Facies and Stratigraphic Controls of the Palaeokarst Affecting the Lower Jurassic Coimbra Group, Western Central Portugal

Abstract

An evolutionary geological/geomorphological model is proposed to explain the spatio–temporal distribution of palaeokarst affecting a Lower Jurassic shallow-marine carbonate succession (Coimbra Group; Sinemurian), cropping out in the Coimbra–Penela region (western central Portugal), in a specific morphostructural setting (dolomitic hills). Field and laboratory data allowed a detailed facies/microfacies characterization and diagenetic interpretation to be made, with special regard to the evolution of porosity. High facies/microfacies heterogeneity and contrasts in porosity, providing efficient hydraulic circulation by the development of meso- and macropermeability, significantly influenced and controlled the earliest karst-forming processes (i.e., inception), as well as the subsequent degree of karstification during the mesogenetic and telogenetic stages of the Coimbra Group.