323,698 research outputs found
Tethyan magnetostratigrapy from Pizzo Mondello and correlation to the Late Triassic Newark APTS
No full textWe present magnetostratigraphic data and preliminary C13 and O18 stable isotope data from an expanded (≈430m-thick) Upper Triassic marine section at Pizzo Mondello from the Sicani Basin of Sicily and review biostratigraphic data from the literature that can be used to define the location of the Carnian/Norian and Norian/Rhaetian boundaries. Pizzo Mondello offers good potentials for
magnetostratigraphic correlation of marine biostratigraphic and chemostratigraphic data with the continental Newark astrochronological time scale (APTS) for development of an integrated Late Triassic time scale. The relatively stable average values of 18O centered around 0‰ are a strong indication that the Cherty Limestone at Pizzo Mondello suffered very little diagenetic overprinting. The Carnian/Norian boundary at Pizzo Mondello seems to be associated with a positive shift of C13 although further work is necessary to evaluate its paleoenvironmental significance. A statistical approach was applied to evaluate various Pizzo Mondello to Newark magnetostratigraphic correlations. Two correlation options, neither unequivocal, have the highest and nearly equivalent correlation coefficients. Option #1 predicts the base of Pizzo Mondello to be correlative with the middle part of the Newark APTS, whereas in Option #2 the base of Mondello starts towards the early part of the Newark APTS. According to sampling density and average sediment accumulation rates of 20-30m/m.y., polarity intervals with durations equal to or less than ≈170 k.y. may have been undersampled at Pizzo Mondello. Accordingly, we filtered the high resolution Newark APTS and performed further statistical correlations from which we conclude that Option #2 is preferred. With this option, the Carnian/Norian boundary based on conodonts corresponds to basal Newark magnetozone E7 at about 228 Ma (adopting Newark astrochronology), implying a long Norian with a duration of 20m.y. and a Rhaetian of about 6 m.y. duration. These ages are in fact not inconsistent with the few high quality radiometric dates that are available for Late Triassic time scale calibration. We suggest that Pizzo Mondello is a good candidate for a GSSP for the base of the Norian whereas we find that sections of the "Hallstatt" type , which may be more fossiliferous but have erratic and typically very low average rates of sediment accumulation, are more difficult to correlate with each other and with expanded sections such as Pizzo Mondello and the Newark
Triangulated riemann surfaces with boundary and the Weil-Petersson Poisson structure
No full textGiven a hyperbolic surface with geodesic boundary S, the lengths of a maximal system of disjoint simple geodesic arcs on S that start and end at ∂S perpendicularly are coordinates on the Teichmiiller space T(S). We express the Weil-Petersson Poisson structure of T(S) in this system of coordinates, and we prove that it limits pointwise to the piecewise-linear Poisson structure defined by Kontsevich on the arc complex of S. At the same time, we obtain a formula for the first-order variation of the distance between two closed geodesics under Fenchel-Nielsen deformation
Triassic and Jurassic calcareous nannofossils of the Pizzo Mondello section: a SEM study.
No full textPizzo Mondello is a 500 m thick pelagic-hemipelagic succession cropping out in Sicily, consisting of a nodular cherty limestone facies association of late Carnian to late Norian age. The uppermost portion was attributed to the Rhaetian and is represented by the plane-bedded Portella Gebbia Limestone. The section has been proposed as stratotype for the base of the Norian stage. The calcareous nannofossil content of limestones was studied with Scanning Electron Microscope (SEM) in two portions of the Pizzo Mondello section, one within “La Cava” that encompasses all proposed horizons for the base of the Norian, and one within the Portella Gebbia Limestone in the uppermost part of the section.
Calcareous nannofossil assemblages of the first portion display a low diversity, being constituted exclusively by calcispheres, that may constitute up to 40% of the sediment volume. Species richness increases in the upper portion. Initially, samples are dominated by Prinsiosphaera triassica, a nannolith of unknown taxonomic affinity. Rare calcareous dinocysts (Thoracosphaera cf. geometrica) and coccoliths are present in few samples. Uppermost samples are still dominated by "calcispheres" comparable to Thoracosphaera, but also yield a variety of coccoliths and nannoliths.
Calcareous nannofossil biohorizons was calibrated with conodont and radiolarian biostratigraphy. On this basis of this integrated work, specimens attribuited to cf. Thoracosphaera, observed in the lower portion of the section, are late Carnian to early Norian, while samples dominated by Prinsiosphaera, with rare Thoracosphaera and coccoliths are Rhaetian. The calcareous nannofossil assemblage of the uppermost samples, along with radiolarians and the absence of conodonts, point to a Jurassic age (Pliensbachian) for the uppermost Portella Gebbia Limestone at Pizzo Mondello. In conclusion, the age of the uppermost part of the Pizzo Mondello section is Jurassic, i.e., younger than previously thought. Calcareous nannofossils are present from the base of section and exhibit a significant taxonomic diversity, thus providing an auxiliary biostratigraphic frame for the Rhaetian - Jurassic interval in this area
Tethyan magnetostratigraphy from Pizzo Mondello ( Sicily ) and correlation to the Late Triassic Newark astrochronological polarity time scale
No full textWe present the magnetostratigraphy and stable isotope stratigraphy from an expanded (~430-m-thick) Upper Triassic marine limestone section at Pizzo Mondello, Sicily, and review published biostratigraphic information that can be used to defi ne the location of the conodont Carnian-Norian and Norian- Rhaetian boundaries in this section. Pizzo Mondello offers good potential for magnetostratigraphic correlation of marine biostratigraphic and chemostratigraphic data with the continental Newark astrochronological polarity time scale (APTS) for development of an integrated Late Triassic time scale. The relatively stable average values of 18O centered on 0‰ are a strong indication that the Cherty Limestone at Pizzo Mondello suffered very little diagenetic overprinting.
