Wild mountain rivers and dry streams

Researchers at the University of Jena have made significant progress in the exploration of the Tambach Basin as part of the BROMACKER project. With the help of research drillings, they were able to analyse complete sequences of the deposits of this important geological area for the first time. The results were published in the scientific journal »Palaeogeography, Palaeoclimatology, Palaeoecology«.

What did the habitat of the prehistoric dinosaurs look like 294 million years ago? How did the landscape in the Tambach Basin develop at that time? And: can we deduce anything about our climate today? Thanks to scientific drilling near Finsterbergen and Tambach-Dietharz as part of the BROMACKER project in 2022 and 2023, these questions can now be answered, at least in part.

The answer is provided by 200 and 250 metre long sediment cores—a kind of archive of the layers. The researchers can read from them how the sediments were deposited spatially and temporally and how the environmental conditions developed during the early Permian. The drilling sites were specifically selected in order to obtain complete sediment sequences of the Tambach Formation and to relate these to regional outcrops and the Bromacker excavation site.

The drill cores trace a landscape

The results show that the area was initially characterised by wild mountain rivers from a high area to the east of Tambach. These rivers, which carried water all year round, cut canyons up to 100 metres deep into the highlands and deposited coarse debris in the foreland. As the erosion progressed, the relief and thus the power of the rivers decreased, but they continued to carry water all year round and regularly flooded the Tambach basin. The rocks of the Bromacker sandstone, at the level of which the site is located, show signs of the rivers drying up at times, while large areas of the basin were nevertheless flooded during rainy seasons.

At the same time, the researchers found rock fragments from a newly formed low mountain range to the west of the basin in the deposits—an indication of tectonic upheavals in the region. The increasing size of these fragments reflects the increasing height difference to this rising low mountain range. The way in which the sedimentary rocks are stacked on top of each other shows that they were deposited by irregularly flowing streams—comparable to today’s river systems in very dry regions such as Central Asia.

These environmental conditions had a significant influence on the animals and plants living there. The findings at the Bromacker indicate that the climate became increasingly drier and more seasonal, and that living organisms were able to adapt to these new conditions.

»The drillings have given us the opportunity to trace the different depositional conditions and their development in time and space in a way that was not even remotely possible before«, says first author Jakob Stubenrauch, doctoral candidate at the Institute of Geosciences at Friedrich Schiller University Jena. »This means that we are increasingly able to place the bromacker in the context of the development of environmental conditions. The creatures that we find at the Bromacker lived in a habitat that was not only dry and seasonal, but above all became drier and more seasonal.«

Such findings are also significant for pressing current issues, as they allow the Tambach Formation to be categorised in the Early Permian—a transitional phase between a global ice age and the beginning of a greenhouse climate. This period marks the most recent transition of this kind in geological history and could therefore serve as a blueprint for the current global warming on Earth. If you want to understand how ecosystems such as the Bromacker were affected, what processes took place and what consequences they had, you need to understand the sedimentary sequences of this period.