Chitinozoaires et acritarches ordoviciens de la plate-forme du Saint-Laurent (Québec et sud-est de l’Ontario)

A first inventory of Ordovician Chitinozoa and acritarchs is established for the St. Lawrence Lowland in the Ottawa, Montreal, and Quebec City areas. Thirty-six Chitinozoa taxa and forty-five acritarch taxa from one hundred and thirty-one samples are recognized. Six species of Chitinozoa are new: Acanthochitina? cancellata, Eisenackitina obsoleta, E. luter, Hercochitina? duplicitas, H. lauriae and Sphaerochitina gracqui. Eight species of acritarchs are new: Gorgonisphaeridium? parvum, Lophosphaeridium patulum, Multiplicisphaeridium fusum, Pseudoundulatisphaera alveolus, Veryhachium obiditum, V. v-cicumorumatum, V. maximal and V. permutata.

In presenting the palynological results, the terminology of Chazy, Black River, Trenton and Utica groups sensu Clark (1972a) is employed. In the Chazy Group, the Chitinozoa and acritarchs of the Rockcliffe Formation around Ottawa are comparable with those of the Laval Formation in the Montreal region. In these two areas the Black River Group rarely contains identifiable microfossils. In the Quebec City region, the palynological assemblages change progressively in composition from the upper part of the Trenton Group to the lower part of the Utica Group. In Portneuf County, six Chitinozoa microfaunas (C1 to C6) and three acritarch microfaunas (A1 to A3) are recognized from the top of the Deschambault Formation to the Deschambault Member of the Lotbiniere Formation. The assemblages C3 to C5 and A1 to A3 are present in Utica shales from C2 to C4 and C6 to C4.5 in the Montreal County. The microfaunas and microfloras of the Trenton Group in the Quebec City region have not been adequately recognized in the vicinity of Ottawa and Montreal; the microfaunal assemblages of the Chazy Group differ but the microfloras are inadequately known. The Utica Group around Montreal is totally comparable with its assemblage of acritarchs. In the Ottawa region, the Chitinozoa of the Eastview Formation is comparable with that of the Tonti Formation and the Microfauna of the Quebec City region; those from the Billings Formation are not comparable with any sites here. In the Montreal region, five microfaunas from the Chazy and five microfaunas from the Trenton are recognized. The last microfauna from the Lotbiniere Formation in the Quebec City area. Previously described taxa include species reported from Oklahoma, Indiana, Shropshire, and the Baltic region.