Abstract

Sand-sized carbonate fecal pellets are a common to dominant constituent of many shallow marine tropical environments. Ovoid pellets 100-1000 mu in median diameter predominate. Pellets may be soft or hardened by intragranular micritization or cementation. Single grain settling of pellets collected from eight shallow marine environments in south Florida and the Bahamas permits calibration with the hydrodynamic behavior of quartz spheres. Well-hardened carbonate pellets settle at rates equivalent to quartz spheres having a median diameter 70 percent to 100 percent of the pellet size. Soft carbonate pellets containing abundant silt settled as quartz spheres 90 to 30 percent in diameter. Soft carbonate pellets composed mainly of aragonite needle mud settled as quartz spheres 60 to 25 percent in diameter. From this data, preliminary estimates can be made of the shear velocities necessary for entertainment of pellet or peloidal sands and the propensity of suspended versus bedload transport of different grain types and sizes.

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