New Occurrences of Oldhamia in Eastern Yukon, Canada: Stratigraphic Context and Implications for Cambrian Deep-Marine Biostratigraphy

摘要

For over a century, the ichnogenus Oldhamia has been used as an index fossil for Cambrian deep-marine siliciclastic successions. New specimens from the Cambrian of Selwyn Basin, eastern Yukon, Canada, provide an opportunity to constrain the chronostratigraphic range of Oldhamia and test its potential for more detailed biozonation. The upper part of Narchilla Formation (Arrowhead Lake Member) yields O. antiqua, O. curvata, O. flabellata, and O. radiata. The overlying Gull Lake Formation yields a less diverse assemblage of O. antiqua, O. curvata, and O. flabellata. The upward disappearance of O. radiata is consistent with models that infer increasing complexity of Oldhamia ichnospecies through time but may also be a function of limited sampling. Regional stratigraphic correlations suggest Oldhamia appeared in Arrowhead Lake Member during Cambrian Stage 3. Archaeocyathans and trilobites from Gull Lake Formation confirm that Oldhamia was present during Cambrian Stages 3 to 4. A younger age limit on Oldhamia in Selwyn Basin is provided by syn-volcanic detrital zircons recovered from the base of the overlying Old Cabin Formation, which yield an age of 499.89 +/- 0.14 Ma (earliest Guzhangian). Oldhamia appears to be a reliable index fossil for Cambrian Series 2 and Series 3 in Selwyn Basin.