Saltrio Formation

The Saltrio Formation (Also known as the Broccatello Formation) is a geological formation in Italy and Switzerland. It dates back to the Early Sinemurian, and would have represented a pelagic or near-epicontinental environment, judging by the presence of marine fauna such as the nautiloid Cenoceras.^[2][3] The Fossils of the Formation were described on the late 1880s and revised on 1960s, finding first marine biota, such as Crinoids, Bivalves and other fauna related to Epicontinental basin deposits.^[4]

Saltrio Formation
Stratigraphic range: Early Sinemurian ~199–196 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
“Salnova” quarry, where most of the fossils come from
Type	Geological formation
Unit of	Calcari Selciferi Lombardi Unit
Underlies	Moltrasio Formation
Overlies	Tremona Formation
Lithology
Primary	Limestone
Location
Coordinates	45.9°N 8.9°E / 45.9; 8.9
Approximate paleocoordinates	33.1°N 14.8°E / 33.1; 14.8
Region	Lombardy
Country	Italy  Switzerland
Type section
Named for	Saltrio
Named by	Antonio Stoppani[1]
Saltrio Formation (Italy) Show map of Italy Saltrio Formation (Lombardy) Show map of Lombardy

Salnova Quarry

Machinery suitable for processing the stone extracted in the Salnova Quarry

The main outcrop of the formation, represents an active private extraction site. The first extraction activities of the famous Saltrio stone give back to the times of the ancient Romans, with modern reports of activity in this quarry since 1400.^[5] In the Monte Oro area, on the southern slope of Monte Orsa, there were numerous trench quarries which were used to extract this precious rock, used both for structural constructions and for the production of artefacts and artistic works. In more recent times the mining activity has been transformed and we have moved from the extraction of stone for construction to the extraction for the production of stabilized and split crushed stone, useful for the production of motorway foundations and mixtures for the production of asphalt. To date it is the only active quarry where Saltrio stone is extracted.^[5]

In today's quarry what is mainly known as the Saltrio Formation emerges, i.e., a group of stratified rocks dating back to the Lower Jurassic. The stratigraphy, however, is much more complex, even if so far no study has focused on this topic. Inside the quarry, Dolomia principale sediment emerges dating back to the Upper Triassic (Norian); yet the succession is dominated by the Saltrio Formation, here 15-20 meters thick.^[6]

Above, the Moltrasio Formation emerges, a greyish-brown limestone composed of biocalcarenite and containing widespread nodules of spongolitic silica. This rock is rarely fossiliferous except in the contact areas between the Formations. At the roof of the Moltrasio Fm, a whitish yellow limestone emerges, again of marine-pelagic origin, where there is a lot of micro-diffused silica within the sediment.^[6]

Since the early 1900s, fossil finds have been known in the Salnova Quarry and in the various quarry sites present in the surroundings of this site. The first written testimonies, and subsequent revisions, are reported starting from the sixties by Giulia Sacchi Vialli. The scholar describes the fossil faunas of Saltrio by listing and detailing various taxa belonging to ammonoids, nautiloids, gastropods, crinoids, brachiopods and bivalves.^[4]

In that period, the great phase of extraction of ornamental stone using manual-mechanical methods had just ended in the quarry. Paleontologists could only recover fossils from the waste flakes near the quarry and therefore the possibility of seeing more specimens was limited to the length of manual operations. In those years, however, the quarry was acquired by Salnova SPA (1969): the purpose of the extracted material, and therefore the extraction method and processing, changed. From classic and manual extraction we move on to the use of heavy mechanical means and extraction with explosives: the moved rubble increases considerably, making it easier to observe other specimens, new lithologies and above all different faunas.^[5]

