-Volgade 5-7, DK-1350, Copenhagen, Denmark

(Received 2 March 2000; accepted 15 August 2000)

Abstract – Late Ordovician to earliest Silurian is an important geological period marked by large geo-logical and biological events. However, the strata and fossils of this interval are not complete in manyparts of the world. Based on studies of 43 sites in South China, in particular the continuous sectionson the Yangtze platform, we recognize a complete succession including seven graptolite zones and twoshelly faunas. In ascending order, the graptolite zones are the Dicellograptus complanatus,Dicellograptus complexus, Paraorthograptus pacificus (including Lower Subzone, Tangyagraptus typi-cus Subzone and Diceratograptus mirus Subzone), Normalograptus extraordinarius–Normalograptusojsuensis, Normalograptus persculptus, Akidograptus ascensus and Parakidograptus acuminatus zones.The shelly faunas are the Foliomena–Nankinolithus and Hirnantia faunas, which may be correlatedwith D. complanatus Zone and N. extraordinarius–N. ojsuensis to part of N. persculptus zones respec-tively. The biozonation through this interval from the Yangtze region can be correlated with that ofother parts of the world such as Dob’s Linn in Scotland, Spain and Portugal, Thuringia–Saxonia–Bavaria, Bohemia, Poland, Kazakhstan, Kolyma, Malaya Peninsula, Yukon, Canadian Arctic Islands,Nevada, Argentina, Niger and Victoria, Australia. The Hirnantian Substage, which has been pro-posed by us recently, includes the N. extraordinarius–N. ojsuensis Zone, Hirnantia fauna and N. per-sculptus Zone. The base of the Hirnantian Substage is marked by the First Appearance Data (FADs)of N. extraordinarius and N. ojsuensis, which have been determined to be synchronous on a globalscale.

§Author for correspondence: [email protected]

a mapping unit. Following upon the acceptance of anAshgill age for the Wufeng Formation, a related prob-lem, the age of the Hirnantia–Dalmanitina-bearingKuanyinchiao Formation, arose during the 1960s. Thisproblem was not solved until Rong (1979) placed theKuanyinchiao Formation with a global correlation ofthe Hirnantia fauna.

Mu (1954) initially subdivided the Wufeng grapto-lites into two zones, the Pleurograptus lui Zone in thelower part and the Dicellograptus szechuanensis Zonein the upper. The graptolite biozonation was signifi-cantly improved when Mu and co-workers defined fivegraptolite zones from the Wufeng Formation acrossthe Yangtze region at the 1965 Convention of thePalaeontological Society of China, Nanjing. The fivezones were the Pleurograptus lui (W1), Dicellograptus

szechuanensis (W2), Tangyagraptus typicus (W3),Diceratograptus mirus (W4) and Paraorthograptus uni-formis (W5) zones, in ascending order. Unfortunately,this zonation was not published until 1974. Mu (1974)finally published the five Wufeng graptolite zones with an additional one, the Diplograptus bohemicusZone (W6), at the top of the Wufeng Formation.The Pleurograptus lui Zone was renamed theAmplexograptus disjunctus yangtzensis/Pleurograptuslui Zone by Mu (1980) and then the Amplexograptusdisjunctus yangtzensis Zone by Mu et al. (1993). Chen& Zhang (1995) and Chen et al. (1995) abandoned theAmplexograptus disjunctus yangtzensis Zone sinceRiva (1987) demonstrated that the zonal fossil was ajunior synonym of Amplexograptus latus (Elles &Wood). Chen & Zhang (1995) and Chen et al. (1995)

624 C H E N X U A N D OT H E R S

Figure 1. Distribution of the latest Ordovician to earliest Silurian strata with the reference sections and localities from theYangtze platform and its neighbouring areas. 1 – Cuijiagou, Ningqiang (Chen in Mu et al. 1993), 2 – Qiaoting, Nanjiang (Liu,Chen & Zhang, 1964), 3 – Fucheng, Nanzheng (Chen, Xu & Cheng, 1994), 4 – Gaojiawan, Xixiang (Yu, Fang & Zhang, 1988), 5– Bajiaokou, Ziyang (Fu & Song, 1986), 6 – Yangjiaba, Chengkou (Ge in Zhu et al. 1977), 7 – Xintan, Zigui (Mu, 1954), 8 –Jianyangping, Xinshan (the present paper), 9 – Maliangping, Baokang (Ge in Mu et al. 1993), 10 – Tangya, Yichang (Mu et al.1993), 11 – Wangjiawan, Yichang, (Mu et al. 1984, the present paper), 12 – Fenxiang, Yichang (Mu et al. 1984), 13 –Huanghuachang, Yichang (Mu et al. 1984), 14 – Shibangou, Hanyuan (Feng, Yu & Fang, 1991), 15 – Qiaodingshan, Hanyuan(Mu et al. 1993, Feng, Yu & Fang, 1991), 16 – Maokoshan, Hanyuan (Feng, Yu & Fang, 1991), 17 – Binlingxiang, Hongya (Muet al. 1993), 18 – Weiyuan (Mu and Chen field excursion in 1965, unpub. data), 19 – Shuanghe, Changning (Mu et al. 1978), 20 –Yanzikou, Bijie (Rong in Zhang et al. 1964), 21 – Donggongsi, Zunyi (Chen in Zhang et al. 1964), 22 – Honghuayuan, Tongzi(Chen in Zhang et al. 1964, the present paper), 23 – Hanjiadian, Tongzi (Chen in Zhang et al. 1964), 24 – Kuanyingqiao, Qijiang(Chen in Zhang et al. 1964, Jin et al. 1982), 25 – Yanwanggou, Huayingshan (Mu, 1954), 26 – Ganxi, Yanhe (Mu et al. 1993), 27– Ludiping, Songtao (Rong in Zhang et al. 1964, the present paper), 28 – Huangban, Songtao (Mu et al. 1993, the presentpaper), 29 – Datianba, Xiushan (Ge Zhi-zhou et al. in Mu et al. 1993), 30 – Wentang, Dayong (Chen and Rong field excursion in1990, unpub. data), 31 – Nishi, Shimeng (Ge Zhi-zhou et al. in Mu et al. 1993), 32 – Yuyangguan, Wufeng (Ge in Mu et al.1993), 33 – Huaqiao, Changyang (Ge in Mu et al. 1993), 34 – Wulipai, Linxiang (Mu et al. 1993), 35 – Beigongli, Jingxian (Li,1984), 36 – Sinianpan, Hexian (Zhang Quan-zhong et al. 1966), 37 – Tangshan, Nanjing (Mu, Pan & Yu, 1955), 38 – Lunshan,Jurong (Chen et al. 1988), 39 – Helixi, Ninggou (Li, 1984), 40 – Xinkailing, Wuning (Yu & Fang, 1986), 41 – Dafuping, Anhua(Liu & Fu, 1984), 42 – Shengping, Xingan (Chen et al. 1981), 43 – Guting, Chongyi (Chen, Xiao & Chen, 1987).

proposed that the D. szechuanensis Zone should bereplaced by Dicellograptus complexus Zone since theformer is obviously a junior synonym of the latter.They also abandoned the P. uniformis Zone. Theyspecified two species, N. bohemicus (Marek) (based onthe Chinese specimens) and N. extraordinarius(Sobolevskaya), as zonal index forms. They acceptedthe Normalograptus persculptus Zone, which was untilthen considered as the lowest Silurian biozone, as thehighest Ordovician graptolite zone.

During 1996 to 1998, four reference sections, theWangjiawan (Loc. 11 of Fig. 1) and Fenxiang (Loc.12), Yichang County, western Hubei Province,Honghuayuan (Loc. 22), Tongzi County, northernGuizhou Province and Ludiping (Loc. 27), SongtaoCounty, northeastern Guizhou Province, were re-measured and re-collected layer by layer through theWufeng Formation to the base of LungmachiFormation by the present authors. We propose that theTangyagraptus typicus Zone and Diceratograptus mirusZone should be two subzones of the Paraorthograptuspacificus Zone. The First Appearance Datum (FAD) ofP. pacificus (Ruedemann) is lower than that ofTangyagraptus typicus Mu but higher than that of D.complexus Davies. Thus, the lower part of the P. pacifi-cus Zone is temporarily referred to as the LowerSubzone. P. pacificus (Ruedemann) is a more appropri-ate zonal fossil because of its wide palaeogeographicdistribution and common occurrence within the inter-val. The occurrence of Paraorthograptus uniformis Mu& Li in the interval with N. extraordinarius and N.ojsuensis from the Wangjiawan and Fenxiang sectionsindicates that Mu’s Paraorthograptus uniformis Zoneshould be a part of the Normalograptus extraordinar-ius–N. ojsuensis Zone.

Koren (in Apollonov, Bandaletov & Nikitin, 1980)has considered that Normalograptus bohemicus(Marek) (=Glyptograptus bohemicus Marek, 1954) is asubjective junior synonym of Normalograptus persculp-tus s.s. (=Glyptograptus? persculptus forma B, Koren,1980). Storch & Loydell (1996) recently demonstratedthat Normalograptus bohemicus (Marek) is conspecificwith Normalograptus persculptus (Elles & Wood) basedon their re-study of the type specimens of the formerand additional specimens collected from both theCzech Republic and Wales. Thus, the conception of N.persculptus (Elles & Wood) has been slightly broad-ened. We recognize that the form which occurs in theYangtze region and has been referred to as N. persculp-tus is indeed N. persculptus (Elles & Wood) sensustricto. However, Fan (Fan Jun-xuan, unpub. Mastersthesis, Nanjing Institute of Geology & Palaeontology,1998) recently concluded that the species which Muand his successors (1993) as well as Wang et al. (1987)called ‘Glyptograptus bohemicus’ or ‘Diplograptusbohemicus’ from below the Kuanyinchiao Formation is conspecific with Normalograptus ojsuensis (Koren & Mikhailova) based on his morphometric study of

these two forms. Thus, the Chinese pre-Hirnantiaspecimens identified to ‘Glyptograptus bohemicus’ or‘Diplograptus bohemicus’ by Chinese authors should beassigned to Normalograptus ojsuensis (Koren &Mikhailova) rather than Normalograptus persculptus(Elles & Wood). N. extraordinarius (Sobolevskaya) nowis known to be a widely distributed species not only inSiberia, Kazakhstan, Europe and Australia, but also inthe Yangtze region of China. Thus, we prefer to use theN. extraordinarius–N. ojsuensis Zone for the interval inChina between the Diceratograptus mirus Subzone(below) and the N. persculptus Zone (above), which wasformerly called the N. bohemicus–N. extraordinariusZone in Chen et al. (1995).

Rong (1984a) suggested that the base ofKuanyinchiao Formation (Hirnantia-bearing beds) isdiachronous across the Yangtze region and may corre-spond to the base of the Diceratograptus mirusSubzone in northeastern Guizhou. The top of theKuanyinchiao Formation was regarded to be alwaysbelow the base of the N. persculptus Zone. In theYangtze Gorge area, however, he noted later (in Chenet al. 1995) that the top of Hirnantia-bearing beds mayreach into the N. persculptus Zone. The brachiopodfauna of the strata below the N. extraordinarius–N.ojsuensis Zone is a very low diversity fauna character-ized by Manosia. The Manosia assemblage is particu-larly abundant in the Diceratograptus mirus Subzoneand extends to the N. extraordinarius–N. ojsuensisZone (see Fig. 2). At the Honghuayuan section (Loc.22 of Fig. 1), some elements of the Hirnantia faunasuch as Eostropheodonta and Hindella may extend intothe higher beds, possibly corresponding to A. ascensusZone where the real Hirnantia is absent.

