Cambrian stratigraphy of the När 1 deep well, Gotland

The Cambrian sequence of the När 1 core (Närborringen 1) on southern Gotland, Sweden, has a thickness of 175.15 m. It consists of Lower and Middle Cambrian siliciclastic deposits, succeeded by a thin wedge (c. 2 m) of Upper Cambrian alum shale and dark grey limestone (stinkstone). The Lower Cambrian (File Haidar Formation) comprises 117. 23 m of predominantly light-coloured sandstone sequences and subordinate shale beds. Excluding trace fossils and supposed vendotaenid “algae”, it is poorly fossiliferous and cannot be tied easily to the Lower Cambrian trilobite biochronological scale. The Middle Cambrian is dominated by argillaceous siltstones and has a thickness of 55.9 m. The upper half of the Middle Cambrian sequence is richly fossiliferous and characterized by trilobites indicative of the Eccaparadoxides oelandicus Stage. Accordingly the Paradoxides paradoxissimus and P. forchhammeri Stages are missing. The Upper Cambrian is richly fossiliferous and has yielded Agnostus pisifonnis and Schmalenseeia amphionura indicative of the A. pisiformis Zone