Summary: The Tremiti recall every year thousands of tourists from around the world. The wonders seen, admired and photographed every day are nothing more than the effect of the course of nature over millions of years. Tourist experience comes a detailed study of the formation and history of the archipelago from a geological point of view and lithology. A tourist route with a high scientific content.
(1) Geologist GeoResearch Center of Italy - geoblog (website: http://www.geobalocchi.blogspot.com/ ) (2) Survey e collaboratore del GeoResearch Center Italy - GeoBlog (sito internet: http://www.ricercasperimentale.blogspot.com/ ).
Introduzione
L'Arcipelago delle Tremiti è costituito da tre isole più grandi (San Domino, San Nicola, Caprara), da un isolotto più piccolo (Cretaccio) e da un'ulteriore small island moved eastward about 10 miles (20 kilometers), called Pianosa. The archipelago is located north of the Gargano Peninsula and 12 miles (22 kilometers) off the coast of Molise.
It is therefore small islands (two square kilometers the largest island of San Domino) easily walkable and circumnavigation in two hours using small boats.
aspects
lithological succession is characterized by outcrops of marine sedimentary lithologies ranging in age from the Paleocene and the Pliocene followed on average, in angular unconformity (Unconformity angular), a succession of continental clastic Pleistocene Upper-Middle (Fig. 1).
The marine succession is mainly represented by a series limestone, dolomitic limestone and limestone-marl passing up a series of lists and the open sea with flint nodules, to close with neritic environment of the calcarenites . From bottom to top, are the following distinct lithological units (SELL, 1971, Channell, 1979; Brozzetti, 2006): Formation of the Bue Marino (dolomite and limestone and calcarenites bioconstructions organogenic neritic environment; Paleocene upper), Training Caprara (compact dolomite with chert nodules and lists of the pelagic environment; Eocene) Formation of San Domino (including a number of lithofacies Low water: organogenic limestones and calcarenites in nummulites bioconstructions; lower-middle Eocene) Formation of Cretaccio (dolomitic limestone and marl glauconitiche yellow, yellow-whitish, the environment variable from coast to open sea; Langhian-Messinian pp), Training San Nicola (dolomitic limestone in the formation of angular unconformity Cretaccio organogenic limestone and the roof of sea bass and richly bioclastic, pp Messinian, middle Pliocene) (Fig. 2).
The continental deposits (Ram, 1989; Brozzetti, 2006), rarely surfacing in complete sequence, are characterized by underlying calcareous conglomerates (Middle Pleistocene), followed by a few meters of limestone Marly (Middle Pleistocene), and a succession of sandy-silty deposits of wind (Loess and Loess Red Yellow Middle Pleistocene-sup., of the Upper Pleistocene Loess Bruno.) sporadic intercalations containing gravel. Finally, resulting from the decalcification of the typical loess "croutons" interleaved at several levels within the continental succession.
aspects
Islands tectonic quakes occur with a dipping stratigraphy to the SE (south coast of San Domino in fig. 3) NE-SW direction and defining an emphasis on monoclonal (Fig. 4), which represents the southern flank of a loose fold with vertical axial plane and hinge line with direction N60 (p-diagram greek fig. 1) (SELL, 1971, Ram, 1989; Brozzetti, 2006).
NO
Along the coast of the island of San Nicola is visible in the contact between the formation of angular unconformity and the overlying formation Cretaccio San Nicola (Fig. 5). Note the large fold that deforms the Formation of Cretaccio and normal faults that cut both formations.
Other structures are visible at the Grotta del Bue Marino (fig. 6 and 7) where you can see both the stratigraphic dip SE, has many faults.
An interesting structure is the "presumed fault probably active" localized outcropping in the upper part of the island of San Nicola (Fig. 8). Rejection (moving two blocks) and probably represents a transcurrent movement left, highlighted by the step that has formed between the two blocs. In fact, in the non-activity of the fault (fault stops and not moving), the erosion would have even without the two blocks show the step (Panizzi, 1995; Panizzi, 1988).
From a geomorphological point of view of geography and morphology of coastal tourism is the one that attracts the visitor, becoming the predominant element of the landscape.
This morphology may be contained in three main morphotypes:
- a high cliff coast : characterized by the presence of a vertical slope (above the sea) generally rocky and formed by the erosive action of waves on rocks (fig . 5 and 9);
- low rocky shore slopes gently into the sea : often the shoreline is jagged and broken into large bays (Fig. 3, 4 and 10);
- low sandy coast: the only presence is in Arenas set the island of San Domino.
may be separated if the escarpment cliffs lives is in direct contact with the sea and subject to the processes of marine erosion (Fig. 5 and 9). When the foot of the slope sediments accumulate (of different nature: sandy shoreline, slope debris, landslides) that separate from the sea and thus the erosion of the waves does not change its shape, it is called dead cliff (Fig. 11).
The process of formation of a cliff can be outlined below (Panizzi, 1995) (Fig. 12):
- Escarpment in direct contact with the sea, where the processes of chemical weathering and physical disintegration accentuate the cracks in the rocks the top of the cliff;
- actions marine erosion dig a furrow of the hinged base of the cliff (Fig. 13);
- collapse of a portion of the escarpment;
- accumulation of debris at the foot of the cliff that can be removed from the waves and then the process continues (cliff alive), or if the deposits persist without being removed, protect the base of the slope, resulting in an erosion of the sea cliff died.
