Pianosa-Birth of an Island Nineteen million years of geological history, from the first rocks to the deer migration in the last glacial period

The oldest deposits of the island are Miocene in age and outcrop along most of the western cliff and at Cala della Ruta. The Miocene includes two formations: Marina del Marchese Formation and Golfo della Botte Formation. The first, of Burdigalian age, is characterized by ~150 m outcropping thickness of marl-prevalent succession; the second, of upper Tortonian - Messinian age, is composed of ~300 m thickness of clayey-sandy deposits, which are conglomeratic in the upper part. Between the two Miocene formations there is a wide stratigraphic gap spanning the late Burdigalian - early Tortonian interval. During this period, the tectonic uplift of the area prevented new sedimentary series formation. The deposition restarted with Golfo della Botte Formation unconformably resting on Marina del Marchese one; today, the two formations show the same bed setting but different strike: 15°-20° the first and 5°-10° the second. The Pianosa Formation rests unconformably on both Miocene ones and it shows a sub-horizontal setting. The unconformity between the Pianosa Formation and the depositions of Golfo della Botte Formation, of late Tortonian - early Messinian age, shows that a second uplift occurred between the two sedimentary phases, probably induced by the emplacement of Elba and Montecristo's granitic plutons,. This uplift determined surfacing and tilting of Upper Miocene deposits and consequently further deformation of Lower Miocene one. Pianosa Formation is composed by a dozen metres of biocalcarenites, poor of inorganic components but rich of fossils (mainly molluscs, algae, bryozoans, echinoids and in minority crustaceans and fishes) which evidence a shallow marine environment. Along mostly of the western cliff and at Cala dell'Alga on the eastern coast, protruding on the morphological profile, there is a reddish-brown, well-lithified, rich of fluoroapatite, oxide and iron carbonate level, which divides in two units the sedimentary succession of the Pianosa Formation. Sediments below this level (lower unit) present sub-horizontal setting and are Piacenzian in age, whereas the upper one (upper unit) show clinostratification and is Early Pleistocene in age. The two units of Pianosa Formation are paraconformably related and the oxidation-fosfatization of the lower unit top evidences that between the two sedimentary episodes a period of emergence occurred. Above the Pianosa Formation unconformable rest shell deposits, relating to the early Late Pleistocene (“Tyrrhenian age”) sea rise. These consist of a few metres thick- succession rich in fossils, informally well known as “Panchina”, and sporadically outcropping along the eastern and southern low-line coast of the island. Finally, deposits of continental environment close the Pianosa Succession. They are characterized by sandy clays and red sandstones, which are related to aeolian and colluvial accumulations or breccias of collapsed caves and holes. The island surface typically consist of vast well-developed red soils, sometimes the older ones filled caves, which include many terrestrial vertebrate fossils, date back to Late Pleistocene-Holocene. The presence of these fossils is undoubtedly related to the phases connecting the island with the mainland.