Simonetta Cirilli

Synchrony of the Central Atlantic magmatic province and the Triassic-Jurassic boundary climatic and biotic crisis

The evolution of life on Earth is marked by catastrophic extinction events, one of which occurred ca. 200 Ma at the transition from the Triassic Period to the Jurassic Period (Tr-J boundary), apparently contemporaneous with the eruption of the worlds largest known continental igneous province, the Central Atlantic magmatic province. The temporal relationship of the Tr-J boundary and the provinces volcanism is clarified by new multidisciplinary (stratigraphic, palynologic, geochronologic, paleomagnetic, geochemical) data that demonstrate that development of the Central Atlantic magmatic province straddled the Tr-J boundary and thus may have had a causal relationship with the climatic crisis and biotic turnover demarcating the boundary.

Motion of Africa and Adria since the Permian: paleomagnetic and paleoclimatic constraints from northern Libya

Abstract Paleomagnetic and biostratigraphic data from the Al Azizia Formation of northwestern Libya, consisting of uppermost Middle Triassic/lowermost Upper Triassic limestones, shed new light on the latitudinal drift of Africa and Adria and related climatic changes. A characteristic component of magnetization carried by magnetite delineates paleomagnetic poles which are coincident with coeval poles from the Southern Alps. Data from this study and the literature are integrated, showing that relatively unrotated remnants of the Adria margin like the Southern Alps (e.g., the Dolomites), Istria, Gargano, Apulia and Iblei moved in close conjunction with Africa since at least Permian times. A Permian–Cenozoic apparent polar wander (APW) curve for Africa/Adria is constructed. The paleolatitude trend for northern Libya calculated from this APW superposed to the zonal latitudinal bands of relative aridity and humidity typical of modern-day climate predicts that northern Libya drifted northwards from the equatorial belt to the arid tropic during the Triassic, and crossed the humid subequatorial/arid subtropical boundary zone at Late Triassic times. This inference is fully supported by Permo-Triassic palynological and facies analysis from this study and the literature. We conclude that a zonal climate model coupled with paleomagnetically constrained paleogeographic reconstructions provides a powerful null hypothesis for understanding past climatic conditions.

Stratigraphical and palaeoenvironmental analysis of the Permian-Triassic transition in the Badia Valley (Souther Alps, Italy)

Abstract A sedimentological, palynological and microfaunal integrated analysis was carried out across the Permian-Triassic transition in a 35 m thick section near Seres (Badia Valley, northern Italy). This section includes the uppermost part of the Bellerophon Formation and the base of the Werfen Formation (Tesero Horizon and the lowermost Mazzin Member). The Bellerophon Formation (”badiota facies”) displays a general shallowing-upward trend. It has been subdivided into three intervals on the basis of facies, microfacies, biofacies and palynofacies associations. The Bellerophon-Werfen Formation boundary was located at the boundary between a thin black organic-rich layer and a 50 cm thick limestone bed, containing in the upper part the first oolitic beds. The palynological assemblages show throughout the Bellerophon Formation a gradual decrease of exclusive Permian palynomorphs and a concomitant increase of Triassic ranging forms. Triassic palynomorphs were found in the lower part of the Tesero Oolitic Horizon (TOH), where the Permian-Triassic transition can be recognized. Foraminifers with Triassic affinity appear just above the proposed Permian Triassic transition. This multidisciplinary approach led to evidence the palaeoenvironmental evolution which was characterized by variations in the water column oxygenation from dysoxic to oxic conditions related to climatic and/or physiographic changes influencing the water layering. Palynofacies studies show a shift from relatively distal to more proximal conditions which reached the maximum during the deposition of the black organic-rich level at the upper boundary of the Bellerophon Formation. The overlying shallowing upward cycle at the base of the TOH starts with an anoxic transgressive layer and ends with the oolitic beds.

THE PRATI DI STUORES/STUORES WIESEN SECTION (DOLOMITES, ITALY): A CANDIDATE GLOBAL STRATOTYPE SECTION AND POINT FOR THE BASE OF THE CARNIAN STAGE

The Prati di Stuores/Stuores Wiesen section (Dolomites, Italy) is proposed as a candidate Global Stratotype Section and Point for the base of the Carnian Stage. In addition to being a famous, richly fossiliferous locality, it includes the type-section of the Cordevolian substage. The section is located near Pralongia, along the southern slope of the crest separating the Badia/Abtei and Cordevole valleys. Below the levels with Trachyceras aon , the section contains a rich ammonoid fauna that chacterizes the lower part of the Regoledanus Subzone and subsequently records the first appearances of the mid-high latitude genus Daxatina ( Daxatina sp., D. cf. canadensis ) and of traditional Trachyceras with species different from T. aon . Moreover, the Daxatina cf. canadensis Subzone is recognised above the Regoledanus Subzone. Very rare conodonts of the Budurovignatus group and species of Gladigondolella from the diebeli Assemblage Zone occur. Gondolella polygnatyformis, already known from the Aon Subzone, is absent. Palynomorphs, foraminifers, gastropods, bivalves, brachiopods, microcrinoids and holothurian sclerites were studied. Variations in frequency and taxonomic diversity of these faunas suggest anaerobic-disaerobic bottom conditions for the lower-middle part of the section (0-105 m), followed by a more stable oxygen content in the upper portion. Magnetostratigraphy showed four intervals with normal polarity and three intervals with reversed polarity. The Daxatina cf. canadensis Subzone falls close to the normal polarity interval S2n. The present study proposes the FAD of the cosmopolitan genus Daxatina as a marker of the base of the Carnian Stage, placing it at a lower stratigraphic level than previously indicated in the Stuores area. The Prati di Stuores section is proposed as GSSP of the Ladinian-Carnian boundary.

