Ammonites and stratigraphy of the Achdorf Formation (Braunjura Group; Aalenian) at the type locality of the Wilflingen-Bank near Gosheim (W Swabian Alb)

The crassicostatum and viallii ammonite biohorizons (Bifidatum Subzone, Opalinum Zone, Lower Aalenian, Achdorf Formation) are described from the Wilflinger Steige near Gosheim. A new subzone, the Obtusiformis Subzone is introduced and includes a new pustulifera biohorizon of the Murchisonae Zone, the ammonite faunas are described. The ammonite assemblage of “lens 1” of Geisingen is reviewed and assigned to the Obtusiformis Subzone. The sehndensis / murchisonae biohorizon is provisionally proposed as the oldest biohorizon of the Murchisonae Subzone (Murchisonae Zone). The ammonite biohorizons are correlated with sections in Germany and abroad. The evolution of the ammonite morphogenera Ludwigia and Staufenia is discussed.