The Middle Cambrian Paradoxides paradoxissimus Superzone on Öland, Sweden

Abstract

Trilobites from the Middle Cambrian Paradoxides paradoxissimus Superzone on Öland are reviewed, including species found in glacial erratic boulders in Germany and Denmark. The fauna recorded contains 20 species including 10 agnostids. The succession, up to 70 m thick, comprises the Äleklinta Member of the Borgholm Formation (previously known as the Paradoxissimus sandstone or siltstone) and a thin overlying conglomerate, here informally referred to as the Mörbylilla conglomerate, forming the base of the Alum Shale Formation. The thin Granulata Conglomerate, including a limestone layer previously correlated with the Exsulans Limestone, forms the base of the Äleklinta Member. It has yielded several species characteristic of the Triplagnostus gibbus Zone, e.g. Ctenocephalus exsulans, Bailiella tenuicincta, Solenopleura parva, Parasolenopleura aculeata and T. gibbus. The Äleklinta Member contains T. gibbus, Ellipsocephalus lejostracus and P. aculeata, all indicative of the T. gibbus Zone. The overlying Mörbylilla conglomerate contains reworked (?) specimens of E. lejostracus and T. gibbus associated with Acidusus atavus, Tomagnostus fissus, Ptychagnostus affinis, Onymagnostus hybridus, Tomagnostella cf. truncata, Hypagnostus parvifrons and H. mammillatus. Most of these agnostids are found in small stinkstone pockets within the conglomerate. Tomagnostus bothrus? is recorded in Scandinavia for the first time. The fauna shows that the conglomerate represents the A. atavus Zone. The stinkstone pockets indicate that the conglomerate was deposited under dysoxic “Alum Shale” conditions. In the beach section at Mörbylilla, the 0.16 m thick Mörbylilla conglomerate is overlain by an anthraconite bed, up to 0.6 m thick, representing the Exporrecta Conglomerate Bed.

Keywords:

• Middle Cambrian
• Öland
• Sweden
• trilobites
• biostratigraphy

Acknowledgements

Alfred Buchholz, Stralsund, is thanked for kindly lending us several key specimens for the study and discussing various stratigraphical issues with us. The illustrated specimen of P. jemtlandicus? was borrowed from F. Rudolph, Wankendorf. Various taxonomical details have been discussed with R.A. Robison, Kansas, USA. Linda Wickström, SGU, Uppsala, permitted access to study the collection of Tessini sandstone kept at the Swedish Geological Survey. Referees J. Laurie, AGSO, Canberra, Australia and P. Ahlberg, Geological Institution, University of Lund, are thanked for many constructive corrections that greatly improved the original manuscript.