2. Biozonation

The Ashgill graptolites of the Yangtze region (WufengFormation) are highly diverse. The region was a semi-enclosed platform in this time interval, and lay at a lowlatitude within the warm water Pacific realm.Consideration of the high individual abundance ofgraptolites as well as the high species diversity in theWufeng Formation, in the light of recent palaeoecologi-cal models (e.g. Finney & Berry, 1998), leads us to sug-gest that the Yangtze region may have experienced highand stable organic productivity. Chen & Zhang (1995)have reviewed the Wufeng graptolites described by Muet al. (1993). They concluded that the Wufeng graptoloidfauna includes 30 genera and about 80 species ratherthan the 27 genera and 176 species recognized by Mu etal. (1993). However, the diversity of the Wufeng grapto-lite fauna is still very high and more than half of the lateAshgill fauna are endemic species. In the present study,the Ashgill to earliest Llandovery biozones from theChientsaokou Formation to the base of the LungmachiFormation are based mainly on four reference sections:the Wangjiawan, Fenxiang, Honghuayuan and

Ordovician–Silurian biozonation of Yangtze region, China 625

Ludiping sections. In the present systematic collectionsfrom these four sections, only four monospecific genera,Neurograptus, Nymphograptus, Orthoretiograptus andSinoretiograptus described by Mu et al. (1993) have notyet been re-collected since they are all based on very rarespecimens. The ranges of the graptolites and shelly fossilgroups, mainly brachiopods, are demonstrated on fourrange charts (Figs 3–6). We also demonstrate someimportant forms of the related graptolite fauna inFigure 7 and the shelly fauna in Figure 8. Finally, we listthe important species for which we differ significantly inour interpretations from those of Mu et al. (1993) inTable 1. The following abbreviations indicate differentbiozones: Dc, Dicellograptus complexus Zone; L–Tt,Lower Subzone to Tangyagraptus typicus Subzone of the Paraorthograptus pacificus Zone; Dm,Diceratograptus mirus Subzone of the P. pacificus Zone;Neo, Normalograptus extraordinarius–N. ojsuensis Zone;Np, N. persculptus Zone.

2.a. Foliomena–Nankinolithus Zone

The Foliomena–Nankinolithus Zone is widely recog-nized from the Chientsaokou Formation and corre-sponding units (lower Ashgill) on the Yangtzeplatform. The brachiopods from this horizon belongto the Foliomena fauna and trilobites to theNankinolithus fauna. The Foliomena fauna wasrecorded from rocks of Caradoc to mid-Ashgill age inmany localities from South China, North China,

Avalonia, Baltica, Laurentia, Kazakhstan, SouthernEurope, Sibumasu and others (Cocks & Rong, 1988;Rong & Zhan, 1995; Rong, Zhan & Harper, 1999). Ithas been commonly recovered from the lower Ashgillrocks in South China.

Rong et al. (1994) described a Kassinella–Christiania association in the early Ashgill Foliomenafauna of northern and northeastern Guizhou. A singlespecimen of Foliomena collected there is associatedwith Orbiculoidea, Paterula, Glyptorthis, Dedzetina,Leptestiina, Sericoidea, Kassinella, Eoplectodonta andChristiania in the Chientsaokou Formation atDonggongsi, Zunyi, northern Guizhou. In this regionthe Foliomena fauna is associated with a low diversitytrilobite assemblage that includes Nankinolithus. Thisassociation has been recovered from the southernmostareas of the Upper Yangtze epicontinental sea, andoccurred in relatively near-shore, shallower environ-ments adjacent to Dianqian Land during the earlyAshgill. However, the Foliomena fauna from Tangtouand Huangnekang formations (early Ashgill) ofsouthern Jiangsu, southern Anhui and westernZhejiang, east China, is more diverse, and includes thebrachiopods Philhedra, Dedzetina, Kozlowskites,Leptestiina, Christiania, Foliomena, Cyclospira andothers (Cocks & Rong, 1988). It is associated with amore diverse trilobite fauna (Lu & Zhou, 1981). Inaddition to Nankinolithus, there occur Lonchodomas,Ovalocephalus, Shumardia, Corrugatagnostus, Nileus,Cyclopyge, Microparia, Dionide, Miaopopsis and 27


Figure 2. Ashgill to earliest Llandovery biozonation of South China employed by Mu An-zhi and colleagues, compared to thatof the present study.

Figure 3. Lithological column and the vertical distribution of graptolite and shelly fossils from Wangjiawan, Yichang, westernHubei (Loc. 11).



Table 1. Revision of the Ashgillian graptolites described by Mu et al. (1993)

Graptolite zonation(present paper)

Revised species Species described (present study) by Mu et al. (1993) Dc L–Tt Dm Neo Np

Dicellograptus graciliramosus Yin & Mu D. graciliramosus Yin & Mu + + +Leptograptus transformis Chen +

D. ornatus E.& W. D. ornatus E.& W. + + +D. excavatus Mu + +

D. complexus Davies D. szechuanensis Mu + +D. anceps (Nicholson) D. anceps (Nicholson) +

D. brevis Mu & Chen +Glyptograptus gracilis (Ge) G. gracilis Ge +

G. mirus Mu & Lin (pars) +Diplograptus acutus Lin +D. carcharus Lin +

Normalograptus ojsuensis Diplograptus bohemicus +(Koren & Mikhailova) (Marek)

D. vicatus Lin +D. wangcangensis Mu & Li +Diplogr. vicatus Lin (pars) +Glyptogr. sp. +

N. angustus (Perner) Glyptogr. salignus Lin +C. miserabilis E.& W. + +C. pygmaeus Ruedemann +

N. sp. Climacogr. angustatus Ekström + +C. celsus Ekström + +

N.? spicatus (Ge) C. spicatus Ge +G. salignus Lin +

N. extraordinarius (Sobolevskaya) Diplograptus orientalis Mu et al. +N.? sp. C. raricaudatus Ross & Berry + +

C. corneus Ge + +

Amplexograptus latus Elles & Wood A. regularis Mu & Lin + + + + cf.A. disjunctus yangtzensis +Mu & Lin (pars)A. inuiti (Cox) +A. suni (Mu) + +

A. sp. nov. A. gansuensis yichangicus +Mu & Lin (pars)

Pseudoclimacograptus chiai (Mu) Amplexogr. hubeiensis Mu & Lin + +Pseudoclimacogr. yilingensis +Mu & LinPseudocli. arcanus Lin +

Climacograptus? hastatus (T.S. Hall) C. hastatus T.S. Hall + + + + +C. hastatus finis Ge + + +C. hastatus tentaculatus Ge + + +C. hastatus tumidulus Ge +C. cf. tridentatus Lapworth +C. acutus Ge + +C. abnormispinus Ge +C. yingpanensis Ge +

Climacograptus? hastatus vesicicaulis(Ge) Climacograptus vesicicaulis Ge + + +C. tubuliferus Lapworth + + +

Appendispinograptus. longispinus hvalross Climacograptus bellulus + + + +(Ross & Berry) Mu & Zhang (pars.)

C. bicornis (Hall), Ge 1993 +C. longispinus T.S. Hall (pars.) + +C. xintanensis Ge + +C. cf. hvalross Ross & Berry +C. textilis Ge +C. textilis yichangensis Ge + +

A. hubeiensis (Ge) Climacograptus hubeiensis Ge + + + +C. hanyuangensis Ge +

A. supernus (Elles & Wood) Climacograptus supernus + + + +Elles & WoodC. bellulus Mu & Zhang (pars.) +C. minor Ge + +C. notabilis Ge +C. superus longus Ge + +

A. supernus sinicus (Ge) Climacograptus sinicus Ge + + +C. diplacanthus Bulman, Ge (1993) +

A. venustus (Hsu) Climacograptus venustus Hsu + +C. venustus simplex Ge +

other genera represented by a total of 41 species.Although Foliomena, Christiania and Nankinolithusare also present in the Chientsaokou Formation, thetrilobites and brachiopods in the Tangtou Formationare more diverse than those in the ChientsaokouFormation. Moreover, only a single specimen ofFoliomena and no Cyclospira have been recovered from

the latter, whereas these two genera are common in theTangtou Formation. It should be pointed out that thebrachiopods in the Tangtou Formation represent atypical Foliomena fauna inhabiting a relatively deeperwater regime (Sheehan, 1973).

Two species of graptolites, Dicellograptus cf. john-strupi (Hadding) and Rectograptus pauperatus (Elles &


Table 1. (Cont.)

Graptolite zonation(present paper)

Revised species Species described (present study) by Mu et al. (1993) Dc L–Tt Dm Neo Np

C. aequus Ge + +C. mirus Ge & Jiao + +

A. leptothecalis (Mu & Ge) Climacograptus leptothecalis + +Mu & Ge

A.? fibratus Ge Climacograptus fibratus Ge + +Anticostia fastigata (Davies) Orthograptus sextans Li +

Diplograptus palaris Lin +D. ostreatus Lin +

A. uniformis (Mu & Lin) Glyptograptus uniformis Mu & Lin + + + +Orthograptus maximus Mu Orthograptus maximus Mu + + +

O. rigidus Lee ?Glyptograptus triangulatus Mu & Lin +Glyptograptus lobosus Lin +

Orthograptus sp. aff. O. maximus Mu Orthograptus xinanensis Li + +O. augescens Li +O. yangziensis Li +

Rectograptus obesus Li Rectograptus truncatus obesus Li + + + +R. abbreviatus E. & W. Rectograptus abbreviatus E. & W.

R. abbreviatus holoensis Li +Rectograptus ensiformis Li +R. carnei T.S. Hall +R. gracilis sinicus Li +Orthograptus tsunyiensis (Mu) ?

R. uniformis (Mu & Lee) R. uniformis (Mu & Lee) + + + +R. truncatus (Lapworth) ?

R. socialis (Lapworth) R. socialis (Lapworth) +R. pauperatus (E. & W.) + +

R. songtaoensis Li R. songtaoensis Li + + + +R. intermedius (E. & W.) ?

Paraorthograptus pacificus (Ruedemann) Paraorthograptus pacificus + + cf. cf.(Ruedemann)P. angustus Mu & Li +P. typicus Mu +

P. brevispinus Mu & Li P. occidentatus (Ruedemann) + + + +P. longispinus Mu & Li P. longispinus Mu & Li + +

P. nanchuanensis Li ?P. simplex Li +

Nymphograptus velatus Elles & Wood Nymphograptus sichuanensis Mu +Pararetiograptus sinensis Mu Pararetiograptus sinensis Mu + +

P. regularis Mu + +P. turgidus Mu +

Paraplegmatograptus uniformis Mu Paraplegmatograptus uniformis Mu + + +P. gracilis Mu + +P. formosus Mu + +

P. connectus Mu P. connectus Mu + + + + ?P. hubeiensis Mu + +P. sextans Mu +

Yinograptus disjunctus Yin & Mu Yinograptus disjunctus Yin & Mu + + +Y. robustus Mu + + + +Y. gracilispinus Mu + +Y. brevispinus Mu +

Yangzigraptus yangziensis Mu Yangzigraptus yangziensis Mu + + +Y. minutus Mu +

Biozone abbreviations: Dc, Dicellograptus complexus Zone; L–Tt, Lower Subzone to Tangyagraptus typicus Subzone of the Paraorthograptuspacificus Zone; Dm, Diceratograptus mirus Subzone of the P. pacificus Zone; Neo, Normalograptus extraordinarius–N. ojsuensis Zone; Np,N. persculptus Zone.

