Accretion mechanisms and diagenetic controls on textures of Upper Cambrian shallow marine carbonate microbialites, Gallatin Formation western Wyoming

Microbialites are considered some of the earliest records of life on Earth, but varying levels of preservation often complicate our ability to unravel the depositional and post-depositional processes that control microbialite morphological attributes. Here we examine the role of sedimentation, metazoan skeletal clasts, and diagenetic environment on the formation of stromatolitic-thrombolitic carbonate microbialites from the Upper Cambrian Gallatin Formation of western Wyoming. Microbialites exhibit dome shaped decimeter-scale columns that occur as part of shallowing upward parasequences deposited during the Late Cambrian marine transgression recorded throughout the Cordilleran of Laurentia. Data derived from thin section point counts, clast size to depositional angle comparisons, and chromatic mesosequencing (CMS) reveal a prevalence of coarse-grained agglutinated textures. The presence of trace fossils, ooid clasts, and trilobite thoracic fragments within micritic microfacies indicate metazoan bioturbation and proximal skeletal fossil origin. Allochthonous clasts in precipitated microspar and micrite suggest an active integration of the grains by microbial mat communities. Evidence of biogenicity includes the incorporation of very fine to medium sand-sized grains at high angles as well as the presence of the calcimicrobes Girvanella and Renalcis in micrite and microsparitic laminae. These observations suggest coarse-grained microbialites may be more common in the Paleozoic than previously thought and has important implications for using insights from modern coarse-grained microbialites to interpret the paleoecology and taphonomy of microbialites from the early Paleozoic.