The fauna present at the base of the Saltrio Formation is condensed and includes ammonoids of species attributed to the entire Upper Sinemurian. The taxa attributable to the Lower Sinemurian found in the Saltrio quarries probably come from the base of the formation or have been reworked.^[4] According to Sacchi-Vialli, the Formation includes taxa indicative of all the biozones between the Bucklandi Zone (Lower Sinemurian) and the Obtusum Zone, and possibly also of the Oxynotum Zone of the Upper Sinemurian, present at the base of the Formation.^[4] The contact between the Main Dolomite and the Saltrio Formation also contains selachian teeth, glauconite and phosphated internal models of ammonites.^[7]

Environment

Nautiloid found in situ on the Salnova Quarry

Since the beginning of the jurassic, from Hettangian to earliest Sinemurian on the western Lombardy Basin there was a notorious continental area that was found to be wider than previously thought, where a warm humid paleoclimate developed.^[8] The basin facies are characterized by a gradual transition from Upper Rhaetian shallow-water carbonates to Lombard siliceous limestone and thick Lower Liassic series.^[9] The Dinosaur Fossils found on the Saltrio formation can have been translated from this area, or alternatively, the Arbostora swell (that was located at the north of the Saltrio formation, on Switzerland).^[9] This was an emerged structural high close to the Saltrio Formation, that caused a division between two near subsiding basins located at Mt. Nudo (East) and Mt. Generoso (West).^[9] It settled over a carbonate platform linked with other wider areas that appear along the west to the southeast, developing a large shallow water gulf to the north, where the strata deposited was controlled by a horst and tectonic gaben.^[9]

The Saltrio layers represent a unique sedimentary environment that is different from both the "Formazione di Saltrio" and the "Saltrio calcarenite" described by earlier researchers. These layers are characterized by being transgressive deposits, meaning they formed as the sea advanced over previously exposed land. The Saltrio deposits show signs of stratigraphic condensation, which refers to slow sediment accumulation over time, often resulting in hardgrounds, surfaces drilled by marine organisms, and the presence of minerals like Glauconite and Phosphorite.^[9] Biologically, these layers are rich in fossils, especially Encrinite (crinoid-rich limestones) and bivalve lumachellas (fossilized bivalve shells). Other marine creatures like cephalopods and brachiopods appear occasionally. Faunas from the condensed Saltrio beds indicate early subsidence in the Hettangian. Additionally, the involutine limestones with a rich ammonite fauna support subsidence during the same period. The sediment composition varies in different areas, often containing reworked material from older rocks.^[9] The Saltrio environment was complex, with different layers showing distinct conditions. In some areas, the Saltrio layers blend with the "Broccatello d'Arzo", a related limestone formation, but they can still be separated based on differences in their structure and fossil content. The region also experienced sedimentary discontinuities, where layers were not deposited continuously, likely due to tectonic activity or submarine erosion.^[9] Overall, the Saltrio paleoenvironment reflects a shallow marine setting with fluctuating sea levels, rich marine life, and periods of sediment reworking and erosion, all influenced by local tectonics.^[9]

Several outcrops of the so-called “terra rossa” paleosoils were also found, including at Castello Cabiaglio-Orino, a dozen of kilometers West of Saltrio.^[10][11] This outcrops show that the emerged areas that on the Hettangian-Sinemurian, the current location of the modern Maggiore Lake were covered with forests, what was proven by the presence of large plant fragments on the Moltrasio Formation.^[8] The plants have been recovered between the locations of Cellina and Arolo (eastern side of Lake Maggiore), from rocks that have been found to be coeval in age to the Saltrio Formation.^[12] The Flora includes genera such as Bennettitales (Ptilophyllum), terrestrial Araucariaceae (Pagiophyllum), and Cheirolepidiaceae (Brachyphyllum), that developed on inland areas with dry-warm conditions.^[12]

