Unusual microbialite formation in the South Atlantic: Implications for past climate change

Marine microbialites are globally significant indicators of Relative Sea Level (RSL), oceanography, and paleoclimate, forming restricted carbonate banks worldwide. A unique carbonate bank with laminated stromatolite structures was discovered on the southeastern coast of Brazil. Geochemical, isotopic, and radiocarbon analyses were conducted to characterize the microbialite and reconstruct its paleoenvironment. The Castelhanos microbialite, composed of white and pink-brown laminae, formed on abrasion terraces under open marine conditions. Radiocarbon dating indicates an age range of 3900 to 3000 years BP, and its geochemical signature is characteristic of shallow marine microbialites. The δ¹³C and δ¹⁸O isotopic signatures align with global Quaternary marine and lagoonal microbialites, indicating RSL oscillations consistent with South Atlantic curves. Similar to Shark Bay in Australia, the Castelhanos microbialite formed during marine transgressions and regressions over the past 6000 years in the South Atlantic. This research offers important insights into Earth's history and the effects of climate change on coastal and marine ecosystems by reconstructing the paleoenvironment of a unique marine microbialite.