UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



23 



F2 



• 2538 



Parastrophina - Kellerella 

 Association 



100 + *8217 

 / \ -k 8256 

 626 / •• 626 



T, 8214 \&»8 * 



Acculina - Dulankarella 's* \* . 8226 

 Association \„ £«223b 



622 ^-* \ B219 



8223* \* 

 6220 . 

 8215-». w 390 

 85258 X »| U ~V 

 - 1.0 -0.8 -0.6 -0.4 e ; 3 ,T^ 



Zhilgyzambonites - X31 * 

 Foliomena Association 8255 



F3 



0.6 



Zhilgyzambonites - 8J55 

 Foliomena Association ,„.'< 



Mabella - Sowerbyella 

 Association 



8128b 8257 8 228 



Acculina - Dulankarella 

 Association 



626 . .,. '" 



T" -0.4 



8135 



0.2* 



100b 

 0.6 



F1 



1.0 



8128 

 2 

 F-1024b" 



V7611 

 V 



F-1018 

 V F-1018a 



Tesikella Association 



J5258 



)1^oT+ 



— 



8223 



• 8215 

 8220 



• 



\ 



100 4, 



82233^628 

 8223b ■& 

 8214* * 



8219 



8256 i, * B 226 1 



8217* * 

 948 



Parastrophina - Kellerella 

 Association 



8135 . 



- 0.4 



8251 



- 0.2 

 390 



Mabella - Sowerbyella 

 Association 



F1 



0.4 m" 0.6 0.8 1 .0 



F-1024b 



--0.2 



F-1018 Y 7613 • B137IJ 



6230 ■ B 843" - 

 8128b ,„,.8128a 



8157 

 8228 



▼ 



T 



8128 



Tesikella Association 



Biuay 

 -0.6 F-1018a 



Fig. 9 Two-dimensional principal component analysis plots on first (Fl ). second (F2) and third (F3) eigenvectors of selected brachiopod samples from the 

 Anderken Formation shown on Tables 1-6. 



sorbulakensis formed a separate monotaxic community which in- 

 habited a mobile sandy bottom in peritidal environments, perhaps 

 tidal flats. 



2. The Tesikella Association (average Diversity Index 1.18; observed 

 range 0.33-2. 16, N=7). This is a low-diversity strophomenide-domi- 

 nated brachiopod association. It is widespread in shallow marine 

 environments of BA-2, which are mainly fine-grained sands with 

 subhorizontal stratification, occasional storm beds with mollusc 

 coquinas and locally abundant plant remains of Akdalaphyton 

 caradoci. This association is defined by the index species Tesikella 

 necopina, an endemic species and genus restricted only to the Lower 

 Anderken Formation. This species pursued an opportunistic life 

 strategy and expanded into environments inhabited mostly by gas- 

 tropod and bivalved mollusc communities, in which 

 rhynchonelliformean brachiopods, if they occur, are an insignificant 

 component of the assemblage and show patchy distribution. Traces 

 of tidal currents, ripple marks and occasional storm beds suggest 

 rather turbulent environments occasionally affected by seasonal 

 storms. Shells in all the samples are mostly disarticulated (Table 2) 

 and some contamination by allochthonous shells from adjacent 

 associations cannot be excluded. However, results of the Principal 

 Component Analysis show that all the samples referred to the 

 Tesikella Association form a distinct cluster and are characterised by 

 low positive values of Fl and negative values of the two other 

 maximum directions of variation (F2 and F3). Sample 1018, which 

 may be contaminated by allochthonous shells, shows low negative 

 values of F3 similar to the samples of the Mabel la-Sowerbyella 

 Association (Fig. 9). 



In its pioneer stage, the Tesikella Association is characterised by 

 the appearance of Tesikella necopina in mollusc-dominated environ- 

 ments, where it is the only brachiopod ( Samples 127,7611,81 27-2b, 

 8138), or where it comprises more than 50% of the brachiopod fauna 

 together with Longvillia lanx, Sowerbyella nikavishnikovae (up to 

 34%) and Eodalmanella extern (up to 18%). At its mature stage the 

 association includes four to eight species usually common in the 

 Sowerbyella-Mabella Association, e.g. Christiania egregia (up to 

 35%), Sowerbyella nikavishnikovae (up to 50%) and Pionodema 

 opima (56% in one sample). All the other taxa constitute less than 5% 

 of individuals in any particular sample. Among other groups bivalved 

 molluscs, the trilobites "Isotelus" romanovskyi, Lonchodomas 



tecturmasi and Dulanaspis levis anderkensis occur. The echinoderm 

 fauna is dominated by the cystoidean Clivosocystis minusculus 

 Stukalina which is known only from columnals. The abundance of 

 coquinas and plant remains suggests biogenic fixation of a sandy 

 substrate. 



Sample 1018 from the Kotnak Mountains is placed within the field 

 of the Tesikella Association (Fig. 9), but differs in high taxonomic 

 diversity and the occurrence of taxa characteristic of the Sowerbyella- 

 Mabella and Acculina-Dulankarella associations, e.g. 

 Anoptambonites orientalis, Glyptomena onerosa, Limbimurina sp. 

 and Acculina kulanketpesica. This sample came from a bed of 

 bioclastic sandy limestone, which is an atypical lithology for the 

 Tesikella Association, more likely to have been deposited within a 

 bar system, and contains an allochthonous brachiopod coquina 

 representing a mixture of several life associations. The abundance of 

 coarse elastics and storm beds formed mostly by the bivalve 

 Ctenodonta sp. (Samples 1017, 1019) in the Anderken Formation of 

 this section suggest turbulent depositional environments within a 

 shore-face zone comparable with the lower part of the Otar beds in 

 the Dulankara Formation of the Dulankara section in the south- 

 eastern Chu-Ili Range (Popov etal. 2000). 



3. Mabella-Sowerbyella Association (average Diversity Index 1 .30; 

 observed range 0.83-1 .86, N=9) is another low diversity association 

 of BA-2 dominated by strophomenides. It is recognised in the 

 Anderkenyn-Akchoku, Kopalysai and Buldukbai-Akchoku sections 

 by the predominance of Mabella conferta and Sowerbyella 

 nikavishnikovae which together comprise 40-80% of individuals in 

 the assemblage. Glyptomena onerosa, Shlyginia fragilis and 

 Anoptambonites orientalis mainly occur in this association (Table 

 3). As in the mature Tesikella Association, orthides are represented 

 only by Eodalmanella extera and Pionodema opima, which do not 

 usually co-occur. This association is confined to a fine clastic substrate 

 of silts and fine-grained sands, usually with traces of bioturbation 

 and locally abundant concentrations of the plant Akdalaphyton 

 caradoci. In samples from the Anderkenyn-Akchoku section 

 brachiopods are preserved disarticulated, but in the Kopalysai and 

 Buldukbai-Akchoku sections the number of articulated specimens 

 increases up to 50 percent, suggesting rapid burial and lack of 

 significant post-mortem displacement of the shells. The most com- 

 mon trilobites in the associated faunal assemblage are Lonchodomas 



