Petrified trees of the Kyffhauser (Pennsylvanian, Thuringia): Growth habitat, fossilisation and palaeoclimatic-palaeoecological implications

Petrified woods from the Kyffhauser (Siebigerode Fm., Saale Basin) are among Germany's most voluminous occurrences of petrified trees. We reconstruct the provenance and fossilisation of the silicified logs and accompanying fossil plants based on sediment architectures documented in 15 quarries, plant-anatomical analyses of 112 specimens from eight collections and cathodoluminescence microscopy of silicified tissues. The up to 20 m long Agathoxylon trunks derived from 40 m tall cordaitaleans and conifers. Alluvial processes, the erosion of adjacent basement slopes during floods and storms were the main forces to recruit large woody debris from seasonally dry forests growing in extrabasinal habitats. A climatically controlled high discharge variability and the large-scaled, low-sinuous channel geometry ensured transport of the trunks across a 60 km distance towards the basin centre. Deposition of the logs occurred during the waning flood stage accompanied by the formation of four large woody debris-induced sedimentary structures. The stratigraphic occurrence of silicified trunks indicates a hydrodynamic window of log entombment constrained by river morphology, discharge regime, wood shape, and wood density. The synsedimentary to early postsedimentary silicification was a millennium-scale two-phase process and resulted in selective tissue preservation referred to as "pointstone". Imprints from associated floodplain deposits reveal sparse riparian vegetation consisting of ferns, calamitaleans, pteridosperms, and juvenile to shrub-like cordaitaleans. Results demonstrate the potential of multidisciplinary approaches in interpreting plant taphocoenoses and highlight the Kyffhauser as a crucial locality to elucidate late Palaeozoic vegetation dynamics.