Platform margin palaeokarst development from the Albian of Gorbea (Basque-Cantabrian region, N Iberia)

Palaeokarst structures at different scales occur in inner and outer settings of the Albian Gorbea rimmed carbonate platform. The best palaeokarst development occurs on the platform margin environment, from where we describe three principal horizons: Axular, Aitzgorrigain and Itxingote. The first two (Axular and Aitzgorrigain) are characterised by cavernous porosity and laminated carbonate infills. Their development occurred in two respective single stages during short-term subaerial exposure. The last palaeokarst (Itxingote) is characterized by channel and vug porosity and miscellaneous infills, including quartz sandstones. This palaeokarst developed multiepisodically in a complex way throughout the middle Albian (3.5 m.a.). During karst evolution, sedimentary wedges composed of autochthonous and allochthonous carbonates as well as siliciclastics were deposited in adjacent slope and basin environments, mainly as lowstand deposits. The palaeokarsts originated by subaerial exposure caused by relative sea level falls. Synsedimentary tectonic activity is closely related to relative sea level changes; moreover, it influenced palaeokarst location, morphology and development.