Ammonitico Rosso
The Ammonitico Rosso is a Mesozoic formation in Italy . The intensely red colored sediment belongs to the cephalopods - tuber limestone .
etymology
The name Ammonitico Rosso, often also known as Rosso Ammonitico among Italian geologists and stonecutters, is derived from the Italian ammonitico ( containing ammonites ) and rosso (red).
Initial description
In 1827 Tomaso Antonio Catullo first described the Rosso Ammonitico under the name Calcarie rosse ammonitiche . He was followed in 1847 by Leopoldo Pilla in a bulletin for the Société géologique de France . Only in 1956 was the Rosso Veronese Ammonitico of Giorgio Dal Piaz formalized by an entry in the stratigraphic lexicon.
introduction
The Ammonitico Rosso is a facies of fine-grained, more or less clay-rich limestone and marl-like limestone, which are colored red by iron oxides (especially hematite ) and are characterized by a bulbous structure. The colors range from dark red to pink and purple to green. The tubers are lighter and more calcareous than the surrounding, dark-colored, marly-clayey matrix and show clear outlines. They are generally irregular in shape and flattened and elongated in the layering plane.
Within the sediment many hardened layers are present, so-called hard bottom ( English hard grounds ) that by a fine, iron / magnesium-rich phosphate skin are covered. Between the individual layers, there can be a rapid change of fauna in the fossils involved . In addition, bioturbation can be observed in many horizons . The determination of the ammonites in reduced sediment parts was able to prove their affiliation to different biozones and thus show a clear condensation of these lithofacies.
Another characteristic is the lack of carbonate grains , such as those found on shallow limestone platforms, and the lack of typical terrigenous sediment inclusions. The bulk of the sediment is of biogenic origin and consists of the skeletal remains of planktonic and benthic organisms. The resulting sedimentation velocities were consequently very low and were in the millimeter range per millennium. Stratigraphic interruptions and sedimentation cessation can often be observed. The Ammonitico Rosso is a typical condensed sequence of layers. This results in very reduced layer thicknesses which, moreover, extend over a very long period of time.
Unfortunately, the term Ammonitico Rosso was used both lithostratigraphically and lithofacially, which caused some confusion. In the meantime it has become clear that there is no uniform facies Ammonitico Rosso, but a multitude of similar lithotypes.
Sedimentology
Sediment petrography
Sediment petrographically, the facies Ammonitico Rosso (after Dunham 1962) are mainly Mudstone and Wackestone , bioclastic Packstone is far rarer. Under these limestone layers of arenites , conglomerates and breccias of different sizes can be embedded. The breccia clasts can be of intraformational and remanufactured origins, or other formations. In the first case, the presence of syndepositional faults may possibly be assumed. Wave and current stratifications are also observed as sedimentary structures, which indicate fine-grain turbidites or storm deposits.
Storage room
The Facies Ammonitico Rosso reveals relatively deep marine deposits, with a minimum depth of 200 to 300 meters. In spite of this deep milieu, it indicates an agitated and ventilated deposit environment, responsible for oxygen enrichment in the sediment and a rich and diversified marine fauna. There is no evidence of anoxic conditions.
The lime sludge also contains a detritic component of biological origin, arising from the remains of various marine organisms. The deposit area is often associated with tectonic distortion areas in which relatively stable high areas alternate with rapidly sinking basins. The high areas carry a condensed sediment sequence like the Ammonitico Rosso, whereas the basins are characterized by turbiditic series.
Paleogeographically , the southern Alps were in the Lower Jurassic at 25 to 35 degrees north latitude. In the course of the Middle and Upper Jurassic, it moved equatorially and reached its southernmost position in the Kimmeridgium at 10 degrees north latitude. Then it drifted in the Lower Cretaceous again to the north and was located during the Valanginian to 20 and finally in the Aptian to 30 degrees north latitude.
