Record of a dense succession of drowning phases in the Alpstein mountains, north-eastern Switzerland: part I—the Lower Cretaceous Tierwis Formation (latest Hauterivian to latest Barremian)

Abstract In the Alpstein massif of north-eastern Switzerland, a complete succession uppermost Hauterivian to Barremian condensed hemipelagic sediments crops out. This is known as Tierwis Formation, comprising in ascending order, Altmann and Drusberg members. The sedimentary bears number fossiliferous glauconite- or phosphate-rich beds. A large newly discovered ammonites from these key beds several poorly explored levels Formation allows for new age calibration. dating well revised sequence stratigraphic interpretations geochemistry contribute better understanding lithostratigraphic complexity its spatio-temporal relationship with Schrattenkalk Formation. observations, backed by ammonites, shows that type-section paratype-section do not cover same interval because dynamic sedimentation processes erosion submarine channels. We suggest phosphatic conglomerate Dursberg Member middle late corresponds Chopf Bed, which we recognised first time Alsptein massif. strongly thickens toward southeast progressively covers an upward extended range. Furthermore, key-surfaces highlight dense drowning phases occurred through latest interval. onset glauconite-rich associated major phase, followed Faraoni oceanic anoxic event. change rhythmic marl-limestone alternation takes place over polyzonal conglomerate. coincides second phase Mid-Barremian Event, calibrated on Tethyan ammonite biozonation.