Wood), have been recorded from the ChientsaokouFormation at Jiadanwan, near Donggongsi of Zunyi(Loc. 21 of Fig. 1) (see Zhang et al. 1964). The formerwas first reported and described by Hadding (1912)from the Zone of Pleurograptus linearis of Bornholm,

Denmark. The latter was described by Elles & Wood(1907) from the Dicranograptus clingani Zone toPleurograptus linearis Zone at Dob’s Linn, Scotland.Mu et al. (1993) have described R. pauperatus alsofrom the Dicellograptus complexus Zone of the


Figure 4. Lithological column and the vertical distribution of graptolite and shelly fossils from Fenxiang, Yichang, westernHubei (Loc. 12).

Wufeng Formation. However, we have not recognizedthis species in the Wufeng Formation of the presentfour reference sections.

At the Honghuayuan and Ludiping sections (Locs22 and 27 of Figs 1, 5 and 6), we found Dicellograptuscomplanatus Lapworth at the base of the Wufeng


Figure 5. Lithological column and the vertical distribution of graptolite and shelly fossils from Honghuayuan, Tongzi, northernGuizhou (Loc. 22).


Figure 6. Lithological column and the vertical distribution of graptolite and shelly fossils from Ludiping, Songtao, northeasternGuizhou (Loc. 27).

Formation. This is the first time that D. complanatushas been reported from the Yangtze region. The graptolite fauna from these two sections may indicatethe upper D. complanatus Zone. The fauna consists of 12 genera and 21 species, including several well-known species such as Amplexograptus latus (Elles & Wood), Anticostia fastigata (Davies) andAppendispinograptus supernus (Elles & Wood).Among the members of this assemblage, only the cos-mopolitan Appendispinograptus longispinus (T.S.Hall), is limited in the D. complanatus Zone. All thespecies of Dicellograptus, Normalograptus, Anticostia,Rectograptus, Orthograptus, Amplexograptus, Pseudo-climacograptus and Pararetiograptus, as well as otherAppendispinograptus species, extend to the succeedingDicellograptus complexus Zone (Figs 5, 6). At theLudiping section, the FAD of D. complexus Davies isat bed AFA 382, 1.15 m above the LAD (last appear-ance datum) of D. complanatus Lapworth. This lowestWufeng Formation fauna indicates that the base of theWufeng Formation at this section lies slightly belowthe top of the D. complanatus Zone. It is, however, thelowest base of the Wufeng Formation within theYangtze region. At most localities in the Yangtzeregion, the base of the Wufeng Formation is roughlycoincident with the base of the D. complexus Zone.

The Chientsaokou Formation, characterized by theshelly Foliomena–Nankinolithus fauna with a few grap-tolites, is early Ashgill in age. The occurrence of the D.complanatus fauna at the base of the Wufeng Formationfrom Honghuayuan and Ludiping is in agreement withthe biostratigraphic implications of this underlyingfauna and likewise places the base of the WufengFormation in the lower Ashgill. The ChientsaokouFormation is characterized by mudstone and shale andis distributed around Dianqian Land. It appears to havebeen deposited in near-shore, low energy, mudstonefacies or a mixed facies environment. The top of the unitalso may be diachronous, from within the upper D. com-planatus Zone (as at Honghuayuan and Ludiping) intothe lowermost D. complexus Zone (Donggongsi, Zunyi,Loc. 21 of Fig. 1).

2.b. Dicellograptus complexus Zone

The D. complexus Zone, which is reported from all 43Wufeng Formation localities, is the most widely dis-tributed of the Ordovician biozones in South China.This biozone not only covers the whole Yangtze plat-form but also the whole Xiangwan basin as well as theslope belt in between. The base of the zone coincideswith the FAD of the eponymous form based on theHonghuayuan and Ludiping sections (Figs 3, 5),where the boundary between the D. complexus Zoneand the underlying D. complanatus Zone is within acontinuous graptolite sequence. In the succeeding levelto the base of the D. complexus Zone, more endemicforms occur, such as Dicellograptus sp. aff. D. com-

planatus Lapworth, D. ornatus Elles & Wood,Paraplegmatograptus connectus Mu, Rectograptussongtaoensis Li, R. uniformis Mu & Li, Appendispino-graptus? fibratus (Ge) and Pararetiograptus sinensisMu. The species D. sp. aff. D. complanatus Lapworthdescribed by Chen (as D. cf. complanatus in Mu et al.1993) is similar to D. complanatus Lapworth in generalcharacters, but the stipes of the former are narrowerand more uniform in width. It might be a geographicalsubspecies of D. complanatus. However, D. sp. aff. D.complanatus ranges into higher strata than D. com-planatus. In the middle to upper part of the D. com-plexus Zone, Dicellograptus anceps (Nicholson), D.minor Toghill, Leptograptus annectans amplectensRuedemann, Rectograptus abbreviatus (Elles & Wood)and Climacograptus? hastatus (T.S. Hall) occur withtwo endemic forms, such as Dicellograptus gracili-ramosus Yin & Mu and Yinograptus disjunctus (Yin & Mu). Other widely distributed species in this inter-val include Leptograptus macer Elles & Wood,Dicellograptus complanatus arkansasensis Ruedemann,Amplexograptus latus (Elles & Wood), Normalograptusangustus (Perner), Rectograptus socialis (Lapworth),Appendispinograptus longispinus hvalross (Ross &Berry), A. supernus (Elles & Wood), A. hubeiensis (Ge)and Anticostia fastigata (Davies). Many of thesespecies continue into this zone from the underlying D.complanatus Zone.

The diversity of the D. complexus Zone is obviouslygreater than that of the lower D. complanatusZone. There are 17 genera and a total of 41 species in the D. complexus fauna (not the generaNeurograptus, Nymphograptus, Orthoretiograptusand Sinoretiograptus, Mu et al. 1993). About halfof the species (22 species) are endemic. Ten genera, including Neurograptus, Nymphograptus,Orthoretiograptus, Sinoretiograptus, Yangzigraptus,Yinograptus, Paraplegmatograptus, Arachniograptus,Pleurograptus and Paraorthograptus, originate in thiszone. This pattern indicates that a burst of speciationin graptoloids, especially in reteograptids and archire-tiolitids, began in this time interval. The Ashgill grap-toloid radiation took place during the D. complexusZone and Paraorthograptus pacificus Zone interval,which was followed by the climax episode of the lateAshgill mass extinction (Chen & Rong, 1991).

2.c. Paraorthograptus pacificus Zone

The base of the P. pacificus Zone coincides with theFADs of Paraorthograptus pacificus (Ruedemann), P.brevispinus Mu & Li, Paraplegmatograptus uniformisMu, Leptograptus planus Chen and Dicellograptustumidus Chen. The P. pacificus Zone may be subdi-vided into three parts: the Lower Subzone, theTangyagraptus typicus Subzone and the Dicerato-graptus mirus Subzone. The middle and upper parts correspond to the Tangyagraptus typicus and



Figure 7. For legend see facing page.

Diceratograptus mirus zones, respectively, of Mu et al.(1984, 1993).

2.c.1. Lower Subzone

In a similar fauna to that of the D. complexus Zone, 17genera and 42 species have been recognized from thisinterval. Among them, 19 species are cosmopolitan orintercontinental. The diversity of the fauna is almostthe same as that of the underlying D. complexus Zone,and the fauna consists mostly of the same species as inthe D. complexus Zone with the addition of seven newspecies. In addition to the five species that appear atthe base of the zone as mentioned above, two further species, Pararetiograptus parvus Mu andPseudoreteograptus nanus Mu, originate within thesubzone. This subzone and the underlying strata havenot yet been restudied from the Wangjiawan sectionbecause of poor exposures.

2.c.2. Tangyagraptus typicus Subzone

The base of the subzone is marked by the FADs ofTangyagraptus typicus Mu, T. remotus Mu & Chen, T.flexilis Mu & Chen and T.? grandis Mu & Chen. Aremarkable faunal change occurs at this level. Itinvolves not only the occurrence of the Tangyagraptusspecies but also the appearance of many new species ofDicellograptus, Normalograptus, Paraorthograptus,Paraplegmatograptus, Yinograptus and Sunigraptus.The most important of these additional new species

are Dicellograptus mirabilis Mu & Chen,Normalograptus normalis (Lapworth), N. tatianae(Keller), Paraorthograptus longispinus Mu & Li and Yinograptus dubius Mu. The tangyagraptid species group, characterized by the presence of spe-cialized secondary thecal cladia, is derived fromDicellograptus. The entire stratigraphic range ofTangyagraptus is limited to the T. typicus Subzone.Several new normalograptids, such as N. normalis(Lapworth), first appear within the subzone andbecome abundant higher up the succession in lowerSilurian strata. There are four species ofNormalograptus in this subzone, two of which origi-nate near the top of the unit.

The diversity of the T. typicus Subzone reaches alate Ordovician peak with a total of 18 genera and 53species. Among them, only 23 species are cosmopoli-tan or intercontinentally distributed. The Manosiainarticulate brachiopod assemblage occurs near thetop of the subzone and flourishes in the succeedingDiceratograptus mirus Subzone.

2.c.3. Diceratograptus mirus Subzone

This Subzone occupies only a very thin stratigraphicinterval. At the Ludiping section where the WufengFormation reaches its greatest thickness (17.53 m), theD. mirus Subzone is only 0.4 m in thickness. The baseof D. mirus Subzone is marked by the FAD ofDiceratograptus mirus, which is another specializedbranch from Dicellograptus. Normalograptids, such as


Figure 7. Important Ashgillian to earliest Llandovery graptolites from the Yangtze region. (a–b) Paraplegmatograptus uni-formis Mu, 1978, T. typicus Subzone of P. pacificus Zone, Wufeng Formation, Wangjiawan, Yichang, Hubei, AFA84. (a) mainpart of the rhabdosome; (b) proximal end of the rhabdosome. (c, m) Parakidograptus acuminatus (Nicholson, 1867), P. acumina-tus Zone, Lungmachi Formation, Wangjiawan, Yichang, Hubei, AFA107, AFA108. (d) Paraorthograptus pacificus(Ruedemann, 1947), T. typicus Subzone of P. pacificus Zone, Wufeng Formation, Honghuayuan, Tongzi, Guizhou, AFA287. (e,ab) Normalograptus extraordinarius (Sobolevskaya, 1974), N. extraordinarius–N. ojsuensis Zone, Wufeng Formation,Wangjiawan, Yichang, Hubei and Honghuayuan, Tongzi, Guizhou, AFA97, AFA290. (f) Appendispinograptus venustus (Hsu,1959), T. typicus Subzone of P. pacificus Zone, Wufeng Formation, Wangjiawan, Yichang, Hubei, AFA86. (g, h, i, aa)Akidograptus ascensus Davies, 1929, A. ascensus Zone, Lungmachi Formation, Wangjiawan, Yichang, Hubei, AFA105-106,AFA106, AFA106, AFA108. (j) Diceratograptus mirus Mu, 1963, D. mirus Subzone of P. pacificus Zone, Wufeng Formation,Wangjiawan, Yichang, Hubei, AFA95. (k) Appendispinograptus supernus (Elles & Wood, 1906), D. mirus Subzone of P. pacificusZone, Wufeng Formation, Wangjiawan, Yichang, Hubei, AFA95. (l) Normalograptus sp. aff. N. persculptus (Elles & Wood,1907), N. persculptus Zone, Base of the Lungmachi Formation, Wangjiawan, Yichang, Hubei, AFA101b. (n) Yinograptus dis-junctus (Yin & Mu, 1945), D. complexus Zone, Wufeng Formation, Honghuayuan, Tongzi, Guizhou, AFA276. (o)Normalograptus madernii (Koren & Mikhailova, 1980 in Apollonov, Bandaletov & Nikitin, 1980), N. persculptus Zone, Base ofthe Lungmachi Formation, Wangjiawan, Yichang, Hubei, AFA101b. (p) Dicellograptus complexus Davies, 1929, D. complexusZone, Wufeng Formation, Honghuayuan, Tongzi, Guizhou, AFA277. (q) Normalograptus persculptus (Elles & Wood, 1907), N.persculptus Zone, Lungmachi Formation, Wangjiawan, Yichang, Hubei, AFA102. (r) Tangyagraptus typicus Mu, T. typicusSubzone of P. pacificus Zone, Wufeng Formation, Wangjiawan, Yichang, Hubei, AFA89. (s) Dicellograptus complanatus(Lapworth), D. complanatus Zone, Wufeng Formation, Ludiping, Songtao, Guizhou, AFA379. (t) Dicellograptus anceps(Nicholson), D. complexus Zone, Wufeng Formation, Ludiping, Songtao, Guizhou, AFA384. (u) Normalograptus ojsuensis(Koren & Mikhailova, 1980 in Apollonov, Bandaletov & Nikitin, 1980), N. extraordinarius–N. ojsuensis Zone, WufengFormation, Wangjiawan, Yichang, Hubei, AFA99. (v) Pararetiograptus sinensis Mu, 1974, Lower Subzone of P. pacificus Zone,Wufeng Formation, Ludiping, Songtao, Guizhou, AFA395. (w) Anticostia fastigata (Davies, 1929), T. typicus Subzone of P.pacificus Zone, Wufeng Formation, Wangjiawan, Yichang, Hubei, AFA89. (x, y) Orthograptus maximus Mu, 1945(=Glyptograptus posterus Koren & Tzai, 1980 in Apollonov, Bandaletov & Nikitin, 1980), T. typicus Subzone of P. pacificusZone, Wufeng Formation, Wangjiawan, Yichang, Hubei, AFA89. (z) Dicellograptus ornatus Elles & Wood, T. typicus Subzoneof P. pacificus Zone, Wufeng Formation, Honghuayuan, Tongzi, Guizhou, AFA287. All the figures are × 6.5.


