Lombardy Basin Research Articles

Patterns of extinction and recovery across the Triassic–Jurassic boundary interval in three resilient Southern Tethyan carbonate platforms

During the end-Triassic extinction (ETE), carbonate platform biocalcifiers suffered high extinction rates that have been linked to volcanically-induced global changes in climate and carbon cycle. Most studies have been focused on the classical sections of the Northern Calcareous Alps (NCA, Austria) and Lombardy Basin (Italy), where the extinction of the aragonitic Dachstein-type biota (involutinid foraminifera and megalodontid bivalves) coincides with the demise of the carbonate platform and with the initial negative carbon isotope excursion (CIE) of the reference sections for the Triassic/Jurassic Boundary (TJB).In this study, we present a detailed facies analysis, bio- and carbon-isotope stratigraphy of three Southern Tethyan carbonate platform sections, Mt. Messapion (Greece), Valle Agricola and Mt. Sparagio (southern Italy) that instead show persisting carbonate productivity across the TJB and potentially preserve the most detailed record of timing and patterns of the ETE in these ecosystems.In the studied sections, the disappearance of the Dachstein-type biota is observed within a positive δ13Ccarb excursion that, according to our study, correlates with that documented in the Schattwald beds (NCA) and Malanotte Fm (Lombardy Basin) above the initial CIE. This level represents the true extinction of the Dachstein-type biota, while the disappearance in the Northern Tethyan sections of the NCA and Lombardy Basin represents a pseudoextinction coinciding with the carbonate platform demise. Above the ETE, Southern Tethyan carbonate platform sections are characterized either by microbial laminites or ooid and oncoid limestones and low-diversity associations.This study reveals a possible paleogeographic and/or latitudinal control on the response of biocalcifiers and carbonate platform ecosystems during the ETE. The Dachstein-type biota was resilient to the environmental perturbations associated with the initial CIE in Southern Tethys, but probably failed to survive subsequent and/or prolonged stress. Despite extinctions, Southern Tethyan carbonate platforms adapted to environmental disturbances through a shift of the dominant carbonate production style from aragonitic biocalcification to chemical and microbially-mediated CaCO3 precipitation. The ecosystem recovery was slow and aragonitic biocalcifiers (dasycladacean algae) reappeared during the early Sinemurian.

Suboxic conditions prevailed during the Toarcian Oceanic Anoxic Event in the Alpine-Mediterranean Tethys: The Sogno Core pelagic record (Lombardy Basin, northern Italy)

Suboxic conditions prevailed during the Toarcian Oceanic Anoxic Event in the Alpine-Mediterranean Tethys: The Sogno Core pelagic record (Lombardy Basin, northern Italy)

CALCAREOUS NANNOFOSSIL TAXONOMY AND BIOSTRATIGRAPHY OF THE TOARCIAN-LOWER BAJOCIAN COLLE DI SOGNO SECTION (LOMBARDY BASIN, SOUTHERN ALPS, ITALY)

Calcareous nannofossil biostratigraphy was conducted in the Toarcian-lower Bajocian interval at Colle di Sogno (Lombardy Basin, Southern Alps, Northern Italy) where the type-section of the Sogno Formation consisting of pelagic marly limestone, marlstone and marly claystone was established. Semiquantitative analyses of calcareous nannofossil assemblages allowed to achieve a high-resolution biostratigraphy based on several biohorizons, including zonal/subzonal markers and additional events. The NJT5 to NJT9 Zones of the standard nannofossil zonation established for the Mediterranean Province were identified. The biostratigraphy obtained at Colle di Sogno was compared to published nannofossil events calibrated with ammonite zones in sections from SE Spain, S France, Portugal and N Algeria. This assessment evidenced some discrepancies in the succession of events of the standard zonation and, furthermore, resulted in the revision of the age of a few datums. Moreover, some new/additional nannofossil biohorizons are proposed as subzonal markers. A morphometric analysis of the genus Watznaueria was conducted to identify diagnostic features for unambiguous species identification. The species W. colacicchii and W. contracta are distinguished on the basis of the coccolith width/central area width ratio, whereas W. britannica britannica is discriminated by the size - as in the original definition of the species - relative to the new subspecies W. britannica minor. The new species W. gaetanii differs from all other Watznaueria taxa by the bridge ultrastructure. In the Toarcian-Aalenian interval a progressive increase in size of Watznaueria specimens is paralleled by the progressive closure of the central area and the modification of the central area structure passing from a cross (W. colacicchii and W. contracta) to a double-button bridge (W. gaetanii) to a single-button bridge (W. britannica). These intrageneric evolutionary innovations accelerated in the Aalenian under stable paleoceanographic conditions and an oligotrophic regime.

