The history of the opening seaway from the westernmost Tethys to the
Central Atlantic is traced by the analysis of the sedimentary facies
development in the external Rif basin of Northern Morocco and the
geological and seismic data from the Moroccan Atlantic continental
margin.
In the Rif basin, after the early Sinemurian, sedimentary facies dated
by ammonites, foraminifers and brachiopods, indicate a progression of
rapid subsidence resulting from extensional tectonic (tilted blocks,
escarpment fault breccias, neptunian dykes etc.) from the N and NE to
the S and SW.
From the Toarcian to the Bajocian, deltas progress from the W and SW
into the `'Rides sud-rifaines'' realm. From the late Bathonian to the
Oxfordian, deep-sea fans develop in the external Rif. During the same
period, deltaic sediments fill in the Middle Atlas basin of Eastern
Morocco and progress into the external Rif. The top of the Jurassic is
characterised by carbonate deposits.
At the northwestern corner of Africa, the subsidence of the sedimentary
basins by rifting is initiated in the late Triassic; however, at the
Mazagan transect of the Atlantic continental margin, the tectonic
pattern characteristic of a passive continental margin appears clearly
only in the early Jurassic. At the foot of the Mazagan escarpment, the
sedimentary record shows a foundering of the first bloc during early to
middle Lias. A thermal uplift phase is indicated by emersion of the
African margin shoulder in late Liassic, and thermal relaxation starts
in the middle Jurassic. The morphology of this transect, compared with
the conjugate side of the American continent is most easily explained by
the uniform sense simple shear model.