Ordovician biogeography of Sibumasu 43 Biogeography and palaeogeography of the Sibumasu terrane in the Ordovician: a review

R A Fortey and L R M Cocks Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

Key words: biogeography, palaeogeography, Sibumasu, Shan-Thai, Thailand, Burma, China, Aus- tralia, Ordovician, trilobites, brachiopods

Abstract as on Figs1 and 2) terrane embraces much of the Malay peninsula, extending northwards into Following an extensive review of previous work, and a con- West Thailand and Burma and southwards into sideration of new faunas from Thailand, the integrity of the western Indonesia (Sumatra) It is bounded to Sibumasu palaeocontinent (Sumatra, Malaysia, West Thai- the east by the Uttaradit-Nan to Raub-Bentong land and Burma) in the early Palaeozoic is reinforced% Its lower Ordovician faunas have been claimed to show affinity sutures, and to the west by what Metcalfe (1992) with North China/Australia, but for the upper Ordovician, termed the Shan boundary (also possibly an an- we describe undoubted similarity to South China, both in cient suture) Thus it comprises a tract of land fossils and sedimentary facies% The possible resolution of some 4000 km long, clearly a continental entity these difficulties is discussed, and the provisional conclu- sions reached that (a) Sibumasu was most similar to South of sufficient size to have acquired its own palae- China; (b) South China and North China may not have been ogeographic signature Several major neigh- so far apart as has been suggested; and (c) Indochina carries bouring terranes have been referred to in rela- a different faunal signal from any of these other terranes% tion to the history of Sibumasu These are (Fig1): the Indochina terrane immediately to the east; the South China terrane, today comprising Introduction many of the most populous regions of China south of the Tsinling (Chin Ling) suture; the The palaeogeography of Australasia is becom- North China terrane (including the northern part ing progressively better understood for the 150 of China and associated regions of Korea); and Ma period following the breakup of Pangaea; the Australian continent, which was already but there remain many unsolved problems in constituted in something like its present form, the Palaeozoic The period with which we are although the Tasman fold-belt to the south (in- concerned, the Ordovician (495-443 Ma), was a cluding New South Wales and much of Victoria) time of general continental dispersal (Scotese and montane Queensland were mobile belts in and McKerrow, 1990) long predating the assem- the Ordovician bly of Pangaea, and the disposition of the con- Here we review published evidence for the tinental masses at this time is still under investi- palaeogeographic position of the Sibumasu gation SE Asia has been divided into a number terrane in the Ordovician, referring to evidence of terranes (e)g), Mitchell, 1981; Burrett et al), derived from fossils and also in relation to the 1990; Metcalfe, 1992), each bounded by major sedimentary sequences developed over this im- faults These terranes have histories which are portant area These fossil faunas have been de- variably decoupled from that of their neigh- scribed in disparate publications over the last bours — that is, their contiguity today is no seventy years (many listed in Ingavat-Heimche, guarantee of proximity in the past 1994) This review also provides a salutary re- The Sibumasu (sometimes called Shan-Thai, minder of the uncertainties that still apply to

Biogeography and Geological Evolution of SE Asia, pp 43-56 Edited by Robert Hall and Jeremy D Holloway © 1998 Backhuys Publishers, Leiden, The Netherlands 44 R) A) Fortey and L) R) M) Cocks

with greater sensitivity to substrate, but whose distribution patterns frequently track those of the trilobites Taken together with various other indicators, these fossils provide a powerful way of discriminating ancient biogeographic prov- inces — and hence an indication of ancient ge- ography and plate distribution Both trilobites and brachiopods had different communities related, for example, to water depth, within any given palaeocontinent These have received different descriptions according to biogeographic fashion: in this paper we shall simply refer to them as biofacies The shelf biofacies are, in general most useful to recog- nise faunal similarities of palaeogeographic sig- nificance — thus, two shelf faunas identical as to species are likely to have been closely related geographically (Cocks and Fortey, 1982) Even among shelf faunas there were evidently taxa which (at least at generic level) were distributed widely within a single palaeoclimatic belt Since Sibumasu occupied a tropical position in the Ordovician, such pandemic taxa are also distrib- uted in other tropical contemporary sites — for example, in Laurentia, Australia and Siberia — and their palaeogeographical usefulness is lim- ited Deeper water faunas, for example the Ordovician trilobite cyclopygid biofacies, may have even wider distribution in global terms (Fortey and Cocks, 1986; Cocks and Fortey, 1990) and thus be of little significance in dis- Fig1 Modern map showing the boundaries of the various criminating which continent was close to an- terranes in SE Asia% other However, they are important in a different way because they allow recognition of the mar- gins of these ancient cratonic areas, to which they were confined Also, their orientation understanding much of Lower Palaeozoic geog- should make geographic sense, because deep- raphy, and of the sometimes ambiguous signals water faunas should align with others of their given by biogeographic evidence kind, and generally face outwards towards an- cient oceans Thus the faunal approach we use to deduce the former geography of Sibumasu is Biogeographic methods and materials twofold: (1) comparison of Ordovician shelf fau- nas with their contemporaries in other terranes; The principal evidence for Ordovician biogeog- (2) orientation of biofacies into onshore-off- raphy used in this account comes from trilobites shore gradients In all comparisons identity of and brachiopods, with important additional species is considered more important than ge- contributions from fossil Mollusca, especially neric-level similarity — although the latter has nautiloids Trilobites have been used for many often proved useful for more global studies years to discriminate biogeographic areas (e)g), This approach is complemented by compar- Whittington and Hughes, 1972), and they are ing sedimentary sequences in several areas in particularly useful as a highly speciose group different terranes; if there are striking lithological with distinctive morphologies that tend towards and/or sequence similarities this supplies addi- endemicity which is related to, and dependent tional evidence for geographical continuity upon, past continental configurations and cli- However, there are many areas of Sibumasu for matic zones Brachiopods are sessile organisms which the details of the sequences are imper- Ordovician biogeography of Sibumasu 45

