Freshwater microbialites from Laguna Bacalar, Quintana Roo, Mexico: effects controlling their growth
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Abstract
Microbialites are among the oldest direct evidence of life on Earth. They reached their greatest abundance and diversity during the Proterozoic and decline thereafter. The decline has been attributed to grazing and/or burrowing by metazoan, to changes in ocean chemistry leading to a drop in carbonate saturation, or to substrate and elemental competition with other organisms capable of precipitating calcium carbonate (CaCO3). Here we examine the freshwater microbialites of Laguna Bacalar (Mexico) in hope of better understanding the various factors controlling their growth, and internal fabric. It was concluded that microbialite growth was controlled by the supersaturation of water with regards to CaCO3, however, the laminated (stromatolitic) and clotted (thrombolitic) fabric were dependent on sediment transport and availability. The presence of gastropods and bivalves appeared not to influence growth due to the fast growth rate employed by microbialites as well as to the endolithic growth of the cyanobacteria present.