The Kechabta Basin is part of the Mejerda foreland Basin in front of the Numidian nappes. It bears a thick (over 2,000 m) succession, Serravallian to Messinian in age, corresponding to (in stratigraphic order) the Hakima, Oued... [ view full abstract ]
The Kechabta Basin is part of the Mejerda foreland Basin in front of the Numidian nappes. It bears a thick (over 2,000 m) succession, Serravallian to Messinian in age, corresponding to (in stratigraphic order) the Hakima, Oued El Melah, Kechabta, Oued Bel Khedim and Chaabet Et Tebbala formations.
The Hakima Fm. (500 m thick) unconformably overlies Cretaceous or Eocene limestones, and records the first Miocene transgression in this basin. It represents an overall regressive sequence beginning with offshore grey-brown claystones, followed by upper offshore to shoreface sandy storm beds alternating with claystones, then by shoreface sandstones bearing hummocky-cross stratification and wave ripples, then by beach facies characteristic with laterally-continuous, even lamination or low-angle cross-bedding bioturbation and wavy bedding. The sequence ends with fluvial to alluvial fan deposits (conglomerate-filled channels, claystones with paleosols).
The Oued El Melah Formation (350 m thick) consists of regularly alternating grey coloured clays and gypsum layers. These facies are interpreted as lagoonal/sabkha deposits.
The Tortonian Kechabta Fm. (1300 m thick) corresponds again to a regressive coastal sequence similar in facies to the Hakima Fm., but without the fluvial member at its top. The parasequences ends with thicker sandstone deposits than in the Hakima Fm.
The Messinian Oued Bel Khedim formation, 300 m thick, is made of alternating grey-black marine claystones and gypsum layers at the base, and lacustrine limestone at the top.
The Messinian Chaabet Et Tebbala Formation (150 m), locally preserved, comprises breccias, subaerial travertines, fluvial red clays and conglomerate-filled channels. The Messinian deposits are associated to the Messinian Salinity Crisis. They are bounded by two subaerial erosional surfaces at the base and top of the formation.
Overall, the Serravallian-Tortonian succession is interpreted as recording two tectonic pulses followed by relaxation of stresses, represented by two major regressive sequences filling the flexural basin. The intervening Oued El Melah Fm. marks the beginning of the second flexuration phase. The first erosional phase, at the base of the Messinian breccias, is referred to the intra-Messinian tectonic phase.