Reduction in animal abundance and oxygen availability during and after the end-Triassic mass extinction.

The end-Triassic biodiversity crisis was one of the most severe mass extinctions in the history of animal life. However, the extent to which the loss of taxonomic diversity was coupled with a reduction in organismal abundance remains to be quantified. Further, the temporal relationship between organismal abundance and local marine redox conditions is lacking in carbonate sections. To address these questions, we measured skeletal grain abundance in shallow-marine limestones by point counting 293 thin sections from four stratigraphic sections across the Triassic/Jurassic boundary in the Lombardy Basin and Apennine Platform of western Tethys. Skeletal abundance decreased abruptly across the Triassic/Jurassic boundary in all stratigraphic sections. The abundance of skeletal organisms remained low throughout the lower-middle Hettangian strata and began to rebound during the late Hettangian and early Sinemurian. A two-way ANOVA indicates that sample age (p < .01, η2 =0.30) explains more of the variation in skeletal abundance than the depositional environment or paleobathymetry (p < .01, η2 =0.15). Measured I/Ca ratios, a proxy for local shallow-marine redox conditions, show this same pattern with the lowest I/Ca ratios occurring in the early Hettangian. The close correspondence between oceanic water column oxygen levels and skeletal abundance indicates a connection between redox conditions and benthic organismal abundance across the Triassic/Jurassic boundary. These findings indicate that the end-Triassic mass extinction reduced not only the biodiversity but also the carrying capacity for skeletal organisms in early Hettangian ecosystems, adding to evidence that mass extinction of species generally leads to mass rarity among survivors.

Paleowildfire at the end-Triassic mass extinction: Smoke or fire?

Polycyclic Aromatic Hydrocarbons (PAHs) are routinely used as proxies for wildfire in geological sediments associated with large igneous province (LIP) driven CO 2 increases and mass extinction events. One example is the end-Triassic mass extinction event (ETE) driven by Earth's most laterally extensive LIP, the Central Atlantic Magmatic Province (CAMP). However, many PAH records often lack critical information including identifying specific source(s) of PAHs (e.g., pyrogenic vs. petrogenic), intensity of paleowildfire events, whether PAHs represent predominant smoke signals that can travel substantial distance from the burn origin, and if evidence of PAH as markers for soil erosion exists. To better understand ETE wildfire events, a detailed evaluation of PAH distributions from the Italcementi section in the Lombardy Basin, Italy covering the latest Rhaetian was undertaken. We report the best evidence of wildfire activity occurs above the initial carbon isotope excursion (CIE) which is routinely used to chemostratigraphically correlate between ETE sections, rather than within the initial CIE as evidenced at other sections. This wildfire event was intense, short-lived, and occurred during a calcification crisis and δ 13 C org anomaly, thereby linking terrestrial and marine ecosystem stress. Evidence of a more prolonged but less intense wildfire event and/or evidence for smoke signals takes place above this interval before the onset of a second calcification crisis. By comparing PAH records from Italy, Greenland, Poland, the UK, and China, during the ETE, few sections show evidence for intense (i.e., higher-temperature) wildfire activity during the initial CIE. However, these investigated PAH records show prolonged increases in the low-molecular-weight (LMW) combustion-derived PAH phenanthrene . We interpret this to represent widespread (and possibly more intense) wildfire activity further from the deposition sites, since LMW combustion-derived PAHs are the major PAHs in smoke aerosols that can travel vast distances, and/or less intense wildfire activity that characteristically produce LMW combustion-derived PAHs. In comparing PAH data, we find widespread wildfire activity across multiple basins supporting wildfire activity was an important ecological stressor in the terrestrial realm during the ETE. • Polycyclic aromatic hydrocarbons in the end-Triassic extinction show two fire events. • Global polycyclic aromatic hydrocarbon comparisons support widespread fire activity. • End-Triassic extinction wildfire events had different intensities. • Polycyclic aromatic hydrocarbon ratios support conifer burning. • Carbon isotope excursions not associated with wildfire events in Northern Italy.

