Facies, depositional environment, and palaeoecology of the Middle Triassic Cassina beds (Meride Limestone, Monte San Giorgio, Switzerland)

The Ladinian Cassina beds belong to the fossiliferous levels of the world-famous Middle Triassic Monte San Giorgio Lagerstätte (UNESCO World Heritage List, Canton Ticino, Southern Alps). Although they are a rich archive for the depositional environment of an important thanatocoenosis, previous excavations focused on vertebrates and particularly on marine reptiles. In 2006, the Museo Cantonale di Storia Naturale (Lugano) started a new research project focusing for the first time on microfacies, micropalaeontological, palaeoecological and taphonomic analyses. So far, the upper third of the sequence has been excavated on a surface of around 40m2, and these new data complete those derived from new vertebrate finds (mainly fishes belonging to Saurichthys, Archaeosemionotus, Eosemionotus and Peltopleurus), allowing a better characterization of the basin. Background sedimentation on an anoxic to episodically suboxic seafloor resulted in a finely laminated succession of black shales and limestones, bearing a quasi-anaerobic biofacies, which is characterized by a monotypic benthic foraminiferal meiofauna and has been documented for the first time from the whole Monte San Giorgio sequence. Event deposition, testified by turbidites and volcaniclastic layers, is related to sediment input from basin margins and to distant volcanic eruptions, respectively. Fossil nekton points to an environment with only limited connection to the open sea. Terrestrial macroflora remains document the presence of emerged areas covered with vegetation and probably located relatively far away. Proliferation of benthic microbial mats is inferred on the basis of microfabrics, ecological considerations and taphonomic (both biostratinomic and diagenetic) features of the new vertebrate finds, whose excellent preservation is ascribed to sealing by biofilms. The occurrence of allochthonous elements allows an insight into the shallow-waters of the adjoining time-equivalent Salvatore platform. Finally, the available biostratigraphic data are critically reviewe

Co-occurrence of Neusticosaurus edwardsii and N. peyeri (Reptilia) in the Lower Meride Limestone (Middle Triassic, Monte San Giorgio)

A newly opened excavation in the Cassina beds of the Lower Meride Limestone (Monte San Giorgio UNESCO World Heritage List, Canton Ticino, Switzerland), has yielded a pachypleurosaurid (Reptilia: Sauropterygia) specimen which is identified as Neusticosaurus peyeri. The resulting co-occurrence of N. peyeri and N. edwardsii, the latter so far regarded as the sole species of the genus present in this horizon, challenges the hypothesis of a single anagenetic lineage in Neusticosaurus species from Monte San Giorgio. In addition, it leads to a reconsideration of the phylogenetic inferences about Neusticosaurus evolution in the Monte San Giorgio area. The stratigraphic distribution of the Neusticosaurus species in the Monte San Giorgio basin is updated on the basis of recent find

Integrated Ladinian bio-chronostratigraphy and geochrononology of Monte San Giorgio (Southern Alps, Switzerland)

New biostratigraphic data significantly improve the age assignment of the Ladinian succession of Monte San Giorgio (UNESCO World Heritage List site, Southern Alps, Switzerland), whose world-famous fossil marine vertebrate faunas are now dated to the substage and zone levels. High-resolution single-zircon U-Pb dating was performed using ID-TIMS and chemical abrasion (CA) pre-treatment technique on volcanic ash layers intercalated in the biostratigraphically-defined intervals of the Meride Limestone. It yielded ages of 241.07±0.13Ma (Cava superiore beds, P. gredleri Zone), 240.63±0.13Ma (Cassina beds, P gredleri/P. archelaus transition Zone) and 239.51±0.15Ma (Lower Kalkschieferzone, P. archelaus Zone). Our results suggest that the time interval including the vertebrate-bearing Middle Triassic section spans around 4Myr and is thus significantly shorter than so far assumed. The San Giorgio Dolomite and the Meride Limestone correlate with intervals of the Buchenstein Formation and the Wengen Formation in the reference section at Bagolino, where the Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian was defined. The new radio-isotopic ages of the Meride Limestone are up to 2Myr older than those published for the biostratigraphically-equivalent intervals at Bagolino but they are consistent with the recent re-dating of the underlying Besano Formation, also performed using the CA technique. Average sedimentation rates at Monte San Giorgio are by more than an order of magnitude higher compared to those assumed for the Buchenstein Formation, which formed under sediment-starved pelagic conditions, and reflect prevailing high subsidence and high carbonate mud supply from the adjoining Salvatore/Esino platforms. Finally, the high-resolution U-Pb ages allow a correlation of the vertebrate faunas of the Cava superiore/Cava inferiore beds with the marine vertebrate record of the Prosanto Formation (Upper Austroalpine), so far precluded by the poor biostratigraphic control of the latte

