Clasts derived from rhizocretions in shallow-marine Miocene clastic deposits of northern Hungary: an example of zombie biogenic structures

Disc- and cylindrical-shaped clasts of fine- grained calcareous and ferruginous rock, each with a centraltunnel, occur in shallow marine brackish Miocene sandy deposits of the Egyházasgerge Formation in Hungary. Previously, these have been interpreted as enigmatic biogenic (?) structures. After field and laboratory examina tion and comparisons with sub-recent rhizoclasts in subsoils developed on Quater nary fine-grained deposits in SE Poland, they are re-in terpreted as redeposited rhizocretions possibly washed out of the coeval continental deposits of the Salgó tarján Lignite Formation. Most are fragmented and abraded. They are termed rhizoclasts and are presented as an example of zombie structures in herited from another environment where they played a different role. Such rhizoclasts can be con sidered as an indicator of the source of the clastic material transported from a vegetated landmass on which moderate or poorly drained soils develop and plant roots penetrate the fine-grained substrate. In such soils, iron was mobilized, then fixed by oxidation, as the watertable and oxygen levels fluctuated.