Toarcian Stage

Toarcian turnover

The Toarcian Age (183–174 Ma) is the fourth and last age in the Early Jurassic Epoch of the Jurassic Period of the Mesozoic Era. It occurs after the Pliensbachian Age, and before the Aalenian Age.

Geophysical

"During the Pliensbachian–Toarcian interval of the Early Jurassic, there is a well-known second order marine extinction that is observable at the species and genus levels. Ammonite diversity data from successions throughout Europe and parts of the Arctic suggest that this extinction may have been multi-phased with diversity declining over six separate intervals. The main-phase of decline begins at the Pliensbachian–Toarcian boundary and extends into the Lower Toarcian, to a level that is correlative with the Tenuicostatum/ Serpentinum Zone boundary." (Caruthers, Smith, & Gröcke, 2013)
Cooling coincided with a massive volcanic event, the North Sea Dome, which restricted the flow of seawater and the associated heat that it carried from the equator towards the North Pole region (Korte et al. 2015)
The Toarcian oceanic anoxic event (T-OAE), also called the Jenkyns event occurred at the end of this Age (Kemp et al., 2024)
- Seawater warming of up to 5°C, widespread ocean deoxygenation ("anoxia"), ocean acidification, increased chemical weathering and a faster hydrological cycle.
- Extinctions of mostly marine animal life.
- This event lasted about 300,000 years

Biological

Large conifers and seed plants continue to dominate
An ambiguous plant from China, Nanjinganthus dendrostyla, referred to as the oldest known angiosperm (Fu et al., 2018; Fu et al., 2020),
- Many researchers question the interpretation of these fossils, and attribute this taxon to an extinct gymnsoperm (Sokoloff et al. 2020; Coiro et al., 2019; Bateman, 2020)

Above: Figure 2 from Fu et al. 2018, showing fossils of Nanjinganthus

Above: Reconstruction of Nanjinganthus