Annachiara Bartolini

Correlating the end-Triassic mass extinction and flood basalt volcanism at the 100 ka level

New high-precision U/Pb geochronology from volcanic ashes shows that the Triassic-Juras- sic boundary and end-Triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial fl ood volcanism in the Central Atlantic Mag- matic Province to <150 ka. This narrows the correlation between volcanism and mass extinc- tion by an order of magnitude for any such catastrophe in Earth history. We also show that a concomitant drop and rise in sea level and negative δ 13 C spike in the very latest Triassic occurred locally in <290 ka. Such rapid sea-level fl uctuations on a global scale require that global cooling and glaciation were closely associated with the end-Triassic extinction and potentially driven by Central Atlantic Magmatic Province volcanism.

Valanginian Weissert oceanic anoxic event

Biotic changes in nannofossils and radiolarians associated with the Valanginian δ 1 3 C anomaly are documented at Ocean Drilling Program Hole 1149B in the Pacific Ocean: they are coeval and similar to those previously documented in the Tethys, suggesting a global perturbation of marine ecosystems. A marked increase in abundance of Diazomatolithus, absence of nannoconids, and a Pantanellium peak characterize the Valanginian δ 1 3 C excursion. Such changes are interpreted as being due to global enhanced fertility and a biocalcification crisis under conditions of excess CO 2 . The occurrence of organic C-rich black shales in the Southern Alps and in the Pacific in the interval corresponding to the δ 1 3 C excursion suggests a Valanginian oceanic anoxic event (OAE). Volcanism of the Parana-Etendeka large igneous province (ca. 132 Ma) was presumably responsible for an increase of CO 2 , triggering a climate change and accelerated hydrological cycling, possibly causing an indirect fertilization of the oceans. Widespread nutrification via introduction of biolimiting metals at spreading ridges could have significantly increased during the Gondwana breakup and simultaneous tectonic events in three separate oceans. There is no paleontological or δ 1 8 O evidence of warming during the Valanginian OAE. On the contrary, both nannofossils and oxygen isotopes record a cooling event at the climax of the δ 1 3 C excursion. Weathering of basalts and burial of organic C-rich black shales were presumably responsible for CO 2 drawdown and establishment of reversed greenhouse conditions.

Carbon isotope stratigraphy and carbonate production during the Early–Middle Jurassic: examples from the Umbria–Marche–Sabina Apennines (central Italy)

Abstract The carbon isotopic signature of carbonates depends on secular variations of organic carbon and carbonate carbon production/burial rates. A decrease in carbonate productivity makes the organic/carbonate carbon ratio unstable up to the point that even minor variations in the organic carbon reservoirs can provoke carbon isotopic shifts. The δ13C positive shifts of the middle Carixian (early Pliensbachian) and the early Bajocian recorded in the Umbria–Marche–Sabina domain represent a good example of this mechanism. Both sedimentology and lithostratigraphy of pelagic platform–basin carbonate systems in this area show that important changes in the source of carbonates correspond to the observed isotopic shifts. The middle Carixian event is in fact well correlatable to the drastic reduction of benthic carbonate production on rift-related intrabasinal highs, which then became pelagic carbonate platforms. The early Bajocian event is concomitant with the beginning of a long hiatus on the pelagic carbonate platforms and with a drop of the biodiversity of calcareous organisms followed by the onset of biosiliceous sedimentation in basins.

Towards accurate numerical calibration of the Late Triassic: High- precision U-Pb geochronology constraints on the duration of the Rhaetian

Numerical calibration of the Late Triassic stages is arguably the most controversial issue in Mesozoic stratigraphy, despite its importance for assessing mechanisms of environmental perturbations and associated biologic consequences preceding the end-Triassic mass extinction. Here we report new chemical abrasion–isotope dilution– thermal ionization mass spectrometry zircon U-Pb dates for volcanic ash beds within the Aramachay Formation of the Pucara Group in northern Peru that place precise constraints on the age of the Norian- Rhaetian boundary (NRB) and the duration of the Rhaetian. The sampled ash bed–bearing interval is located just above the last occurrence of the bivalve Monotis subcircularis, placing this stratigraphic sequence in the uppermost Norian, perhaps ranging into the earliest Rhaetian. Zircon U-Pb dates of ash beds constrain the deposition age of this interval to be between 205.70 ± 0.15 Ma and 205.30 ± 0.14 Ma, providing precise constraints on the age of the NRB. Combined with previously published zircon U-Pb dates for ash beds bracketing the Triassic-Jurassic boundary, we estimate a duration of 4.14 ± 0.39 m.y. for the Rhaetian. This ends a prolonged controversy about the duration of this stage and has fundamental implications for the rates of paleoenvironmental deterioration that culminated in the end-Triassic mass extinction.

