Saltrio Formation | |
---|---|
Stratigraphic range: Hettangian-Sinemurian ~ | |
![]() “Salnova” quarry, where most of the fossils come from | |
Type | Geological formation |
Unit of | Calcari Selciferi Lombardi Unit |
Sub-units |
|
Underlies | Moltrasio Formation |
Overlies | Tremona Formation |
Thickness | 20 m |
Lithology | |
Primary | Fine to compact arenitic limestones |
Location | |
Coordinates | 45°54′N8°54′E / 45.9°N 8.9°E |
Approximate paleocoordinates | 33°06′N14°48′E / 33.1°N 14.8°E |
Region | Lombardy |
Country | Italy, Switzerland |
Type section | |
Named for | Saltrio |
Named by | Taramelli [1] |
The Saltrio Formation (Also known as the Broccatello Formation and Alpe Perino Limestone) is a geological formation in Italy and Switzerland. [2] It dates back to the Latest Hettangian-Early Sinemurian, and would have represented a coastal to shallow environment, judging by the presence of marine fauna such as the nautiloid Cenoceras . [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]
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] 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]
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 sponge spicules, 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]
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]
During the late Hettangian to early Sinemurian, the western Lombardy Basin formed part of the Southern Alps area, passive margin of Adria and formed part of an evolving rift system linked to the western Tethys, where horst-and-graben tectonics created alternating shallow platforms and subsiding troughs. [13] Structural highs such as Monte Campo dei Fiori, the Varese-Arbostora swell, and Monte Nudo defined the basin architecture, producing shallow carbonate platforms, emergent land, and subsiding depocenters. [13] [14] [15] The main inner land was the Malossa-Zandobbio palaeohigh system in the Po Plain, tied with the Saltrio area by a regional belt of positive blocks. [16] This Highs, if assumed as a single unit probably got 1,000-3,000 km² of intermittently exposed terrain. [17] Indicators of subaerial conditions are widespread: at Castello Cabiaglio-Orino, thick "terra rossa" paleosols developed directly above the Rhaetian Zu Limestone, showing rhizoliths, alveolar structures, and meteoric diagenesis, what confirms that large areas of the basin margin were exposed. [13] Palynological assemblages from these horizons indicate Hirmeriellaceae-dominated forests with associated Araucariaceae and Sciadopityaceae, and understory of Lycopodiopsida, Equisetidae and Ferns, as well potential Characeae, adapted to marsh or ponded settings in a Tropical subhumid climate. [13] Large plant fragments in the basal Moltrasio Formation like Bennettitales ( Ptilophyllum ) and Conifers ( Pagiophyllum , Brachyphyllum ) further attest to extensive vegetated landscapes bordering the basin. [13] [18] These emerged lands bordered a gulf-shaped embayment, open northward, where shallow-marine carbonate platforms alternated with rapidly subsiding basins. [19] Towards the Early Sinemurian the Arbostora swell submerged into a shallow open sea (ramp-slope), still bordered south and southwest by emerged land supported by terrigenous sands from eroded igneous/metamorphic rocks and terrestrial plants in the limestones. [13] [20]
