Figure 21. Cross section through the Ordovician carbonate platform in the Port aux Choix area. The platform is cut by a series of steeply dipping extensional faults. A body of hydrothermally altered dolomite (porosity) is mappable across the entire area, in some cases spatially limited around the faults but generally up to 10 km wide (and extending an unknown distance offshore), at least 8 km long, and up to 300 m thick. Dolomite porosity is most extensive in the upper Catoche Formation, spottier in the peritidal Aguathuna and Spring Inlet Member, and extends as high as the lower Table Point Formation.