14 



L.E. POPOV, L.R.M. COCKS AND I.F. NIKITIN 



Fig. 1 Generalised map of the Chu-Ili Range and West Balkhash Region (including the southern part of Lake Balkhash), showing the boundaries of the 

 Early Palaeozoic tectonofacies belts, mainly after Nikitin et al. ( 1991 ), and the position of the brachiopod localities discussed in the text: 1, Anderkenyn- 

 Akchoku; 2, Kujandysai; 3, east side of Kopalysai River; 4, Buldubai-Akchoku Mountain; 5, Tesik River; 6, Burultas Valley; 7, south-east side of Karatal 

 River near Sorbulak spring; 8, 7 km southwest of Karpkuduk Well, Kotnak Mountains. 



palaeogeography. Up until now, little assessment of the faunas 

 contained within these tectonic plates has been made, particularly in 

 relationship to contemporary faunas from other areas. One such 

 plate is that forming the Chu-Ili Range, and termed here the Chu-Ili 

 Plate (Fig. 1 ). Within the Chu-Ili Plate the successions have been 

 known for some time (e.g. Nikitin 1972, 1973). However, although 

 a number of papers have been published on aspects of some of the 

 contained Ordovician faunas, much remains to be done. A central 

 formation within the unit is the Anderken Formation of early Caradoc 

 age. This immediately underlies the Dulankara Formation, whose 

 brachiopods from its lowest Otar Member we have recently revised 

 ( Popov et al. 2000). Although some pioneering descriptions of some 

 of the Anderken brachiopods were published by Rukavishnikova 

 ( 1956) and some individual species have been published in a number 

 of publications, e.g. Popov (1980, 1985) and Nikitin & Popov 

 ( 1983), the whole brachiopod fauna from the formation has never 

 been published, and this is the chief purpose of the present paper. In 

 addition, six brachiopod-dominated associations can be identified 

 from the Anderken Formation. LEP and LRMC are responsible for 

 the whole paper and IFN for input into the systematic palaeontology 

 and biofacies sections. 



OUTLINE OF GEOLOGY AND FOSSIL 

 LOCALITIES 



The Chu-Ili Plate (Fig. 1), as recognised here, is a small part of Asia 

 today, and is traceable from the Zailiyskiy Alatau Range in the 

 southeast to the northern Betpak-Dala Desert in the northwest, 

 where it disappears under late Palaeozoic and Mezo-Cenozoic de- 

 posits. To the southwest it is bordered by the large Dzhalair-Najman 

 Fault and northward-dipping homoclinal sequences of Upper 

 Cambrian and Lower to Middle Ordovician age which are mainly 

 siliciclastic slope rise deposits (e.g. the Dzhambul Formation), indi- 

 cating passive margin development, and several thrust sheets 

 consisting of dismembered ophiolites of the early Palaeozoic 

 Ashchisu Formation (Toporova et al. 1971). The Dzhalair-Najman 

 Fault mainly follows an early Palaeozoic suture which separates the 

 Lower Palaeozoic Chu-Ili Plate from the Middle to Upper Ordovician 

 volcanic island-arc association traceable along the northeastern 

 margin of the Betpak-Dala-North Tien Shan tectonofacies belt of 

 Nikitin (Nikitin et al. 1991), which is the same as the Djezkazaan- 

 Kirgiz (4.1) tectonofacies unit of Sengor & Natalin (1996). To the 



