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