The ammonites from the Saltrio Formation allow the formation to be dated to the Early Sinemurian. Animals probably lived in emerged parts of carbonated platform or an area to the northwest, whose presence had never been established. In the early Sinemurian, the Arbostora swell became again a shallow open sea (ramp-slope), still surrounded South and South-West by emerged land. The dinosaur bones where washed on this period, flowed into a gulf of the Mt. Nudo basin, where they became fossilized. The latter possibility was suggested by Lualdi (1999), in which he analyzed the local geology based on the presence of terrestrial plants and terrigenous content (sands from igneous or metamorphic rocks exposed to sub-aerial erosion) in the limestones.^[12] Terrestrial plants are essentially represented by leaves and small branches of Araucariaceans and Bennettitales, the typical flora of the early Mesozoic. However, plants and sand (which are not abundantly referred) can be carried by wind and ocean currents. Also, according to the most current paleogeographic maps, truly continental land located closer these Jurassic times lower were the Mountains of Sardinia, Corsica, distanced many tens of kilometers WNW.^[13] Coeval and slightly younger in age, large dinosaurs, carnivorous and herbivorous, were present as shown in various footprints of the lower Jurassic (Hettangian-Sinemurian) in the province of Trento, around 160 kilometres (99 mi) east of Saltrio, which changed the traditional view of the palaeoenvironments and paleogeography of the region, considered a tropical sea with small islands of the atoll type.^[14] Fossil footprints and tracks are preserved in tidal carbonates deposited in a relatively narrow carbonated platform in Trento, flanked to the east and west by relatively deep marine basins. Large theropods could not live in an atoll, since large areas had to be emersed to provide food and fresh water, and their herbivorous prey needed land with vegetation.^[15]

"It is more likely that the Peri-Adriatic Platforms worked with temporary continental bridges that connected with Laurasia Gondwana in central Tethis, allowing migration between the two hemispheres and colonization of local coastal habitats. During the marine transgressions, some of these lands were isolated, implicating genetic Mutations in their terrestrial faunas, with typical biological consequences, as endemism and possible dwarfism".^[16]

Invertebrate fauna

Porifera

Porifera
Genus	Species	Material	Location	Notes	Images
Endostoma[17]	E. spp.	Spicules & Imprints	Broccatello of Arzo	A Calcareous sponge, member of the family Endostomatidae inside Calcaronea.
Stellispongia[17]	S. spp.	Spicules & Imprints	Broccatello of Arzo	A Calcareous sponge, member of the family Stellispongiidae inside Calcaronea.
Neuropora[18]	N. cf. undulata	Spicules & Imprints	“Salnova” quarry	A Demosponge, member of the family Neuroporidae inside Axinellida.

Brachiopoda

Rhynchonellata
Genus	Species	Material	Location	Notes	Images
Arzonellina[19]	A. exotica	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Arzonellinidae inside Terebratulida.
Aulacothyris[17]	A. waterhousi	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Zeilleriidae inside Terebratulida.
Cirpa[4][17][20][18]	Cirpa fronto C. variabilis	Shells	Broccatello of Arzo “Salnova” quarry	A Rhynchonellatan, member of the family Wellerellidae inside Rhynchonellida. Identified originally as "Rhynchonella variabilis".
Furcirhynchia[17]	F. cf. melvillei	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Rhynchonellidae inside Rhynchonellida.
Liospiriferina[4][17][20][18]	L. rostrata	Shells	Broccatello of Arzo “Salnova” quarry	A Rhynchonellatan, member of the family Spiriferinidae inside Spiriferinida. Was identified originally as "Spiriferina haasi".
Lobothyris[4][17][20][18]	L. punctata	Shells	Broccatello of Arzo “Salnova” quarry	A Rhynchonellatan, member of the family Lobothyrididae inside Terebratulida. Was identified originally as "Terebratula punctata".
Prionorhynchia[17][19][21]	P. belemnitica P. greppini P. ssp.	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Prionorhynchiidae inside Rhynchonellida.
Rimirhynchia[17]	R. aff. anglica	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Rhynchonellidae inside Rhynchonellida.
Rhynchonella[4][17][20][18]	R. acanthica	Shells	Broccatello of Arzo “Salnova” quarry	A Rhynchonellatan, member of the family Wellerellidae inside Rhynchonellida. Another series of Specimens of uncertain placement.
Rhynchonellina[17]	R. alpina R. ssp.	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Dimerellidae inside Rhynchonellida.
Tetrarhynchia[17]	T. spp.	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Tetrarhynchiidae inside Rhynchonellida. Juvenile forms.
Spiriferina[4][17][20][18]	S. expansa S. rostrata	Shells	Broccatello of Arzo “Salnova” quarry	A Rhynchonellatan, type member of the family Spiriferinidae inside Spiriferinida. It is a rather a complex series of specimens, whose classification is controversial.
Sulcirostra[19]	S. alpina	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Dimerellidae inside Rhynchonellida.
Zeilleria[17]	Z. sarthacensis Z. (Zeilleria) indentata	Shells	Broccatello of Arzo	A Rhynchonellatan, member of the family Zeilleriidae inside Terebratulida.

