UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



21 



Quadrangle 73°22'30" to 73°30' E; 45° to 45°05' N). A summary of 

 the Ordovician geology and lithostratigraphy of this locality is in 

 Nikitin et al. (1980, text-figs 18, 20). The Anderken Formation 

 consists mainly of siliciclastic rocks with a thick unit of polymict 

 conglomerates at the base and a number of carbonate mud-mounds 

 in the upper part (Fig. 3). The carbonate unit in the top of the 

 sequence is a bed of nodular algal limestone about 6- 1 m thick with 

 numerous Girvanella sp., Cyclocrinites nikitini and Mastopora 

 reticulata and brachiopods of the Acculina—Dulankarella Associa- 

 tion (Locality 1041a of Nikitin = Sample 390/76 of Kovalevskii). 

 which underlies a lens of massive, micritic limestone up to 20 m 

 thick which forming the mud-mound core. The unit thins about 200 

 m westward from Locality 1041 a, where it is represented by bedded 

 and nodular limestone with the brachiopods Pionodema opima, 

 Dulankarella larga and Mabella conferta (Sample 818). The upper- 

 most 10 m of the underlying unit, of fine-grained sandstone 

 intercalating with siltstone, contains a different brachiopod assem- 

 blage with Tesikella necopina (Sample 818a), in association with 

 abundant cystoid columnals. 



Locality 7. Sorbulak spring on the east side of the 

 River Karatal 



In the south Betpak-Dala Desert, about 20 km west of Baigara 

 Mountain, the Anderken Formation is well exposed on both sides of 



the River Karatal (Fig. 1, locality 7). Here it rests on the graded 

 sandstones and siltstones of the Llandeilo to Lower Caradoc upper 

 Baigara Formation (Fig. 2), or is in contact with intrusives. About 2 

 km south-east of the Karatal river, south of Sorbulak spring, it 

 comprises (1) polymict conglomerates more than 50 m thick, (2) 

 medium- to fine-grained sandstones 169-170 m thick with 

 Ectenoglossa sorbulakensis about 10-15 m above the base of the 

 unit (Fig. 3, Sample 1024); and (3) intercalating fine-grained slightly 

 calcareous sandstones and siltstones about 60 m thick with the 

 Tesikella Association in the upper 20 m of the unit. The upper part of 

 the section is an unfossiliferous unit of intercalating fine-grained 

 sandstones, lilac and red siltstones and mudstones several hundred 

 metres thick, which is overlain by the basal conglomerate of the 

 Dulankara Formation. 



Locality 8. Kotnak Mountains 



This incomplete section of the Anderken Formation is situated west 

 of the Kotnak Mountains, about 7 km SW of Karpkuduk Well. There, 

 about 1 .5 km north-east of the salt marsh (Figs 1 , 3, 8), the formation 

 consists of: ( 1 ) siltstone about 70 m thick with some storm beds of 

 calcareous sandstone about 10-20 cm thick with a coquina of the 

 bivalve Ctenodonta sp. (Samples 1017, 1019); (2) sandstone inter- 

 calating with siltstone in the upper part, total 40 m thick, with 

 brachiopods of the Tesikella Association in the lower 10 m of the unit 



QUATERNARY 



Salt marsh 



DEVONIAN 



ES 



ORDOVICIAN 

 Anderken Formation 



Conglomerate 



Sandstone 



vv^j Sandstone and 

 t>;r i£3 siltstone 



*':X 



Sandstone with coquina 

 storm beds 







i i_ 



2 km 



Fig. 8 Geological map showing the distribution of the Anderken Formation and the position of fossil localities in the area about 7 km south-west of 

 Karpkuduk well, Kotnak Mountains. 



