Jurassic Stratigraphy and Synsedimentary Tectonics on Southwestern Margin of Central High Atlas, Morocco

Bernd Klug, Paul Wurster, Johannes Stets

Westernmost deposits of the Jurassic Central High Atlas trough crop out in the vicinity of Aguim. The trough was inundated by a southward-directed tongue of the Tethyan sea from the early Liassic to the middle Dogger. Several thousand meters of marine sediments accumulated in the depocenter east of Beni Mellal.

The basal Jurassic unit consists of very mature, fine-grained sandstones and intercalated siltstones that were deposited in a deltaic system during the Hettangian. Lateral thickness and facies trends indicate maximal subsidence to the northwest, whereas basinal influence increased in a northeasterly direction. Marine transgression reached the study area in the early Sinemurian and culminated in the early Pleinsbachian. It established an extensive coastal sabkha which was recorded as a sequence of dolo-mudstone and local gypsum beds. Interbedded pelites are due to episodic flooding by ephemeral streams. Red siltstones overlying the carbonate series correlate with Pliensbachian regressive sediments to the east.

Supratidal sedimentation was controlled by vertical movements on east-northeast and east-trending faults. Stratigraphic sections next to the fault planes reveal distinct changes in subsidence and lithofacies within the dolomitic unit. Overlying strata were affected by local erosion causing angular unconformities. Block faulting in the Aguim region consequently preceded and also extended into the late Early-Middle Jurassic tectonic events within the Central High Atlas. It favors a pattern of extensional rift-related structures that generated the Liassic High Atlas trough.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.