Aganane Formation

The Aganane Formation is a Pliensbachian (Early Jurassic) geologic formation in the Azilal, Béni-Mellal, Ouarzazate, Tinerhir and Errachidia provinces, central Morocco, being the remnant of a local massive Carbonate platform, and known mostly for its rich tracksites (up to 1350 tracks in 1988) including footprints of thyreophoran, sauropod and theropod dinosaurs. This formation has been dated to the Pliensbachian stage of the Lower Jurassic, thanks to the find of the ammonite Arieticeras cf. algovianum, indicator of Middle Domerian (=Uppermost Pliensbachian) in the upper zone, and lower delimitation by the foraminifers Mayncina termieri and Orbitopsella praecursor (indicators of Carixian=Lower Pliensbachian age). The dinosaur tracksites are all located a few metres below the Pliensbachian-Toarcian limit, being coeval and connected with the lowermost layers of the continental Azilal Formation. The Aganane Formation was also coeval with the Jbel Taguendouft Formation and the Tamadout 1 Formation, all developed along a local "platform-furrow" in the Middle Atlas Mountains, that act as a barrier controlling the western border of the Jurassic Atlas Gulf. The nearshore sections, including both carbonate platforms and close to sea terrestrial facies where located on an isolated internal domain thanks to the control of the barrier, allowing the Aganane Formation to develop on a hot and humid climate, where a local algal marsh had intermittent progradations, intercalated with a layer of terrigenous continental origin. The ichnosites were developed in tidal flats and coastal deposits suitable to sea flooding.

The Aganane Formation is a member of the Pliensbachian facies section of the Central Atlas, which are distributed from west to east: The Aït Chitachen Formation & Aït-Bazzi Formation at Demnate (continental-fluvial, coastal lagoon), the Aganane itself at Azilal. At Tazoult, part of the Azilal profile contacts the bottom with the karst Talmest-Tazoult Formation, then a section where the Aganane itself indicates an eastward expansion of the carbonate facies, finally, the most recent Pliensbachian strata belong to the Amezraï Formation (Intertidal to coastal marine), this last change being the result of a transgression where we see a westward advance of the Imilchil pelagic facies.

At Tazoult, the presence of a Diapir (the Tazoult salt wall) is remarkable. In the Pliensbachian, this area begins with the deposition of the Talmest-Tazoult Formation, and then is invaded from the west by the shallow marine carbonate platform of the Aganane Formation. At this time, a decrease in the growth rate of the diapir is detected compared to the Sinemurian. In fact, with the eastward extension of the Aganane Formation, the Tazoult salt wall registers a major change towards shallower facies, confirming a higher diapir relief and a decrease in water depth towards this area during the Pliensbachian, not excluding a complete stop of diapir activity in this interval.