Fig2 Differing previous palaeogeographies of Gondwana in the Early Ordovician% A, from Laurie and Burrett, 1992; B, from Cocks and Fortey, 1988 (in the latter North China is not shown; it was imagined then as some distance away)% 46 R) A) Fortey and L) R) M) Cocks fectly known, and we naturally concentrate Lower to lower Middle Ordovician faunas upon those areas that we have studied in the field and which are the best documented The An Ordovician (probably upper Tremadoc) tri- most fully known Ordovician succession is that lobite fauna from the top 100 m of the Tarutao in southern Thailand, Satun Province, of which Formation (Stait et al), 1984) is the earliest Ordo- many details have only recently been available vician yet discovered in Sibumasu Five genera Several different palaeogeographies have been were recognised, and of two named species published (e)g), Fig2) both were newly named All the genera identi- fied are widely distributed in Tremadoc strata, and comparative species were discussed from Ordovician sequence and palaeontology in both palaeotropical China and Laurentia The southern Thailand fauna is not, therefore, biogeographically criti- cal The palaeontology and stratigraphy of the Or- The clastic rocks of the Tarutao Formation are dovician of southern Thailand and the adjacent succeeded by a thick carbonate succession areas of northern Malaysia is now comparatively grouped in the Lower to basal Middle Ordovi- well-known Ordovician rocks crop out over a cian Thung Song Formation (the equivalent stra- discontinuous north-south belt for several hun- ta on Langkawi Island are known as the Lower dred kilometres, and sections have been studied Setul Limestone) These limestones are shallow- particularly in the southern area, to either side of water, peritidal, even partially lagoonal in origin the Thai-Malaysia border Outcrops extend on The fossil faunas are sparse, in spite of excellent to two offshore islands: Tarutao Island on the exposures around the coast of Tarutao Island Thai side of the border, and Langkawi Island on The limestones resemble in lithology many oth- the Malaysian side Earlier studies by Kobayashi er lower-mid Ordovician carbonate platform se- and his colleagues (summarised in Kobayashi quences, e)g), from North China/Korean plate, and Hamada, 1984) tended to be descriptions of central Australia, much of Laurentia and the San ‘spot faunas’ — small collections of a few inver- Juan terrane of Argentina From the base of the tebrate fossils published as separate notes — Thung Song Formation Stait and Burrett (1984a) and their mutual relationships are not obvious recorded a polyplacophoran mollusc, Chelodes However, Wongwanich et al) (1983, 1990) have whitehousei, the same species as from the Nin- published more complete accounts of the Palae- maroo Formation, central Queensland This sim- ozoic stratigraphy in Satun Province, based on ilarity is interesting, but we note that the genus successions in Tarutao Island and the adjacent Chelodes is actually pan-tropical in the Ordovi- mainland, from which a better picture of the re- cian, since other species are known from as far gional stratigraphy can be gained This succes- away as Alabama which formed part of Lauren- sion provides the principal factual base on tia (Runnegar et al), 1979) The gastropod-bear- which to hang our biogeographical assessment ing limestones of Pulau Langgon (Langkawi) herein yielded a distinctive gastropod operculum, On Tarutao Island the Cambrian-Ordovician Teichiispira (Yochelson and Jones, 1968), which boundary lies within the upper part of the Taru- has a similar pan-palaeotropical distribution tao Formation, a thick siliciclastic formation of Here (Fig3E-I) we figure some silicified brachio- sandstones and siltstones An upper Upper pods from the sparsely fossiliferous lower mas- Cambrian trilobite fauna described by Shergold sive member of the Thung Song Formation; et al) (1988; also Kobayashi, 1957) provides a these, too are mainly genera (Syntrophina and lower limit for our discussion They comment Archaeorthis?) with global palaeotropical distri- (p 305) that the fauna “more closely resembles bution in the early Ordovician (Ibexian) and assemblages from Vietnam, western Yunnan, Si- one apparently endemic form of no biogeo- chuan and into Gangsu and eastern Qinghai graphical significance (gen nov?) While these Provinces of China, and central Australia” being examples indicate an interesting capacity for lar- inhabitants of an inshore detrital environment vae of inshore, eurytopic genera to disperse The fauna is distinguished from those of the around low palaeolatitudes, they do not contrib- Sino-Korean platform by the absence of some ute critically to arguments on palaeogeography typical genera found there, rather than by the Fragments of the trilobite Leiostegium, similarly presence of diagnostic endemic genera; further- widespread, occur with them Laurie and Burrett more, the species listed in Shergold et al) (1988) (1992) described two brachiopods (Spanodonta are not known outside Sibumasu floweri and Aporthophyla tiangjinshanensis?) Ordovician biogeography of Sibumasu 47

Fig3 New faunas from Thailand and Burma% 3A-D, brachiopods from the Upper Naungkangyi Group, Linwe, Neyaungga, Southern Shan States, Burma% A, Leptellina (Leptellina) minor Cocks and Zhan, BC 52418, latex cast of a dorsal interior, x 5; B- D, Saucrorthis irravadica (Reed), B,BC 52411, latex cast of dorsal exterior, x 4, C, BB 37702, ventral interior mould, x 5, D, BB 37668, latex cast of dorsal interior, x 4% 3E-I, brachiopods from the Thung Song Formation (Upper Tremadoc), Langa Bay, north of Malaka inlet, Taratao island, Satun Province, south Thailand; 3E-G, Archaeorthis? sp% BC 51248, dorsal and side views of conjoined valves, and ventral interior of another valve, x 4; 3H, Syntrophina sp% BC 51247, dorsal interior, x 4; 3; 3I, BC 51249, orthide gen% nov?, dorsal interior, x 4; 3J-O, brachiopods and trilobites from the Satun Shale Formation (Llandeilo-Caradoc), track to Ban Pa Kae, 3%5km east of Route 4078, 10km north of Langu, Satun Province, Thailand; 3J, syntrophiid, BC 52142, internal mould of small ventral valve, x 6; 3K, eoorthid, BC 52141, internal mould of dorsal valve, x 4; 3L-M, Ovalocephalus, 3L, In 9300, pygidium, 3M, In 9301, a thoracic segment plus cranidium, both x 5; 3N, Encrinurella sp%, In 9303, slightly distorted cephalon, x 5% 3O, Hungioides sp%, In 9302, pygidium, x 2%

