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Algeria presents a very large variety of geological contexts. Four great fields are morphologically distinguished from north to south of the country.

  • The Tell Atlas tellien (or Tell), made up of reliefs and littoral plains

  • The High lands;

  • The Sahara Atlas constituting a long succession of reliefs, which are NE-SO oriented, extend from Morrocco to the Tunisian borders;

  • The Sahara which conceals the main part of the hydrocarbon resources, a desert which is made of large stretches of dunes (Eatern Erg and western Erg), it is also made of stony plains (regs) and strewn with oasis. The solid mass of Eglab in the West and the solid mass of the Hoggar in the East form, practically, the southern most limit of the Algerian Sahara, border with Mauritania, Mali, Niger and Libya

From a tectonic point of view Algeria is divided into two major units separated by a south atlas crack :

-- The North of Algeria which bears the mark of the alpine tectonic ;
-- The Saharan platform , relatively stable where the tectonic is less marked.

The tectonic is a result of a collision between Africa and Europe , at the origin of the Algerian Alpine chain which is still leaning on the northern side of the southern block.

Initiated at the Lias (180 Ma ) but considered as neat only from the Malm these movements , associated to the opening of the North Atlantic carried on discontinuously up to the Mio-Pliocene . The end of the Pliocene and the Quaternary are relatively stable eras.

Enchaînement géodynamique au Jurassique (a) et au Crétacé (b)

Enchaînement géodynamique à l'Oligocène (a) et au Quaternaire (b)

The alpine chain of Northern Algeria has resulted from this collision which has materialised by :
• In the Jurassic (180-140 Ma), the opening of the N-S Atlantic coupled by a sinistral sliding following an E-W direction which predicts the future alpine direction.

• In the lower Cretaceous , the sliding through rotation engenders a compression in Spain , which shows in the folding of the Medium-Atlas.

• In the upper Cretaceous the sinistral sliding mitigates to leave room for a compressive movement reaching its climax at the terminal Cretaceous.

• In the tertiary, the beats alternate through convergence and distensions :

  • At the Eocene, subductive phenomena mitigate while compression induces an important deformation which shows in Europe and North Africa;
  • At the Oligocene , the area is subjected to a distension phase responsible for the setting up of the grabens ;
  • At the Moi-Pliocene , the compression resumes through senestral sliding and with the tectonic deformation of of the High Atlas , responsible for the setting up of the large Tellian Atlas water tables ( from El Asnam to Annaba ) ;
  • At the Plio-Quaternary , movements are much more discreet.

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