Transgressive erosion expressed as a Glossifungites-bearing woodground: An example from the Blackhawk Formation, Utah

Horizontal and inclined U-shaped trace fossils are commonly associated with the Cruziana and Glossifungites ichnofacies, but have rarely been described as a component of the Teredolites ichnofacies (xylic substrates). This study provides several examples of morphologies of Glossifungites saxicava from the Campanian Sunnyside Coal (Blackhawk Formation) that exhibit both xenoglyphs and bioglyphs. Glossifungites along this surface are locally present as compound ?Thalassinoides suevicus-Glossifungites, which may represent a combination of commensalism, an exploited structural weakness, refugium from predators, and/or a secondary behavior of the presumed crustacean tracemakers. The trace-fossil assemblage also contains Teredolites clavatus and Teredolites longissimus and Radichnus isp. locally. Stratigraphically, this trace assemblage is important because it marks a marine flooding surface/transgressive surface of erosion between the Sunnyside and Grassy members of the Blackhawk Formation.