THE FIRST GIANT PALEODICTYON: A NEW ICHNOSPECIES FROM THE MID-CAMBRIAN OF ALBERTA

A new and large ichnospecies of Paleodictyon Meneghini, 1850, was discovered on Helena Ridge at Castle Mountain, Banff National Park. This new ichnospecies is preserved in hyporelief on the sole of a thick dolomitic mudstone talus block near the mid-Cambrian Stephen-Eldon Formation boundary. The trace is formed of linear mesh structures in an overall radiating net. The dimensions of this trace are exceptionally large with mesh diameters of 25-40 mm and string diameters of 5-10 mm. The trace fossil is compared to Treptichnus, Squamodictyon, and Protopaleodictyon, but these ichnogenera are rejected because of the angularity of stringer branching and the overall radiating nature of the trace. The trace was formed in a mid-inner carbonate platform paleoenvironment. This fits with previous interpretations that Paleodictyon and other graphoglyptids originated in shallow marine environments during the Early Paleozoic before migrating to deeper facies after the Ordovician. What remains unusual is the lithology in which this trace was located. This may represent one of the first recorded occurrences of Paleodictyon in non-siliciclastic material.