Geoturism Balearic Islands

The geology of Formentera is basically comprised of materials from two stratigraphic periods: Late Miocene (11-6 Ma) and Quaternary (2.5 Ma to date). The latter is divided into two periods: Pleistocene and Holocene.

One of the most outstanding places regarding the Pleistocene geological record of Formentera is, without doubt, Cala en Baster. The cliffs of this location show a well-defined stratigraphic succession and their strata reflect the climate variation of the area over the last hundred thousand years. 

The lower levels, deposited when the current cliff was still not formed, correspond to an old beach and contain mollusc with a body protected laterally by a shell composed of two pieces or valves, generally symmetrical in a bilateral plane<strong>.</strong></p></div>">bivalve fossils. Laterally, and in the same unit, one can observe how the sediments no longer have marine fossils and, to the contrary, they have land plant root moulds (rhyzocretions), which denotes a sandy area behind the beach, where the waves could not reach.

After this episode, a very significant change in the sedimentation is seen, proven by a unit of dark brown silts with different sized layers of Sedimentary rock whose main component is calcium carbonate (CaCO3). Its origin can be chemical, organic or detritic.</p><p><br></p></div>">limestone gravel that greatly contrasts with the landscape. 

This unit was caused by the action of an old ravine. Its colour is mainly due to the oxidation of iron minerals contained in the sediment. 

At a specific time during the Late Pleistocene this fluvial deposit was interrupted and an intensive stage of dune formation began, which appears in the tectonic, eustatic or antropical processes</span></p></div>">outcrop with a clear colour and its typical cross stratification. 

This abrupt change in the deposition was the result of a low sea level, which left large areas of the seabed sand exposed which were later displaced by the wind. Lithologically they comprise calcarenites, corresponding to the known marès.

 Among these fossil dunes, every now and then, a fossilised shell of a land Mollusc equipped with a fleshy foot and with the body generally protected by a single-piece shell, normally in a spiral shape. The gastropods include snails and limpets, among others.<strong>&nbsp;&nbsp;</strong></p><p><br></p></div>">gastropod can be seen that has been carried by the wind due to its lightness. 

The last unit corresponds to some more recent Quaternary dunes formed by a mix of sands and silts that give the upper part of the cliff its orange colour. 

The action of rain on the talus causes silts to dissolve with the water, run down its walls and stain it.