Figure 8. For legend see facing page.

N. sp. aff. N. angustus (Perner) and N. imperfectus(Legrand), first appear in this subzone. There are atotal of 17 genera and 38 species in this unit with 18cosmopolitan or intercontinentally distributed species.However, in the shallow water areas such asHonghuayuan and Ludiping, the diversity of late D.mirus fauna decreased substantially compared withthat of the early D. mirus fauna. Despite this overalldiversity decline, it is noteworthy that the speciesdiversity of Normalograptus increased from fourspecies in T. typicus Subzone to five species in the pre-sent subzone. If this pattern of diversity change can betaken at face value (the subzone is markedly thinnerthan neighbouring units, so that some differences indiversity may reflect unequal sampling intervals orsampling opportunities or both), then normalograp-tids had begun to increase their representation in thelatest Ordovician graptolite faunas of this region inthe upper parts of the P. pacificus Zone, that is, priorto the onset of mass extinction.

2.d. Normalograptus extraordinarius–N. ojsuensis Zone

The base of N. extraordinarius–N. ojsuensis Zone is marked by the FADs of N. extraordinarius(Sobolevskaya) and N. ojsuensis (Koren & Mikhailova).The appearance of Paraorthograptus uniformis Mu & Lisuggests that Mu’s P. uniformis Zone may correspond toa part of the present zone. Neodiplograptus shanchon-gensis (Li) first appears in the same level as P. uniformisMu & Li.

The N. extraordinarius–N. ojsuensis Zone fauna con-tains 11 genera and 31 species in the deeper water faciesfrom Yichang (Locs 10–13 of Fig. 1). Among them,17 species are cosmopolitan or intercontinentally distributed. The N. extraordinarius–N. ojsuensis faunais dominated by Normalograptus species. The nineNormalograptus species (seven of which are interconti-nentally distributed) present in this interval comprise29 % of the fauna as well as the great preponderance of

newly evolved species in the assemblage. In the rela-tively more shallow water facies such as at theHonghuayuan section near Tongzi, the N. extraordinar-ius–N. ojsuensis Zone includes only the two eponymousforms associated with N. angustus (Perner), N. normalis(Lapworth), as well as a new subspecies of N. extraordi-narius (Sobolevskaya). Thus, normalograptids makeup the entire graptolite fauna in the shallower facies ofthis zone. The episode of mass extinction reached itspeak in the deeper area of central Yangtze (Yichangregion) within the interval of this zone.

2.e. Hirnantia fauna

The well-known Hirnantia fauna is a short-lived(Hirnantian), widely distributed, relatively shallowand cool water brachiopod assemblage (Havlícek,1976; Brenchley, 1984; Sheehan, 1988; Rong & Harper,1988; Sheehan & Coorough, 1990, 1996; Owen,Harper & Rong, 1991; Brenchley et al. 1994;Brenchley, Carden & Marshall, 1995; Harper & Rong,1995; Rong, Zhan & Harper, 1999, and others). It isknown from the Hirnantian rocks of South China,Sibumasu, Tibet, Kazakhstan, Baltica, Avalonia,Southern Europe, Northern Africa, South America,Laurentia and other palaeoplates. It is characterizedby the association of typical, distinctive con-stituents such as Hirnantia, Dalmanella, Kinnella,Paromalomena, Eostropheodonta, Plectothyrella andHindella (=Cryptothyrella). In addition, Cliftonia,Leptaena (=Leptaenopoma) and Fardenia or Coolinia(=Chilidiopsis) are sometimes common. We found themajority of these taxa associated with Dalmanitina inthe Kuanyinchiao Formation at Ludiping, Songtao,northeastern Guizhou, which represents a near-shore,shallower water and lower diversity manifestation ofthe Hirnantia fauna that is typical in the Yangtzeregion. However, the Hirnantia fauna of theKuanyinchiao Formation in the Yichang area, westernHubei and Changning, southern Sichuan, comprises


Figure 8. Representative Ashgillian shelly fossils from the Yangtze region. (a) Skenidioides hubeiensis Zeng, brachial internalmould, Miaopo Formation (early Caradoc), Huanghuachang, Yichang, western Hubei. (b–d) Cyclospira sp., ventral, anteriorand dorsal views, Pagoda Formation (mid-late Caradoc), Liangshan, Nanzheng, southern Shaanxi. (e) Leptaena trifidum(Marek & Havlícek, 1967), brachial internal mould, Kuanyinchiao Formation (Hirnantian), Qicaoba, Yichang, western Hubei.(f) Foliomena sp., ventral exterior, locality and horizon as in (b). (g) Nankinolithus wanyuanensis Chen & Jian, cranidium,Linhsiang Formation (early Ashgill), Hanyuan, central Sichuan (following Lu Yenhao, 1975, pl. 38, fig. 12). (h) Dysprosorthissinensis Rong, 1984b, brachial internal mould, Kuanyinchiao Formation (Hirnantian), Tangya, Yichang, western Hubei. (i, r)Hirnantia sagittifera (M’Coy), pedicle and brachial internal moulds, Kuanyinchiao Formation (Hirnantian), Tangya (i) andHuanghuachang (r), Yichang, western Hubei. (j) Hindella crassa incipiens (Williams), pedicle internal mould, locality and hori-zon as (r). (k,m) Kinnella kielanae (Temple), brachial and pedicle internal moulds, locality and horizon as (r). (l) Draborthiscaelebs Marek & Havlícek, 1967, brachial internal mould, locality and horizon as (i). (n) Amorphognathus ordovicicus Branson& Mehl, oral view, × 100, top of the Wufeng Formation (Normalograptus extraordinarius–N. ojsuensis Zone), Wangjiawan,Yichang, western Hubei. (o) Dalmanella testudinaria (Dalman), brachial internal mould, Kuanyinchiao Formation(Hirnantian), Yanzikou, Bijie, northwestern Guizhou. (p) Paromalomena polonica (Temple), brachial internal mould, localityand horizon as (i). (q, t, v) Dalmanitina sp., cranidium, hypostome and pygidium, Kuanyinchiao Formation (Hirnantian),Donggongsi, Zunyi, northern Guizhou. (s) Mirorthis mira Zeng, brachial internal mould, locality and horizon as (r). (u)Eostropheodonta parvicostellata (Rong, 1984b), three pedicle internal moulds, Kuanyinchiao Formation (Hirnantian),Fenxiang, Yichang, western Hubei. All scale bars are 2 mm with the exception of the bar for n (0.2 mm).

more taxa and lived in deeper water environmentalconditions. In addition to the genera mentioned above, Philhedra, Acanthocrania, Pseudopholidops(very abundant), Toxorthis, Onniella, Draborthis,Dysprosorthis, Mirorthis, Triplesia, Aegiromena,Sphenotreta, Dorytreta and others are also present,along with Dalmanitina, Platycoryphe and Leonaspis(Rong, 1984b). The assemblages of Yichang andChangning are similar to that of the Kosov bed ofBohemia (Marek & Havlícek, 1967).

Hirnantia sagittifera at Honghuayuan, Tongzi,northern Guizhou, has been recovered from the lowerpart of the Kuanyinchiao Formation (Hirnantia bed:AFA295–305) (Fig. 5) and is associated withDalmanella testudinaria, Kinnella? sp., Cliftonia? sp.nov., Leptaena trifidum, Paromalomena polonica,Eostropheodonta parvicostellata, Plectothyrella sp.,Hindella crassa incipiens and a few others. In the upperpart of the unit (shelly bed: AFA306–311c) no H. sagittifera specimens have been found, butDalmanella testudinaria, Leptaena trifidum, Paro-malomena polonica, Eostropheodonta parvicostellata,Plectothyrella sp. and Hindella crassa incipiens extendup to the upper part in which Eospirifer sp., Nalivkiniasp., Hyattidina? sp., Brevilamnulella? sp., Pseudo-pholidops sp., Palaeoglossa? sp., Trucizetina? sp. and afew others occur. It is interesting to note that some ofthe last-named genera also occur from the level ofAFA305 (Fig. 5) with H. sagittifera. Thus, the brachio-pod assemblage in the upper part of the KuanyinchiaoFormation at Honghuayuan is mixed, containingsome typical elements of the Hirnantia fauna, alongwith some distinctive taxa, such as Nalivkinia andEospirifer, which have not been found in the typicalHirnantia fauna. Stratigraphically, the Hirnantia sagit-tifera-bearing beds (AFA295–305) may be correlatedwith the upper part of the Normalograptus extraordi-narius–N. ojsuensis Zone and part of the N. persculptusZone, whereas the overlying shelly beds (AFA306–311c) may correspond to part of the N. persculptus,Akidograptus ascensus and part of Parakidograptusacuminatus Zone. Therefore, Honghuayuan may beone of the well-exposed sections across the Ordovician–Silurian boundary in a continuous sequence of shellyfacies with graptolite controls.

It should be pointed out that the Hirnantia fauna(the lower and upper boundaries of the Hirnantiabeds) is diachronous within the Yangtze region. Thetiming of the first appearance of the Hirnantia faunadiffers markedly among the studied sections. At rela-tively shallow water sites such as Ludiping, SongtaoCounty, northeastern Guizhou, the Hirnantia fauna(AFA414–416) occurs immediately above theDiceratograptus mirus Subzone (AFA413) (see Fig. 6),indicating that the Hirnantia fauna appears at the baseof the N. extraordinarius–N. ojsuensis Zone. As far aswe know, this is one of the earliest occurrences of theHirnantia fauna in South China (Rong et al. 1999).

