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Minor climatic and physiographic differences have caused dramatic differences in sedimentation between the tidal flats of Andros, northwestern Bahamas, and Caicos in the southeastern Bahama chain.
Both tidal flats are leeward of large islands and adjacent to broad, shallow platforms that provide carbonate mud to the flats. Each flat forms a sediment wedge 4 m (13 ft) thick (Andros flats are 200 × 30 km, 125 × 19 mi; Caicos, 60 × 10 km, 37 × 6 mi), and each contains an outer channeled flat and an inner algal marsh. Both flats have cementation and protodolomite forming on channel-margin levees and the inner algal marsh.
Differences in rainfall, wind regime and orientation promote important sedimentological differences. Andros receives nearly twice as much rainfall as Caicos; gypsum forms in cemented crusts in Caicos, but not on Andros. Andros receives brief strong pulses of northwest wind following passage of 40 to 60 winter cold fronts per year. The northwest exposure of the margin of the Andros flat thus is flooded several times each year by sediment-laden waters. This flooding focuses on the shore and channel margins, building broad, strongly laminated levees. Caicos flats, in contrast, face south, and neither winter cold fronts nor summer trade winds blow onshore. Levees are poorly developed. Caicos is dominated by brisk easterly trade winds, causing persistent turbidity in nearshore waters. This is dispersed through tidal channels, largely filling interdistributary ponds to a level at which organic-rich intertidal algal mats can flourish. Lower energy conditions on Andros provide insufficient sediment to fill ponds.
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