The Famennian is the final age or stage of the Late Devonian Epoch in the geological timescale, spanning approximately from 372.2 to 358.9 million years ago (Ma). It is named after the Famenne region in the Ardennes, Belgium, where rocks of this age were first studied.
Stratigraphy
- Period: Devonian
- Epoch: Late Devonian
- Preceded by: Frasnian Stage
- Followed by: Tournaisian Stage (Lower Carboniferous)
The base of the Famennian Stage is defined by the first appearance of the conodont species Palmatolepis triangularis. Its top, which also marks the base of the Carboniferous Period (specifically the Tournaisian Stage), is defined by the first appearance of the conodont species Siphonodella sulcata. The Global Stratotype Section and Point (GSSP) for the base of the Famennian is located at the Coumiac Quarry, Lieu-dit La Serre, near Montagne Noire, France.
Paleogeography and Climate
During the Famennian, the supercontinent Gondwana was situated in the Southern Hemisphere, while the continent of Euramerica (formed by the collision of Laurentia and Baltica) was located near the equator. The climate was generally warm, but there is evidence of cooling events, particularly towards the end of the Devonian. Sea levels fluctuated, and periods of widespread anoxia (lack of oxygen) occurred in marine environments.
Paleontology and Events
The Famennian is notable for being a period of significant biotic change, primarily associated with the Late Devonian Extinction Event, also known as the Kellwasser Event. While the most severe phase of this extinction is often placed near the Frasnian-Famennian boundary or within the late Frasnian, its effects continued into the Famennian, particularly impacting marine life.
- Marine Life: Reef-building organisms (tabulate and rugose corals, stromatoporoids) suffered severe declines. Many groups of ammonoids, trilobites, and conodonts also experienced significant losses. Surviving groups often diversified in the aftermath, though with a reduced overall biodiversity compared to the earlier Devonian.
- Vertebrates: Jawed fish, including placoderms, acanthodians, and sarcopterygians (lobe-finned fish), continued to evolve. Crucially, the Famennian saw the continued evolution and diversification of early tetrapods, some of the earliest land-dwelling vertebrates, such as Ichthyostega and Acanthostega, which still retained many aquatic features.
- Terrestrial Life: Forests dominated by early trees like Archaeopteris were widespread, contributing to significant global changes in atmospheric CO2 levels and soil formation. The continued evolution of land plants led to more complex terrestrial ecosystems.
The widespread anoxic events, possibly linked to fluctuating sea levels, cooling episodes, and changes in oceanic circulation, are thought to have been major drivers of the Famennian faunal turnovers.