Microboring versus recrystallization: Further insight into the micritization process

SEM observations of lightly etched thin sections of Bahamian sediments reve al an unusual process of micritization that involves carbonate precipitatio n in microborings concurrent with endolithic activity. A coccoid cyanobacte rium, tentatively identified as Solentia sp., bores tunnels, which initiall y penetrate just beneath grain surfaces and eventually extend throughout th e entire grain. These tunnels are filled by radial fibrous aragonite, which is precipitated as the microorganism advances. Extensive multicyclic repet itions of this process result in obliteration of original grain textures wi th almost complete preservation of grain margins and rare empty bore holes. The rapidly filled tunnels cannot be detected by resin cast embedding tech niques that are commonly used to study microboring, This type of multicycli c boring and concurrent filling of bore holes forms micritized grains that can be difficult or impossible to distinguish from micritized grains formed by recrystallization.