The La Coulee Formation, a new post-Acadian continental clastic unit bearing groundwater calcretes, Gaspe Peninsula, Quebec

A 1 km(2) erosional remnant of the La Coulee Formation, a previously unreco gnized stratigraphic unit, has been studied in the Perce area of the Gaspe Peninsula. It unconformably overlies folded Cambrian to Devonian rocks and is unconformably overlain by the mid-Carboniferous Bonaventure Formation. T he erosional remnant includes the lowest 60 m of this newly identified form ation of unknown thickness. Original sedimentary facies are limited to 50 m of breccia debris flows passing stratigraphically upward into 10 m of cong lomeratic debris flows. Groundwater calcrete formation has partially or com pletely transformed the lowest 30 m of the sequence. The depositional envir onment is interpreted as being related to a proximal continental alluvial f an. The nearby presence of a saline body of water is inferred to account fo r thick and massive groundwater calcrete formation and water-saturated debr is flows in a relatively arid climatic context. Most of the formation was e roded prior to deposition of the Bonaventure Formation. However, the basal groundwater calcretes were more widely preserved. They underlie the Bonaven ture Formation in most of the Perce area and in the Saint-Elzear area, clos e to a hundred kilometres to the southwest. Post-sedimentary faulting has a ffected both the La Coulee and Bonaventure formations.