Fauna of the lower Beauharnois Formation (Beekmantown Group, Lower Ordovician), Grande-Île, Quebec

Abstract

Lenses of bioclastic packstone and grainstone within the lower dolomite sequence of the Ogdensburg Member, Beauharnois Formation (Beekmantown Group, Lower Ordovician), in the Valleyfield region, Quebec, bear a distinct diverse faunal assemblage. This Isoteloides–Goniotelina–Ribeiria assemblage is characterized by brachiopods Finkelnburgia armanda (Billings) and Finkelnburgia cullisoni Ulrich and Cooper, molluscs Ribeiria calcifera Billings, "Maclurites" affinis (Billings), and Ceratopea canadensis (Billings), and trilobites Isoteloides canalis (Whitfield), Isoteloides peri Fortey, Bolbocephalus convexus (Billings), Goniotelina subrectus (Bradley), Strigigenalis caudata (Billings), and Hystricurus conicus (Billings). Precise correlation of this lower Beauharnois megafauna is with the Strigigenalis caudata Zone of the Catoche Formation, Cassinian Stage, of western Newfoundland, the Oxford Formation of southeastern Ontario, the Fort Cassin Formation, Cassinian Stage, Canadian Series of New York–Vermont, and the Ross–Hintze trilobite Zone G2 of Utah, Upper Ibexian Series (Tulean Stage). Conodonts include Acodus comptus (Branson and Mehl), Acodus delicatus (Branson and Mehl), Colaptoconus emarginatus (Barnes and Tuke), Colaptoconus quadraplicatus (Branson and Mehl), Scolopodus subrex Ji and Barnes, Drepanoistodus angulensis (Harris), and Oepikodus communis (Ethington and Clark). This fauna corresponds to the Oepikodus communis–"Microzarkodina" marathonensis Zone, which has its lowest limit above the middle of Zone G2 in the Ibex area of Utah. In western Newfoundland, the fauna correlates with the Oepikodus communis – Protoprioniodus simplicissimus Assemblage Zone of the Catoche Formation, and the Prioniodus elegans and Oepikodus evae zones in the Cow Head Group.