The Saltrio Formation (Also known as the Broccatello Formation) is a geological formation in Italy and Switzerland.[2] It dates back to the Early Sinemurian, and would have represented a near-epicontinental to shallow environment, judging by the presence of marine fauna such as the nautiloidCenoceras.[3][4] 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.[5][6] It´s sandstones have been historically used in construction.[7]
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.[8] 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.[8]
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.[9]
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.[9]
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.[6]
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.[8]
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.[6] 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.[6] The contact between the Main Dolomite and the Saltrio Formation also contains selachian teeth, glauconite and phosphated internal models of ammonites.[10]
Description
Salnova in Saltrio seen from the viewpoint above the quarry
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.[11] 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.[11] 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.[11]
The stratigraphic sequence at the Galli quarry, located at an elevation of approximately 700 meters on the southeastern flank of the ridge above Saltrio, represents one of the most detailed exposures of the Saltrio Formation.[12] This section, reaching a total thickness of about 17 meters, begins atop underlying dolomite and consists of a series of carbonate-dominated layers that reflect varying depositional conditions in a marine setting.[12]
Closeup of the Saltrio Limestones
At the base, a thin dolomitic breccia layer (up to 1 meter thick) contains angular dolomite fragments embedded in a lighter calcareous-dolomitic matrix. This is overlain by a 0.3-meter-thick marly limestone with minor detrital components, displaying an olive-gray to greenish hue and iron oxide stains. Next is a 0.8-meter saccharoidal limestone with sparse marl, glauconite, and quartz grains, followed by a thin (0.1–0.2 meter) reddish-brown clay horizon.[12]
Above this, a 1-meter oolitic limestone features intact and broken ooids in a compact calcareous cement, grading from white to grayish-yellow. This transitions into a 3-meter unit of finely to coarsely detrital marly limestone rich in organic fragments, shifting from gray-pink at the base to yellowish upward, with iron oxide patches. A 0.8-meter calcareous breccia with diverse clasts and ooids follows, exhibiting irregular surfaces.[12]
The upper part includes a 5.5-meter marly limestone with minimal detritus, progressing from gray-ashy at the base to dark smoky due to bituminous content. The sequence concludes with a 5-meter dark limestone containing chert nodules, which become more abundant and marly toward the top, before passing into overlying cherty limestones approximately 200 meters thick.[12]
Paleoenvironment
Nautiloid found in situ on the Salnova Quarry
From the Hettangian to earliest Sinemurian, the western Lombardy Basin featured a notable continental area, wider than previously estimated, characterized by a warm, humid paleoclimate. This region transitioned gradually from Upper Rhaetian shallow-water carbonates to Lombardian siliceous limestones and thick Lowermost Jurassic. Dinosaur fossils from the Saltrio Formation may have been transported from this continental zone or the Arbostora swell in Switzerland, an emerged structural high that divided the subsiding Monte Nudo (east) and Monte Generoso (west) basins. The swell overlay a carbonate platform connected to broader shallow-water areas extending west to southeast, forming a large northern gulf influenced by horst and graben tectonics. Outcrops of "terra rossa" paleosols, including those at Castello Cabiaglio-Orino, west of Saltrio, indicate emerged lands during the Hettangian-Sinemurian, with forests covering the modern Lake Maggiore area, evidenced by large plant fragments in the coeval/younger Moltrasio Formation.[13][14] Recovered flora from Cellina and Arolo on Lake Maggiore's eastern side includes Bennettitales (Ptilophyllum) and Conifers (Pagiophyllum, Brachyphyllum), suggesting inland dry-warm conditions.[15]
Calcareous Sponge-dominated bioherms represent the main facies of the Saltrio Formation
