DIGGING INTO THE HANGENBERG EXTINCTION: TRACE FOSSILS OF THE LATE DEVONIAN CLEVELAND SHALE

The Hangenberg extinction event has been recognized in the uppermost Cleveland Shale and is well exposed in northeastern Ohio. At the Tiedeman Rd. locality outside of Cleveland, OH, nearly 15 m of the Cleveland black shale and several meters of the overlying Bedford Formation are exposed, and detailed geochemistry has allowed for the Hangenberg extinction event to be recognized in the upper approximately 3 meters of the Cleveland shale at this locality. Here, Cleveland Shale is nearly devoid of fossils, with a pronounced exception between 2.5 and 3 meters below the top of the formation. At this interval there are numerous, relatively large, pyritized, vertically oriented burrows that are obvious along bedding planes. A total of 148 burrows were measure with the average burrow width of 4.4 mm. Further analysis using CT scanning revealed two distinct populations of pyritized burrows; 1) larger, vertical burrows that preserve a range of behaviors and morphologies, and 2) abundant, smaller (< 0.5 mm in burrow width), horizontal to sub-horizontal burrows likely produced by nematodes. These burrows are significant as they are recognized in sediments with a redox signal of anoxic to euxinic and reveal the fluctuating nature of bottom water conditions associated with this extinction interval.