Skeletal debris, shed from the top of patch reefs, forms a wedge of reef-flank sediment which angularly onlaps the reef mass at the uppermost reef flank and grades into lagoonal sediments in deeper water. Major avenues of sediment transport are reef-face channels, which connect sand channels of the reef top with upper sections of the reef flank. Maximum distance of sediment transport off the reef top is less than 100 m.

The understanding of compositional and textural trends across patch reefs is enhanced by use of a working model based on substrate type, biofacies development, particle breakdown, and sediment transport by wave action. Sediment composition provides the basis for recognition of the following microfacies: sediment pockets, sand channels, reef-face channels, reef flank, interreef lagoon, and open lagoon. These microfacies are transitional and, in the preceding order, display the following trends: from the reef top lagoonward, the abundance of Homotrema, coral, and red algae in the sediment decreases and the abundance of Halimeda and Foraminifera (excluding Homotrema) increases. Interreef lagoons are distinguished from open lagoons by a lower molluscan content in the sediment.

Because of the effects of irregular particle shapes and variable particle densities, textural trends are secondary in delineating patch reef facies. Sand-size particles dominate each facies from the reef top to the lagoon. The absence of silt and clay is characteristic of the reef top. Gravel is nearly evenly distributed, in part because of the large Halimeda content of the sediment (25-60%). Generally, mean grain size decreases from the reef top lagoonward, whereas sorting progresses from poor to very poor.

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