Wild mountain rivers and dry streams

As part of the BROMACKER project, scientists have made significant progress in their research into the Tambach Basin. Through exploratory drilling, they have been able to analyse, for the first time, complete sequences of the deposits in this important geological area. The findings have been published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

What did the habitat of the early dinosaurs look like 294 million years ago? How did the landscape of the Tambach Basin develop at that time? And: can we draw any conclusions for our current climate from this? Thanks to scientific drilling near Finsterbergen and Tambach-Dietharz as part of the BROMACKER project in 2022 and 2023, scientists can now answer some of these questions.

The answers are provided by sediment cores 200 and 250 metres long – a kind of archive of the strata. From these, the researchers can determine how the sediments were deposited spatially and temporally, and how environmental conditions evolved during the early Permian. The drilling sites were specifically selected to obtain complete sedimentary sequences of the Tambach Formation and to correlate these with regional outcrops and the Bromacker excavation site.

The drill cores trace a landscape

The results show that the area was initially shaped by wild mountain rivers flowing from a highland region east of Tambach. These rivers, which carried water all year round, carved canyons up to 100 metres deep into the highlands and deposited coarse boulders in the foreland. As erosion progressed, the relief and thus the power of the rivers diminished, yet they continued to carry water 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, whilst during rainy seasons large areas of the basin were nevertheless flooded. 

At the same time, the researchers found rock fragments in the deposits from a newly formed low mountain range to the west of the basin – an indication of tectonic upheavals in the region. The increasing size of these fragments reflects the growing difference in elevation relative to this rising low mountain range. The way the sedimentary rocks are stacked on top of one another shows that they were deposited by irregularly flowing streams – comparable to modern river systems in very arid regions such as Central Asia.

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

“The boreholes have given us the opportunity to trace the various depositional conditions and their development over time and space in a way that was previously not even remotely possible,” says lead author Jakob Stubenrauch, a PhD student at the Institute of Earth Sciences at Friedrich Schiller University Jena. “This also allows us to place the Bromacker increasingly well within the context of evolving environmental conditions. The organisms we find at the Bromacker lived in a habitat that was not only dry and seasonal, but above all was becoming increasingly dry and seasonal.”

Such findings are also significant for pressing contemporary issues, as they allow the Tambach Formation to be dated to the early Permian – a transitional phase between a global ice age and the onset of a greenhouse climate. This period marks the most recent geological transition of its kind and could therefore serve as a blueprint for the current global warming on Earth. Anyone wishing to understand how ecosystems such as that of the Bromacker were affected, what processes were at work and what consequences they had, must understand the sedimentary sequences of this period.