Locally the uppermost Hettangian beds are adscribed to the Alpe Perino Limestone, that records the development of a small carbonate platform on the Monte Nudo high, with basal beds of Ostracod-rich mudstones and marls interbedded with plant remains (Castello Cabiaglio-Orino section), reflecting restricted lagoons or marsh-like ponds on the inner platform. [13] [21] Then the facies evolve in repeated shallowing-upward cycles with stromatolitic-rich tidal flats and fossil-rich (gastropods, bivalves, echinoids, Dasycladales, and Foraminifera) shoals, marking a dominance of shallow subtidal to intertidal settings in the Monte Nudo basin margin, with limited terrigenous input but clear evidence of proximity to land. [21] This unit is either part of the "Late Hettangian hypothesis", being a shallower section vs the Saltrio Beds representing later transgressive/drowning deposits or is part of the "Early Sinemurian hypothesis", and Alpe Perino may in part overlap with earliest Saltrio Beds on different tectonic blocks and the two represent slightly diachronous shallow-platform vs. outer-ramp equivalents. [13]
The Saltrio Formation itself records a shallow open marine depositional environment on a subsiding carbonate platform along the passive margin, while shallow intertidal sectors are seen at Castello Cabiaglio-Orino, with reworked Triassic lithoclasts. [13] 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., Saltriovenator zanellai) 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. [22]
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]
Taxa | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Ammobaculites [13] | A. sp. | Castello Cabiaglio-Orino; M. Sasso del Ferro | Tests | Simple agglutinated Ammomarginulininae benthic foraminifera | |
Involutina [13] | I. cf. liassica | Castello Cabiaglio-Orino | Tests | Early Jurassic Involutinidae, typical of outer-platform wackestones | |
Lenticulina [13] | L. sp. | Widespread in Alpe Perino & Moltrasio-Saltrio facies | Tests | Hyaline benthic foraminifera of Nodosariidae; typical in open-subtidal facies | |
Reophax [13] | R. sp. | Alpe Perino | Tests | Simple agglutinated benthic foraminifera of Reophacidae | |
Siphovalvulina [13] | S. sp. | Alpe Perino | Tests | Shallow-subtidal benthic foraminifera of Siphovalvulinidae | |
Vidalina [13] | V. martana | Alpe Perino; Moltrasio-Saltrio facies | Tests | Early Jurassic benthic foraminifera of Involutinidae-like affinity; common on Liassic platforms |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Corynella [22] [23] |
|
| Spicules & Imprints | A Calcareous sponge of the family Endostomatidae. | |
|
| Spicules & Imprints | A Calcareous sponge of the family Endostomatidae. | ||
Stellispongia [23] |
|
| Spicules & Imprints | A Calcareous sponge of the family Stellispongiidae. | |
Neuropora [24] |
|
| Spicules & Imprints | A Demosponge of the family Neuroporidae. A notorious reef developing genus |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Arzonellina [25] |
|
| Shells | A Terebratulidan of the family Arzonellinidae. | |
Aulacothyris [23] |
|
| Shells | A Terebratulidan of the family Zeilleriidae. | ![]() |
|
| Shells | A Rhynchonellidan of the family Wellerellidae. Identified originally as "Rhynchonella variabilis". | ||
Furcirhynchia [23] |
|
| Shells | A Rhynchonellidan of the family Rhynchonellidae. | |
|
| Shells | A Rhynchonellidan of the family Spiriferinidae. Was identified originally as "Spiriferina haasi". | ||
|
| Shells | A Terebratulidan of the family Lobothyrididae. Was identified originally as "Terebratula punctata". | ![]() | |
Prionorhynchia [23] [25] [27] |
|
| Shells | A Rhynchonellidan of the family Prionorhynchiidae. | |
Rimirhynchia [23] |
|
| Shells | A Rhynchonellidan of the family Rhynchonellidae. | |
|
| Shells | A Rhynchonellidan of the family Wellerellidae. | ||
Rhynchonellina [23] |
|
| Shells | A Rhynchonellidan of the family Dimerellidae. | |
Tetrarhynchia [23] |
|
| Shells | A Rhynchonellidan of the family Tetrarhynchiidae. | |
|
| Shells | A Rhynchonellidan of the family Spiriferinidae. | ![]() | |
Sulcirostra [25] |
|
| Shells | A Rhynchonellidan of the family Dimerellidae. | |
Viallithyris [26] |
|
| Shells | A Rhynchonellidan of the family Rhynchonellidae. | |
