Colonization and reef growth on a Late Pleistocene rocky shore and abrasion platform in Western Australia

Abstract

A low, rocky shoreline and attached abrasion platform of Late Pleistocene age are marked by a sharp disconformity within the Tamala Limestone Formation, exposed at Cape Burney facing the Indian Ocean near Geraldton, Western Australia. Colonization by an intertidal to shallow subtidal biota dominated by encrusting coralline red algae, oysters, and tube-dwelling worms occurs on a sandstone surface with a channeled topographic relief of 20–30 cm. The encrusting cup coral Rhizotrochus tuberculatus also is present, and this report details what is probably the first fossil occurrence of that species. The ancient rocky shore above this level retains trace fossils characteristic of a boring barnacle, probably belonging to Lithotrya. Herein named the Cape Burney sandstone, the distinctive unit on which the disconformity sits is assigned member status within the Tamala Limestone. Shell beds with a diversity of 35 species, dominated in volume by robust gastropods such as Turbo intercostalis and T. torquatus, thinly drape portions of the disconformity surface. Succeeding the shell drapes is a reef limestone with a maximum thickness of more than 2 m. The limestone is a massive accumulation of collapsed but otherwise mostly undisturbed coral fronds belonging primarily to a robust species of Acropora. Herein named the Bootenall limestone, this unit is assigned member status within the Tamala Limestone. Based on an analysis of electron spin resonance (ESR) from Acropora samples, the fringing reef developed between 120 ka and 132 ka, in the terminal stage of coastal transgression during the last interglacial period (Oxygen Isotope Substage 5e). □Ancient rocky shores, intertidal abrasion platform, hard-substrate colonization, reef succession.