Sedimentology and Geobiology of Deep Carbonate Slopes from the Osprey and Nearby Reefs (Queensland Plateau, NE Australia)

The Queensland Plateau (QP) is a drowned small continent SE off Australia and is characterized by vast atoll-like reef platforms which have been poorly investigated only. The reefs are located on basement highs and exhibit carbonate deposits of up to 2000 m of thickness. Some of the reef slopes located at the western margin of the QP were investigated during a German expedition in 2009 (http://www.deepdownunder.de) using the ‘Cherokee’-ROV from the MARUM (Bremen) down to ca. 800m water depth. The expedition’s goals were to investigate the steep slopes of the Osprey Reef and other reefs (Holmes-, Bougainville-, and Shark Reef), big allochthonous blocks (“Cipit Boulder” type - known from Triassic reef slopes of the Dolomites/Italy), microbial cementation processes, and benthic community analyses. Special foci were set on so-called “living fossils” like hexactinellid & lithistid sponges, echinoderms (e.g. stalked crinoids), deep water corals, and brachiopods, with observations on exceptionally deep-migrating (800m) Nautilus communities. The slopes are characterized by often vertical walls down to 600m which exhibit grooves where shallow water sediments are channelized during big storms and quakes. The talus deposits consist of carbonate sediments dominated by Halimeda chips, reef debris and decametre-scale boulders. These boulders show distinctive dark microbial Fe/Mn crusts covering on the protected surfaces from normal sediment flux. Fluffy sediments covering the exposed top surfaces are cemented by microbial activity forming brownish microbialites like those known from deep reef cave environments. The talus blocks are settled by organisms mainly of the so-called “living fossils”. Soft bottoms of the vast plains between the boulders are characterized by an intense bioturbation activity by endo- and epibenthic assemblages (e.g. invertebrates and demersal fish). Geological settings and benthic distribution were analysed by sampling and imaging methods applied to underwater video footage gained by the ROV ‘Cherokee’.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California