Dinosaurs diversified in two steps during the Triassic. They originated about 245 Ma, during the recovery from the Permian-Triassic mass extinction, and then remained insignificant until they ...exploded in diversity and ecological importance during the Late Triassic. Hitherto, this Late Triassic explosion was poorly constrained and poorly dated. Here we provide evidence that it followed the Carnian Pluvial Episode (CPE), dated to 234-232 Ma, a time when climates switched from arid to humid and back to arid again. Our evidence comes from a combined analysis of skeletal evidence and footprint occurrences, and especially from the exquisitely dated ichnofaunas of the Italian Dolomites. These provide evidence of tetrapod faunal compositions through the Carnian and Norian, and show that dinosaur footprints appear exactly at the time of the CPE. We argue then that dinosaurs diversified explosively in the mid Carnian, at a time of major climate and floral change and the extinction of key herbivores, which the dinosaurs opportunistically replaced.
The Late Triassic Carnian Pluvial Episode (CPE) was a time of biological turnover and environmental perturbations. Within the CPE interval, C-isotope and sedimentary records indicate multiple pulses ...of depleted carbon into the atmosphere-ocean system linked to discrete enhancements of the hydrological cycle. Data suggest a similar cascade of events to other extinctions, including being potentially driven by emplacement of a large igneous province (LIP). The age of the Wrangellia LIP overlaps that of the CPE, but a direct link between volcanism and the pulsed CPE remains elusive. We present sedimentary Hg concentrations from Western Tethys successions to investigate volcanic activity through the previously established CPE global negative C-isotope excursions (NCIEs). Higher Hg concentrations and Hg/TOC are recorded just before and during NCIEs and siliciclastic inputs. The depositional settings suggest volcanic Hg inputs into the basins over the NCIEs rather than increases of Hg drawdown or riverine transport. Differences in Hg and Hg/TOC signals between the basins might be linked to coeval LIP style or the temporal resolution of the sedimentary successions. Overall, our new data provide support for a link between pulses of Wrangellia LIP volcanism, NCIEs, and humid phases that mark the CPE in the Western Tethys.
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.
We investigated for magnetostratigraphy the Rio Nigra and Rio Frommer stratigraphic sections from Alpe di Siusi/Seiser Alm (Dolomites, northern Italy) in order to improve the calibration of the ...Triassic time scale. Both sections are characterized by ammonoid and conodont associations typical of Longobardian (late Ladinian, Middle Triassic) age. Moreover, the Rio Nigra section is constrained by a U-Pb zircon date of 237.77 ± 0.05 Ma. Building on the recently verified Newark-Hartford astrochronological polarity timescale for the Late Carnian–Rhaetian (plus the Hettangian) and through magnetostratigraphic correlations of an updated inventory of Tethyan marine stratigraphic sections from the literature, some of which are provided with U-Pb zircon age constraints, we propose a revised Geomagnetic Polarity Time Scale for the entire Triassic.
•New U-Pb constrained Ladinian magnetostratigraphy improves Triassic chronology.•Using recent magnetostratigraphic data to update the Geomagnetic Polarity Timescale•Updated Geomagnetic Polarity Timescale led to a duration of 50.5 Myr for Triassic.
The Triassic of the Dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms. The ...reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological, palaeobotanical, pedological, and geochemical proxies. The Triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts. During the Triassic, the Dolomites were placed at an intertropical northern latitude of about 16–18° and were generally dominated by dry climate and elevated temperature. At least five pulses toward moister climate are however documented, dated to Early Olenekian, Middle Anisian, Late Ladinian, “Middle” Carnian, and Late Norian times. Within this variable climatic scenario, the carbonate systems record a global evolutionary trend from Late Permian–Early Triassic regional shelves, rich in loose micrites and bio-calcarenites, to Anisian–Ladinian, synsedimentary cemented, steep sided (35–40°), high-relief platforms, and back to Carnian low angle ramps. Moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms, probably because of the reduced space competition by syndepositional cementation structures. The Permo-Triassic boundary extinction dramatically impacted on the calcified organism communities, but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary. The Early Triassic and earliest Anisian were commonly associated with hyperhaline, sometimes evaporitic conditions. Intervals of moister climate and efficient river discharge are however documented by earliest Induan and early Olenekian sediments. The latter terrigenous deposits matched a crisis in the carbonate production. After a return to arid conditions, during the Anisian, a fluctuation toward moister climate developed, associated to a massive continental vegetation cover. The Anisian tectonic activation of the region fragmented the previous carbonate shelf, triggering the development of three generations of fast prograding, but globally backstepping, isolated platforms, recording an increasing role of the synsedimentary cementation. A dry climate dominated the Late Anisian and Early Ladinian interval. At the time, a fast subsidence pulse was associated with platform drowning and basinal anoxia. Only a few aggrading pinnacles were able to survive, providing the nuclei for larger prograding platforms. During a dry climate interval, massive syndepositional cementation generated a major source of carbonate. Carbonate production stayed active through the Ladinian magmatic phase, but the onset of volcanism was associated with a large modification in the platform carbonate facies, which became dominated by automicrites. Moist climate phases are well documented again during the Late Ladinian, followed by a return to dry conditions. The Late Ladinian–Early Carnian platforms prograded toward the eastern Dolomites depocentre, eventually infilling almost the whole of the accommodation space. The middle portion of the Carnian recorded renewed, sharply moist phases, associated with the demise of the rimmed platforms and with the return to loose sediment ramps. At least four separated humid fluctuations can be identified in this Carnian interval alone. Climate then returned to persistent aridity, until the Late Norian moist phase.