Deposition models
Classically, the deposition area of the Ammonitico Rosso is interpreted as a pelagic high zone on which the accumulated lime sludge shows signs of sedimentation stop and dissolution. This indicates an increase in the deposition depth and an achievement of the carbonate compensation depth (English carbonate compensation depth or CCD for short ), the pressure-temperature conditions of which led to a solution of calcite . The presence of hard grounds and stratigraphic gaps suggest a deposition depth near or within the oscillation range of the CCD. In this context, synsedimentary movements at paleohigh-limiting disturbances may well have led to a local deepening of the sedimentation level and pushed it below the CCD. The depth of the CCD can also rise or fall due to changed ocean currents.
Another deposit model asserts a drop in the eustatic sea level, as was the case, for example, in the Upper Toarcian . As a result, the sediment load now came under the influence of storm waves and superficial ocean currents and thus partially or completely lost its micro-fraction . The result was a significant decrease or even a stop in the sediment volume.
However, the sedimentation models cannot be generalized - they are anything but unambiguous and must therefore be assessed under their respective stratigraphic and spatial framework.
There is no modern analogue to the Facies Ammonitico Rosso. Nevertheless, most of the scientific researchers agree on the following points:
- The facies are the typical result of a condensed sedimentation on clumps that arose from the breaking of carbonate platforms. The high altitudes, in turn, had sunk below the Euphotic Zone .
- Separated from the continental margin and surrounded by deep basins, the sedimentation on the eyries consisted only of slowly falling pelagic rain and the benthic components present in the sediment .
- Deep currents were temporarily noticeable, as evidenced by intraclasts, taphonomically rearranged ammonites of considerable size, frequent erosion discordances and layered traction traces preserved in sedimentary channels.
- The deep environment was ventilated, recognizable by the red color of the sediment.
Diagenesis
The diagenesis plays a very important role after sedimentation in the physico-chemical and biochemical conversion of the sediment. So far, there has been great uncertainty about the diagenetic processes after sedimentation of the Ammonitico Rosso, especially with regard to their chronological sequence. So far, two models have been widely used in the literature:
- submarine selective solution of the still unconsolidated sediment. The insoluble residues collect in the matrix.
- Dissolution and reprecipitation during the diagenetic solidification of the sediment.
The second model is currently preferred. In this case, solution and reprecipitation take place mainly during the early diagenetic phase and only to a lesser extent during the actual sedimentation. The decisive factor is the load pressure, which leads to a partial carbonate solution in the solidifying sediment. The solution was selective, since the aragonite component present in the ammonite shells went into solution before the calcite. The dissolved carbonate then precipitated again as calcite in the interstices between the sediments, cavities were filled and tubers formed between the clayey and metallic residues. These were then crushed by the sediment load. However, their hardening was delayed or even prevented by the pressure release process. The penetration of the tuber surfaces with the surrounding matrix was often accompanied by the formation of stylolites .
Carbonate solution , the accumulation of insoluble residues and the biochemical effects of microorganisms contributed to the color change of the Facies Ammonitico Rosso. The carbonate solution mainly affected the aragonite shells of pelagic marine animals, such as B. the ammonites. Due to the color changes from mostly red / reddish to gray or even green, the appearance of the rock changed in a haunting way.
Stratigraphy and Age Position
The lithofacies of Ammonitico Rosso is diachronous. It occurs in series of rocks from different epochs, some of which can be very different in time.
The facies are generally found in the Jura ( Upper Pliensbachian to Tithonian ) and thus cover a period of around 40 million years. Their main distribution was in the Upper Lower Jurassic (Toarcium to Aalenium ). It can occur much earlier, for example, in the Friuli Dolomites ( southern Italian Alps ) during the Middle Triassic in the Anisian . The Rosso Ammonitico Lombardo in western Lombardy was deposited during the Pliensbachian, Toarcian and Aalenian, while the Rosso Ammonitico Veronese further east is assigned to the Bajocian up to and including the Lower Tithonian. The latter facies have a large number of layer gaps that have arisen due to the suspension of sedimentation. The decline of the Ammonitico Rosso facies was quite rapid and occurred on the Jura / Chalk border. It was replaced by pelagic deposits with a higher content of calcium carbonate - probably due to a lowering of the CCD. The exact causes of this event are still controversial even today and are attributed to significant changes in ocean currents and / or to an explosive development of calcareous planktonic organisms - the main suppliers of pelagic sediments.
