Heterogenous mixed-layer clays from the Cretaceous Greensand, Isle of Wight, southern England

The sea-cliffs of the Isle of Wight were deposited during a period of overall sea-level rise starting in the Barremian (Lower Cretaceous) and continuing into the Aptian and Albian. They consist of fluvial, coastal and lagoonal sediments including greensands and clays. Numerous episodes of erosion, deposition and faunal colonization reflect condensation and abandonment of surfaces with firmgrounds and hardgrounds. This study focused mainly on shallow marine cycles where variations in clay mineralogy would not be expected, because overall system composition, sediment source, and thermal history are similar for all the samples in the studied section. Instead we found a wide variety of clay assemblages even in single samples within a 200 m interval. In this interval, distinct clay mineral assemblages were found and can be described as consisting of Alrich, Fe-rich and intermediate Fe and Al compositions with respect to 2:1 and 1:1 layers in mixed-layer arrangements. Nearly pure glauconite-nontronite clays exist in the