The Flysch represent a vast group of rock formations of microcrystalline limestones and more or less calcareous sandstones, alternating with clays and marls. Their main characteristic is the marked stratification, underlined by the rhythmic alternation of light colors (arenaceous limestone layers) and darker ones (marl or clay). In the stretch that takes you from here to Cassio these layers locally called "rive" are wonderfully exposed and take different names" Riva dlà gata, Costa dell'inferno, Groppo, Malacosta, Riva d'Naròla.
They derived from the sedimentation of very fine sands and calcareous muds by turbidity currents which, in the second half of the Cretaceous, regularly distributed fine deposits on very deep seabeds. The stratifications produced by these turbidity currents, defined by geologists as turbidites, always have a characteristic appearance: the lower part of the layers is made up of very fine cemented sands and the upper part, even several meters thick, is made up of flaky gray marl. The fine sands represent the sediment that was first deposited by the turbidity current, while the marl derives from the calcareous mud which is then slowly settled. Each layer was produced by a single turbidity current and the phenomenon can be considered instantaneous, if compared to the very long geological times measurable in millions of years.In some fortunate cases the current of turbidity is deposited with relative delicacy and, on the basal surface of the layer, the appearance that the seabed had at that moment remains imprinted, with the traces of the organisms that colonized it, crawling and feeding on mud. The most characteristic fossil trace, from which the name helminthoid flysch derives, is that of the Helminthoidea labirintica.
Sometimes, with a bit of luck, at the base of the thicker layers, fossil remains of bivalve molluscs (Inocèrami) are found, undoubted evidence of the marine origin of these rocks.
The Devil's Falls represent what remains of a resistant and extensive conglomerate-arenaceous bank transversal to the Baganza valley. This bank, now verticalized, is made up of cemented pebbles and sand, some present in its originally lower part and the others in the upper part. Due to colossal orogenic thrusts millions of years ago, it was raised from the bottom of a vast sea together with other sediments, until it assumed a vertical position. The pebbles and sand that compose it, coming from an ancient mountain chain that has now disappeared, were transported to the bottom of an ancient sea, about eighty million years ago. After their cementation and very slow emergence, they were eroded by rainwater and torrents which shaped them in the way we see them today.
Geology and Via Francigena
The geological landscape that the Via Francigena crosses in the province of Parma, from the city to the Cisa Pass, is multiple and complex. The first part of the Francigena path winds along rocks formed in the last 5 million years, witnessed by the marine sedimentary cycle of the Pliocene with fossil faunas typical of these outcrops, which will give way to river, marsh and lacustrine sediments of a continental environment. The marine domain of the so-called "Padan Gulf" spans a period of approximately 4.5 million years, ending with the definitive retreat of the sea, in the period during which the subsoil structures of the Po Valley were built.
After Fornovo, climbing towards Cassio and Berceto, the geological landscape becomes more and more varied and complex: from the ophiolitic cliff of Mount Prinzera to the flysch of Monte Sporno and Monte Cassio, crossing the varicolored clays and the sandstones of Scabiazza, passing the "wall ” of the enigmatic conglomerates of the Salti del Diavolo that emerge between Val Taro and Val Baganza.
From the Berceto bridge, up to the sources of the Baganza stream, before immersing itself in the territory of Alta Lunigiana, the nature of the rocks becomes even more complex, with the
spectacular outcropping of the "Rombecco granite", formed in the belly of the earth around 300 million from years ago.
STIRONE geosite of regional importance
River stretch with bed deeply embedded in the rocky substrate, along which a succession of very fossiliferous layers is brought to light, of stratigraphic interest for the Plio-Pleistocene limit. Along the riverbed the fossils make up a fraction of the alluvial material transported.
PRINZERA geosite of regional importance
Ophiolitic relief with extraordinary morphological prominence along the ridge between Taro and Sporzona, mainly formed by bluish-black serpentinized peridotites, with magnetite.
The ophiolites are magmatic fragments of oceanic crust incorporated into the mountain during the Apennine orogeny and testify to a remote past in which the Ligurian Tyrrhenian Sea, in the Middle Jurassic, about 180 million years ago, occupied this sector between the plate
GROPPO DEL VESCOVO geosite of regional importance
The Groppo del Vescovo looks like "a white petrified wave" that emerges from the soft green landscape of the meadows and pastures of the ridge area of the High Tuscan-Emilian Apennines. The particularity of this outcrop is linked both to factors of a geological-stratigraphic nature of the rocks present (contrast between the compactness of the limestone rocks, with the greater erodibility and alterability of the clay lithotypes present at the base and roof of the Groppo del Vescovo outcrop ) and to factors of a positional nature (the "support" position of the layers compared to the Tuscan side of the Apennine ridge). These factors were enhanced by the meteoric alteration which operated a "selective erosion" which acted with greater intensity on the clayey lithotypes compared to the calcareous ones.
ROMBECCO geosite of regional importance
It is an extensive light-coloured rocky mass, with beautiful views even from the ridge on which the Alta Via runs.
The Rombecco granite is actually a breccia, that is, a rock formed by fragments of different nature and with an angular shape, in which however the majority is made up of large granite fragments.
Granite is a rock of magmatic origin, formed following the solidification of a magma rich in silica, in magma chambers located at depths of 15-20 km, inside the earth's crust, where the slow
cooling has allowed the complete crystallization of the component minerals.
Turbidite layers produced by the resedimentation of a mixture of fine sand and carbonate mud
Fossil traces of Helmintoidea labirintica at the roof of the layers from which the name Flysch to helminthoides
numbers and map legend geositi text
1) Stratigraphic section of the Stirone stream
3) Devil's jumps and flysch of Monte Cassio
4) Bishop's Group
5) Rombecco granite
The helminthoides that give their name to these rocks are fossil "tracks" left by worms that grazed on the seabed in long moments of calm. Photo from the Geological Service Archive
Flysch up close: their main characteristic is the marked stratification, underlined by the rhythmic alternation of light (limestone-arenaceous layers) and dark (marl or clay) colours. (photo P.
Small strip of a succession that includes red haptics and Majolica (Malm-Neocomian) incorporated into the basic complexes with stratigraphic contact on the Malm radiolarites
Small cliff with evident crest made up of greenish radiolarites and pleated whitish siliceous limestones covered by radiolaritic gravel, the latter used in the past to make mill wheels, visible circular extraction impressions
Cretaceous stratigraphic succession including various terms, among which the Dei Salti del Devil conglomerates are of particular interest, forming a kind of ridges and spiers transversal to the Val Baganza and the spectacular outcrops of the flysh of Monte Cassio