Silicification of trilobites and biofilm from the Cambrian Weeks Formation, Utah: Evidence for microbial mediation of silicification

Abstract We report on silicified trilobite sclerites with associated biofilm from the Cambrian Weeks Formation, Utah (USA), that support a role for microbial biofilms in silicification. Silicified are typically small (<3 mm) and incompletely preserved. All studied specimens partly coated 5–20 µm (rarely >500 µm) of silica-cemented matrix. High-resolution scanning electron microscope (SEM) study reveals presence two different forms carbon-rich threads, ribbons mats, coating both Crystalline-looking threads composed Si, O, C interpreted as Rippled to smooth mats more C, less Si trace N post-silicification. Embedded silica matrix molds framboids we interpret originally framboidal pyrite was engulfed by silica. These data indicate precipitation continued into surrounding following propagation sulfate-reducing bacteria feeding organic matter present sclerite neighboring sediment. This strongly supports model bacterially mediated decay is key silicification carbonate bioclasts provides first direct evidence community (biofilm). A literature review extends past fossil frequently than recognized, suggesting might be common but overlooked.