Inoceramids and biostratigraphy at the Turonian/Coniacian boundary; based on the Salzgitter-Salder Quarry, Lower Saxony, Germany, and the SΠupia Nadbrze˝na section, Central Poland

Abstract

The candidate Global Standard Stratotype-section and Point for the base of the Coniacian Stage, the Salzgitter-Salder section, Germany, and the SΠupia Nadbrzeżna section, central Poland, provide together a continuous record of the inoceramid succession and events across the Turonian/Coniacian boundary interval, that can be correlated throughout Europe and beyond. The Turonian/Coniacian boundary interval marks a radical change from the Upper Turonian, Mytiloides/Inoceramus-dominated fauna to the Cremnoceramus-dominated fauna of the topmost Turonian and Lower Coniacian. The Cremnoceramus clade is basically composed of three lineages: waltersdorfensis, with subspecies waltersdorfensis (ANDERT) and hannovrensis (HEINZ); deformis, with subspecies erectus (MEEK), dobrogensis (SZASZ) and deformis (MEEK); and crassus, with subspecies inconstans (WOODS) and crassus (PETRASCHECK). Rare Inoceramus species range throughout the boundary interval, and in the middle Lower Coniacian representatives of the genus Tethyoceramus SORNAY (non HEINZ) appear. Twelve species and/or subspecies of these genera are described and illustrated. The inoceramids provide the basis for the subdivision of the uppermost Turonian – Lower Coniacian boundary interval into 7 inoceramid zones. The upper Upper Turonian is divided into the Mytiloides scupini Zone and the Cremnoceramus waltersdorfensis Zone. In the Lower Coniacian the following zones are distinguished, in ascending order: Cremnoceramus deformis erectus, C. waltersdorfensis hannovrensis, Cremnoceramus crassus inconstans, Cremnoceramus crassus + C. deformis deformis and Inoceramus gibbosus. The inoceramid marker proposed for the base of the Coniacian, formerly referred to as Cremnoceramus rotundatus (sensu TRÖGER non FIEGE) is a synonym of Cremnoceramus erectus (MEEK), and its first appearance marks the base of the deformis erectus Zone and the base of the Coniacian Stage. The Salzgitter-Salder section, despite some problems concerning a possible hiatus or condensation at the boundary represents the best available potential stratotype for the Turonian/Coniacian boundary.