VUB geologists pinpoint geological age Maastricht quarries for the first time

Researchers use new techniques to determine when limestone layers and fossils were formed during dinosaur age, 66 to 73 million years ago

 Geologists from the Vrije Universiteit Brussel and KU Leuven, in collaboration with Maastricht Natural History Museum and Dutch conservation organisation Natuurmonumenten, have mapped the million-year-old rocks in the quarries near Maastricht. Using modern techniques, the researchers were able for the first time to determine the age of the various limestone layers and fossils much more precisely, and have dated their formation back to the last dinosaur age, 66 to 72.9 million years ago, when the region was still a lively underwater world. Their results have been published in the journal Newsletters on Stratigraphy.

“By comparing changes in the chemical composition of the rocks with other locations in the rest of the world, we were able to determine much more precisely how old the limestone layers are and therefore also the fossils found in them,” explains geologist Johan Vellekoop, who carried out the work during his postdoc at VUB. “Thanks to this research, we can learn more about the development of life in the subtropical seas around Maastricht millions of years ago.”

The area around Maastricht is geologically very interesting because there are rocks on the surface that were formed millions of years ago, when the region was still a shallow, subtropical sea. Shells and skeletons of marine animals have piled up over time and formed a layer of limestone about 100 metres thick. During the many excavations carried out in recent years, such as in the former ENCI quarry, several unique fossils have been discovered, says Vellekoop. The most famous is the Maastricht Mosasaurus, a marine reptile that could grow to a length of 18 metres, while sea turtles and even some dinosaur remains have also been found, all of which can be seen in the city’s Natural History Museum. The exact age of these fossils was unknown until now.

In the new study, the geologists studied the chemical composition of the rocks. “We also measured the concentrations of chemical elements,” says Vellekoop’s colleague Pim Kaskes. “These analyses indicated that the shallow Maastricht sea was rich in oxygen during this entire period and was therefore very suitable for sustaining a diverse ecosystem brimming with life.”

The last six million years of the dinosaur era are known worldwide as the “Maastrichtian” period. “It‘s fantastic that we have now been able to date the former underwater world from our own backyard so accurately and can therefore compare it directly with regions on the other side of the world,” says Kaskes.

For decades, limestone was extracted in the region around Maastricht, in various quarries, such as ENCI and Hallembaye. Many of these have since been transformed into nature reserves. As a result, the rock walls are becoming overgrown and inaccessible for geological research. To record the geological heritage of the Maastricht region for the last time, the Maastrichtian Geoheritage Project was set up by researchers four years ago. In addition to collecting rock material, they made an accurate 3D model of the quarry using camera images from a drone. The collected image and rock material has now been carefully archived at the Natural History Museum, where it remains freely accessible for future research.