Based on Mu et al. (1979), Rong (1984a) correlatedthe base of the Kuanyinchiao Bed at Ganxi, YanheCounty, northeastern Guizhou, with the Dicerato-graptus mirus Subzone (=upper Paraorthograptus pacificus Zone). However, having checked the grapto-lite lists (see Mu et al. 1979) and their ranges, this conclusion should be further confirmed. There are two horizons (ACC97a, lower and ACC97b, upper) at the top of the Wufeng Formation at Ganxi.ACC97a contains Dicellograptus ornatus Elles &Wood, Yinograptus sp., Appendispinograputs venustus(Hsu), Rectograptus abbreviatus (Elles & Wood) andothers, and was correlated with Tangyagraptus typicusSubzone (=middle Paraorthograptus pacificus Zone)(Mu et al. 1979). It is followed in this paper. ACC97byields Yinograptus sp., Amplexograptus latus (Elles &Wood) [=A. suni (Mu)], Paraplegmatograptus sp.,Pararetiograptus sp. and others, and was correlatedwith Tangyagraptus typicus Zone by Mu and others(1979) (see Rong, 1984a). However, those taxa in thebed of ACC97b (such as Yinograptus andAmplexograptus latus) can extend into higher hori-zons. It is likely, therefore, that the assignment of theACC97b to the Diceratograptus mirus Subzone(=upper Paraorthograptus pacificus Zone) cannot beexcluded. If this is correct, the Kuanyinchiao Bed atGanxi may be correlated with the horizon youngerthan the Diceratograptus mirus Subzone (that is,younger than Paraorthograptus pacificus Zone).Further investigation on this section is needed.

At Honghuayuan, Tongzi County, north ofDianqian Land, Hirnantia and its associates(AFA295–305) appear a little higher stratigraphicallythan the base of the N. extraordinarius–N. ojsuensisZone (AFA290) (see Fig. 5).

At deeper water sites towards the central part of theYangtze platform, such as those in the Yichang area(Wangjiawan and Fenxiang) (see Figs 3 and 4), theHirnantia fauna (AFA 100–101, AFA144–145) is knownfrom a higher level above the base of the N. extraordinar-ius–N. ojsuensis Zone (AFA 97, AFA 141). There theshelly fauna is stratigraphically between the N. extraordi-narius–N. ojsuensis Zone and the N. persculptus Zone. Itcannot be excluded that the Hirnantia fauna may extendto the Normalograptus persculptus Zone.

The Honghuayuan section further indicates thatmany typical constituents of the Hirnantia fauna such as Dalmanella, Paromalomena, Eostropheodonta,Plectothyrella and Hindella, extend to Akidograptusascensus Zone or even higher.

It is clear that occurrences of the Hirnantia faunacoincide with the sea-level drop associated with latestOrdovician glaciation. During this regression, theappropriate habitat for Hirnantia fauna developed firstin the shallow water regime, whereas the conditionswere established somewhat later, at the time of maxi-mum regression, along the deeper water regime in theYichang and other areas of the Yangtze platform.


2.f. Normalograptus persculptus Zone

The base of the N. persculptus Zone is marked by theappearance of Normalograptus persculptus (Elles &Wood), N. avitus (Davies), N. wangjiawanensis (Mu &Lin), N. tortithecatus (Hsu), Pseudorthograptus angus-tifolius (Chen & Lin), Glyptograptus laciniosusChurkin & Carter, G. lungmaensis Sun, etc. The N. per-sculptus Zone fauna contains only biserial graptoloids,predominately normalograptids. This fauna includesonly 9 genera and 29 species. Thus, the diversity at thegeneric level continued its dramatic decline. Amongthe 29 species, 17 are cosmopolitan or intercontinen-tally distributed. Five of these species, includingNormalograptus extraordinarius (Sobolevskaya), Para-orthograptus brevispinus (Mu & Li), Climacograptus?hastatus (T. S. Hall), Amplexograptus sp. aff. A. latus(Elles & Wood) and Paraplegmatograptus sp. (P. connec-tus group), are only supported by one or two speci-mens. These are all survivors from the D. mirus Zoneextinction climax event but all expired in the N.persculptus episode. This last episode was identified byChen & Rong (1991) as the epilogue episode. The sam-ples from the D. mirus Subzone to N. persculptus Zonehave been continuously and densely collected throughthe shallow water to deeper water facies belts in theYangtze region. It seems unlikely that the disappear-ances of some taxa are the result of a Signor-Lippseffect.

Mu (1988) correlated the European Akidograptusascensus Zone with the ‘Glyptograptus persculptus’Zone of China. This correlation depends on data frombefore 1988. Based on the present detailed collectionsfrom the four reference sections mentioned above, theNormalograptus persculptus Zone and Akidograptusascensus Zone are easily distinguished.

2.g. Akidograptus ascensus Zone

The base of the Zone coincides with the FADs ofAkidograptus ascensus Davies. Neodiplograptus bicau-datus Chen & Lin and Normalograptus lubricus (Chen& Lin) are also newcomers and occur at a slightlyhigher level. There are a total of 6 genera and 23species in this Zone. Among them, 13 species occurelsewhere. Thus, more than half of the Lungmachi A.ascensus Zone fauna have an intercontinental distribu-tion. The A. ascensus Zone is widely distributedthrough the Yangtze platform. It appears to reach itsmaximum thickness at Ludiping, where it is 8.22 mthick. At Yichang, in the central part of the Yangtzebasin, for instance, it is only 0.18 m thick.

2.h. Parakidograptus acuminatus Zone

The base of the P. acuminatus Zone is marked by theappearance of P. acuminatus (Nicholson), as well asmany globally or intercontinentally distributed species

such as Normalograptus praemedius (Waern), N. rec-tangularis (M’Coy) and Pseudorthograptus illustris(Koren & Mikhailova) followed at slightly higher lev-els by Hirsutograptus sinitzini (Chaletskaya), etc. TheP. acuminatus Zone fauna contains a total of 11 generaand 39 species. Among them, 5 genera and 21 speciesare new. Twenty-two species are cosmopolitan orintercontinentally distributed. Thus, a substantial fau-nal turnover occurs at this level. Half of the generapresent in the P. acuminatus Zone are newly evolved inthis interval.

3. Correlation

A global correlation of the Ashgill to earliestLlandovery is based mainly on the graptolitesequences as well as the shelly Hirnantia fauna.Elements of the Hirnantia fauna occur in many sec-tions that we have examined from the Yangtze plat-form (Locs 2–4, 7–15, 18–24, 26, 28, 29, 35, 37 and 40of Fig. 1). A complete graptolite sequence withoutshelly Hirnantia fauna has been known from He Xian(Loc. 36 of Fig. 1; Zhang et al. 1966) and Jurong (Loc.38 of Fig. 1; Chen et al. 1988) in the Lower Yangtzeregion. The palaeogeographic setting of the Yangtzeregion (particularly its nature as a semi-enclosed sub-tropical platform) fostered development of the mostdiverse and continuously preserved Ashgill graptolitefauna in the world. Despite high levels of endemism,the fauna includes a very good representation of thewidely distributed species that were present during thelatest Ordovician. These widely distributed elementsof the Wufeng Formation fauna permit global correla-tion of this unit.

3.a. Dob’s Linn, southern Scotland

The Dob’s Linn section was approved as the GlobalStratotype Section and Point (GSSP) of the Ordovician–Silurian boundary (Holland, 1984; Williams, 1988).The Hartfell Shale and Birkhill Shale are the lithos-tratigraphic units that include the uppermostOrdovician and lowermost Silurian strata. However,continuous graptolitic shale within this interval is present only from the Dicranograptus clingani Zone to lower Pleurograptus linearis Zone, and from theupper Normalograptus persculptus Zone to higherLlandovery graptolite zones. Between these two con-tinuous graptolitic shales, there are 28 m of mostlypale grey, barren mudstone or shale (Williams, 1982b).Two graptolitic bands bear a Dicellograptus complana-tus fauna in the D. complanatus Zone (Williams,1982b). Five graptolitic bands comprise the D. ancepsZone including Bands A and B in the D. complexusSubzone, and Bands C to E in the P. pacificus Subzone.

Toghill (1970) described the graptolites from the complanatus Band, including D. complanatusLapworth, Rectograptus socialis (Lapworth) and


Normalograptus miserabilis (Elles & Wood). Thesespecies are also present at the Ludiping section,Songtao, northeastern Guizhou. Toghill also recordedrare examples of Plegmatograptus nebula Elles &Wood from the complanatus Band. However, it has notyet been found from the D. complanatus Zone of theYangtze region. P. nebula Elles & Wood occurs mainlywithin the D. clingani and P. linearis zones (Williams,1982a). Plegmatograptus became extinct by the middleAshgill (D. complexus Zone) where it was replaced byits descendent Paraplegmatograptus.

The Bands A and B contain a D. complexus–D.anceps fauna with a total of 9 genera and 12 species.All of them occur in the D. complexus Zone of theYangtze region as well, except Normalograptus nor-malis Lapworth. N. normalis Lapworth appears a bithigher in the Yangtze region (in the Diceratograptusmirus Subzone), and is most abundant in theParakidograptus acuminatus Zone. Williams (1982b)proposed Dicellograptus anceps (Nicholson), whichoccurs in both bands A and B, as the zonal species forthis interval. Based on the continuous sections fromthe Yangtze region, D. anceps occurs from the middleD. complexus Zone into the lower part ofTangyagraptus typicus Subzone. Thus, the presence ofD. anceps and absence of P. pacificus (Ruedemann)from Bands A and B at Dob’s Linn indicate that thesetwo bands may correlate to an interval above the mid-dle D. complexus Zone and below the base of the P.pacificus Zone in the Yangtze region. The occurrenceof D. anceps is later than that of D. complexus in theYangtze region. This implies that the base of the ‘D.complexus Subzone’ at Dob’s Linn may not be higherthan that of D. anceps as suggested by Williams(1982b, fig. 2; see Fig. 9 herein). Dicellograptus ancepsmay extend into the N. extraordinarius Zone based onits occurrence in the Dob’s Linn section.

Williams (1982b) reported the species Plegmato-graptus? craticulus Williams and Orthoretiograptusdenticulatus Mu (this species was first cited by Wang etal. (1977) from Mu et al.’s manuscript) from the D.anceps Zone at Dob’s Linn. Based on his illustratedspecimens, P.? craticulus Williams may be a junior syn-onym of Paraplegmatograptus uniformis Mu, whichwas first cited by Wang et al. (1977) from Mu et al.’smanuscript. Orthoretiograptus denticulatus specimensillustrated by Williams (1982b, p. 43, pl. 4, figs 13–15,text-figs 12a–d) may not be Orthoretiograptus, butrather Pararetiograptus sinensis Mu 1974. These twospecies are well-known components of the D. com-plexus and P. pacificus zone faunas in the Yangtzeregion.

The Bands C and D from the Dob’s Linn sectioncontain a P. pacificus fauna that Williams (1982b)referred to as the P. pacificus Subzone of his D. ancepsZone (Fig. 9). Twelve genera and 16 species have been recorded from these two bands. However,except for Paraorthograptus pacificus (Ruedemann),

Plegmatograptus? nebula lautus Koren & Tzaj andNymphograptus velatus Elles & Wood, most of themcontinue from the lower bands. P. nebula lautus Koren& Tzaj was described based on incomplete specimenswithout proximal ends. Thus, we are not sure whetherit is a plegmatograptid. Nymphograptus velatus Elles &Wood (D. anceps Zone) is the only species which hasnot yet been recorded in the Yangtze region within thisinterval. Thus, the whole fauna is comparable withthat of the P. pacificus Zone fauna from the Yangtzeregion.