Implications of a combined biostratigraphic and palaeomagnetic study of the Umbrian Maiolica Formation

Abstract The study of a 275.5 m thick section of white, pelagic limestones occupying the valley of the Fonte del Giordano river on the southern slope of Mt. Montagnola has yielded a biostratigraphically controlled clear magnetic reversal pattern after thermal cleaning. The magnetic stratigraphy of the lower 131 m of the section (Calpionellid zones) is correlatable with the M-sequence of oceanic magnetic anomalies between M-19 and M-14. The reversal stratigraphy of the upper 81.5 m of the section (Radiolaria zone) has also been tied to the oceanic polarity time scale by making linear interpolation for a missing 63 m thickness underneath it. Besides the Fonte del Giordano section two Berriasian outcrops each with a different bedding attitude were studied at Gubbio and near Cagli for tectonic tilt test giving positive results. The mean palaeomagnetic pole position for the Late Jurassic/Early Cretaceous after bedding correction is: Φ = 19.1°, Λ = 288.2°, k = 148.7, α95 = 10.2° (N = 3), confirming the presence of a large swing in the polar path, a common behaviour of apparent polar wandering for the peri-Adriatic region during this time.

Phytoplankton response and geochemical evidence of the lower Toarcian relative sea level rise in the Umbria-Marche basin (Central Italy)

Abstract Quantitative and qualitative analyses have been carried out on the lower Toarcian organic rich lithologies of the Umbria-Marche domain (Marne di Monte Serrone formation) with the aim to emphasize the potential of organic and geochemical parameters as palaeoenvironmental indices. The organic matter and phytoplankton data suggest that the palaeoenvironmental evolution of this area was controlled by a third order cyclicity, induced by climatic-eustatic fluctuations. During the early Toarcian sea level rise, two different phases have been recognized. The phase of facies retrogradation, referable to the Transgressive System Tract, lying in the early and middle part of the D. tenuicostatum Zone. This phase was characterized by a relative increase of basinal CaCO 3 , a better fertility within the photic zone and a decrease of sea bottom oxygenation and of the micronutrients in surface waters. The maximum flooding event, at the top of the retrogradation phase, corresponds with the maximum of palaeoenvironmental distality, sedimentary starvation and total organic carbon (TOC) values. The phase of facies progradation, corresponding to the High Stand System Tract, occurred in the uppermost portion of the D. tenuicostatum Zone. This phase induced a more efficient water circulation, producing a re-oxygenation at the sea bottom, a better nutrient recycling and a reflourishing of nannoplakton. The CaCO 3 in the basin was mainly extrabasinal because the carbonate platforms started producing and exporting the carbonate mud basinwards again. This approach confirms that eustatic fluctuations strongly influenced the variations of phytoplankton total abundance and species diversity and the distribution of organic matter in the sediments. It also regards a significant tool for the investigation of lithologies where the lack of significant sedimentary structures does not give detailed palaeoenvironmental information.

Triassic pelagic deposits of Timor: palaeogeographic and sea-level implications

Abstract In West Timor, Triassic deposits are found in the Parautochthonous Complex, as well as in the Allochthonous series of Sonnebait. A detailed biostratigraphic investigation, integrating field observations and facies analysis, allowed the reconstruction of a synthetic lithostratigraphic succession for the Upper Triassic; a stratigraphic transition from Carnian shales to Upper Norian–Rhaetian limestones is also shown by this study. The fossil content predominantly originates from an open marine environment; lithostratigraphic Units A–E are dated on the basis of radiolaria and palynomorphs, and Unit H, on ammonites and conodonts. The presence of pelagic bioclasts, together with normal grading, horizontal laminations, and current ripples, is indicative of a distal slope to basin environment. The ammonite rich condensed limestone of Unit H was deposited on a ‘pelagic carbonate plateau’ exposed to storms and currents. The organic facies have been used as criteria for biostratigraphy, palaeoenvironmental interpretation, and sequence stratigraphy. The palaeontological analysis of the Triassic succession of West Timor is based on the investigation of radiolaria and palynomorphs, in the marls and limestones of Units A–E, and also on ammonites and conodonts in the condensed limestone of Unit H. Units A and B are Carnian (Cordevolian) in age, based on the occurrence of the palynomorph Camerosporites secatus , associated with ‘ Lueckisporites ’ cf. singhii , Vallasporites ignacii , Patinosporites densus and Partitisporites novimundanus . Unit C is considered as Norian, on the basis of a relatively high percentage of Gliscopollis meyeriana and Granuloperculatipollis rudis. Unit D contains significant palynomorphs and radiolaria; the organic facies, characterized by marine elements, is dominated by the Norian dinocysts Heibergella salebrosacea and Heibergella aculeata ; the radiolaria confirm the Norian age. They range from the lowermost Norian to the lower Upper Norian. Unit E also contains radiolaria, associated in the upper part with the well-known marker of the Upper Norian, Monotis salinaria . For Unit E, the radiolaria attest to a Lower to Upper Norian age based on the occurrence of Capnodoce and abundant Capnuchosphaera ; the upper part is Upper Norian to Rhaetian based on the presence of Livarella valida . Finally, the blocks of condensed limestone with ammonites and conodonts of Unit H allowed the reconstruction of a synthetic stratigraphic succession of Upper Carnian to Upper Norian age. Our stratigraphic data lead to the suggestion that the Allochthonous complex, classically interpreted as a tectonic melange of the accretionary prism of the Island Arc of Banda, is a tectonically dismembered part of a Triassic lithostratigraphic succession.

