Significance of microbial binding in the formation and stabilization of a silurian carbonate forereef slope

Abstract

The effect of microbial binding for the stabilization of steep carbonate slopes is well documented in Cenozoic examples but its significance and relationship with abiotic marine cements in Paleozoic reef systems and steep slopes is not clearly established. Here, samples from a Late Silurian (Ludlovian) reef complex are evaluated by using an integrated approach that involves petrographic and isotope analyses, cathodoluminescence microscopy, and environmental scanning electron microscopy. This study reveals the in situ production of mineral fabrics of microbial origins, including micrite, peloidal micrite with dendritic fabrics, meniscus, and bridge-like cements. This study stresses the leading role of microbes in the early lithification stages that led to the stabilization of Silurian steep carbonate slopes. These findings are further supported by the occurrence of fossilized microbes and extracellular polymeric substance. The micritic cements are the first step in the diagenetic paragenesis followed by abiotic fibrous and equant calcite cements whose stable isotope values are in concert with estimated values of calcite precipitated in equilibrium with Silurian seawater. Results from this project provide insights into the relationship between microbial binding and early abiotic marine cements in ancient reef systems and, further, provide evidence for a consortia of microbes that existed 440 Ma ago.