Cyanobacterial and chemical composition of the stromatolites in Salgada lagoon, Neogene of Rio de Janeiro state, Brazil

Salgada lagoon is a coastal aquatic body in northern Rio de Janeiro state. The geological evolution of the lagoon is associated with the oscillation of sea level during the Late Neogene. The lagoon presents microbial mats, stratiform stromatolites, individual and continuous stromatolites. Stromatolites are laminated carbonate build-ups formed by the metabolic activity of microbial mats. This study identified 31 species of cyanobacteria in stromatolites and microbial mats. The Family Synechococcaceae is the most frequent. Nine species are usual throughout the evolution of the calcareous stromatolites. Microbial mat types include flat, tufted, polygonal and blister forms, all produced mainly by filamentous cyanobacteria. Skeletal remains include bivalves, gastropods, ostracods, foraminifers and other taxons. The high frequency of cyanobacteria in the area occurs because of their adaptation to hypersalinity allied to low competition. The results indicate that a variety of paleoenvironmental and sedimentary events occurred in the lagoon and may be applied to the interpretation of ancient stromatolites.