Abstract: Structural Framework and Carbonate Facies Mosaic in the Jurassic High Atlas Trough, Morocco

By

John E. Warme

The modern central and eastern High Atlas Mountains in southern Morocco coincide with a Jurassic trough 600 km long and 100 km wide, developed on the periphery of the Mesozoic Alpine System. A rift origin for the basin is evidenced by its elongate geometry, and its sedimentary sequence: abrupt marine flooding and carbonate deposition in the Lower Jurassic (Lias), over a Lower Mesozoic red bed-evaporite-basalt sequence, resting on Paleozoic phyllites. The Jurassic carbonates are expressed as a mosaic of shelf, slope and basinal facies, all superbly exposed owing to high relief, simple structure and desert weathering.

The central axis of the basin contains 3-4 km of section, including 400 m of "deepwater", micrite-rich, organic buildups of varying proportions and up to 50 m thick. In the Upper Lias they abruptly change to a thicker sequence of alternating micrites and marls, which grade into 1500 m of monotonous Middle Jurassic (Dogger) marls. The marls are punctuated by spectacular horizons of coral patch-reefs, which finally give way to continental beds.

To the north and south of the axial carbonates are trough-margin limestones with well-developed turbidites, channels and slumps, all containing shelf debris. Peripheral to them are shelf deposits, which on the southern margin contain coral reefs and bivalve biostromes, oolite bars, tidal flats and teepee structures all exposed in continuous outcrop. Continental beds interfinger from the southern margin, finally covering the whole basin.

Subsequent major deformation occurred as Alpine events in the Tertiary, with the development of en echelon broken anticlines and intervening broad synclines, fitting a model of major compressive wrenching.

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