NEW ARCHITECTURES OF DEEP-WATER CARBONATE BUILDUPS - EVOLUTION OF MUDMOUNDS INTO MUD RIDGES (MIDDLE DEVONIAN, ALGERIAN SAHARA)

Spectacular, totally exhumed, carbonate mud buildups of Givetian age c an be found in the southern Ahnet basin of the central Sahara. Their g eometries range from isolated mud mounds to mud ridges up to 8 km long . The latter are the result of lateral coalescence of closely spaced, individual mounds. Mounds up to 40 m high and ridges up to 85 m high s how original slopes of 25-degrees to 65-degrees. Frame-builders in the massive core of the buildups are restricted to scattered small tabula te and solitary rugose corals. The total absence of stromatoporoids, c olonial rugose corals, and algae, as well as the lack of debris at the toes of the buildups, shows that they were constructed in deep water below the photic zone and storm wave base. The arrangement of the buil dups in north- to northwest-trending clusters and ridges suggests that their distribution was controlled by early Variscan extensional movem ents inherited from Precambrian patterns.