Syndepositional deformation in the Kurkiselkä esker, Kiiminki, Finland

Syndepositional and metadepositional deformation structures from an esker section in Kiiminki, Finland, are described and discussed. The small folds are suggested to be a response of cohesive, hydroplastic material to the drag of turbulent flow, and the accompanying differential pressure conditions. The data indicate a rippling mechanism. The small folds have a transition into more complicated structures derived mainly from syndepositional or metadepositional horizontal movements, apparently in part gravity-induced, which operated contemporaneously with the rippling mechanism. The syndepositional deformation structures of the category described are rather common in the Oulu vicinity, probably due to the widespread occurrence of water-laid deposits composed of fine sand, a grain size that favours this kind of deformation. They can readily be confused with deformation structures of other origin, which exist in juxtaposition within the same area.