Clay explorations for the production of ceramics and bricks exposed magnificent sedimentary sequences from the Cretaceous. These sequences present sedimentary facies associated with depositional environments ranging from marginal marine to freshwater lacustrine with frequent spillings of detrital material, resulting from the frequent variations of the mean sea level throughout the Early Cretaceous.

The old exploration fronts of the FACEAL lagoon constitute the best place to observe the Cretaceous sediments of the strip between Paderne and Tunes, which, in general, are sediments rich in microorganisms, such as foraminifera and ostracods. Also part of the fossil content are calcareous algae (representing episodic transgressions) and charophytes (freshwater green macroalgae).

The clays that were mined on the Cretaceous Tunes-Mem Moniz rim were deposited in coastal lagoons and the remarkable thickness of this deposit means that the depositional environment remained stable for many thousands of years. The accumulation of rainwater at the base of the slope is due to the impermeability provided by the clay.