In the early Sinemurian, the Arbostora swell submerged into a shallow open sea (ramp-slope), still bordered south and southwest by emerged land. Dinosaur bones were likely washed into the Monte Nudo gulf during this phase, supported by terrigenous sands from eroded igneous/metamorphic rocks and terrestrial plants in the limestones. While plants (mainly Araucariaceae and Bennettitales leaves/branches) and sands could have been transported by wind or currents, the nearest major continental land was the Sardinia-Corsica mountains, tens of kilometers WNW.[16] Coeval dinosaur footprints in Trento province (160 km east of Saltrio) challenge the traditional atoll model, indicating larger emerged lands for sustaining herbivorous prey and fresh water.[17][18] The Peri-Adriatic platforms likely featured temporary continental bridges connecting Laurasia and Gondwana across central Tethys, enabling migration and potential isolation leading to endemism and dwarfism in terrestrial faunas.[19]
The Saltrio Formation records a shallow open marine depositional environment on a subsiding carbonate platform along the Tethyan passive margin. The 17-meter-thick sequence at the Galli quarry transitions from basal dolomitic breccia (transgressive reworking) through marly and oolitic limestones (higher-energy subtidal shoals) to bituminous, cherty limestones (deeper open-shelf with reduced oxygenation). Faunal assemblages, dominated by cephalopods (ammonites like Asteroceras, nautiloids Cenoceras), bivalves (Cardinia), gastropods (Pleurotomaria), and brachiopods (Lobothyris punctata), indicate normal-marine, oxygenated waters with deepening trends.[12] Fragmentary ichthyosaur remains and bioeroded dinosaur bones (e.g., Saltriovenatorzanellai) suggest transport from nearby terrestrial sources into a proximal slope or ramp, that is, an open subtidal zone some dozen of meters depth reached by the effects of storm waves and with constant bottom currents.[4] The Broccatello sector represents a deeper-water carbonate mound environment formed during episodes of platform drowning, made up of stromatactis limestones originated through early diagenetic processes involving organic matter decay, with abundant sponges, along brachiopods, crinoids, and mollusks, lacking photic-dependent organisms. The facies reflect a benthic, sponge reef-dominated carbonate factory in a deeper setting.[20]
Regional studies link this to platform drowning amid rifting, with carbon-isotope excursions implying volcanic influences and ocean perturbations. A modern analogue is the Bahama Banks, featuring oolitic shoals and lagoons in a subtropical passive-margin setting.[12]
An Ophiuridan of the family Ophiodermatidae. Extant tropical species like Ophioderma are benthic predators and scavengers that show the same short spines seen in Palaeocoma.[32]
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.[33][34] Latter has been confirmed to be Marine Diapsid material.[35]
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
MSNM V3664, very fragmentary and disarticulated skeleton
MSNM V3659, one maxillary or dentary tooth (Referred material)
Cava Salnova quarry
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.[4] 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.[4]
1 2 3 Weishampel, David B; et al. (2004). "Dinosaur distribution (Early Jurassic, Europe)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 532–534. ISBN0-520-24209-2.
↑ Leuzinger, P. (1925). "Geologische Beschreibung des Monte Campo dei Fiori u. der Sedimentzone Luganersee-Valcuvia. Mit 3 Tafeln und 6 Textfiguren. Inaugural-dissertation". Buchdruckerei Emil Birkhäuser & Cie., Basel. 1 (1): 1–177.
↑ Lualdi, A. (1999). New data on the Western part of the M. Nudo Basin (Lower Jurassic, West Lombardy) Tubingen Geowissenschaftliche Arbeiten, Series A, 52, 173-176.
1 2 Dalla Vecchia, F.M. (2001). "A new theropod dinosaur from the Lower Jurassic of Italy, Saltriosaurus". Dino Press. 3 (2): 81–87.
1 2 3 4 Parona, C.F. (1895). "I fossili del Lias di Saltrio in Lombardia; Parte 2: Gasteropodi". Bollettino Società Malacologica Italiana. 18: 161–184.
F. M. Dalla Vecchia. 2001. Terrestrial ecosystems on the Mesozoic peri-Adriatic carbonate platforms: the vertebrate evidence. VII International Symposium on Mesozoic Terrestrial Ecosystems. Asociación Paleontología Argentina, Publicación Especial 7:77-83
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