Turonian is a geological stage belonging to Mesozoic (secondary era) and more exactly to upper Cretaceous. Its age is about 90 million years.
Simplified stratigraphical scale (the millions of years (MY) correspond to the period's beginning)
4500 MY
540 MY
250 MY
65 MY
Precambrian
Paleozoic (primary era)
Mesozoic (secondary era)
Cenozoic (tertiary + quaternary eras)
Triassic
Jurassic
lower Cretaceous
upper Cretaceous
250 MY
203 MY
135 MY
96 MY
92 MY
88 MY
Cenomanian
Turonian
Senonian
Turonian has been defined in Touraine where it is present in three different marine levels. From bottom to top (from the most ancient to the most recent), we find:
- a clayey chalk , corresponding to a quiet sedimentation in relatively deep sea (several tens of metres).
- a micaceous chalk, called also white tuffeau (limestone with small brilliant specks of white mica). The sedimentation had to be made in little less quiet and little less deep water.
- the yellow tuffeau (sandy limestone, passing locally to sands), characteristic of a shaken sedimentation in little deep sea.
The white tuffeau is a soft stone of construction which hardens in the open air. It served to the construction of castles, churches and houses typical of Touraine. This stone does not resist well to the atmospheric pollution. And so all the outside of the towers of Tours's cathedral was redone with a more resistant stone.
Yellow tuffeau has also been used as construction stone. Some ancient subterranean quarries were converted to mushroom farms. The numerous troglodytic houses visible in Touraine were dug in cliffs of yellow tuffeau.