Bryozoans from temperate Pleistocene deep-water mounds, Great Australian Bight, Australia

The Great Australian Bight, an enormous latitude-parallel shelf, has been the site of heterozoan carbonate deposition since Eocene time. Facing the Southern Ocean, the shelf is a high-energy, storm-dominated, mid-latitude carbonate system, with wave abrasion depth of ~70 meters and swell wave-base of ~120mwd. The facies transition upslope is marked by numerous bryozoan-rich build-ups. These structures, visible on seismic images, were drilled during ODP Leg 182. The mounds, at ~200 to ~ 350mwd, are muddy and characterised by prolific bryozoan growth. Sea-floor relief is up to 40 rn and hundreds of metres laterally. No mounds are presently growing. The youngest mounds probably grew during glacial low-stands when upwelling provided the nutrients needed for high productivity. Bryozoans are diverse, with 74 genera identified, representing all growth forms in both cheilostomes and cyclostomes. Sand/mud fractions comprise the same genera as coarser fractions, but with delicate branching, articulated branching and articulated zooidal forms more numerous.