LIME-MUD LAYERS IN HIGH-ENERGY TIDAL CHANNELS - A RECORD OF HURRICANEDEPOSITION

During or immediately following the transit of Hurricane Andrew (Augus t 23-24, 1992) across the northern part of the Great Bahama Bank, thin laminated beds of carbonate mud were deposited in high-energy subtida l channels (4 m depth) through the ooid shoals of south Cat Cay and Jo ulters Cays. During our reconnaissance seven weeks later, we observed lime-mud beds exposed in the troughs of submarine oolite dunes and rip ples. The mud layers were underlain and locally covered by ooid sand. The mud beds were lenticular and up to 5 cm thick. Their bases cast th e underlying rippled surface. The layers were composed of soft silt- a nd sand-sized pellets and peloids and in some areas contained freshly preserved Thalassia blades and other organic debris along planes of la mination. The beds had a gelatinous consistency and locally had been p enetrated by burrowers and plants. Layers of lime mud had also settled on bioturbated, plant-stabilized flats and in lagoonal settings but w ere quickly reworked and made unrecognizable by the burrowing of organ isms. Thicker, more cohesive (and therefore older) mud beds and angula r mud fragments associated with ooids from Joulters Cays have similar characteristics but lack fresh plant fragments. We infer that these ol der beds were similarly deposited and thus record the passage of previ ous hurricanes or tropical storms. Storm layers are preserved within c hannel sediments because migrating ooids prevent attack by the burrowi ng activity of organisms.