A spectacular Cruziana trace fossil site from the Lower Ordovician of Brittany (Crozon Peninsula, NW France)

 

Authors: Elicki O, Paris F

Published in: Bulletin of Geosciences, volume 101, issue 1; pages: 19 - 33; Received 3 September 2025; Accepted in revised form 30 March 2026; Online 3 May 2026

Keywords: Ordovician, Cruziana furcifera, Cruziana barriosi, Cap de la Chevre Formation, Beg-Ar-Gwin, Brittany,

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Abstract

From the Cap de la Chevre Formation (Fm.) of the Crozon Peninsula (Beg-Ar-Gwin locality, Brittany, northwestern France) an exceptional trace-fossil site is described and discussed. A mass occurrence of remarkably large-sized trilobite trails of Cruziana furcifera d’Orbigny, 1842, is reported for the first time in France. An additional layer exposes Cruziana barriosi Baldwin, 1977, which represents the only trilobite trace of this second assemblage, and occurs in large numbers. Cruziana barriosi is first reported from Europe outside Iberia. The Cruziana furcifera and Cruziana barriosi trace-fossil assemblages from Beg-Ar-Gwin, which both represent the Cruziana rugosa group, show very low ichno-diversity (n = 2-3). The ichnocoenoses and the sedimentological characteristics of the host rock suggest an ecologically unstable, transitional marginal-marine depositional system exposed to elevated ecological stress. Palaeogeographically situated in high southern latitudes, the assemblages and deposits show close relations to similar Gondwanan occurrences, as on the Iberian Peninsula and in the Middle East. The Cruziana rugosa group, in particular, is confirmed as a valuable tool for stratigraphic correlation, as well as for refining palaeoecological-palaeogeographic reconstruction models for this part of Gondwana. The stratigraphic position of the Cap de la Chevre Fm. is evaluated. Based on the Beg-Ar-Gwin trace fossil assemblages, a depositional age of early to middle Floian (Early Ordovician) is most likely, at least for the fossil-bearing upper part of the Cap de la Chevre Fm.

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