Implications of migrating geoid anomalies for the interpretation of high-level fossil coral reefs
Uplift of islands is frequently inferred from high-level fossil coral reefs, and evolutionary chronologies and regional geotectonic models are developed on the assumption that only uplift and glacio-eustatic fluctuations constitute observed shoreline movements. This practice is unsatisfactory, as it omits the effects of geoidal eustasy. The “emergence” of selected islands with high-level fossil coral reefs in the Pacific, Atlantic, and Indian Oceans is reviewed and the likely contribution of geoidal eustasy highlighted, particularly in cases in which geotectonic reasons for island uplift are absent or doubted. A simple model is used to illustrate the similar effect of uplift and of the passage of a positive geoid anomaly on coastal geomorphology. The possibility of island emergence either having been incorrectly calculated or being simply illusory is shown graphically. Uplift of particular islands must be inferred or deduced independently of high-level fossil coral reefs.