28 Jul 2023
 | 28 Jul 2023

Reviews and syntheses: Sediment-stressed reefs over the past 420 Myr

Tanja Unger, Stephen W. Lokier, Markus Aretz, Mathhieu Saillol, and Adrian Immenhauser

Abstract. The evolution of reefs over geologic time is diverse and includes a range of different builders. An understanding of the consequences of natural and anthropogenically-driven sediment influx to reef systems is crucial to planning future protection and mitigation strategies. Most reef systems are associated with clear water settings, however, many reef communities have evolved in turbid water environments stressed by high rates of sediment influx. Conventionally, these mixed carbonate-clastic environments have been considered unfavourable to reef organisms. Utilising case-studies of sediment-stressed reefs from the Devonian to Recent, we clearly demonstrate that reef organisms can survive, and even thrive, under the influence of clastic sediment influx. Ten case-studies were selected on the basis of: i) the presence of a mixed carbonate-clastic matrix, and ii) the existence of a coral framework. For each example, the system was characterised in terms of sediment input, organism growth forms (with a focus on corals) and the overall reef morphology. The host sediment from Cenozoic reefs was found to be typically better-described than that within Paleozoic and Mesozoic communities. This may be due to the closer affinity between Cenozoic communities and recent species when compared to more ancient systems. The same reasoning accounts for the paucity of data describing the internal structure of many fossil reefs, a feature also related to outcrop quality. This study clearly demonstrates that, while reefs in sediment-impacted environments are common, there is no general developmental model that can be applied to all reefs. No relationship was identified between the nature of the reef builders, the character of the siliciclastic component and the reef structure. We demonstrate that, in the majority of cases, the clastic matrix within reefs, both ancient and recent, is insufficiently described – this inhibits understanding of mixed carbonate-clastic reef systems and significantly compromising forecasts of future reef development.

Tanja Unger et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1728', Anonymous Referee #1, 10 Aug 2023
  • RC2: 'Comment on egusphere-2023-1728', Michael Risk, 06 Sep 2023

Tanja Unger et al.

Tanja Unger et al.


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Short summary
Sediment-stressed marine environments are regarded as hostile for reefal organisms, but throughout Earth’s history, some reefs formed in environments with sediment influx. Based on ten case studies (420 Ma to Recent), we compile evidence from reefal organisms that flourished despite significant sediment influx. With increasing anthropogenic stress on reefs, there is a need to understand systems providing shelter for the tolerant coral species that can thrive under various stressors.