Moltrasio Formation

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Moltrasio Formation
Stratigraphic range: Middle Sinemurian-Lower Pliensbachian
~196–188 Ma
Calcare di Moltrasio Campo dei Fiori.JPG
Outcrop
TypeGeological formation
Unit ofMonte Generoso Basin
Sub-unitsOsteno Outcrop
Underlies
Overlies
Lithology
PrimaryLimestone
Location
Coordinates46°00′N 9°06′E / 46.0°N 9.1°E / 46.0; 9.1Coordinates: 46°00′N 9°06′E / 46.0°N 9.1°E / 46.0; 9.1
Approximate paleocoordinates33°12′N 15°36′E / 33.2°N 15.6°E / 33.2; 15.6
RegionLombardy
Country Italy
Type section
Named forMoltrasio
Named byAntonio Stoppani[1]
Year defined1857
Moltrasio Formation is located in Italy
Moltrasio Formation
Moltrasio Formation (Italy)

The Moltrasio Formation also known as the Lombardische Kieselkalk Formation is a geological formation in Italy. This Formation mostly developed in the Lower or Middle Sinemurian stage of the Lower Jurassic, where on the tectonic activity modified the current marine and terrestrial habitats.[2] 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.[2] This was mostly due to the post-Triassic crisis, that was linked locally to tectonics.[3] The Moltrasio Formation is considered a continuation of the Sedrina Limestone and the Hettangian , and was probably a shallow water succession, developed on the passive margin of the westernmost Southern Alps.[3][4] It is known due to the exquisite preservation observed on the Outcrop in Osteno, where several kinds of marine biota have been recovered.[5]

Fossils[]

Exceptional fossilization[]

Apart from the Eocene of Monte Bolca, the Sinemurian of Osteno is the only fossil deposit in Italy in which soft bodies are preserved. The Osteno site was discovered in 1964. It was recovered from a series of 6 metres (20 ft) package of fine laminated, gray, spongiolitic, micritic limestone.[6] Coroniceras bisulcatum allowed to date the outcrop as the Bucklandi zone, lower Sinemurian.[6] The outcrop is a good documentation of a particularly complete fauna and flora of the Lower Jurassic which is not exactly common in the Southern Alps.[6] The Osteno outcrop, part of the formation, is worldwide known due to the exceptional preservation of mostly marine biota, including rare fossilized components, helping to understand the ecosystems of the local Sinemurian margin of the .[7] The high local variety of fossils found is most likely due to unique conditions of preservation, where phosphatized soft tissues have not been observed in any fish or polychaetes, but they are common in crustaceans (33%) and also occur in a smaller percentage of teuthids (14%).[8] Soft part preservation through phosphatization in this deposit includes the muscles and branchia of Crustaceans, fish tissues, and the digestive tracts of , polychaetes, and nematodes. These fossils are interpreted as having been preserved in a stagnant, restricted basin with anoxic conditions likely within the sediment pore waters.[5]

Nematoida[]

Genus Species Material Location Notes Images

Eophasma[9][5][6]

Eophasma jurasicum

  • A complete specimen

Osteno Outcrop.[9]

A nematode, type member of the family Eophasmidae inside Desmoscolecida.[10] A rare find, since nematode fossils are absent in most Mesozoic marine rocks.[9]

Eophasma jurasicum.JPG

Annelida[]

Genus Species Material Location Notes Images

[11][5][6]

Melanoraphia maculata

  • A nearly complete specimen

Osteno Outcrop.[11]

A polychaete, member of the group with incertade sedis assignation. This polychaete was probably an open swimmer more than a subtrate dweller.[11]

Melanoraphia maculata.JPG

Crustacea[]

Genus Species Material Location Notes Images

Aeger[12][13][5][6]

  • Aeger foesteri
  • Aeger muensteri
  • Aeger robustus
  • Aeger rostrospinatus
  • Aeger elongatus
  • Aeger macropus
  • Multiple specimens, complete and incomplete

Osteno Outcrop.[13]

A decapod, type member of the family Aegeridae. This genus is the most abundant local crustacean, and was a shrimp-like creature that was probably necrophagous.[13]

Aeger foersteri.JPG

Coleia[12][14][5][15][16][6]

  • Coleia vialiii
  • Coleia medilerranea
  • Coleia cf. antiqua
  • Coleia pinnnai
  • Coleia popeyei
  • Multiple complete specimens

Osteno Outcrop.[13]

A decapod, type member of the family Coleiidae. Probably a bottom dweller predatory crustacean.[14]

Coleia viallii osteno.JPG

[12][14][5][16][6]

  • Pseudoglyphea amylochelis
  • Multiple complete specimens

Osteno Outcrop.[13]

A decapod, member of the family . Probably a bottom dweller predatory crustacean.[14]

Mecochirus[12][17][14][5][16][6]

  • Mecochirus germari
  • Multiple complete specimens

Osteno Outcrop.[13]

A decapod, member of the family Mecochiridae. Rather rare compared to other local crustacean genera.