Nevertheless, the Ammonitico Rosso appears even in the Lower Cretaceous , as was proven by a northern Italian find in 2011. The site is located near Selva in the province of Bolzano , about 40 kilometers from the Austrian border. Their exact ages are Upper Valanginian to Lower Skin Vivian .
Italian authors separate the Rosso Ammonitico Veronese into a Rosso Ammonitico Inferiore ( Upper Bajocian to Lower Callovian ), a Rosso Ammonitico Medio (Upper Callovian to Middle Oxfordian ) and a Rosso Ammonitico Superiore (Lower Kimmeridgian to Upper Tithonian). In the past, the entire facies was divided into an Ammonitico Rosso Inferiore des Dogers and an Ammonitico Rosso Superiore des Malms.
Stratigraphically above the Ammonitico Rosso are the Radiolariti , the Rosso ad Aptici (both Malm) and the Maiolica or the Biancone (Lower Cretaceous). The Ammonitico Rosso in the Asiago area is underlain by the Calcari Grigi ( Hettangian to Unteres Pliensbachian), further to the north at the Puezkofel from the Dolomia principale and to the south in the Monti Lessini and on Monte Baldo from the Oolite di San Vigilio .
Fossils
The fossils in the Ammonitico Rosso document the pelagic character of the sediment - including numerous, mostly thin-shelled cephalopods (ammonites and their aptychs , nautiloids, as well as rostra and phragmocones from belemnites ). Among the ammonites the taxa Arieticeras , Aspidoceras , Calliphylloceras , Dactylioceras , Hildaites , Hildoceras , Mercaticeras , Mesodactylites and Phylloceras can be mentioned. There are also some pelagic bivalves , for example the taxon Bositra buchi , brachiopods , echinodermata , gastropods , sponge needles and often deformed and corroded stems and plates of crinoids . The cephalopods are mostly preserved as inner prints and without an aragonite shell, which was removed diagenetically after embedding the sediment. The discovery of the sea crocodile Neptunidraco ammoniticus is spectacular .
In the Apennines of Umbria (as Rosso Ammonitico Umbro ) and the Marche , the Ammonitico Rosso shows an extraordinary stratigraphic continuity and has delivered a very large number of very well-preserved fossils - including key fossils for biozones, which could be examined both biostratigraphically and historically. Around 500 ammonite taxa were discovered here, which had already been described by Michele Mercati in 1574 and recorded in wonderful copperplate engravings by Antonius Eisenhoit (see also Monte Petrano site ).
The microfauna is also very varied with radiolarians , foraminifera such as lenticulina and protoglobogerina , ostracods , calpionella , coccoliths , dinoflagellates , etc.
distribution
The Ammonitico Rosso is a characteristic sediment of the Tethys , which from the Triassic onwards penetrated westward along the northern slopes of the Kontental valley from Gondwana . From the Cretaceous onwards, however, this ocean closed due to the gradual northward drift of the African and Indian plates . Today the facies can be found along the resulting Alpine suture in sediments of Triassic and predominantly Jurassic ages. The alpine collision belt stretches from the Betides in southern Spain to the Himalayas . The facies Ammonitico Rosso is also present in North Africa, for example in the chains of the Atlas , in the Rif in Morocco , in the Kabylia in Algeria and in the Dorsal in northwestern Tunisia , e.g. B. at Djebel Zaress 40 kilometers southwest of Zaghouan . Their age here covers callovium to tithonium.
The facies continues east of the Alps in the Dinarides , in the Carpathian Arch and down to Greece ( Ionian Zone ). In Turkey it is found in the Pontids in the southeast of the Black Sea . Even in Oman , Ammonitico Rosso is coming up.