Carbon- and oxygen-isotope signature of the Toarcian Oceanic Anoxic Event: insights from two Tethyan pelagic sequences (Gajum and Sogno Cores – Lombardy Basin, northern Italy)

Carbon- and oxygen-isotope signature of the Toarcian Oceanic Anoxic Event: insights from two Tethyan pelagic sequences (Gajum and Sogno Cores – Lombardy Basin, northern Italy)

Schizosphaerella size and abundance variations across the Toarcian Oceanic Anoxic Event in the Sogno Core (Lombardy Basin, Southern Alps)

Abundance and size variations of nannofossil Schizosphaerella punctulata were quantified in the uppermost Pliensbachian–Lower Toarcian succession recovered with the Sogno Core (Lombardy Basin, Northern Italy). High-resolution nannofossil biostratigraphy and C-isotopic chemostratigraphy identified the Jenkyns Event within the Toarcian oceanic anoxic event (T-OAE) interval. Absolute abundances and morphometric changes of “small S. punctulata” (< 7 μm), S. punctulata (7–10 μm; 10–14 μm; > 14 μm) and “encrusted S. punctulata” (specimens with a fringing crust) show large fluctuations across the negative δ13C Jenkyns Event. The Schizosphaerella crisis is further characterized by a decrease in average valve size in the early–middle Jenkyns Event. The abundance fall was caused by the failure of S. punctulata specimens >7 μm and “encrusted S. punctulata” that along with the increased relative abundance of small specimens, produced the reduction of average dimensions also documented in the Lusitanian and Paris Basins, although with a diachronous inception. The average valve size from the Lombardy Basin is ~2 μm smaller than in these other basins. Hyperthermal conditions associated with excess CO2 and ocean acidification possibly forced the drastic reduction of S. punctulata abundance/size. In the pelagic succession of the Sogno Core there is a strong positive correlation between the S. punctulata (> 7 μm) absolute abundance/size and the CaCO3 content, with a negligible contribution by small specimens (< 7 μm). Encrusted specimens testify selective neomorphic processes: the diagenetic crust seems diagnostic to separate S. punctulata from S. astraea.

Paleoceanographic inferences from benthic foraminifera across the early Aptian Ocean Anoxic Event 1a in the western Tethys

The paleoenvironmental impact of the early Aptian Ocean Anoxic Event 1a (OAE 1a, ca. 121 Ma) has been investigated in detail in the Cismon Core (Lombardy Basin, western Tethys) by using different geochemical and micropaleontological proxies. We provide the first high-resolution data of benthic foraminiferal assemblages through the upper Barremian - lower upper Aptian stratigraphic interval. Benthic foraminifera data are integrated with calcareous nannofossil and planktonic foraminifera records to create a comprehensive characterization of bottom and surface waters across OAE 1a. Benthic foraminiferal communities are indicative of a marked change in bottom-waters around the “nannoconid decline” (latest Barremian) due to increased flux of organic matter to the seafloor and intermittent dysoxic conditions probably promoted by pulses of higher productivity during the initial Greater Ontong Java Event (GOJE). Benthic foraminifera experienced a marked crisis in abundance (“benthic foraminiferal crisis” BFC) ca. 35 kyr before the OAE 1a, in correspondence with the “nannoconid crisis” and the onset of the most intense GOJE phase. The literature survey shows that the BFC is commonly recorded before the OAE 1a onset in several stratigraphic sections worldwide, and therefore, it is here proposed as a global event. At Cismon, deep-water anoxia was reached at the OAE 1a onset and lasted for ca. 300 kyr, promoted by higher productivity and eventually enhanced water stratification during the super-greenhouse climate. The continuation of OAE 1a was marked by a benthic foraminiferal repopulation event, probably resulting from the influx of relatively cooler and oxygenated waters. In turn, the OAE 1a was marked by intermittent anoxic to dysoxic conditions, likely in response to primary productivity sustained by N-fixing bacteria. The distribution and abundance of benthic foraminifera documented in other sections across the Selli Level equivalent show different features that point to local factors such as paleodepth and increased runoff. The post-OAE 1a was characterized by dysoxic conditions coupled with moderate organic matter flux to the seafloor. At the Cismon site and worldwide, the termination of OAE 1a coincided with the return of relatively more abundant benthic taxa in response to the restoration of favorable conditions allowing the development of diversified benthic foraminiferal communities.

