Stratigraphy, depositional setting, and diagenetic history of the Saint-Jules Formation (Upper Devonian or Mississippian), a newly identified post-Acadian red clastic unit in the southern Gaspé Peninsula, Quebec

Abstract

The Saint-Jules Formation, a post-Acadian continental clastic unit previously mapped as part of the Bonaventure Formation (pre-Namurian unit), was recently identified in the southern Gaspé Peninsula of Quebec. The Saint-Jules Formation in the study area is confined to a small post-sedimentary graben. The unit is characterized by fault-controlled, oxidized, and poorly sorted detritus that underwent short transportation by fluvial processes. The Saint-Jules Formation is locally overlain by a massive groundwater calcrete several metres in thickness, which is tentatively correlated with the calcretization event that has affected the base of the La Coulée Formation grey clastics (pre-Namurian unit). The calcrete has developed within the karstified upper beds of the Saint-Jules Formation, which brings new insights into the potential hosts of such calcretes and on the potential stratigraphic confusion that such diagenetic overprints can create. Partial erosion of both the La Coulée and Saint-Jules clastic rocks, as well as the massive groundwater calcretes, occurred prior to deposition of the Bonaventure Formation. Like the La Coulée and Bonaventure formations, the Saint-Jules is undated, but unconformably overlies Acadian structures (Middle Devonian) and predates Mabou Group units (Namurian).