During the secondary (or Mesozoic) era, thick marl formations (mixture of clay and limestone) were deposited several times in our region. The first level, at our feet, dates back to the Lias, a period of the Secondary Era dated from 185 to 170 million years ago.
It corresponds to a period of deepening of the Alpine sea which accommodates vast quantities of clay-quartz sediments in an oxygen-poor environment, which is at the origin of the black color of these rocks. Source : geoparchauteprovence.com/partir-a-la-decouverte/#1573