Stratigraphic and palaeontological analyses of the Middle Triassic (latest Anisian–Ladinian) in Muschelkalk facies are performed here to further unravel the palaeogeographic evolution of Sardinia in ...this time-frame. These shallow marine successions reveal a significant palaeontological record comprising facies and marker fossils (ammonoids, bivalves, conodonts, foraminifera etc.) reflecting a regional transgressive episode recorded throughout the West Mediterranean, after the Permian–Triassic biotic crisis. Particularly rich in the Nurra and Sarcidano-Gerrei areas, the facies/fossil record indicates the progressive westward settling of carbonate platforms, and consequently the development of new migration and irradiation routes for Sephardic faunas from the southeast (Palaeotethys) and Alpine faunas (Neotethys) from the northeast. Based on new findings and the revision of palaeontological associations previously reported, comparisons were made with associations of adjacent domains (Balearic Islands, Levantine area), thus refining their palaeoecological distribution and better framing Sardinia as a key area in the palaeogeographic evolution of the West Tethys during the Ladinian.
The Triassic Period is bracketed by two of the ‘big five’ Phanerozoic mass extinctions. Though long viewed as a period of climatic stability, emerging data suggest multiple climatic swings and at ...least one severe ecological crisis. Linking these climatic instabilities with probable causes is hampered by poor age control within the Triassic time scale. Here we present new Re–Os ages for shale sections straddling Middle–Upper Triassic stage boundaries. Nominal Re–Os isochron ages of 236.6 and 239.3Ma for the top and base of the Ladinian (upper Middle Triassic) bring absolute time into the contentious Triassic time scale, and place the beginning of the Late Triassic about 12m.y. earlier than previously assigned. A marked decrease in initial 187Os/188Os in Upper Ladinian shale records input from Wrangellian flood basalts — an instigator in the Carnian (Late Triassic) Pluvial Event and accompanying radiation of key fossil groups (e.g., dinosaurs and calcareous nanoplankton). An absolute time scale is proposed for the Anisian–Ladinian–Carnian boundaries based on Re–Os geochronology.
•New Re–Os ages for sections straddling Middle–Upper Triassic stage boundaries•Nominal Re–Os isochron ages of 236.6–239.3Ma for the Ladinian stage•Decrease (187Os/188Os)i in late Ladinian records input from Wrangellian eruption.
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.
During Middle-early Late Triassic (∼243–235?Ma) a diffuse igneous activity developed in the Southern Alps (Italy). Sparse lava flow and pyroclastic succession remnants of such Southern Alps Triassic ...Igneous Rocks (SATIR) crop out in the Brescian Prealps, the Vicentinian Alps (Recoaro-Schio-Posina), Non Valley, Dolomites and Julian Alps. Plutonic rocks are found in two main plutonic complexes (Monzoni and Predazzo) and a small stock (Cima di Pape). Coeval igneous products can be traced eastward to Austria and Dinarides, for a total length of ∼450?km.
The coeval formation of major late Anisian-late Ladinian carbonate platforms in the subsiding eastern Dolomites, and significant uplift and subaerial erosion in the western Dolomites suggest, for these areas, the occurrence of large-scale strike-slip and extensional tectonics with the development of horst-and-graben structures.
This study reports the first complete review of the SATIR activity, including new mineral chemical data on 14 samples, 61 major and trace element whole rock analyses and 7 Sr-Nd-Pb isotopic ratios for volcanic and plutonic samples from Dolomites (lavas plus Monzoni and Predazzo plutonic rocks) and Vicentinian Alps lavas. Despite the variable post-magmatic modifications, the large areal distribution of the products and their wide spectrum of chemical compositions, these samples show rather common geochemical and mineralogical characteristics and define major and trace element trends that can be associated with nearly close-system magmatic evolution. Minor upper crustal contaminations can be observed in specific cases, mostly in the most differentiated products (SiO2 >70?wt%).
