stromatolitos

Stromatolites are layered sedimentary structures formed by microbial mats, mainly cyanobacteria, in shallow, sunlit waters. Through the trapping, binding, and mineral precipitation mediated by microbial activity, these mats accumulate laminated beds that grow upward as new material is deposited.

The processes involve microorganisms secreting extracellular polymeric substances that bind sediment grains. Photosynthetic activity raises pH, promoting carbonate precipitation and cementation of grains into calcite or aragonite. The resulting laminations record cyclic growth and environmental conditions, producing dome- or columnar forms that can persist for long periods.

Stromatolites provide important records of early life. Fossil stromatolites appear in rocks about 3.5 billion years old, representing some of the oldest known life-forms. They flourished through much of the Precambrian and contribute to understanding early environmental conditions and the evolution of oxygenic photosynthesis, processes linked to the Great Oxidation Event.

Today, intact stromatolites survive in a few protected settings, notably in Shark Bay, Australia, and in hypersaline lagoons of the Bahamas and Caribbean. Modern stromatolites are sensitive to environmental change, coastal development, pollution, and overgrazing, making them vulnerable to decline.

In the rock record, stromatolites are common in Archean and Proterozoic sequences. They are distinguished from thrombolites by their laminated, layered fabric, whereas thrombolites show clotted, non-laminated textures. Mineralogical preservation can involve calcite, aragonite, or silica, depending on diagenesis.