from the lower Ordovician which they regarded known from only two localities: on Langkawi as “important confirmatory evidence for Or- Island and in the Canning basin, Australia How- dovician juxtaposition of the Shan Thai terrane ever, it would be impossible to make the same and western Australia” (p 16) Spanodonta is claim for Aporthophyla, because the genus has 48 R) A) Fortey and L) R) M) Cocks an almost pan-tropical Ordovician distribution Kobayashi and Hamada (1964) described a (its type species comes from Nevada), particu- small fauna from the Satun Shale (?=Thung Wa larly in marginal terranes (Cocks and Rong, Shale of Bunopas, 1983); the trilobite therein, 1989), and the Sibumasu species was not identi- Basiliella satunensis, belongs to a genus which cal with any other and in fact compared with is widely distributed in the mid-Ordovician and one (A) tiangjinshanensis) only previously de- not palaeogeographically critical Here we fig- scribed from North China Jell et al) (1984) de- ure for the first time a small fauna from strati- scribed a gastropod, Peelerophon oehlerti, from graphically below the Pa Kae Formation, as de- higher in the Thung Song Formation, from low- scribed by Wongwanich et al) (1990, Figs2, 3), er Arenig limestones (according to conodont collected from an isolated outcrop lying on the evidence) This gastropod species has a long roadside 3 km to the east of the type section of stratigraphic range (Tremadoc to Arenig) and a the Pa Kae Formation The fauna is from an im- very wide geographical distribution: Argentina, pure, and now thoroughly decalcified shaly Tasmania, western Australia (and a related spe- limestone Rare brachiopods include a small cies is in the Montagne Noire, France) Jell et al) ventral valve showing a spondylium and proba- (1984) made much of this distribution as reflect- bly referable to a syntrophiid (Fig3J) and two ing Ordovician Gondwana, and noticed that, different fragmentary orthids including an eoor- unusually, this gastropod cuts across palaeocli- thid (Fig3K) none of which are of much assist- matic zones, occurring from low to high palaeo- ance in determining palaeogeography The trilo- latitudes but not, apparently, outside Gondwa- bites Encrinurella, Ovalocephalus, an agnostid na: “it was eurythermal but unable to cross ma- (Arthrorhachis sp not figured) and a jor oceanic barriers” (p 169) Yu (1989) has sub- dikelokephalinid (Hungioides sp) are associat- sequently recorded P) oehlerti from South Chi- ed The Encrinurella species (Fig3N) is similar na The distribution is certainly different from to the type species illustrated by Reed (1906); the pan-tropical taxa noticed above As will be the genus occurs also in the upper Ordovician noted from all our faunas, the Gondwanan link Tangtou Formation of the South China plate is well proven in general for Sibumasu, but does (Tripp et al), 1989) Ovalocephalus (Fig3L) is not help in identifying the closest Gondwana or tentatively compared with O) primitivus Lu, peri-Gondwanan terranes to Sibumasu in Ordo- which co-occurs with Hungioides in the Dawan vician time Formation of Hubei Province The range of Nautiloids from Tarutao and Langkawi Islands dikelokephalinids in general does not extend from the Thung Song Formation or its equiva- into the Upper Ordovician; Hungioides (Fig3O) lents were described by Stait and Burrett has an unusually wide peri-Gondwanan distri- (1984b) and Stait et al (1987), who considered bution, extending as far west as Portugal and earlier literature All are described as shallow Germany A different species of Ovalocephalus water assemblages The faunas range in age is very common in the overlying Pa Kae Forma- from the mid-Ibexian to Whiterockian (approxi- tion This genus is considered absolutely charac- mately Arenig-Llanvirn), and are quite diverse teristic of, and confined to, the South China Nautiloid-bearing limestones of this kind extend plate before the Ashgill (Lu, 1975) along the whole length of Sibumasu (Ingavat et Finally, a cyclopygid faunule described from al), 1975, Kobayashi, 1961, 1984) The faunas further south in Malaysia (Kobayashi and Hamada, have been compared at the generic level with 1971) probably also belongs within the mid-Or- those of the North China platform and the dovician time interval Cyclopygid biofacies is a Georgina basin, western Queensland In view of deep-water association almost independent of the lithological similarities between the palaeocontinent distribution, but invariably as- palaeotropical limestones in these areas this is sociated with sites near former continental mar- perhaps not surprising gins (Cocks and Fortey, 1990) The brachiopods in general are poorly known from Sibumasu at this time: the fauna described by Hamada (1964) Mid-Ordovician faunas from calcareous shales near Satun on the west coast of southern Thailand is recorded as three In southern Thailand and adjacent Malaysia stra- different species of Cyrtonotella, Multicostella? ta following the massive limestones are not well- sp and new species of Rafinesquina and exposed, faunas are small ‘spot samples’, and Oepikina? and needs revision, for example one their stratigraphic relationships are still under of the ‘Cyrtonotella’ is a plectambonitoid and investigation Clastic rocks are predominant the ‘Rafinesquina’ is a glyptomenid Ordovician biogeography of Sibumasu 49

