Applying geotechnical borehole databases in the search for interglacial deposits in Denmark

Geotechnical investigations conducted in preparation for infrastructure development provide high-quality borehole data in standardised digital formats. In Denmark, such geotechnical borehole data are not required to be reported to the national well database (Jupiter) and are mainly archived in privately owned databases. Accessible interglacial and interstadial terrestrial deposits are rare in Denmark, and these borehole data have the potential to identify interglacial and interstadial deposits, with significant implications for ongoing palaeoclimate, palaeoenvironmental and archaeological research. In this study, we compiled data from six major geotechnical companies, resulting in a database with over 550 000 boreholes. From this database, we identified 1850 boreholes containing samples associated with interglacial and interstadial ages. Through extensive filtering for well-documented lacustrine or palustrine deposits, we selected 161 boreholes and referenced them to 39 different geographical occurrences. Of these 39 occurrences, 36 were either new terrestrial deposits or provided substantial new records to known interglacial and interstadial sites. Our findings demonstrate that access to these privately owned geotechnical borehole data can be a valuable resource for identifying rare near-surface geological deposits, allowing the discovery of several new Pleistocene sedimentary archives that warrant further investigation.