Panorama of the Rotzo area with several of the Outcrops visible: Tonezza mountain at the left, Val d´Assa cliff in the center-front and Campolongo mountain in the right
The Rotzo Formation (also known in older literature as the Noriglio Grey Limestone Formation) is a geological formation in Italy, dating to roughly between 192 and 185 million years ago and covering the Pliensbachianstage of the Jurassic Period in the Mesozoic Era. Known mostly for being the main formation with recorded Plicatostylidae reefs, yet dinosaur tracks have been reported from the formation.
Paleoenvironment
Succession of the Formation in Vajo dell'Anguilla (Verona Province)
Has been traditionally classified as a Sinemurian-Pliensbachian Formation, but a large and detailed dataset of isotopic 13C and 87Sr/86Sr data, estimated the Rotzo Formation to span only over the Early Pliensbachian, bracketed between the Jamesoni-Davoei biozones, marked in the Loppio Oolitic Limestone-Rotzo Fm contact by a carbon isotope excursion onset similar to the Sinemu-Pliens boundary event, while the other sequences fit with the a warm phase that lasts until the Davoei biozone. A more recent work reinforced this datation, constraining the lowermost levels to 192.30 Ma and the uppermost to 185.99 Ma. The Rotzo Formation represented the Carbonate Platform, being located over the Trento Platform and surrounded by the Massone Oolite (marginal calcarenitic bodies), the Fanes Piccola Encrinite (condensed deposits and emerged lands), the Lombadian BasinMedolo Group and Belluno BasinSoverzene Formation (open marine), and finally towards the south, deep water deposits of the Adriatic Basin. The Pliensbachian Podpeč Limestone of Slovenia, the Aganane Formation & the Calcaires du Bou Dahar of Morocco represent regional equivalents, both in deposition and faunal content.
This formation was deposited within a tropical lagoon environment, similar to modern Bahamas which was protected by oolitic shoals and bars from the open deep sea located to the east (Belluno Basin) and towards the west (Lombardia Basin). It is characterized by a rich paleontological content. It is notable mostly thanks to its great amount of big aberrant bivalves, among which is the genus Lithiotis, described in the second half of the nineteenth century. The unusual shape of Lithiotis and Cochlearites shells, extremely elongated and narrow, characterized by a spoon-like body space placed in a high position, rarely preserved, seems to suggest their adaptation to soft and muddy bottoms with a high sedimentation rate. The Bellori outcrop displays about 20 m of limestones with intercalated clays and marls rich in organic matter and sometimes fossil wood (coal) and amber. The limestones are well stratified, with beds 10cm to more than one metre thick, whereas the clayey levels range between 3 and 40cm in thickness.
An in-situ bed of Pachygervillia from the lower Rotzo Formation
The sedimentary cover of the Southern Alps has been recognized as a well-preserved section of the Mesozoic Tethys' southern continental margin, featuring a horst and graben structure linked to the rifting associated with the opening of the central North Atlantic that in the Late Triassic and Early Jurassic, created elevated blocks separated by troughs. While the western margin (Piedmont and Lombardy) quickly submerged in the Early Jurassic (As seen by the Moltrasio Formation), the eastern regions maintained shallow water sedimentation, including the Friuli and Trento Platforms, this last one latter evolving into a pelagic plateau, and separated from the Lombardian basin by the Garda escarpment fault system.
The Early Jurassic Calcari Grigi Group represents the shallow-water sedimentation phase of the Trento Platform, revealing several sites over an area of about 1,500km2. The continuity of dinosaur tracks from the Hettangian-Pliensbachian interval indicates a stable connection between the Southern Alps' carbonate tidal flats and nearby vegetated lands and freshwater sources, although the exact locations of these lands remain uncertain. Detailed sedimentological studies of the Calcari Grigi Group, particularly the Rotzo Formation, describe it as a shallow subtidal platform with an inner lagoon bordered by oolitic shoals.
