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The AAPG/Datapages Combined Publications Database
Journal of Sedimentary Research (SEPM)
Abstract
Middle Jurassic Shoaling of the Central High Atlas Sea Near Rich, Morocco
Richard G. Stanley
ABSTRACT
The Early and Middle Jurassic High Atlas sea extended as a marine trough across what is now the central and eastern portions of the High Atlas Mountains, southern Morocco. The sedimentary infilling of this sea is recorded by a thick sequence of limestones and marls punctuated by spectacular coral-algal reef horizons. A 1,200 m-thick section of Aalenian and Bajocian sediments near Rich, Morocco, was studied in detail to document the upward-shoaling, basin-to-reef transition.
The lower 900 m of the section represents deeper-water deposition: it consists of monotonously interbedded, dark-hued marls and lime mudstones and wackestones that hear a pelagic fossil fauna, and scattered turbidites of lime grainstone. An overlying transitional sequence about 200 m thick records progressive shallowing, as shown by 1) increased fossil diversity and abundance, 2) an increase in algally micritized particles, 3) a change from a pelagic to a benthic shelled fauna, 4) an increase in limestone-to-marl ratio, and 5) the appearance of small bioherms with scleractinian coral framework. The sequence is capped by a 100 m-thick horizon of very fossiliferous limestones and superbly preserved coral-algal reefs that grew in shallow water.
Several lines of evidence suggest that some of the reefs grew on submarine ridges that were uplifted by Middle Jurassic tectonic movements.
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