The filament event near the Cenomanian-Turonian boundary in Tunisia: filament origin and environmental signification

Near the Cenomanian-Turonian boundary, the filament event corresponds to the massive occurrence of thin elongate shells, probably bivalves which constitute, in the Bahloul Formation, about 40% of allochems. This biosedimentary event was described in several areas, such as in Tunisia, Algeria, Morocco, North America, Oman and Tibet. In Tunisia, filaments are well represented within well laminated black shales constituting the Bahloul Formation, late Cenomanian – early Turonian in age. These black shales were deposited under anoxic conditions developed in an outer ramp environment. Filaments are particularly abundant in the upper part of the Bahloul Formation, which is topped by a condensation level exhibiting encrusted ammonites associated with frequent burrows, and phosphatic and glauconitic grains. In terms of depositional environments, the filament concentrations announce an evolution towards “normal”-marine conditions, which followed the anoxic conditions favouring black-shale formation. This trend coincided with a deepening that led to maximum flooding at the condensation surface. The petrographic study of samples taken along a N-S transect shows a clear evolution of filament structures from distal to proximal ramp. Limestones deposited in the outer ramp environment mainly contain well preserved “pelagic” bivalve shells showing a thin-shelled structure composed of elongated filaments. Laterally, toward the proximal ramp, the bivalve shells are progressively disintegrated, the filaments being arranged parallel to bedding. In an even more proximal setting, filaments appear finer, highly fragmented and arranged without preferential orientation. The Cenomanian-Turonian “pelagic” bivalves thus probably lived in an outer ramp environment and their thin shells disintegrated progressively into filaments. This happened during high energy conditions generated by storms.The filament event, which is associated to other bio-events expressed by the extinction and the first occurrence of some pelagic species, could be used to establish local to global correlations.When the ammonite Watinoceras, the main early Turonian marker, is rare or absent, the filament-rich facies could indicate the proximity of the Cenomanian-Turonian boundary.At a global scale, the filament event illustrates a sea-level rise in relation with eustatic and climatic changes. The maximum flooding of this transgressive event was identified in several localities and dated about 93 Ma. The very high sea-level conditions are favourable to accumulation and preservation of organic-rich facies such as black shales, which illustrate the anoxic event OAE2.The abundance of filaments near the Cenomanian-Turonian boundary is an indicator of high organic productivity following a climatic change to warmer conditions. The latter have clearly influenced oceanic water-masses circulation, water column stratification and nutrient partitioning

Improvement Axial Dispersion Calculation in Fibrous Garnished Fixed Beds Using the Neural Method

To determine accurately the physical modeling of flow through porous media and / or in chemical reactors, especially in the field of low Reynolds numbers, it is essential to compute the coefficient of axial dispersion. In prior studies, we employed the neural method to compute axial dispersion within fixed beds with parallelepiped and spherical packings. In the present study we apply the same method of calculation on heterogeneous fixed beds with large anisotropy using data from Poirier and Trinh on fibrous beds. Such an investigation could be however very useful while one has the desire to predict the mixing process to characterize the axial dispersion in fixed beds of anisotropic particles and when experimental measurements are not accessible and / or difficult to implement as for reactors and / or industrial complex porous media. To show also the robustness and applicability of this method, the calculation results obtained will be modeled using expressions similar to those proposed by Poirier and Trinh, so that we can compare our results with those obtained by these authors, under the same operating conditions. Furthermore, our study offers a comprehensive analysis encompassing all three examined fixed bed configurations, namely parallelepiped, spherical, and fibrous arrangements

Physical properties of nanosized cobalt doped TiO<SUB align="right">2 films grown by pulsed laser deposition

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Ostracod Response to a Major Middle Jurassic Sea-Level Fall: A Case Study from Southern Tunisia (North Gondwana) with Implications on Regional Stratigraphy and Palaeoenvironmental Reconstruction