In Italy, the Ammonitico Rosso is widespread and appears in addition to the occurrences in the southern Alps in the Apennines of Umbria and the Marche, as well as in the southern Apennines as far as western Sicily . In the Alps, it can be found in the Lugano Prealps , in Mendrisiotto ( Ticino , Switzerland ), in Brianza , on the Grigna , in the Bergamasque Alps , in the Judikarian Alps on the Tridentine threshold , on the west shoulder of the Bellunese trough , in the Dolomites and the Venetian Alps .
In general, the spread of the Ammonitico Rosso facies was tied to pulses of strong oceanic expansion with the accompanying steady sea high level. The sediment input from the continents was low at these times. In the Upper Triassic and Jurassic, the facies were directly related to an expansion of the oceanic area of the Neotethys and the subsequent breakup and disintegration of the continental margins of Europe and Africa. This also applies to the Adriatic Plate , the foundation of the Southern Alps and the Ur-Apennines.
use
Ammonitico Rosso is a limestone of high ornamental quality, which, because of its hardness and rich coloring, was widely used both in architecture as a building block (internal and external) and in sculpture for sculptures. Its different shades of color, which range from red-violet to coral yellow and yellow to green, are very beautiful. In construction, it is mainly used for borders and paving, but also generally for cladding, steps, stairs, pillars, columns, balustrades, building and mantelpieces, etc. The higher its lime content, the better its mechanical properties and especially its translucency.
The Ammonitico Rosso is known under various names in Italy and is particularly valued as Veronese marble ( Marmo rosso di Verona ). The Verona Arena is a very good example . Numerous churches, palaces, funerary monuments and sculptures were created from the reddish lime, as testimony to the Baptistery of Cremona , the Baptistery of Parma , the Basilica of San Zeno Maggiore in Verona, the Duomo Vecchio (Old Cathedral) in Brescia and others.
Strictly speaking, the term marble for the rock is not geologically correct, since the Ammonitico Rosso, unlike a real marble, was not metamorphosed and did not undergo any recrystallization . The use of the term comes from the stone industry, which names all limes or dolomites as marble, which break in granular form, are extremely hard and solid, are difficult to work with and take up a polish.
There are still around 700 quarries in northern Italy where Ammonitico Rosso is mined, mainly in the provinces of Verona , Padua and Brescia . It is still an important economic factor in these provinces. In addition to Carrara marble , Veronese marble is one of the most important resources for marble and agglo-marble in Italy and one of the best known internationally.
The facies of the Ammonitico Rosso are often traversed by tectonic fractures - which negatively affects their mechanical and aesthetic properties and the rock is then only used as piece goods, e.g. B. can be used in dams and breakwaters. Varieties such as the Rosso Ammonitico Lombardo - a marl-rich limestone from the Upper Lias - and others from the Italian peninsula are only rarely mined due to their increased clay content and the resulting disadvantages.
See also
literature
- J. Aubouin: Reflection on the faciés «ammonitico rosso» . In: Bulletin de la Sociéte Géologique de France . tape 7 , 1964, pp. 475-501 .
- P. Beccaro: Radiolarian correlation of Jurassic siliceous successions of the Rosso Ammonitico Formation in the Southern Alps and Western Sicily (Italy) . In: Eclogae Geologicae Helvetiae . tape 99 , 2006, pp. 21-33 .
- F. Cecca, E. Fourcade and J. Azema: The disappearance of the "Ammonitico Rosso" . In: Palaeogeography, Palaeoclimatology, Palaeoecology . tape 99 , 1992, pp. 55-70 .
- A. Farinacci and S. Elmi (Eds.): Rosso Ammonitico Symposium Proceedings . Editioni Tecnoscienza, Rome 1981, p. 602 .
- P. Grandesso: Gli strati a Precalpionellipi del Titoniano ei loro rapporti con il Rosso Ammonitico Veneto . In: Mémoires Science Géologie (University of Padova) . tape 32 , 1977, pp. 3-14 .