Upper Ordovician faunas cies level Cocks and Fortey (1997) showed that some of the brachiopods (e)g), Aegiromena pla- Upper Ordovician faunas of southern Thailand nissima) were identical (a) with those from the have recently been described for the first time Panghsa-pyé Beds of the Northern Shan States by Fortey (1997) and Cocks and Fortey (1997) (Reed, 1915) and (b) with those from the Hirn- The Pa Kae Formation (Caradoc) is a striking antian of the South China platform Hence, the series of bedded red limestones with abundant closest faunal comparison for Sibumasu in the syneresis cracks The upper part of the Lower latest Ordovician is once again with South Chi- Setul Limestone on Langkawi Island is regarded na The similarity continues between the two as probably correlative with the lower part of areas into the early Silurian, with the two se- the Pa Kae Formation on the basis of shared tri- quences becoming different only in late Llando- lobite species (Kobayashi and Hamada, 1978) very times among a rich trilobite fauna comprising nearly forty species (Fortey, 1997) These species are almost all identical to those from the Pagoda Northern Thailand and Burma Formation, which is extensively exposed over several provinces within the South China plat- Much less is known about the Ordovician suc- form (Ji, 1986); in fact Fortey (1997) described cession in Thailand north of the peninsula, and only two species from Thailand as new, and the deposits there are generally more tectonised there are three genera which have so far only than in the South However, it is likely that the been reported from the South China plate and Lower Ordovician limestones were part of a sin- Thailand The similarity is all the more signifi- gle, if now discontinuous sedimentary belt, as cant because the distinctive and unusual litholo- shown by, for example, the similarity of the nau- gies of the Pa Kae and Pagoda Formations are tiloid faunas and lithologies (Kobayashi, 1961; strikingly similar — including the colour and the Ingavat et al), 1975; Stait and Burrett, 1984b) It syneresis cracks The latter had formerly been has not been questioned that only one terrane is taken as ‘mudcracks’ in China, and said to be represented Northwards into Burma, the Ordo- indicative of shallow-water deposition, but trilo- vician successions are known from the Southern bites and other fossils support instead an open Shan States, which seems to be a northward shelf setting, and the re-interpretation of the sy- continuation of the Thai sequence (Garson et neresis cracks is consistent with this (Ji, 1985) al), 1976), including a thick development of ear- Cocks and Rong (1988) recorded a depauperate ly Ordovician limestones However, in the Foliomena brachiopod fauna from the same Northern Shan States, the early Ordovician lime- beds, which is also present in the correlative stones are not present (Mitchell et al), 1977), and rocks in South China Faunas of the same age the whole sequence is dominated by clastics are unknown from central Australia and rare Given the otherwise striking continuity of the and poorly known from the North China plat- Sibumasu terrane, this difference is significant form, while contemporary faunas from New Ordovician palaeontology in Burma still relies South Wales are completely different even at heavily on the descriptions of Reed (1906, 1915, generic level (Webby, 1973, 1974) Thus there is 1936) These faunas have never been fully re- good evidence of faunal and lithological com- vised, and their palaeogeographical value is ac- parison with South China for the Pa Kae Forma- cordingly to be treated with some caution, al- tion This is continued with the overlying Wang though we have revised brachiopod faunas Tong Formation, which marks a return to clastic (Cocks and Zhan, 1998) from the Shan States deposition, and completes Ordovician sedimen- collected by Mitchell et al) (1977) in their survey tation The lower part is entirely graptolitic, but Our comments below on the trilobites are pre- higher in the section at the top of the Ordovician liminary, but important to illustrate the problems there is a thin development of the latest Ordovi- involved There is some evidence that Reed mis- cian Hirnantia fauna — including some seven associated some pygidia and cephalic parts For brachiopod genera (making up 74% of the total example, Calymene liluensis Reed, 1915 has a abundance) and the typical trilobite Mucro- pygidium assigned to it which actually probably naspis mucronata (Cocks and Fortey, 1997) belongs to an Ovalocephalus species (men- The Hirnantia fauna sensu lato is practically tioned above as a common element of the Pa pandemic It is associated with a widespread cli- Kae Formation of Thailand), and is certainly not matic decline more or less coincident with the that of any calymenid; on the other hand, a ce- end-Ordovician glaciation However, at the spe- phalon illustrated as Encrinurella insangensis 50 R) A) Fortey and L) R) M) Cocks

(Reed, 1915, Plate 8, Fig15) is a plausible candi- onomic terms; there are another five trilobite date for that of Ovalocephalus) The type speci- species from the Naungkangyi Beds which re- mens of E) insangensis illustrated by Reed quire examination before a modern interpreta- (1906) are quite different from those he as- tion can be made Nonetheless it is clear that the signed to the same species in 1915, and repre- species named can be compared with faunas sent Encrinurella in the strict sense The two from South China, and/or Gondwana margin main trilobite faunas of the Northern Shan States faunas from central Asia They are completely are those of the Hwe Mawng Beds and Upper different from those described from New South Naungkangyi Beds respectively — both clastic Wales by Webby (1973, 1974 and Percival, deposits The former includes ‘Ogygites’ (now 1991) This has been further reinforced by re- Birmanites) birmanicus; the genus is well cent work on the Shan States brachiopods by known in the Middle Ordovician of central and Cocks and Zhan (1988), which shows that both southwest China, but it also occurs in Vietnam Llanvirn/Llandeilo and also early to middle and Kazakhstan The asaphid species described Caradoc faunas are present, with the main Up- by Reed (1915) as Ptychopyge thebawi invites per Naungkangyi fauna from the Caradoc That comparison with what Kobayashi and Hamada fauna includes two endemic strophomenoid (1964) described as Basiliella satunensis from genera, but the remaining 29 genera are more Thailand An Ampyx and Illaenus species con- nearly similar to the contemporary Shihtzupu tribute nothing palaeogeographically because Formation fauna from South China (Xu et al), both are pandemic 1974) and to a lesser extent North China, and The Upper Naungkangyi fauna includes an very different from contemporary brachiopod obvious Neseuretus (Neseuretinus) species faunas in Australia and Laurentia For example, (named Calymene birmanica Reed by Reed in the orthoid Saucrorthis (Fig3B-D) is known 1915), a taxon of exclusively inshore Gondwa- only from South China and Burma The Shan nan distribution, and confined to warm temper- States fauna is again different from that of uncer- ate to tropical palaeolatitudes (Turkey and east- tain late Ordovician age from southern Thailand wards); it, too, is a familiar component of Middle (Hamada, 1964), which is poorly characterised Ordovician faunas of the South China plate and needs revision, particularly since the latter is (Shensi and Szechuan Province: Lu, 1975) Dean the only other known possible Caradoc fauna in (1967) noted that Reed’s original (1906) type addition to the Shan States from the Sibumasu specimen of ‘Calymene’ birmanica is different palaeocontinent from those he later assigned to the same species The uppermost Ordovician (Hirnantian) Pan- (see also Lu et al, 1965, Pl 128, Fig13), and ghsa-pyé beds were discussed by Cocks and Fortey and Morris (1982) pointed out that the Fortey (1997), and considered identical to cor- specimen is close to Neseuretus (Neseuretus) relative beds in southern Thailand Reed’s trilo- tristani, a widespread species of Llanvirn-Lland- bite species Dalmanites hastingsi was regarded eilo age in Europe) Ovalocephalus occurs in the as a likely synonym of the widespread species same fauna as Reed considered in 1915, as men- Mucronaspis mucronata; and several of the bra- tioned previously We think it likely that the cra- chiopods were equally cosmopolitan; but some nidium of Reed’s Calymene (Pharostoma) lilu- species were less widespread globally, and only ensis is now referable to Xuanenia (see Tripp et occur in Burma, Thailand and South China al), 1989), a genus otherwise known only from the South China platform Reed’s Cheirurus sub- mitis is very similar to Hadromeros xiushanensis Ordovician palaeogeographical reconstruc- (Sheng), a species widespread in the later Ordo- tions of SE Asia vician over the South China platform (see Ji, 1986) The species Reed described as Holometo- It is generally recognised that China, Australia pus wimani would now be assigned to Dula- and its peripheral terranes were at low palaeo- naspis Chugaeva, a genus also described from latitudes, and allied to a large Ordovician Gond- the Caradoc Gondwanan marginal terranes of wana continent, which already included Africa, Kazakhstan and Kirgizia In general, the species India, Antarctica and much of southern Europe comparisons of the trilobites suggest to us that (Cocks and Fortey, 1988) The south pole, and the Upper Naungkangyi Beds may be of Lland- cooler-water faunas, lay in the west of Gondwa- eilo to Caradoc age, rather than somewhat older na What is at issue is the relative positions of as Reed suggested Virtually all the forms named North and South China, and the various other by Reed require reconsideration in modern tax- terranes which were part of, or marginal to, Ordovician biogeography of Sibumasu 51

