Early-Middle Frasnian (early Late Devonian) sedimentology and magnetic susceptibility of the Ardennes area (Belgium): identification of severe and rapid sea-level fluctuations

peer reviewe

Linking the variation of Sediment Accumulation Rate to short term sea-level change using cyclostratigraphy: case study of the Lower Berriasian hemipelagic sediments in central Tunisia (Southern Tethys)

peer reviewe

Evolution of Miocene siliciclastic deposits in central Tunisia: Case study of the Khechem El Artsouma section

En Tunisie, au cours du Miocène, suite à la phase de plissement NE-SW (direction atlasique), les dépôts silicoclastiques sont mis en place dans un environnement deltaïque au sud-ouest et une plate-forme marine interne au nord-est du pays. Dans cet article, nous présentons la coupe de Kechem El Artsouma, du Miocène, qui est représentative des dépôts de Tunisie centrale. Cette zone est particulièrement intéressante car elle correspond à la zone de transition entre les dépôts de delta et marins peu profonds. Nous proposons une combinaison de techniques telles que l'analyse des faciès, la susceptibilité magnétique et la mesure de la teneur en carbonate pour améliorer l'interprétation et la reconstruction des paléo-environnements et de leur évolution au cours du Miocène. Huit faciès sont identifiés, situés dans un domaine fluviatile, lagunaire et un domaine de plage. Les dépôts de la Formation Ain Grab (Langhien) sont interprétés comme déposés en phase transgressive, suivis par les dépôts de la Formation de Béglia (Serravallien) en phase régressive. La Formation de Saouaf (Serravallien-Tortonien inférieur) correspond à une phase transgressive et régressive. La coupe Kechem El Artsouma permet de proposer un modèle sédimentaire pour les dépôts du Miocène de la zone de transition en Tunisie centrale.After a NE-SW folding phase (Atlasic direction) during the Miocene, siliciclastic sediments from a deltaic environment were deposited in the south-western part of Tunisia while an internal offshore platform formed in the north-eastern part of the country. In this paper we focus on the Khechem El Artsouma Miocene section which is representative of central Tunisia deposits. This area is particularly interesting to study, because it corresponds to a transition zone between deltaic and shallow marine deposits. Facies analysis, magnetic susceptibility measurements and carbonate content measurements are combined to propose a reconstruction of the paleoenvironments and their evolution through the Miocene. Eight facies are identified, from fluviatile, swamp and evaporitic lagoon environments to shore environments. The deposits of the Ain Grab Formation (Langhian) are interpreted as transgressive, followed by the Beglia Formation (Serravalian), which are interpreted as regressive. The whole Saouaf formation (Upper Serravalian - Lower Tortonian) corresponds to a transgressive and regressive sequence. The Djebel Khechem El Artsouma section permits the proposal of a complete sedimentary model for the Miocene deposits from this central Tunisia transition zone

Interactions mère-enfant typique et dysphasique : comment utiliser les gestes pour formuler une devinette ?

Cet article étudie l’usage des gestes par 18 dyades mère-enfant dysphasique en comparaison avec 18 dyades mère-enfant typique dans une situation de jeu de devinette par indices. Tous les enfants sont âgés entre 5 et 7 ans.Les analyses concernent la proportion, les rôles ainsi que la nature sémiotique des gestes utilisés comme indices dans le jeu de devinettes. Les résultats aboutissent à des différences quantitatives et qualitatives dans l’emploi des gestes entre les deux types de dyades. Même si globalement la devinette se profile comme une activité essentiellement verbale, il apparait que les enfants mobilisent plus souvent les gestes pour la production d’indices que leurs mères et que les dyades mère-enfant dysphasique présentent des taux plus élevés de gestes que les dyades mère-enfant typique.Par ailleurs, les résultats mettent en évidence des spécificités chez les enfants dysphasiques. Ils semblent utiliser davantage de gestes déictiques et certains d’entre eux ont recours plus souvent aux gestes illustratifs, se substituant au verbal. L’étude montre également une certaine hétérogénéité des dyades dans les deux groupes de la population.This paper investigates the use of gestures by 18 mother-SLI children dyads compared to 18 mother-typically developing children dyads in a guessing game situation. All children are between 5 and 7 years old.Analyses concern the proportion, the roles and the semiotic nature of gestures used as clues in the guessing game. Results show both quantitative and qualitative differences between the two types of dyads. Even though the guessing game stands out as an essentially verbal activity, it appears that children make use of gestures as clues more frequently than their mothers and that mother-SLI children dyads produce a higher rate of gestures than mother-TD children dyads.In addition, results highlight several specific characteristics of SLI children. They seem to produce more deictic gestures and some of them make use of more illustrative gestures as substitutes for verbal productions. The study also shows that, to some extent, dyads in both types of population are quite heterogeneous (in their behavior)

Interactions mère-enfant typique et dysphasique : comment utiliser les gestes pour formuler une devinette ?

