The Schinznach Formation (Upper Muschelkalk Group, former «Hauptmuschelkalk», «Trigonodusdolomit» and «Lettenkohle») exists in all three siting regions and is about 65 to 75 m thick (Fig. 4‑7; Pietsch et al. 2016). It consists of macrofossil-poor to bioclastic limestone and local macrofossil-rich dolostone (Fig. 4‑8). Intervals with oncoids and ooids may occur locally. Later diagenesis led to a partial or complete dolomitisation and successions of cementing and leaching events determine the remaining porosity. Especially in dolomitised bioclastic or oolitic beds, reduced sectors of open porosity exist. However, the porous shoal facies is relatively rare compared to southern Germany (Adams & Diamond 2017). The Schinznach Formation was subdivided into five members:
Leutschenberg and Kienberg Members (lower and middle part of the former «Hauptmuschelkalk»): In the study area, the two lowermost members of the Schinznach Formation are generally hard to separate in the boreholes and are combined in the present study (Jordan & Deplazes 2019). The combined thickness varies between ca. 20 and 30 m. They consist of a bedded succession of limestone (micrite, mudstone) with a varying content of bioclastic limestone (biomicrite, wackestone, packstone) (Fig. 4‑9a & b). Ooids and oncoids also occasionally occur. Some parts of the succession are dolomitised.
Liedertswil Member (upper part of the former «Hauptmuschelkalk»): The thickness of this member varies between ca. 2 and 12 m. It consists mostly of a thin- to medium-bedded succession of partly bioturbated, glauconitic limestone (micrite, mudstone) with some bioclasts mostly concentrated in coquinas (Fig. 4‑9c). The upper boundary to the overlying unit of the Stamberg Member is defined by the onset of post-sedimentary, persistent and complete dolomitisation (Pietsch et al. 2016). This petrographic, diagenetic boundary is therefore diachronous.
Stamberg Member (approx. former «Trigonodusdolomit»): The thickness of this member varies between ca. 30 and 40 m. In the lower part it comprises bedded, macrofossil-poor dolostone (mudstone, wackestone), which resembles the Liedertswil Member but is fully dolomitised (Fig. 4‑9d). The upper part is characterised by partly porous dolostone with chert nodules and is locally sandy or anhydritic. In the porous dolostone, vugs with a size of up to 3 cm occur, which may originate from dissolved shells (Fig. 4‑9e). Additionally, oolite horizons may occur (Fig. 4‑8).
Asp Member (ca. former «Lettenkohle»): The thickness of this member varies around ca. 5 m. The Asp Member can generally be separated into two parts. The lower part consists of a fossiliferous, often bituminous shale or claystone with thin dolostone interbeds (Fig. 4‑9f). The upper part is characterised by dolostone with anhydrite nodules and nodular layers (Fig. 4‑9g).