A specific characteristic of SATIR is their calcalkaline to shoshonitic affinity, resembling the derivation from subduction-modified mantle sources, a feature at odds with the coeval strike-slip and extensional tectonics. Geochemical modelling, petrological considerations and geological constraints allow us to propose a model in which the SATIR mantle sources reflect previous subduction metasomatism (likely occurred during Variscan times). These metasomatised mantle sources were reactivated ∼90–100 Myr after the end of the subduction, when continental rifting caused a raise of the geotherms and passive upwelling of asthenospheric mantle.
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•The first complete review of the Middle Triassic magmatism of Southern Alps is presented.•The composition of the igneous rocks indicates subduction-modified mantle sources.•The geochemical message is at odds with the geological evidences of continental rifting stages.
Many Middle-Late Triassic (Ladinian-Carnian) global and local humid climate events that impacted on global palaeontological evolution and mineral distribution have been recorded in the rocks. The ...lacustrine sedimentary sequence of the Yanchang Formation in the Ordos Basin in the northeastern Tethys region may be an important example of control by global humid climate events. As revealed by an established chronostratigraphic framework and the study of organic carbon isotopes, elemental geochemistry and clay minerals, the Chang 7 Member of the Yanchang Formation was deposited in the Ladinian-Carnian, and the high total organic carbon (TOC) and total nitrogen (TN) contents indicate the high productivity of the ancient lake. The observed elemental ratios (Sr/Cu, Rb/Sr and Al2O3/MgO) and high contents of mixed-layer smectite indicate humid climate events in the Chang 73 and Chang 71 members. The increases in weathering degree, surface temperature and terrigenous clastic material input indicate enhancement of the hydrological cycle driven by a warm-humid climate. The arid-wet transitions, the negative excursions of the studied organic carbon isotope and the temperature fluctuations during the deposition of the Chang 73 and Chang 71 members of the Yanchang Formation are consistent with the Carnian humid event (CHE) and Ladinian-Carnian humid interval (L-CHI). The palaeontological diversity and the development of organic shales, turbidity currents and sandy debris flows in the Chang 7 Member may represent the continental sedimentary responses to coeval global humid climate events. The isochronous eruptions of volcanoes around the Ordos Basin may have intensified the global greenhouse effect and become an important factor driving the multi-stage humid climate events in the Ordos Basin.
•The chronostratigraphic framework of the Middle-Late Triassic in the Ordos Basin has been established.•The organic carbon isotope excursion of the CHE and L-CHI occurred in the Ordos Basin.•The sedimentary characteristics of the Chang 7 Member suggest the response to the global humid climate events.•The isochronous eruptions of volcanoes around the Ordos Basin may have intensified the global greenhouse effect.
Our knowledge of the diversity and evolution of South American Triassic pseudosuchians has greatly improved in the past 15 years, due to new discoveries, but also to the revision of several ...historically important specimens. One of the earliest descriptions of pseudosuchians from the Triassic of Brazil stems from the classic work of Huene from the first half of the 20th century, who described several species, including such influential taxa as Rauisuchus tiradentes or Prestosuchus chiniquensis, which have recently been reviewed. The more poorly known proposed second species of Prestosuchus, P. loricatus, is the focus of the present work. The original material included some elements of the axial skeleton (cervical and caudal vertebrae, ribs, osteoderms) and the hindlimb (ischia, calcaneum, metatarsus), collected from the Dinodontosaurus Assemblage Zone of the Chiniquá area, west of São Pedro do Sul. “Prestosuchus” loricatus shows numerous differences to P. chiniquensis, including the shape of cervical neural spines, presence of epipophyses on the cervical vertebrae, presence of a pit in the iliac articulation of the ischium, lack of longitudinal furrows in the dorsolateral surface of the ischial shafts, the more slender calcaneal tuber and a less pronounced ventral pit in the calcaneum, and is thus referred to a new genus, Schultzsuchus gen. nov. Phylogenetic analysis indicates an early branching position within Poposauroidea for Schultzsuchus, making it the oldest known member of this clade in South America.
