The Role of Fluid Seepage in the Erosion of Mesozoic Carbonate Escarpments

Abstract

AbstractMesozoic submarine carbonate escarpments are erosional features that host box canyons, the formation of which had been attributed to seepage erosion in view of their similarity to subaerial box canyons. The latter had been cited as diagnostic of groundwater activity, although the efficacy of fluid seepage as an erosive agent in bedrock remains controversial. Here we use multibeam echosounder data from the Blake, Campeche, Malta and Florida Escarpments to demonstrate that box canyon formation is, in general, a significant process eroding carbonate escarpments. Numerical modeling based on parameters from the Florida Escarpment shows that box canyons can initiate and retrogressively evolve by fluid seeping via joints, which causes a reduction in rock strength due to fluid pressure and dissolution, resulting in periodic block failure at the canyon head. Box canyon elongation is promoted by an exponential distribution of joint density, an increase in joint density, joints oriented perpendicular and parallel to the escarpment, or an increase in the thickness of the flowing groundwater zone and slope gradient of the escarpment. The angularity of the canyon head decreases with a decrease in joint density and when joint density is uniform, whereas the canyon width is regulated by the extent of the joint set zone. Since the key factors contributing to box canyon formation along the Florida Escarpment appear to characterize the Blake, Campeche and Malta Escarpments, the groundwater model for box canyon formation should be applicable to these escarpments as well.