摘要
Greenish clays often occur as thin layers in Early Cretaceous shallow-water carbonatesediments of Istria where they mark the top of fining upwards sequences. When they showevidence of subaerial exposure and pedogenesis they are considered paleosols. The claymineralogical composition is as follow: (1) randomly oriented I/S mixed layer, (2) regularlyoriented I/S mixed layer, (3) illitic material, (4) kaolinite and (5) chlorite. The insoluble limestoneresidue situated immediately below the greenish clays is dominated by smectite, and also containskaolinite and illitic material. The very high smectite content in the insoluble residue is probablythe result of additions of volcanic dust during carbonate sedimentation. That clay mineralcomposition in the pelitic material clearly indicates the influence of both pedogenic and diageneticprocesses. It may also indicate additional volcanic dust contribution before and during thesubaerial exposure.
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. That 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.
