Calcare di Sogno
Stratigraphic range: Lower Toarcian-Late Bajocian
~
TypeGeological formation
Sub-unitsLivello a Pesci
UnderliesFormazione delle Radiolariti
OverliesCalcare di Domaro, Calcare di Morbio, Unnamed limestones[note 1]
ThicknessTypically 120–140 m (390–460 ft)
East and west 70–100 m (230–330 ft)
Lithology
PrimaryMarl, marly limestone & abundance of clay
Secondary: Alternation of marly limestones and marls, presence of graded Chalcudites
OtherLimestones with nodules of flint & subordinate marls
Location
Coordinates45°48′N 9°18′E / 45.8°N 9.3°E / 45.8; 9.3
Approximate paleocoordinates33°24′N 18°54′E / 33.4°N 18.9°E / 33.4; 18.9
RegionLecco Province
Country Italy
Type section
Named forSogno
Named byGaetani & Poliani
Calcare di Sogno is located in Italy
Calcare di Sogno
Calcare di Sogno (Italy)
Calcare di Sogno is located in Lombardy
Calcare di Sogno
Calcare di Sogno (Lombardy)

The Calcare di Sogno ("Sogno Limestone"; also known as the Sogno Formation) is a geological formation in Italy, dated to roughly between 182-169 million years ago and covering the Lower Toarcian-Late Bajocian stagess of the Jurassic Period in the Mesozoic Era.[1] Thallatosuchian remains are known from the formation, as well fishes and other taxa.[2]

Description

During the Early Jurassic, concretely towards the Toarcian, the Lombardy Basin became a relatively deep, fully pelagic area, located between the so called Lugano High, at the west, and the Trento Plateau to the east, with several troughs and palaeohighs (West to east: Monte Nudo Trough, Lugano High, Generoso Trough, Corni di Canzo High, Albenza Plateau, Monte Cavallo High, Sebino Trough and Botticino High).[3] The formation is characterized by a disposition of regional deposition equivalent to the German Posidonia Shale, with a benthonic setting and deposition trends, mostly populated by marine fauna.[4] The environment of the formation was related to a marginal marine deposit, with probably epicontinetal deposition from near land environments, being connected to the central European seas and the North African currents of the Toarcian.[5] The formation is linked with the Toarcian Anoxic Event, that is measured in the “Fish Level”, that is also the most fossiliferous section.[6]

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.[7] 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.[8] As the Sogno Formation was deposited mostly on a Pelagic setting, influenced by both the European and African bioregions, taxa of several provenance mix on this layers. 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.[9] The overall structure of this microtaxa assemblage trends to suggest a correlation with the biohorizon seen in coeval layers in the Lusitanian Basin, where is observed a common trend in the Western Tethys of north-south migration pathway for several organisms, including calcareous nannoplankton and ammonites.[9]

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 Basins), as local result of the Lower Toarcian Jenkyns Event, indicating changues in ocean acidification and fertility rather than temperature.[10]

Fossil content

Ichnofossils

Genus Species Location Material Type Origin Notes Images

Planolites[7]
  • Planolites isp.
  • Colle di Sogno

Cylindrical burrows

Pascichnia

  • Polychaetes

Burrow-like ichnofossils referred to vermiform deposit-feeders. Sometimes considered a junior synonym of Palaeophycus.[11]
Planolites fossil

Molluscs

GenusSpeciesStratigraphic positionMaterialNotesImages

Bositra[1][4]
  • Bositra buchii
  • All the Formation

Shells

A posidoniid ostreoidan. The habitat and mode of life of Bositra has been debated for more than a century. There have been different interpretations, such as a pseudoplanktonic organism,[12] a benthic organism related to open marine floor, where it was the main inhabitant of the basinal settings, and a hybrid mode, where it has a life cycle with holopelagic reproduction controlled by the change on Oxygen levels, and even a chemosymbiotic lifestile, related to the large crinoid rafts, being the main "Safe conduct" to evade anoxic events. All the opinions along the years led to a large study in 1998, where the size/frequency distribution, the density of growth thanks to the lines related to the shell size and the position of the redox boundary by total organic carbon diagrams has revealed that Bositra probably had a benthic mode of life.[13]
Thousands of specimens in one matrix

Collina[1][4]

Collina gemma
  • Mount Brughetto
  • Mount Cornizzolo

Shells

A Dactylioceratidae ammonite. Present and abundant on the Mediterranean Toarcian realm.

