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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 60 (1976)

Issue: 7. (July)

First Page: 1054

Last Page: 1072

Title: Evolution of Modern Caribbean Fringing Reef, Galeta Point, Panama

Author(s): I. G. Macintyre (2), P. W. Glynn (3)


Thirteen closely spaced core holes were drilled across a modern fringing reef at Galeta Point, Panama, along two transect lines which, when combined, extend from inshore mangroves to the outer reef slope. Cores indicate that the reef is at least 14 m thick and directly overlies the calcareous argillaceous siltstone of the middle Miocene Gatun Formation. Cores contain six distinct sedimentologic units: reef Acropora palmata, fore-reef coral heads, fore-reef talus, fore-reef pavement, reef-flat rubble, and back-reef sediments facies.

Eighteen radiocarbon dates of coral samples from cores permitted detailed reconstruction of the stages of development of Galeta reef. Originally a typical Caribbean Acropora palmata fringing reef established about 7,000 years B.P., subsequently it was restricted vertically by sea level and horizontally by unconsolidated sediments, and within the last 2,000 years corals have ceased to contribute actively to its framework.

Accumulation rates for the main framework facies average between 3 and 4 m/1,000 years and generally are higher than values reported from other Caribbean or Pacific reefs. During the latter stages of reef development, deposition rates decreased considerably (0.6 to 0.7 m/1,000 years), except for the fore-reef talus, where accumulation rates more than doubled over the last 2,000 years (2.5 m/1,000 years).

The early postdepositional cement in Galeta reef is dominantly submicrocrystalline magnesium calcite with minor quantities of acicular aragonite. Submarine cementation is a near-surface phenomenon that is most prevalent in facies formed under conditions of high agitation and/or slow accumulation. Therefore, the well-developed cement crusts and infilled rims of the Acropora palmata facies, formed under both high agitation and rapid accumulation, grade into a dense matrix cement in the agglomerate limestone of the slower accreting fore-reef pavement and in extensively bored and infilled corals of the coral-head facies in the fore reef. Cements are absent or generally developed poorly in the deeper fore-reef talus, or protected reef-flat rubble and back-reef sediments facies. Thus the ag tation and associated winnowing action that are responsible for developing primary porosity in one zone of the reef tract also may promote the early destruction of this porosity by enhancing the precipitation of submarine cements.

Galeta reef apparently was able to keep pace with the rising sea level of the Holocene transgression and completely masked the relief of the erosional surface on which it was established. Encroachment of mangroves on the reef flat, absence of skeletal-frame accumulation, and thick talus cover at the fore reef indicate that Galeta reef is an example of climax zonation in a fully developed Caribbean fringing reef.

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