The Middle Cambrian Paradoxides paradoxissimus Superzone on Oland, Sweden

摘要

Trilobites from the Middle Cambrian Paradoxides paradoxissimus Superzone on Oland 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 70m thick, comprises the Aleklinta Member of the Borgholm Formation (previously known as the Paradoxissimus sandstone or siltstone) and a thin overlying conglomerate, here informally referred to as the Morbylilla 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 Aleklinta 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 Aleklinta Member contains T. gibbus, Ellipsocephalus lejostracus and P. aculeata, all indicative of the T. gibbus Zone. The overlying Morbylilla 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 Morbylilla, the 0.16m thick Mo¨rbylilla conglomerate is overlain by an anthraconite bed, up to 0.6m thick, representing the Exporrecta Conglomerate Bed.