EXPLORING THE MICROFOSSIL RECORD OF THE LATE DEVONIAN HANGENBERG EVENT IN THE CLEVELAND SHALE, OHIO

The Hangenberg event is one of the major pulses of extinction associated with the late Devonian mass extinction. This global crisis devastated entire ecosystems and represents a major turning point in the evolution of many faunal groups. Multiple causes have been proposed, and it is likely the Hangenberg event was the result of some combination of periodic or sustained anoxic conditions, volcanism leading to ocean acidification or hypercapnia, wildfires, perturbations of the carbon cycle, and/or eustatic sea level changes. The Hangenberg event is primarily associated with the Hangenberg Black Shale in Europe, though correlating black shale horizons have been found globally. The palynological record of the Hangenberg crisis has been used by researchers in Poland’s Holy Cross Mountains to decipher local causes of extinction during the event, but little palynological study of the Hangenberg event has been done elsewhere. Here, we analyze the microfossil record in a section of the Cleveland Shale in northeastern Ohio that captures the Hangenberg event. We present acritarch and miospore abundance and diversity throughout the end of the Hangenberg event, as well as geochemical analysis of Hg records in this section. Both Hg and fossil abundance are normalized to total organic carbon to account for preservation biases.

Microfossil abundance has several dips through the section, culminating in a complete lack of microfossils at the end of the event. Abundance then increases dramatically in the overlying Bedford Formation. In general, we find that acritarch and miospore abundances parallel one another, though miospores are slightly more abundant in the very upper Cleveland Shale and the lowest Bedford. Our initial study of the Cleveland Shale palynological record shows similar trends and taxa as in the Hangenberg Black Shale in Poland. In particular, the index miospore Retispora lepidophyta is uncommon but present in our upper Cleveland shale layers and in the Hangenberg Black Shale (Marynowski and Filipiak 2007). However, in samples taken from above the black shale in both Poland and Ohio, R. lepidophyta is by far the dominant miospore species. The correlation of palynological records in the Cleveland Shale with the Hangenberg Black Shale shows consistency of miospore response to the cause or causes of the Hangenberg event.