Formation, morphology and preservation of high-energy carbonate lithofacies: Evolution of the cool-water Recherche Archipelago inner shelf, south-western Australia

Cool-water carbonate environments are responsible for up to one third of the carbonate sediment produced on continental shelves, and are useful modern analogues for many geologically ancient carbonate deposits. On modern and ancient high wave-energy carbonate ramps, it has been suggested that wave abrasion generally limits sediment accumulation to the outer shelf. Sediment are produced on the modern inner shelf, although few studies have investigated processes of sedimentation in these energetic environments. The Recherche Archipelago, in the west of the Great Australian Bight (GAB), was examined to better identify processes of carbonate sedimentation and preservation on extremely high energy shelves. Surficial sediments, video traverses, multibeam sonar data, cores and shallow seismics were analysed. These data reveal that the topographically varied environment of the Recherche Archipelago experienced gradual, episodic accumulation of a prograding sediment wedge, with substantially thicker deposits located on the lee side of topographic highs. Modern sediment accumulation is largely restricted to the shoreface and inner shelf, where the highly discontinuous, storm influenced blanket of Holocene sediment comprises a shore-attached quartzose sediment prism, leeward accretionary wedges and rhodolith beds above a laterally-continuous Pecten-dominated basal transgressive lag. Storm events play an important role in these environments, resulting in a mostly bare ‘shaved’ middle and outer shelf, onshore sediment transport, reworking of particles and periodic removal of sediment. The modern Recherche Archipelago is a high energy end-member of cool-water carbonate environments, in which calcareous algae dominate sediment production. Modern Esperance Bay provides a useful analogue for the interpretation of high-energy palaeoenvironments, and demonstrates that in addition to sea level change, wave energy and local geomorphology are important considerations for carbonate facies reconstructions. This study has presented new information for carbonate inner shelves that differs from classic carbonate ramp models, showing that ancient rhodolith-bearing carbonate deposits have the potential to form and be preserved in very high energy settings.