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The latest Triassic was an interval of prolonged biotic extinction culminating in the end-Triassic Extinction (ETE). The ETE is now associated with a perturbation of the global carbon cycle just before the end of the Triassic that has been attributed to the extensive volcanism of the Circum-Atlantic Magmatic Province (CAMP). However, we attribute the onset of declining latest Triassic diversity to an older perturbation of the carbon cycle (delta13Corg) of global extent at or very close to the Norian/Rhaetian boundary (NRB). The NRB appears to be the culmination of stepwise biotic turnovers that characterize the latest Triassic and includes global extinctions of significant marine and terrestrial fossil groups. These biotic events across the NRB have been largely under- appreciated, yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the Late Triassic. Here, we present new and published delta13Corg data from widespread sections (Italy, Greece, ODP, Australia, New Zealand, USA, Canada). These sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the NRB. The disturbance extended across the Panthalassa Ocean to both sides of the Pangaean supercontinent and is recorded in both the Northern and Southern Hemispheres. The onset of stepwise Late Triassic extinctions coincides with carbon perturbation (delta13Corg) at the NRB, indicating that a combination of climatic and environmental changes impacted the biota at a global scale. The NRB event may have been triggered either by gas emissions from the eruption of a large igneous province pre-dating the NRB, by a bolide impact of significant size or by some alternative source of greenhouse gas emissions. As yet, it has not been possible to clearly determine which of these trigger scenarios was responsible; the evidence is insufficient to decisively identify the causal mechanism and merits further study.

The Global Boundary Stratotype Section and Point (GSSP) of the Jurassic–Cretaceous boundary (JKB) is the last among the GSSPs in the Phanerozoic to be chosen. The Berriasian Working Group of the International Subcommission on Cretaceous Stratigraphy decided in 2016 to use the base of the Calpionella alpina Subzone as the primary marker for the formal definition of the JKB. This definition is satisfactorily applicable for near continent, shallow offshore deposits within the Western Tethys, North Atlantic and central-south America. Unfortunately, the primary marker taxon cannot be found in the Pacific and circum-Pacific regions since the distribution of calpionellids is limited to the Western Tethys and neighboring regions. Radiolarians are good candidates for defining the JKB, because they are widespread and can be found both in shallow and deep pelagic sedimentary facies worldwide. We carried out detailed field observations and careful sample collections in a 5-m thick interval around the JKB in the Bosso Valley section (Northern Apennines), which is one of potential candidates for GSSP of the JKB. The Maiolica Formation, which includes the JKB, is characterized by white to light gray, well-bedded micritic limestones with abundant light gray to black chert layers and nodules. In this study, after selection of samples acid-etched in the field, we observed the etched surface with a scanning electron microscope in the laboratory. Our detailed observations revealed that both micritic limestone and chert generally contain abundant radiolarian tests. Most of them in limestones are replaced by calcite, so that it is impossible to isolate radiolarian tests from rock samples with acid treatment. On the other hand, radiolarian tests within chert layers or nodules are too recrystallized to preserve their original surface ornamentation. The best preserved radiolarian tests are included in micritic limestone near chert layer or nodules. Careful and systematic sampling enabled us to get enough material to establish phylogenetic analysis on radiolarians.

Rich and well preserved radiolarian assemblages from the Middle Triassic radiolarian cherts of the Monte Facito Formation, Lagonegro succession (Southern Apennines, Italy), contain new Late Anisian taxa. These radiolarian cherts represent the oldest deep-water sediments of the Lagonegro Basin, representing pelagic conditions since the Late Anisian. Six new species are here described: Tiborella tribullata , Baratuna lucana , Hozmadia lagonegroensis , Hozmadia (?) simplex , Bulbocyrtium multiporatum , Planispinocyrtis curta .

The base of the Rhaetian stage (Norian/Rhaetian boundary, NRB) is still awaiting formal designation by the International Commission on Stratigraphy. At present, only the 4.30-m-thick Steinbergkogel section (Austria) has been proposed as GSSP (Global Stratotype Section and Point) candidate for the base of the Rhaetian. Here we present data from the 63-m-thick Pignola-Abriola section (Southern Apennines, Italy) that we consider an alternative candidate for the Rhaetian GSSP. The Pignola-Abriola basinal section, represented by hemipelagic-pelagic carbonate successions belonging to the Lagonegro Basin, matches all the requirements for a GSSP: 1, it is well exposed with minimal structural deformation; 2, it is rich in age diagnostic fossils (e.g. conodonts and radiolarians); 3, it yields a geochemical record suitable for correlation (e.g. d13Corg/carb); and 4, it has a robust magnetostratigraphy and is correlated with the Newark APTS for age approximation of the NRB and additional Rhaetian bioevents. In the Pignola-Abriola section, we opt to place the NRB at the 44.4 metre level, coincident with a prominent negative shift of ca. 6& of the d13Corg. This level is located 50 cm below the FAD of conodont Misikella posthernsteini s.s within the radiolarian Proparvicingula moniliformis Zone. Both the negative d13Corg shift and the FAD of Misikella posthernsteini occur within Pignola-Abriola magnetozone MPA-5r, at ~205.7 Ma, according to magnetostratigraphical correlation to the Newark APTS. We also illustrate the coeval Mt. Volturino stratigraphical section deposited below the calcite compensation depth (CCD) within the same Lagonegro Basin and characterized by a detailed radiolarian biostratigraphy and strong d13Corg negative shift around the NRB.

Comparison of radiolarian assemblages from marls in the Gorgo a Cerbara section in the Umbria–Marche Basin in central Italy and a siliceous sequence (BB1 section) near Babazhadong in southern Tibet indicates similar faunas comparable to those in the Aurisaturnalis carinatus zone and the Turbocapsula costata zone. Several significant species, Archaeodictyomitra lacrimula (Foreman), A. excellens (Tan Sin Hok), Dictyomitra communis (Squinabol), and Aurisaturnalis carinatus perforatus Dumitrica and Dumitrica-Jud, which are common in older strata, make their last occurrences near the base of the Turbocapsula costata zone in these two areas. Comparison with the Gorgo a Cerbara section provides an accurate age constraint for the siliceous succession in southern Tibet, which contains no fossils other than radiolarians. The comparison indicates a close connection between the western and eastern Tethys during the Barremian to early Aptian. The correlation testifies that the radiolarian zonation in southern Tibet is applicable for the whole Tethys. The siliceous succession in BB1 section encompasses the early Aptian Oceanic Anoxic Event 1a (OAE 1a). The early Aptian OAE 1a is located in the upper part of the Aurisaturnalis carinatus perforatus subzone. The first occurrence biohorizon of the genus Turbocapsula and the evolutionary first appearance biohorizon of T. costata costata (Wu) are useful markers for constraining the OAE 1a in the Tethys.