Middle and Upper Ordovician graptolites from the St. Lawrence Lowlands, Quebec, Canada

Abstract

Eleven species of Middle and Upper Ordovician graptolites are described and illustrated, a lectotype is selected for Orthograptus reudemanni (Gurley) and the occurrence of eighteen other species is recorded. The specimens were collected from sections along the Bécancour, Nicolet, Nicolet Sud-Ouest, and St. François Rivers of the St. Lawrence Lowlands, Quebec. The graptolite zonal scheme proposed by Riva for eastern North America is reviewed and adopted in the present study.

Stratigraphy, structure, and graptolites of an Ordovician and Silurian sequence in the Terra Cotta Mountains, Alaska Range, Alaska

“…Zones of Nemagraptus gracilis and C. bicornis (Woods Hollow Shale), Marathon region, Texas (Berry, 1960). Zone of N. gracilis in the St. Lawrence lowlands, Quebec (Walters, 1977), in the Shelve district, British Isles (Strachan, 1986), and in Taimyr in the former USSR (Obut and Sobolevskaya, 1964). Also found in China (Wang and Jin, 1977).…”

The position of graptolites within Lower Palaeozoic planktic ecosystems

“…Synrhabdosomes occur in several morphotypes, but usually in small colonies such as simple dichograptids (Beckly & Maletz, 1991;Zalasiewicz 1984), various diplograptids and Saetograptus , as well as in Rhabdinopora flabelliforme. Complex central structures of floats have been recorded (Ruedemann 1947;Kozlowski 1949;Bulman 1970), but restudy of the original material has shown them to consist of nothing but abiogenic preservational artifacts (Rickards 1975;Walters 1977). Synrhabdosomes have been associated with both sexual (Zalasiewicz 1984) and asexual (Bulman 1970;Kozlowski 1949) reproduction of graptolites.…”

Taconian mélanges in the parautochthonous zone of the Quebec Appalachians revisited: implications for foreland basin and thrust belt evolution

“…This indicates that the black shales in the tectonosome units at Pointe Aubin are most likely blocks of Utica Shale from the underlying auto-chthonous platform. Walters (1979) identified graptolites within fault blocks ranging from the C. americanus to O. ruedemanni zones, meaning that they are, in fact, chronostratigraphic equivalents to the Upper Ordovician sequences of the foreland basin. New palynological data presented here also suggest that the tectonosome slices are imbricated foreland basin rocks that contain chitinozoan species reported in units of the Black River, Trenton, Utica, and Sainte-Rosalie groups of the Laurentian platform.…”

“…Siliciclastic rocks of the upper turbidite unit in the parautochthonous zone of the Québec City area were originally assigned to the Les Fonds Formation and the Breault and Chambly members of the Nicolet Formation, by Clark and Globensky (1973). Following detailed stratigraphic and sedimentologic work by Walters (1979), Walters et al (1982), and Beaulieu et al (1980), the parautochthonous flyschoid sediments were correlated to the Sainte-Perpétue and Sainte-Monique members of the redefined Rivière Nicolet Formation in the autochthonous zone ( Fig. 4).…”

“…Based on graptolite data (Riva 1972;Walters et al 1982), the age of the stratigraphic units within the Les Fonds Formation is Late Ordovician. Most of the graptolites collected from the mudstones (assemblage C) of the Les Fonds Formation along the section belong to the Caradocian C. spiniferus Zone (Riva 1972;Walters 1979;Walter et al 1982). However, graptolites collected in the chaotic units and thrust slices belong to the N. gracilis, C. americanus, O. ruedemanni, and C. spiniferus zones (St-Julien 1968;Riva 1972;Walters 1979;Walters et al 1982).…”