[12][17][14][16][18]

  • Palaeastacus meyeri
  • Multiple complete specimens

Osteno Outcrop.[13]

A decapod, member of the family Erymidae. The species was originally included in the genus Eryma as E. meyeri, although the specimens reveal morphological characters diagnostic of Palaeastacus.[18]

Eryma[12][17][14][16][18][19]

  • Eryma sinemuriana
  • Multiple complete specimens

Osteno Outcrop.[13]

A decapod, type member of the family Erymidae. The species was originally identified as Pustulina sinemuriana.[18]

Xiphosurida[]

Genus Species Material Location Notes Images

[20]

  • Ostenolimulus latus
  • A nearly complete specimen

Osteno Outcrop.[20]

A horseshoe crab, member of the family Limulidae. This genus represents the oldest Jurassic limulid and only the second xiphosuran known from Italy.[20] Also indicates that this family were a diverse and widespread clade during the Jurassic.[20]

Thylacocephala[]

Genus Species Material Location Notes Images

Ostenocaris[21][5][6][22]

Ostenocaris cypriformis

  • Multiple specimens, complete and incomplete

Osteno Outcrop.[21]

A thylacocephalan, type member of the family Ostenocarididae inside Conchyliocarida.[23] Originally Interpreted as a bizarre Cirriped.[24] Ostenocaris is the most common fossil of the formation, and the main identified thylacocephalan from the formation. In the first interpretations, the genus was shown as a filter-feeding organism, which used the cephalic sac as a burrowing organ to ensure adhesion to the substrate.[24] Based on the presence of Coprolites associated to the genus, with abundant masses of alimentary residues (hooks of cephalopods, vertebrates, remains of Crustacea) in the stomach of these organisms, Ostenocaris cypriformis was probably a necrophagous organism, and the cephalic sac can be tentatively interpreted as being a burrowing organ employed during the search for food, or as an organ of locomotion with intrinsic motility.[25]

Ostenocaris cypriformis.JPG

Cephalopoda[]

Genus Species Material Location Notes Images

Arietites[5][6]

  • Arietites bucklandi
  • Shells

Osteno outcrop.[5][6]

An ammonitidan, type member of the family Arietitidae inside Psiloceratoidea. The main ammonite identified locally.

Coroniceras[5][16][6]

  • Coroniceras bisulcatum
  • Shells

Osteno outcrop.[5][6]

An ammonitidan, member of the family Arietitidae inside Psiloceratoidea. It was less common than other ammonites, although index for some locations.

Oxynoticeras[5][6]

  • Oxynoticeras oxynotum
  • Shells

Osteno outcrop.[5][6]

An ammonitidan, type member of the family Oxynoticeratidae inside Ammonitida. It was not the most abundant ammonite, but was rather common.

Angulaticeras[5][16][6]

  • Angulaticeras sp.
  • Shells

Osteno outcrop.[5][6]

An ammonitidan, member of the family Schlotheimiidae inside Psiloceratoidea. It was not the most abundant ammonite, but was rather common.

[5][16][6]

  • Ectocentrites sp.
  • Shells

Osteno outcrop.[5][6]

An ammonitidan, member of the family Lytoceratidae inside Lytoceratina. It was not the most abundant ammonite, but was rather common.

[5][26][27][16][6]

  • Ostenoteuthis siroi
  • A complete specimen with soft tissue

Osteno outcrop.[5][6]

A , type member of the family Ostenoteuthidae. A unique group of coeloids, only found at this location. Coleoids with ten arms each bearing pairs of hooks, Ostenoteuthis measure between 18 and 30 cm length.[27]

Ostenoteuthis siroi.jpg

[27][6]

  • Uncinoteuthis cuvieri
  • A complete specimen with soft tissue

Osteno outcrop.[5][6]

A , member of the family Ostenoteuthidae. A unique group of coeloids, only found at this location.[27]

Uncinoteuthis cuvieri.jpg

Echinoderms[]

Genus Species Material Location Notes Images

[16][6]

  • Palaeocoma milleri
  • Multiple specimens

Mount Campo dei Fiori.[6]

An ophiuridan, member of the family Ophiodermatidae inside . Extant tropical species like Ophioderma are benthic predators and scavengers that show the same short spines seen in Palaeocoma.[6]

Palaeocoma milleri 34.jpg

Hemichordata[]

Genus Species Material Location Notes Images

[28]

Megaderaion sinemuriense

  • A nearly complete specimen with soft tissue

Osteno Outcrop.[28]

An acorn worm, member of the family Harrimaniidae inside Enteropneusta. It was a large sized member of its family. This genus probably lived linked to sand bottoms, where it made burrows to hide and find food.[28]

Chondrichthyes[]

Genus Species Material Location Notes Images

[16][6]

Ostenoselache stenosoma

  • Multiple specimens

Osteno Outcrop.[16]

An , type member of the family inside Elasmobranchii. A unique genus of shark, only found in the Osteno Formation. With an elongated eel-shaped morphology, the specimens found measure at least 240 mm in length, with a neurocranium with a long, complex rostrum.[16] It has been suggested it was an animal able to produce electric shocks, probably to kill prey.[16]

Ostenoselache stenosoma.JPG

Squaloraja[29][16]

Squaloraja polyspondyla

  • Multiple specimens

Osteno Outcrop.[16]

A chimaerid, type member of the family Squalorajidae inside . This genus belongs to a lineage of ray-like chimaeras.

