pellets are the excreta of various marine organisms (figure below).
These grains collect in protected lagoons and shallow intertidal ponds, environments of somewhat lower energy than those where grapestone and botryoidal grains form. pellets commonly are not preserved but disaggregate into micrite during the dewatering and compaction of shallow burial. Where hardened by marine cements, the pellet may be preserved intact. This commonly occurs on open platforms where pellets are winnowed and washed by currents.
Peloids are grains of indeterminate origin. They are sand or silt-size and usually subangular in shape, though often they are rounded and resemble fecal pellets. Peloids retain no internal structures to identify their origins, which are probably diverse and include micritization of grains by boring algae and fungi (right figure).
Wednesday, March 06, 2013