Coal petrological and xylotomical characterization of Miocene lignites and in-situ fossil tree stumps and trunks from Lusatia region, Germany: Palaeoenvironment and taphonomy assessment

Abstract

The present paper investigates rank and composition of coal as well as depositional and hydrogeological settings persisting during the stage of peat accumulation and evaluates taphonomy and conditions for the in-situ preservation of outstanding fossilized stump and trunks, using coal petrological and xylotomical analyses. The obtained results are further interpreted and compared with existing literature records. Lignite samples and fossil wood specimens were collected from the 2nd MFH (2nd Miocene Seam Horizon) or its equivalent present at Meuro, Piskowitz, and Welzow-Süd open-cast mines located in Lusatia, Germany. The examined lignite samples indicate low rank coals at lignite or subbituminous rank stage and are characterised by slight dominance of attrinite over textinite, ulminite, suberinite, cutinite porigelinite, resinite, and corpohuminite macerals. Waterlogged conditions prevailing in the mire are associated with peat accumulation under anoxic conditions accompanied by low decomposition rates. The determined facies indicators suggest a moderate to high as well as low gelification of the organic matter for the Meuro and Piskowitz open-cast mines, respectively. In Meuro open-cast mine, the prevalence of herbaceous plant in a mire or a bacterial/fungal degradation of woody plant tissues can be envisaged, whereas in the Piskowitz open-cast mine, it is suggested that peat formed in a wet forest mire environment with a limited oxygen supply and a relatively low bacterial/fungal degradation. The studied fossil wood specimens revealed the presence of Quasisequoioxylon piskowitzense preserved as an in-situ fossilized stump, as well as Taxodioxylon cryptomerioides and Sciadopityoxylon wettsteinii species preserved as fossilized trunks. The examined species belong to the families of Sciadopityaceae and Cupressaceae Li sensu lato. The taphonomy of the in-situ fossilized stump and trunks can be explained by nutrient-, and oxygen-poor oligotrophic mires distinguished as raised bogs and suggesting generally anoxic conditions during Middle to late Miocene Climate transition.