Gondwana Reconstructions of Sibumasu and these two areas Although revision of Reed’s tri- adjacent areas in the Ordovician have been pre- lobite faunas from Burma is overdue, the brachi- sented several times by Clive Burrett and his co- opods from there compare with South China workers (Burrett and Stait, 1985, 1987; Burrett et rather than North (Cocks and Zhan, 1988) Bur- al), 1990; Laurie and Burrett, 1992) These au- mese trilobite faunas include Neseuretus (Ne- thors repeatedly emphasise the similarity of the seuretinus) with a Gondwanan distribution ex- Ordovician faunas to those of North China and tending to temperate palaeolatitudes Latest Or- central Australia, and adduce evidence which dovician sequence and faunas from the whole places the Sibumasu terrane adjacent to, and to Sibumasu terrane are also like those of South the west of Australia The most recent version China (Fig2) of this Ordovician palaeogeography is 5 The oceanward edge of the Sibumasu terrane that of Laurie and Burrett (1992, Fig3) This re- is probably marked by a cyclopygid biofacies construction shows South China removed by fauna in Malaysia, that is, this edge should line some 40 degrees of latitude from North China, up with marginal sites on other plates and Shan-Thai (Sibumasu) approximately half There is thus a difference between earlier and way between the two and adjacent to Australia later Ordovician biogeographic signals, the Our review of the faunal evidence from Sibu- former providing apparently strong evidence for masu as interpreted by previous workers em- similarity between North China and Australia phasises the following points: (and suggesting a placement of Sibumasu next 1 There is a number of pan-palaeotropical to Western Australia), the latter rather indicating forms (brachiopods Syntrophina and Aportho- a close relationship with the South China plate phyla, molluscs Teichiispira and probably Che- The North and South China plates have been lodes) The detailed palaeobiogeographical use placed far apart on Ordovician continental re- of these is limited, but they do require that the constructions (e)g), Burrett et al), 1990) This terranes on which they are found could not leads to a paradox How can Sibumasu appar- have been too far from the palaeoequator ently ‘switch’ between one and the other? Three 2 There is a small number of peri-Gondwanan explanations can be considered with regard to forms (the gastropod Peelerophon; trilobite the biogeographic history of Sibumasu: Hungioides); interesting though these are (and 1 Either the North China, or the South China potentially important in correlating rocks), they biogeographic ‘signal’ is misleading cannot ‘fine tune’ the biogeography 2 Sibumasu moved from being adjacent to 3 In the Lower Ordovician to basal mid-Ordovi- North China to being adjacent to South China cian limestones (and to a lesser extent inshore during the Ordovician sandstones) of Sibumasu there is a fauna of up 3 The wide separations of North and South Chi- to nine nautiloid species which are supposedly na plates given in previous reconstructions are strongly similar to those of North China (and misleading; Sibumasu ‘bridges’ the two platform Australia); this is augmented by one To attempt to discriminate between these brachiopod (Spanodonta) The cephalopod fau- possibilities we consider the whole sequences nas of North China (‘Yellow River Province’) are (thickness, lithology and faunas) for those areas different from those of South China (‘Yangtze under contention River Province’) according to Chen and Teichert (1988, Fig2) “related, respectively, to low lati- tudes or tropical areas, and mid-latitudes or tem- Sequences of SE Asian Ordovician compared perate zones” (ibid p 153) These differences may lie behind the supposed placement of Direct comparisons of sedimentary successions North and South China plates at quite different palaeolatitudes (e)g), Burrett et al), 1990; Laurie In a brief review we cannot consider all the se- and Burrett, 1992) quences developed in the possibly adjacent pal- 4 Mid- to upper Ordovician trilobite faunas aeoplates (Fig4) We have compared the best- from Sibumasu are strikingly similar to those of known areas of Sibumasu (S Thailand and the South China plate The fauna of the Pa Kae northern Shan States, Burma) discussed in some Formation of southern Thailand is exactly simi- detail above, with representative sections from lar to that of the Pagoda Limestone; Fortey North China, South China, and central Australia (1997) listed many species in common, and Chinese Ordovician stratigraphy has recently three genera (Quyania, Elongatanileus, been extensively reviewed by Chen et al) Hanjiangaspis) are not yet recorded outside (1995), wherein many sections from each prov- 52 R) A) Fortey and L) R) M) Cocks ince of China were described; from South China cal type in Sibumasu would seem to demand we have selected the sections at Yichang and considerable transport of the former terrane Huayinshan as most typical of platform deposi- Since Sibumasu lies outboard of the Indo-China tion Chen et al) (1995, Fig2) show a shallow to terrane it becomes less remarkable to postulate deep water gradient across the South China an extensive movement of this terrane also Un- plate — cyclopygid biofacies lie at the edge of der this scenario, Sibumasu moved from adja- the basin to the South For North China we have cent to North China in the early Ordovician to selected the Zibo section, Shandong Province close to South China in the later Ordovician (column 26 of Chen et al)); for central Australia Even so, the change from one ‘provincial’ type the stratigraphy and section is taken from the to another seems to be abrupt and coincident southern Georgina basin (Shergold, 1985) In with the ending of deposition of the previously general, the succession in southern Thailand stable carbonate platform appears to be similar to that of the Yangtze plat- However, there is recent evidence that the form; thick, calcareous lower Ordovician is fol- supposed contrast between faunas of North Chi- lowed by a comparatively ‘condensed’ younger na and South China may not be as profound as Ordovician succession; the Pagoda Limestone li- claimed, for example, by Chen and Teichert thology is identically developed in both areas; (1988) Zhou and Fortey (1986) reviewed the and the ‘Hirnantia fauna’ is a thin intercalation Ordovician trilobites of the North China plat- within graptolitic deposition which closes the form and found considerable similarity between Ordovician However, Yangtze successions are, the North China and the Yangtze platforms in in general, much thinner particularly by compar- the Tremadoc, even including species in com- ison with the southern Shan States But the se- mon Differences increased in the Arenig How- quence evidence would overall support the no- ever, Chen Ting-en (in Chen et al), 1995) listed tion of Sibumasu as adjacent to, if not actually similar nautiloid faunas in the Arenig of the docked with, South China Aligning deep-water Hunghuayuan Formation (South China) and the marginal biofacies would imply that the Malay- Liangchiashan Formation (North China) These sian end of Sibumasu lay close to what is now include several genera listed (e)g), by Laurie and Hainan Island Burrett, 1992, Fig2) from the lower Ordovician of Sibumasu, and presumably regarded by them as typical of the North China platform Of the Ambiguous palaeogeographic interpretations Chisiloceras-Cochilioceras Assemblage Zone Chen (in Chen et al), 1995 p 16) states “it not The major problem remains of how to account only is widely distributed in the different plates for the previously claimed alignment of Sibu- of China, but also in North America and NW masu with North China/Australia rather than Europe” (i)e), Baltica) This implies that some of South China (Laurie and Burrett, 1992) It is the nautiloids may have been very widespread, compounded by the intercalation, on present as was the case of the pan-palaeotropical mol- geography, of the Indo-China terrane between luscs and brachiopods mentioned previously, Sibumasu and South China This terrane has not which are not useful as more than indicators of been discussed previously in this review The tropical climates In the Ashgill brachiopods, Ordovician succession in the Indo-China terrane Zhan and Cocks (1998) have demonstrated is dominated by clastic rocks, and lacks thick, close links between North and South China, platform carbonates of Thung Song type A re- with endemic genera known only from those cent review (Zhou et al), 1997) shows that the two palaeoplates In sum, it may not be neces- trilobite faunas are dominated by genera (even sary to invoke such wide separation of North species) known from cool water palaeolatitudes and South China to explain such faunal differ- of western Gondwana Thus it seems probable ences as there are The change in the faunas in that the Indo-China terrane had an Ordovician Sibumasu in the mid-Ordovician may be more position well distant and to the west of where it allied to a biofacies shift, perhaps associated is now, only interpolating itself in its present with a widespread deepening event accompa- position between Sibumasu and China by sub- nied by the appearance of clastic rocks Finally, sequent transcurrent movement along the mar- it is worth adding that over North China, as in gin of Gondwana The close juxtaposition today central Australia, the latest Ordovician is not of trilobite species similar to those found near present — if deposited at all it may have subse- the Ordovician pole in Indo-China with litholo- quently been eroded away This, of course, is gies and faunas of undoubted Ordovician tropi- entirely negative evidence, and it would be ac- Ordovician biogeography of Sibumasu 53

