Algal Cup Reefs

Sediments of Algal Cup Reefs

Beginning millimeters below the living surface, internal sediments accumulate in these voids. Coarse grained skeletal sand derived from the surface of the reef is characteristic of the larger voids; lime mud with the tests of planktic foraminifera and planktic algae occurs generally in the smaller voids. Most specimens from the interior of the reefs show multiple generations of internal sediment that vary in grain size, composition and colour. The sand sized sediment are pumped into the voids by the frequent and intense wave action; the lime mud settles out in the smaller, less agitated pores.

Cememtation of internal sediments and surrounding growth frame begins several centimeters below the living surface. It is so pervasive that marble-hard reef rock is developed within 0.5 m or less. The cement is principally magnesium-calcite.