Late Ordovician brachiopods from the Chingiz Terrane, Kazakhstan, and their palaeogeography

Abstract

The Late Ordovician Akdombak Formation of the Chingiz-Tarbagatai Terrane, Kazakhstan, has yielded brachiopods from four successive horizons, three Katian and the upper one of Hirnantian age. Comparable faunas of an earlier Katian age are also described from the upper part of the Taldyboi Formation, also within the Chingiz-Tarbagatai Terrane, but there are no Hirnantian rocks there. The new subfamily Alpeisinae is erected within the Wangyuiidae (Plectorthoidea), and the following new genera are introduced: Holmerglossa (Linfguloidea), Wrightiops (Craniopsoidea), Buminomena (Strophomenoidea), Alpeis, Ashinaorthis and Enbektenorthis (all Orthoidea) and Rongatrypa (Atrypoidea), as well as 10 new species: Bokotorthis minuta, Craniops pristinus, Chonetoidea enbektenensis, Dalmanella kotyrzhalica, Diambonioidea koknaiensis, Enbektenorthis molesta, Kassinella kasbalensis, Kozlowskites botobaicus, Leangella (Leangella) bakanasensis Phragmorthis eximia and Strophomena (Tetraphalerella) namasensis. Eleven ecological associations are recognized, which inhabited a spectrum of depths ranging from Benthic Assemblage Zone (BA) 1 to BA 5 depth ranges. Comparison of the faunas with the neighbouring Kazakh terranes is chiefly with the Chu-Ili, North Tien Shan and Boshchekul terranes since, although others have Late Ordovician faunas, their brachiopods are unknown or unrevised. There is much in common between the brachiopods of the Kazakh terranes, but individual faunas contain different species, many of which are endemic to one terrane. The Chingiz-Tarbagatai brachiopods show some similarities to contemporaneous faunas from the equatorial sectors of Gondwana, including Australia, and some with North China and South China, but have very little in common with those from Baltica and Laurentia. Thus the Chingiz-Tarbagatai Terrane was probably part of an archipelago which lay in a subequatorial position to the north-west of the Australasian sector of Gondwana and the adjacent South China continent in the Late Ordovician.

http:zoobank.org/urn:lsid:zoobank.org:pub: C502E307-C67D-4216-869D-17D199812088

Keywords:

• Ordovician
• Katian
• Hirnantian
• Brachiopoda
• Kazakhstan
• biogeography

Acknowledgements

The material described here was chiefly collected by O. P. Kovalevskii, M. A. Borrisiak and I. F. Nikitin. This paper has only been possible through access to the field notes and maps made by these late and warmly remembered former colleagues. Further specimens were collected by I. M. Kolobova and L. E. P. Thanks go to the Natural History Museum, London for facilities; in particular, some of the photographs were taken there by Phil Crabb. L. E. P. acknowledges support from the National Museum of Wales. The paper has benefitted from the constructive comments of Lars Holmer (Uppsala University), Ian Percival (Geological Survey of New South Wales) and Enrique Villas (Zaragoza University).