Glossar

 

Quaternary boreholes

Deposits of unconsolidated rocks from the Quaternary – the most recent geological time period from around 2.5 million years ago to the present – provide information on erosion processes and tectonic activity in the past. These deposits are therefore investigated using boreholes.

The data from the Quaternary boreholes can be used to reconstruct past processes and understand them better. This allows more reliable conclusions to be drawn about how the landscape will evolve in the future and therefore about the long-term safety of a deep geological repository. In comparison, Nagra’s exploratory (deep) boreholes are used mainly to investigate deeper consolidated rock layers.

Locations of the quaternary boreholes

The Quaternary boreholes are used for the geological exploration of scientifically selected areas of Northern Switzerland. Depending on the geological situation, the boreholes are located both within and outside the siting regions Jura Ost, Nördlich Lägern and Zürich Nordost (see map). The locations of the boreholes depend on where the Quaternary deposits occur, based on information from seismic measurements. Unconsolidated rocks are mainly found in the area of today's river courses. These often coincide with old erosion channels/troughs that were carved by glaciers and later filled in again. Nagra is investigating such troughs with Quaternary boreholes. The focus of the work is on the Lower Aare Valley, the Riniker Feld and the Thur Valley.

Current status: all Quaternary boreholes completed

Nagra drilled Quaternary boreholes between March 2018 and December 2020. There were a total of eleven boreholes: In 2018, drilling was carried out in Riniken-1&2, Untersiggenthal Gebenstorf-Brüel, Gebenstorf-Vogelsang and Marthalen-Oobist. In 2019, Nagra drilled the Quaternary boreholes Neuhausen, Trüllikon-Rudolfingen, Hochfelden-Strassberg and Kleinandelfingen-Laubhau. The Andelfingen-Niederfeld borehole was completed in April 2020. It reached a depth of 324 metres. The Adlikon-Dätwil borehole was started in September 2020 and completed in December 2020. It was drilled to a depth of 313 metres. Quaternary boreholes at such great depths are very challenging. Although the drilling work has been completed, the investigation of the rock samples obtained will continue.

Procedure for drilling a Quaternary borehole

The thickness of the unconsolidated rock layer and thus the position of the top of the solid rock is determined while still at the drilling site. The rock samples obtained in the Quaternary boreholes in the form of drilling cores are transported to the Institute of Geological Sciences of the University of Bern. There, further investigations take place, such as determining the age of the sediments. The results of the investigations so far are as expected: the presumed depth of the troughs was largely confirmed, with a few exceptions. The lake sediments encountered in the troughs are basically suitable for the application of age determination methods. New drill cores are currently being analysed. Their dating is extremely complex and will take some time.

Quartärbohrungen der Nagra: Aus der Vergangenheit für die Zukunft lernen (in German)

 

Quartärbohrungen der Nagra: Auf der Bohrstelle (in German)

 

Interview zu den Quartärbohrungen der Nagra: Die jüngste Erdgeschichte erkunden (in German)

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