Geochemical Evidence of Biotic Influence in Brazilian Pre-Salt Carbonates

摘要: The Cretaceous pre-salt lacustrine carbonates in the Santos Basin, offshore Brazil, are as geologically enigmatic they economically valuable. Much debate has centered lately on extent to which microbes may have played a role their genesis. In marine carbonates, biotic and abiotic calcites can be distinguished based isotopic elemental compositions. this study, we applied these geochemical tests thin sections bulk core samples from well BM-S-22 Guarani-1ST (3-ESSO-004-SPS). Modern calcite-producing taxa often show positive linear covariance carbon oxygen isotope These trends anchored most end at carbonate compositions extend more negative values those precipitated faster. Guarani analyzed study less variation than many modern calcifiers (like echinoderms, corals, algae), though range is somewhat consistent with others foraminifera). enrichment Sr over calcite cements shown plot of Mg/Ca vs Sr/Ca. same between Sr/Ca enrichment, suggesting influence precipitation. data, along scanning electron microscope images showing fossilized microbes, seem undeniable evidence that biological processes least some origin Brazilian carbonates.