NEW DATA ON THE EARLY JURASSIC BIODIVERSITY OF THE LOMBARDY BASIN (SOUTHERN ALPS, ITALY) AND THE EARLIEST RECORD SPHENODUS (CHONDRICHTHYES, NEOSELACHII)

At the beginning of the Jurassic, the initial stages of the rifting that preceded the opening of the Alpine Tethys led to the establishment of the Lombardy basin, characterized by a shallow water marine palaeoenvironment inhabited by highly diversified ecological communities. Macrofossil records from the whole Lower Jurassic succession of Lombardy are currently mostly confined to invertebrates. The earliest occurrence of marine vertebrates is from the Sinemurian Moltrasio Limestone of Osteno (Varese), subsequent to the Triassic/Jurassic boundary (TJB) post-crisis recovery. Here, we describe material from the Roncola section (Roncola San Bernardo, Bergamo) of the Sedrina Limestone (upper Hettangian), consisting of a dense accumulation of crinoid skeletal remains belonging to Balanocrinus ticinensis Hess, 2006. Among them are three isolated neoselachian teeth assigned to the genus Sphenodus Agassiz, 1843. This new discovery is significant and extends our knowledge of the biodiversity of the Lombardy basin Jurassic, mainly because these dental remains represent the earliest vertebrate macrofossils ever documented from this area after the Triassic/Jurassic boundary. Sphenodus (which ranges from the Sinemurian to the Danian) is a fairly ubiquitous Sinemurian neoselachian shark but this new record moves its First Appearance Datum (FAD) back to the Hettangian stage.

GEOMETRIA E CARATTERI STRATIGRAFICI DELLA SEQUENZA CENOMANIANA NEL BACINO LOMBARDO (ALPI MERIDIONALI)

The Cenomanian Sequence in the area between the lakes of Lecco and Iseo (Lombardy Basin, Southern Alps) represents a depositional unit bounded by two main unconformities and relative conformities. The unconformities progressively develop from SW to NE, with hiatuses spanning in age the Early Cenomanian and the Late Cenomanian-Turonian respectively.&#x0D; A complete section of the Cenomanian Sequence consists of Early Cenomanian red marls with pelagic turbidites and pebbly mudstones (Marne rosse) followed by two calcareous chaotic layers enclosing a succession of thin bedded, fine grained siliciclastic turbidites (Torbiditi Sottili), of Middle to Late Cenomanian age.&#x0D; The association of chaotic layers with the enclosed wedge shaped body of turbidites and the development of unconformities towards the north, point out that the Cenomanian basin developed in a mobile area where deposition was controlled by sinsedimentary tectonics. Moreover, the Cenomanian basin is, so far, the youngest Cretaceous basin clearly documented in the Southern Alps, oriented east-west, therefore crosswise to the structures related to the Jurassic rifting. Stratigraphic data strongly suggest that the tectonic evolution of the northern margin of the Cenomanian Lombardy Basin was generated by compression with the development of antiform structures.The sandstone unit pinches out towards the north and east, and thins more gradually towards the south. It represents a wedge shaped body, which parallels E-W paleocurrent trends and onlaps onto the northern margin of the Cenomanian basin. The two chaotic layers are basinally extended and show facies changes and thinning from north to south. They derived from sliding and slumping of the northern slope of the basin.

THE BARREMIAN-TURONIAN EROSIONAL UNCONFORMITY IN THE M. MISMA AREA (LOMBARDY BASIN, SOUTHERN ALPS)

An erosional unconformity has been recognized by means of lithostratigraphy and calcareous plankton biostratigraphy in the Cretaceous succession of the M. Misma area (Southern Alps, Lombardy Basin). Due to synsedimentary tectonism, after a Cenomanian sliding and slumping phase, channelized sandstones and conglomerates, of Late Turonian age, have been scoured in the Barremian-Albian succession.

