FIGURE 2. Photosynthetic microbial mat communities on microbialites.

a, Surface of shallow–intermediate facies mound contains rounded tufts of larger, purple-pigmented filamentous cyanobacteria (Oscillatoria sp. and Calothrix sp.; shown in b) that are surrounded by green-pigmented mat of filamentous cyanobacteria (Pseudoanabaena sp. and Fischerella sp.; shown in c). b, Scanning electron microscopy (SEM) photomicrograph of uncalcified aggregates of purple-pigmented bacteria on microbialite surface. SEM specimens were fixed, dehydrated, critical point dried and Ir coated. c, Loose networks of filamentous green-pigmented cyanobacteria often bind trapped sediment. d, Calcification of the cyanobacteria filaments and their extracellular matrix at the surfaces of the microbialites perpetuates microbialite growth by providing a lithified substrate for the development of subsequent microbial mats.