Ancient fluid flow within foreland terrains

Abstract

Summary Dewatering of the front Ranges of the Canadian Cordillera in the Campanian and Maastrichtian was achieved by expulsion of connate fluids from thrust sheets during active translation. Each major thrust sheet behaved as a separate hydrodynamic unit. Flow was consistently from hinterland to foreland sections of basal-sheet aquifers. The rate of fluid expulsion exceeded that of rock translation during hydrofracturing. Two flow systems, separated in time, utilized basal-sheet aquifers. Fluid flow at the margin of foreland basins in the Southern Pyrenees in the Oligocene was focused within both the crystalline infrastructure and the sedimentary suprastructure. Ascending metamorphic fluids passed from shear zone conduits in the basement into and through the basin margin, creating ghost vertical and lateral fluid fronts within the sedimentary pile. Connate fluids escaped via cleavage network channelways. Ponding of metamorphic and connate volumes of the fluid budget occurred at high levels close to the leading edge of natural strain within the basin margin, where excess fluid pressures were achieved.