The specimens described by Williams (1982b) asDicellograptus ornatus Elles & Wood from Band E dif-fer somewhat from one another and do not agreeexactly with the form of D. ornatus sensu stricto. Hisspecimens illustrated in plate 1, figure 6 and text-fig.6f, 6g represent Dicellograptus mirabilis Mu & Chen,which occurs in the Tangyagraptus typicus Subzoneand Diceratograptus mirus Subzone in the Yangtzeregion. Williams’ (1982b) specimen illustrated in plate1, figure 8 is a specimen of Dicellograptus turgidus Mu,which occurs commonly in the Tangyagraptus typicusSubzone of P. pacificus Zone in Yangtze. Thus, itappears that these two species extend to a higher hori-zon, into the N. extraordinarius Zone at Dob’s Linn.The most important member of the Band E fauna isNormalograptus extraordinarius (Sobolevskaya),which indicates the existence of N. extraordinarius–N.ojsuensis Zone at this level. Williams (1983) stated thatthe D. anceps–N. extraordinarius zonal boundary lieswithin the pale, unfossiliferous mudstone that occurs ashort distance above the D. anceps bands. If the FADof N. extraordinarius (Sobolevskaya) coincides withthe base of the named zone, then the base of the N.extraordinarius–N. ojsuensis Zone should lie belowBand E at Dob’s Linn.

The FAD of N. cf. persculptus (Elles & Wood) (=N.parvulus (H. Lapworth; see Zalasiewicz & Tunnicliff,1994)) is about 0.7 m above the base of the Birkhillshale at the Linn Branch section (Williams, 1983).Melchin (pers. comm., 1998) has re-examined thegraptolite specimens of the Linn Branch section andconfirms that no typical specimens of Normalograptuspersculptus (Elles & Wood) occur there. Since there isan unfossiliferous interval between the extraordinariusBand and the Birkhill graptolite succession, the exactlocation of the base of the N. persculptus Zone at LinnBranch remains uncertain. However, the N. persculptusZone from Linn Branch may partly correlate to the N.persculptus Zone in Yichang. The N. persculptus faunafrom Linn Branch includes N. parvulus (H. Lapworth)(=G. cf. persculptus of Williams, 1983), N. avitus(Davies), N. normalis (Lapworth), N. miserabilis (Elles& Wood) (=N. angustus (Perner)), N. medius(Törnquist) and N. pseudovenustus (Legrand)(=Glyptograptus? venustus cf. venustus Legrand:Williams, 1983). N. normalis occurs from the D. mirusSubzone and extends to the Rhuddanian strata near


Yichang. N. angustus (Perner) is a long-lived species,which occurs from the D. complanatus Zone to theRhuddanian strata in the Yangtze region. N.pseudovenustus (Legrand) occurs in the N. persculptus-bearing beds from Djerance region of Algeria(Legrand, 1986). N. medius first appears in the P.acuminatus Zone of the Yangtze platform sections andis not present at lower levels.

As Melchin, Koren & Williams (1998) pointed out,the world-wide occurrences of A. ascensus and P.acuminatus have been dealt with in different ways. Inmany parts of the world, including Kazakhstan,Kolyma, Bohemia, Poland and Thuringia, as well asthe present study area in the Yangtze region of China,a distinct interval with abundant A. ascensus occursbelow the first appearance of P. acuminatus, and isoften recognized as a separate A. ascensus Zone belowthe P. acuminatus Zone (Apollonov, Bandaletov &

Nikitin, 1980; Koren et al. 1979; Storch & Loydell,1996; Schauer, 1971; Teller, 1969; Chen & Lin, 1978).Melchin, Koren & Williams (1998) also noted that thespecimens of P. acuminatus s.l. that occur in the lowerpart of the combined P. acuminatus–A. ascensus Zone(that is, with the early A. ascensus specimens at thebase of the Silurian System) at Dob’s Linn differ fromtypical specimens of P. acuminatus s.s. They referredthese early representatives to the subspecies P. acumi-natus praematurus (Davies). This suggests that theFADs of A. ascensus and P. acuminatus acuminatusmay not coincide even at Dob’s Linn. Whatever thecase at Dob’s Linn, it is clear that in many regionsoccurrences of A. ascensus and P. acuminatus acumina-tus reliably define two distinct intervals, and it is thelower of these two that most nearly corresponds to theSilurian GSSP at Dob’s Linn. A fuller understandingof these species ranges, and such a secure correlation


Figure 9. Correlation of the Ashgill to earliest Llandovery biozones between Yangtze and different continents. * was reportedby Melchin, McCracken & Oliff (1991) as N. bohemicus Zone.

of the base of the Silurian System, will emerge only bythe evaluation of these species and their ranges relativeto a carefully and consistently defined set of otherspecies ranges. It is our hope that the data presentedhere from the Yangtze platform will contribute to thiseffort.

3.b. Spain and Portugal

The glaciomarine sediments of Hirnantian age and theearliest Llandovery graptolite shale are widely distrib-uted in the West Asturian–Leonese Zone, IberianCordillera, Central Iberian Zone and Ossa-MorenaZone with low diversity shelly and graptolite faunas(Gutiérrez-Marco, Robardet & Piçarra, 1998). A typi-cal Hirnantian fauna including Hirnantia sagittiferaand Plectothyrella crassicosta chauveli occurs from thelower part of the ‘Criadero Quartzite’ in the southernCentral Iberian Zone, Spain. The lowest Llandoverygraptolites have been documented as ascensus–acumi-natus Zone from the four tectonic belts as mentionedabove. Ashgillian conodonts of the Amorphognathusordovicicus Zone have been also documented fromTruchas syncline of the north Central Iberian Zone.Although to conduct a precise correlation between theIberian Peninsula and the Yangtze region is prema-ture, the Hirnantian to earliest Llandovery fossilsequence is similar between these two regions.

3.c. Thuringia–Saxonia–N. Bavaria, Germany

Two different facies, the Thuringian facies (east) andBavarian facies (west) are recognized from this regionthrough Ordovician to Silurian (Jaeger, 1988).Although the lithofacies of these two areas are different, the graptolite sequences are similar.Normalograptus persculptus (Elles & Wood)(=Diplograptus bohemicus (Marek), Jaeger, 1977) wasdescribed by Jaeger (1977) from the uppermost DöbraSandstone (Bavarian facies belt). The Akidograptusascensus Zone was recognized as the lowest biozonefrom the Thuringian facies belt (Ronneburg andOelsnitz) by Schauer (1971) and from the Bavarianfacies belt by Stein (in Jaeger, 1988). The overlyingstrata are assigned to the P. acuminatus and C. vesicu-losus zones, which are readily correlated with thosezones in the Yangtze region (Fig. 9).

3.d. Bohemia

Glyptograptus bohemicus Marek was the first grapto-lite described from the upper Kosov Formation byMarek (1954). Since then, both the Czech and Chineseworkers have used it as a zonal fossil for the latestOrdovician biozone (Mu, 1974; Storch, 1988). Thetype specimens as well as additional materials from theCzech Republic and Wales have been re-studied byStorch & Loydell (1996). They concluded that

‘Glyptograptus bohemicus (Marek)’ is a junior subjec-tive synonym of Normalograptus persculptus (Elles &Wood). This revision is accepted here. From the re-description of N. persculptus (Elles & Wood) given byStorch & Loydell (1996), we note that the definition ofN. persculptus (Elles & Wood) has been slightly broad-ened. As noted in Section 1, Fan (Fan Jun-xuan,unpub. Masters thesis, Nanjing Institute of Geology &Palaeontology, 1998) recently has made a morphomet-ric study of these taxa and their relations to the speciesrecorded from the Yangtze region. He concluded thatthe ‘Glyptograptus bohemicus’ materials described byChinese authors in the past agree very well withNormalograptus ojsuensis (Koren & Mikhailova).Thus, we refer the ‘Glyptograptus bohemicus’ materialsdescribed by Mu and his colleagues to Normalograptusojsuensis (Koren & Mikhailova).

N. persculptus (Elles & Wood) occurs at the top ofthe Kosov Formation with only a few other grapto-lites, such as Normalograptus sp. aff. N. miserabilis(Elles & Wood) and N. normalis (Storch, 1988). Theoccurrence of the persculptus graptolite fauna indi-cates that the Hirnantia fauna in Bohemia may be per-sculptus Zone in age. However, it is difficult tocorrelate the N. persculptus Zone of Bohemia withother regions in the world (Storch & Loydell, 1996).We are inclined to the view that N. persculptus Zone ofBohemia may roughly correspond to the same zone inthe Yangtze region, that is, to a level somewhere withinthe N. persculptus Zone, however, its exact location rel-ative to the base of this zone cannot be determined(Fig. 9).

The Akidograptus ascensus Zone has also beenemployed by Storch & Loydell (1996). The base of thezone lies 70 cm below the base of the Silurian black shales, and yields Akidograptus ascensus,Normalograptus angustus, Neodiplograptus lanceolatusStorch & Serpagli, as well as the highest identifiable‘Glyptograptus bohemicus’ (that is, N. persculptus s.l.).The whole A. ascensus Zone fauna may include more species, such as Neodiplograptus modestus,Neodiplograptus sp. aff. N. parvulus (Lapworth), N.parajanus (Storch), N. elongatus (Churkin & Carter),Cystograptus ancestralis Storch, Normalograptus sp.aff. N. praemedius (Waern) and N. trifilis (Manck). TheP. acuminatus Zone fauna has been recorded by Storch(1988). It is marked by the incoming of three species,Parakidograptus acuminatus, Neodiplograptus diminu-tus apographon (Storch) and Normalograptus longifilis(Manck). The first two species have also been recordedfrom the P. acuminatus Zone of the Yangtze region.

3.e. Poland

A typical Hirnantia fauna, containing Hirnantia sagit-tifera, Eostropheodonta, Dalmanella testudinaria andtrilobites Mucronaspis mucronata etc., occurs in theuppermost Ashgill silty beds from the Holy Cross


Mountains, southeastern Poland (Temple, 1965;Teller, 1969). ‘Ashgillian’ to early Llandovery fossilsand strata have been recorded from the Lebork bore-hole, northern Poland, Peribaltic depression andPodiasie depression, eastern Poland, as well as theCarpathian and Holy Cross Mountains, southeasternPoland. However, from the fossils and strata throughthe Ordovician–Silurian boundary interval, theLebork 1G-1 borehole sequence in northern Poland is probably the most important (Tomczyk &Tomczykowa, 1976). In ascending order, the sequenceis Mucronaspis mucronata, Normalograptus persculp-tus, Akidograptus ascensus and Parakidograptusacuminatus zones, etc. Thus, it is correlative with thoseof the Yangtze region.

3.f. Southern Kazakhstan

Middle Ashgill to earliest Llandovery graptolite-bear-ing strata with Hirnantia–Dalmanitina beds are welldeveloped in southern Kazakhstan (Apollonov,Bandaletov & Nikitin, 1980). The lower Subzone of the Appendispinograptus supernus Zone, theAppendispinograptus longispinus Subzone, includes A.supernus, A. longispinus hvalross and Rectograptusamplexicaulis (Hall). These species are all commonforms from the Dicellograptus complanatus Zone tothe Lower Subzone of the Paraorthograptus pacificusZone in the Yangtze region. Without a set of morecharacteristic species in the A. longispinus Subzone insouthern Kazakhstan, precise correlation betweensouthern Kazakhstan and the Yangtze region may notbe possible at this level.

