The Walker Cay-Grand Cays area is on the northwestern part of the Little Bahama Bank, 130 nautical mi northeast of Miami, Florida. This study was made to provide detailed data on the sediment changes that occur within a small, complex, shelf-edge carbonate area.

On a typical traverse seaward across the area, the environments observed are: (1) shallow bank with muddy calcarenite; (2) oolite bars; (3) islands of lithified Pleistocene calcarenite, (4) patch reefs with a Gorgonacea, Montastrea, Agaricia, Diplora assemblage; (5) the fringing reef, largely "dead" and algal encrusted, except for scattered growth of Acropora and Millepora; (6) a deeper, forereef zone of live Montastrea with patches of coarse coralgal calcarenite; and (7) a rock platform with little sediment cover, lying at a depth of about 65 ft and sloping gradually seaward until it reaches a depth of 85-125 ft where it intersects the very steep continental slope.

On traverses across these environments, 135 bottom samples were collected. The sand-size fractions of the samples were impregnated with polyester resin and thin-sectioned. The data resulting from point counts of these thin sections were analyzed by R and Q mode factor analysis. In the Q-mode analysis, 5 factors accounted for 96 percent of the variation in the data. Mapping of these factors led to a relatively simple pattern of sedimentation: a broad area of skeletal sand composed of variable percentages of Halimeda, mollusks, foraminifers, and pellets, separated in protected areas by carbonate mud, around the reefs by coralgal sand, and in areas of strong tidal flow, by sand bars of superficial oolite.

Lithification of Recent carbonates occurs as: (1) beachrock; (2) subaerial crusts about 3 in. thick on beach ridges; (3) thin, well-indurated algal mats near the edge of a mangrove swamp; and (4) semilithified blocky submarine crusts on some oolite bars. Another diagenetic change in the sediment is "micritization" of the grains, particularly on some of the "older" stabilized oolite bars, where the oolitic coatings are being destroyed. This process, if continued, might lead to the misinterpretation of these deposits as pellet sands.

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