Cornaptychus[1][4]

Cornaptychus lythensis
  • Mount Brughetto
  • Mount Cornizzolo
 Shells

An indeterminate ammonite. Some of the specimens found are very fragmentary, making its identification complex.[4]

Dactylioceras[1][4]

Dactylioceras polymorphus
  • Mount Brughetto
  • Mount Cornizzolo
 Shells

Type member Dactylioceratinae family of Ammonites. A common mediterranean genera, found on deposits along all europe.

Harpoceras[1][4]

Harpoceras sp.
  • Mount Brughetto
  • Mount Cornizzolo
 Shells

Type reprensentative genus of the Harpoceratinae ammonite family

Hildaites[1][4]

Hildaites sp.
  • Mount Brughetto
  • Mount Cornizzolo
 Shells

A Hildoceratidae ammonite

Mesodactylites[1][4]
  • Mesodactylites sapphicus
  • Mesodactylites sp.
  • Mount Brughetto
  • Mount Cornizzolo
 Shells

A Nodicoeloceratinae ammonite

Arthropods

Genus Species Stratigraphic position Material Notes Images

?Antrimpos[14][15]

?Antrimpos sp.
  • Mount Cornizzolo

1 complete specimen, MSNM i10852

A Penaeidae Decapodan.

Archaeopalinurus[16]

Archaeopalinurus cfr. A. levis
  • Mount Cornizzolo

Various specimens

A Palinuroidean Decapodan.

Coleia[14]

Coleia cf.banzensis
  • Mount Cornizzolo

15 specimens, complete and incomplete

An Erymidae Decapodan.

?Etallonia[14][15]

?Etallonia sp.
  • Mount Cornizzolo

Single Isolated chelae, MSNM i10855

An Axiidae Decapodan.

Gabaleryon[15]

Gabaleryon garassinoi
  • Mount Brughetto
  • Mount Cornizzolo

Various specimens

A Coleiidae Decapodan. Was confussed with Proeryon hartmanni specimens.

Proeryon[1][14][16]

Proeryon hartmanni
  • Mount Brughetto
  • Mount Cornizzolo

Various specimens

An Erymidae Decapodan Crustacean, common on the mediterranean rocks.

Uncina[17]

 Uncina cf.posidoniae

Uncina alpina
  • Mount Cornizzolo

Isolated chelae, MSNM i10851, il0863, i10864

An Astacidean Decapodan of the family Uncinidae. A large decapodan, with sizes up to 40 cm.

Fish

Genus Species Stratigraphic position Material Notes Images

Leptolepis[2][18]
  • Leptolepis coryphaenoides
  • Leptolepis sp.

Monte Cornizzolo

+100 specimens

Type member of the family Leptolepidae inside Leptolepiformes. It is the most abundant fish found on the formation.

Pachycormus[2][18]
  • Pachycormus sp.

Monte Cornizzolo

Several Especimens

The main member of the family Pachycormidae inside Pachycormiformes. Large sized fish, able to reach near 1.4 m long.

Pholidophorus[2][18]
  • Pholidophorus sp.

Monte Cornizzolo

Several Especimens

Type member of the family Pholidophoridae inside Pachycormiformes. A small sized fish, mostly related to marine deposits, associated with various predatory behaviours, including coeloids and Crocodrylomorphs.

Crocodyliformes

Genus Species Location Material Notes Images

cf.Pelagosaurus[2]

cf. Pelagosaurus sp.
  • Monte Cornizzolo

Various specimens MSNM V4012, MSNM V4013.

