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Late Ordovician trilobites from the Mayatas Formation, Atansor area, north-central Kazakhstan

Published online by Cambridge University Press:  07 September 2017

L. M. E. McCobb  and
L. E. Popov
L. M. E. McCobb
Affiliation:
Department of Natural Sciences, National Museum Wales, Cathays Park, Cardiff CF10 9NP, UK. E-mail: [email protected]; [email protected]
L. E. Popov
Affiliation:
Department of Natural Sciences, National Museum Wales, Cathays Park, Cardiff CF10 9NP, UK. E-mail: [email protected]; [email protected]
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Abstract

Two trilobite faunas of Late Ordovician (Katian) age are described from the Mayatas Formation in the Stepnyak region of north-central Kazakhstan. The older, oligotaxic fauna derives from flanks of a carbonate build-up, and is dominated by numerous Sphaerexochus specimens. Amphilichas is also relatively common, with Pliomerina and indeterminate asaphids present as rare components. The overlying unit of siliceous argillites contains a different assemblage, representing the raphiophorid biofacies and comprising seven genera. The poorly preserved fauna is dominated by blind trilobites (a new genus of trinucleid, the three-segmented raphiophorid Pseudampyxina, Malongullia?, Lonchodomas and Arthrorhachis) and at least two species of large-eyed Telephina, suggesting that they occupied the disphotic zone in deep water offshore. A single cranidium of the odontopleurid Primaspis is also present. The trinucleid, Iputaspis stepnyakensis gen. et sp. nov., has an unusual pit arrangement, with E1 and E2 aligned in sulci and all I arcs irregularly arranged. The Atansor area is located within the Stepnyak tectonostratigraphical unit, which probably represented an Ordovician active margin of the Kalmykkol–Kokchetav Microplate. Some of the genera represented in the faunas have affinities with Australia and South China and, also, there is a possible link to European peri-Gondwana.

Keywords

biogeographyillaenid–cheirurid biofaciesKatianraphiophorid biofaciestaxonomy
Type
Articles
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 107 , Issue 1 , March 2016 , pp. 33 - 52
Copyright
Copyright © The Royal Society of Edinburgh 2017 

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