Small biostromes and patch reefs in lagoonal marls, siltstones and sandstones.

They are built of colonial corals, faceloid and dendroid, adapted to a soft substratum (clayey bottom). They are preserved in the rock in situ, the dimensions of the colonies varying from several centimeters to several tens of centimeters.
Massive colonies dominate the central parts, and dendroid corals, the peripheries.