A Thalattosuchian marine crocodrylomorph of the family Teleosauridae.The specimens found where of small size, with several characters such as opened neurocentral vertebral sutures and non sutured caudal pleurapophyses, that led to expeculate a possible juvenile or subadult status.

Flora

Several plant leaves and fragments of wood were not identified.[18]

Genus Species Stratigraphic position Material Notes Images

Ginkgo[14][18]
  • Ginkgo digitata
  • Mount Brughetto
  • Mount Cornizzolo

Leaves

Affinities with the Ginkgoaceae. Arboreal plants related to the modern Ginkgo species.

Pagiophyllum[14][18]
  • Pagiophyllum kurri
  • Mount Brughetto
  • Mount Cornizzolo

Leaves

Affinities with the Cheirolepidiaceae and Araucariaceae. Arbustive to arboreal plants with several leaf morphotypes, probably from nearshore environments.

See also

Notes and references

Notes

  1. ↑ Bioturbed hazel-gray limestones in planar layers of about 20 cm, with concentration of gray flint and gray & reddish marls, along with calcareous marl.[1]

References

  1. 1 2 3 4 5 6 7 8 9 10 SGN (2000). "Carta Geologica d'Italia 1:50.000 – Catalogo delle Formazioni (Fascicolo I)". Quaderni, Serie III, del SGI. 7 (1): 22–31. Retrieved 10 May 2022.
  2. 1 2 3 4 5 Delfino, M.; Dal Sasso, C. (2006). "Marine reptiles (Thalattosuchia) from the Early Jurassic of Lombardy (northern Italy)". Geobios. 39 (2): 346–354. doi:10.1016/j.geobios.2005.01.001. hdl:2318/79280. S2CID 128423512. Retrieved 10 May 2022.
  3. ↑ Gaetani, M. (2010). "From Permian to Cretaceous: Adria as pivotal between extensions and rotations of Tethys and Atlantic Oceans" (PDF). Journal of the Virtual Explorer. 36 (5): 13–24. doi:10.3809/jvirtex.2010.00235. Retrieved 10 May 2022.
  4. 1 2 3 4 5 6 7 8 9 Gaetani, Maurizio; Poliani, Giuseppe (1978). Il Toarciano ed il Giurassico medio in Albenza (Bergamo) (84 ed.). Milan: Riv. It. Pal. Strat. pp. 349–382. Retrieved 10 May 2022.
  5. ↑ Gaetani Escursione, M.; Erba, E. (1990). "Il Bacino Lombardo: un sistema paleo alto/fossa in un margine continentale passivo durante il Giurassico" (PDF). Congr. Naz. Soc. Geol. It. 75 (2): 1–23. Retrieved 10 May 2022.
  6. ↑ Channell, J. E. T.; Casellato, C. E.; Muttoni, G.; Erba, E. (2010). "Magnetostratigraphy, nannofossil stratigraphy and apparent polar wander for Adria-Africa in the Jurassic–Cretaceous boundary interval". Palaeogeography, Palaeoclimatology, Palaeoecology. 293 (1): 51–75. doi:10.1016/j.palaeo.2010.04.030. Retrieved 10 May 2022.
  7. 1 2 Erba, E.; Gambacorta, G.; Visentin, S.; Cavalheiro, L.; Reolon, D.; Faucher, G.; Pegoraro, M. (2019). "Coring the sedimentary expression of the early Toarcian Oceanic Anoxic Event: new stratigraphic records from the Tethys Ocean". Scientific Drilling. 26 (4): 17–27. doi:10.5194/sd-26-17-2019. hdl:2434/698406. S2CID 210961368. Retrieved 10 May 2022.