The upper Subzone of the A. supernus Zone inKazakhstan, the Paraorthograptus pacificus Subzone,includes Paraorthograptus pacificus, Appendispino-graptus supernus, A. longispinus hvalross, Dicellograptusornatus, D. minor, Normalograptus tatianae, N. cf. nor-malis, Rectograptus amplexicaulis, Orthograptus max-imus Mu (=Glyptograptus posterus Koren & Tzaj) andAmplexograptus latus (Elles & Wood) (=A. stukalinaeMikhailova). Most of these species are also commonin Paraorthograptus pacificus Zone fauna in Yangtze.

The FAD of N. ojsuensis is located near the LAD ofParaorthograptus pacificus (Ruedemann) and a littlelower than the FAD of Normalograptus extraordinarius(Sobolevskaya) in southern Kazakhstan (Apollonov,Bandaletov & Nikitin, 1980). In the Yangtze regionsections, the FADs of N. ojsuensis and N. extraordinar-ius coincide, and both appear immediately followingthe extinction of Diceratograptus mirus in Yichangarea (deeper water area). Among the sections in thisarea (such as at Wangjiawan), Paraorthograptus pacifi-cus and many of the associated species continue intothe interval of the N. extraordinarius–N. ojsuensisZone whereas among the southern, more near-shoresections (e.g. Honghuayuan), the P. pacificus assem-blage disappears with D. mirus. This consistent pattern

of occurrence relative to the highly distinctive andshort-lived D. mirus, suggests that the simultaneousorigin of N. ojsuensis and N. extraordinarius in our sec-tions reflects the true timing of their evolutionary ori-gins. Thus, the recorded FAD of N. extraordinarius(Sobolevskaya) from southern Kazakhstan may be alittle later than that in the Yangtze region.

The Hirnantia–Dalmanitina-bearing beds in south-ern Kazakhstan include two graptolite species, N.ojsuensis (Koren & Mikhailova) and N. extraordinarius(Sobolevskaya) (=Glyptograptus persculptus forma A).Thus, the occurrence of the Hirnantia–Dalmanitinafauna in southern Kazakhstan may be comparable tothe majority of localities in the Yangtze region. Koren(in Apollonov, Bandaletov & Nikitin, 1980) hadalready recognized that ‘Glyptograptus persculptusforma B’ (=N. persculptus s.s.) was synonymous with‘Glyptograptus bohemicus Marek’. Mu & Lin (1984)and Chen (1984) also suggested that ‘Glyptograptuspersculptus forma B’ from southern Kazakhstan is ajunior synonym of Glyptograptus bohemicus Marek.However, recent investigations by Storch & Loydell(1996) demonstrate that ‘G. persculptus forma B’ issynonymous with N. persculptus (Elles & Wood).Thus, the ‘G. persculptus forma A’ and ‘G. persculptusforma B’ from Kazakhstan, which occur separately,may represent the N. extraordinarius–N. ojsuensis Zoneand N. persculptus Zone, respectively, as recognized inthe Yangtze region and elsewhere.

The N. persculptus Zone from southern Kazakhstanincludes the eponymous form as well as N. angustus(Perner), N. normalis (Lapworth) and ‘Pseudoclimaco-graptus’ sp. Among them only the last, which is anearly representative of Metaclimacograptus, has notyet been recognized in the Yangtze region. TheHirnantian shelly fauna from southern Kazakhstan isassociated with the N. persculptus graptolite fauna(field number 287) at north Krylo section II(Apollonov, Bandaletov & Nikitin, 1980). Along theZhideli river, there occurs a limestone bed (field num-ber 264) yielding a typical Hirnantia fauna(Apollonov, Bandaletov & Nikitin, 1980) which isunderlain by pacificus Zone (263) and overlain bymudstone (267) with some graptolites. The latter is inturn overlain by A. ascensus–P. cf. acuminatus-bearingbeds (269, 270). It suggests that the brachiopod faunamay be corresponding to the extraordinarius Zone andpart of the persculptus Zone.

Koren et al. (1979) did not recognize a separateAkidograptus ascensus Zone in southern Kazakhstan.However, 2.5–3 km northwest of the Ojsu section,there is a graptolite fauna (F-290) above the Hirnantiabeds (Apollonov, Bandaletov & Nikitin, 1980). Thisgraptolite fauna includes Akidograptus cf. ascensusDavies, Normalograptus angustus (Perner), N. sp. ex gr. N. normalis, Neodiplograptus modestus primusMikhailova and Normalograptus cf. madernii (Koren &Mikhailova). This assemblage appears to be a typical


Akidograptus ascensus Zone fauna. The A. ascensusfauna also occurs at the Dulban section (F-280 ofApollonov, Bandaletov & Nikitin, 1980, p. 10). Bed F-280 yields Akidograptus sp., Normalograptus angustus,N. acceptus, N. sp. ex gr. N. normalis and N. madernii.Both of these two graptolite-bearing beds withAkidograptus ascensus or Akidograptus sp. lie strati-graphically below occurrences of Parakidograptusacuminatus Zone fauna (Apollonov, Bandaletov &Nikitin, 1980). These observations suggest the presencein southern Kazakhstan of a separate A. ascensus Zonebelow the P. acuminatus Zone, which is comparable tothe situation in the Yangtze region.

The Parakidograptus acuminatus Zone in southernKazakhstan (in the sense used herein) includes P.acuminatus, Normalograptus acceptus, N. sp. aff. N.angustus, Akidograptus ascensus cultus Mikhailova,Metaclimacograptus fidus Koren & Mikhailova andM. pictus Koren & Mikhailova. The first three speciesare common in the P. acuminatus Zone of the Yangtzeregion. Metaclimacograptus is also present in the P.acuminatus Zone of the study area, but is representedby different species.

3.g. Kolyma, northeastern Siberia

The Appendispinograptus supernus Zone in this areaincludes Dicellograptus complanatus, numerous sub-species of A. longispinus, Paraorthograptus pacificusand Rectograptus amplexicaulis, etc. (Koren et al.1979). The A. longispinus Subzone of Kolyma con-tains mainly D. complanatus and species of the R.amplexicaulis group. The P. pacificus Subzone includesP. pacificus, R. amplexicaulis, A. longispinus hvalross,A. supernus, Climacograptus? hastatus, Normalo-graptus cf. angustus and D. complanatus, etc.Additional species occur in the upper part of theSubzone. These newcomers include P. pacificus affinis,Normalograptus tatianae and Nymphograptus velatus.However, Koren et al. (1983) reported that N.ojsuensis, N. angustus, N. normalis, P. pacificus andother new species occur near the top of the P. pacificusSubzone. Since the graptolite diversity from Kolyma isrelatively low compared to that of the Yangtze region,it is difficult to make a precise correlation with thesesubzones. The A. supernus Zone of Kolyma is roughlycorrelative with the D. complanatus Zone to P. pacifi-cus Zone interval in the Yangtze region (Fig. 9).

Mirny Creek, Kolyma River is the type locality ofNormalograptus extraordinarius (Sobolevskaya). TheN. extraordinarius–N. ojsuensis Zone at this localitycontains mainly N. extraordinarius, N. ojsuensis, N.angustus, N. normalis and a few others (Oradovskaya& Sobolevskaya, 1979). The FADs of N. ojsuensis(108-2/1.3-5) and N. extraordinarius (107-1/1.2) arefrom successive collections separated by 2 m in theMirny Creek section. Compared with the 89 m thickness of the N. extraordinarius and N. persculptus

zones in this section, the 2 m separation may not besignificant. However, from the Ina River section,Normalograptus ojsuensis occurs at the base of the N.extraordinarius Zone (Koren et al. 1983). This occur-rence further supports the inference that the FAD ofN. ojsuensis is coincident with that of N. extraordinar-ius in Kolyma region.

The upper Tirekhtyakh horizon was further studiedas two parts, the lower N. extraordinarius Zone and the upper N. persculptus Zone by Koren, Oradovskaya& Sobolevskaya (1988). The N. persculptus Zoneincludes N. persculptus, N. angustus, N. normalis, N.mirnyensis (Obut & Sobolevskaya) (closely related toN. angustus) and N. torosus Koren & Sobolevskaya.

Koren, Oradovskaya & Sobolevskaya (1988) reportedthat the most complete and well-known section ofthe Tirekhtyakh horizon and the overlying Chalmakhorizon is exposed along Mirny Creek. The systemicboundary between the Ordovician and Silurian systems is drawn at the base of unit 73, which is 1.5 mthick and coincides with the base of the MautFormation. The index species Akidograptus ascensusoccurs at the base of unit 74, 1.5 m above the bound-ary, and Parakidograptus acuminatus occurs in thelower part of the unit 75, 11 m above the boundary.Their report (1988) clearly described two separatedgraptolite horizons that may correspond to theAkidograptus ascensus and Parakidograptus acumina-tus zones in the Yangtze region.

It was reported that a Hirnantia fauna occurs fromthe Q Horizon of the Omulev Mountains, Kolyma(Oradovskaya in Koren et al. 1983). Rong & Harper(1988, p. 395) concluded that the Kolyma brachiopodfauna has no species common to the Hirnantia faunaand is better assigned to the Lower Edgewood fauna.

3.h. Malaya Peninsula

Uppermost Ordovician to lower Silurian graptoliteand shelly sequences have been reported from theLangkawi Islands, northwestern Malaya (Jones, 1973).The Normalograptus persculptus Zone spans 1.1 mthick platy black siltstones with N. persculptus (Elles &Wood), Neodiplograptus modestus (Lapworth) andGlyptograptus temalaensis Jones. The top of the Zoneis marked by a thick bed of gritty siltstone carryingshelly fossils amongst which Dalmanitina malayensis isprominent. There are 13.8 m thick cherty beds withoutfossils above the D. malayensis bed. The Cystograptusvesiculosus Zone and younger graptolite zones havebeen recognized above the cherty beds. Rong (1979)correlated the N. persculptus, D. malayensis as well asthe unfossiliferous cherty beds to the N. persculptusZone to P. acuminatus Zone interval. If the identifica-tion of N. persculptus from the Langkawi Islands iscorrect (it has not yet been described), the shelly bedswith the endemic Dalmanitina malayensis should becorrelated to the upper N. persculptus Zone or higher


level. Thus, the Dalmanitina malayensis beds may be alittle higher than that of the Hirnantia-bearing bedsfrom Yangtze region.

In southern Thailand, close to the border withMalaysia, a Hirnantia fauna containing Hirnantiasagittifera, Aegiromena planissima, Paromalomena sp.etc., as well as trilobite Mucronatus mucronata, hasbeen recognized (Cocks & Fortey, 1997). Graptoliteshave been identified by Rickards as N. persculptusfauna, immediately underlying the shelly beds(Wongwanich et al. 1990, p. 6). It indicates that theHirnantia beds from southern Thailand are correlativewith that of the Langkawi Islands. However, the com-ponents of the shelly fauna between Langkawi andsouthern Thailand are a little different; the Hirnantianbrachiopods as well as Dalmantina mucronata areabsent at Langkawi. On the other hand, the Hirnantiafauna of southern Thailand does not fully agree withthose of the Shan State of Burma and Yichang,Yangtze as suggested by Cocks & Fortey (1997). Manydistinctive brachiopod taxa of the Hirnantia faunaelsewhere, such as Kinnella, Dalmanella, Cliftonia,Eostropheodonta, Plectothyrella and some others, arenot present in these collections. Stratigraphically, weassume that the Hirnantia beds of southern Thailandare probably the equivalent of the upper part of N.persculptus Zone.

