112 



L.R.M. COCKS AND ZHAN REN-BIN 



what he identified as the new species Orthis (Dalmanella) emancipata 

 from Bawzaing. which he listed together with some unfigured 

 molluscs, crinoids and the trilobite Ogygites cf. yunnanensis Reed. 

 Later he listed and described a further fauna from the Namnoi 

 Horizon, Southern Shan States (Reed 1936: 82), including the new 

 brachiopod Orthis (Paurorthis) hehoensis together with trilobites 

 such as undoubted Annamitella which Dr R. A. Fortey confirms is 

 restricted to beds no younger than Llandeilo, and is more probably 

 of Llanvirn age. Comparably, also from the Southern Shan States, 

 the Natural History Museum possesses several blocks (BC 52144- 

 52153) from Twinzontaung, collected and presented by T. O. Moms 

 in 1929. These contain hundreds of specimens, mostly external 

 moulds of a monospecific although unidentified orthoid which again 

 has an earlier Ordovician aspect. 



There is also the latest Ordovician (Hirnantian) fauna from the 

 Panghsa-pye' Beds, originally described by Reed ( 1915) and revised 

 by Cocks & Fortey (1997). Thus there are at least three Ordovician 

 horizons present in the Shan States, (a) the Llanvirn-Llandeilo, (b) 

 the Caradoc fauna described here, and (c) late Ashgill faunas from 

 the Panghsa-pye Beds. 



PALAEOGEQGRAPHICAL ANALYSIS 



The Ordovician was a period of continental dispersal (Cocks & 

 Fortey 1990) and southeast Asia has been recognized as consisting 

 of a number of terranes, one of which is the Sibumasu (or Shan-Thai) 

 terrane including much of the Malay Peninsula, West Thailand, 

 Burma and western Indonesia. The Indochina terrane lies immedi- 

 ately to the east of Sibumasu and the South China terrane to the 

 northeast (Mitchell 1981, Burrett et al. 1990). The tectonic bounda- 

 ries of the Sibumasu terrane are the Uttaradit-Nan to Raub-Bentong 

 sutures to the east and the Shan boundary to the west (Bender 1983, 

 Metcalfe 1992). The Shan States of Central to North Burma (Fig. 1 ) 

 lie in the western part of the Sino-Burman Ranges. The Naungkangyi 

 Group and its equivalents in the Shan States were deposited at the 

 northern end of the Sibumasu palaeocontinent in the Late Ordovician. 

 From the marine benthic shelly fossils found in these rocks, we can 

 evaluate its relationships with other contemporary terranes. Table 1 

 shows the faunal affinity indices between eight Caradoc brachiopod 

 faunas calculated by three different formulae as recommended by 

 Rong et al. (1995) (for faunal lists see Appendix). 



FAUNAL ASSOCIATIONS 



Much of the new Naungkangyi material comes from localities 

 AM77 and AM78 north-west of Linwe in the Neyaungga-Ye-ngan 

 area. Southern Shan States (Mitchell et al. 1977) at longitude 

 96°33'E and latitude 2 1 ° 14'N. The material was collected by A.H.G. 

 Mitchell as blocks, which were split up in the Natural History 

 Museum by one of us (LRMC). Collection AM77 yielded 45 

 specimens, of which 20 (44.4%) were Saucrorthis irravadica, 7 

 (15.6%) were Leptellina (Leptellina) minor and one was Onniella 

 chaungzonensis; the remainder were 7 varied bryozoans (15.6%), 9 

 crinoids (20%) and a single conulariid. Collection AM78 yielded 

 185 specimens of which 122 (65.9%) were Leptellina (Leptellina) 

 minor, 23 (12.4%) were Dirafinesquina giobosa and one each were 

 Nicolella sylvatica, Glyptomena sp. and another unidentified orthoid, 

 together with 21(11 .4%) crinoids, 5 (2.7%) the trilobite Neseuretus 

 birmanicus, 3 (1.6%) various bryozoans, 5 (2.7%) gastropods of 

 three different kinds, and one conulariid. Even though most of the 

 brachiopods were disarticulated and formed pail of a shell hash, the 

 fact that 62 ventral valves and 60 dorsal valves of Leptellina 

 (Leptellina) minor were counted in AM78 indicates, nevertheless, 

 that the distance of transportation from the original life habitat to the 

 area of final burial is unlikely to have been great. 



