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Maritime Sediments and Atlantic Geology Maritime Sediments and Atlantic Geology Vol. 20 APRIL, 1984 No. 1 Systematic ichnology of the Middle Ordovician Trenton Group. St. Lawrence Lowland, eastern Canada D. TjJULLon and R.H. PlcJayiAM De.pcvitmejtt o-fL Qe.o£ogy, llrviveju>-ULy o/ New Bnuru>uxick, T/iejd£JU-d.on, N.B. £38 5A3 Carbonate sediments of the upper Middle Ordovician Trenton Group between Montreal and Quebec City in the St. Lawrence Lowland, eastern Canada, contain a diverse and abundant trace fossil assemblage consisting of Arenicolites sp., ?Calycraterion sp., Chondrites spp., Circulichnis montanus, Clematis- chnia sp., ?Conostichnus sp., Cruziana problematica, Cruziana sp., cf. Diplichnites sp., Furculosus car- pathicus, Helminthopsis hieroglyphica, Helminthopsis sp., Oichnus paraboloides, Palaeophycus tubularis, Palaeophycus sp., ?Plagiogmus sp., Planolites beverleyensis, P. montanus, Planolites sp., ?Rhizocorallium cf. R. irregulare, ?Rosselia sp., Scalarituba misouriensis, Scolicia sp., Skolithos linearis, Skolithos sp., Teichichnus rectus, Teichichnus sp., Trichichnus sp., Trypanites weisei, Vermiforichnus clarkei and Zoo- phycos sp. as well as informally diagnosed loop, oblique and pronged burrows and bryozoan borings. Of these forms, only Chondrites spp., Palaeophycus tubularis, Palaeophycus sp., Planolites spp., Teichichnus spp. and Trypanites weisei are abundant; the remainder are rare to only moderately common. Neverthe- less, in this paper we describe all the trace fossils in detail and in doing so attempt to resolve several current and controversial problems of nomenclature regarding certain ichnogenera. Sediments of the Trenton Group were deposited initially in lagoons followed in turn by offshore "bar", shallow and, finally, deeper offshore shelf environments. The trace fossils do not exhibit significant variation with respect to these broad depositional regimes and, instead, each environment is character- ized by assemblages typical of the Cruziana ichnofacies as recognized in clastic sequences. The major factor primarily limiting the spatial and temporal trace fossil distribution was substrate and its primary characteristics, in turn a reflectance of food availability and environmental energy levels. Dans les Basses Terres du St-Laurent de l'Est canadien, les calcaires du Groupe de Trenton (Ordovicien moyen superieur) renferment, entre Montreal et Quebec, un assemblage d'ichnofossiles abondants et varies comprenant: Arenicolites sp., ?Calycraterion sp., Chondrites spp., Circulichnis montanus, Clema- tischnia sp., ?Conostichnus sp., Cruziana problematica, Cruziana sp., cf. Diplichnites sp., Furculosus carpathicus, Helminthopsis hieroglyphica, Helminthopsis sp., Oichnus paraboloides, Palaeophycus tubu- laris, Palaeophycus sp., ?Plagiogmus sp., Planolites beverleyensis, P. montanus, Planolites sp., ?Rhizo- corallium cf. R. irregulare, ?Rossetia sp., Scalarituba missouriensis, Scolicia sp., Skolithos linearis, Sko- lithos sp., Teichichnus rectus, Teichichnus sp., Trichichnus sp., Trypanites weisei, Vermiforichnus clarkei et Zoophycos sp. On y trouve Sgalement des galeries en boucle et fourchues, des terriers obliques ainsi que des perforations de bryozoaires, tous identifies de faipon informelle. De toutes ces formes, seules les suivantes sont presentes en abondance: Chondrites spp., Palaeophycus tubularis, Palaeophycus sp., Planolites spp., Teichichnus spp., et Trypanites weisei; les autres sont rares ou peu communes. N6an- moins, nous decrivons en detail toutes les traces fossiles et tentons par le fait mSme de rSsoudre plusieurs problemes de nomenclature chez certains ichnogenres qui font a l'heure actuelle l'objet de debats. Le dep5t des sediments du Groupe de Trenton s'est initio dans un milieu de lagune puis de barre, de plate-forme de haut-fond et, finalement, de plate-forme d'eau profonde. Les traces fossiles ne varient pas de fagon significative d'un environnement de deposition a l'autre. On remarque plut0t que chaque environnement se caract6rise par des assemblages typiques de l'ichnofacies a Cruziana tel qu'on l'observe dans les sequences detritiques. Le substrat et ses caracteristiques de base, qui refletent la disponibilite de la nourriture et les conditions energetiques du milieu, constituent l'eiement majeur qui a, avant tout, limite la distribution spatiale et temporelle des traces fossiles. [Traduit par le journal] INTRODUCTION Detailed and systematic trace fossil abundant and well-preserved body fossils studies of carbonate rocks, particularly and are generally frustrated by the typi- of Lower Paleozoic age, are far out- cally poor preservation, usually as a re- numbered by comparable studies in their sult of carbonate cementation and re- clastic counterparts. In part this is be- crystallization, of