Link between long-lasting evaporitic basins and the development of thick and massive phreatic calcrete hardpans in the Mississippian Windsor and Percé groups of eastern Canada

Part of the Viséan (upper Mississippian) succession in the upper Paleozoic Maritimes Basin of eastern Canada is overprinted by massive phreatic calcrete hardpans that can exceed 10 m in thickness and that are characterized by the thorough mineral replacement of most of their host sediment by calcite, similar to those that are currently forming around salt lakes in Quaternary sediments of central Australia. The precise timing and paleogeography of this Carboniferous event was until now poorly known, but lateral correlations over a large study area indicate that phreatic calcretization occurred in the vicinity of large evaporitic basins following a marine transgression and regression cycle in Chadian to Holkerian times. This relation confirms that the previously proposed model for modern analogs in central Australia, which states a genetic link between the salt lakes and the thick and massive phreatic calcrete hardpans, can be applied to ancient environments, and that such occurrences may be used to infer the former presence of an evaporitic basin in their vicinity. Finally, our relatively large dataset indicates that the stable isotopes of carbon and oxygen are successful in differentiating ancient marine carbonates from ancient phreatic calcretes.