A NEW COELACANTH SPECIMEN WITH ELONGATE RIBS FROM THE MIDDLE TRIASSIC (LADINIAN) KALKSCHIEFERZONE OF MONTE SAN GIORGIO (CANTON TICINO, SWITZERLAND)

A new finding of a coelacanth from the upper Ladinian upper Kalkschieferzone of the Meride Limestone Formation of Monte San Giorgio (UNESCO World Heritage area) is described. It represents the first known coelacanth from the Middle Triassic that undoubtedly bears elongate thin ribs. The incompleteness of the specimen prevents a reliable taxonomic assignment or the erection of a new species, however some characters, mainly scale morphology, are very similar to those of the holotype of Heptanema paradoxum Bellotti, 1857 from the roughly coeval Perledo Formation of Northern Italy. Elongate ribs are not reported in original descriptions of H. paradoxum, however small portion of ribs are visible among the scales of the holotype. Accordingly, the new specimen is tentatively ascribed to Heptanema as Heptanema cf H. paradoxum

Phylogenetic Relationships of the Triassic Archaeosemionotus Deecke (Halecomorphi, Ionoscopiformes) from the 'Perledo Fauna'

The lagerstatten in the Monte San Giorgio have provided excellent fossils representing one of the most important windows to the marine life during the Triassic. Among these fossils, fishes are abundant and extraordinarily well preserved. Most of these fishes represent extinct lineages and were difficult to understand and classify during the early years after discovery. These difficulties usually led to a mixture of species under the same taxonomic name. This is the case of fishes referred to the genus Archaeosemionotus. The name bearing type of A. connectens, the type species of this genus, represents a basal halecomorph, but most other fishes referred to this genus represent basal ginglymodians. Therefore, we conducted this study to clarify the taxonomic status and phylogenetic relationships of A. connectens, which is a member of the family Furidae (Halecomorphi, Ionoscopiformes) representing the second cladistically supported evidence of ionoscopiforms in the Triassic and it is thus one of the two oldest reliable records of this group. Ionoscopiforms have a long stratigraphic range, though their fossil record is rather patchy. In our analysis, the sister taxon of Archaeosemionotus is Robustichthys from the Anisian of China, and they together form a clade with Furo, which is known from several localities ranging from the Early to the Late Jurassic. Other ionoscopiforms are so far known from the Kimmeridgian to the Albian and it is thus evident that recent efforts have concentrated on the later history of the group (Late Jurassic to Cretaceous). The phylogenetic relationships obtained for the Ionoscopiformes do not show a clear palaeobiogeographic pattern, but give important new insights into the origin, divergence date and early history of this clade

Evolution of western Tethyan involute Heterostegina from late Bartonian to the end-Priabonian

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OLIGOCENE CORAL AND ALGAL REEF AND RELATED FACIES OF VALZEMOLA (SAVONA, NW ITALY)

The  terrigenous and carbonate sediments of the transgressive Oligocene cycle of the Tertiary Piedmont Basin outcropping in the area of Valzemola(Savona, western Liguria, Northwest Italy) and which are referable to the Molare Formation are analysed. The terrigenous sequence, represented by breccias, conglomerates and sandstones, overlies with an angular unconformity dolomitic or calcareous-dolomitic lithologies referable to the San Pietro dei Monti Dolomite Formation. These sequences are locally characterized by rich associations of coralline algae and corals, which by providing a stable substrate allowed the development of a true reef build up. Subsequently the bioherm was suffocated by fluvial sandstone and conglomerate. This may be associated with an intensification in the amount of terrigenous material being brought into the basin. A progressive shallowing continues until the introduction of conditions suitable for calcareous deposition in an intertidal or supratidal environment. The analysis of this reef deposit was carried out by examining seven stratigraphic sections. The paleoecological study of the coral fauna and the algal assemblage, the latter characterized by the significant presence either of the genus Lithophyllum, or of Lithothamnion, allowed some hypothesis on the environmental conditions which characterized this sector during the Late Oligocene. Nine different facies could be shown, from those seven directly connected to the reef and two to nearshore environments proving a regressive phase. Facies I: conglomeratic-sandstone representing a stage of colonization in a dominantly terrigenous environment. Facies II: coral framestone, representing a stage of diversification ("an inner reef front" near to the "reef crest"). Facies III: coral bafflestone representing a colonization stage in an "inner reef slope". Facies IV: coral bindstone representing a stage of domination in a "reef crest" environment. Facies V: coral bindstone alternating with floatstone, gives evidence of a colonization stage in a carbonate environment. Facies VI: coral and algae floatstone, representing a facies of accumulated reef debris. Facies VII: coral rudstone, representing an accumulation facies comparable with that of the "rubble & pavement zone" of the back reef. Facies VIII: conglomerates and sands of a shallow marine environment, represent a regressive sequence. Facies IX: massive limestones with undulated-zoned structures, rhizoliths, calcite veins and pisoliths, evidence of an intertidal or supratidal environment