Marginal-marine to non-marine ostracod assemblages from the Bajocian (Mid-Jurassic) of southern Tunisia, precisely from the Krachoua Formation at the Kef El Anneba section near the Beni Kheddache area, are here described and tested for their utility to improve the stratigraphic accuracy and palaeoenvironmental reconstructions. This particular microfauna consists of 11 species belonging to 6 genera and represents 2 distinct types of species-rich assemblages from this time interval, allowing the interpretation of the depositional setting of the fossiliferous horizon from which the samples derive. The first ostracod assemblage is mainly composed of the brackish to shallow marine species Fastigatocythere sp. Mette, 1995; Vernoniella aff. V. bajociana Bate, 1965b; Paracypris sp. A, Paracypris sp. B, Fabanella sarda Malz et al., 1985; Marslatourella aff. M. bathonica Andreu, 1999; and Fabanella aff. F. bathonica Oertli, 1957. This ostracod biofacies reflects marginal marine (shallow platform, restricted lagoon) conditions in the studied area. In contrast, the second ostracod assemblage is exclusively dominated by the non-marine limnic species Alicenula sp., Theriosynoecum pusilla Rohr, 1976; Theriosynoecum aff. T. aveyronensis Rohr, 1976; and Theriosynoecum sp. Such ostracod biofacies reflects the establishment of (a) permanent freshwater lake(s) in the studied area, triggered by the total emersion of the Bajocian Krachoua platform, presumably as response to the short-term sea-level fall event JBj3 of Haq (2017). The recognized ostracod species from the upper part of the Krachoua Formation at Kef El Anneba section (Medenine area) are particularly similar to those already described from the neighbouring sections of Kezzani (Dhaher area) and Krachoua (Tataouine area), facilitating a stratigraphic calibration of the Krachoua Formation, as well as regional correlations of the respective Bajocian continental event within the southern Tunisian palaeogeographic domain. Moreover, the biogeography of the studied ostracod microfauna from the Mid-Jurassic of southern Tunisia provides further arguments to support the hypothesis of significant biological exchanges between Laurasian and Gondwanan islands, as recently demonstrated by means of a charophyte microflora, indicating that Peri-Tethyan biogeography remained relatively uniform during that time interval and challenging the previous assumption of their endemism

Preparation of Sb: SnO2 thin films and their effect on optoelectrical properties

The present study focuses on pure and antimony (Sb)-doped tin oxide thin film and its influence on their structural, optical, and electrical properties. Both undoped and Sb-doped SnO2 thin films have been grown by using a simple, inexpensive pyrolysis spray technique. The deposition temperature was optimized to 450 �C. X-ray diffractions pattern have revealed that the films are polycrystalline and have a tetragonal rutile-type crystal structure. Undoped SnO2 films grow along (110) preferred orientation, while the Sb-doped SnO2 films grow along (200) direction. The size of Sb-doped tin oxide crystals changes from 26.3 to 58.0 nm when dopant concentration is changed from 5 to 25 wt.%. The transmission spectra revealed that all the samples are transparent in the visible region, and the optical bandgap varies between 3.92 and 3.98 eV. SEM analysis shows that the surface morphology and grain size are affected by the doping rate. All the films exhibit a high transmittance in the visible region and show a sharp fundamental absorption edge at about 0.38–0.40 nm. The maximum electrical conductivity of 362.5 S/cm was obtained for the film doped with 5 wt. % Sb. However, the carrier concentration is increased from 0.708 9 1018 to 4.058 9 1020 cm3. The electrical study reveals that the films have n-type electrical conductivity and depend on Sb concentration. We observed a decrease in sheet resistance and resistivity with the increase in Sb dopant concentration. For the dopant concentration of 5 wt.% of Sb in SnO2, the Rs and q were found minimum with the values of 88.55 (X cm-2) and 2.75 (X cm), respectively. We observed an increase in carrier concentration and a decrease in mobility with the addition of Sb up to 25 wt.%. The highest figure of merit values 2.5 9 10–3 X-1 is obtained for the 5wt% Sb, which may be considered potential materials for solar cells’ transparent windows