AUSTRALIA (Georgina Basin) ?

BURMA (Southern Shan States) SOUTH ETHABUKA (Sil.) THAILAND PANGHSA-PYE

NORTH SOUTH SOUTH LINWE CHINA CHINA CHINA SHALE (Zibo) (Huayin-Shan) (Yichang) ?

BADOU (Sil.) GEZHUANG KINLE (Sil.) WANG TONG MITHAKA 1-2 SILTSTONE PA KAE MACHIAKOU PAGODA (Sil.) 6-9 3 CARLO 10 SATUN Base of MEITAN austrodentatus 4 DAWAN Zone BEIAN- 11 NORA ZHUANG 5 FENGHSIANG THUNGSONG (CAMB.) COOLIBAH ZIFANG- NANT- ZHUANG THUNG KELLY SINKUAN - SONG CREEK (CAMB.) (CAMB.) TARUTAO (to 200m)

DOKTOYE NINMAROO LIMESTONE (CAMB.)

0

100 m (CAMB.)

200 m

KEY TO NUMBERED FORMATIONS 1 = WUFENG 2 = LINHSIANG 3 = FENGDONGGANG 4 = HUNGHUAYUAN 5 = TUNFTZU 6 = WUFENG 7 = LINHSIANG 8 = PAGODA NGWETAUNG 9 = MIAOPO 10 = KUNIUTAN 11 = HUNG-HUAYUANG (?CAMB.)

