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Age, internal stratigraphic architecture and structural style of the Oligocene–Miocene Numidian Formation of northern Tunisia

Riahi S., Soussi M., Ben-Ismail-Lattrache K.

Annales Societatis Geologorum Poloniae

2015

Vol. 85, No. 2

345--370

The stratigraphy of the Numidian Formation of northern Tunisia and its internal organization are updated. Planktonic foraminifera point to a mainly Oligocene–Early Miocene age of this formation in the majority of the sections studied. Some key lithological horizons are recognized within the early Miocene succession, allowing lateral correlation between the outcrops of the Mogod and Kroumirie mountains. These include: (1) a conglomeratic interval, up to 1–2 m thick and rich in reworked glauconitic boulders, limestone fragments of the Tellian (Eocene) and pectinid bivalves; and (2) a relatively continuous glauconitic level. In the new stratigraphic scheme, the Zouza, Ben Metir and Sejnene sections represent the entire Numidian Formation. A lower unit (200–700 m thick), highly pelitic with subordinate sandstone beds was distinguished, overlain by an upper unit which is sandier, especially in its uppermost part (1,000–1,500 m thick). In the present study, these have been stratigraphically dated as Oligocene–Early Miocene p.p. (Rupelian–Chattian; P19–P21 zones) to Aquitanian (N4 Zone) and Miocene (Aquitanian–early Burdigalian; N4–N5 zones), respectively. In the areas studied, the sandy succession assigned to the Kroumirie Member begins with a sandstone unit with an erosional base or a major discontinuity, locally marked by conglomerates made up of various reworked components. It rests generally on a thick shale unit that characterises the upper part of the Zouza Member. The thinner, uppermost succession of the Numidian Formation represents the Babouch Member, dated as Burdigalian (N6–N7 zones). Within the framework of the new proposal, the total stratigraphic thickness of the Numidian Formation in northern Tunisia does not exceed 2,200–2,600 m. Internally, the Numidian Formation is transected by the Intra-Numidian Thrust and back-thrust faults, associated with faulted folds that are recognized in outcrop on different scales and in seismic sections. Along these thrust and/or reverse faults, the middle to upper Eocene deposits have undergone uplift and are exposed at the surface (e.g., Dowar Larmel in Meloula-Tabarka, Gaâret Sejnene and Sidi M’chreg sections).

Malm-Berriasian formations of northern Tunisia: updated biostratigraphy, regional correlations and western Tethys geodynamic context

Boughdiri M., Sallouhi H., Cordey F., Maalaoui K., Soussi M.

Volumina Jurassica

2006

Vol. 4, no. 1

148-149

Upper Jurassic – lowermost Cretaceous formations in northern Tunisia include the Zaress Fm. of the Tunisian “Dorsale” (Ammonitico Rosso facies: Middle Callovian-Oxfordian) and the corresponding beds from Fahs and Jédidi fms (radiolarian-bearing series: Upper Bajocian-Oxfordian) of the nearby surrounding exposures and the “Tunisian Trough”, respectively. These heteropic facies are overlain by the marl/limestone alternations of the Beni Kleb Fm. (Kimmeridgian – Middle Berriasian). Recent integrated biostratigraphic investigations (ammonites, radiolarians, calpionellids) undertaken in different palaeogeographical domains of northern Tunisia allowed a precise dating of the Malm -Berriasian fms. Revised lithostratigraphy and regional correlations lead to the recognition of an updated facies repartition in central and northern Tunisia. Within the North Maghrebian Range, main palaeogeographical segments can be outlined considering facies affinities: the North-South Axis successions of Central Tunisia show close affinities with those described from the Middle and Central AurŻs Range (eastern Algeria). The Tunisian “Dorsale” series are to be compared with corresponding beds of northern AurŻs, Hodna Mounts and the South Tellian Border (Tiaret area), in Algeria, and with the Prérif and Mésorif Upper Jurassic facies, in Morocco. Deeper facies of the Tunisian Dorsale surrounding outcrops and the “Tunisian Trough” are closer to successions described in ancient literature from the Babors and the West Numidian Range of Algeria. All these equivalent successions from the external segments of the Maghrebian Range are quite distinctive from the Internal Rif and Kabylias “Dorsales calcaires” series. Both facies types have evolved in clearly different palaeogeographical realms related with the tectonic evolution of north- and south-western Tethys margins since the Triassic – Early Jurassic times.