Reefs, Mounds, and Paleoenvironments
Coral-bearing bioconstructions are described for the first time from upper Lower Carboniferous (Upper Mississippian) shallow-water limestone olistoliths of the southern Montagne Noire (Mont Peyroux Nappe), southern France. Microbial-induced wackestones and microbial boundstones dominate major parts of the Brigantian Roque Redonde Formation and Serpukhovian Roc de Murviel Formation, which follows on top of a paleokarst. Further subtidal facies are intercalated. The short-lived bioconstructions consist of thin monospecific and polyspecific coral biostromes, coral bioherms (patch reefs) growing in high-energy turbulent environments, and a single example of a large shallow-water microbial buildup that formed below fair-weather wave base in dimmed light. The contribution of rugose corals to the bioconstructions varies from active framebuilding in the biostromes and bioherms to passive dwelling of sparse fauna in the microbial buildup. Microbial structures are of special importance within polyspecific biostromes and patch reefs. In a delicate balanced system they are responsible for growth or suffocation of the coral-dominated bioconstructions. That co-occurrence of coral boundstones and microbial boundstones appears to be a widespread characteristic of small reefs in Late Viséan and Early Serpukhovian time. Factors limiting the growth of the bioconstructions in southern France include rapid sea-level variations, tectonic instability of the shelf, and intrinsic paleobiological features of the rugose corals, like their fragility and inability to encrust mobile substrates. Comparable upper Lower Carboniferous coral-bearing bioconstructions of the Paleotethys realm and the epeiric seas of northwestern Europe are discussed.