The volcanism began with a first and main phase in late Sinemurian to Toarcian times around 191 to 178 Ma.
[2] These cones produced tuffite deposits made largely of lapilli with rare volcanic bombs.
[4] Beneath a lahar deposit at Korsaröd (Djupadal Formation), Early Jurassic plant fossils including wood, pollen and spores have been exceptionally well preserved.
[4] The volcanism is possibly the result of decompression melting of the lithospheric mantle beneath.
[1][2][4] The background to the volcanism is the break-up of Pangea, and thus it is analogous to the much more voluminous Karoo-Ferrar flood basalts of Southern Africa.