About This Item
Share This Item
Reefs on the eastern coast of Carriacou (southern Grenadines) are considered to be representative of this part of the Caribbean. The upper Southesk stage of the Upper Devonian reefs closely resembles these modern reefs. Similarities are (1) narrow reef crest zone a few 10s of feet wide, (2) a slightly broader rubble zone just inside the reef, (3) lagoonal sediments consisting of fine- to coarse-grained coral-algal particles, making up about 80% by area of the reef complexes, (4) interior parts of the lagoon are progressively finer grained and poorly sorted, (5) sediment filling of the lagoon occurs from the reef inward, depending on lagoon topography and rates of sediment supply, (6) active reef growth was established at suitable depths (40-100 ft) during a rise in sea le el and progresses from a submerged to a nearly emergent reef bank, and (7) stromatoporoids fulfilled the same role as modern corals, and algae-like Renalcis acted as encrusting frame-builders.
Differences include (1) the lack of abundant terrigenous sediments, forereef talus, and carbonate mud in Carriacou reefs, (2) lack of ripples and cross-stratification, but the presence of prominent planar bedding in the Devonian lagoonal deposits, and (3) the less diverse fauna with less marked differentiation of growth forms in Devonian reefs. These are not significant differences and can be explained in terms of different basin sedimentation, organisms, preservation, diagenesis, etc. Modern reefs provide useful prototypes for testing concepts and models of Devonian reefs and banks. The Miette and Ancient Wall reef complexes (and others) are comparable to modern offreef drape types.
End_of_Article - Last_Page 862------------