WARME, JOHN, Colorado School of Mines, Golden, CO

ABSTRACT: Carbonate Facies and Sequences in the Jurassic High Atlas Rift, Morocco

The modern east-west High Atlas ranges of Morocco represent a classic transtensional rift basin filled with an array of carbonate facies. This exposed rift serves as a tectonic and stratigraphic model for understanding subsurface rifts worldwide. An incipient Triassic continental rift was broad, shallow, and accumulated red beds, evaporites, and extrusives. These units are abruptly overlain by a thick Early and Middle Jurassic marine carbonate facies mosaic that evolved in response to movements on individual rift fault blocks that were overprinted by eustatic sea level changes.

A typical north-south cross section exhibits a central platform with massive sponge-algal buildups, flanked outward by deep half-graben turbidite basins, reefy platform margins, shallow cyclic carbonate shelves, and rift-margin sabkhas. Thick deep-water marls attest to continued rift subsidence, and massive olistoliths and shelf debris intercalated with turbidites demonstrate syn-sedimentary block-fault movement. Late-stage deposition included a fairway of rhomboid-shaped atolls that formed in response to continued basement faulting. Post-Jurassic tectonic transpression, using mainly the original rift faults, caused tectonic inversion and formed the present Jura-style High Atlas anticlinal upthrusts separated by broad synclines. Inversion, together with north African desert climate, formed the extensive and instructive outcrops of the present-day Atlas.

AAPG Search and Discovery Article #90910©2000-2001 AAPG Distinguished Lectures