Record of a dense succession of drowning phases in the Alpstein mountains, northeastern Switzerland: Part II—the Lower Cretaceous Schrattenkalk Formation (late Barremian)

Abstract The Schrattenkalk Formation represents a complete succession of Lower Cretaceous shallow-water carbonate platform series cropping out in the Alpstein massif north-eastern Switzerland. is traditionally divided into two sedimentary units, “Lower” and “Upper” Schrattenkalk, separated by more marly Rawil Member. habitually dated to late Barremian, while Member are early Aptian. New field observations, however, call lithostratigraphic dichotomy question, as neritic carbonates disrupted several key surfaces associated with karstic episodes and/or transgressive sediments, corresponding ammonite-rich hemipelagic deposits on distal shelf. A large number ammonites were collected Drusberg well rare from Formation. These macrofauna allow precise dating onset across its successive phases progradation. Three bodies fourth intermediate rock body at top defined, based new biostratigraphic data updated interpretations sequence stratigraphy geochemical data. shows progressive along studied transect, following SE progradation over time. oldest refer upper Barremian T. vandenheckii Zone youngest uppermost M. sarasini Subzone. discontinuity key-beds highlight three flooding events. first drowning phase, which correlates "Sartousiana" event, dates middle (upper —lower G. sartousiana Zone). second represented Member, an incipient drowning, seems coincide latest Taxy event (usually reported I. giraudi lowermost zones) according ammonite discoveries. final demise platform, situated close Barremian-Aptian boundary, related exposure consecutive event.