Field work is hard work
Before starting the actual field work, we clamber a little further down the gorge. We’re now at the bottom of a waterfall that towers some 10 metres above us, where a massive outcrop of Hohgant sandstone forms a slight overhang. Maira pulls out her tablet and jots down a few notes. She also uses it to measure the orientation of the rock strata, and the software plots this data directly into a digital map. “It’s a great tool, but for certain types of observations you still can’t beat a traditional field book,” she says.
Meanwhile, Stefan and Lukas are hard at work, hammering away at the hard rock to break off samples. Ideally, Maira would also like to take a sample from the upper section of the rocky overhang – but that high-hanging fruit proves too much of a challenge even for the climbing skills of the geologists. Their work is interrupted by an enthusiastic Stephan, who comes scrambling up the slope: “There are some pretty big fossils down there,” he says. “But I’m not sure if I’ve found the base of the rock formation yet.” The researchers are still uncertain as to where the boundary lies to the rock layer below. We fight our way further through the rugged terrain. The rocks in this part of the stream are polished smooth, so that the large fossils Stephan discovered are now clearly visible. “This might be the boundary between the strata,” he says. But he and Maira clearly have doubts, so we press on.
Soon, we find what we’re looking for: at the very next rocky outcrop, Lukas spots the boundary between the brown sandy rocks, which include the Hohgant sandstone, and the light-grey Schrattenkalk limestone below. A strip, only a couple of centimetres thick, marks the contact between the two strata. “There’s a gap of up to 80 million years here,” says Lukas with a grin. “The limestone was deposited around 125 million years ago, but the sandstone layer only came along around 45 million years ago.”
That means this spot next to the river spent some time at the Earth’s surface 45 million years ago before it was submerged by the ocean. During that period, rivers transported large quantities of quartz sand from the hinterland to the sea, which eventually became part of the Hohgant sandstone. But where exactly did the sand come from? It seems unlikely to have come from the nearby Aar massif, which was still covered by calcareous sediments at that time. It might have come from the Black Forest massif. Yet, the irregular grains in the sandstone would surely be much more rounded if they had travelled such a long distance.
Commissioned by swisstopo
This would be a fascinating topic for the scientists to study, but their current brief leaves little leeway to pursue it, explains Lukas. As project manager, he is responsible for keeping everything on track: “We were commissioned to carry out the study by the Federal Office of Topography (swisstopo). Their primary goal is to evaluate potential sites for quarrying suitable hard rock.” It may seem surprising that such a meticulously mapped country as Switzerland shouldn’t know exactly where to find the right kind of rock in the right quantities, but much of the current data is incomplete. Faced with looming shortages of the necessary materials, swisstopo commissioned the Georesources Switzerland Group to compile an inventory of all potential hard rock occurrences.