their contained trace cause paleontologists are generally at- fossils. Yet many Lower Paleozoic car- tracted to carbonates by their normally bonate sequences abound in trace fos- sils of various kinds and with careful MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 20, 1-41 (1984) and detailed analysis their systematics 071l-1150/84/0l0001-41$7.50/0 2 FILLION and PICKERILL can be resolved at the ichnogeneric and reviews can be found in the referenced even the ichnospecific level. papers. In this paper we describe the systema- tics of a suite of trace fossils contain- STRATIGRAPHIC, SEDIMENTOLOGIC ed in carbonates of the upper Middle AND ENVIRONMENTAL SETTING Ordovician Trenton Group exposed bet- In the St. Lawrence Lowland between ween Montreal and Quebec City in the Montreal in the southwest and Quebec St. Lawrence Lowland, eastern Canada City in the northeast, a distance of '(Fig. 1). This study is one of the first approximately 250 km (Fig. 1), the up- of its kind in Lower Paleozoic carbon- per Middle Ordovician Trenton Group ate sequences and highlights several con- has been subdivided into many litho- troversial and taxonomical problems re- stratigraphic units several of which, be- garding certain ichnogenera. A com- cause of their overall similarity, are panion paper (Fillion et al. 1984) has candidates for synonymy (Harland and evaluated their spatial and temporal Pickerill 1982). Because such strati- distributional patterns and primary con- graphic revision has not been attempted trolling parameters within the sequence to date, the previously established units but, until now, the systematics remain are retained herein. Figure 2 summarizes unpublished despite the many recordings the Trenton Group stratigraphy and by previous authors of 'burrows', 'tracks' places it in context with underlying and and 'trails' (eg. Flower 1945; Clark et overlying formations. More detailed al. 1972; Clark and Globensky 1975, lithostratigraphic and biostratigraphic 1976a). summaries are available in Clark (1972), As the content of this paper is de- Clark and Globensky (1975, 1976a,b,c) cidedly taxonomic only a brief summary Riva (1968, 1969, 1972). Figure 3 sum- of the stratigraphic, sedimentologic and marizes the essential characteristics environmental setting of the Trenton and interpreted environment of deposi- Group is presented below. More detailed ng. 1 - Simplified geological map of the St. Lawrence Lowland between Montreal and Quebec City. Numbered localities are: 1. Saint Constant, 2. Tie Bizard, 3. Montreal, 4. Cap Saint Martin, 5. Saint Vincent de Paul, 6. Terrebonne, 7. L'Epiphanie, 8. Saint Roch, 9. Saint Esprit, 10. Saint Jacques, 11. Highway 158/Riviere Ouareau, 12. Highway 158/Riviere Rouge, 13. Pont Corriveau, 14. Barrage savoie, 15. Pont Bournival, 16. Saint Louis de France, 17. Radnor des Forges, 18. Grondines, 19. Saint Casi- mir, 20. Pont Saint Alban, 21. Pont Rouge, 22. Neuvitle. Maritime Sediments and Atlantic Geology 6 SW NE Montreal Joliette Trois-Rivieres St Marc Pont-Rouge Quebec City Utica Group Tetreauviile ;Tetreauvilie ;•-"••; Gtondinti Mimbcf •. .GfondBiwi Member.". Gtondntf Mitnbif.. ••Kieuvilte"-.".."" •Neuville-."..".." '.Neuville .* IH/O* Trenton Mnnrranl -rSatnl Catimir MamtMr-: T^AINT CAIINVR MMIBV Group -£oirit tosW Member - "Saint Commt Member" .... x _ Deschambault_L _ Deschambaytt •Deschamlpau,J .! J l j ._L _ )eschambaylt _p - Deschambault -L -Deschambaylt i 1 i I , 1 . r~ 1 1 m i.J , t , f -J\^ -Mile End^M -.Ouqreay. i'. | \ — ilMTtapp.'.y.'.j^ 1 Black SLeray -_— jj^yT ' t^'V^III'Aigle lili River S Low vi 1 te- - - £ Lowville Group •rPamelia 'I*! ! ! ! -Iftmelia-I-I-I-Z"! "-'^'•K'^'V: Chazy J Laval* 1 7 - T • r Laval \ Group ftPpecambrianiiV-. 1 .(Vecambnan ^ i . Pwoambrian r> mm '•.---•.Mlw'.'n Fig. 2 - Stratigraphic profile of Middle Ordovician lithostratigraphic units between Montreal and Quebec City showing the relationship of the upper Middle Ordovician Trenton Group to underlying and overlying units. Modified after Harland and Pickerill (1982). tion of each formation, generalized de- environment of migrating subtidal shoals, tails of which are given below. bars and large ripples (Harland and The basal Trenton Group formations Pickerill 1982). Additionally, the forma- comprise, from southwest to northeast, tion contains more continuous parallel- the Mile End, Ouareau, Fontaine, Saint laminated or low-angle cross-stratified Alban and Pont Rouge Formations. beds which represent ephemeral beaches These are generally thin (2-6m) and con- developed when shoals and bars were sist of irregular beds of micritic and intermittently built up to sea level. argillaceous calcisiltites which alternate Scouring appears to have been common with thin shales. The shales and most and subtidal channels and runnels
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