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Abstract: The northern part of the N–S-trending basin of the Limagne graben, located in the northern part of the Massif Central (France), contains Oligocene and Miocene calcareous lacustrine deposits. The area is known for its stromatolite reefs surrounded by marl, clay and uncemented carbonate sand with oncolites. Because the origin of the carbonate accumulated by cyanobacteria has long been debated, the clayey deposits associated with the stromatolites were analysed using XRD, SEM and K–Ar dating methods. The results show a monotonous assemblage of carbonates, dioctahedral smectite, illite–smectite (Reichweite) R=0, glauconitic illite and abundant orthoclase. Detrital minerals such as quartz and detrital illite are found near the basin''s borders but are very scarce in its central part, indicating a lack of detrital input from the regional basement. Hence, the abundant orthoclase found in all the clayey deposits of the Limagne Basin cannot be linked to erosion of the surrounding Hercynian basement. The SEM analysis showed the orthoclase crystals to have a tabular morphology with sharp boundaries and to be embedded within a clay matrix, whilst the K–Ar dating of the orthoclase and glauconitic illite yielded ages ranging from 90 to 66±2Ma, i.e. Turonian to Maastrichtian. These two results clearly indicate that the fill of the Limagne Basin, composed mainly of carbonate, clay and orthoclase, must have been partly due to the erosion of an Upper Cretaceous sedimentary blanket once covering the Massif Central basement. This cover was probably constituted of chalk, dioctahedral smectite, I/S and glauconitic illite, associated with authigenic orthoclase and flint. Flints are found reworked in the alluvial formations of the Late Pliocene Lower Bourbonnais sands and clays (‘Sables et argiles du Bourbonnais’) and in the Pleistocene terraces. Moreover, relicts of the Upper Cretaceous cover were preserved during the sedimentary filling of the Cenozoic Limagne Basin. Authigenic orthoclase of similar shape has been described in the Chalk Group of the Paris Basin and from localities in northern France and Belgium. The mineral is rare in the Turonian chalk but increases rapidly at the base of the Coniacian to Campanian chalk; it has also been noted that the number of orthoclase crystals increases as the quantity of clastic components decreases. Similar orthoclase crystals were found associated with dioctahedral smectite in the decarbonated residues of the Coniacian to Santonian chalk from Fécamp and Etretat (northern France). Moreover, our results are consistent with other data from within and around the Paris Basin, such as the palaeogeography and facies distribution of the Chalk formations, the residual flints in the clay-with-flints of the southern Paris Basin and around the Morvan, and apatite fission-track thermochronology data from the Hercynian basement of the Massif Central and the Morvan. All these data indicate a major connection between the Paris Basin and the Tethys, and an extensive palaeocover on the Massif Central and Morvan basement. [Copyright &y& Elsevier]

We investigate the potential use in traditional ceramics of several clays collected in the Numidian Flysch Formation (Upper Oligocene) at Tabarka, and Sejnane; Northern part of Tunisia). The valorisation of these adopts the technique of dry process, which requires a mixture of powdered clay with 7% water. This allows rapid drying of uncooked tiles. The tiles are fired at four different temperatures (1000 °C, 1050 °C, 1100 °C and 1150 °C) in order to optimize technological parameters such as shrinkage, water absorption and flexural strength. The obtained tiles show acceptable drying and firing shrinkage (not exceeding 3%), and bending strength (between 13 and 16 N/mm2) which are close to the required standards (EN ISO 10545–4, 15N/mm2 for wall tiles). The absorption ranges from 10 to 20%, which classifies these products in group BIII according to the international standards (ISO 13006 and EN ISO 10545–3). Variation of shrinkage and water absorption with the firing temperature reveals that optimal range is 1125–1150 °C for the Tabarka samples, whereas the Sejnane products might be fired at lower values (~1025 °C). The Tabarka fired pieces exhibit strong brightness. These results suggest that these latter clays could be used for white products such as sanitary ware formulations while those from Sejnane ones are more appropriated for colored (red) applications. The X-ray diffraction on the fired tiles powders shows the formation of quartz which is initially present in the crude clays, and mullite that is present at all firing temperatures. Moreover, the presence of mullite due to the richness of Al 2 O 3 in Tabarka clays could support their refractory properties. • Potential use in traditional ceramics of Numidian Flysch was investigated. • Obtained tiles show acceptable firing shrinkage 3% and bending strength at 16 N/mm2. • Shrinkage and WA optimal range is 1150 °C for Tabarka and 1025°C for Sejnane samples. • Fired tiles shows the formation mullite, especially in Tabarka clays richer in Al 2 O 3. • Abundant clayey geological raw material of Numidian can be used on ceramic industry. [ABSTRACT FROM AUTHOR]