Ammonite biostratigraphy of the Aalenian and Lower Bajocian (Middle Jurassic) near Böttstein (Canton Aargau, Northern Switzerland)

A stratigraphic section exposing strata from the upper boundary of the Opalinus Clay to the middle of the Passwang Formation (Middle Jurassic) is described from the abandoned Schmidberg clay pit near Böttstein in the Aare Valley (Aargau, Jura, northern Switzerland). The beds are finely discriminated biostratigraphically from the Lower Aalenian (Opalinum Zone, Bifidatum Subzone) to the Lower Bajocian (Laeviuscula Zone, Trigonalis Subzone). The parts of the Passwang Formation investigated correspond to the formal Sissach Member and incorporate the combined Waldenburg to Brüggli members. This lithostratigraphical interval is subdivided here informally into the Schmidberg and Frickberg members. The formal definition will follow in further work. The strata focused on herein are correlated with other sections in Switzerland and Southwest Germany.