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

Uchman Alfred, Dávid Árpád, Fodor Rozália

Geological Quarterly

2023

Vol. 67, No. 1

art. no. 4

Disc- and cylindrical-shaped clasts of fine-grained calcareous and ferruginous rock, each with a central tunnel, 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 examination and comparisons with sub-recent rhizoclasts in subsoils developed on Quaternary fine-grained deposits in SE Poland, they are re-interpreted as redeposited rhizocretions possibly washed out of the coeval continental deposits of the Salgótarján Lignite Formation. Most are fragmented and abraded. They are termed rhizoclasts and are presented as an example of zombie structures inherited from another environment where they played a different role. Such rhizoclasts can be considered 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 water table and oxygen levels fluctuated.

Nodulichnus hungaricus igen. et isp. nov. from the Early Miocene of North Hungary

Fodor Rozália, Dávid Árpád

Annales Societatis Geologorum Poloniae

2022

Vol. 92, No. 2

181--200

The Early Miocene shallow-marine Salgótarján Lignite Formation of northern Hungary is host to a hitherto unknown trace fossil, here named Nodulichnus hungaricus igen. et isp. nov. This trace is a vertical, straight, or slightly winding, non-branching, tubular structure, 2–5 mm in diameter, and 50–100 mm long. It is filled with globose pellets, which are 0.5–0.6 mm in diameter. Generally, this trace fossil is isolated, but it may occur in clusters. Ethologically, it is a dwelling structure (domichnion), where the producer organism was living during high tide. Additionally, Nodulichnus hungaricus igen. et isp. nov. is accompanied by Ophiomorpha nodosa (Lundgren, 1891), Gyrolithes nodosus (Mayoral and Muñiz, 1998), Thalassinoides isp., Planolites isp. and Tomaculum problematicum (Groom, 1902), which occur sparsely at this level. The trace fossil assemblage is interpreted as being evolved in a ‘low-energy’, sandy beach setting.