Fringing reef growth and morphology: a review

Abstract

Fringing reefs are generally not simple veneers of coral growth along tropical shorelines. Extensive research over the past few decades, based on radiocarbon dating of Holocene reef deposits, has indicated that they can develop in a complex variety of ways even though the surface morphology may appear relatively simple. The principal factor that appears to determine the growth and morphology of fringing reefs is the available accommodation space. Sea-level fluctuations are important, primarily because the sea surface determines the absolute accommodation space for a given reef. This means that a reef established during a period of sea-level rise will be able to accrete vertically as space is created above it. If, however, the reef establishes at, or grows to, the sea surface, thereby occupying all the available accommodation space, it can no longer accrete vertically and begins to build laterally. The morphology and chronostratigraphy of a range of Holocene fringing reefs are described, on the basis of which six fringing reef growth models are identified. In model A, the fringing reef is established at depth and primarily accretes vertically towards the sea surface. Reef growth in model B initiates at sea level and due to the lack of vertical accommodation space grows laterally. Model C has a similar morphology to model B; however, the reef progrades over a non-reefal sediment wedge. Episodic lateral and vertical growth occurs in model D, with a stepwise progradation of the reef front. The remaining models are characterised by seaward reef framework behind which unconsolidated sediments accumulate. In model E, reef-crest growth forms a barrier leading to the development of a backreef lagoon. Model F has a similar morphology to model E, except that the reef crest is formed by hurricane rubble accumulation rather than framework accretion, and is periodically reworked.