Coring the sedimentary expression of the early Toarcian Oceanic Anoxic Event: new stratigraphic records from the Tethys Ocean

Abstract. The Toarcian Oceanic Anoxic Event (T-OAE) interval was cored at Colle di Sogno and Gajum in the Lombardy Basin (Southern Alps, northern Italy). The Sogno and Gajum cores recovered 26.83 and 31.18 stratigraphic metres, respectively, of pelagic sediments consisting of marly limestones, marlstone, marly claystone, and black shale. Drilling at both sites resulted in 100 % recovery of unweathered material. The pelagic succession comprises a relatively expanded black shale interval of 4.98 m in the Sogno core and 15.35 m in the Gajum core, with lower and upper boundaries without evidence of hiatuses. The Sogno and Gajum cores can be considered reference sections for the pelagic lower Toarcian interval of the western Tethys and will provide high-resolution micropaleontological, inorganic and organic geochemical, isotopic multiproxy data. Integrated stratigraphy and cyclostratigraphy are predicted to result in estimates of durations and rates to model the ecosystem resilience to the extreme perturbations of the T-OAE and gain a better understanding of current global changes and help provide better projections of future scenarios.

THE LOWER BAJOCIAN GAETANI LEVEL: LITHOSTRATIGRAPHIC MARKER OF A POTENTIAL OCEANIC ANOXIC EVENT

In this paper we document in detail the transition from the Rosso Ammonitico Lombardo to the Radiolarites outcropping at Alpe Turati (Albavilla, Como) in the Lombardy Basin of the Southern Alps. At this location, the Jurassic succession was deposited on a flank of the Corni di Canzo paleohigh: as found on other structural shallow areas, the upper Pliensbachian–Toarcian–Aalenian interval is represented by pseudonodular to nodular marly limestones of the Morbio Limestone and Rosso Ammonitico Lombardo units. In the early Bajocian deposition of biosiliceous sediments is ubiquitously testified by the Radiolarites (Bajocian–Callovian). At Alpe Turati, the interval immediately below the basal green member of the latter unit, consists of a 10 cm thick black shale, pointing to oxygen-depleted bottom waters. Dysoxia persisted during the Bajocian–Callovian as evidenced by dark green stratified cherts. Calcareous nannofossil biostratigraphy indicate an early Bajocian age for the black shale that correlates with the core of a distinct C isotopic negative anomaly also known in various basins outside the Southern Alps. Very dark grey to black lithologies of early Bajocian age have been documented in a few sections from Poland, Corsica and Morocco. We name Gaetani Level the black shale interval in recognition of Maurizio Gaetani’s pioneering and extensive work on Jurassic sedimentary successions of the Lombardy Basin. The association of the Gaetani black shale with a C isotopic anomaly suggests that it could be the sedimentary record of an Oceanic Anoxic Event whose regional to global extension must be ascertained.

SEDIMENTOLOGIA E STRATIGRAFIA DELLE SUCCESSIONI RETICHE AL CONFINE FRA LOMBARDIA E TRENTINO

This paper deals with Rhaetic facies at the Lombardy-Trentino border, in the Giudicarie Region. This area is characterized by important facies changes crossing strike slip faults. Two coeval sections, showing remarkable facies differences, are examined in detail, in order to describe the transition between the Rhaetic Lombardy Basin and the peritidal Trento Platform. The western section shows clear lombardian features and includes two marly formations: the Argillite di Riva di Solto and the Calcare di Zu. They are characterized by asymmetric marl-limestone cycles, developed on a metric scale, and show a shallowing upward evolution, from poorly oxygenated fairly deep environments to tidal flats. The upper portion of this section is referred as a new unit, the Tremalzo limestone, that is characterized commonly by a clear peritidal bathymetric cyclicity. The wholly carbonate eastern section is considered entirely Tremalzo limestone. It shows a similar evolution, but it was deposited in shallower environments on the western margin of the Trento Platform. Both sections are mud- dominated, but storm waves and tidal currents at times produced lenticular grainy beds. A detailed sedimentological analysis shows that these facies were deposited in a ramp system, the dynamics of which were mainly controlled by eustatic fluctuations and climatic cycles.

Environmental change during the Triassic–Jurassic boundary interval of an equatorial carbonate platform: Sedimentology and chemostratigraphy of the Ghalilah Formation, United Arab Emirates

