. Bulletin of the British Museum (Natural History), Geology. 152 APOLLONOV, KOREN, NIKITIN, PALETZ & TZAI C A I T I E S K ARASAY RIVER ZHIDEU RIVER D U R B E N WELL 0 I s u S P R 1 N G ANZHAR RIVER ir^-i~i — i~zL r _ t A 4 A 1 » 1 k_J—_»_—_»—-_* —_»-=_*[ JT. 2 [=q^pc|3 [jffiE^ f—g^5 10 tn-a|5A6-^2^3 Fig. 5 Chart showing the lateral variation of different lithogenetic types within the Ordovician- Silurian boundary interval in South Kazakhstan. D, Durben Limestones; O, Ojsu Limestones; U, Ulkuntas Limestones. 1, black mudstones; 2, green sandstone; 3, detrital thin-bedded micro- crystalline
. Bulletin of the British Museum (Natural History), Geology. 152 APOLLONOV, KOREN, NIKITIN, PALETZ & TZAI C A I T I E S K ARASAY RIVER ZHIDEU RIVER D U R B E N WELL 0 I s u S P R 1 N G ANZHAR RIVER ir^-i~i — i~zL r _ t A 4 A 1 » 1 k_J—_»_—_»—-_* —_»-=_*[ JT. 2 [=q^pc|3 [jffiE^ f—g^5 10 tn-a|5A6-^2^3 Fig. 5 Chart showing the lateral variation of different lithogenetic types within the Ordovician- Silurian boundary interval in South Kazakhstan. D, Durben Limestones; O, Ojsu Limestones; U, Ulkuntas Limestones. 1, black mudstones; 2, green sandstone; 3, detrital thin-bedded micro- crystalline limestone; 6, sandstone; 7, conglomerate and gritstone; 8, tuffite; 9, unconformity; 10, non-deposition; 11, fossils: (a) trilobites, (b) graptolites, (c) brachiopods, (d) corals, (e) other fauna groups. the acuminatus graptolite assemblage may be due to the widespread early Llandovery transgres- sion. A great crisis in graptolite evolution within the extraordinarius and persculptus Zones took place at the end of the Ordovician regressive cycle. The basal lower Silurian deposits (the acuminatus Zone) outside the Chu-Ili Mountains are established in eastern Central Kazakhstan in the Otyzbes Mountains, near the Kombabasor Lake east of the town of Bajanaul and at the watershed of the Akzhar-Zhartas Rivers north- east of Karaganda (Bandaletov 1969; Apollonov et al. 1980; Fig. 1 herein). The uppermost Ashgill deposits (the Dalmanitina mucronata beds of the Durben horizon) are known from the Zhaksykon River basin at the Sarysu-Teniz watershed in the Chingiz Range (near the town of Akdombak) and south-western Chingiz area (Nikitin 1972; Nikitin et al. 1980). The systemic boundary in the regions within the neritic development is defined by the appearance of the diagnostic brachiopods Eospirifer cinghizicus and Holorhynchus cinghizicus and tabulate corals (Borisyak et al. 1969; Nikitin 1972). However, direct correlation between the graptolite and shelly sequences within
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