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High-precision U-Pb zircon age from the Triassic of Italy : Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs

The Triassic time scale is poorly constrained due to a paucity of high-precision radiometric ages. We present a 206 Pb/ 238 U age of 230.91 ± 0.33 Ma (error includes all known sources) for zircon from an ash bed in the upper Carnian (Upper Triassic) of southern Italy that requires a major revision of the Triassic time scale. For example, the Norian stage is lengthened to more than 20 m.y. The section containing the ash bed is correlated with other Tethyan sections and, indirectly, with the Newark astronomical polarity time scale (APTS). The dating provides also a minimum age for some important climatic and biotic events that occurred during the Carnian. We note a coincidence between these events and the eruption of the large igneous province of Wrangellia, but the possible link between volcanism and climatic and biotic events requires further scrutiny.

Late Holocene annual growth in three Alpine stalagmites records the influence of solar activity and the North Atlantic Oscillation on winter climate

Annual growth rates and the ratio of dark to light-colored calcite within single annual laminae in three contemporaneously deposited Holocene speleothems from Grotta di Ernesto, an Alpine cave in northern Italy, respond to changes in surface temperature rather than precipitation. Based on monitoring of present-day calcite growth, and correlation with instrumental data for surface climatic conditions, we interpret a higher ratio of dark to light-colored calcite and the simultaneous thinning of annual laminae as indicative of colder-than-present winters. Such dark and thin laminae occur in those parts of the three stalagmites deposited from AD 1650 to 1713 and from AD 1798 to 1840, as reconstructed through lamina counting. These periods correspond to the well-known Maunder and Dalton Minima of solar activity. An 11-yr cyclicity in growth rate, coupled with reduced calcite deposition during the historic minima of solar activity, is indicative of a solar influence on lamina thickness. Spectral analysis of the lamina thickness data also suggests that the North Atlantic Oscillation variability influenced winter temperatures. Based on the present-day controls on cave calcite formation, we infer that high-frequency changes in solar activity modulated the seasonal duration of soil CO2 production.

Middle Triassic orbital signature recorded in the shallow-marine Latemar carbonate buildup (Dolomites, Italy)

A new time-frequency analysis of sea-level–controlled carbonate-platform cycles in the Middle Triassic Latemar massif (Dolomites, Italy) reveals a strong depositional signature with characteristics of dominant forcing by climatic precession. Modes corresponding to long and short precession components at 1/(21.7 k.y.) and 1/(17.6 k.y.) underwent amplitude modulations matching Earth9s orbital eccentricity with major frequency components at 1/(400 k.y.), 1/(125 k.y.), and 1/(98 k.y.). Obliquity appears as a minor component at 1/(35.4 k.y.). The Latemar signature thus constitutes the oldest pristine Milankovitch signature yet observed in the geologic record. Its fidelity rivals that of the Pliocene-Pleistocene record originally used to confirm the theory of orbitally forced climates. This evidence deepens a widely noted disagreement between radiometric and cyclostratigraphic time scales for the Latemar buildup. The Latemar cycles indicate that orbitally forced sea-level oscillations were operative in the ice-free Middle Triassic hothouse world.

Discovery of a major negative δ13C spike in the Carnian (Late Triassic) linked to the eruption of Wrangellia flood basalts

Major climate changes and mass extinctions are associated with carbon isotope anomalies in the atmosphere-ocean system and have been shown to coincide with the onset of large igneous provinces (LIPs) and, by association, their emissions of greenhouse gases and aerosols. However, climatic and biological consequences of some known LIP eruptions have not yet been explored. During the Carnian (Late Triassic) large volumes of flood basalts were erupted to form the so-called Wrangellia LIP (western North America). This huge volcanic province is similar in age to a major climatic and biotic change, the Carnian Pluvial Event (CPE), but no evidence of a causal relationship exists other than timing. Here we report a sharp negative δ 13 C excursion at the onset of the CPE recorded in organic matter. An abrupt carbon isotope excursion of ∼−4‰ occurs in terrestrial and marine fossil molecules, whereas total organic carbon records an ∼−2‰ shift. We propose that this carbon isotope negative shift was caused by an injection of light carbon into the atmosphere-ocean system linked to the eruption of Wrangellia flood basalts. This carbon-cycle perturbation occurs slightly before two major evolutionary innovations: the origin of dinosaurs and calcareous nannoplankton.

