In the three siting regions, the Malm Group above Wildegg Formation comprises the Villigen Formation, Schwarzbach Formation as well as the «Felsenkalke» and «Massenkalk» (Fig. 4‑51). The top of this unit is truncated by a major diachronic erosive unconformity, overlain by residual deposits from the Eocene («Siderolithic Group»; Chapter 3). At the northeastern boundary of the map of Fig. 4‑50 in southern Germany, the last preserved Mesozoic rocks are of Early Tithonian age (Hangende Bankkalke Formation; Zaugg et al. 2008, Koch 2019). In the southwest of the map, the erosion has nearly reached the base of the Villigen Formation. North of Olten, at the western edge of the map, even the Wildegg Formation is missing, and the erosion has reached late Middle Jurassic sediments. In the JO siting region, an approximately 50 m succession of the Malm Group above Wildegg Formation, i.e. Villigen Formation, was found in the BOZ1, and BOZ2 boreholes (Fig. 4‑50). In the NL and ZNO siting regions, parts of the «Felsenkalke» and «Massenkalk» are preserved beneath the unconformity. The thickness of the Malm Group above Wildegg Formation has been confirmed in boreholes, between 175 and 250 m in NL and between 230 and 240 m in ZNO.
The Villigen Formation mostly consists of well-bedded limestone (mudstone, packstone, (bio-) micrite) with generally similar characteristics in all the siting regions (Fig. 4‑51, Fig. 4‑52a – c). Some of the layers are glauconitic and some fossiliferous with sponges (boundstone), crinoids, bivalves, and ammonites. In NL and ZNO, the Villigen Formation has a thickness between ca. 60 and 80 m (Fig. 4‑51). The Villigen Formation is subdivided into the Geissberg, Crenularis, Wangen and Letzi Members in the western part of Northern Switzerland, and into the Hornbuck, Küssaburg and Wangental Members in the eastern part (Gygi 1969, 2000b).
The Schwarzbach Formation (former «Mittlere Malmmergel») consists mostly of a bedded succession of glauconitic limestone (argillaceous) and some glauconitic, calcareous marl (Fig. 4‑52d). It has similar characteristics in the NL and ZNO siting regions and is a lateral equivalent of the Baden Member of the Burghorn Formation. The limestones consist of different carbonate textures (mudstone, wackestone, some packstone) and lithotypes (micrite, biomicrite, biopelmicrite). The Schwarzbach Formation has an increased clay-mineral content in comparison to the underlying and overlying formations (Fig. 4‑51). The boundary to these formations is gradual rather than abrupt. The Schwarzbach Formation is fossiliferous and comprises sponges, ammonites, belemnites, bivalves, and some crinoids. Traces of bioturbation are common. It has a thickness in the range between ca. 10 and 25 m.
The «Felsenkalke» (former «Quaderkalk», «Plattenkalk» or «Bankkalk») and «Massenkalk» represent two different facies units that were deposited next to each other. They are regarded here in combination as an informal unit in the rank of a formation and have a thickness in the range between ca. 85 and 155 m (Fig. 4‑51). They share similar characteristics in NL and ZNO. The «Felsenkalke» unit largely consists of typically micritic, mostly well-bedded limestone (mudstone, wackestone to packstone, micrite, biopelmicrite) with decimetre-scale marl and limestone (argillaceous) interbeds (Fig. 4‑52e). Many horizons of the «Felsenkalke» are fossiliferous, including ammonites, some sponges, belemnites, crinoids, and brachiopods. The «Massenkalk» consists of massive limestone with algal sponge bioherms (boundstone, packstone, biomicrite to pelmicrosparite) up to decametres in size (Fig. 4‑52f). Additionally, benthic fauna such as echinoderms can be found. The strata of the «Massenkalk» are originally dominated by siliceous sponges and also diagenetic siliceous nodules may occur. In some intervals, the sponges are no longer visible because of dolomitisation and dedolomitisation, leading to a saccharoidal limestone (Koch 2011). Such saccharoidal limestones are characterised by brown-yellow colour, variable dolomitic content and vugs (Geyer et al. 2023). These processes can also spread from the «Massenkalk» into the «Felsenkalke». The differentiation between the two facies units in boreholes can be gradual. «Felsenkalke» and «Massenkalk» also contain palaeokarst features that are filled with siderolithic claystone («Boluston»; Fig. 4‑52g, Chapter 3).