Bivalves

Bivalvia
Genus	Species	Material	Location	Notes	Images
Astarte[4][18][22]	A. praeobliqua	Shells	“Salnova” quarry	A Clam, type member of the family Astartidae inside Carditida. Some shells identified as Cardium probably belong to this genus.
Avicula[4][18][22]	A. sinemuriensis	Shells	“Salnova” quarry	A Pearl Oyster, member of the family Pteriidae inside Ostreida. Abundant and rather easy to identify.
Calvaentolium[4][18][22]	C. hehlii	Shells	“Salnova” quarry	A Scallop, member of the family Pectinoidae inside Pectinida. It was identified originally as "Pecten (Pseudamusium) hehlii".
Cardinia[4][18][22]	C. hybrida C. similis C. rugosa	Shells	“Salnova” quarry	A Clam, type member of the family Cardiniidae inside Carditida. Epicontinental deposits genus, rather abundant locally. Cardinia rugosa was first discovered on this formation.
Cardium[4][18][22]	C. cf. multicostatum	Shells	“Salnova” quarry	A Clam, member of the family Cardiniidae inside Carditida. Rare locally, with some specimens considered dubious.
Chlamys[4][18][22]	C. textoria	Shells	“Salnova” quarry	A Scallop, member of the family Pectinoidae inside Pectinida. It was identified as "Pecten (Chlamys) textorius".
Fimbria[4][18][22]	F. semireticulata	Shells	“Salnova” quarry	A Clam, member of the family Lucinidae inside Lucinida. Was first identified on the Formation.
Goniomya[4][18][22]	G. verbana	Shells	“Salnova” quarry	A Clam, member of the family Lucinidae inside Lucinida. First identified on the formation.
Gryphaea[4][18][22]	G. arcuata	Shells	“Salnova” quarry	An Oyster, type member of the family Gryphaeidae inside Ostreida. Related with specimens of the Blue Lias Formation.
Lima[4][18][22]	L. (Plagiostoma) stabilei L. (Radula) succincta L. (Radula) valmariannae L. spp.	Shells	Broccatello of Arzo “Salnova” quarry	A File Clam, member of the family Limidae inside Pectinida. Included on the Genus Plagiostoma, the status of the species is rather dubious.
Lucina[4][18][22]	L. ? liasina	Shells	“Salnova” quarry	A Clam, type member of the family Lucinidae inside Lucinida. Uncertain classification due to be based on fragmentary shell remains.
Modiolus[4][18][22]	M. vomer	Shells	“Salnova” quarry	A Mussel, member of the family Mytilidae inside Mytilida. Identified as the genus "Modiola", now junior synonym of Modiolus.
Myoconcha[4][18][22]	M. scabra	Shells	“Salnova” quarry	A Clam, member of the family Pleuromyidae inside Pholadida. Rather rare and controversial genus.
Ostrea[4][18][22]	O. cf. chillyensis	Shells	“Salnova” quarry	An Oyster, type member of the family Ostreidae inside Ostreida. Rather Abundant genus, but lacks specimens enough complete for a formal identification.
Pecten[4][18][22]	P. (Pseudamusium) diblasii P. (Chlamys) subalpinus P. spp.	Shells	Broccatello of Arzo “Salnova” quarry	A Scallop, type member of the family Pectinoidae inside Pectinida. Mistake for other related genera on the deposit, it is among the most abundant local Scallops, although the affinities with the genus Pecten haven't been proved.
Pholadomya[4][18][22]	P. sp.	Shells	“Salnova” quarry	A Clam, type member of the family Pholadomyidae inside Pholadomyida. Mostly incomplete specimens, what makes nearly impossible to assigante a concrete species.
Plagiostoma[4][18][22]	P. giganteum P. spp.	Shells	Broccatello of Arzo “Salnova” quarry	A File Clam, member of the family Limidae inside Pectinida. Identified originally as "Lima (Plagiostoma) gigantea".
Pleuromya[4][18][22]	P. cf. angusta P. saltriensis P. galathea	Shells	“Salnova” quarry	A Clam, type member of the family Pleuromyidae inside Pholadida. Present on most of the deposits of the formation, with P. saltriensis being first discovered on the location.
Sphaeriola[4][18][22]	S. sp.	Shells	“Salnova” quarry	A Clam, member of the family Lucinidae inside Lucinida. Identified originally as "Fimbria (Sphaeriola) sp.".
Terquemia[4][18][22]	T. heberti	Shells	“Salnova” quarry	A Clam, member of the family Prospondylidea inside Pterioida. Is based on a few specimens

