RESPONSE OF PLEISTOCENE EPIBIONT COMMUNITIES TO TERRIGENOUS SEDIMENTATION ON THE WESTERN AUSTRALIAN COAST

Fossil reefs from the Last Interglacial (Marine Isotope Stage 5e) are exposed at Red Bluff, Western Australia. Acroporid corals with plate-form colonies dominate the reef framework that is exposed along a marine terrace approximately 5 m thick. Coral plates were systematically removed from the outcrop along a vertical transect, and the epibiont communities preserved on them were examined. Community growth sequences found on these plates were strikingly different from the complex patterns established in the Caribbean and South America, as nearly all plates sustained epibiont growth only to very early stages of succession. Both coarse and fine sediments were plainly observed in association with the coral plates. Epibiont growth persisted during deposition of fine sediment, but ceased after the appearance of the coarser sediment. Petrographic analysis revealed that the sediments are similar in basic composition, but a distinct boundary is present between a coarse-grained packstone and a finer-grained, carbonate mud-rich, wackestone. These differing clasts suggest deposition during respectively high and low energy regimes. Thus, terrigenous sedimentation appears to be an important control on epibiont community structure.