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 & Hal