Shallow-platform palaeoenvironmental conditions recorded in deep-shelf sediments: C and O stable isotopes in Upper Jurassic sections of southern Germany (Oxfordian-Kimmeridgian)

A high-resolution carbon and oxygen isotope analysis of Late Oxfordian–Early Kimmeridgian deep-shelf sediments of southern Germany is combined with investigation of nannofossil assemblage composition and sedimentological interpretations in order to evaluate the impact of regional palaeoenvironmental conditions on isotopic composition of carbonates. This study suggests that carbonate mud was essentially derived from the Jura shallow platform environments and also that the isotopic signature of carbonates deposited in the Swabian Alb deep shelf indirectly expresses the palaeoenvironmental evolution of the platform. Short-term fluctuations in d 13 C and d 18 O are probably controlled by changes in salinity (fresh-water input versus evaporation) in platform environments. Long-term fluctuations in carbon and oxygen isotope record throughout the Late Oxfordian–Early Kimmeridgian result from the interplay of increasing temperature and decreasing humidity, which both control the trophic level. Changes from mesotrophic to oligotrophic conditions in platform environments and in the deep-shelf surface waters are inferred. During the Late Oxfordian (Bimammatum Subzone to Planula Zone), the d 13 C curve displays a positive shift of about 1x, which is comparable in intensity to global perturbations of the carbon cycle. This evident isotopic shift has not been documented yet in other basinal settings. It can be reasonably explained by local palaeoenvironmental changes on the Jura platform (salinity, temperature, and nutrient availability) that controlled platform carbonate production, and the geochemistry of overlying waters. However, increasing carbonate production on the Jura platform and related positive d 13 C shifts recorded in the

Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction.

The temporal coincidence between large igneous provinces (LIPs) and mass extinctions has led many to pose a causal relationship between the two. However, there is still no consensus on a mechanistic model that explains how magmatism leads to the turnover of terrestrial and marine plants, invertebrates and vertebrates. Here we present a synthesis of ammonite biostratigraphy, isotopic data and high precision U-Pb zircon dates from the Triassic-Jurassic (T-J) and Pliensbachian-Toarcian (Pl-To) boundaries demonstrating that these biotic crises are both associated with rapid change from an initial cool period to greenhouse conditions. We explain these transitions as a result of changing gas species emitted during the progressive thermal erosion of cratonic lithosphere by plume activity or internal heating of the lithosphere. Our petrological model for LIP magmatism argues that initial gas emission was dominated by sulfur liberated from sulfide-bearing cratonic lithosphere before CO2 became the dominant gas. This model offers an explanation of why LIPs erupted through oceanic lithosphere are not associated with climatic and biotic crises comparable to LIPs emitted through cratonic lithosphere.

Investigation on Late Domerian-Early Torcian Lagenina andGlomospirella assemblages in the Umbria-Marche Basin (Central Italy)

Abstract In the Umbria-Marche area, during the Sinemurian-Carixian, due to tectonic/eustatic events the carbonateplatform (Calcare Massiccio Fm) was drowned, and a basin with a differentiated topography was established. The pelagic sedimentation was represented at first by a calcareous lithofacies (Corniola Fm) and later on by a clayey and marly lithofacies (Marne del Monte Serrone Formation =MS). The sediments here considered belong to the lower part of the MS, and they are Late Domerian-Early Toarcian in age. The micropaleontological assemblages show a progressive deepening of the sedimentary environment from middle shelf to outer shelf-upper bathyal conditions. This trend is compatible with a general sea-level rise in the European and North African domains during the Early Toarcian. In the clayey and/or marly sediments of the Late Domerian-Early Toarcian, many foraminifers, such as Miliolina which are abundant in the Carixian, disappear or become very rare. Only Lagenina, both sculptured and smooth, survive and are associated with siliceous Glomospirella which are very common or dominant. The benthic foraminiferal assemblages are associated with large ostracods, macroinvertebrates, and often with thin flat bivalves. Within the MS sediments of the Tenuicostatum Zone, sculptured Lagenina and Glomospirella, decrease in size and abundance and finally disappear together with the bivalves, both in disaerobic-anoxic conditions and in aerobic environments. Their disappearance can be related to the deepening of the basin.

