Frasnian

The Frasnian is a stage of the Middle Devonian epoch in the geologic timescale. It is named after the Frasne region in France, where rocks used to define the stage were studied. The Frasnian lies between the Givetian and Famennian stages and is globally correlated with a time interval that lasted roughly from about 382 to 372 million years ago, spanning about 10 million years. The lower boundary is defined by markers in the fossil record, while the upper boundary marks the onset of the Famennian.

During the Frasnian, much of the Earth's landmasses were assembled in the southern hemisphere supercontinent Gondwana, with extensive shallow epicontinental seas that facilitated reef growth and diverse marine faunas. Global climates were generally warm, and sea levels were relatively high, supporting widespread carbonate platforms and carbonate- dominated sedimentation in many regions. Stratigraphic sections from various regions reveal carbonate and siliciclastic successions that record fluctuations in sea level and burial events.

The Frasnian is notable for a major biotic crisis toward its end, the Frasnian–Famennian extinction event, one of the most significant mass extinctions of the Phanerozoic. Many reef-builders and other marine groups declined substantially, and there was a protracted recovery that culminated in the Famennian. The stage is followed by the Famennian, marking a transition to another phase of Devonian ecological and evolutionary dynamics.