The Carnian Pluvial Episode was a phase of global climatic change and biotic turnover that occurred during the early Late Triassic. In marine sedimentary basins, the arrival of huge amounts of ...siliciclastic sediments, the establishment of anoxic conditions, and a sudden change of the carbonate factory on platforms marked the Carnian Pluvial Episode. The sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as, for example, an extinction among ammonoids and conodonts in the ocean, and a turnover of the vertebrate fauna and the flora on land. Multiple negative carbon-isotope excursions were recorded during the Carnian Pluvial Episode in both organic matter and marine carbonates, suggesting repeated injection of 13C-depleted CO2 into the ocean–atmosphere system, but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood. We here review the existing carbon-isotope records and present new data on the carbon-isotope composition of organic carbon in selected sections of the western Tethys realm that record the entire Carnian Pluvial Episode. New ammonoid, conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections. The results provide biostratigraphically constrained composite organic carbon-isotope curves for the Carnian, which sheds light on the temporal and causal links between the main carbon-isotope perturbations, and the distinct environmental and biotic changes that mark the Carnian Pluvial Episode. The carbon-isotope records suggest that a series of carbon-cycle perturbations, possibly recording multiple phases of volcanic activity during the emplacement of the Wrangellia Large Igneous Province, disrupted Carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years.
Quantitative petrologic analysis on carbonates was carried out on stratigraphic sections encompassing the Carnian Pluvial Episode from northwestern Sichuan Basin, South China and eastern Southern ...Alps. The Carnian Pluvial Episode, or CPE, is a period of climate change that occurred between the early Carnian and the beginning of the late Carnian (Late Triassic) and coincides with multiple, sharp negative excursions in the record of δ13C that are thought to be evidence of perturbations of the global carbon cycle. During the CPE, relevant environmental modifications and biological turnovers occurred in the marine realm. In particular, microbial carbonate platforms, that were dominant in northwestern Sichuan Basin and throughout Tethys, underwent widespread demise and the microbial component in shelf carbonate sediments sharply decreased and was replaced by ooid- and skeletal grains. Our results show a Tethys-wide coincidence between this change in the carbonate factory. Most notably, both in eastern and western Tethys microbial carbonate production recovered in the late Tuvalian, and the timing of recovery was not influenced by differences of basin evolution and geodynamic setting that characterize such distant domains.
•Carbonate production synchronously switched from microbial to bioclastic-oolitic at the onset of the CPE in Tethys.•The recovery of microbial carbonate production occurred in the late Tuvalian/early Norian throughout Tethys.•The change of carbonate factory coinciding with CPE may be related to lowering of seawater saturation state.
In the early Late Triassic a period of increased rainfall, named the Carnian Pluvial Event (CPE), is evidenced by major lithological changes in continental and marine successions worldwide. The ...environmental change seems to be closely associated with a negative carbon isotope excursion that was identified in a stratigraphic succession of the Dolomites (Italy) but the temporal relationship between these phenomena is still not well defined. Here we present organic-carbon isotope data from Carnian deep-water stratigraphic sections in Austria and Hungary, and carbonate petrography of samples from a marginal marine section in Italy. A negative 2–4‰ δ13C shift is recorded by bulk organic matter in the studied sections and is coincident with a similar feature highlighted in higher plant and marine algal biomarker carbon-isotope records from the Dolomites (Italy), thus testifying to a global change in the isotopic composition of the reservoirs of the exchangeable carbon. Our new observations verify that sedimentological changes related to the CPE coincide with the carbon cycle perturbation and therefore occurred synchronously within the western Tethys. Consistent with modern observations, our results show that the injection of 13C-depleted CO2 into the Carnian atmosphere–ocean system may have been directly responsible for the increase in rainfall by intensifying the Pangaean mega-monsoon activity. The consequent increased continental weathering and erosion led to the transfer of large amounts of siliciclastics into the basins that were rapidly filled up, while the increased nutrient flux triggered the local development of anoxia. The new carbonate petrography data show that these changes also coincided with the demise of platform microbial carbonate factories and their replacement with metazoan driven carbonate deposition. This had the effect of considerably decreasing carbonate deposition in shallow water environments.
•New δ13CTOC data from Carnian (Late Triassic) sections of the western Tethys basins•A negative δ13CTOC shift always coincides with the onset of the Carnian Pluvial Event.•C-cycle disruption led to the abrupt sedimentological changes observed in the studied basins.
The Carnian Pluvial Episode (Late Triassic) was a time of global environmental changes and possibly substantial coeval volcanism. The extent of the biological turnover in marine and terrestrial ...ecosystems is not well understood. Here, we present a meta-analysis of fossil data that suggests a substantial reduction in generic and species richness and the disappearance of 33% of marine genera. This crisis triggered major radiations. In the sea, the rise of the first scleractinian reefs and rock-forming calcareous nannofossils points to substantial changes in ocean chemistry. On land, there were major diversifications and originations of conifers, insects, dinosaurs, crocodiles, lizards, turtles, and mammals. Although there is uncertainty on the precise age of some of the recorded biological changes, these observations indicate that the Carnian Pluvial Episode was linked to a major extinction event and might have been the trigger of the spectacular radiation of many key groups that dominate modern ecosystems.
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