Zeilleria [6] [23] |
|
| Shells | A Terebratulidan of the family Zeilleriidae. | |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
|
| Imprints | A Cyclostomatidan of the family Cerioporidae. |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
|
| Shells | A Clam of the family Astartidae. Some shells identified as Cardium probably belong to this genus. | ![]() | |
|
| Shells | |||
|
| Shells | A Scallop of the family Pectinoidae. It was identified originally as "Pecten (Pseudamusium) hehlii". | ||
|
| Shells | A Clam of the family Cardiniidae. | ||
|
| Shells | A Clam of the family Cardiniidae. | ||
Entolium [5] |
|
| Shells | A Scallop of the family Pectinoidae. | |
|
| Shells | A Scallop of the family Pectinoidae It was identified as "Pecten (Chlamys) textorius". | ![]() | |
|
| Shells | ![]() | ||
Gresslya [5] |
|
| Shells | A Clam of the family Pleuromyidae. | |
|
| Shells | |||
|
| Shells | An Oyster of the family Gryphaeidae. | ![]() | |
|
| Shells | ![]() | ||
|
| Shells | ![]() | ||
Mactromya [5] |
|
| Shells | An Adapedont of the family Edmondiidae. | |
|
| Shells | A Mussel of the family Mytilidae. Identified as the genus "Modiola", now junior synonym of Modiolus. | ![]() | |
|
| Shells | A Clam of the family Pleuromyidae. | ||
|
| Shells | ![]() | ||
Parallelodon [5] |
|
| Shells | A Clam of the family Parallelodontidae. | |
|
| Shells | A Scallop of the family Pectinoidae. | ![]() | |
|
| Shells | A Clam of the family Pholadomyidae. | ![]() | |
|
| Shells | A File Clam of the family Limidae. Identified originally as "Lima (Plagiostoma) gigantea". | ||
|
| Shells | A Clam of the family Pleuromyidae. | ||
|
| Shells | A Clam of the family Lucinidae. Identified originally as "Fimbria (Sphaeriola) sp.". | ||
|
| Shells | A Clam of the family Prospondylidea. | ||
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Anticonulus [29] |
|
| Shells | A Snail of the family Trochidae. | |
Bathrotomaria [6] |
|
| Shells | A Snail of the family Pleurotomariidae. | |
Coelostylina [29] |
|
| Shells | A Snail of the family Coelostylinidae. | |
Discohelix [22] |
|
| Shells | A Snail of the family Discohelicidae. | ![]() |
Discotoma [6] |
|
| Shells | A Snail of the family Pleurotomariidae. | |
|
| Shells | A Snail of the family Pleurotomariidae. | ![]() | |
Ptychomphalus [6] |
|
| Shells | A Snail of the family Eotomariidae. | |
Pyrgotrochus [6] |
|
| Shells | A Snail of the family Pleurotomariidae. | |
|
| Shells | |||
Trochotoma [6] |
|
| Shells | A Snail of the family Pleurotomariidae. | |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
|
| Shells | An Ammonitidan of the family Arietitidae. | ||
|
| Shells | An Ammonitidan of the family Arietitidae. | ![]() | |
Arnioceras [2] |
|
| Shells | An Ammonitidan of the family Arietitidae. | |
Asteroceras [2] |
|
| Shells | An Ammonitidan of the family Arietitidae. | ![]() |
Aulacoceras [6] |
|
| Phagmocones | A Belemnite of the family Aulacoceratidae. | |
|
| Shells | A Nautilidan of the family Cenoceratidae. Cenoceras was identified as member of the genus Nautilus originally. | ![]() | |
|
| Shells | An Ammonitidan of the family Arietitidae. | ||
Crucilobiceras [12] |
|
| Shells | An Ammonitidan of the family Eoderoceratidae. | |
Eparietites [23] |
|
| Shells | An Ammonitidan of the family Arietitidae | |
Euasteroceras [2] |
|
| Shells | An Ammonitidan of the family Arietitidae | |
Lytoceras [12] |
|
| Shells | An Ammonitidan of the family Lytoceratidae | |
Microderoceras [2] |
|
| Shells | An Ammonitidan of the family Eoderoceratidae. | ![]() |
Nannobelus [6] |
|
| Phagmocones | A Belemnite of the family Belemnitidae. | |
|
| Shells | An Ammonitidan of the family Oxynoticeratidae. | ![]() | |
Paltechioceras [23] |
|
| Shells | An Ammonitidan of the family Echioceratidae. | |