- HC Jenkyns: Origin of red nodular limestones (Ammonitico Rosso, Knollenkalke) in the Mediterranean Jurassic: a diagenetic model . In: KJ Hsü and HC Jenkyn, Pelagic Sediments: on Land and under the Sea (Eds.): Special Publication Number 1 of the International Association of Sedimentologists . tape 1 , 1974, p. 249-271 .
- L. Martire, P. Clari, F. Lozar and G. Pavia: The Rosso Ammonitico Veronese (Middle-Upper Jurassic of the Trento Plateau): a proposal of lithostratigraphic ordering and formalization . In: Rivista Italiana di Paleontologia e Stratigrafia . tape 112 , 2006, p. 227-250 .
- A. Préat, S. Morano, J.-P. Loreau, C. Durlet and B. Mamet: Petrography and biosedimentology of Rosso Ammonitico Veronese (middle-upper Jurassic, north-eastern Italy) . In: Facies . tape 52 , 2006, p. 265-278 .
Individual evidence
- ^ TA Catullo: Saggio di zoologia fossile delle provincie Venete . In: Tipografia del Seminario . tape 5-348 . Padova.
- ↑ Notice on the calcaire rouge ammonitifère de l'Italie . In: Commissione italiana di stratigrafia della Società geologica italiana (ed.): Carta geologica d'Italia - 1: 50,000: catalogo delle formazioni (Fascicolo VI) . S.EL.CA, Florence 2007, p. 140-144 .
- ^ G. Dal Piaz: Voce "Rosso Ammonitico di Verona" . In: Lexique Stratigraphique International, 1 Europe (11 Italie) . 87, Congr. Geol. Int. Mexico, Paris 1956.
- ^ A. Farinacci and S. Elmi (eds.): Rosso Ammonitico Symposium Proceedings . Technoprint, Rome 1981, p. 602 .
- ^ RJ Dunham: Classification of carbonate rocks according to depositional texture . In: WE Ham - Classification of carbonate rocks (Ed.): Amer. Assoc. Petrol. Geol. Memoir . tape 1 , 1962, pp. 108-121 .
- ↑ G. Muttoni, E. Erba, DV Kent and V. Bachtadze: Mesozoic Alpine facies deposition as a result of past latitudinal plate motion . In: Letters to Nature . tape 434 , 2005, pp. 59-63 .
- ↑ A. Préat et al .: Facies . In: Petro Journal . vol. 52, no 2, 2006, p. 265-278 , doi : 10.1007 / s10347-005-0032-2 .
- ^ F. Cecca et al.: The disappearance of the Ammonitico Rosso . In: Palaeogeography, Palaeoclimatology, Palaeoecology . vol. 99, 1992, pp. 55-70 .
- ↑ M. Farabegoli et al .: M. Bivera Formation, an atypical Middle Triassic Rosso Ammonitico facies from Southern Alps, Italy . In: Giornale di Geologia, ser. 3 ° . vol. 462. Bologna 1984, p. 33-46 .
- ^ L. Martire et al .: The Rosso Ammonitico Veronese (Middle-Upper Jurassic Jurassic of the Trento plateau): a proposal of lithostratigraphic ordering and formalization . In: Rivista Italiana di Paleontologia e Stratigrafia . vol. 112, no 2, 2006, p. 227-250 .
- ↑ A. Luke Eder: The Biancone & Rosso Ammonitico facies of the northern plateau Trento (Dolomites, Southern Alps, Northern Italy) . In: Ann. Naturhist. Mus. Vienna, Series A . vol. 113. Vienna 2011, p. 9-33 .
- ↑ Bernard Balusseau and Élie Cariou: moyen Sur l'âge des séries you Jurassique supérieur et du Djebel Zaress (Tunisie) . In: Geobios . vol. 16, no 1.Lyon 1983, p. 117-123 .