Geomorfologia della Baia Baratti (Livorno – Toscana) e della sua spiaggia

Geomorphology of the Baratti Bay and its beach (Leghorn, Tuscany)

Abstract

Some information about the wave climate and the geological setting of the bay and of its vicinity is given and the Stratigraphy and sedimentological characteristics of Pliocene to Recent deposits of the bottom of the bay and of the surrounding area are dealt with. The ten meter high cliff bordering the North-Eastern part of the bay is cut in three sandy beach deposits of Tyrrhenian age, alternating with red muddy sands of colluvial origin. The cay sands and pebbly sands are locally cemented to form a beach rock. Here the lower beach lies directly on the calcareus and arenaceus rocks of the « Alberese» and « Macigno» groups and contains pebbles and boulders of these rocks while on the West toe of the Poggio della Fornace there is a layer of red muddy sand between the lower beach sand and the rocks of the basement. During the regressive fluctuations of the Tyrrhenian transgression, the red muddy sands were colluviated and the eolian sands of the Fosso delle Fate and Fosso delle Grotte were accumulated. Large amounts of iron minerals and slags derived from the Etruscan metallurgical industry, which flourished near Baratti from the VI to the II century b. C., are mixed with the sand of the beach and are included in the younger level of cemented beach sand outcropping in the low tide terrace. The results of the detailed bathymetric and geological survey of the bottom of the bay are shown in figs 1 and 4. The textural analysis of the bottom sands of the bay showed a slight longshore drift of the coarser materials from S to N and a migration of the finer ones towards the center of the bay where the slag and sand deposit rich in iron minerals is thicker than 1 meter. The evolution of the bay during the Quaternary may be outlined as follows: Baia Baratti is developed in a valley draining the Piombino head, cut since lower Pliocene and partially filled by beach and wind-blown sediments during the Quaternary transgressions. Since the last glaciation the sea has been sapping the bay which at present is not fed by any sediments neither from the land not from the surrounding coasts. The Etruscans modified the regular arcuate shape of the coast by making harbor facilities, near Baratti. The sea has almost completely eroded the Etruscan build-up and therefore the present shape of the coast should be in equilibrium with the sea. A very slow erosion of the whole beach may be forecast simply as a consequence of the grinding-up of the beach materials.