Shelf-to-Basin Resedimented Carbonates of the Southern Margin of the Jurassic Central High Atlas Trough, Morocco

Beverly Halliwell Hazlett, John E. Warme

The Central High Atlas Mountains occupy the site of an Early to Middle Jurassic east-west-trending seaway known as the Central High Atlas trough. Late Triassic-Early Jurassic continental rifting, combined with a transtensional structural regime, formed a system of pull-apart basins comprising the trough. A thick sequence of carbonate shelf-to-basin-plain deposits filled the trough and were later uplifted and exposed during the Oligocene Alpine orogeny.

Stratigraphic analysis of 50 km² located along the trough's southern shelf margin reveals a 1,200 m-thick wedge of slope and basin-plain deposits. These deposits are divided into four lithostratigraphic units: (1) pelagic mudstones, (2) channel deposits composed of grainstones and packstones interbedded with marls and mudstones, (3) turbidite deposits composed of grainstones, packstones, and wackestones cyclically interbedded with marls and mudstones, and (4) cyclically interbedded marls and mudstones. This laterally continuous thick wedge of resedimented deposits suggests that a line source of platform-margin sediments fed coalescing base-of-slope aprons. These aprons probably accumulated in an actively subsiding half-graben parallel to the shelf margin.

While tectonics played the major role in basin evolution, sea level fluctuations and climate influenced the influx of carbonate and terrigenous sediments. Rapid cessation of mid-Sinemurian shallow-water platform deposition and regionally transgressive Domerian-Toarcian marls indicate eustatic sea level rises affected basin sedimentation. Periodic climate changes, perhaps related to the Milankovitch effect, may have led to systematic variations in carbonate sediment supply, resulting in cyclic sedimentation.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.