Italy Geopaleontological Description Part 2
In the Western and Central Alps, as well as in Tuscany, the Permian appears in part with metamorphic facies (pseudogneiss, mica schists, talcoscists, besimaudites), passing through varicolored schists, sandstones, quartzites, conglomerates (anagenites, verrucano), as well as brown schists here and there with remains of Walchia , Sphenopteris , Neuropteris , Callipteris , etc .; while in the Eastern Alps, in addition to the arenaceous and conglomeratic forms, there also appear, especially at the base, limestones in Schwagerina , Fusulina , Brachiopods ( Spirifer , Rhynchonella , Productus , etc.), bituminous limestones and dolomites with Voltzia , Bajera , Avicula , Pecten , Bellerophon , Athyris , Spirifer .
In Sicily, small but very interesting outcrops of richly fossilized marine limestone Permico ( Schwagerina , Spongne, Brachiopods, Bivalves, Gastropods, Nautiloides, Ammonites, Phillipsia , etc.) were discovered in the Sosio valley north of Palermo .
In Sardinia various arenaceous, conglomemic and even schistose formations in Walchia , Callipteris , etc. must be referred to this period.
Important eruptive formations are also attributed to the Permic period (varî porphyries, often quartziferous, porphyrites, spilites, tuffs, etc.) which extend over hundreds of square kilometers. in various parts of the Alps.
According to Itypemba, the lands of the Secondary or Mesozoic Era, while on the whole they band or cloak irregularly the Alpine region constitute the backbone of the Apennines, appearing also here and there in Sicily and Sardinia; they are essentially calcareous, of marine deposit (sometimes of atollic facies ) and often very fossiliferous, with a total power of over 1000 meters.
Triassic . – It generally begins in northern Italy (especially the Alps) with detrital, coastal formations, almost as the last phase of the Permic series, such as micaceous sandstones, quartzites, conglomerates (anagenites, servinus, etc.), the so-called Werfenian , sometimes with remains of Equiseti, Voltzie. Sometimes limestones with Pseudomonotis , Turbonilla , Naticella , etc. appear very early.
At the top there are powerful limestone series, more or less dolomitic, sometimes a little arenaceous, often passing through more or less schistose marl, with remains of Equisetum and Voltzia , often with innumerable remains of siphon algae (Gyroporella or Diplopora ) , and with a very rich and varied fauna (hence the name of Muschelkalk ) to Rhizocorallium , Dadocrinus , Encrinus liliiformis , Terebratula vulgaris , Rhynchonella , Spirigera trigonella , Daonella , Halobia , large Omphaloptycha , Ceratites trinodosus and binodosus , Trachiceras , sometimes also with fish and reptile remains. Famous and rich is the fauna of the cliff limestone of Esino.
Finally, the Triassic series closes with other considerable limestone and dolomite formations (the so-called main Dolomite ), with gigantic Megalodon Gumbeli and Dicerocardium , Pleutomaria solitaria , Gervillia exilis , marls (with the well-known fauna of S. Cassiano) and schists in Carnites , Myophoria , Myoconcha , Pisces, etc. (the so-called Raibliano ), chalky areas, ending at the top with limestones in Avicula contorta , dolomitic limestones in Terebratula gregaria , Plicatule, Cardite, Cardii, Mussels, sometimes with large molds of Megalodont ( Conchodon), Lumachelle, etc., constituting the so-called Rhaetian or Infralias (the Dachstein of the Germans) of passage between the Triassic and the Liassic.
In the southern Apennines, on the other hand, the Triassic series begins with varicolored siliceous schists with Fucoids or Chondrites and Radiolarî, as well as Halobie, Posidonomie, etc., and continues upwards with fossiliferous marly limestones ( Cassianella , Myophoria , Cardita , etc.) and with powerful compact or stratified dolomites with Megalodontids and Giroporelle, with Wortenia , Neritopsis , Gervillia exilis , Avicula , Mytilus . Pecten , Myophoria , Myoconcha , Cardita, etc., as well as with the ichthyofauna of Giffoni. The endogenous formations, almost only marine, are generally not very important in the Triassic, except in some regions, for example in Trentino, such as porphyries, porphyrites, melafiri, diabase, as well as various tuffs, as well as very varied sienitic, granite and similar rocks. but not always of a sure age. From an economic point of view it should be remembered that dolomite is sometimes metalliferous (galena, blende, chalcopyrite, calamine) and that the famous white and gray marbles of the Apuan Alps belong to the Triassic.
Jurassic . – Very complex and varied training. Its lower part, or Liassic , is mostly represented by brownish or gray limestones, but sometimes also reddish, with many Ammonites ( Arietites , Arieticeras , Amaltheus , Lytoceras , Hildoceras ), Belemniti, Aegoceras , Harpoceras , Phylloceras , Rhacophillites , Pettini , Mussels, Lime, Avicule, many Brachiopods ( Terebratula , Pygope aspasia , Rhynchonella , Spiriferina , Waldheimia , Spirifer ). In the southern Apennines limestones prevail in Terebratule, Rinconelle, Lime, Pettini, Megalodi, etc.
Very varied gray or varicolored limestones follow to constitute the true Jurassic , but mainly reddish in color (hence the name of Rosso ammonitico ), among which Hildoceras , Harpoceras , Phylloceras , Coeloceras , Lioceras , Aspidoceras , Peltoceras , Posidonomya alpina are predominant , Pholadomya , Pecten , frequent Brachiopods (Rinconelle, Terebratule, etc.), sometimes also Nerinee and Coralli limestones or marly or arenaceous or siliceous limestones, or flint nodules, or finally special Aptici schists.
Finally, the Jurassic series generally ends with the gray limestones of the so-called Titonico , or whitish (the majolica of the Lombardi, the biancone of the Veneti, the rocky limestone of the Apennines), passing through the lower Cretaceous period, with many Corallarî, Brachiopods (among which we will remember Pygope diphya , Pygopejanitor , and others), Belemnites, Diceratids, many Ammonites.
There are also types of intermediate regimes, which almost become the rule when dealing with large river basins. This is especially important for the Po, whose average monthly flows show much less marked fluctuations than those of the Alpine and Apennine tributaries; since the different regimes of the two sides compensate each other in some way, giving rise to a much more regular trend (see Po).
The intensity of the floods, a characteristic common to most of the Apennine and island rivers, is accompanied by an intense erosive action, also favored by the great diffusion of clayey, sandy rocks, etc. not very resistant.
In southern Italy and Sicily, where intense evaporation is associated with prolonged drought in the summer, many minor streams are dry for a very long period; the so-called rivers , very numerous in Calabria and Sicily, remain dry for many months, indeed many carry surface water only during periods of floods, when they tear enormous quantities of materials from the land crossed, which are almost always very erodible; these in the lower section, in which the transport energy naturally decreases due to the lesser slope, clutter up the bottom, which is therefore very large in proportion to the development of the watercourse.