Other characteristic forms of the islands are represented by numerous coves along the coast to form small coves called "set" (Cala del Bue Marino, fig. 6 and 7, Cala of Moray fig. 13, the English Cala, Cala of the Swallows, etc.).. Associated with them are the numerous caves of karst coasts located mostly along the coasts of the island of San Domino.
La Grotta del Bue Marino (fig. 6 and 7) is a hollow dome-shaped rounded and slightly elongated in the direction NE-SW. The entrance to the sea is narrow and low. La Grotta delle Viole (Fig. 14) appears as a round shape with a cavity opening to the sea and of rectangular shape (the shape of the opening is influenced by stratification), while the terminal portion of the cave opens up , showing the sky (well, cave, fig. 14 and 15).
The genesis of the caves (Castiglione, 1978; Panizzi, 1995) of San Domino is related to the dissolution of carbonate rocks by rain water that alter the lithologies on the surface topography and the sea water attacks from below. As a result loosely formed cavities within the rock si allargano formando, inizialmente, una piccola grotta generalmente a forma di cupola e invasa dalle acque marine (a testimonianza che il carsismo procede dal basso, per maggiore alterazione chimica da parte dell’acqua del mare). L’assottigliamento della volta, in tempi successivi, provoca il suo collasso per gravità formando un’apertura verso l’alto. I detriti che si depositano all’interno del piccolo bacino possono essere successivamente allontanati per effetto del trasporto da parte del moto ondoso.
La diversità tra le grotte lungo la costa NO e quelle lungo la costa SE di San Domino è legata alla struttura monoclinalica dell’isola (rilievo a cuesta; PANIZZA, 1995). Infatti a SE le coste sono basse e i processi di dissoluzione con maggiore facilità possono formare delle grotte a pozzo con la volta collassata, mentre lungo le coste alte a NO, la successiole stratigrafica presenta uno spessore maggiore e quindi più resistente ai processi di alterazione permettendo il formarsi di grotte a cupola (in prossimità del mare) e non a pozzo con il succesivo collasso della volta.
Con molta probabilità le piccole baie dell’isola di San Domino, possono essersi formate a causa dei processi carsici che inizialmente hanno generato una grotta a forma di pozzo con la volta collassata. I processi erosivi del moto ondoso insieme ai processi di alterazione chimica, put in the small inner basin connected with the sea forming a small bay, which with the passage of time has been extended until the present structure (Fig. 15).
Other forms of dissolution of carbonates are represented by pyramids and grooves due to stagnation of water along fractures and on the surface of the rock that the chemical alteration. After the removal of stagnant water are brought to light forms of dissolution (Fig. 10).
number of slope deposits cover the costs or NO on the island of San Nicola. A landslide of considerable rotational sliding scale and probably active, is located along the NE (Fig. 16) with the detachment of some blocks highlighted by the opening of fractures and their respect for lowering the ground level, while at the bottom of the scree slope is visible at different grain sizes. A landslide along the coast to overturn NO (Fig. 11) shows a block rotated slightly to the north and the base of the slope you see a thick blanket of debris.
Geological History Tremiti
Initial investigation and first came to attention in the late nineteenth century and the early years of the twentieth century. Tremiti islands were in fact subject of research aimed at identifying the age and nature of the soil.
was a period very active studies, during which the foundations of knowledge Tremiti. From the beginning it was thought seriously to steer them in the broader science of geological relationships between the Italian peninsula to the west and the Balkan Peninsula to the east.
The islands were in fact a large limestone bridge that would have combined the Gargano promontory with Dalmatia and that it would split into two basins of the Adriatic Sea, leaving the southern Adriatic and Ionian-depression in the North Adriatic pit, reaching the depth of 200 meters off the coast of Ancona.
The geological events that led first to the formation of the rocks that make up the archipelago and subsequently to the genesis of that, we are place in a period that lasted about 200 million years. At the beginning of this period, geologists trace the split of Pangea, the supercontinent that is believed would include all land. At the beginning of removal of the plates (or plates) so determinatisi ensuing open expanses of ocean. The space gradually formed between the African and Eurasian plate was occupied by the Tethys Sea, a vast ocean whose depth were formed on the thick carbonate platforms (which includes also the rocks of the Tremiti) due to sedimentation, which lasted for about 120 million years, the carbonate remains of countless marine organisms.
Subsequently, the tectonic movements led to il ravvicinamento della zolla africana e di quella euroasiatica, causando la frattura, l'accavallamento e l'emersione di parte delle piattaforme carbonatiche.
Gli eventi geologici che hanno interessato il Mediterraneo ed in particolare il bacino Adriatico negli ultimi 65 milioni di anni (durante il Cenozoico e il Quaternario), hanno portato alla configurazione attuale dell'arcipelago delle Tremiti.
Durante il Quaternario, le isole Tremiti, già emerse, sono state interessate da processi di erosione e modellamento, principalmente a causa delle variazioni del livello marino dovute alle glaciazioni.
E’ proprio a questo ultimo periodo che si fa risalire la formazione dei sedimenti continentali (löess, crostoni calcarenitici, conglomerates and gravels) that cover the most ancient carbonate rocks of marine origin, consisted primarily of dolomite, limestone and doloareniti.
The testimony of a geological evolution of the Tremiti turns out to be long and difficult. This is testified by the morphology, geologic structures (planes of stratification, tilt and bending of the same, the fault plane) and the presence of fossilized remains of unquestionably related to marine organisms such as shells, corals, skeletal remains of fish.
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