Inoceramid bivalves from the Coniacian (Upper Cretaceous) of the Staffhorst shaft (Lower Saxony, Germany) - Stratigraphical significance of a unique succession

The Staffhorst shaft (Lower Saxony, Germany) ranks amongst the critical sections for documentation of the inoceramid record of the Euramerican Coniacian Stage (Upper Cretaceous). In spite of a number of disadvantages (i.e., interval sampling and stratigraphical gaps), this section does provide details of the inoceramid distribution across insufficiently known substage boundary intervals of the Coniacian. The lower-middle Coniacian boundary is marked by the Inoceramus gibbosus Zone, at the top of the lower Coniacian, followed by the Volviceramus koeneni Zone of the lower middle Coniacian. The zone of I. gibbosus Schlüter, 1877 succeeds the Cremnoceramus-dominated lower Coniacian and usually is missing in the Euramerican biogeographic region. In addition to the index species, the V. koeneni Zone is characterised by Volviceramus exogyroides (Meek and Hayden, 1862), a North American taxon that was poorly documented in Europe hitherto. The base of the upper Coniacian is best documented by the common appearance of Sphenoceramus subcardissoides (Schlüter, 1877) and of Magadiceramus subquadratus (Schlüter, 1887). Inoceramus fasciculatus Heine, 1929, and the stratigraphically earliest 'sphenoceramids', are good proxies for this boundary. The record from the Staffhorst shaft confirms and supplements recent reports on the inoceramid succession of the Coniacian across the entire Euramerican biogeographic region.