Shore platform morphological inheritance from past higher sea levels in a microtidal setting

Abstract

Shore platforms along rock coasts have long puzzled geomorphologists regarding their age and formative processes. This study combines cosmogenic nuclide (CN) dating and micro-erosion meter (MEM) measurements to investigate the evolution of microtidal shore platforms on the Otway Coast of Victoria, Australia. CN concentrations across four platforms reveal significantly high values (up to 123,831 atoms g−1) compared to previous studies, indicating formation predating the Holocene. Cross-shore CN distribution shows peak concentrations at the seaward edge, decreasing landward. MEM data collected over 44 years demonstrate active contemporary erosion, with downwearing rates closely related to elevation and tidal inundation frequency. Numerical modelling of both CN concentrations and MEM-calculated downwearing rates suggest platform initiation during at least the Last Interglacial period, with subsequent modification during the Holocene. The results indicate that platform width is morphologically-inherited from past higher sea levels, while the contemporary cross-shore morphology results from Holocene downwearing processes. This study provides evidence for long-term morphological inheritance in shore platform evolution, challenging the notion of purely Holocene formation in resistant lithologies. The findings highlight the complex interplay between inherited landforms and ongoing erosive processes in shaping rock coast geomorphology, contributing to our understanding of coastal landscape evolution over glacial-interglacial timescales.