3.i. Yukon, Canada

The Ashgill graptolite biostratigraphy of the Peel River,Yukon, was reported by Lenz & McCracken (1982,1988), and Chen & Lenz (1984). The Dicellograptusornatus Zone of the Yukon Territory containsDicellograptus ornatus, D. minor, Amplexograptus latus,Rectograptus abbreviatus, Anticostia cf. fastigata,Appendispinograptus supernus, A. longispinus hvalross,Climacograptus? hastatus, Pararetiograptus sinensis Mu(=Retiograptus pulcherrimus Keble & Harris, Lenz1977; Orthoretiograptus denticulatus Mu, Chen & Lenz,1984, Lenz & McCracken, 1988) and Arachniograptuslaqueus. It roughly corresponds to the Dicellograptuscomplexus Zone as suggested by Chen & Lenz (1984)and Lenz & McCracken (1988).

The P. pacificus Zone is recognized by the presenceof abundant P. pacificus and A. supernus. The otherspecies present include Anticostia cf. fastigata,Amplexograptus latus, Rectograptus abbreviatus andAppendispinograptus leptothecalis Mu & Ge.

Diceratograptus mirus Mu (=Diceratograptus cf.mirus Mu, Chen & Lenz, 1984), discovered from thetop of the P. pacificus Zone indicates the existence ofthe D. mirus Subzone in the Yukon. Diceratograptusmirus is associated there with D. ornatus, P. pacificus,A. supernus, A. cf. longispinus, C? sp. ex. gr. C.?hastatus, Amplexograptus latus and Arachniograptuslaqueus etc. All of these species except Arachniograptuslaqueus are also present in the D. mirus Subzone of the

Yangtze region. Different species of Arachniograptusoccur in these two regions.

The P. pacificus and P. acuminatus zones in the Yukonare juxtaposed across a cryptic unconformity at whichthe N. extraordinarius and N. persculptus zones are miss-ing. This is most likely a consequence of regression andsubmarine erosion induced by the Hirnantian glacia-tion (Melchin, 1987; Lenz & McCracken, 1988).Parakidograptus acuminatus occurs together withAkidograptus ascensus, Normalograptus cf. trifilis,Cystograptus vesiculosus and Neodiplograptus modestusdiminutus etc. Of the Yangtze platform zones, this faunais most similar to that of the P. acuminatus Zone.

3.j. Canadian Arctic islands

Melchin (1987) erected the Anticostia fastigata Zone(originally referred to as the ‘Orthograptus fastigatus’Zone) from the Canadian Arctic islands and suggestedthat this Zone is correlative with the Dicellograptuscomplexus Zone. His Paraorthograptus pacificus Zonecontains Amplexograptus latus (Elles & Wood) andAppendispinograptus supernus (Elles & Wood) fromHuff ridge. In the Arctic islands, the P. pacificusZone is succeeded immediately by an interval containing ‘Neodiplograptus bohemicus (Marek)’ andNormalograptus shanchongensis (Li) (Melchin,McCracken & Oliff, 1991). Following previous inter-pretations of the Yangtze region graptolites, Melchin,McCracken & Oliff (1991) referred this fauna to the N.bohemicus Zone. Storch & Loydell (1996) suggestedthat these pre-Hirnantia Canadian specimens of N.bohemicus, like the type materials of N. bohemicus(Marek), may be synonymous with Normalograptuspersculptus (Elles & Wood). However, Fan’s (Fan Jun-xuan, unpub. Masters thesis, Nanjing Institute ofGeology & Palaeontology, 1998) demonstration thatthe Chinese ‘N. bohemicus’ from the N. extraordinar-ius–N. ojsuensis Zone is instead identical withNormalograptus ojsuensis (Koren & Mikhailova) raisesthe possibility of a similar relation for the CanadianArctic materials. Based on its location between clearlycorresponding P. pacificus and N. persculptus zones, wetentatively correlate the ‘N. bohemicus’ Zone ofMelchin, McCracken & Oliff (1991) with the N. extra-ordinarius–N. ojsuensis Zone in the Yangtze region.Melchin (pers. comm., Dec. 1998) also has recentlycome to the conclusion that his specimens referred as‘N. bohemicus (Marek)’ are N. ojsuensis (Koren &Mikhailova).

The Normalograptus persculptus Zone from ArcticCanada includes Normalograptus cf. persculptus (Elles& Wood), N. wangjiawanensis (Mu & Lin) andNeodiplograptus shanchongensis (Li). The intervalabove the N. persculptus Zone in the Canadian Arcticislands lacks A. ascensus and P. acuminatus. Melchin,McCracken & Oliff (1991) placed the base of the post-N. persculptus zone (their P. acuminatus Zone) at the


FADs of N. madernii and N. lubricus. This N.madernii–N. lubricus fauna, which they recognized as alower subzone of the P. acuminatus Zone, is succeededby an upper subzone characterized by the appearanceof Hirsutograptus sinitzini. Obviously it is impossibleto confirm the relations of A. ascensus and P. acumina-tus based on these data.

3.k. Eureka, Nevada, USA

Continuous graptolite, conodont and chitinozoansequences through Dicellograptus ornatus, Paraortho-graptus pacificus, Normalograptus extraordinarius andN. persculptus zones have been documented recentlyfrom Vinini Creek, and the Monitor Range, nearEureka, Nevada (Finney et al. 1999). From the grapto-lite fauna, the Dicellograptus ornatus Zone may corre-late with the Dicellograptus complexus Zone of theYangtze region. Most of the P. pacificus Zone fromNevada may be correlative to the same zone of theYangtze region. The Tangyagraptus typicus andDiceratograptus mirus faunules have not yet beenfound in Nevada. The Normalograptus extraordinariusZone of Nevada is marked by the FADs of N. extraor-dinarius (Sobolevskaya) and N. pseudovenustus(Legrand). The FAD of Normalograptus ojsuensis(Koren & Mikhailova) is little earlier than that of N.extraordinarius (Sobolevskaya) from the Vinini Creeksection. The vertical distribution of these two speciesis similar to that of Mirny Creek, southeasternSiberia. Thus, this zone in Nevada is broadly correla-tive with the N. extraordinarius–N. ojsuensis Zone ofthe Yangtze region, but is slightly younger at its base.We would instead place the base of the zone at the firstappearance of N. ojsuensis.

From the Monitor Range, Nevada, Normalograptuspersculptus (Elles & Wood) and Glyptograptus lacinio-sus (Churkin & Carter) occur in the upper N. persculp-tus Zone. Conodonts of the Amorphognathusordovicicus Zone as well as chitinozoans occur throughP. pacificus and N. extraordinarius zones but exhibit alittle change in their taxonomic composition.However, conodonts and chitinozoans considered typ-ical of the Early Silurian appear in the N. persculptusZone.

3.l. Talacasto, Argentina

Cuerda, Rickards & Cingolani (1988) reported grapto-lites of the Normalograptus persculptus Zone from theTalacasto region, listing among the fauna N.persculptus, N. angustus, N. normalis and N. rectangu-laris. However, the last-named species are less knownfrom the N. persculptus Zone elsewhere. The graptoliteassemblage from the overlying beds, includingTalacastograptus leanzai Cuerda, Rickards &Cingolani, Metaclimacograptus robustus (Cuerda,Rickards & Cingolani) and Lagarograptus praeacinaces

Cuerda, Rickards & Cingolani, seem to be representa-tives of late Rhuddanian graptolite faunas, althoughCuerda, Rickards & Cingolani (1988) suggested theywere a P. acuminatus Zone fauna. Among these newforms, Metaclimacograptus robustus has been recog-nized from the C. vesiculosus Zone at Honghuayuansection in the Yangtze region.

3.m. Djado plateau, Niger and Hodh, Mauritania

Legrand (1993) recognized Normalograptus ojsuensis(=Glyptograptus (Glyptograptus?) ojsuensis Koren &Mikhailova, Legrand, 1993) from the Djado plateau,Niger. Associated forms are Normalograptus sp., inar-ticulate brachiopods and trinucleid trilobites.Underwood, Deynoux & Ghienne (1998) reportedthat Normalograptus persculptus (=Persculptograptuspersculptus s.l.: Underwood, Deynoux & Ghienne,1998, fig. 5S) occurs with Normalograptus extraordi-narius (=N. cf. extraordinarius typical forms,Underwood, Deynoux & Ghienne, 1998, fig. 5H,G)from their lower persculptus Zone (at Hodh,Mauritania). It is important that N. persculptus (Elles& Wood) occurs together with N. extraordinarius(Sobolevskaya) in the N. persculptus Zone fromFenxiang (Fig. 4) and Huanghuachang, Yichang. TheDjado plateau and Hodh are the only two localities ofthe latest Ordovician graptolites known from withinGondwana land near the Ordovician South Pole.

3.n. Darraweit Guim, central Victoria, Australia

Thick clastics (Bolinda Shale and Darraweit GuimMudstone) and turbidites (Deep Creek Siltstone)occupy the Dicellograptus ornatus–Amplexograptuslatus Zone to Parakidograptus acuminatus Zone inter-val from central Victoria (VandenBerg, Rickards &Holloway, 1984). The D. ornatus–A. latus Zone in theBolinda Shale contains Dicellograptus minor, D. orna-tus, Appendispinograptus supernus, Climacograptus?hastatus, Normalograptus angustus, Paraorthograptuspacificus, Rectograptus amplexicaulis, Anticostia fasti-gata and ‘Orthoretiograptus denticulatus’, etc. Amongthem ‘O. denticulatus’ may be Pararetiograptus sinensisMu. The graptolite fauna indicates that this zone maybe equivalent to the D. complexus Zone through P.pacificus Zone interval in the Yangtze region.

The N. extraordinarius–N. ojsuensis Zone includesone of the zonal fossils. N. extraordinarius as well as N.angustus associates with the trilobite Songxites dar-raweitensis (Campbell). Normalograptus persculptusoccurs at the top of the Deep Creek Siltstone associ-ated with N. normalis and N. angustus. VandenBerg,Rickards & Holloway (1984) described theirParakidograptus acuminatus sp. cf. P. acuminatusacuminatus (Nicholson) based on a single whole rhab-dosome (NMV PL698). They reported there is nodirect evidence of its stratigraphic relationship with the


beds containing N. persculptus. From the text-figureand description of this specimen, we are inclined to theview that P. acuminatus sp. cf. P. acuminatus acuminatus(VandenBerg, Rickards & Holloway, 1984, fig. 12) is P.acuminatus praematurus (Davies). Davies (1929) sug-gested originally that P. acuminatus praematurus occurswithin the N. persculptus Zone. Rickards (1988) in hisdiscussion of the position of the base of the Silurian,lowered the base of the P. acuminatus Zone to includethese P. acuminatus praematurus-bearing strata. So far,P. acuminatus praematurus has not yet been found fromChina. We are not sure whether the occurrence of P.acuminatus praematurus in the Deep Creek siltstoneindicates the existence of the Yangtze A. ascensus Zonein central Victoria, although this is likely if Melchin,Koren & Williams (1998) are correct in their interpreta-tion of the ranges of these taxa. We interpret the occur-rence of P. acuminatus praematurus, with its more‘primitive’ features, to indicate the presence in theVictorian succession of a stratigraphically lower levelwithin the Silurian than that marked by the FAD ofP. acuminatus.

Acknowledgements. The present paper is supported by theBasic Science Research Program of the Chinese Academy ofSciences (KZ952-J1-401 and KZ952-J1-023), NationalNatural Science Foundation (no. 49872005 and 49672083) aswell as the Special Funds for Major State Basic ResearchProject (G200077700). Partial support was also provided bythe Department of Geological Sciences, New York StateUniversity. We thank Dr M. Melchin for his helpful com-ments and discussion, and J. and J. Enterprise for providinggood indoor working facilities in the town of Harvard,Massachusetts, USA. The graptolite illustrations weredrafted by Miss Wu Minghua and the brachiopods werephotographed by Mr Deng Dongxing.

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650 Ordovician–Silurian biozonation of Yangtze region, China

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