UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 



15 





Chu-lli Plate 



Zhalair-Najman Synclinorium 



Central pari 



Southern part 



Burultas tectonofacies belt 



Assemblage of 

 fore-arc basin and 

 onlap assemblage 

 (Sarytuma Zone) 



Subduction-accretion complex 



Burubaital Package 



(dismembered 



ophlollte) 



Maikul Packege 



(slope-rise 



deposits) 



Zhalgyz Packege 



(dtsmembered 



ophlollte) 



Darbaza Packege 

 (carbonate platform) 



Zhalalr 

 Formation 



Zhalair Formation 



(siiistone and mudstone, interlayers of limestone and tuff) 



Chokpar 



Chokpar 

 Formation 



Ulkuntas 

 Limestone 



> 



Chokpar Formation 



(siltstone and mudstone, bla 



Kyzylsai 

 Formation 



Kyzylsai Formation 



(sandstone, polymlct 

 and siltstone) 



Dulankara Formation 



(conglomerate polymict, sandstone, siltstone, lenses of limestone) 



Anderken Formation 



(conglomerate pofymlct. sandstone, siltstone and limestone) 



Kopaly 



Baigara Fm. 



(limestone, 

 sandstone and 

 siltstone) 



Ka ratal 

 Formation 



(sandstone, 

 siltstone. 

 mudstone, and 

 tuff) 



Kogashik 



Aktau 



Ungur 



Dzhambul 

 Formation 



(sandstone, 

 quartzose, 

 siltstone and 

 mudstone, 

 graded) 



Beke Formation 



(sandstone, siltstone 

 and mudstone, graded) 



Uzunbulak Formation 



(sandstone, siltstone and 

 mudstone, interlayers of 

 limestone, mass flow 

 deposits) 



"Akzhal" Formation 



(limestone, bedded, 

 conglomerate and 

 sandstone at the base) 



PrecambHan basement 



Unnamed formation of 

 sandstone and graded 

 siltstone. with 

 olistostrome horizon 

 at the base 



Oisaksaul Formation 



(conglomerate, sandstone, 

 siltstone and limestone) 



Alakul 

 Bolgozha / Limestone 

 Formation 



(siliceous shales, black, 

 siliceous; extrusives 

 and tuff, rhyolite-dacite. 

 mass flow deposits) 



Burubaital 

 Formation 



(black and red 



radiolarian 



chert) 



Maikul 

 Formation 



(sandstone, 

 quartzose. 

 siltstone and 

 mudstone, 

 graded) 



Zhalgyz 

 Formation 



(sandstone, 

 olcano-clastic and 

 siltstone, graded 

 black shale, 

 basaltic extrusives 

 and tuff) 



Darbaza Formation 



(quartzes 

 limestone 

 dolomite) 



niDiroiii 



Angular unconformity 



Discontinuity 



q Stratigraphic contact 

 unknown 



Fig. 2 Chart showing the correlation between the Lower Palaeozoic lithostratigraphic units in the Chu-lli Plate and the Burultas tectonofacies belt. 



north-east of the Chu-lli Plate lies the Burultas tectonofacies belt 

 (Fig. 2), which represents an accretionary wedge suggesting active 

 margin development, island arc volcanism and subduction of the 

 oceanic crust under the Chu-lli Plate from the early Arenig to the 

 Llandeilo Pygodus anserinus Biozone (Koren et al. 1993). By the 

 Caradoc, subduction and volcanism had ceased as a result of the 

 docking of a small terrane or island arc, the Mynaral-South 

 Dzhungaria tectonofacies belt of Nikitin et al. ( 1 99 1 ). 



The Ordovician deposits in the central part of the Chu-lli Plate, the 

 Dzhalair-Najman Synclinorium, form a nearly continuous sequence 

 of siliciclastic and carbonate rocks from Arenig to Ashgill in age 

 (Fig. 2), which are relatively unmetamorphosed and chiefly dip 

 gently to the northeast. They are covered conformably by Silurian 

 deposits (Nikitin et al. 1980) or unconformably by the Devonian. 

 The Ordovician stratigraphy and major lithostratigraphic units were 

 described by Keller (1956) and Nikitin (1972). 



The Lower to Middle Caradoc deposits, which are the main source 

 of the brachiopods described here, are termed the Anderken Forma- 

 tion, which is a transgressive sequence of mainly siliciclastic deposits 

 that contain variably developed lens-like carbonate units in the upper 

 part representing mud mounds or algal build-ups (Nikitin et al. 1974; 

 1996). They are best developed in the following eight general 

 localities (Figs 1,3): 



Localites 1-2. Area between the Ashchisu and 

 Sarybulak rivers. 



In the south-eastern part of the Chu-lli Range the best sections of the 

 Anderken Formation are located in a block with faulted margins 

 between the rivers Ashchisu and Sarybulak (Fig. 1, localities 1-2; 



Figs 3, 4). Here the Anderken Formation overlies, with a slight 

 angular unconformity, graded sandstones, siltstones and mudstones 

 of the Beke Formation, which is Llandeilo to early Caradoc in age, 

 dated by numerous graptolites of the Hustedograptus teretiusculus 

 and Nemagraptus gracilis Biozones (Tsai 1976). The Anderken 

 comprises six lithostratigraphic units traceable up to 40 km along 

 strike, overlain unconformably by Devonian deposits. These units 

 are (in ascending order): 



Unit 1. Polymict, pebbly conglomerate, with sandy matrix and with 

 some beds of sandstone and gritstone. Thickness from 45 m to 120 

 m, with maximum values in the Anderkenyn-Akchoku section. 



Unit 2. Coarse- to medium-grained sandstone with subhorizontal 

 stratification alternating with abundant cross-bedded sets. Lenses of 

 polymict, pebbly conglomerate represent shallow channels formed 

 by tidal currents. Thickness varying from 52 m in the Kujandysai 

 section in the west to 180 m in the Anderkenyn-Akchoku section 

 (Figs 3, 5). The upper part contains the lingulide Ectenoglossa 

 sorbulakensis, the trilobite "Isotelus" romanovskyi Weber and gas- 

 tropods (Samples 8130-1, 7612). The middle part of the unit in the 

 Anderkenyn-Akchoku section contains a carbonate mud-mound up 

 to 16 m thick with a core built of light grey micritic limestone. On the 

 flanks there is bedded biomicrite with the brachiopods Skenidioides 

 sp., Christiania sp. and Kellerella misiusi, the trilobites 

 Mesotaphraspis spinosus Lisagor, Selenoharpes sp., Acrolichas sp. 

 Eokosovopeltis romanovskyi and Sphaerexochus aff. hisingeri War- 

 burg. Illaenus sp. was noted from about 1 .0-1 .5 m below the top of 

 the mud-mound in the eastern part of its exposure (Sample 8226). 

 Cystoid and crinoid columnals are abundant. 