Oxygen isotopic evidence for Late Triassic monsoonal upwelling in the northwestern Tethys

The oxygen isotopic composition of conodonts from the Pizzo Mondello section in the Sicani Basin (Sicily, Italy), on the northwestern Tethys margin, has been used to reconstruct regional paleoseawater conditions. The δ 18 O phos values (21‰–21.9‰) measured by sensitive high-resolution ion microprobe (SHRIMP II) are consistent with previously published δ 18 O phos data from the contemporaneous marginal Hallstatt-Meliata Basin (20.3‰–22.5‰) located farther north, but are distinctly higher than those previously reported from the open ocean setting of the nearby Lagonegro Basin (18.7‰–20.0‰). This ∼2‰ offset represents a temperature differential of ∼8 °C, suggesting that sea-surface temperatures along the northwestern margin (Sicani and Hallstatt-Meliata basins) of the Tethys Ocean were lower than in the open ocean (Lagonegro Basin) during the late Carnian (Tuvalian 2) to early Norian (Lacian). We interpret the cooler waters of the marginal basins to reflect coastal upwelling driven by strong monsoonal systems, as predicted by existing paleoclimate models for this region.

A vertebrate nesting site in northeastern Italy reveals unexpectedly complex behavior for late Carnian reptiles

Abstract We interpret 13 large subcircular or horseshoe-shaped depressions discovered in Late Triassic peritidal carbonate rocks of the Dogna Valley in Udine Province, northeastern Italy, to be reptile nests. These trace fossils show truncation of strata, elevated ridges of massive sediment, and sediment infill within the depression differing in shape and sedimentary structures from the host sediment. The palynological assemblage of a shaly interbed close to the nest layer indicates a Tuvalian age (late Carnian). Archosaurian footprints, produced possibly by aetosaurs, are on a surface 130 cm above the nest-bearing layer. The trackmakers are considered the most probable nest makers.

SELECTED AMMONOID FAUNA FROM PRATI DI STUORES/STUORES WIESEN AND RELATED SECTIONS ACROSS THE LADINIAN-CARNIAN BOUNDARY (SOUTHERN ALPS, ITALY)

The ammonoid fauna of the Prati di Stuores/Stuores Wiesen section (Dolomites, north-eastern Italy) was studied in detail. This section was proposed as stratotype for the Carnian GSSP, with the first appearance of Daxatina cf. canadensis as primary marker, based on preliminary data. The validity of this proposal is confirmed by the present study, which integrates collections from the Prati di Stuores/Stuores Wiesen section and from others, particularly Bec de Roces (Passo Campolongo) and Antersass (Badia Valley). Ammonoids collected in these localities belong to three biostratigraphic units: regoledanus , canadensis and aon subzones. These subzones constitute, in the Southern Alps, the Ladinian/Carnian boundary interval. Regoledanus Subzone: the north American species Zestoceras enode is most probably documented in this biostratigraphic interval. Canadensis Subzone: the base is marked by the first appearance of Daxatina canadensis , and at least, another north American species, Daxatina laubei , seems to be present. Two species of Zestoceras were found: Z. barwicki e Z. lorigae sp.n. Two species o f Trachyceras , distinct from T. aon , are represented in the canadensis Subzone: T. muensteri and T. bipunctatum . These species predate the first appearance o f Trachyceras , justifying the canadensis Subzone to be included in the Carnian also on the basis of nomenclatural stability. Other significant taxa of this subzone are Rossiceras ? armatum and Sirenotrachyceras thusneldae . Aon Subzone: the ammonoid fauna of this subzone is extensively treated in existing literature and thus not further discussed. Taxonomical notes and stratigraphic consequences: the new subfamily Anolcitinae (family Trachyceratidae) is erected. At present, Frankites regoledanus , F. apertus and F. sp. A have been recognized in the Southern Alps. The lectotype of Ammonites ( Trachyceras ?) Regoledanus was defined. The latter species is exclusive of the regoledanus Subzone, whereas the distribution of the two other species encompasses the defined GSSP. The shell morphology of F. apertus and the north American species F. sutherlandi is identical. The suture line is also comparable, hence the two species are considered synonyms. This synonymy is relevant for long-distance correlations. The lectotypes o f Trachyceras ruturanum and T. laricum were also defined.

