Reexamination of selected invertebrate ichnogenera of the Upper Ordovician Georgian Bay Formation of Southern Ontario

Abstract

The Upper Ordovician Georgian Bay Formation of Southern Ontario consists of a sequence of alternating grey shale and grey carbonate layers. It is overlain by the red shales of the Queenston Formation and underlain by the grey shales of the Blue Mountain Formation. The environment of deposition of the Georgian Bay Formation is believed to be a shallow shelf setting periodically subjected to high energy storm conditions. A reexamination of several ichnogenera represented by specimens m the collections of the Royal Ontario Museum's Department of Invertebrate Palaeontology has led to updated interpretations of the material. In addition, other ichnogenera represented by specimens collected by the author have been studied. Ichnospecies found to be present were Chondrites isp., cf. Diplocraterion bic/avatum (Miller, 1875), D. helmerseni (Öpik, 1929), Lingulichnus verticalis Hakes, 1976, Lockeia siliquaria James, 1879, Palaeophycus tubularis Hall, 1847, Phycodes flabellus (Miller and Dyer, 1878), Rusophycus pudicus Hall, 1852, Skolithos magnus Howell, 1944, S. verticalis (Hall, 1843), Trichophycus lanosus Miller and Dyer, 1878, and T. venosus Miller, 1879. The traces found in the Georgian Bay Formation are assignable to the Cruziana ichnofacies.