Carbonate mud banks of central Florida Bay contain three types of sediment wedges which provide evidence that pulses of rapid physical sedimentation are a dominant cause for bank growth and migration.

Most dramatic are layered to laminated wedges of carbonate mudstone flanking eastern, southern, or western bank margins. Depositional units are 0.5 to 1.5 m thick and compose up to 70% of the existing bank. Units have erosional basal contacts; basal shelly sand grades upward to a layered to laminated mudstone containing no pellets, no burrowing, no seagrass rootlets, and few sand-size skeletal grains. Three features suggest rapid deposition: vertical escape burrows extending upward from the basal sand, vertical smooth-walled water-escape fractures in the lower part, and abundant seagrass blades incorporated into the layers.

The second type of wedge is a layered, pelleted mudstone to packstone otherwise similar to that described above.

The third type of wedge is a bioturbated, soft-pellet wackestone to packstone as much as 1 m thick and flanking only southern bank margins. It contains horizontal to inclined seagrass rhizomes throughout and has minor autochthonous mollusks.

The layered wedges are interpreted to record rapid subtidal sedimentation during rare superstorms (extreme hurricanes), the first type from storms of sufficient violence to destroy most pellets. The third wedge type records persistent lee-side accumulation from lesser hurricanes and winter storms. This deposition, although rapid, is slow enough to be in continuous association with a seagrass-community influence.

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