MADI, A., Laval University, Quebec, Quebec; B. L. MAMET, University of Montreal, Montreal, Quebec; and P. A. BOURQUE, Laval University, Quebec, Quebec

ABSTRACT: Community Structure and Depth-Energy Zonation of Waulsortian-Type Mound and Bank Complexes, Bechar Basin, Northwestern Algeria

The Bechar Upper Visean mound and bank complexes are the result ofbioconstruction and bioaccumulation by sponges, bryozoans, crinoids and algae. They form several superposed shallowing upward parasequences. Thevertical facies zonation of a parasequence is, from base to top: (1) a sponge-dominated bafflestone with rare bryozoans, crinoids and, at the top, the red alga Fasciella; (2) a sponge-fenestrate bryozoan bafflestone with a progressive increase of red algae (Fasciella, Ungdarella) and a decrease of the sponges; (3) a crinoid-intraclast grainstone with sponge-bryozoan bafflestone intraclasts, large crinoid ossicles, reworked red algae and bryozoans, and first occurrence of foraminifers; (4) a crinoid packstone-grainstone rich in bryozoan detritus with foraminifers, the green alga ssinella and Saccaminopsis chains; (5) a coated grain-oolite grainstone rich in foraminifers, Fasciella and the green alga Koninckopora which locally forms algal banks; (6) an algal-peloid packstone-grainstone with abundant green algae (Paleoberesella, Kamaenella, Kamaena). This vertical sequence is depth-energy dependent. Facies 1 to 3 constitute the mound facies that grew during sea-level highstands below storm wave base in the sub-euphotic zone. Facies 4 is composed of crinoid-algal banks that locally developed on the top and the flanks of the mounds. Facies 5 and 6 are sand sheets that buried the mounds during sea-level lowstands in high-energy euphotic zone. The Bechar mounds show some similarities with the classical Waulsortian mounds. However, their richness in large sponge bodies is unique.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.