Paracoroniceras [2] |
|
| Shells | An Ammonitidan of the family Arietitidae. | |
Paradasyceras [2] |
|
| Shells | An Ammonitidan of the family Juraphyllitidae. | |
Promicroceras [23] |
|
| Shells | An Ammonitidan of the family Eoderoceratidae. | |
Schlotheimia [12] |
|
| Shells | An Ammonitidan of the family Schlotheimiidae | |
Vermiceras [2] |
|
| Shells | An Ammonitidan of the family Arietitidae. | |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Terebella [22] |
|
| Tubiform structures | A terebellid, member of the family Terebellidae | ![]() |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
|
| Multiple ossicles | A Sea lily of the family Isocrininae. | ||
|
| Spines & Ambulacrum | An Echinoidean of the family Miocidaridae. | ||
|
| Multiple ossicles | A Sea lily of the family Millericrinida. | ![]() | |
|
| MSNVI 044/017, dorsally-ventrally oriented ophiuroid | 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. [34] | ![]() | |
|
| Multiple ossicles | A Sea lily of the family Pentacrinitidae. | ![]() | |
Plegiocidaris [6] |
|
| Spines & Ambulacrum | An Echinoidean of the family Cidaridae. | ![]() |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Notidanoides [10] |
|
|
| A Crassodontidanidae Hexanchiform | |
Indeterminate |
|
| Non-determined afinitties | ||
Sphenodus [10] |
|
|
| An Orthacodontidae Synechodontiform | |
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. [35] [36] Latter has been confirmed to be Marine Diapsid material. [37]
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
|
|
| A Neoichthyosaurian of the family Ichthyosauridae. | ![]() | |
|
|
| 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 | ![]() | |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Indeterminate |
|
| A Pterosaur, referred originally to "Pterodactylus longirostris" | ![]() | |
Genus | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
S. zanellai |
|
| A potential Ceratosaur. 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] | ![]() | |
Potential Dasycladaceae are seen on intertidal facies, while Characeae are seen at the base. [13]
Taxa | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Cayeuxia [13] | C. spp. | Alpe Perino; Castello Cabiaglio-Orino | Imprints | Calcareous green alga of Udoteaceae; typical of shallow subtidal facies | |
Thaumatoporella [13] | T. spp. | Alpe Perino Limestone | Imprints | Encrusting calcified alga, typical of Liassic shallow-marine platforms |
Taxa | Species | Locality | Material | Notes | Images |
---|---|---|---|---|---|
Callialasporites [13] | C. spp. | Castello Cabiaglio-Orino | Pollen | Araucariaceae Conifer | ![]() |
Cerebropollenites [13] | C. macroverrucosus | Castello Cabiaglio-Orino | Pollen | Sciadopityaceae Conifer | ![]() |
Classopollis [13] | C. torosus | Castello Cabiaglio-Orino | Pollen | Cheirolepidiaceae Conifer, dominant palynomorph | |
Concavisporites [13] | C. crassexinius | Castello Cabiaglio-Orino | Spores | Trilete spore of Lycophyte affinity | |
Gliscopollis [13] | C. meyeriana | Castello Cabiaglio-Orino | Pollen | Typical of Jurassic-Cretaceous Cheirolepidiaceae | |
Granulatisporites [13] | G. punctatus | Castello Cabiaglio-Orino | Spores | Trilete spore of Lycopodiales | |
Lycopodiacidites [13] | L. rugulatus | Castello Cabiaglio-Orino | Spores | Trilete spore of Lycopodiaceae | ![]() |
Microreticulatisporites [13] | M. fuscus | Castello Cabiaglio-Orino | Spores | Trilete spore of probable Lycophyte origin | |
Porcellispora [13] | P. longdonensis | Castello Cabiaglio-Orino | Spores | Incertae sedis; affinities with Bryophyta. | |
Uvaesporites [13] | U. argenteaeformis | Castello Cabiaglio-Orino | Spores | Trilete spore of Selaginellaceae. | ![]() |
{{cite journal}}
: CS1 maint: DOI inactive as of August 2025 (link) CS1 maint: url-status (link)