Calcare di Sogno

Last updated
Calcare di Sogno
Stratigraphic range: Lower Toarcian-Late Bajocian
~182–169  Ma
Type Geological formation
Sub-unitsLivello a Pesci
Underlies Formazione delle Radiolariti
Overlies Calcare 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
Primary Marl, marly limestone & abundance of clay
Secondary: Alternation of marly limestones and marls, presence of graded Chalcudites
Other Limestones with nodules of flint & subordinate marls
Location
Coordinates 45°48′N9°18′E / 45.8°N 9.3°E / 45.8; 9.3
Approximate paleocoordinates 33°24′N18°54′E / 33.4°N 18.9°E / 33.4; 18.9
Region Lecco Province
CountryFlag of Italy.svg  Italy
Type section
Named for Sogno
Named byGaetani & Poliani
Italy relief location map.jpg
Blue pog.svg
Calcare di Sogno (Italy)
Italy Lombardy location map.svg
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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]

Contents

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

GenusSpeciesLocationMaterialTypeOriginNotesImages

Planolites [7]

  • P. 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 Planolites.jpg
Planolites fossil

Molluscs

GenusSpeciesStratigraphic positionMaterialNotesImages

Bositra [1] [4]

  • B. 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 Bositra buchi 45.jpg
Thousands of specimens in one matrix

Collina [1] [4]

C. gemma

  • Mount Brughetto
  • Mount Cornizzolo

Shells

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

Cornaptychus [1] [4]

C. lythensis

  • Mount Brughetto
  • Mount Cornizzolo
Shells

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

Cornaptychus lythensis.jpg

Dactylioceras [1] [4]

D. polymorphus

  • Mount Brughetto
  • Mount Cornizzolo
Shells

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

Dactylioceras group.jpg

Harpoceras [1] [4]

H. sp.

  • Mount Brughetto
  • Mount Cornizzolo
Shells

Type reprensentative genus of the Harpoceratinae ammonite family

Harpoceras NT.jpg

Hildaites [1] [4]

H. sp.

  • Mount Brughetto
  • Mount Cornizzolo
Shells

A Hildoceratidae ammonite

Hildaites fasciculatus.jpg

Mesodactylites [1] [4]

  • M. sapphicus
  • M. sp.
  • Mount Brughetto
  • Mount Cornizzolo
Shells

A Nodicoeloceratinae ammonite

Arthropods

GenusSpeciesStratigraphic positionMaterialNotesImages

?Antrimpos [14] [15]

?A. sp.

  • Mount Cornizzolo

1 complete specimen, MSNM i10852

A Penaeidae Decapodan.

Antrimpos undenarius detail 34.jpg

Archaeopalinurus [16]

A. cfr. A. levis

  • Mount Cornizzolo

Various specimens

A Palinuroidean Decapodan.

Archaeopalinurus laevis Cene.JPG

Coleia [14]

C. cf.banzensis

  • Mount Cornizzolo

15 specimens, complete and incomplete

An Erymidae Decapodan.

?Etallonia [14] [15]

?E. sp.

  • Mount Cornizzolo

Single Isolated chelae, MSNM i10855

An Axiidae Decapodan.

Etallonia raineralberti.JPG

Gabaleryon [15]

G. garassinoi

  • Mount Brughetto
  • Mount Cornizzolo

Various specimens

A Coleiidae Decapodan. Was confussed with Proeryon hartmanni specimens.

Proeryon [1] [14] [16]

P. hartmanni

  • Mount Brughetto
  • Mount Cornizzolo

Various specimens

An Erymidae Decapodan Crustacean, common on the mediterranean rocks.

Proeryon.JPG

Uncina [17]

U. cf.posidoniae

U. 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.

Uncina.JPG

Fish

GenusSpeciesStratigraphic positionMaterialNotesImages

Leptolepis [2] [18]

  • L. coryphaenoides
  • L. sp.

Monte Cornizzolo

+100 specimens

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

Leptolepis NT.jpg

Pachycormus [2] [18]

  • P. 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.

Pachycormus.jpg

Pholidophorus [2] [18]

  • P. 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.

Pholidophorus NT.jpg

Crocodyliformes

GenusSpeciesLocationMaterialNotesImages

cf. Pelagosaurus [2]

cf. P. 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.

