The abundance of reefs and the biota that they include vary through geologic time, punctuated by periods of rapid change. To understand the dynamics of such change, Matysik et al. document the structure, dimensions, and spatial patterns of microbial-dominated patch reefs in mixed carbonate-siliciclastic environments on the northern margin of Gondwana during the Early Devonian “crisis” in metazoan reef development. Despite different composition, these reefs show close similarities in shape and spatial arrangement with present-day coral patch reefs, suggesting comparable controls. Additionally, the strata show a close relation between metazoans and microbialites in reefs and reef-associated strata, illustrating that microbialites can compete successfully, even in the presence of metazoans, given elevated nutrient supply and elevated temperatures.
Composition and morphology of Early Devonian microbial and metazoan patch reefs: Qasr Member of the Jauf Formation, northwestern Saudi Arabia by Michał Matysik, Khalid Al-Ramadan, and Robert Riding