Where's the reef: The role of framework in the Holocene

Abstract

Holocenereef models generallyemphasizethe role of in-placeandinterlocking framework in the creationof a rigid structure thatrises aboveits surroundings. By extension, a numberof ancientbiohermaldepositshave been disqualifiedas "true reefs" owing to their lack of recognizable framework, Fifty-four cores from several eastern Caribbean sites ( Fig. 1) clearly demonstrate that in-place and interlocking frameworkis notconunon in thesereefs thatarecomprisedof varyingmixturesof recognizablecoral (primaryframewerkj.Ioose sediment/rubble and secondary frameworkmade up mostly of coralgalfragments bound togetherby submarinecementationandbiological encrustation. Recoveryofprimaryandsecondaryframeworkrangedfrom22%(avg.)in branching-coral faciesto 33% in intervals dominated byhead corals. Accretionrate decreased as expectedwith waterdepth. However. therecoveryof recognizablecoralgenerallyincreasedwith water depth. inversely to presumed coral-growth rates.This pattern reflects a spectrum in the relative importanceof coral growth(primaryconstruction), bioerosion,hydromechanicalbreakdown andthe transportof sedimentand detritus. The relativeimportance of each is controlledby the physical-oceanographic conditionsat the site of reef developmentandwilldictateboththe architecture of the reef and thecharacterof its internalfabric. We donot proposethat framework reefs do no exist, as they most assuredlydo. However, the fact that so many modem reefs are not dominated by in-place andinterlocking frameworksuggeststhat its use as the primarydeterminantof ancientreefs may be unreasonable. We, therefore, propose the abandomnent of framework-based models in favor of those that treat framework generation, physical/biological degradation, sedimentation, and encrustation as equal partners in the development of modem and ancientreefs alike.

Origins and development of Holocene coral reefs: a revisited model based on reef boreholes in the Seychelles, Indian Ocean

“…In contrast, Hubbard et al (1986Hubbard et al ( , 1998 suggested an incremental accumulation with alternating episodes of sedimentation and coral colonization. Pauses in growth are interpreted as reflecting changes in conditions, in nutrient supply and in temporary "drowning" of the substrate or spatial variability.…”

“…It may be impossible to differentiate algally encrusted in place coral from encrusted coral debris, given the narrow perspective afforded by cores. In an important reappraisal, Hubbard et al (1998) suggested, on the basis of 74 cores in contrasting areas in the Caribbean, that corals comprise less than 30% of Holocene reef interiors, and that less than half of this volume is "in place". Many shallow holes have been drilled, but with varying success.…”

Dissolution Rates of Biogenic Carbonates in Natural Seawater at Different pCO2 Conditions: A Laboratory Study

“…Carbonate sediments make up the majority of CaCO 3 stored on coral reefs and are important to the development of reef structures by lithification and by acting as infilling of reef framework (Hubbard et al 1998;Eyre et al 2014). These reef structures provide important habitats for a large number of species and alleviate potentially destructive wave energy and coastal erosion.…”

Depth‐Related and Species‐Related Patterns of Holocene Reef Accretion in the Caribbean and Western Atlantic: A Critical Assessment of Existing Models

“…Less readily apparent is the fact that the interiors of many (or possibly most?) of these structures contain less than 30% recognizable coral, with only a portion of that in place (Conand et al, 1997;Hubbard et al, 1998). The remainder is sand and rubble caused by ubiquitous bioerosion plus void space.…”