Freshwater to low salinity expression of Cretaceous Glossifungites demarcated autogenic stratigraphic surfaces, central Utah

One of the most important contributions that S. George Pemberton made to the field of ichnology was the identification that burrowed firmgrounds associated with the Glossifungites Ichnofacies, commonly demarcate important sequence stratigraphic allogenic surfaces, and more recently described autogenic surfaces. This study considers an outcrop example from the Turonian Ferron Sandstone of central Utah, wherein high and low abundance monospecific suites of Glossifungites isp. are preserved landward of marginal-marine settings, recording colonization in channels under low salinity conditions. High abundances of Glossifungites isp. are associated with sloped areas of the erosional surfaces due to environmental preference, and with clay-rich underlying lithologies owing to either substrate selection or toponomy. These suites of the Glossifungites Ichnofacies demarcate surfaces at the bases of small, stacked channels encased in coastal plain strata. Stacking suggests repeated colonization related to an autogenic process. The enclosing strata and estimated position of the shoreline indicate a more landward affinity than previously reported for the ichnogenus Glossifungites, which is normally related to erosional nearshore processes or, less commonly, to offshore submarine channel development. Glossifungites-like burrows are constructed in modern freshwater settings by subaqueous insects, such as mayfly nymphs, but the trace fossil widths reported from the Ferron Sandstone are up to one and a half times larger than these modern examples. This suggests that the described trace fossils were made by marine-recruited, brackish-water crustaceans that created similar-sized burrows, or if constructed by subaqueous insects, the tracemakers were divergent in size or body plan from known modern tracemakers.