Cyanobacterial and sedimentary composition in polygonal microbial mats from Pernambuco Lagoon, Rio de Janeiro, Brazil

Abstract

he Pernambuco Lagoon is a hypersaline water body located in the Massambaba barrier-island, coastal plain of Rio de Janeiro State, southeastern Brazil. Its marginal environments are characterized by the development of microbial mats resulting from the organic activity produced by sediment trapping and binding in the matrix. The aim of this study is to characterize the cyanobacterial and sedimentary composition of these mats, mainly those with polygonal morphology, where a porous compact structure limits and forms polygonal fi ssures and cracks. The MEV and SED analysis show a calcitic and sodium chlorate composition and dominance of fi lamentous cyanobacteria Microcoleus chthonoplastes (Thuret) Gomont 1892 in the polygonal microbial mats. The disposition of fi lamentous forms on the surface level and the spherical ones in the deeper layers results in a stratifi cation of the mats. These observations are useful in the identifi cation of similar organic generated deposits in the fossil record.