Recent sedimentary facies of Roatan (Bay Islands, Honduras), a Caribbean oceanic barrier reef system

This project was developed to investigate systematically patterns of recent sedimentary facies around one of the rare Caribbean examples of an oceanic barrier reef system. Seventeen sediment samples collected around Roatan (Bay Islands, Honduras) range from fine to very coarse bioclastic sand. Sorting is either moderate or poor, which suggests a weak influence of transport processes. Occurrence and abundance of major grain types are principally comparable to other modern reefal systems; however, there are some differences in terms of absolute grain abundance. Corals and calcareous algae are very abundant in marginal reefal sediments where they reach average amounts of 24% and 32%, respectively. Lagoonal sediments contain on average 14% foraminifera, 15% molluscs, 16% Halimeda, and 31% fine material (<125 mu m). Statistical analyses revealed five sedimentary facies including algal-rich rudstone, coralgal grainstone, mixed skeletal pack-floatstone and foraminiferal-molluscan wackestone. The facies distribution pattern results from the interplay of the ecology of carbonate-producers, carbonate production and destruction, sediment stability, depositional energy, and reef morphology. Roatan is a mixed carbonate-siliciclastic system, although despite the proximity to a metamorphic island, the average content of siliciclastics in reefal (2%) and lagoonal (17%) sediments is not very high. The lack of higher amounts of siliciclastic material is attributed to the absence of permanent river systems and a high carbonate production rate. Non-skeletal grains (peloids) are common in protected areas of the Roatan marginal reefs, although ooids are rare in the system as a whole. Reduced skeletal grain formation and decreased sedimentation rate seem to be responsible for the peloid enrichment in areas near the reef-lagoon transition zone.