All the other material at our disposal were either small collections 

 or single isolated museum specimens from a wide variety of locali- 

 ties. Thus a proper assessment of the associations and hence 

 communities of the Naungkangyi Group must await more substan- 

 tial systematic collecting. However, even with the small amount of 

 material available, it is clear that the brachiopod diversity of the 

 Naungkangyi Group, although quite large when the Group is consid- 

 ered as a whole, is nevertheless rather small when the individual 

 localities and horizons are considered separately. This diversity is 

 much less than, for example, in the neighbouring Shihtzupu Forma- 

 tion in South China, from which individual beds have yielded over 

 20 different brachiopods from lithologies which are broadly similar 

 to the Naungkangyi Group. The conclusions reached are that the 

 Naungkangyi associations known to us probably colonized only the 

 shallower parts of the contemporary Ordovician shelf and that the 

 contemporary middle to deeper water faunas are either not preserved 

 or have not yet been found. 



1. The Caradoc Naungkangyi fauna is closest to the early Caradoc 



Shihtzupu Formation fauna of South China (Xu et al. 1974). 

 During the later Caradoc. the purple-red Pagoda Limestone was 

 deposited on the vast area of the Yangtze Platform with a deep- 

 water Foliomena fauna quite different from the shallower-water 

 (probably BA2 to BA3 according to Boucofs ( 1975) concept of 

 Benthic Assemblages) Naungkangyi fauna. There are many com- 

 mon components between the Naungkangyi and Shihtzupu faunas: 

 some genera (such as Saucrorthis) are only recorded from these 

 two areas. This confirms that the South China and Sibumasu 

 terrenes were not far apart, a relationship which continued into 

 the Ashgill (Cocks & Fortey 1997, Fortey & Cocks 1998). 



2. The Naungkangyi fauna shares some similarity with the Caradoc 



fauna of the Bala District, Wales (Williams 1963), as is shown by 

 the nine common genera, Lingulella. Nicolella. Skenidioides. 

 Dalmanella. Onniella, Sowerbyella, Glyptomena, Bellimttrina 

 and Cyclospira. However, these nine genera are widespread or 

 even cosmopolitan, and thus the data indicate only that the 

 Naungkangyi fauna was faunally connected to many other areas 

 in Caradoc times. 



3. Also similar to the Naungkangyi fauna is the one from the late 

 Caradoc Pingliang Formation of Shaanxi. North China (Fu 1982, 

 Rong & Zhan 1996). This fauna overlies graptolitic shales and 

 underlies the even shallower-water Beiguoshan Formation fauna 

 of Ashgill age (Rong & Zhan 1996), and thus represents the 

 transition between shallow and deep water faunas. The constitu- 

 ents in common with the Naungkangyi fauna are Skenidioides. 

 Leangella (Leangella), Sowerbyella and Bellimurina, but in 

 addition there are some typical representatives of the deeper- 

 water Foliomena fauna, including Foliomena itself. Since the 

 Pingliang fauna has a comparatively high affinity index with the 

 Shihtzupu fauna of South China, we can postulate that South 

 China, North China and Sibumasu were close together during the 

 Late Ordovician, with North China a little further away from the 

 other two, and that the faunas on them were controlled by 

 comparable environmental factors. 



4. The Caradoc fauna from New South Wales. Australia (Percival 



1 99 1 ) has no common constituents with any of our listed contem- 

 porary faunas apart from cosmopolitan genera such as Ptycho- 

 pleurella, Skenidioides and Sowerbyella. This is also true of the 

 mid Ashgill (Zhan & Cocks 1998), and indicates that Australia 