The conodont Carnian-Norian boundary is located 12.5 m above a positive shift of 13C. A statistical approach was applied to evaluate various Pizzo Mondello to Newark magnetostratigraphic correlations. Two correlation options have the highest correlation coeffi cients. In option #1, the base of Pizzo Mondello correlates with the middle part of the Newark APTS, whereas in option #2, the base of Pizzo Mondello starts toward the early part of the Newark APTS. We prefer option #2 in which the Carnian-Norian boundary based on conodonts, as well as its closely associated positive 13C shift, correspond to Newark magnetozone E7 at ca. 228–227 Ma (adopting Newark astrochronology), implying a long Norian with a duration of ~20 m.y., and a Rhaetian of ~6 m.y. duration.
These ages are in fact not inconsistent with the few high-quality radiometric dates that are available for Late Triassic time scale calibration. Based on its good exposure, accessibility, stratigraphic thickness and continuity, and multiple chronostratigraphic correlation possibilities, we propose Pizzo Mondello as global stratigraphic section and point for the base of the Norian.
Keywords: magnetostratigraphy, biostratigraphy, Late Triassic, Tethys, Sicily, Newark astrochronological polarity time scale
Evolutionary Process from Mockina bidentata to Parvigondolella andrusovi: Evidence from the Pizzo Mondello Section, Sicily, Italy
No full textDuring their last phase of evolution, the pectiniform conodont elements manifested an evident trend of simplification and miniaturization. This phase started from the late Norian (Sevatian) in the Late Triassic and the evolutionary process of genus Mockina to Parvigondolella, in particular between Mockina bidentata and Parvigondolella andrusovi, is one of the most significant examples. Parvigondolella has been reported worldwide since it was first described in the early 1970s. However, it has recently been suggested that genus Parvigondolella is an ecostratigraphic morphotype of genus Mockina, and thus a phenotype controlled by the environmental conditions, and not an independent taxon. In the Pizzo Mondello Section (Sicily, Italy), transitional forms between M. bidentata and P. andrusovi have been found at different evolutionary stages. We have investigated the oceanic conditions at the time by using redox-sensitive elements (Mn, Fe, V, Cr, and Ni) and seawater temperatures from biogenetic δ18Ophos to understand the possible environmental influences on the phylogenetic evolution between Mockina and Parvigondolella. The geochemical and isotope analyses indicate that the redox condition and temperature were stable during the evolution of genus Parvigondolella in Pizzo Mondello, confirming that genus Parvigondolella is a real taxon and not a phenotype. A new conodont species named Parvigondolella ciarapicae n. sp. is described here for the first time
Palermo e il suo mare
No full textL’articolo descrive un progetto per il concorso di “Riqualificazione urbana di Mondello”, luogo di balneazione nella città di Palermo. Il progetto di riqualificazione che nasce dall’idea che il waterfront possa costituire un punto d’incontro tra città e mare, articola diversi spazi della città, dall’isolato di Valdesi alla passeggiata a mare fino alla piazza di Mondello. L’intervento progettuale, che stabilisce un corretto rapporto tra architettura e preesistenza, si basa su un profondo senso della misura, intendendo con questo termine la capacità di dosare il gesto architettonico rispetto alle condizioni di contorno che sono assunte come prioritarie nell’intervento
The Carnian/Norian boundary interval at Pizzo Mondello (Sicani Mountains, Sicily) and its bearing for the definition of the GSSP of the Norian Stage
No full textWe present the magnetostratigraphy and stable isotope stratigraphy from an expanded (~430-m-thick) Upper Triassic marine limestone section at Pizzo Mondello, Sicily, and review published biostratigraphic information that can be used to defi ne the location of the conodont Carnian-Norian and Norian-Rhaetian boundaries in this section. Pizzo Mondello offers good potential for magneto-stratigraphic correlation of marine biostrati-graphic and chemostratigraphic data with the continental Newark astrochronological polarity time scale (APTS) for development
of an integrated Late Triassic time scale.
The relatively stable average values of δ18O centered on 0‰ are a strong indication that the Cherty Limestone at Pizzo Mondello suffered very little diagenetic overprinting. The conodont Carnian-Norian boundary is located 12.5 m above a positive shift of δ13C. A statistical approach was applied to evaluate various Pizzo Mondello to Newark magnetostratigraphic correlations. Two correlation options have the highest correlation coefficients. In option #1, the base of Pizzo Mondello correlates with the middle part of the Newark APTS, whereas in option #2, the base of Pizzo Mondello starts toward the early part of the Newark APTS. We prefer option #2 in which the Carnian-Norian boundary based on conodonts, as well as its closely associated positive δ13C shift, correspond to Newark magnetozone E7 at ca. 228–227 Ma (adopting Newark astrochronology), implying a long Norian with a duration of ~20 m.y., and a Rhaetian of ~6 m.y. duration. These ages are in fact not inconsistent with the few high-quality radiometric dates that are available for Late Triassic time scale calibration. Based on its good exposure, accessibility, stratigraphic thickness and continuity, and multiple chronostratigraphic correlation possibilities, we propose Pizzo Mondello as global stratigraphic section and point for the base of the Norian
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