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

For over a century, the ichnogenus <i>Oldhamia</i> 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 <i>Oldhamia</i> and test its potential for more detailed biozonation. The upper part of Narchilla Formation (Arrowhead Lake Member) yields <i>O. antiqua, O. curvata, O. flabellata</i>, and <i>O. radiata</i>. The overlying Gull Lake Formation yields a less diverse assemblage of <i>O. antiqua, O. curvata</i>, and <i>O. flabellata</i>. The upward disappearance of <i>O. radiata</i> is consistent with models that infer increasing complexity of <i>Oldhamia</i> ichnospecies through time but may also be a function of limited sampling. Regional stratigraphic correlations suggest <i>Oldhamia</i> appeared in Arrowhead Lake Member during Cambrian Stage 3. Archaeocyathans and trilobites from Gull Lake Formation confirm that <i>Oldhamia</i> was present during Cambrian Stages 3 to 4. A younger age limit on <i>Oldhamia</i> 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). <i>Oldhamia</i> appears to be a reliable index fossil for Cambrian Series 2 and Series 3 in Selwyn Basin.