22 



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



Table 1 Composition of Ectenoglossa Association from the Anderken Formation showing number of complete shells, ventral and dorsal valves 

 respectively. 



Sample number 

 Number of specimens 

 Ectenoglossa sorbulakensis 



7612 



8130a 



8130- 



27 



1 



2 



24:3:2 



0:1:0 



0:2:0 



8223-1 



0:1: 



8227-10 



8227^10 



8227-80 



F-1024 



6 



4 



3 



12 



6:0:0 



0:3:4 



0:3:3 



0:8:12 



(Sample 1018a) below a bed of skeletal calcareous sandstone about 

 5 m thick with an allochthonous brachiopod fauna with a mixture of 

 taxa of the Tesikella and Mabella-Sowerbyella Associations (Sam- 

 ple 1018); (3) intercalating beds of sandstone and pebbly polymict 

 conglomerate about 80-90 m thick; and (4) siltstone with a few beds 

 of fine-grained sandstone, total 130 m thick and overlain 

 unconformably by Devonian conglomerate. 



FAUNAL ASSOCIATIONS 



The Anderken Formation is a transgressive sequence from near shore 

 to outer shelf deposits with predominantly siliciclastic deposition. 

 The lower part of the formation, below the main horizon with 

 carbonate build-ups in theAnderkenyn-Akchoku, Kujandysai, 

 Buldukbai-Akchoku and Burultas sections, was formed in tide- 

 dominated environments of mostly tidal flat deposits with 

 characteristic sets of pebbly conglomerates, cross-bedded and lami- 

 nated sands, coquina storm beds and traces of tidal currents. Carbonate 

 build-ups in the upper part of the formation preserve numerous 

 traces of photosynthetic activity and contain a diverse flora of green 

 and red algae (Nikitin et al. 1974); suggesting formation in shallow 

 depths within the euphotic zone. The outer shelf deposits are recorded 

 only in the south-eastern Chu-Ili Range and consist of silt and mud 

 containing graptolites. The benthic fauna is dominated by trilobites 

 but includes one of the earliest records of the Foliomena brachiopod 

 fauna. Apollonov (1975) has described the trilobite associations of 

 the middle and late Ordovician of the Chu-Ili Plate. 



A matrix based on the distribution of about 1800 brachiopod 

 specimens from 33 samples within the Anderken Formation was 

 subjected to Principal Component Analysis (Etter 1999). Plots of 



eigenvectors corresponding to three maximum directions of varia- 

 tion (F1-F3) are illustrated on two two-dimensional diagrams (Fig. 

 9). The Diversity Index is calculated as the number of species minus 

 1 divided by the natural logarithm of the number of brachiopod 

 individuals in the sample (for details see Williams et al. 1981 ).The 

 analysis of taxonomic composition and relative abundance of 

 brachiopod taxa from numerous localities and samples in the 

 Anderken Formation allows recognition of six brachiopod associa- 

 tions characterised below. They are interpreted within the Benthic 

 Assemblage (BA) scheme of Boucot (1975). 



1. The Ectenoglossa Association. This is a monospecific lingulide 

 association of BA-1 with Ectenoglossa sorbulakensis in the 

 Anderkenyn-Akchoku, Kujandysai and Buldukbai-Akchoku sec- 

 tions, the east side of the Kopalysai River and on the southern side of 

 the Karatal River south of Sorbulak spring (Table 1 ).The assemblage 

 shows patchy distribution in lithologies of coarse- to medium- 

 grained sands with subhorizontal and cross-bedded stratification. In 

 most of the localities shells are disarticulated on the bedding surfaces 

 and only in Sample 7612 do conjoined valves predominate (89% of 

 individuals). A cluster of six articulated shells preserved in life 

 position inclined from 62°-80° to the bedding surface was recovered 

 from Sample 8227-40 in the Buldukbai-Akchoku section, which 

 confirms the infaunal mode of life of this lingulide. The gastropods 

 Lophospira sp. and Latitenia kasachstanica Vostokova and the 

 bivalved molluscs Endomionia fecinda, Ctenodonta sp. and 

 Cyrtodontal subcentralis (Khalfin 1958), which are widespread in 

 similar lithologies and form coquina storm beds, do not co-occur 

 together with the lingulides; for example, in Sample 8 1 30 a bedding 

 surface with Ectenoglossa sorbulakensis and a storm bed with 

 molluscs and the trilobite Eokosovopeltis romanovskyi are separated 

 by an interval only about 2.5 m thick. It is likely that Ectenoglossa 



Table 2 Composition of Tesikella Association from the Anderken Formation showing number of complete shells, ventral and dorsal valves respectively. 



Sample numbers 



127 



818a 



F-1018a 



7611 



8128 



F-1018 



F- 1024b 



Number of specimens 



18 



22 



32 



7 



18 



172 



20 



Diversity index 



0.33 



0.65 



0.58 



0.51 



1.38 



3.11 



2.16 



Trematis sp. 



0:0:1 















Tesikella necopina 



3:14:12 



0:13:12 



0:16:7 



1:5:5 



0:4:2 



1:4:3 



0:2:2 



Longvillia lanx 







0:4:5 







2:7:3 





Glyptomena onerosa 













0:1:5 





Christiania egregia 













0:7:18 



0:2:7 



Limbimurina sp. 













0:1:1 





Isophragma imperator 













1:36:34 





Acculina kulanketpesica 











0:0:1 



0:1:2 





Mabella conferta 





1:0:0 









0:1:2 





Shlyginiafragilis 













0:6:4 





Anaptambonites orientalis 













1:4:3 





Sowerbyella rukavishnikovae 







0:10:11 







0:8:17 



0:9:10 



Bicuspina rukavishnikovae 













3:1:9 





Plectorthis bundtasica 











0:0:1 



1:6:7 





Dolerorthis expressa 













1:12:9 





Phragmorthis conciliata 













0:4:4 



0:1:0 



Eodalmanella extera 





4:4:0 





0:0:1 





1:28:22 





Pionodema opima 











2:8:5 







Rhynchotrema sp. nov. 











1:0:0 







Didxmelasma cf. transversa 













0:0:1 





8127-2b 



8138 

 2 



0:1:0 



0:2:0 