Pelagosaurus BW.jpg

Flora

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

GenusSpeciesStratigraphic positionMaterialNotesImages

Ginkgo [14] [18]

  • G. digitata
  • Mount Brughetto
  • Mount Cornizzolo

Leaves

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

Ginkgo digitata 2.jpg

Pagiophyllum [14] [18]

  • P. kurri
  • Mount Brughetto
  • Mount Cornizzolo

Leaves

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

Pagiophyllum rotzoanum.JPG

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]

Related Research Articles

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<span class="mw-page-title-main">Moltrasio Formation</span> Geological formation in Italy and Switzerland

The Moltrasio Formation also known as the Lombardische Kieselkalk Formation is a geological formation in Italy and Switzerland. This Formation mostly developed in the Lower or Middle Sinemurian stage of the Lower Jurassic, where on the Lombardian basin tectonic activity modified the current marine and terrestrial habitats. Here it developed a series of marine-related depositional settings, represented by an outcrop of 550–600 m of grey Calcarenites and Calcilutites with chert lenses and marly interbeds, that recovers the Sedrina, Moltrasio and Domaro Formations. This was mostly due to the post-Triassic crisis, that was linked locally to tectonics. The Moltrasio Formation is considered a continuation of the Sedrina Limestone and the Hettangian Albenza Formation, and was probably a shallow water succession, developed on the passive margin of the westernmost Southern Alps. It is known due to the exquisite preservation observed on the Outcrop in Osteno, where several kinds of marine biota have been recovered.

The Röddinge Formation is a geologic formation in Skåne County, southern Sweden. It is Early Jurassic (Sinemurian-Toarcian) in age. It is a unit with a limited degree of exposure, being identified mostly by its deposits on the Fyledalen Fault Zone, specially on Kurremölla, where is present the main fossil deposit. It is a unit known mostly for large museum collections and estimated to have a thickness of several hundreds of meters. It is also known for its large iron deposits. It is correlated with the mostly marine Rya Formation of western Skåne County, the Volcanic deposits of the Djupadal Formation and specially the Sorthat Formation of Bornholm. Most likely, the coarse-grained nature of the Röddinge Formation is linked to rapid erosion of a tectonically active hinterland.

The Toarcian extinction event, also called the Pliensbachian-Toarcian extinction event, the Early Toarcian mass extinction, the Early Toarcian palaeoenvironmental crisis, or the Jenkyns Event, was an extinction event that occurred during the early part of the Toarcian age, approximately 183 million years ago, during the Early Jurassic. The extinction event had two main pulses, the first being the Pliensbachian-Toarcian boundary event (PTo-E). The second, larger pulse, the Toarcian Oceanic Anoxic Event (TOAE), was a global oceanic anoxic event, representing possibly the most extreme case of widespread ocean deoxygenation in the entire Phanerozoic eon. In addition to the PTo-E and TOAE, there were multiple other, smaller extinction pulses within this span of time.

The Breistroffer Event (OAE1d) was an oceanic anoxic event (OAE) that occurred during the middle Cretaceous period, specifically in the latest Albian, around 101 million years ago (Ma).

<span class="mw-page-title-main">Tafraout Group</span> Geological formations in Morocco

The Tafraout Group is a geological group of formations of Toarcian-Aalenian age in the Azilal, Béni-Mellal, Imilchil, Zaouiat Ahansal, Ouarzazate, Tinerhir and Errachidia areas of the High Atlas of Morocco. The Group represents the remnants of a local massive Siliciclastic-Carbonate platform, best assigned to succession W-E of alluvial environment occasionally interrupted by shallow marine incursions and inner platform to open marine settings, and marks a dramatic decrease of the carbonate productivity under increasing terrigenous sedimentation. Fossils include large reef biotas with richness in "lithiotid" bivalves and coral mounts, but also by remains of vertebrates such as the sauropod Tazoudasaurus and the basal ceratosaur Berberosaurus, along with several undescribed genera. While there have been attributions of its lowermost layers to the Latest Pliensbachian, the current oldest properly measured are part of the Earliest Toarcian regression ("MRST10"), part of the Lower-Middle Palymorphum biozone. This group is composed of the following units, which extend from west to east: the Azilal Formation ; the Amezraï Formation ; the Aguerd-nˈTazoult Formation ; the Tafraout Formation & the Tagoudite Formation. They are connected with the offshore Ait Athmane Formation and the deeper shelf deposits of the Agoudim 1 Formation. Overall, this group represents a mixed carbonate-siliciclastic system of several hundred meters thick, dominated by deposits of shallow marine platforms linked to a nearby hinterland dominated by conglomerates. The strata of the group extend towards the central High Atlas, covering different anticlines and topographic features along the mountain range.

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