A re-evaluation of the relationship between trace fossils and dysoxia

Geochemical and palaeontological methods are used to determine the oxygenation histories of Jurassic sequences at Ravenscar, North Yorkshire, and Lyme Regis, Dorset. The ichnology of these sequences is compared with interpreted oxygen levels, allowing current models of oxygen-related trace fossil occurrence to be tested. These case studies support pre-existing models of trace fossil occurrence in demonstrating that burrow diversity, diameters and depth of infaunal tiering increase with increasing oxygen levels. The case studies suggest that trace fossil ethologies may not always be a reliable indicator of palaeo-oxygenation: in some cases, substrate consistency may have a greater influence over ethology than oxygen levels. Chondrites is confirmed as a common constituent of dysoxic settings; however, other trace types may also be indicative of such settings.