Marginal marine spring carbonates defining an emergent rocky shoreline at Cape Freycinet, Western Australia

Abstract

Modern and Holocene tufa microbialites have been documented globally on groundwater spring-fed supratidal rock coasts. Here, we document the first emergent facies assemblage and demonstrate its utility as a palaeo-shoreline (and sea-level) indicator. At Cape Freycinet, Western Australia, discrete palaeo-spring-associated deposits comprise five distinct facies that collectively define a Quaternary shoreline on a granitic rock coast similar to the contemporary coast. A palaeosol facies, passes laterally seaward into tufa microbialite on sub-horizontal bedrock, associated with oncoids. The most seaward facies is a microbially-cemented sand representing deposition in the upper-intertidal to supratidal zone of a sandy embayed beach, flanked by prominent headlands. A tufa-lithoclast breccia indicates occasional high-energy events. Facies distributions are controlled by bedrock topography in relation to palaeo-sea-level and the distinct suite of marginal marine, springline-associated facies define a Quaternary palaeo-shoreline at ca. +13 m above sea-level. The approach demonstrates the utility of marginal marine microbialite and related carbonate deposits as indicators of Quaternary sea-level on rock coasts.