Orbigny named it after the French city of Tours in the region of Touraine (department Indre-et-Loire), which is the original type locality.

[citation needed] The base of the Turonian Stage is defined as the place where the ammonite species Watinoceras devonense first appears in the stratigraphic column.

The official reference profile (the GSSP) for the base of the Turonian is located in the Rock Canyon anticline near Pueblo, Colorado (United States, coordinates: 38° 16' 56" N, 104° 43' 39" W).

[6] The top of the Turonian Stage (the base of the Coniacian) is defined as the place in the stratigraphic column where the inoceramid bivalve species Cremnoceramus rotundatus first appears.

In the Tethys domain, it contains the following ammonite biozones: Other important index fossils are species of the inoceramid genus Inoceramus (I. schloenbachi, I. lamarcki and I. labiatus).