In situ preservation and paleoenvironmental assessment of Taxodiacea fossil trees in the Bükkalja Lignite Formation, Bükkábrány open cast mine, Hungary

Abstract

In summer 2007 sixteen Taxodium tree trunks were found in situ standing position in the Bükkábrány open cast mine. The fossil trees were exposed during the excavation of the overburden layers of the Bükkalja Lignite Formation (BL). The Bükkábrány discovery is a global novum because the trees are very well preserved but not fossilized that makes the most detailed and direct analysis feasible. In spite of the 7–8 million years passed, the actual site and the host formation is rather intact, lacking tectonic deformations, deeper burial and/or dewatering during uplift. Organic petrology of tree trunks and sedimentology of the overburden sands are the subjects of this study. The extremely good preservation of fossil trunk tissues, presence of high amount of cellulose and moisture content along with the slightly gelified state of the wood and the lack of deformation indicate that there was only limited alteration during the early diagenesis. Chemical investigation of standing trunks fossil driftwood nearby the Late Miocene trees, and the fossil woods in the underlying lignite have revealed that their cellulose and total phenol concentrations were significantly lower than in intact recent trees, applied for reference. Yet their preservation levels were quite high, also proving that the chemical degradation of the fossil wood tissues had not been taken place extensively in the mire and the trees remained exceptionally well preserved. Sudden burial of the trees by strand plain sand beds indicates flooding by heavy storms or tsunamis, which interrupted and terminated the peat formation and preserved the trunks from later oxidation and biodegradation.