The Coste dell'Anglone ichnosite for example, situated on the margin of this lagoon within a sandy barrier complex, was influenced by pioneer plants like Hirmeriellaceae in semi-arid conditions. Sedimentary structures indicate a shallow water tidal environment with heterolithic stratification pointing to steady flows at low current velocities. The presence of dinosaur tracks and supratidal markers suggests repeated subaerial exposure, contrasting with previous interpretations of the site as fully subtidal.
These findings align with the lagoon-barrier island complex scenario, featuring a subtidal ramp gently inclined to the west and an intertidal-supratidal barrier island complex trending approximately N-S, now corresponding to the Mt. Brento-Biaina and Mt. Baldo chains.
Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
The presence of the families Centropyxidae and Difflugiidae testifies the presence of a mixed marine-terrestrial depositional system, lacking large bodies of water.
A Demosponge, member of Suberitidae. Monospecific assamblages with encrusting and symbiont forms are found abundantly on lagoonal facies, distributed in several stratigraphic horizons.
A clam, member of Neomiodontidae. The so-called Eomiodon horizon represents the lower Rotzo Formation, with this genus considered an opportunistic shallow infaunal suspension feeder, and the marker genus for brackish environments.
An oyster, member of Plicatostylidae. On the Rotzo formation this genus become abundant along rootlets, indicative of a very shallow and restricted lagoon or marsh environment.
An oyster, member of Plicatostylidae. A large bivalve, up to 70 cm length. This genus was found to be a bivalve with a byssate juvenile stage that developed different modes of life on the adulthood depending on the individual density and bottom firmness.
A clam, member of Astartidae. Is considered a genus that evolved from shallow burrowing ancestors, becoming a secondarily semi-infaunal edgewise recliner adapted to photosymbiosis.
Local forms are likely derived from giant decapods (probably Erymids). Turning chambers are linked to the behaviour of animals such as Callianassa. The atypical "isp. B" resemble more tunnels done by either Stomatopods or Malacostraca.
A polychaete of the family Dorvilleidae. Unlike the modern counterparts that live in deeper environments, this species is found linked with shallow marine facies
A specimen found in Roverè di Velo, housed in the University of Padua collection under the number 27519 and previously indentified as a marine reptile, was latter found to be a fish lower jaw.
The tracks adscribed share some morphological affinity with those referred to the Ankylosauridae, such as the ichnogenera Metatetrapodus and Tetrapodosaurus, and probably belonged to medium-sized Scelidosaurs or other kind of Thyreophorans.
It wears morphological and morphometrical appearance that suggests relationships with a "prosauropod" trackmaker.
The local footprints may have belonged to a genus similar to Lamplughsaura
Flora
Rotzo Formation nearby land hosted Bahamian-type biomes (San Salvador Island Mangroves in the picture) with nearby "Taxodium swamp"-like coniferous associations dominated by the Pagiophyllum producer
The Rotzo Formation was deposited on a Lagoon on the emerged Trento Platform, leading to a well preserved fossil flora record, collected and studied since the 19th century. The great level of floral fossilization has even allow to discovery fossil amber on the Bellori section. This amber has allowed to determine that the environment was a shallow tropical lagoon, only a few metres deep, closed seawards by oolitic shoals and bars. This levels are dominated by a high abundance of Classopollis sp. (Cheirolepidiaceae), associated with dry and wet climates in coastal areas. The abundance of this group of conifers is also proven by the high presence of cuticles of Pagiophyllum cf. rotzoanum. Beyond this genera, spores are highly diversified, including from Sphenophyta, Selaginellales to Ferns, with abundance (more than 50%) of trilete spores (Deltoidospora), what suggest a good freshwater availability corresponding to a wet climate, proven also by the presence of aquatic miospores of algae such as Botryococcus and Pseudoschizaea. The climate was arid on some seasons with monsoon months. The abundance of marine fauna on this sediments, including fragments of corals, bryozoans, bivalves, echinoids, and foraminifera, suggest transport from brackish lagoons and marshes, probably occurred during storm events. Overall data points to a marshy and/or submerged paleoenvironment, comparable to the present-day Taxodium swamp or cypress swamp and a Bahamian-type marine environment in a rather wet monsoonal climate as in the modern southeastern Asia. The abundant presence of glossy black charcoal little fragments point to wildfires being a consistent local landscape feature.
