Stratigraphy, sedimentology and structure of the Numidian Flysch thrust belt in northern Tunisia

The Oligo-Miocene Numidian Flysch of northern Tunisia has long been divided into three distinct lithostratigraphic units considered as vertically superimposed: the lower unit or the " Zouza member" , the middle unit or the " Kroumirie member" and the upper unit or the " Babouch member" According to this reconstruction the two first members are mostly Oligocene in age and only the third member was assigned as early Miocene in age. In this study, we present new biostratigraphic data, based on planktonic foraminiferal analysis, demonstrating that both the Zouza and the Kroumirie members are Oligocene-early Miocene in age and are, therefore, coeval.Four distinct facies associations have been identified within the Numidian Flysch including: (a) massive sandstones; (b) conglomerate; (c) an interbedded mudstone-sandstone association; and (d) a mudstone facies association. Slide-slump units and injectionite sands occur within the more mud-rich associations. The likely depositional setting is a muddy slope-apron system, cut locally by sand-rich channels, which fed channel-terminal lobe deposits. Paleocurrent data support strongly a flow from N and NW. Modal analysis, demonstrates that the Numidian sandstones are quartz-arenite type (QFL, 97.25:1.25:1.5) derived from middle to high grade-metamorphic and granitic rocks. Zircon geochronology, yielding ages of 514 ± 19. Ma from Tunisia and 550 ± 28. Ma from Sicily, would support the basement terrain that crops out along the Algerian coast and forms part of Calabro-Peloritani-Kabylian zone, as the most likely parental source of the Numidian Flysch for both Sicily and Tunisia. Zircon data from the Fortuna Formation yields ages of 1698 ± 67. Ma, which is more compatible with an African craton source (Fildes et al., 2009).Structural consideration of the basal contact of the Numidian Flysch with the underlying Tellian rocks, as well as newly interpreted seismic data; confirm the allochthounous position of the Numidian complex and its displacement southward.Facies comparison with the equivalent Oligo-Miocene Bejaoua siliciclastic deposits outcropping towards the south shows that the Numidian complex is an " out-of-sequence thrust unit" and that the two Oligo-Miocene sedimentary systems are quite distinct and were sourced from wholly different source regions. © 2009 Elsevier Ltd.