Squaloraja polyspondyla.JPG

[29]

Myriacanthidae indet

  • Multiple specimens

Osteno Outcrop.[16]

A chimaerid, member of the family inside Chimaeriformes.

Hybodontiformes[29]

Hybodontiformes indet

  • Multiple specimens

Osteno Outcrop.[16]

A shark, member of the family Hybodontiformes.

Palaeospinax[30][16]

Palaeospinax pinnai

  • Multiple specimens

Osteno Outcrop.[16]

A Shark, type member of the family Palaeospinacidae inside Synechodontiformes. Open water swimmer.

Actinopterygii[]

Genus Species Material Location Notes Images

Cosmolepis[16][31][6]

Cosmolepis ornatus

  • Multiple specimens

Osteno Outcrop.[31]

A primitive actinopterygiian, member of the order Palaeonisciformes. A late surviving representative of the family.

[16][31][6]

Pteroniscus sp.

  • Multiple specimens

Osteno Outcrop.[31]

A primitive actinopterygiian, member of the order Palaeonisciformes. A complicated genus, whose modern status is rather dubious.

Peripeltopleurus[16][31][6]

Peripeltopleurus sp.

  • Multiple specimens

Osteno Outcrop.[31]

A primitive actinopterygiian, member of the family Peltopleuridae inside Neopterygii. A genus related with the Epicontinental deposition

Dapedium[16][31][6]

Dapedium sp.

  • Multiple specimens

Osteno Outcrop.[31]

A primitive actinopterygiian, type member of the family Dapediidae inside Holostei. Probably a Coral Environment wanderer.

Furo[16][31][6]

Furo sp.

  • Multiple specimens

Osteno Outcrop.[31]

A primitive actinopterygiian, type member of the family inside . Open water swimmer, probably forming schools.

Pholidophorus[16][31][6]

Pholidophorus bechei

  • Multiple specimens

Osteno Outcrop.[31]

A primitive actinopterygiian, type member of the family Pholidophoridae inside Teleostei. Open water swimmer, probably forming schools. It is the main fish recovered on the formation.

Pholidophorus NT.jpg

Pholidolepis[16][31][6]

Pholidolepis sp.

  • Multiple specimens

Osteno Outcrop.[31]

A primitive Actinopterygiian, member of the family Pholidophoridae inside Teleostei. Open water swimmer, probably forming schools.

Sarcopterygii[]

Genus Species Material Location Notes Images

Undina[5][6]

Undina (Holophagus) cf. gulo

  • Scales

Osteno Outcrop.[31]

A Coelacanth, member of the family Latimeriidae inside Coelacanthiformes. Isolated scales of coelacanths analogous to the genus Holophagus are quite frequent on the Osteno deposits. A series of teeth can also be identified to this genus.

Undina gulo.jpg

Plants[]

Genus Species Material Location Notes Images

[32][6]

Equisitites bunburyanus

  • Stems

Osteno Outcrop.[31]

A Horsetail, member of the family Equisetaceae inside Equisetales. A freshwater-related plant, that grew as fast as modern bamboo on tropical settings.

Pachypteris[32][6]

Pachypteris cf. rhomboidalis

  • Fronds

Osteno Outcrop.[31]

A tree fern, member of the family Umkomasiaceae inside Peltaspermales. Fronds of large tree ferns, related to humid ecosystems.

Otozamites[32][6]

  • Otozamites bunburyanus
  • Otozamites sp.
  • Fronds

Osteno Outcrop.[31]

A spermatopsidan, member of the family Bennettitales inside . Cycad-like flora, common on dry settings.

Zamites[32][6]

Zamites sp.

  • Fronds

Osteno Outcrop.[31]

A spermatopsidan, member of the family Bennettitales inside . Cycad-like flora, common on dry settings.

Bennettitales Zamites Wedel.jpg

Williamsonia[32][6]

Williamsonia sp.

  • Fronds

Osteno Outcrop.[31]

A spermatopsidan, member of the family Bennettitales inside . Cycad-like flora, common on dry settings.

Williamsonia life restoration - MUSE.jpg

Pagiophyllum[32][6]

  • Pagiophyllum sp. A
  • Pagiophyllum sp. B
  • Fronds

Osteno Outcrop.[31]

A coniferophytan, member of the family Araucariaceae inside Pinopsida.

Brachyphyllum[32][6]

  • Brachyphyllum sp. A
  • Brachyphyllum sp. B
  • Brachyphyllum sp. C
  • Fronds

Osteno Outcrop.[31]

A coniferophytan, member of the family Cheirolepidiaceae inside Pinopsida.

See also[]

References[]

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