The Numidian sand event in the Western Rif Chain (Northern Morocco)

We report on new sedimentological and biostratigraphical data concerning the “Numidian sandstones” outcropping in the Western Rif Belt. The analyzed sections are located south of Tangier city, close to the 9th April dam and pertain to the Intrarif Sub-domain, which, in turn, is part of the External Rif domain. In the western peri-Mediterranean chains, the “Numidian sandstones” display constant lithological features. We analysed six well-exposed lithostratigraphic sections, which are organized in three portions: (1) the “sub-Numidian”, mainly dominated by varicolored clays, (2) the “Numidian sandstones”, which includes predominantly massive quartzarenitic sandstones, sometimes interbedded with mudstones, and, finally, (3) the “supra-Numidian”, characterized by alternation of light green marls and thin-bedded siltstones. Stratigraphic sections of the “Numidian sandstones” were measured and described to provide detailed sedimentological characterization and facies analysis. The “sub-Numidian”, thick more than 100 meters, is commonly made of varicoloured clays, which in all the studied sections shows a horizon rich in Tubotomaculum. In the study area, the “Numidian sandstones” are about 1100 m thick; their facies analysis have been performed by using Pickering et al. (1995) classification scheme. The basal part of the examined sections shows similar characteristics: proximal channels filled by very thickbedded disorganised pebbly sandstones and amalgamated structureless sandstones (Facies A1.4 and B1.1). The base of the beds is scoured and sometimes shows decimetresized mud clasts torn away from the substratum. Paleocurrents measurements, mainly indicated by flute casts, are from southeast to northwest. Upward, coarse-grained quartzarenitic sandstones mainly characterize the middle part of all the sections. They are organized in massive and thick-bedded pebbly-sandstones, micro-conglomerates (Facies A2.4 and A2.5), and disorganised thick sandstones strata, often marked by fluid escape structures (Facies B1.1), revealing flows processes controlled by high-density turbidity currents and debris flows. These deposits evolve to plurimeter- to decimetre-thick mediumgrained sandstone and mud couplets (Facies C2.3) with a mainly fining-and thinning-upward trend, which we consider to be attributable to lobe and fringe lobe deposition. Commonly, the uppermost part of the sections shows a restoration of disorganised pebbly sandstones facies (Facies A1.4). The “supra-Numidian” caps the thick “Numidian sandstones” and is made up by about 200 m of bioturbated marls rich in planktonic foraminifera and fine-grained silty/muddy deposits. These latter show sedimentary structures related to unidirectional flows, probably owed to deep contourites currents. References Pickering K.T., Hiscott R.N., Kenyon N.H., Ricci Lucchi F. & Smith R. (editors) 1995. Atlas of architectural styles in turbidite systems. London: Chapman & Hall