A CRITICAL REVIEW OF SEA-LEVEL CHANGE DURING THE FRASNIAN/FAMENNIAN MASS EXTINCTION

The terminal Frasnian mass extinction is widely regarded to have occurred during a rapid, high amplitude sea-level fall (e.g. Sandberg et al. 2002)that terminated a prolonged phase of Mid-Late Devonian transgression. Key evidence for this sea-level history has been derived from Euramerican sections and conodont facies changes. In particular, the proliferation of icriodids is held to indicate shallowing. However, the supposed regression occurs during a widespread phase of anoxic deposition in many sections (e.g. the Upper Kellwasser Horizon) and clearly had no influence on global redox levels. Key evidence for the regression has come from the western United States but sedimentary facies analysis in this region reveals little marked change across the Frasnian-Famennian (F-F) transition. We would suggest that sea-level variations were minor (and therefore unimportant) during the crisis interval. Other work in China and Australia similarly suggests that there was no major sea-level fall at the F-F boundary. Instead this interval was a global highstand characterised by extensive anoxic deposition.

Sandberg, C.A., Morrow, J.R., & Ziegler, W. 2002. Late Devonian sea-level changes, catastrophic events, and mass extinctions. Geol. Soc. Amer. Spec. Paper 356, 473-487.