Contribution to the sedimentology of the Messinian carbonates of the Chelif Basin (Boukadir, Algeria)

Abstract

The Messinian (Upper Miocene) is characterized at the level of its marginal basins by the development of numerous carbonate platforms. This study concerns the Messinian platform of the Boukadir region in the south of the Chelif Basin in Algeria. It is composed of a lower prograding rimmed platform and an upper aggradational homoclinal ramp resting upon the Tortonian–Lower Messinian Blue Marl Formation, and its thickness reaches ~280 m in the Chelif Basin. The upper red-algae unit is uniform and subhorizontal with a minimum thickness of 90 m. Petrographic analysis of the upper ramp reveals three different microfacies, characterized by Lithothamnium, foraminifera, high porosity, and a microsparitic matrix. MF1 is a packstone, MF2 a packstone/bindstone deposited above the fair-weather wave base and MF3 is a wackestone to packstone deposited below this level. The upper unit is made up entirely of autochthonous biogenic elements without significant external fluvial contribution. It was formed in a shallow marine environment, with very high productivity and a significant export of the sediments produced. This aggradation was followed by a rapid exhumation (regression) transforming all the aragonite into calcite. The platforms correspond to the T2 complex reef formation (6.7–5.95 Ma) documented on the other Messinian carbonate platforms in the South of the Alboran Sea that formed just before the Messinian Salinity Crisis.

Karstic geomorphology of carbonate Ouarsenis Piedmont (Boukadir region, Chelif) in Algeria: The role of the Messinian Salinity Crisis

“…The upper Lithothamnium unit outcrops at the top of the platform and is composed of very homogeneous red algae carbonate beds with a variable thickness. Along the piedmont, this formation shows a thickness of at least 80 m (Moulana et al, 2021) and a consistent nearly homoclinal ~ 5 • dip. The lower bioclastic carbonate unit below is heterogeneous: bed thickness and facies display frequent lateral and vertical changes.…”

“…3-A) are overlain by two Messinian bioclastic carbonate units (grouped in orange in Fig. 3-A) with low dips (Neurdin-Trescartes, 1992;Moulana et al, 2021). The lower bioclastic carbonate unit is ~70 m thick and the upper lithothamnium carbonate unit is ~80 m thick.…”

“…3). In the Chelif Basin, this structure forms at the surface the El Kherba hill along which continental Pliocene siltstones, sandstones and conglomerates crop out as well as older Marine Pliocene sandstone on its southern edge (Moulana et al, 2021).…”

“…In the study area, the Messinian carbonates were deposited before the Messinian Salinity Crisis (Moulana et al, 2021). They consist in bedded bioclastic carbonates, with a sharp contrast between the two units.…”

“…This study focuses on the marginal Messinian carbonate platform in the northern piedmont of the Ouarsenis mountains that has been only recently classified among the karstic areas of Algeria yet (Moulana et al, 2021). It is located in the Boukadir region on the southern edge of the 20 km wide lower Chelif basin crossed by the Chelif River (Fig.…”