TIDAL FLATS IN A DAISY WORLD

Three classic localities have received intensive study over the past 40 years, the humid climate on-lap and off-lap tidal flats of western Andros, the semi-arid flats on the Caicos platform in the Caribbean, and the arid off-lap areas of the southern Arabian Gulf. The styles of sedimentation differ in many ways due to climate, salinity, and sediment supply but all conform to Gaia principles of self-regulation.

Humid on-lap or transgressive flats of NW Andros Island are eroding, are laced with meandering tidal channels lined with coarser material, and sub- and intertidal sediments with characteristic sedimentary structures are on-lapping supratidal marshes. The off-lap regressive areas of SW Andros are not eroding, have few tidal channels, and inter- and supratidal sediments overlie subtidal sediments. In the short term, sediment supply and wave exposure, rather than changes in sea level, regulate transgressive versus regressive sedimentation at Andros Island. Dolomite forms on supratidal zones at both the Andros and Caicos localities, and the zones of dolomitization are controlled by self-regulating sedimentary processes. Marine cementation is absent.

The extensive arid off-lap tidal flats of the Arabian Gulf for the most part lack meandering tidal channels, and shell debris forms extensive protective barrier islands. Both syndepositionally cemented and mobile ooid sands form in channels and terminate as tidal deltas seaward and landward of the barrier-island trend. Marine cemented grainstones form extensive hardgrounds that underlie prograding sedimentary facies and limit the depth to which tidal channels can erode. Dolomite, anhydrite, and gypsum form on supratidal sabkhas, the sedimentary equivalent of marshes at Andros Island. Abundant sediment supply has allowed these tidal flats to accrete rapidly facilitated by wave-breaking coral reefs and rapidly growing chenier-like barrier islands and spits. Sedimentary, microbial, and diagenetic processes on all tidal flats are interrelated and interdependent in what can be considered a micro-daisy world.