The sedimentology and chemostratigraphy (δ13Ccarb, δ13Corg, Sr concentrations) of the Triassic-Jurassic (Tr-J) boundary interval has been investigated in detail in sections of the Ghalilah Formation exposed in Wadi Ghalilah, Wadi Milaha and Wadi Naqab, northeastern United Arab Emirates. The sequence of events recorded across the Tr-J boundary interval in Ras Al Khaimah reflects significant environmental change that can ultimately be related to CAMP volcanism. Uppermost Triassic limestones of the Sumra Member rich in coral, calcareous sponges and large-size bivalves are interbedded with siliciclastic mudstones and deposited in an open lagoonal environment. These are abruptly followed by oolites with intercalated calcareous mudstones of the Sakhra Member that are devoid of macrofossil. Thrombolitic microbialites that occur in the lowermost Sakhra Member are interpreted to reflect the demise of hypercalcifying marine biota during the Tr-J boundary interval. The oolites of the Sakhra Member are capped by a subaerial exposure surface, followed by peritidal deposits of the Shuba Member. The available, sparse biostratigraphic data of the Ghalilah Formation are critically discussed and support a position of the Tr-J boundary at the base of the Sakhra Member. A negative excursion in δ13Corg occurs in the upper Sumra Member and possibly correlates with the Late Triassic Spelae carbon-isotope event. The δ13Ccarb and δ13Corg values increase across the boundary interval, and an extended positive excursion in δ13Ccarb occurs in the oolites of the Sakhra Member. Sr concentrations increase in the bioclastic limestones of the uppermost Sumra Member and peak in the oolites of the upper Sakhra Member. High Sr concentrations also occur at correlative stratigraphical levels in the Lombardy Basin (Italy), and are interpreted as an Early Hettangian seawater signal, reflecting the global-scale reduction of biological aragonite precipitation and an increased continental weathering flux.

Uranium isotope evidence for an expansion of marine anoxia during the end‐Triassic extinction

AbstractThe end‐Triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia, suggesting that anoxia played a role in suppressing marine biodiversity. However, global changes in ocean anoxia are difficult to quantify using proxies for local anoxia. Uranium isotopes (δ238U) in CaCO3 sediments deposited under locally well‐oxygenated bottom waters can passively track seawater δ238U, which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238U(VI) relative to 235U(VI) in anoxic marine sediments. We measured δ238U in shallow‐marine limestones from two stratigraphic sections in the Lombardy Basin, northern Italy, spanning over 400 m. We observe a ∼0.7‰ negative excursion in δ238U beginning in the lowermost Jurassic, coeval with the onset of the initial negative δ13C excursion and persisting for the duration of subsequent high δ13C values in the lower‐middle Hettangian stage. The δ238U excursion cannot be realistically explained by local mixing of uranium in primary marine carbonate and reduced authigenic uranium. Based on output from a forward model of the uranium cycle, the excursion is consistent with a 40–100‐fold increase in the extent of anoxic deposition occurring worldwide. Additionally, relatively constant uranium concentrations point toward increased uranium delivery to the oceans from continental weathering, which is consistent with weathering‐induced eutrophication following the rapid increase in pCO2 during emplacement of the Central Atlantic Magmatic Province. The relative timing and duration of the excursion in δ238U implies that anoxia could have delayed biotic recovery well into the Hettangian stage.

Calcareous nannofossils at the Triassic/Jurassic boundary : stratigraphic and paleoceanographic characterization

In this work, calcareous nannofossils are identified for the first time in the uppermost Triassic sequence of the Lombardy Basin (Southern Calcareous Alps, Italy). Two zones are recognized, namely the NT2b (latest Triassic) and the NJT1 (earliest Jurassic). Two species resulted to be good markers to constrain the TJB interval: Prinsiosphaera triassica and Schizosphaerella punctulata . Nannofossil data are calibrated with C isotopic chemostratigraphy obtained for carbonate and organic matter. Size reduction of P. triassica and a decline in the abundance of Triassic nannofossils are detected soon after the “precursor Carbon Isotope Excursion (CIE) and culminated during the “initial negative CIE” characterized by lowest nannofossil abundances and small-sized P. triassica . The extinction of Triassic nannofossils occurred in distinctive steps within the “initial negative CIE”, while the Jurassic S. punctulata is first observed at the base of the “main negative CIE”. The latest Triassic nannofossil decline in abundance, size reduction and extinctions, represent a progressive deterioration associated to the Central Atlantic Magmatic Province (CAMP) volcanism. Our findings are consistent with nannofossil changes at supraregional scale and indicate that the massive CAMP flood basalts were preceded by initial volcanic pulses. We speculate that a combination of climate change, fertilization and ocean acidification started to influence the calcification process prior to the “initial negative CIE”. Nannoplankton extinctions were not simultaneous and might imply limited capacity for adaptation in the early stages of evolutionary history. However, originations of new taxa soon after the disappearance of Triassic forms suggest the ability to rapidly overcame extreme stressing conditions.

