The oldest materials of Formentera are from the Late Miocene period, specifically from 11 to 7 Ma.
During this period great coral reefs were formed that typically grew around the pre-existing reliefs arising during the Alpine Orogeny. In Formentera, although these reliefs do not rise above the surface, the fossil reefs do so extensively. One of the best areas for observing them is La Mola.
Diagram representing the coral reef environment that has later given way to the cliffs of La Mola.
The cliffs of La Mola comprise, in a large part, layers of coral colony structures that grew in successive generations during the life of the reef.
These reefs have become subaerially exposed due to a system of faults travelling NNE-SSW causing the elevation of the Promontory of La Mola in relation to the Central cordon. The best known is the fault of Racó de sa Pujada.
Late Miocene cliffs of La Mola.
Normally in these ecosystems, there is a great diversity of marine species of molluscs (bivalves and gastropods). However, at La Mola these fossils almost always appear as internal moulds, a very common preservation of the coral beds of the Balearic Islands. This is because the original calcium carbonate shell dissolves after the sediment has hardened, ant the material that was inside the shell is preserved.
Other fossils found in the area are calcareous algae. All together represent a shallow water environment that is laterally replaced by a set of coastal and continental deposits that emerge in the north of the described sector.
Calcareous algae.
Adjacent to some part of the cliffs at La Mola there are dunes overlapping materials of the the Pleistocene period, although they do not appear in existing geological cartographies. These formed during the lowering of the sea level, exposing large areas of previously submerged sands which, due to the action of the wind, accumulated at the foot of La Mola.
Delimitation of the possible adjacent dunes and associated colluvial deposits.