Gastropods

Gastropoda
Genus	Species	Material	Location	Notes	Images
Pleurotomaria[17][23]	P. cf. gigas P. sp.	Shells	Broccatello of Arzo “Salnova” quarry. Mount Campo dei Fiori	A Sea Snail, type member of the family Pleurotomariidae inside Pleurotomarioidea.
Trochus[23]	T. sp	Shells	“Salnova” quarry. Mount Campo dei Fiori	A Sea Snail, type member of the family Trochidae inside Trochoidea. Rather common, found associated with Echinoderm debris.

Cephalopoda

Cephalopoda
Genus	Species	Material	Location	Notes	Images
Agassiceras[24]	A. nodosaries	Shells	“Salnova” quarry	An Ammonitidan, member of the family Arietitidae inside Psiloceratoidea.
Arietites[24]	A. bucklandi A. raricostatus A. ceratitoides A. kridioides A. dimorphus A. arnoui A. conybeari A. sauzeanus	Shells	“Salnova” quarry	An Ammonitidan, type member of the family Arietitidae inside Psiloceratoidea. The main Ammonite identified locally.
Cenoceras[4][22][18][25]	C. amorettii C. stoppanii C. intermedium C. arare C. spreaficoi C. breislacki C. striatum C. sturi C. balsamocrivellii	Shells	“Salnova” quarry	A Nautilidan, type member of the family Cenoceratidae inside Nautilidae. The most abundant local cefalophod, Cenoceras was identified as member of the genus Nutilus originally.
Coroniceras[4][24]	C. cf. gmuendense C. rotiformis C. bucklandi C. orbiculatus C. bisulcatus	Shells	“Salnova” quarry	An Ammonitidan, member of the family Arietitidae inside Psiloceratoidea. One of the main ammonites identified along the local dinosaur remains.
Oxynoticeras[24]	O. oxynotum	Shells	“Salnova” quarry	An Ammonitidan, type member of the family Oxynoticeratidae inside Ammonitida. Not the most abundant, but rather common.

