Bioturbation in stabilized Quaternary inland dunes of the European Sand Belt in Poland

Late Glacial and Holocene stabilized inland dunes of the European Sand Belt in eastern and central Poland are intensively bioturbated below recent soils and buried palaeosols. In the recent subsoil, a layer of massive, totally bioturbated sand (23–97 cm thick, mean 47 cm) with usually poorly visible bioturbation structures is present. It transits into the underlying transitional layer (51–180 cm thick, mean 112 cm thick), where primary parallel lamination is cross-cut by casts of roots and associated, mostly meniscate, cylindrical burrows. Down the section, the burrows become increasingly vertically oriented, whereas their orientation is variable in the upper part. Burrows in the soil and the totally bioturbated layer are produced for feeding, sheltering, breeding, or a combination of these purposes together by various groups of organisms. The deep, mostly vertical, meniscate burrows are produced by insects for overwintering: they burrow down, feed on roots, and return (in spring) along the same path. They can cluster close to the casts of tree roots. The development of such ichnofabrics requires at least hundreds of years. In some cases, only a part of the transitional layer is preserved between laminated sands because of subsequent erosion followed by rapid deposition. Ichnofabrics document the previous presence of a well-developed soil vegetated with trees. Vertical to oblique meniscate burrows developed in the transitional layer are characteristic of a new ichnosubfacies of the Entradichnus-Octopodichnus ichnofacies, which is named the European Sand Belt ichnosubfacies. This ichnosubfacies may occur in well-aerated, and well-drained, sandy substrates in similar climatic conditions elsewhere.