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 Pliensbachian stage 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
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 Basin Medolo Group and Belluno Basin Soverzene 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 10 cm to more than one metre thick, whereas the clayey levels range between 3 and 40 cm in thickness.
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 1,500 km2. 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.
Biota
Amoebae The presence of the families Centropyxidae and Difflugiidae testifies the presence of a mixed marine-terrestrial depositional system, lacking large bodies of water. Genus/Family Species Provenance Material Notes ImagesCentropyxisC. sp.Tonezza del CimoneIsolated Tests/Shells A testate amoebae, member of the family Centropyxidae inside Arcellinida.DifflugiaD. sp.Tonezza del CimoneIsolated Tests/Shells A testate amoebae, member of the family Difflugiidae inside Arcellinida.PontigulasiaP. sp.Tonezza del CimoneIsolated Tests/Shells A testate amoebae, member of the family Difflugiidae inside Arcellinida.
Foranimifera Genus/Family Species Provenance Material Notes ImagesAgerina A. martana Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Cornuspiridae familyAmmobaculites A. coprolithiformis Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the family Ammomarginulininae.Amijiella A. amiji Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Hauraniidae familyBosniella B. oenensis Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Biokovinidae familyCymbriaella C. Iorigae Monte di Campoluzzo Alpe AlbaIsolated Tests/ShellsA foraminifer of the Hauraniidae familyDuotaxis D. metula Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Duotaxidae familyEverticyclamminaE. praevirgulianaCamporosa Rotzo Monte Cimoncello di Toraro Monte di CampoluzzIsolated Tests/ShellsA foraminifer of the Everticyclamminidae family. Frondicularia F. sp. Bellori Garzon di Scotto Ponte dell`AnguillaraIsolated Tests/ShellsA foraminifer of the family Nodosariinae.Glomospira G. sp. Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the family Ammodiscidae.Haurania H. amiji H. deserta H. ssp. Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte Scandolara Bellori Garzon di Scotto Ponte dell`AnguillaraIsolated Tests/ShellsA foraminifer of the family Hauraniinae.Kristanita K. inflata Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Duotaxidae familyLituosepta L. recoarensis L. compressa L. ssp. Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte Scandolara Bellori Ponte dell`AnguillaraIsolated Tests/ShellsA foraminifer of the Mesoendothyridae family.Meandrovoluta M. asiagoensis Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Monte BaldoIsolated Tests/ShellsA foraminifer of the Cornuspiridae familyMayncina M. termieri Garzon di Scotto Bellori Ponte dell`AnguillaraIsolated Tests/ShellsA foraminifer of the Mayncinidae familyOrbitopsella O. primaeva O. preacursor O. dubari O. circumvulvata O. spp. Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Campomolon Bellori Ponte dell`Anguillara Sega di Noriglio Rotzo Val d'Assa Monte GalloIsolated Tests/ShellsA foraminifer of the Mesoendothyridae family.Ophtalmidium O. concentricum O. sp. Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the family Ophthalmidiidae.Paleomayncina P. termieri Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Planiseptinae family.Pseudocyclammina P. liasica P. spp. Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Pfenderinidae family.Pseudopfenderina P. cf. butterlini Altopiano di Asiago Tonezza del Cimone Altopiano di Folgaria Recoaro Gruppo del Pasubio Monte Baldo Monte ScandolaraIsolated Tests/ShellsA foraminifer of the Pseudopfenderininae family.
Sponges Genus/Family Species Provenance Material Notes ImagesCeractinomorpha indet.IndeterminateVette FeltrineColonial ImprintsA Demosponge.Bauneia B. zignoiMonte Alba Roverè di Velo RoveretoImprintsA Demosponge, member of Chaetetidae.Ellipsactinia E. bonomiVette FeltrineColonial ImprintsA Demosponge, Incertade Sedis.Hexactinellid indet.IndeterminateVette FeltrineColonial ImprintsA Glass sponge.PseudoseptiferP. beneckei P. waehneriLancia refuge Alpe Alba Col Santo Roverè di VeloColonial ImprintsA Demosponge, member of Suberitidae. Monospecific assamblages with encrusting and symbiont forms are found abundantly on lagoonal facies, distributed in several stratigraphic horizons. Stylothalamia S. spp.Vette FeltrineColonial ImprintsA Demosponge, member of Verticillitidae.Tetractinomorpha indet.IndeterminateVette FeltrineColonial ImprintsA Demosponge.
Anthozoa Genus/Family Species Provenance Material Notes ImagesIsastreaI. sp.RotzoColonial ImprintsA Scleractinian Coral, member of Montlivaltiidae. This Coral is often found in the Early Jurassic Tethys range, from the Iberian peninsula to Morocco. Montlivaltia M. trochoidiformis Rotzo Sega di NoriglioColonial ImprintsA Scleractinian Coral, member of Montlivaltiidae.Oppelismilia O. sp.RotzoImprintsA Scleractinian Coral, member of Oppelismiliidae.Pinacophyllum cf. P. sp.RotzoColonial ImprintsA Scleractinian Coral, member of StylophyllidaeStylophyllopsis S. ex gr. rudis RotzoColonial ImprintsA Scleractinian Coral, member of StylophyllidaeSynastrea S. sp.RotzoColonial ImprintsA Scleractinian Coral, member of Synastraeidae
Bryozoa Genus/Family Species Provenance Material Notes ImagesOrbiporaO. circumvulvataSega di NoriglioImprintsA Stenolaematan of the family Aisenvergiidae
Brachiopod Genus/Family Species Provenance Material Notes ImagesGibbirhynchiaG. curvicepsSospiroloShellsA Rhynchonellidan, member of Gibbirhynchiinae. Unusual genus in the Mediterranean region, more common on NW EuropeHesperithyris H. renieri Cornacalda RoveredoShellsA Rhynchonellidan, member of Zeilleriidae. LinguithyrisL. aspasiaBallino SospiroloShellsA Terebratulidan, member of Nucleatidae. Typical Mediterranean region taxon in the PliensbachianLiospiriferinaL. obtusa L. torbolensisCortina d'Ampezzo Sospirolo Torbole RoveredoShellsA spiriferidan, member of Spiriferinidae. LiothyrinaL. norigliensisRotzo Sega di Noriglio CornacaldaShellsA Terebratulidan, member of Terebratellidae.Lobothyris L. punctata Cornacalda RoveredoShellsA Terebratulidan, member of Lobothyrididae.LychnothyrisL. rotzoanaSette Comuni Erbezzo Vajo dell'Anguilla Cimoncello di Toraro