Sedimentology, stratigraphy, and micropalaeontology of the Upper Triassic reefal series in Eastern Sulawesi (Indonesia)

An Upper Triassic (Upper Norian-Rhaetian) carbonate complex, composed of open marine to reefal deposits, has been investigated for the first time in Eastern Sulawesi. The age is based on the occurrence of benthic foraminifera, and also of the Upper Sevatian to Rhaetian conodont Misikella posthernsteini Kozur and Mock. Palynological assemblages contain Upper Triassic-Lower Jurassic palynomorphs. The scleractinian coral Retiophyllia seranica and the chaetetid sponge Blastochaetetes intabulata, together with Solenoporacean algae, are the main framebuilders of the reefal facies. The entire carbonate series, composed of conodont bearing limestones, reefal deposits, and intertidal/supratidal cryptalgal laminites, shows a general regressive trend from a marginal to an inner platform environment. The relationship between microfaunal distribution and sequence analysis is discussed. The Upper Triassic foraminifers and palynomorphs of Eastern Sulawesi show affinities to microfaunas of the Australian-Indonesian southern Tethyan domain, and the general organisation of the platform should be investigated through further studies from Banda Sea dredgings.

The dawn of CAMP volcanism and its bearing on the end-Triassic carbon cycle disruption

The cause-and-effect relationship between the c. 201 Ma eruption of the Central Atlantic magmatic province (CAMP) and the end-Triassic abrupt climate change and mass extinction is at present based on controversial temporal correlations. Upper Triassic sedimentary strata underlying CAMP basalts in Morocco illustrate a clear mineralogical and geochemical fingerprint of early CAMP basaltic eruptions, namely unusually high contents of MgO (10–32 wt%) and of mafic clay minerals (11–84%). In the same rocks a coincident negative carbon-isotope excursion (CIE) is present, equivalent to the so-called ‘initial negative CIE’ recorded worldwide shortly before the Triassic–Jurassic boundary. The new data show that the onset of CAMP activity preceded the end-Triassic carbon cycle disruption and that the initial negative CIE is unequivocally synchronous with CAMP volcanism. The results of this study strongly support the hypothesis that the culmination of pollution of atmosphere and seawater by CAMP-derived volcanic gases was the proximate cause of the end-Triassic mass extinction. Supplementary material: The stratigraphic position of analysed samples, and the C-isotope, bulk-rock mineralogy, element analysis, Mg–Al–Si ternary diagram and trace-element analysis data are available at www.geolsoc.org.uk/SUP18707.

Stratigraphic evidence for Cimmerian events in NW Caucasus (Russia)

The Upper Permian and Triassic sequences of the NW Caucasus present a good record of the Cimmerian events, rather undisturbed by the subsequent Alpine deformations. Original field work with new fossil identifications, microfacies analysis, and sandstone petrography were carried out. During the late Permian, active strike-slip basins were filled by continental clastics successions. Marine ingressions during the latest Permian, led to the formation of sponge reefs and skeletal carbonate ramps. During the Triassic, several siliciclastic wedges were intercalated within the marine carbonate succession. Most important is a conglomerate body made up of serpentinite pebbles of Spathian age (early Triassic), recording the exhumation and erosion of schistose antigorite serpentinites. By the late Anisian a severe deformation affected the Peredovoy (= Fore) Range of the NW Caucasus. Lower Triassic to Anisian sediments deformed also in chevron folds were overlaid with angular unconformity by a siliciclastic, and also volcaniclastic, conglomeratic and arenitic body, up to several hundred meters thick. By the late Ladinian-earliest Carnian, marine sedimentation resumed locally, forming a carbonate ramp during part of the Norian. Towards the end of the Norian, the entire area emerged and was again mildly tilted. The subsequent post-Cimmerian transgression occurred largely during the Middle Jurassic. Consequently, the most important Cimmerian deformations appear to be of early and middle Triassic age.