The Cambrian-Ordovician boundary interval within Alum Shale at Krekling, Norway, is for the first time investigated for biostratigraphy. Samples were taken from the Alum Shale levels, within the almost continuous succession of the Rhabdinopora flabelliformis graptolite. Specimens were photographed and measured for identification. The following subspecies were identified: Rhabdinopora flabelliformis socialis, Rhabdinopora flabelliformis norvegica, Rhabdinopora flabelliformis parabola, Rhabdinopora flabelliformis canadensis, Rhabdinopora flabelliformis flabelliformis. Biostratigraphy of the Cambrian-Ordovician interval has been made according to ranges of subspecies identified. The biostratigraphic ranges of the graptolites do not match previously reported correlations from early Tremadocian and call into question previous biozonations. The Cambrian-Ordovician boundary has been estimated to lie slightly below the first occurrence of trilobite Boeckaspis hirsuta, graptolites Rhabdinopora flabelliformis, within significant increase of vanadium content. Geochemical analysis were made by Dr. Øyvind Hammer and Dr. Henrik Svensen.