Fig. 2

Geologic map of the folded and tabular Jura in the region of St-Ursanne, Canton of Jura. The A16 tunnels of Mont Russelin and Mont Terri are projected onto the map and provide the profile trace for Fig. 3. The Mont Terri rock laboratory is located in the southern limb of the Mont Terri anticline. In this large anticlinal fold, two deep boreholes (numbers 1–2) and 3 important surface outcrops (numbers 3–5) are indicated. Surface outcrops of Opalinus Clay are rare and altered due to weathering. The traces of the axial planes of the Mont Terri, Caquerelle, and Clairemont anticlines and the sinistral strike-slip faults are shown as the key tectonic structures of this map. The Paleogene and Neogene deposits comprise the following formations: Porrentury conglomerates, Terres jaunes, Meeresand, Septarienton, Alsace Molasse, Upper Marine Molasse (red marls and gompholites), and Upper Freshwater Molasse (Formation du Bois de Raube, Vogesenschotter). Further details are given in the legend. This map is based on the Geological Atlas of Switzerland 1:25,000, map No. 40 “St-Ursanne,” (Laubscher 1963), available through swisstopo online under https://map.geo.admin.ch