Geological map of the Middle Triassic Latemar platform (Western Dolomites, Northern Italy)

The Latemar is a Middle Triassic isolated carbonate buildup with a diameter of approximately 3 km, that crops out in the western Dolomites, northern Italy. The platform is an important case study and potential analogue for carbonate hydrocarbon reservoirs. Detailed field mapping of the platform has been carried out on a high-resolution topographic base extracted from airborne LIDAR to produce a geological map at 1:5000 scale. Remote sensing was used for the recognition of structural features and then validated in the field. In addition, high-resolution digital photographs were used to interpret the geology of inaccessible rock walls. This work represents a up-to-date detailed geologic map of the Middle Triassic Latemar platform that enhances its internal units subdivision and highlights its complex shape, characterized by gulfs and internal basins and strongly controlled by synsedimentary tectonics.

A highly diverse siliceous sponge fauna (Porifera: Hexactinellida, Demospongiae) from the Eocene of north-eastern Italy: systematics and palaeoecology

A siliceous sponge fauna, consisting of more than 900 specimens, is described from an early Lutetian tuffite horizon in the Chiampo Valley, Lessini Mountains, north-eastern Italy. Thirty-two taxa (15 Hexactinellida, 17 Demospongiae) are determined and illustrated, belonging to 24 genera, two of which are new (Rigonia gen. nov. and Coronispongia gen. nov.). Among these, 10 new species are proposed: Stauractinella eocenica sp. nov., Rigonia plicata gen. et sp. nov., Hexactinella clampensis sp. nov., Camerospongia visentinae sp. nov., C. tuberculata sp. nov., Toulminia italica sp. nov., Coronispongia confossa gen. et sp. nov., Cavispongia scarpai sp. nov., Corallistes multiosculata sp. nov. and Bolidium bertii sp. nov. Of the genera identified at Chiampo, 14 range back to the Cretaceous, three to the Jurassic and one to the Triassic, while six are still extant. The studied fauna shows affinities with sponges from the Eocene of Spain and the Cretaceous of Germany. The sponge fossils are uncompressed and bodily preserved, but the original siliceous skeleton is dissolved and substituted by calcite. Delicate attachments can be nevertheless documented: some sponges attached to a hard substrate by encrustation, while others were anchored on soft sediments by root-like structures. The presence of different modes of attachment suggests heterogeneous substrate conditions. Small, possibly young, sponges are recorded too. The sponge fauna is essentially autochthonous and lived in the middle-outer part of a carbonate ramp, where it formed clusters. This study extends the geographical and stratigraphical range of many sponge taxa, including Camerospongia, Toulminia, Ozotrachelus and Bolidium, previously documented only from the Cretaceous. The Recent calcified demosponge genus Astrosclera is reported here in the Cenozoic for the first time, having been reported previously in the Triassic only. Additionally, this study documents the second worldwide occurrence of the Recent sphinctozoan genus Vaceletia in the Palaeogene, formerly recorded exclusively in Australia. http://zoobank.org/urn:lsid:zoobank.org:pub:B3466955-8E20-429A-89BE-42BAEB4002E8

REFINED AMMONOID BIOCHRONOSTRATIGRAPHY OF THE BAGOLINO SECTION (LOMBARDIAN ALPS, ITALY), GSSP CANDIDATE FOR THE BASE OF THE LADINIAN STAGE

A refined ammonoid biostratigraphy is reported for a critical interrval of the Bagolino section (Giudicarie Area, Northern Iraly), a candidate for the Anisian/Ladinian stage boundary. The Avisianum Subzone has been documented, and its boundary with the Crassus Subzone has been redefined, on the basis of new findings of Reitziites reitzi, Aplococeras aff. smithi, Aplococeras avisianum, Halilucites rusticus, Parasturia sp. and other significant ammonoids. Six potential criteria for the definition of the Anisian/Ladinian boundary can now be considered in this single stratigraphic section, so that the FO of Eoprotrachyceras curionii is no longer the unescapable choice at Bagolino. Despite several drawbacks, including the absence of palynomorphs and daonellid bivalves, the thermal history preventing the recovery of magnetic and isotopic signals, and a lower sedimentation rate with respect to many other sections of the Southern Alps, the Bagolino section is here accepted as stratotype for the Anisian/Ladinian boundary, but further paleontological and sedimentological studies should be considered.