Syn-depositional alteration of coral reef framework through bioerosion, encrustation and cementation: Taphonomic signatures of reef accretion and reef depositional events

The development of coral reef framework and the preservational character of both in-situ and rubble coral is strongly influenced by a range of physical, chemical and biologically-mediated taphonomic processes. These operate at, or just below, the reef framework-water interface and can be defined as having either a constructive or destructive effect upon primary reef framework (i.e., coral) constituents. Constructional activities add additional calcium carbonate to the primary framework structure via secondary framework growth and early cementation. Destructive processes, which remove or degrade primary (and secondary) framework carbonate, are associated with the effects of either physical (mainly storm) disturbance or biological erosion (termed bioerosion). Key bioeroding groups include the grazing fish and echinoid groups, as well as the activities of an array of infaunal borers. These include specific groups of sponges, bivalves and worms (termed macroborers), as well as cyanobacteria, chlorophytes, rhodophytes and fungi (termed microborers). The relative importance of each process and the rates at which they operate vary spatially across individual reef systems. In addition, many of these processes leave distinctive signatures on, or in, the coral framework. In some cases (e.g., calcareous encrusters) these are the skeletons of the organisms themselves, whilst in other cases the organism may leave behind a trace of their activity (e.g., macro- and microborers). These represent useful palaeoenvironmental tools, firstly because they often have good preservation potential and, secondly because the range and extent of many of the individual species, groups and processes involved exhibit reasonably well-constrained environment and/or depth-related distributions. As a result these taphonomically important organisms or processes can be used to delineate between reef environments in core or outcrop, and to aid the interpretation of reef depositional processes and 'events'. This review summarises current understanding regarding the distribution of these species/processes within contemporary reef settings and considers the suites of taphonomic signatures that may aid in the recognition and interpretation of depositional environments and events. © 2007 Elsevier B.V. All rights reserved.