Algal and bacterial carbonate sediments

Calcified algae and bacteria

Only a few algae and bacteria calcify (Figure A1), but their abundance and wide distribution make them important in limestones of many ages and environments (Figure A2). Microbial carbonates appeared in the Archaean and are significant in Proterozoic carbonate platforms. Calcified cyanobacteria became important in the Cambrian, and calcified green and red algae in the Ordovician. Additional extinct organisms have been regarded as calcified algae or bacteria, but are still of uncertain affinity. These problems of affinity hamper paleocological and phylogenetic interpretations.

Figure A1

Principal groups of calcified benthic algae and cyanobacteria.

Calcified red algae include corallines that are marine, calcitic, occur at all latitudes, and are important reef builders. In contrast, calcified marine green dasycladaleans and halimedaceans are aragonitic and mainly tropical. They mainly produce particulate sediment, although Halimedacreates reefs with its...