Nitrogen isotope record of a perturbed paleoecosystem in the aftermath of the end‐Triassic crisis, Doniford section, SW England

[1] The Triassic-Jurassic transition (TJ) is characterized by successive perturbations of the carbon cycle during a time of biotic disruption as recorded by the carbon isotopic composition of organic matter (δ13Corg). The nitrogen isotopic composition of sedimentary organic matter (δ15Norg) constitutes a key parameter to explore the functioning of the ecosystem during carbon cycle perturbations and biological crises, because it provide information on seawater redox conditions and/or nutrient cycling. Here we report the first continuous δ15Norg record across the TJ transition at the Doniford Bay section (Bristol Channel Basin, UK), combined with δ13Corg, kerogen typology and carbon (δ13Cmin) and oxygen (δ18Omin) isotopic composition of bulk carbonates. The end Triassic is characterized by a major negative excursion both in δ13Corg and δ13Cmin, very low TOC (Total Organic Carbon, wt%) and high δ15Norg values, associated with a sea level lowstand. A second δ13Corg negative excursion occurs during the lower Hettangian. This interval is characterized by phases of carbonate production increase alternated with phases of exceptional accumulations of type I organic matter (up to 12%) associated with lower δ15Norg and δ13Corg. This alternation likely reflects a succession of nutrient input increase to the basin leading to enhanced productivity and eutrophication, which promoted a primary production driven by organic-walled prokaryotic organisms. The following OM export increase generates anaerobic conditions within the basin. These events occur between periods of relatively good seawater column ventilation and nutrient recycling boosting the carbonate producer recovery. Ecosystems remain perturbed in the Bristol Channel Basin during the aftermath of the end-Triassic crisis.

Volutidae (Mollusca: Gastropoda) of the Lakhra Formation (Earliest Eocene, Sindh, Pakistan): systematics, biostratigraphy and paleobiogeography

The paleobiodiversity of the Volutidae (Mollusca: Gastropoda) of the Ranikot Group (Sindh, Pakistan) and particularly of the Lakhra Formation (SBZ 5 biozone, Earliest Eocene), is reconsidered on the basis of new material collected during recent field trips. Ten new species are described (Mitreola brohii sp. nov., Lyrischapa vredenburgi sp. nov., L. brevispira sp. nov., Athleta (Volutopupa) citharopsis sp. nov., A. (Volutocorbis) lasharii sp. nov., Volutilithes welcommei sp. nov., V. sindhiensis sp. nov., Pseudaulicina coxi sp. nov., Sindhiluta lakhraensis sp. nov. and Pakiluta solangii sp. nov.) and one species is in open nomenclature (Lyria sp.). Three new genera are described: Lyriopsis gen. nov. [Volutinae, ?Lyriini, type species: Lyriopsis cossmanni (Vredenburg, 1923)], Sindhiluta gen. nov. [Volutilithinae, type species: Sindhiluta lakhraensis n. sp.] and Pakiluta gen. nov. [?Volutodermatinae, type species: Pakiluta solangii n. sp.]. Two new combinations are proposed: Lyriopsis cossmanni (Vredenburg, 1923) comb. nov. and Athleta (Volutopupa) intercrenatus (Cossmann & Pissarro, 1909) comb. nov. Lectotypes are designated for Lyria cossmanni Vredenburg, 1923, L. feddeni Vredenburg, 1923, Volutospina noetlingi Cossmann & Pissarro, 1909, V. intercrenata Cossmann & Pissarro, 1909 and Athleta (Volutocorbis) victoriae Vredenburg, 1923. With 21 species, this volutid fauna is the most diverse recorded from the Tethys Ocean during Earliest Eocene time. The assemblage is characterized by a strong turnover marked by regional speciation and the appearance of many western Tethyan invaders. Although at the species level, the assemblage documents a strong provincialism, at the genus level, the high number of shared genera between Eastern Tethyan and Old World Tethyan realms begins a phase of long-term homogeneity of volutid assemblages from the Tethyan paleobiogeographic province.

Integrated Stratigraphy of the Potential Candidate Oxfordian GSSP at Thuoux and Saint-Pierre d’Argençon (France)

The Thuoux and Saint-Pierre d’Argencon sections (Subalpine Basin, southeastern France) are proposed as a potential GSSP candidate for the Callovian–Oxfordian boundary. Several aspects of stratigraphy that have recently been applied in the two selected sections are discussed, including ammonite and nannofossil biostratigraphy, palynology, physical stratigraphy, and cyclostratigraphy.