Cet article étudie l’usage des gestes par 18 dyades mère-enfant dysphasique en comparaison avec 18 dyades mère-enfant typique dans une situation de jeu de devinette par indices. Tous les enfants sont âgés entre 5 et 7 ans.Les analyses concernent la proportion, les rôles ainsi que la nature sémiotique des gestes utilisés comme indices dans le jeu de devinettes. Les résultats aboutissent à des différences quantitatives et qualitatives dans l’emploi des gestes entre les deux types de dyades. Même si globalement la devinette se profile comme une activité essentiellement verbale, il apparait que les enfants mobilisent plus souvent les gestes pour la production d’indices que leurs mères et que les dyades mère-enfant dysphasique présentent des taux plus élevés de gestes que les dyades mère-enfant typique.Par ailleurs, les résultats mettent en évidence des spécificités chez les enfants dysphasiques. Ils semblent utiliser davantage de gestes déictiques et certains d’entre eux ont recours plus souvent aux gestes illustratifs, se substituant au verbal. L’étude montre également une certaine hétérogénéité des dyades dans les deux groupes de la population.This paper investigates the use of gestures by 18 mother-SLI children dyads compared to 18 mother-typically developing children dyads in a guessing game situation. All children are between 5 and 7 years old.Analyses concern the proportion, the roles and the semiotic nature of gestures used as clues in the guessing game. Results show both quantitative and qualitative differences between the two types of dyads. Even though the guessing game stands out as an essentially verbal activity, it appears that children make use of gestures as clues more frequently than their mothers and that mother-SLI children dyads produce a higher rate of gestures than mother-TD children dyads.In addition, results highlight several specific characteristics of SLI children. They seem to produce more deictic gestures and some of them make use of more illustrative gestures as substitutes for verbal productions. The study also shows that, to some extent, dyads in both types of population are quite heterogeneous (in their behavior)

Refining the Early Devonian time scale using Milankovitch cyclicity in Lochkovian–Pragian sediments (Prague Synform, Czech Republic)

The Early Devonian geological time scale (base of the Devonian at , Becker et al., 2012) suffers from poor age control, with associated large uncertainties between 2.5 and 4.2 Myr on the stage boundaries. Identifying orbital cycles from sedimentary successions can serve as a very powerful chronometer to test and, where appropriate, improve age models. Here, we focus on the Lochkovian and Pragian, the two lowermost Devonian stages. High-resolution magnetic susceptibility ( – 5 to 10 cm sampling interval) and gamma ray spectrometry (GRS – 25 to 50 cm sampling interval) records were gathered from two main limestone sections, Požár-CS (118 m, spanning the Lochkov and Praha Formations) and Pod Barrandovem (174 m; Praha Formation), both in the Czech Republic. An additional section (Branžovy, 65 m, Praha Formation) was sampled for GRS (every 50 cm). The and GRS records are very similar, so variations are driven by variations in the samples' paramagnetic clay mineral content, reflecting changes in detrital input. Therefore, climatic variations are very likely captured in our records. Multiple spectral analysis and statistical techniques such as: Continuous Wavelet Transform, Evolutive Harmonic Analysis, Multi-taper method and Average Spectral Misfit, were used in concert to reach an optimal astronomical interpretation. The Požár-CS section shows distinctly varying sediment accumulation rates. The Lochkovian (essentially equivalent to the Lochkov Formation (Fm.)) is interpreted to include a total of nineteen 405 kyr eccentricity cycles, constraining its duration to . The Praha Fm. includes fourteen 405 kyr eccentricity cycles in the three sampled sections, while the Pragian Stage only includes about four 405 kyr eccentricity cycles, thus exhibiting durations of and respectively. Because the Lochkov Fm. contains an interval with very low sediment accumulation rate and because the Praha Fm. was cross-validated in three different sections, the uncertainty in the duration of the Lochkov Fm. and the Lochkovian is larger than that of the Praha Fm. and Pragian. The new floating time scales for the Lochkovian and Pragian stages have an unprecedented precision, with reduction in the uncertainty by a factor of 1.7 for the Lochkovian and of ∼6 for the Pragian. Furthermore, longer orbital modulation cycles are also identified with periodicities of ∼1000 kyr and 2000–2500 kyr

Litholog generation with the StratigrapheR package and signal decomposition for cyclostratigraphic purposes

To establish an astronomical time scale, it is useful to perform a visual inspection of the lithological evolution, together with proxies record. It allows to have a clear understanding of the expression of Milankovitch cyclicity. However, performing such an inspection can be challenging due to the large amount of data and high spatial resolution required to perform a sound cyclostratigraphic analysis. To address this problem we present the StratigrapheR package in the free software environment R (https://CRAN.R-project.org/package=StratigrapheR). This package is designed to generate lithologs and to deal with stratigraphical information. StratigrapheR takes advantage of the repetitive nature of sections used for cyclostratigraphic purposes to automate as much as possible the litholog generation while still allowing the visualisation of discrepancies (e.g. lateral variations of thickness and irregular stratification boundaries) and of any particular features (e.g. fossil content, sedimentary structures, stratigraphical intervals, etc.). The package furthermore allows to import vector graphics as SVG files, to export the lithologs in PDF and SVG form, to manipulate stratigraphic interval data and to visualise oriented palaeomagnetic data. The lithologs made in StratigrapheR can be plotted at high resolution directly along the results of time series filtering and/or decomposition methods. This is particularly useful for high-frequency components inspection. Empirical Mode Decomposition (EMD) in particular can be used for visual inspection. It allows to compute different components -also called modes- by iteratively subtracting from the signal the mean envelope curves, defined by local minima and maxima. In the isolated modes, each contiguous local extrema are separated by a zero-crossing. This property furthermore allows the determination of instantaneous frequency and amplitude, using for instance the Hilbert transform. EMD typically decomposes standard cyclostratigraphic time series in maximum 15 modes, which allows all the instantaneous ratios of the modes frequencies - taken two by two- to be calculated in a realistic computational time. These instantaneous ratios of frequencies can then be used to find the signature of Milankovitch cycles by identifying relatively higher ratios distributions at values characteristic of the orbital cycles. Specific ratios intervals can then be isolated and linked back to the parts of the signal that are at their source