The cliffs around the beach of Ault are composed of chalk from the Upper Cretaceous, more precisely from the Turonian and Coniacian (around 83 million years ago to 90 million years ago). They are strewn with flint nodules which highlight the subhorizontal stratification planes (the formation of flint has already been discussed in Discovery of the geology of the cliffs of Étretat, presentation of an excursion from the beach of Tilleul (Antifer) to the Porte d'Amont (Étretat Nord)). The relative proportion of chalk and flint is around 90-95% chalk to 5-10% flint.
Flint horizons are stratigraphic markers. On the cliffs of Ault, the regular flint band called Seven Sisters is recognizable and characterizes the boundary between the Middle Coniacian and the Upper Coniacian (around 87 million years ago). The boundary between the lower and middle Coniacian is marked by the Shoreham 2 marl level, which is more difficult to identify. These lithostratigraphic markings allow in particular the correlation of distant deposits, such as between the Normandy and Picardy coasts, or between the French and English coasts.