Fig4 Comparative Ordovician successions from North China, South China, Burma, South Thailand and central Australia% Vertical dimension thickness% This demonstrates that the overall thickness and characters of the successions of South Thailand compares most closely with South China% Datum line shown is the base of the Middle Ordovician, taken here as the base of the austrodentatus graptolite biozone% 54 R) A) Fortey and L) R) M) Cocks cordingly difficult to disprove the notion that graphic test of a tectonic model% Earth and Planetary Sibumasu preserved the entire sequence of that Science Letters 75: 184-190% Burrett, C% F%, and Stait, B% A% 1987% China and Southeast Asia plate — which would itself have become more as part of the Tethyan margin of Cambro-Ordovician like South China as the Ordovician progressed Gondwanaland% In Shallow Tethys 2% pp% 65-77% Edited by K% G% McKenzie% Balkema, Rotterdam% Burrett, C% F%, Long, J% A% and Stait, B% A% 1990% Early-Middle Conclusions Palaeozoic biogeography of Asian terranes derived from Gondwana% Memoirs of the Geological Society of Lon- don 12: 163-174% A review of faunal evidence for the position of Chen J%-Y% and Teichert, C% 1988% The Ordovician Suborder Sibumasu (Shan-Thai) terrane in the Ordovician Cyrtocerinina (Order Ellesmeroceratida)% Palaeontologia reveals an apparent paradox Lower to lower Cathayana 3: 145-229% Middle Ordovician nautiloid faunas have been Chen Xu et al, 1995% Correlation of the Ordovician rocks of China% International Union of Geological Sciences Publi- claimed to suggest the proximity of Sibumasu to cation 31: 1-104% the North China-Korean-Australian part of Cocks, L% R% M% and Fortey, R% A% 1982% Faunal evidence for Gondwana on the palaeoequator On the other oceanic separations in the Palaeozoic of Britain% Journal hand, the nature of the whole sedimentary se- of the Geological Society of London 139: 465-478% Cocks, L% R% M% and Fortey, R% A% 1988% Lower Palaeozoic quence in southern Thailand, and the taxo- facies and faunas around Gondwana% Geological Society nomic composition of the later Ordovician fau- Special Publication 37: 183-200% nas, compare very closely with sections on the Cocks, L% R% M% and Fortey, R% A% 1990% Biogeography of South China (Yangtze) plate North China and Ordovician and Silurian faunas% Geological Society South China have been placed widely apart in Memoir 12: 97-104% Cocks, L% R% M% and Fortey, R% A% 1997% A new Hirnantia Ordovician continental reconstructions (e)g), fauna from Thailand and the biogeography of the latest Laurie and Burrett, 1992) The question is how Ordovician% Geobios 20: 111-120% to explain this claimed ‘switch’ in faunal affini- Cocks, L% R% M% and Rong Jia-Yu 1988% A review of the late ties? The possibility that Thailand/Sibumasu Ordovician Foliomena brachiopod fauna with new data may have moved, away from the palaeoequator, from China, Wales and Poland% Palaeontology 31: 53-67% Cocks, L% R% M% and Rong Jia-Yu 1989% Classification and re- from North China/Australia towards South view of the brachiopod superfamily Plectambonitacea% China as the Ordovician proceeded, receives Bulletin of the British Museum (Natural History) Geology some support from evidence of considerable 45: 77-163% translation of the neighbouring Indo-China Cocks, L% R% M% and Zhan Ren-bin 1998% Caradoc terrane However, it seems that the differences brachiopods from the Shan States, Burma (Myanmar)% Bulletin of the Natural History Museum (Geology) 54 (in between North and South China plates may press)% have been overemphasised by previous workers; Dean, W% T% 1967% The distribution of Ordovician shelly fau- very similar lower Ordovician nautiloid faunas nas in the Tethyan region% In Aspects of Tethyan Bioge- have recently been recorded from both areas ography% pp% 11-44% Edited by C% G% Adams and D% V% Ager% Special Publications of the Systematics Association At the present state of knowledge, therefore, a 7% close biogeographical and physical proximity of Fortey, R% A% 1997% An Upper Ordovician trilobite fauna from South China and Sibumasu is favoured, based Thailand% Palaeontology 40: 397-449% upon numerous specific identities among later Fortey, R% A% and Cocks, L% R% M% 1986% Marginal faunal belts Ordovician faunas, and several remarkable simi- and their structural implications, with examples from the Lower Palaeozoic% Journal of the Geological Society of larities in sedimentary features However, this is London 143: 151-160% far from certain; there remain many ambiguities Fortey, R% A% and Morris, S% F% 1982% The Ordovician Trilobite in the evidence, which illustrate well the prob- Neseuretus from Saudi Arabia, and the palaeogeography lems of integrating biogeography and palaeoge- of the Neseuretus fauna related to Gondwanaland in the ography for suspect terranes in the Lower Pal- earlier Ordovician% Bulletin of the British Museum (Natu- ral History) Geology 36: 63-75% aeozoic Further planned work should take the Garson, M% S%, Amos, B% J% and Mitchell, A% H% G% 1976% The story further geology of the area around Neyaungga and Ye-ngan, Southern Shan States, Burma% Institute of Geological Sci- ences Overseas Memoir 2: 1-70% Hamada, T% 1964% Some Middle Ordovician brachiopods References from Satun, Southern Thailand% Contributions to Geology and Palaeontology of Southeastern Asia 1: 279-289% Bunopas, S% 1983% Palaeozoic succession in Thailand% In Ingavat, R%, Muenlek, S% and Udomrain, C% 1975% On the dis- Stratigraphic correlation of Thailand and Malaysia% pp% coveries of some Permian fusulinids and Ordovician 37-96% Edited by P% Nutalaya% Geological Society of Thai- cephalopods of Banrai, West Thailand% Journal of the land, Bangkok% Geological Society of Thailand 1: 81-9% Burrett, C% F%, and Stait, B% A% 1985% South East Asia as a part Ingavat-Heimche, R% 1994% Paleozoic palaeontological evi- of an Ordovician Gondwanaland – a palaeobiogeo- dence of Thailand% In Stratigraphic correlation of South- Ordovician biogeography of Sibumasu 55

