Between Rock and Research: Geochronology at Blätterhöhle
August 2025, Lüdenscheid, bright sunshine – perfect conditions for a field trip that turned out to be anything but ordinary. Together with Mirijam Zickel (PhD) and Dr. Janina J. Nett, I set off as part of the Geomorphology and Geochronology working group at the University of Cologne for the Sauerland. Our destination: Blätterhöhle – an inconspicuous rock fissure with a remarkable history. Our excursion was part of the project “Chronology and chorology of Final Palaeolithic and Mesolithic hunter-gatherers at Blätterhöhle, North Rhine-Westphalia”, which investigates the chronological and spatial context of the last hunter-gatherer groups in Central Europe.
A key site of prehistory
Blätterhöhle is located in the northeastern part of the Rhenish Massif, embedded in dolomite and limestone, criss-crossed by caves and fissures. The small entrance was discovered in 1983, explored further only from 2004, and systematically investigated since 2006, after a large collapse block was removed. Beneath it, in the sediments in front of the cave entrance, lie archaeological strata spanning from the Late Upper Palaeolithic through multiple Mesolithic phases—preserved in a unique stratigraphic sequence. Inside the cave itself, investigations further revealed a Neolithic horizon.
For archaeology and geoscience alike, the site is a true treasure trove: traces of hearths, stone tools, animal bones, and even human remains have been found here – including the first systematically excavated Pleistocene human remains from undisturbed contexts in North Rhine-Westphalia and neighboring regions. The location is especially exciting: the cave lies at an ecological interface between the Central Uplands and the North German Plain, and culturally, several prehistorical cultural groups appear to have intersected here.
Why geomorphology is involved
Our working group is not just a bystander: we investigate the sediments geochronologically – specifically with OSL dating (Optically Stimulated Luminescence) and complementary methods. The aim is to reconstruct the chronological sequence of the sediments as precisely as possible and to address open questions, such as the dating of layers 6b (Early Mesolithic) and 6c (Final Palaeolithic). This is particularly important because the sedimentary sequences in the cave entrance area were most likely heavily disturbed by badger burrows. In these mixed layers, numerous Early Mesolithic and Late Neolithic human remains and other finds were recovered (Orschiedt et al. 2012; 2018). Our work aims to resolve these stratigraphic uncertainties.
An essential part of the work involves in-situ measurements of the natural radioactivity in the sediment, as these values are critical for OSL age calculations. Here beryllium oxide(BeO) dosimeters come into play, which our team had placed in the profile several months earlier. These record radiation exposure directly in the ground over an extended period. In parallel, we take sediment samples to determine radioactivity in the laboratory using gamma spectrometry and compare the two methods.
The excursion: sunshine, sediment – and a surprise find
On site we first met the archaeology team led by Wolfgang Heuschen – plus a group of dedicated students working on the excavation. While the archaeologists carefully searched the sediment centimeter by centimeter for traces of the Stone Age, we set to work:
- Retrieving the dosimeters – carefully, since they are small, fragile, and in some cases buried deep in the profile.
- Taking sediment samples – always exactly where a dosimeter had been placed before, to ensure comparability.
- Documenting everything in detail.
The last samples held a surprise: while working in the sediment, a rib bone suddenly appeared – a find that immediately caused a ripple of excitement. For the archaeologists, it was an intriguing piece of the puzzle; for me personally, it was a real highlight: my very first find at my very first excavation site.
Underground – inside the cave
After our work was done, there was still a special “extra” on the schedule: a guided tour inside the cave itself, together with Wolfgang Heuschen. The entrance is small – very small – and guarded by a handpicked colony of harmless but impressively large cave spiders.
Then came crawling, wriggling, squeezing through the narrow passage – not all of our team chose to face this thrill (yes, I admit it – I chickened out…). At the end, a small chamber opened up, where spectacular finds have been made over the past years. Here, far removed from daylight and time, the story of the last hunter-gatherers of Central Europe is being brought to light piece by piece. “Down there it sometimes feels almost meditative – completely removed from reality, immersed in the stillness of another time,” some archaeology students told us, who frequently work at the excavation and seem to genuinely enjoy the tranquility inside the cave.
Conclusion
Blätterhöhle is not a place you simply “visit.” It is a living research site where archaeology and geoscience work hand in hand to create a more precise picture of human history. Our excursion day was a mix of meticulous sampling, inspiring encounters – and a touch of underground adventure.
And yes – there are places where even an ancient rib bone can make the day perfect.