  8. ↑ Erba, E.; Cavalheiro, L.; Dickson, A. J.; Faucher, G.; Gambacorta, G.; Jenkyns, H. C.; Wagner, T. (2022). "Carbon-and oxygen-isotope signature of the Toarcian Oceanic Anoxic Event: insights from two Tethyan pelagic sequences (Gajum and Sogno Cores-Lombardy Basin, norther Italy)". Newsletters on Stratigraphy. 321 (2): 451–477. doi:10.1127/nos/2022/0690. hdl:2434/923620. S2CID 246990063. Retrieved 10 May 2022.
  9. 1 2 Visentin, S.; Erba, E. (2021). "High-resolution calcareous nannofossil biostratigraphy across the Toarcian Oceanic Anoxic Event in Northern Italy: clues from the Sogno and Gajum Cores (Lombardy Basin, Southern Alps)". Rivista Italiana di Paleontologia e Stratigrafia (Research in Paleontology and Stratigraphy). 127 (3): 539–556. Retrieved 10 May 2022.
  10. ↑ Faucher, G.; Visentin, S.; Gambacorta, G.; Erba, E. (2022). "Schizosphaerella size and abundance variations across the Toarcian Oceanic Anoxic Event in the Sogno Core (Lombardy Basin, Southern Alps)". Palaeogeography, Palaeoclimatology, Palaeoecology. 595 (3): 110969. doi:10.1016/j.palaeo.2022.110969. hdl:2434/969201. S2CID 247983702. Retrieved 10 May 2022.
  11. ↑ Keighley, D. G.; Pickerill, R. K (1995). "The ichnotaxa Palaeophycus and Planolites_ historical perspectives and recommendations". Ichnos. 3 (4). doi:10.1080/10420949509386400.
  12. ↑ Hauff, B. (1921). "Untersuchung der Fossilfundstätten von Holzmaden im Posidonienschiefer des Oberen Lias Württembergs". Palaeontographica. 64 (1): 1–42. Retrieved 3 March 2022.
  13. ↑ Röhl, H. J. (1998). "Hochauflösende palökologische und sedimentologische Untersuchungen im Posidonienschiefer (Lias e)[epsilon)] von SW-Deutschland". Tübinger Geowissenschaftliche Arbeiten, Reihe A. 48 (1): 1–189. Retrieved 3 March 2022.
  14. 1 2 3 4 5 6 Garassino, A. (2001). "I crostacei decapodi del Toarciano (Giurassico inferiore) di Sogno (Bergamo, N Italia)". Atti della Società italiana di scienze naturali e del museo civico di storia naturale di Milano. 141 (3): 187–197. Retrieved 10 May 2022.
  15. 1 2 3 Audo, D.; Williams, M.; Charbonnier, S.; Schweigert, G. (2017). "Gabaleryon, a new genus of widespread early Toarcian polychelidan lobsters". Journal of Systematic Palaeontology. 15 (3): 205–222. doi:10.1080/14772019.2016.1167786. S2CID 87613086. Retrieved 10 May 2022.
  16. 1 2 Garassino, A.; Gironi, B. (2005). "Proeryon hartmanni (v. Meyer, 1835)(Crustacea, Decapoda, Eryonoidea) and Archaeopalinurus cfr. A. levis Pinna, 1974 (Crustacea, Decapoda, Palinuroidea) from the Lower Jurassic (Toarcian) of Cesana Brianza-Suello (Lecco, N Italy)". Atti della Società italiana di Scienze naturali e del Museo civico di Storia naturale in Milano. 146 (1): 53–68. Retrieved 10 May 2022.
  17. ↑ Schweigert, G. (2003). "The lobster genus Uncina Quenstedt, 1851 (Crustacea: Decapoda: Astacidea: Uncinidae) form the Lower Jurassic". Stuttgarter Beiträge zur Naturkunde. 332 (4): 1–43.
  18. 1 2 3 4 5 6 Tintori, A. (1977). "Toarcian fishes from the Lombardian basin". Bolletino della Società Paleontologica Italiana. 16 (4): 143–152. Retrieved 10 May 2022.


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