## 2 Geological Framework  
The Neogene basins, in the western part of Algeria, stretch parallel to the Mediterranean coast and lie within the septentrional and meridional Tellian Atlas mountain belts, which belong to the southern branch of the Alpine chain [1; 31]. The intramountainous Chelif Basin is a wide depression of over 450 km filled with Mio-Plio-Quaternary deposits [1; 2; 3; 9; 32; 33]. It is formed by a succession of plains, hills, and folds, boarded by the Dahra and Boumaad Mountains in the north, and the Ouarsenis Mountains in the south. These Tellian belts were structured during the Mesozoic [34] and constitute the substratum of the Neogene deposits. The Middle-Chelif Basin extends from the Sara-El-Maarouf anticline to the Beni-Ghomerian plateau (Figure 2). In its central part, the Quaternary plain forms a narrow strip that stretches for over 50 km. This region is affected by normal and thrust faults, including the so-called \"El-Asnam Fault\". The orientation of these faults is parallel to the synclinal axis of the basin. The cross-sections performed by the National Society of Petroleum [35] and the General Company of Geophysics [7] show that the synclinal axis of this basin appears to be north of the Chelif River. In the southern part of this plain, inlier terrains of Jurassic-to-Silurian age outcrops form the Doui, Rouina, and Temoulga Massifs, from east to west, respectively. These schistity mass are considered to be autochthonous formations [33; 34]. Although the Jurassic formations are predominant in these outcrops, the bedrock is mainly Cretaceous in most of the basin area, and it is composed of Cenomanian to Senonian clays and marls [36]. Several previous geological studies have detailed the lithological and stratigraphical aspect of the Neogene deposits in the Middle-Chelif Basin [2; 9; 32]. The first sedimentary deposit is a red detritic series of conglomerates, poudgues, and marls. [PERSON] [32] and [PERSON] [2] attribute these formations to the Lower Miocene, while [PERSON] [9] and [PERSON] [3] assign them to the Middle Miocene (Serravalo-Tortonian). These formations outcrop on the southern flank of the Tsili Massif, north of El-Amra (Figure 2). Above these formations lies an important intercalation of marls, clays, and limestones of the Lower Toronian [9]. The boreholes and the electric surveying data used in this study [7] show that these formations can reach a considerable thickness of 400 m. This layer lies in discordance over the conglomerate series in the northern part of the basin, and directly over the Cretaceous marls in the south. The passage between the Upper Torotation sandstones and the Lower Tortonian marks is completed abruptly [32]. This contrast can be observed in Kef-Ensoura, north of El-Abadia, and also on the Beni-Ghomerian Plateau, where the two formations outcrop. The Messinian is represented mainly by blue marls with a maximum thickness of 50 m [9]. The marine regression in the Pliocene divided this stage into marine and continental formations [2; 3; 32]. The marine Pliocene is represented by sands and sandstones, while the continental is composed of red sands and conglomerates [2; 9; 32]. The Pliocene constitutes the principal deposits of the Sara-el-Maarouf and the Sara-Belaggoune anticlines, north of Oued-Fodda, and extends eastward by outcropping on a narrow band until the Beni-Ghomerian Plateau. However, this formation does not outcrop in the southern parts of the basin, which suggests that it disappears somewhere under the Quaternary plain. These deposits can reach a thickness of 200 m [9]. The Quaternary is predominant in the wide plain that stretches from Oued-Fodda to Ain-Defla. The Pleistocene formations surround the Holocene alluviums and form the first hills in the northern and southern margins of the plain. The Pleistocene is composed of clays, gravels, and conglomerates. The Holocene is constituted of recent alluviums. The  
Figure 2: Geological map of the Middle-Chelif Basin. Modified and compiled from [33; 36].