Abstract: Carbonate Petrology of Basin-to-Reef Shoaling Sequence in Dogger (Middle Jurassic) of Central High Atlas, Morocco

R. G. Stanley, J. E. Warme

A late stage of sedimentary infilling of the High Atlas trough during Dogger (Middle Jurassic) time has been documented by a petrographic study of a 1,200 m-thick sequence of carbonate rocks exposed near Rich, Morocco. The sequence was studied to determine the events that led to the establishment of coral reefs in the center of a deeply subsided basin.

Most of the sequence consists of rhythmically interbedded marls and fine-grained limestones that probably were deposited in quiet, relatively deep water. The hypothesis of progressive shallowing is supported by several lines of evidence, including upward increases in benthic versus pelagic organisms, shelly versus soft-bodied benthic organisms, and algae and algal-coated particles.

The sequence is capped by a 50 to 100 m-thick zone of scleractinian coral reefs and coral-rich beds that probably formed in shallow, moderately agitated, well-illuminated marine environments. Evidence from local and regional stratigraphic relations and insoluble-residue analyses suggests that some large reef bodies within this zone were established on local submarine topographic highs that formed as a result of tectonic activity during Dogger time.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA