The first appearance of the graptoliteNemagraptus gracilis defines the boundary. The rock section consists primarily of dark-gray shale and mudstone, except for a phosphorite marker bed 1.4 m above the GSSP, and was probably deposited at a water depth exceeding 100 m. Drill cores have revealed almost identical stratigraphy across an area several km wide. Due to heating, possibly from an intrusivedike, the stratotype is unfit for dating by magnetic analysis, but this lack is compensated by the diversity of chemostratigraphic and biostratigraphic options.