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STRATEGRAPHY OF NORTHERN ALGERIA

The stratigraphy of northern Algeria belongs to the mesogean basin. We can distinguish four paleogeographic groups which are: Oran Meseta, the Saharian Atlas, the Constantine SE, and the Tell field. The stratigraphic succession can be summarized as follows

Paleozoic

In the septentrional part, the inferior Paleozoic shows on the surface in the form of gneiss, mica schists, sandstone and quarzites : Mounts of Ghar-Rouban, Tiffrit, Traras, Chenoua, Kabyly. The forming of the ante-Silurien cristallophyllians are badly known. In small Kabyly, they are powerful with 4000 to 5000m, they are covered by a conglomerate followed by schists in Graptolites and limestones with Tentaculites and Orthocers.

In Devonian, sedimentation comprises breaches, covered with asch isto-sandy unit with reefs' limestones at Ghar-Rouban, whereas flyschs settle in the furrows.

• the Carboniferous one is known only in Djurdjura (continental facies); schisto-conglomeratic Visean of Ghar-Rouban and Tlemcen includes eruptive episodes.

Mésozoïque

The Trias evolves from a sandy sedimentation to powerful evaporitic deposits ending in dolomitic limestones with basic intercalations of volcanites.

Into Large Kabyly, part of Permian and Lower Trias consist of red sandstones surmounted by limestones of Mushelkalk in thick benches or plates. A red sandy sedimentation begins again then, accompanied by doleritic intercalations.

In the South, area of Babors, Keuper, saliferous and gypsifre, do rest on limestones of Mushelkalk. This lagoon sedimentation extends all along the Tell zone. In the East, this lagoon Trias, which is argilo-etrital, evolves in Mushelkalk with a carbonated tendency. The evaporitic deposits get generalised at the of the Trias.

• the Jurassic begins by a marine transgression; the Rhetian's calcaro-dolomitic facies with oolites, resting on Keuper, leave room to marls at the superior Lias. In Hodna and in Bousaada, carbonates fill in the atlasic pit.

In Western Tell and Saharan Platform, the deposits are carbonated (200m) in Hettangien-Sinmurien. In Hettangien-Pliensbachien, limestones with ammonites, polypiers, algae and dolomites limestones (200m) underline the amplitude of the transgression.

In the Domerien, the marine environment is generalized in Algeria with in particular the presence in Djurdjura of the facies with ammonitico-rosso.

The Dogger appears in two sectors:
• in Kabylie with a reduced carbonated sedimentation;
• in Tell (thick argilo-carbonated sedimentation), in the High Lands and the mole of Constantine (carbonates), in the atlasic pit (2000m of argilo-sandy deposits). It should be noted that, in Oran's southern edge and in Western Saharian Atlas, Bajocian shows a detrital tendency translating a fluvio-deltaic activity.

In Malm, the sandstones extend towards North underlining a regression.Therefore, the marine fields of the North and the deltaic continental fields of the South get opposed. However, in the South some deposits of marine influences are still observed (High-Lands and atlasic pit).In the East of the Sdrata-Laghouat meridian line, it is a marine field through the superior Jurassic.

the Cretaceous, detrital and siliceous, shows on the surface levels in the Saharian Atlas, where it reaches a power of 1200m.

 In the Neocomian-Barremian, the sea leaves the Tellian Atlas , the Mole of Constantine and the NE of the atlasic pit.  One can observe alternations of sandy - clay episodes and carbonates.

 At the Aptien, a reef carbonated transgression marks the sedimentation in Hodna and Aurs;  the sandstones dominate in the South and the West (river-delta).

 At the Albian, sandstones then flyschs settle in the Saharian Atlas whereas in Tell, there is a domination of sandy - clay facies. In Constantine's SE, a superior Cretaceous transgression starts with carbonate deposits.

 In Cenomania, the sea is present, not very deep in the south (evaporites) or frankly marine in the Tell (pelagic marl 1000m).Cenomania is neritic (300 with 400m of power) in Telagh and Tiaret, carbonated in Hodna.

 Marly Turonian with lamellibranches and Echinodermata covers all Northern Algeria except for High Lands and Constantine.

 In Senonian, the marno-limestone sedimentation proceeds on and is marked by a marine deepening.


Cenozoc

It begins by wide and powerful deposits at Eocene:  marls, limestones and clays in Tell;  gypseous marls, phosphatic limestones and with flint of Hodna;  marls with oysters.

• A the Oligocene one, sedimentation is dominated by the sandstones.

• In lower Miocene, a thick series of blue marls (1000 m+) accompanies the transgression which invades Algeria from Tlemcen to Biskra. The basins of Tafna separate, from lower and medium Chelif, of Hodna, from the Sebaous.

• In higher Miocene, the regression in Burdigalian is followed by a transgression in Chelif (black or blue marls, sands, sandstone,limestones, diatomites, gypsum).


Plio-Quaternary

In Pliocene, of the sandy blue marls (1000 m) settle in Chlif and Mitidja. Everywhere else, sedimentation is lagunary or continental.

 
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