| System (period) | Series (epoch) | Stage (age) | Lower boundary, Ma | ||
|---|---|---|---|---|---|
| Carboniferous | Mis. | Lower | Tournaisian | 358.9±0.4 | |
| Devonian | Upper (Late) | Famennian |  372.2±1.6
| ||
| Frasnian | 382.7±1.6
| ||||
| Middle | Givetian | 387.7±0.8
| |||
| Eifelian | 393.3±1.2
| ||||
| Lower (Early) | Emsian | 407.6±2.6
| |||
| Pragian | 410.8±2.8
| ||||
| Lochkovian | 419.2±3.2
| ||||
| Silurian | Pridoli | older | |||
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | |||||
The Frasnian is a first stage of the Upper Devonian series, corresponding to the Frasnian age of the Late Devonian epoch. It lasted from approximately 382.7 Ma to around 372.2 Ma (million years ago). It is preceded by the Givetian age of the Middle Devonian and is followed by the Famennian age of the Late Devonian. At the end of this age, one of the largest extinctions in Earth's history occurred.
Definition[]
The GSSP of the Frasnian stage and the whole Upper devonian series was ratified in 1986. The lower boundary is fixed in the Col du Puech de la Suque section E in Montage Noire, France, and related to the first appearance of the conodont species Ancyrodella rotundiloba.[2]
Frasnian life[]
Reefs on the coastal shallows formed corals such as Tabulophyllum, Phillipsastrea, Alveolites and Thamnopora. The reefs were home to numerous brachiopods (Devonoproductus, Nervostrophia, Atrypa), bivalves (Modiomorpha, Edmondia, Spathella) and gastropods (Straparollus, Loxonema, Strapardlus) as well as tentaculites like Nowakia. Acanthograptus, a graptolite, was found in the Frasnian marine strata of Colombia. Ammonite genera of this age include Manticoceras, Naplesites, Linguatornoceras and Aulatornoceras. Trilobites still lived on the reefs and on the bottom of the seas. Members of the orders Corynexochida (Scutellum), Phacopida (Phacops, Greenops, Viaphacops), Proetida (Proetus) and Odontopleurida (Kettneraspis) are known from the Frasnian. Eurypterids of this time were not numerous, apparently unable to withstand competition with predatory fish. In contrary to them, scorpions like Petaloscorpio spread to land, where they were probably the main predators. Ctenacaronychus, a mite, was discovered in the Lower Frasnian of Onteora Formation in USA. The insects were probably not yet numerous, since their fossils of this age are unknown.
The vertebrates continued to flourish. Conodonts like Ancyrodella, Polygnathus and Icriodus were still numerous, although the fish were more varied and many of them lived in both sea and fresh waters. In the Frasnian estuary sediments of Miguasha, Canada, various jawlss (Euphanerops), cartilaginous (Diplacanthus, Homalacanthus, Triazeugacanthus), armored (Bothriolepis, Plourdosteus) and bony fish are known. The last include cheirolepidiforms (Cheirolepis), coelacanthiforms (Miguashaia), dipnomorphs (Holoptychius, Quebecius), dipteriforms (Fleurantia, Scaumenacia) and the most important for the future terrestrial life, osteolepiforms (Eusthenopteron, Elpistostege).
Many trilobites and placoderms became extinct at the very end of the Frasnian due to falling sea levels and the onset of cooling. The drop in sea level was interrupted by several large rises, which may have been caused by the fall of comets.[3]
References[]
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
- ↑ "GSSP Table - Paleozoic Era". https://timescalefoundation.org/gssp/index.php?parentid=77.
- ↑ Charles Sandberg, Jared R. Morrow, Willi Ziegler (2002) "Late Devonian sea-level changes, catastrophic events, and mass extinctions". Geological Society of America Special Papers 356: pp. 473–87. DOI:10.1130/0-8137-2356-6.473