The vertical strata (rock-layers) that make up the large rock Rocher de la Baume are derived from limestone sediments deposited horizontally at the bottom of the sea at the end of the Jurassic (Tithonian) period.
These layers, geologically folded for the first time at the end of the Secondary Era during the creation of large east-west oriented geological-folds in the region, (resulting in the creation of the Mont Ventoux and Lure mountains), were subsequently subjected to a second geological-folding during the surrection, uprising phase of the Alps in the Tertiary period. The work of erosion has made these lines and layers of strata visible today.
The Baume rock is framed to the north by a highly eroded anticline (an uprising geological-fold) and to the south by a syncline (a sinking geological-fold). In order to precisely date these strata comparatively speaking, the whole structure is reexamined from its origins. In this way, the order of the successive deposits can be determined using the principle of superposition (or layering) : according to the principle of superposition the oldest layers that were deposited first are covered by the most recent layers .
When the strata contain so-called "dating fossils", the characteristics of these biological markers are used to determine the relative (or comparable) dating of the different layers. Effective "date fossils" have a wide geographical distribution and have lived for a short time on a geological time-scale.
At the Baume rock, ammonite-fossils are used to refine stratigraphic-dating (layer-dating).