Depositional controls on Early Cambrian microbial carbonates from the Montagne Noire, southern France

Lower Cambrian shallow-water carbonates enclosing microbial structures are documented for the first time from the upper Lastours Member of the Montagn e Noire (southern France). Microbial organisms constructed self-supported b oundstones resulting in the formation of exclusively microbial-accreted bui ldups, which exhibit three main types of non-skeletal microbialites: planar stratiform stromatolites, dome-shaped stromatolites and nonlaminated (thro mbolitic) biostromes. In addition, thrombolitic boundstones display four di stinct microbial microstructures: clotted and Renalcis-like forms, branchin g bushy forms, clusters of unbranching straight filaments and crustose form s. The upper member of the Lastours Formation records an upward transition fro m a shaly-dominant open shelf to a protected shelf environment bounded by a surface representing a major subaerial exposure. Initially, at the incepti on of the highstand systems tract, flat stratiform stromatolites formed on open sea subtidal shaly substrates, while stacked domal stromatolites devel oped in peritidal areas which record subaerial exposure. In contrast, progr ading shoal barriers of the transgressive systems tract favoured the establ ishment of thrombolitic boundstones in protected (back-shoal) environments.