Geology

The 200 meter high sea-cliffs of the San Bartolo Hills display a succession of sedimentary layers deposited in a span of time that goes from about 10 and 6 million years ago which, today, geologists call "Messinian", when the geography of the Italian peninsula, still in the process of formation, was very different from its current conformation. And, well we should remember, San Bartolo represents one of the most complete sections of the Messinian in Italy: thanks to the sea which, with the vigour of a hatchet, cut through what was a tranquil northern Marche hill. From a stratigraphic viewpoint, starting form the lower layers, we find the Schlier Formation, highly visible under "la croce" (Monte Castellaro), with its ashy marls and clays alternated with several layers of blackish bituminous marls (pelite).
Next we have the Gypsum-Sulphuriferous Formation, which begins with characteristic levels of evaporitic Limestone, variegated in colour (from whitish to beige - brown) with a "corroded" effect, dolomitic, with the characteristic hydrocarbon odour, where Sulphur and Celestine crystals can be found with a little luck.
Gypsum is much more frequent and can even be found when not associated with the Limestone, present in beautiful crystals of the Selenite variety and fibrous Sericolitis aggregates.
Next we have clayey, rotten-stone marls, beige-light brown in colour, closely stratified, rich in fossils.
Since the first two formations only surface in some areas, where marine erosion has bared the nucleus of the anticlinal fold, a large part of the sea-cliffs has been carved in the overhanging San Donato Formation, characterised by alternating prevalent levels of greyish marled clay and levels of grey-beige sand, in 10 centimetre layers, much thicker in some points.
This formation, which therefore constitutes the fundamental framework of the San Bartolo ridges, is reduced in thickness at this point to only 180-200 meters, a sign which we find in proximity to a high point of the Messinian seabottom where currents and undersea landslides prevented a strong accumulation of sediment.
The area's last and most recent marine formation surfaces in the area external to the sea-cliffs (south-west side of the hill ridge) or in the more elevated areas of San Bartolo (for example the Faro-Imperiale zone): the Colombacci Formation which constitutes the familiar yellowish-ochre "tufa" characteristic of the Pesaro hills.
In reality, it is yellowish-ochre coloured sand, alternated with narrow levels of beige-light brown marl. The mysterious "Colombacci" are characteristic, thin levels of evaporitic limestone, white-beige in colour, slightly marled and fragile, which are cyclically formed when the tide almost laps the seabed sands, in a vast lagoon like basin, more like a lake than the sea.
At the beginning of the Pliocene era, this world made of wooded islands, narrow sea straits, torrents and lagoons was submersed into the powerful "Pliocene Transgression".
The sea deepens by hundreds of metres, the marked sub-tropical climate becomes cooler.
The Messinian era ends and at some point, far away on the African continent, in which the Italian peninsula is embedded, the earliest ancestors of man make their first uncertain steps.
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