New Zealand Journal of Geology and Geophysics abstracts

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Late Ordovician (Hirnantian) shelly fossils from New Zealand and their significance

L. R. M. Cocks

Department of Palaeontology
The Natural History Museum
Cromwell Road, London SW7 5BD, UK

Roger A. Cooper

Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand

Abstract  A poorly preserved fauna of brachiopods, trilobites, corals, molluscs, bryozoans, echinoderms, and ostracods is described from Wangapeka Valley, northwest South Island. It can be dated to the latest Ordovician Hirnantian Stage, equivalent to Bolindian Bo4-Bo5, by immediately underlying graptolite faunas and also by some of its contained shelly fossils. It is one of only two shelly faunas of Middle or Late Ordovician age identified in New Zealand. The trilobite Mucronaspis and the brachiopods Eostropheodonta, Plectothyrella, Cliftonia, and Leptaena all occurring together identify the fauna as part of the very widespread Hirnantia Fauna, although Hirnantia itself and other key elements are absent. The development of this fauna in relatively outer shelf settings such as that at Wangapeka Valley was made possible because the contemporary latest Ordovician global glaciation oxygenated the sea water to far deeper levels than was normal, and also because of the associated glacio-eustatic fall in sea level.

Keywords  Ordovician; brachiopods; trilobites; Hirnantia Fauna

G03003; Online publication date 25 February 2004
Received 3 February 2002; accepted 24 September 2003
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 71-80
0028-8306/04/4701-0071 © The Royal Society of New Zealand 2004

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