Echinoderms

Echinodermata
Genus	Species	Material	Location	Notes	Images
Isocrinus[26]	I. tuberculatus	Multiple ossicles	M. Campo dei Fiori	An Crinoidean, member of the family Isocrininae inside Isocrinida.
Miocidaris[4][22]	M. amalthei	Multiple ossicles	“Salnova” quarry	An Echinoidean, type member of the family Miocidaridae inside Cidaroida. Related to epicontinental to pelagic waters.
Millericrinus[4][22]	M. cf. adneticus	Multiple ossicles	“Salnova” quarry	A Sea lily, type member of the family Millericrinida inside Crinoidea.The main Crinoid identified locally.
Palaeocoma[27]	P. milleri	MSNVI 044/017, dorsally-ventrally oriented ophiuroid	Mount Campo dei Fiori	An Ophiuridan, member of the family Ophiodermatidae inside Ophiodermatina. Extant tropical species like Ophioderma are benthic predators and scavengers that show the same short spines seen in Palaeocoma.[27]
Pentacrinites[4][17][22]	P. tuberculatus P. spp.	Fragments	Broccatello of Arzo “Salnova” quarry	A Sea lily, type member of the family Pentacrinitidae inside Isocrinida. A Pelagic crinoid that live attached to washed wood.

Vertebrate fauna

In 2016 new vertebrate remains were discovered in the Salnova quarry, the remains are being studied to understand if it is a new dinosaur or some other creature.^[28][29] Latter has been confirmed to be Marine Diapsid material.^[30]

Fish

Osteichthyes
Genus	Species	Material	Location	Notes	Images
Notidanoides[7]	N. arzoensis	Isolated Teeth	“Salnova” quarry	A Crassodontidanidae Hexanchiform
Osteichthyes[3]	Indeterminate	Tooth and one jaw fragment	“Salnova” quarry	Non-determined afinitties
Sphenodus[7]	S. helveticus S. cf. alpinus S. stschurowskii	Isolated Teeth	“Salnova” quarry	An Orthacodontidae Synechodontiform

Icthyosaurs

Ichthyosaurians
Genus	Species	Material	Location	Notes	Images
Ichthyosaurus[4][30]	I. spp.	3 Vertebrae Imprints	“Salnova” quarry	A Neoichthyosaurian of the family Ichthyosauridae.
Temnodontosaurus[1][30]	T. cf.platyodon	Isolated Tooth Isolated Vertebrae	“Salnova” quarry	A Neoichthyosaurian of the family Temnodontosauridae. Quoted on the 1880s, specimen that apparently has never been described or figured and whose present repository is unknown

Pterosaurs

Pterosaurs
Genus	Species	Material	Location	Notes	Images
Pterosauria[1][30]	"Pterodactylus" longirostris	Isolated Tooth	“Salnova” quarry	A Pterosaur. Quoted on the 1880s, specimen that apparently has never been fully described or figured and whose present repository is unknown	Dimorphodon, a coeval Pterosaur from UK

Dinosaurs

Theropods
Genus	Species	Material	Location	Notes	Images
Saltriovenator[13][3][2]	S. zanellai[3][2]	MSNM V3664, very fragmentary and disarticulated skeleton MSNM V3659, one maxillary or dentary tooth (Referred material)	“Salnova” quarry.[13]	The oldest known Ceratosaur, falling outside Neoceratosauria, being sister taxa to the maroccan genus Berberosaurus. Saltriovenator is also the largest known Theropod of the Lower Jurassic. It probably was washed into the Sea.[3] Traces on the bones show that the dinosaur carcass remained exposed to the water-sediment interface for months or years, long enough to first be defleshed by mobile scavengers, then colonized by a microbial community that spanned the bone–water interface, which in turn attracted slow-moving grazers and epibionts.[3]	Saltriovenator on an ancient beach

See also

• List of fossiliferous stratigraphic units in Italy
• List of dinosaur-bearing rock formations
• Moltrasio Formation, Sinemurian fossiliferous formation of Italy
• Coimbra Formation, Sinemurian fossiliferous formation of Portugal
• Aganane Formation, Pliensbachian Formation of Morocco