Like many Devonian and lower Carboniferous stages, the Tournaisian is a unit from West European regional stratigraphy that is now used in the official international time scale.

[6] The GSSP for the Tournaisian is near the summit of La Serre hill, in the Lydiennes Formation of the commune of Cabrières, in the Montagne Noire (southern France).

[10] Coal is less common in the Tournaisian than in the rest of the Carboniferous, and forests and swamps were at low-density despite some trees reaching heights of up to 40 meters (131 feet).

There is still much debate over the proportion of spore-bearing (progymnosperm) to seed-bearing (spermatophyte) woody plants, but both were evidently major parts of Tournaisian ecosystems.

[12] Divaricating (widely branching) trunks of Lepidodendropsis lycophytes are by far the most abundant and widespread plant fossils of the Tournaisian, yet there was some minor variation in other flora through time and space.

In eastern North America, lyginopterids and probable progymnosperms were also common, as indicated by leaf form genera such as Adiantites, Rhodeopteridium, and Genselia.

[15] Trilobites experienced their final substantial diversification event in the mid-late Tournaisian, briefly regaining a level of diversity not seen since the Middle Devonian.

By the late Tournaisian, they had recolonized shallower environments and divided into three different biogeographic zones corresponding to North America, Europe, and East Asia.