Stratigraphic significance of Cruziana: New data concerning the Cambrian-Ordovician ichnostratigraphic paradigm

The classic Cambrian-Ordovician ichnostratigraphic paradigm originally developed in Europe is based on the assumption that Cruziana—ichnofossils presumably produced by trilobites—can be used in much the same way as trilobite body fossils have been used in chronostratigraphy. That these ichnofossils can be found in many otherwise unfossiliferous, shallow-marine siliciclastic deposits has made them extremely valuable as correlation tools. The paradigm has been used to date lower Paleozoic units in eastern Canada and Europe. It has also been used as supporting evidence to show close affinities between (1) eastern North America, Wales, and Spain and (2) Spain, northern Africa, and southern Asia. Ichnospecies indicative of the Lower Ordovician (Tremadocian and Arenigian), according to the paradigm, have been recovered from the Lower Cambrian (Atdabanian) Gog Group, near Lake Louise, Alberta, Canada. This discovery indicates that these Ichnospecies cannot be used as global Lower Ordovician index fossils.