Research team uses fossilised wood in quartz to trace Europe’s geological history
Many people are familiar with fossilised wood as a decorative souvenir from museum shops. The fact, however, that it can preserve the geological history of entire regions spanning millions of years is a new discovery. A research team led by geologist Steffen Trümper from the University of Münster – an alumnus of the TU Bergakademie Freiberg – has now demonstrated for the first time that fossilised wood functions as a natural archive from which the geological history of an entire region over hundreds of millions of years can be deduced. Ronny Rößler, Honorary Professor of Palaeobotany at the TU Bergakademie Freiberg, is also involved in the project. The findings extend the previously known timescales for wood mineralisation. They show that fossilised wood can record the subsidence history of a geological basin and reveal tectonic events on a timescale of hundreds of millions of years. Specifically, the study focuses on the Saale Basin, a sedimentary basin that formed around 300 million years ago in what is now central Germany and whose rocks are among the oldest in the vast Central European Basin system. The study has been published in the journal ‘Scientific Reports’.
For their analysis, the researchers examined fossilised wood from the Kyffhäuser Mountains in northern Thuringia. Known since at least the 18th century, these fossils comprise trunks up to 20 metres long, embedded in fluvial red sediments – that is, reddish deposits from ancient river systems. Their colour comes from embedded iron oxides, which indicate a warm, occasionally dry climate. The trunks, which were covered during floods, originate from the tropical dry forests of the supercontinent Pangaea. At that time, the region lay close to the equator. Around 300 million years ago, the now-extinct relatives of conifers grew here. The Kyffhäuser is regarded as a reference site for a type of deposit that formed repeatedly in various basins across Europe. Together, these sites form one of the most extensive deposits of fossilised wood in the Northern Hemisphere. The rocks are among the earliest deposits of the Central European Basin, an economically significant sedimentary basin system which, to this day, harbours raw materials, groundwater and potential for geothermal energy.
The key lies in the quartz, which has permeated and replaced the wood during the fossilisation process. Initially, dissolved silicic acid penetrates the dead wood, coating the cell walls and thus preserving the finest anatomical structures. Over millions of years, the silicic acid eventually crystallises into quartz, replacing the original tissue bit by bit. The study shows that the preservation of these fossils is much more nuanced in terms of structure, geochemistry and the age of the quartz phases than previously assumed. The research team identified five successive generations of silicic acid. Each of these generations contains information about the temperature, pressure and composition of the solutions from which they formed. They document five stages spanning a period of 200 million years from the late Carboniferous to the early Cretaceous. If one takes into account the subsequent uplift to the Earth’s surface, this period extends to as much as 300 million years. This is the longest documented sequence of successive stages of wood mineralisation to date.