Carbon cycle dynamics following the end‐Triassic mass extinction: Constraints from paired δ13Ccarb and δ13Corg records

Constraining the carbon isotopic changes associated with the end‐Triassic mass extinction is key to understanding the causes of the extinction and dynamics of recovery from it. Yet the pattern and timing of δ13C variation surrounding the extinction remain poorly constrained. Here we present close to 1000 new δ13C measurements from six newly sampled sections in Italy. We observe a sharp negative excursion in δ13Ccarb coincident with the disappearance of the Triassic fauna, and two positive excursions above it. The negative δ13Ccarb excursion in these sections does not occur in δ13Corg suggesting a possible diagenetic origin. In contrast, the interval of elevated δ13C occurs in both carbonate and organic carbon, suggesting that it is likely to be a primary feature. The positive excursions in the Lombardy Basin (southern Alps) and Mt. Cefalo (southern Apennines) appear to be time correlative on the basis of their position above the disappearance of characteristically Triassic biota. However, it is less certain that they are time correlative with positive excursions in other sections worldwide, as few options exist that honor both bio‐ and chemostratigraphy. Nonetheless, similarity to other events that are interpreted as global, as well as carbon cycle considerations, suggest that the isotopic enrichment is best interpreted to reflect a shift in the isotope composition of the global surface carbon reservoir. Our data indicate that perturbation of the global carbon cycle was not confined to the immediate vicinity of the extinction interval, but rather persisted for substantial length of geologic time afterwards.

Environmental control on the end of the Dolomia Principale/Hauptdolomit depositional system in the central Alps: Coupling sea-level and climate changes

The Norian in the Western Tethys is characterised by the deposition of early-dolomitised inner platform facies (Dolomia Principale/Hauptdolomit, DP/HD), bordered on the landward side by terrigenous coastal deposits (Keuper) and on the seaward side by calcareous backreef and reefal facies (Dachstein Limestone) passing basinward to open-sea sediments (Hallstatt facies). The inner carbonate platform is locally (Lombardy Basin, Carnic Alps, Central Austroalpine) dissected by normal faults leading to the development of intraplatform troughs. Close to the Norian–Rhaetian boundary, sedimentation records an abrupt environmental change both on platform top and basins all over the Western Tethys (e.g. Western Carpathians, Transdanubian Range, Alps, Central Apennine). The top of the Dolomia Principale locally emerged, reflecting a major eustatic sea-level fall. Emersion is recorded in favourable settings by the development of polycyclic paleosols up to 30 m thick. In the Norian intraplatform basins, the succession is capped by 4 to 8 m of thin-bedded, fine-grained limestones yielding abundant remnants of fishes and terrestrial reptiles. Fossil concentration as well as sedimentological features is indicative of reduced sedimentation rates due to decreased carbonate production, induced by the emersion of the platform top. The sea-level fall was followed by deposition of mixed fine-grained siliciclastic–carbonate successions (e.g. Riva di Solto Shale, Kössen beds, “ Rhaetavicula contorta beds”, Fatra Formation). Stratigraphic evidence indicates a dry climate in the Western Tethys during the Norian, as indicated by the presence of evaporites (Burano, Apennine) and arid to semi-arid coastal to playa settings (Upper Keuper, Germany). In contrast, the basal layers of the basinal shales show evidence of wet climate. The end of the Norian depositional system records two different phenomena: (1) an important sea-level fall was responsible for the emersion of the platform top and deposition of a condensed horizon in the basins; and (2) transition from dry to humid climate. The observed evolution is explained with a global cooling which caused the rapid sea-level fall responsible for the abrupt end of the DP/HD depositional system and the shift of the boundary between arid and temperate climate belts, which modified the distribution and amount of rainfall, triggering the deposition of shales along the Western Tethys margin.

Stratigraphic evolution of the Triassic–Jurassic succession in the Western Southern Alps (Italy): the record of the two‐stage rifting on the distal passive margin of Adria

ABSTRACTThe Triassic–Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break‐up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre‐Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian–Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian–Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian–Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian–Toarcian boundary. This younger rift bridges the gap between the Hettangian–Sinemurian diffuse rifting and the Callovian–Bathonian break‐up. The late Pliensbachian–Toarcian rift, which eventually lead to continental break‐up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins.