Greenish clays often occur as thin layers in Early Cretaceous shallow-water carbonate sediments of Istria where they mark the top of fining upwards sequences. When they show evidence of subaerial exposure and pedogenesis they are considered paleosols. The clay mineralogical composition is as follow: (1) randomly oriented I/S mixed layer, (2) regularly oriented I/S mixed layer, (3) illitic material, (4) kaolinite and (5) chlorite. The insoluble limestone residue situated immediately below the greenish clays is dominated by smectite, and also contains kaolinite and illitic material. The very high smectite content in the insoluble residue is probably the result of additions of volcanic dust during carbonate sedimentation. The clay mineral composition in the pelitic material clearly indicates the influence of both pedogenic and diagenetic processes. It may also indicate additional volcanic dust contribution before and during the subaerial exposure.

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