The stratigraphic and sedimentologic study of the Jurassic rocks (sofs) of the Moroccan Prérif allows to distinguish five lithologic units which are defined by their sedimentary facies:

1. Beni Frassene Group

2. Sidi Redouane Group

3. Amergou Group

4. Sidi Messaoud Group

5. Ech Cherat Group

The first two units are paleogeographically linked to the Prérif Interne area while the sofs of the Amergou Group can be attributed to the Mésorif area by their lithofacies.

The Sidi Messaoud facies are similar to those of the Senhadja Massif (Mésorif zone). The Ech Cherat facies are comparable to those of the sofs which line the southern side of the Ketama Unit (i.e. Tifelouest and Tafraout).

Lithostratigraphic study of these sofs lead to the definition of the eleven formations listed below (from bottom to top):

Formation de transition (Lotharingian - Lower Carixian)

Calcaires massifs (Lotharingian - Domerian)

Ammonitico-Rosso 1 (Carixian)

Calcaires à silex (Carixian - Lower Domerian)

Marno-calcaires gris (Middle Domerian - Lower Toarcian)

Ammonitico-Rosso 2 (Toarcian)

Ammonitico-Rosso 3 (Upper Aaienian - Middle Bajocian)

Alternances marno-calcaires (Middle Toarcian - Bajocian)

Marnes à posidonies (Upper Bajocian - Lower Callovian)

Gréso-oolithique (Upper Oxfordian - Lower Kimmeridgian)

Calcaires à algues (Middle Kimmeridgian - Portlandian)

The paleogeographic evolution of the Prérif Interne from the Liassic to the Upper Jurassic is described with reference to the development of sedimentary facies:

First carbonate seguence (Lotharingian Middle Bajocian): Dolomitic limestones, gravelly limestones containing lituolid foraminifera or corals, and conglomerates with pebbles of granite (Formation de transition; groupe de Beni Frassene) are deposited on the southern edge of the Rif basin. These facies pass to the West into oncolitic limestones with algae and lituolids, superposed by oolitic limestones (Calcaires massifs; Amergou and Sidi Redouane Groups). These sediments are typical of shallow carbonate platform environments.

Starting in the Middle Carixian, the carbonate platform subsided, and openmarine conditions reigned until the Lower Callovian. In this time span, sedimentary evolution was identical for the Beni Frassene and the Sidi Redouane Groups. The following formations are deposited: Ammonitico-Rosso 1, Calcaires à silex, Marno-calcaires gris, Ammonitico-Rosso 2 and the Alternances marno-calcaires. The sofs of the Amergou Group are characterized by condensed sedimentation from the Upper Carixian to the Middle Bajocian. The sequence includes the upper member of the Calcaires massifs, The Ammonitico-Rosso 2 and the Ammonitico-Rosso 3.

These lithofacies formed on a ridge situated in an external position with regard to the sofs of the Beni Frassene and Sidi Redouane Groups.

The first ammonites arriving in the Prérif area (Middle Carixian) show Mesogean characterist ics (Tropidoceras). From the Middle Domerian on the opening of the Atlantic is attested by boreal faunas (Amalthées).

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