Document Type
Article
Abstract
Jeff's Reef (270 32.5' N; 790 58.3' W), a 16m high Oculina coral bank on the shelf-slope break, is the site of modem carbonate sedimentation mixed with relict carbonate and quartz. Surficial sediments from the 94 km2 surrounding area of outer shelf, shelf edge and upper slope are significantly different from reef sediments as judged by wt.% gravel, sand, silt, clay, mud, sorting, skewness and normalized kurtosis. Sand grain types (ooid +pellet+ carbonate rock fragments, barnacles and coral) are also different for reef and non-reef areas. Sediments of non-reef origin in the adjacent areas have significantly larger between-station variance than within-station variance for the above grain size descriptors. These sediments have significant changes in grain size descriptors E-W, and no significant changes N-S.
Sediment on the eastern shelf (48m depth) is unimodal coarse-skewed sand; shelf-edge sediment (80m depth) is bimodal, coarse-skewed sand; and upper slope sediment (140m depth) is unimodal, fine-skewed sand. Gravel fractions of non-reef sediments are dominated by shells and shell hash. By volume, sand fractions are composed of detrital silicate 25.7%, ooids 9.4, pellets 1 0.6, carbonate rock fragments 4.5, molluscs 23.0, barnacles 2.2, forams 10.6, coralline algae 0.3, coral 0.2, echinoderms 2.2, and unknowns 11 .0. Jeff's Reef sediments (70-80m depth) are polymodat gravelly sands with the gravel fractions composed mainly of broken Oculina branches (up to 70% by wt.). By volume, sand fractions are composed of detrital silicate 26.8%, ooids 4.3, pellets 6.7, carbonate rock fragments 3.8, molluscs 23.6, barnacles 7 .3, forams 12.2, coralline algae 0.2, coral 1.1, echinoderms 3.3, and unknowns 1 0.0. Reef top sands contain significantly more coral and barnacles, and significantly less molluscs and carbonate rock fragments than the reef base.
Sediment originated from the reef contains more mud (X = 14.3%) than nearby shelf sediments at the same depth (X= 4.6%). Coral branch gravel is not transported from the reef but export of coral sand is detectable. Current velocities near the reef base exceed 15 cm sec-1 17% of the time in winter and 11% of the time in summer. A 2 km wide band of shell hash between 70-100 m is elongated N-S suggesting transport parallel to the coast.
Publication Date
1987
Recommended Citation
This manuscript is an author version with the final publication available and may be cited as: Hoskin, C. M., Reed, J. K., & Mook, D. H. (1987). Sediments from a living shelf-edge reef and adjacent area off central eastern Florida. Miami Geological Society Memoir, 3, 42-57.
Comments
Florida Atlantic University. Harbor Branch Oceanographic Institute contribution 617.