The early Ladinian lacustrine ecosystem of the Chang 7 Member in the Ordos Basin was proposed as the earliest known Mesozoic-type, trophically multileveled lacustrine ecosystem after the end-Permian ...mass extinction (EPME). However, limited evidence of higher-order trophic levels represented by predatory fish has made this conclusion elusive. In this study, we investigated the external morphology, food inclusions, and geochemical composition of 54 vertebrate coprolites from organic-rich lacustrine sediments of Chang 7 Member, Yanchang Formation, in the Bawangzhuang section, Tongchuan City, Shaanxi Province, China. These coprolites were identified as seven morphotypes in three groups: three heteropolar spiral forms, two amphipolar spiral forms, and two non-spiral forms. Preserved inclusions (fish scales, bone fragments, teeth) indicated that the producers of these coprolites were piscivorous animals. Compared with coprolites previously researched, all coprolites described herein were inferred to be produced by fish: three heteropolar types of spiral coprolites derived from three types of hybodonts, two amphipolar spiral coprolites from coelacanth or Saurichthys with simple spiral valves, and non-spiral coprolites from at least two predatory actinopterygians. Thus, the biodiversity of the lacustrine paleoecosystem, particularly that of predators with upper trophic levels, was substantially enriched. The existence of large carnivorous predators of different taxa as apex predators in a trophically multileveled (at least six levels) lacustrine ecosystem indicates that the early Ladinian lacustrine ecosystem of the Ordos Basin marks the rebuilding of the top-predator trophic structure in the lacustrine ecosystem after the EPME.
•The most detailed coprolite record from the early Ladinian of Ordos Basin, China.•Diverse large carnivorous predators with varying dietary habits are retrieved.•The first Mesozoic-type, trophically multileveled (> 6) lacustrine ecosystem.•Rebuilding the top-predator trophic structure in the paleolake after the EPME.
The Yanchang Formation was deposited during the Middle Triassic in a vast lacustrine basin in the modern Ordos Basin and is a main target for hydrocarbon exploration in Central China. It is divided, ...based on sedimentary cycles and lithology, into the Chang 10 (the oldest) to Chang 1 (the youngest) members. During the deposition of the Chang 7 Member, the Ordos lake system reached its maximum depth and large volumes of organic-rich sediments were deposited. The evolution of the Ordos Basin sedimentary system during this phase is, however, not completely understood, and uncertainty still exists as for the chronostratigraphy of Chang 7 Member. We acquired palynological markers and palynofacies and a high-resolution δ13Corg record through the entire Chang 7 Member, and a ID-TIMS 206Pb/238U date of 240.95 ± 0.033 Ma from a volcanic ash bed in the middle of this Member. These imply that the maximum deepening phase of the lacustrine system was during the earliest Ladinian. Evidence of marine influence in the Ordos Basin at that time and comparison to the sea-level oscillations observed in Western Tethys suggest that a global eustatic rise and highstand may have played a role in determining lake-level variations.
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•We report a zircon age of 240.950 ± 0.033 Ma from the middle portion of Chang 7 Member that indicates an early Ladinian.•The identified palynological assemblage also supports a late Middle Triassic age for Chang 7 Member.•The maximum expansion of the Ordos lake was probably influenced by the early Ladinian maximum in eustatic sea level.
A new species of the actinopterygian fish genus Saurichthys is described on the basis of several specimens from the Sceltrich beds (Meride Limestone Formation) of the UNESCO World Heritage area of ...Monte San Giorgio. The new species shows among other characters, unsegmented lepidotrichia in all fins and elongated and wide paired fins, suggesting a different adaptation for swimming and catching preys with respect to other Saurichthys species of Monte San Giorgio. Phylogenetic analysis suggests that the new species is closely related to the Saurorhynchus species group. The new finding adds further knowledge to the plasticity and functional adaptations of the genus Saurichthys, which was one of the most successful actinopterygians of the Triassic.
