Publications

Abstract. A preliminary study has been made of chitinozoan assemblages derived from the exposed Ordovician-Silurian succession of Anticosti Island, specifically from member 5 of the Ellis Bay Formation to the Chicotte Formation included. As shown by previous studies, there is an important variation in microfaunal composition at the level of member 6 of the Ellis Bay Formation. The assemblage from member 5 contains Conochitina gamachiana, C. miraara and C. taugoatdeaui. These species disappear entirely at the base of the bioherm of member 6 of the Ellis Bay Formation. Above the bioherm the Chitinozoan microfauna consists only of Cyathochitina kukaerikema and Ancyrochitina anoploosa. The Bescie Formation is not rich in organic microfossils. The few fossiliferous horizons have yielded Conochitina sp. 1, a species which could turn out to be an interesting taxon to characterize this unit. Chitinozoans are more common in the succeeding Gun River Formation, the base of which coincides with the first occurrence of Conochitina sp. 2 omnipresent throughout the formation. This species is present with one or more of the following: Conochitina sp. 1, Cyathochitina kukaerikema, Conochitina cf. C. iklaensis, Ancyrochitina sp. and Clathrochitina sp. 1, depending on the collections. The Jupiter Formation has highly diversified assemblages with a large number of chitinozoans. Conochitina proboscifera seems to be the characteristic element of the microfauna which shows distinct variations in composition in each member. It is noteworthy that ? Clathrochitina ampranlaeformis and Conochitina cf. C. proboscifera are the characteristic elements of member 4. No chitinozoans have been isolated from collections made from the Chicotte Formation. Very few data have been published on chitinozoans of the Upper Ordovician-Lower Silurian on a worldwide basis, and this renders all comparisons with the Anticosti succession difficult. The only trustworthy forms that can be used for comparison are Conochitina taugoatdeaui from member 5 of the Ellis Bay Formation and the association of Conochitina proboscifera and Cyathochitina kukaerikema or C. ampanulaeformis in the Jupiter Formation. Conochitina taugoatdeaui is a diagnostic form of the Uppermost Ordovician (F) of the Baltic Provinces; the association of Conochitina proboscifera with Cyathochitina kukaerikema or C. ampanulaeformis in the Jupiter Formation on the other hand may indicate an Upper Llandovery age for this unit.