Geochemistry of rocks associated with the Cretaceous paleokarst in the Actopan platform: paleohydrologic evolution

Abstract

Fronts of the Sierra Madre Oriental expose Cretaceous rocks in the Actopan Platform allowing the study of the paleokarst developed by the exposure of the rocks in the Albian. The development and position of the paleovadose and paleophreatic zones are studied by geochemistry and petrology. The petrologic evidence in the outcrops show dissolutional, depositional, fracturing, brecciation and collapse features extending over the platform. The transgressive cover of the paleokarst does not show any physical (unconformity) or petrologic (conglomerate or breccia) evidence to delineate the contact with the paleokarst. The isotopic composition (δ¹⁸OVPDB and δ¹³CVPDB) and cation chemistry of the paleometeoric water together with the petrologic evidence of the paleokarstic breccias all support the identification of the paleovadose and paleophreatic zones and the limits to those zones. Delineation of paleokarst and of the overlying sedimentary cover can be based entirely on their distinctive geochemical signatures. Cretaceous paleokarstic rocks are important for the prospection of aquifer, petroleum and mineral resources, as well as in civil engineering projects, like dams.