Amber
The Rotzo Formation records one of the few Early Jurassic assamblages with Amber in the world, the nicknamed "Bellori amber" found near the village of the same name. Made mostly of small droplets of less than 1mm with exceptionally preserved morphology its likely the amber producing plants were likely not stressed or affected by disease. Due to the small size animal inclusion have not been found. However various plant materials, identified "mummified wood" and wood tissue are known. Additionally large amounts of CircumpollesCheirolepidiaceous pollen, and occasional freshwater algae Pseudoschizaea remains are included. Several cuticle fragments are attributed to the araucariaceous or Hirmeriellaceae genus Pagiophyllum. Those lived on a coastal and wet palaeoenvironment similar to the present-day Taxodium swamps with monsoonal seasons as in the modern southern Asia. More recently, an additional outcrop with amber, located in Vajo dell'Anguilla, was recovered, with again samples in thousands of thin filaments.
Affinities with Corystospermaceae. Represents the largest "Seed Fern" Leaf in the fossil record, with leaves up to 70cm, having an habit resembling the extant angiosperm Nypa fruticans.
Affinities with the genus Trichopitys, as probably a member of Karkeniaceae, with strong resemblance with the genus Baiera, lumped in some papers as Baiera lindleyana.
Baiera a taxon that has been said to include Trevisania
Affinities with Araucariaceae or Cheirolepidiaceae. Brachyphyllum tropidimorphyrn shows close resemblance between African and Venetian conifers and its distribution suggests a lowland araucarian forest.
Brachyphyllum kendallianum from the Rotzo Formation
A possible Conifer leaf. Was suggested to have affinities with Czekanowskiales, sometimes found inside Ginkgoopsida, yet recent finds of it associated with the cone genera Sphaerostrobus and Ourostrobus points to a coniferophyte affinity, maybe as a member of Palissyaceae.
Incertae sedis inside Coniferales, initially identified as "Yuccites schimperianus", suggested as a member of its own family, the "Pelourdeaceae". A hygrophytic riparian conifer with herbaceous or shrubby habit.
Affinities with Palyssiaceae. Extinct group conifer leaves with similarities with Sequoia or Amentotaxus. Maybe Includes the species "Taxites vicentina".
↑Broglio Loriga, C.; Neri, C. (1976). "Aspetti paleobiologici e paleogeografici delle facies "Lithiotis" (Giurese inf.)". Rivista Italiana di Paleontologia e Stratigrafia. 82 (1): 651–151.
↑Castellarin, A.; Picotti, V. (1990). "Jurassic tectonic framework of the eastern border of the Lombardian basin". Eclogae Geologicae Helvetiae. 83 (3): 683–700.
↑Fugagnoli, A. (2000-04-01). "First Record Of Everticyclammina Redmond 1964 (E. Praevirguliana N. Sp.; Foraminifera) From The Early Jurassic Of The Venetian Prealps (Calcari Grigi, Trento Platform, Northern Italy)". The Journal of Foraminiferal Research. 30 (2): 126–134. Bibcode:2000JForR..30..126F. doi:10.2113/0300126. ISSN0096-1191.
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123456Petti, F.M.; Avanzini, M.; Antonelli, M; Bernardi, M.; Leonardi, G.; Manni, R.; Mietto, P.; Pignatti, J.; Piubelli, D.; Sacco, E.; Wagensommer, A. (2020). "Jurassic tetrapod tracks from Italy: a training ground for generations of researchers". Tetrapod Ichnology in Italy: The State of the Art. Journal of Mediterranean Earth Sciences. 12 (3): 137–165. Retrieved 3 January 2022.
↑Tekleva, M. V.; Polevova, S. V.; Gavrilova, O. A.; Roghi, G.; Neri, M. (2021-03-01). "Pseudoschizaea sp. from the Early Jurassic of Italy: Fine Structure and Comparison". Paleontological Journal. 55 (2): 224–234. Bibcode:2021PalJ...55..224T. doi:10.1134/S0031030121020155. ISSN1555-6174.
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