A shoaling-upward carbonate sequence in the Dogger (Middle Jurassic) of the Central High Atlas of Morocco
Stanley, Richard Graham
Warme, John E.
Master of Arts
A late stage of sedimentary infilling of the High Atlas Trough during Dogger (Middle Jurassic) time has been documented in a petrographic study of a 1,2 m-thick sequence of carbonate rocks exposed near Rich, Morocco. The sequence was studied in order to determine the events that led to the establishment of coral reefs in the center of a deeply subsided basin. Within this sequence, five lithologic units are distinguished and described in detail. The bulk 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 vs. pelagic organisms, shelly vs soft-bodied benthic organisms, and algae and algal-coated particles. The sequence is capped by a 5-1 m-thick horizon 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 relationships and insoluble residue analyses suggests that some large reef bodies within this horizon were established on local submarine topographic highs that formed as a result of tectonic activity during Dogger time.