--> APTIAN FORMATION Lithostratigraphic characterization of on the (NE. Algeria) north side of DJ. BOU ARIF

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APTIAN FORMATION Lithostratigraphic characterization of on the (NE. Algeria) north side of DJ. BOU ARIF

Abstract

The study of Aptian series of Mennchar Ali Gueraa cutting, which is located in the southwestern part of the northern slope of Dj. Bou Arif (NE of Algeria), shows two well-individualized lithostratigraphic units. At the base, there are blackish marl of lower Aptian and they have delivered poor microfauna portrayed in Cythereis blaterensis and Schuleridae. At the top, the deposits are represented by marly- limestone intercalation, containing Oribitolines at the base of the carbonated bar of the Upper Aptian.

The base of the carbonated bar shows beautiful microfacies. The latter contains Acicularia, Haplophragmoides sp. Boueina, ostracods, miliolids, Ammobaculites sp. Cuneolina sp. Valvulammina sp. Orbitolina sp. The oysters, gastropods and sea urchins represent the macrofauna. This reveals the upper Aptian.

The microfaciologic study in this series has helped to highlight two microfacies whose association on the deposit profile defines an inner and medium platform domain (intertidal to high bottom). It is characterized by packstone and microsparitic microfacies including milioles, algae and echinoderms. The second one is the oolitic grainstone microfacies rich in orbitolines, representing a medium platform environment with a high energy (Shoal).

The Aptian Sea must have a shallow depth, as demonstrated with certainty the presence of algae. The limestone Orbitoline seems not to have formed in deep water, as microscopic examination of these rocks reflected that they were formed in rough water (oolitic limestone). Even marl were not formed in great depth, as shown in the presence of perforated bench. The perforation occured due to the existance of lithophagous molluscs.