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The trilobite fauna of the Middle Ordovician Doularg Formation of the Girvan district, Scotland, and its palaeoenvironmental significance

Published online by Cambridge University Press:  03 November 2011

J. K. Ingham  and
R. P. Tripp
J. K. Ingham
Affiliation:
J Keith Ingham, Hunterian Museum, University of Glasgow, Glasgow G12 8QQ, Scotland.
R. P. Tripp
Affiliation:
Ronald P. Tripp, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M55 2C6, Canada.
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Abstract

The Doularg Formation is defined within the Albany Group (Tappins Complex); the formation consists of the unfossiliferous Fence Member at the base, succeeded by the Gorse Member (formerly the “Albany mudstones with nodular limestones”), the Separation Sandstone and the Jubilation Member, a bedded, calcareous, silty mudstone. The last named has yielded the rich assemblage of trilobites described, representing thirty genera and including one new genus and seven new species—Bronteopsis matutina, Bumastoides? rivulus, Agerina laurentica, Tretaspis eximia, Ampyxina medici, Stiktocybele (gen. nov.) bathytera, Platycalymene metoeca: Nileus is the most common trilobite. The trilobite fauna indicates that the Doularg Formation should be correlated with some part of the Benan Conglomerate, the uppermost formation of the Barr Group to the north of the Stinchar Valley, and is probably of Llandeilo age. The trilobite association is most closely allied to that of the slightly older basal Superstes Mudstone, reflecting the strong ecological control affecting deeper water faunas. The affinity of the Jubilation Member trilobites with those of the middle Table Head Formation (Llanvirn) of western Newfoundland, is evidenced by the presence in both of Nileus, Cybelurus, Peraspis, and Bronteopsis. These are the four most common genera in the Jubilation Member, comprising over half the total trilobite specimens, and provide striking evidence of the longevity of deeper water genera.

Keywords

correlationcranidiumfixigenahypostomelibrigenapalaeoecologypalaeo-geography pygidiumstratigraphytaxonomythoracic segment
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 82 , Issue 1 , 1991 , pp. 27 - 54
Copyright
Copyright © Royal Society of Edinburgh 1991

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