eastern Asia pp% 43-54% Edited by P% Angusuwathana, T% Reed, F% R% C% 1915% Supplementary memoir on new Ordovi- Wongwanich, W% Tansathien, S% Wongsomsak and J% cian and Silurian fossils from the Northern Shan States% Tulyatid% IGCP Project 306 and Department of Mineral Palaeontologia Indica (new series) 6 (1): 1-122% Resources, Thailand% Reed, F% R% C% 1936% The Lower Palaeozoic faunas of the Jell, P% A%, Burrett, C% F%, Stait, B% and Yochelson, E% L% 1984% Southern Shan States% Palaeontologia Indica (new series), The Early Ordovician bellerophontid Peelerophon 21 (3): 1-130% oehlerti (Bergeron) from Argentina, Australia and Thai- Runnegar, B%, Pojeta, J%, Taylor, M% E% and Collins, D% H% land% Alcheringa 8: 169-176% 1979% New species of the Cambrian and Ordovician Ji, J%-L% 1985% On the depositional environment of the Pa- chitons Matthevia and Chelodes from Wisconsin and goda Formation in central and southwestern China% Pro- Queensland: evidence for the early history of fessional Papers in Palaeontology and Stratigraphy 12: polyplacophoran molluscs% Journal of Paleontology 53: 87-93 [In Chinese]% 1374-1394% Ji, J%-L% 1986% Upper Ordovician (Middle Caradoc-Early Scotese, C% R% and McKerrow, W% S% 1990% Palaeozoic Ashgill) trilobites from the Pagoda Formation in South palaeogeography and biogeography% Geological Society China% Professional Papers in Stratigraphy and Palaeon- Memoir 12: 1-435% tology 15: 1-33 [In Chinese]% Shergold, J% H% 1985% Notes to accompany the Hay River- Kobayashi, T% 1957% Upper Cambrian fossils from peninsular Mount Whelan Special 1:250 000 Geological Sheet, Thailand% Journal of the Faculty of Science University of southern Georgina Basin% Bureau of Mineral Resources, Tokyo 10: 367-82% Geology and Geophysics Report 251: 1-47% Kobayashi, T% 1961% On the occurrence of Ordovician Shergold, J% H% Burrett, C% F%, Akerman, T% and Stait, B% 1988% nautiloids in North Thailand% Japanese Journal of Geol- Late Cambrian trilobites from Tarutao Island, Thailand% ogy and Geography 32: 79-84% Memoir of the New Mexico Bureau of Mines and Mineral Kobayashi, T% 1984% Older Palaeozoic gastropods and Resources 44: 303-320% cephalopods of Thailand and Malaysia% Geology and Pal- Stait, B% and Burrett, C% F% 1984a% Early Ordovician aeontology of Southeastern Asia 25: 195-199% polyplacophoran Chelodes whitehousei from Tarutao Is- Kobayashi, T% and Hamada, T% 1964% On the Middle land, southern Thailand% Alcheringa 8: 112% Ordovician fossils from Satun, the Malaysian frontier of Stait, B% and Burrett, C% F% 1984b% Ordovician nautiloid fau- Thailand% Japanese Journal of Geology and Geography nas of Central and Southern Thailand% Geological Maga- 35: 205-211% zine 121: 115-124% Kobayashi, T% and Hamada, T% 1971% A cyclopygid-bearing Stait, B%, Burrett, C% F% and Wongwanich, T% 1984% Ordovician Ordovician faunule discovered in Malaysia with a note trilobites from the Tarutao Formation Southern Thailand% on the Cyclopygidae% Geology and Palaeontology of Neues Jahrbuch fur Geologie und Paläontologie Southeastern Asia 8: 1-18% Monatshefte 1984(1): 53-64% Kobayashi, T% and Hamada, T% 1978% Upper Ordovician trilo- Stait, B%, Wyatt, D% and Burrett, C% F% 1987% Ordovician bites from the Langkawi Islands, Malaysia% Geology and nautiloid faunas of Langkawi Islands, Malaysia and Palaeontology of Southeastern Asia 19: 1-28% Tarutao Island, Thailand% Neues Jahrbuch fur Geologie Kobayashi, T% and Hamada, T% 1984% Trilobites of Thailand und Paläontologie Abhandlungen 174: 373-391% and Malaysia% Geology and Palaeontology of Southeast- Tripp, R% P%, Zhou, Z%-Y% and Pan, Z%-Q% 1989% Trilobites from ern Asia 25: 273-284% the Upper Ordovician Tangtou Formation, Jiansu Prov- Laurie, J% R% and Burrett, C% 1992% Biogeographic significance ince, China% Transactions of the Royal Society of Edin- of Ordovician brachiopods from Thailand and Malaysia% burgh, Earth Sciences 80: 25-68% Journal of Paleontology 66: 16-23% Webby, B% D% E% 1973% Remopleurides and other Upper Lu, Y%-H% 1975% Ordovician trilobite faunas of central and Ordovician trilobites from New South Wales% Palaeontol- southwest China% Palaeontologia Sinica (New Series, B) ogy 16: 445-75% 11: 1-463% Webby, B% D% E% 1974% Upper Ordovician trilobites from cen- Lu, Y%-H% Chang, W%-T, Chu, C%-L%, Chien, Y%-Y% and Hsiang, tral New South Wales, Palaeontology 17: 486-510% L%-W% 1965% Trilobites of China% Science Press, Beijing% Whittington, H% B% and Hughes, C% P% 1972% Ordovician geog- 766 pp% [in Chinese] raphy deduced from trilobite distributions% Philosophical Metcalfe, I% 1992% Ordovician to Permian evolution of South- Transactions of the Royal Society, Series B 263: 265-278% east Asian terranes: NW Australian Gondwanan connec- Wongwanich, T%, Burrett, C% F%, Tansathien, W% and tions% In Global perspectives on Ordovician Geology% pp% Chaodumrong, P% 1990% Lower to Mid Palaeozoic 293-305% Edited by B% D% E% Webby and J% R% Laurie% stratigraphy of mainland Satun Province, Thailand% Jour- Balkema, Rotterdam% nal of Southeast Asian Earth Sciences 4: 1-9% Mitchell, A% H% G% 1981% Phanerozoic plate boundaries in Wongwanich, T%, Burrett, C% F%, Wyatt, D% J% and Stait, B% A% mainland S%E% Asia, the Himalayas and Tibet% Journal of 1983% Correlations between the Ordovician of Tarutao Is- the Geological Society of London 138: 109-122% land, Satun Province (Thailand) and Langkawi Islands Mitchell, A% H% G%, Marshall, T% R%, Skinner, A% C%, Baker, M% (Malaysia)% In Stratigraphic Correlations between Thai- D%, Amos, B% J% and Bateson, J% H% 1977% Geology and land and Malaysia pp% 77-95% Edited by P% Nutayala% Geo- exploration geochemistry of the Yadanatheingi and logical Society of Thailand, Bangkok% Kyaukme-Longtawkno areas, Northern Shan States, Xu, H%-K%, Rong, J%-Y% and Liu, D%-Y% 1974% Ordovician Burma% Overseas Geology and Mineral Resources Report, brachiopods% In Handbook of Stratigraphy and Palaeon- Institute of Geological Sciences, London 51: 1-35% tology in Southwest China% pp%144-154% Academia Sinica, Percival, I% G% 1991% Late Ordovician articulate brachiopods Beijing% from central New South Wales% Association of Australa- Yochelson, E% and Jones, C% R% 1968% Teichiispira, a new Or- sian Palaeontologists Memoir 11: 107-177% dovician gastropod genus% Professional Papers of the U%S% Reed, F% R% C% 1906% The Lower Palaeozoic fossils of the Geological Survey 613-B: 1-15% Northern Shan States, Burma% Palaeontologia Indica (new Yu Wen 1989% The occurrence of Peelerophon oehlerti series), 2: 1-154% (Bergeron) from southeast China% Journal of Paleontolo- 56 R) A) Fortey and L) R) M) Cocks

gy 63: 697% from North and Northeast China% Palaeontographica Zhan Ren-bin and Cocks, L% R% M% 1998% Late Ordovician Abteilung A 192: 157-210% brachiopods from the South China Plate and their palae- Zhou, Z%-Y%, Dean, W%-T% and Luo, H%-L% 1997% Ordovician ogeographical significance% Palaeontology 41: (in press)% trilobites from the Hsiangyang Formation, Dali, western Zhou, Z%-Y% and Fortey, R% A% 1986% Ordovician trilobites Yunnan, China% Palaeontology 40: (in press)%