The Calcare di Sogno ("Sogno Limestone"; also known as the Sogno Formation) is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

, dated to roughly between 182 and 169

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

and covering the Lower

Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

-Late

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.9 ±0.8 Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonia ...

stages Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

s of the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

Period in the

Mesozoic Era The Mesozoic Era is the era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of archosaurian reptiles such as the dinosaurs, and of gymnosperms s ...

. Thalattosuchian remains are known from the formation, as well as fish and other taxa.

Description

During the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

, concretely towards the Toarcian, the Lombardy Basin became a relatively deep, fully pelagic area, located between the so-called

Lugano Lugano ( , , ; ) is a city and municipality within the Lugano District in the canton of Ticino, Switzerland. It is the largest city in both Ticino and the Italian-speaking region of southern Switzerland. Lugano has a population () of , and an u ...

High, at the west, and the Trento Plateau to the east, with several troughs and palaeohighs (West to east: Monte Nudo Trough,

Lugano High Lugano ( , , ; ) is a city and municipality within the Lugano District in the canton of Ticino, Switzerland. It is the largest city in both Ticino and the Italian-speaking region of southern Switzerland. Lugano has a population () of , and an u ...

Generoso Trough Monte Generoso (also known as ''Calvagione'') is a mountain of the Lugano Prealps, located on the border between Switzerland and Italy and between Lake Lugano and Lake Como. The western and southern flanks of the mountain lie in the Swiss cant ...

Corni di Canzo High Corni may refer to: Places in Romania * Corni, Botoșani * Corni, Galați * Corni, a village in Cornățelu Commune, Dâmboviţa County * Corni, a village in Bicaz Commune, Maramureș County * Corni, a village in Bodești Commune, Neamţ County * ...

Albenza Plateau Albendazole is a broad-spectrum antihelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, hookworm infection, trich ...

Monte Cavallo High Monte may refer to: Places Argentina * Argentine Monte, an ecoregion * Monte Desert * Monte Partido, a ''partido'' in Buenos Aires Province Italy * Monte Bregagno * Monte Cassino * Montecorvino (disambiguation) * Montefalcione Portugal * Mon ...

, Sebino Trough and Botticino High). The formation is characterized by a disposition of regional deposition equivalent to the German

Posidonia Shale The Posidonia Shale (, also called Schistes Bitumineux in Luxembourg) geologically known as the Sachrang Formation, is an Early Jurassic (Early to Late Toarcian) geological formation in Germany, northern Switzerland, northwestern Austria, souther ...

, with a benthic setting and deposition trends, mostly populated by marine fauna. The environment of the formation was related to a marginal marine deposit, with probably epicontinental deposition from near land environments, being connected to the central European seas and the North African currents of the Toarcian. The formation is linked with the Toarcian Anoxic Event, that is measured in the “Fish Level”, that is also the most fossiliferous section.

Environment

Two cores, the Colle di Sogno and Gajum are among the best sections that recovered the ecological changes in the Pliensbachian-Toarcian Lombardy Basin. Carbon-and oxygen-isotope data calibrated against nannofossil biostratigraphy has shown that the palaeobathymetry of the deposits was about 1000 and 1500 m, being the deepest records of the T-OAE in the western Tethyan region. As the Sogno Formation was deposited mostly in a pelagic setting, influenced by both the European and African bioregions, taxa of several provenances mix in this layer. The Nannofosil assemblage, that ranges from moderate/poor to good decreasing in the Toarcian AOE (drastic decrease in total abundance is observed in the Fish Level), includes the taxa '' Lotharingius'' (''L. hauffii'', ''L. sigillatus'', ''L. crucicentralis'', ''L. velatus''), '' Discorhabdus ignotus'', '' Diductius constans'', '' Carinolithus'' (''C. poulnabronei'', ''C. superbus''), '' Mitrolithus jansae'' and '' Watznaueria sp.1'' in the Gajum Core, while the Sogno Core shows abundance of the genera '' Biscutum'', '' Calyculus'', '' Carinolithus'' and '' Crepidolithus'', whereas '' Bussonius'', '' Diductius'', '' Similiscutum'', '' Parhabdolithus'' and '' Tubirhabdus'' are extremely rare. The overall structure of this microtaxa assemblage trends to suggest a correlation with the biohorizon seen in coeval layers in the

Lusitanian Basin The Lusitanian Basin is a rift Depression (geology), basin remnant located on both the mainland and continental shelf off the west-central coast of Portugal. It covers an area measuring and extends north-south from Porto to Lisbon. The basin var ...

, where a common trend is observed in the Western Tethys of north–south migration pathway for several organisms, including calcareous nannoplankton and ammonites. A local index genus for environment evolution is '' Schizosphaerella spp.'' (specially ''S. punctulata''), showing a lower valve size than in coeval layers on connected basins (Lusitanian and

Paris Basin The Paris Basin () is one of the major geological regions of France. It developed since the Triassic over remnant uplands of the Variscan orogeny (Hercynian orogeny). The sedimentary basin, no longer a single drainage basin, is a large sag in ...

s), as local result of the Lower Toarcian Jenkyns Event, indicating changes in ocean acidification and fertility rather than temperature.

Fossil content

Ichnofossils

Molluscs

Arthropods

Fish

Crocodyliformes

Flora

Several plant leaves and fragments of wood were not identified.

Notes and references

Notes

References

{{DEFAULTSORT:Calcari Grigi Di Noriglio Formation Geologic formations of Italy Jurassic System of Europe Jurassic Italy Toarcian Stage Limestone formations Marl formations Shallow marine deposits Fossiliferous stratigraphic units of Europe Paleontology in Italy Formations