Jurassic limestones of the seaward edge of the Mazagan carbonate platform, Northwest African continental margin, Morocco ( DSDP Leg 79).

Abstract

During Leg 79 Jurassic limestones were recovered at four sites drilled at the front of the Mazagan Plateau, making it possible to reconstruct depositional conditions at the outer edge of the continental margin. At Site 544 limestones are composed of cyanobacterial crusts grading upward into bioclastic grainstones and wackestones. At Site 545 Jurassic limestones occur as constituents of debris flows, which are embedded with Miocene nannofossil oozes. The rock fragments were derived from oolitic shoals, coral bioherms and deeper shelf deposits. At Site 546, located upon a salt dome, two fragments of Jurassic oolitic limestone were embedded into middle Miocene calcareous ooze. Site 547, which is located in a small structural sub-basin at the base of the margin, demonstrates that marine deposition started with the development of stromatolites overyling(?) Triassic continental red beds. The upward change in limestone composition suggests that the shallow-water platform edge retreated landward during the late Tithonian and Early Cretaceous as the Mazagan Escarpment was formed.-from Authors