The Moltrasio Formation also known as the Lombardische Kieselkalk Formation is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

in Italy. 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.Muttoni, G., Erba, E., Kent, D. V., & Bachtadse, V. (2005). Mesozoic Alpine facies deposition as a result of past latitudinal plate motion. Nature, 434(7029), 59-63. Here it developed a series of marine-related depositional settings, represented by an outcrop of 550–600 m of grey

Calcarenite Calcarenite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) sand-size (0.0625 to 2 mm in diameter), carbonate grains. The grains consist of sand-size grains of either corals, shells, o ...

s and

Calcilutite Calcilutite (also known as cementstone) is a type of limestone that is composed of predominantly, more than 50 percent, of either clay-size or both silt-size and clay-size detrital (transported) carbonate grains. These grains consist either of f ...

s with chert lenses and marly interbeds, that recovers the

Sedrina Sedrina is a ''comune'' (municipality) in the Province of Bergamo in the Italian region of Lombardy, located about northeast of Milan and about northwest of Bergamo. As of 31 December 2010, it had a population of 2,559 and an area of .All demo ...

, Moltrasio and Domaro Formations. This was mostly due to the post-Triassic crisis, that was linked locally to tectonics.Jadoul, F., & Galli, M. T. (2008). The Hettangian shallow water carbonates after the Triassic-Jurassic biocalcification crisis: The Albenza Formation in the western Southern Alps. Rivista Italiana di Paleontologia e Stratigrafia, 114(3), 453-470. The Moltrasio Formation is considered a continuation of the Sedrina Limestone and the

Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassi ...

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 Claino con Osteno (Comasco: ) is a '' comune'' (municipality) in the Province of Como in the Italian region of Lombardy, located about north of Milan and about north of Como. It is a small ''comune'' on Lake Lugano, composed of a series of ...

, where several kinds of marine biota have been recovered.Pinna, G. (1985). Exceptional preservation in the Jurassic of Osteno. Philosophical Transactions of the Royal Society of London. B, Biological Sciences, 311(1148), 171-180.

Fossils

Exceptional fossilization

Apart from the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

Monte Bolca Monte Bolca is a lagerstätte near Verona, Italy that was one of the first fossil sites with high quality preservation known to Europeans, and is still an important source of fossils from the Eocene. Geology Monte Bolca was uplifted from the T ...

, 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 package of fine laminated, gray, spongiolitic, micritic

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

.Pinna, G. (2000). Die Fossillagerstätte im Sinemurium (Lias) von Osteno, Italien. In Europäische Fossillagerstätten (pp. 91-136). Springer, Berlin, Heidelberg. '' Coroniceras bisulcatum'' allowed to date the outcrop as the Bucklandi zone, lower

Sinemurian In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian an ...

. 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. 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 Monte Generoso Basin.Tang, C. M. (2002). Osteno: Jurassic Preservation. Exceptional Fossil Preservation: A Unique View on the Evolution of Marine Life, 251. 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%).Wilby, P. R., & Briggs, D. E. (1997). Taxonomic trends in the resolution of detail preserved in fossil phosphatized soft tissues. Geobios, 30, 493-502. Soft part preservation through phosphatization in this deposit includes the muscles and branchia of

Crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

ns, fish tissues, and the digestive tracts of

coleoids Subclass Coleoidea, or Dibranchiata, is the grouping of cephalopods containing all the various taxa popularly thought of as "soft-bodied" or "shell-less" (i.e., octopuses, squid and cuttlefish). Unlike its extant sister group, Nautiloidea, whose ...

polychaetes Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ...

, and

nematodes The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

. These fossils are interpreted as having been preserved in a stagnant, restricted basin with anoxic conditions likely within the sediment pore waters.

Nematoida

Annelida

Crustacea

Xiphosurida

Thylacocephala

Cephalopoda

Echinoderms

Hemichordata

Chondrichthyes

Actinopterygii

Sarcopterygii

Plants

References

{{Reflist Geologic formations of Italy Jurassic System of Europe Early Jurassic Europe Sinemurian Stage Limestone formations Paleontology in Italy Geography of Lombardy