A lamellibranch-stromatolite bioherm in the Lower Keuper (Ladinian, Middle Triassic), South Germany

Summary A unique small bioherm, 0.7 m in diameter and 0.25 m high, is described from the Lower Keuper in South Germany. Its core consists of the attached right valves of the tiny oyster-like lamellibranchPlacunopsis ostracina (Pectinacea). It is overgrown by a cm-thick laminated stromatolitic crust formed by microbial mats and sponges. The bioherm was dolomitized during early diagenesis and represents the temporary transition from restricted marine to more saline depositional environments. It is one of the stratigraphically youngestPlacunopsis bioherms found so far in the Germanic Triassic.