Upper lower Cambrian trilobiidid

Upper lower Cambrian (provisional Cambrian Series 2) trilobites are described from three sections through the Shuangyingshan Formation in the Beishan area, northwestern Gansu Province, China. The trilobite fauna is dominated by eodiscoid and 'corynexochid' trilobites, together representing at least ten genera: Serrodiscus, Tannudiscus, Calodiscus, Pagetides, Kootenia, Edelsteinaspis, Ptarmiganoides?, Politinella, Dinesus and Subeia. Eleven species are described, of which seven are identified with previously described taxa and four described under open nomenclature. The composition of the fauna suggests biogeographic affinity with Siberian rather than Gondwanan trilobite faunas, and the Cambrian Series 2 faunas described herein and from elsewhere in northwestern China seem to be indicative of the marginal areas of the Siberian palaeocontinent. This suggests that the Middle Tianshan-Beishan Terrane may have been located fairly close to Siberia during middle-late Cambrian Epoch 2. Key words: Trilobita, taxonomy, palaeobiogeography, lower Cambrian, Cambrian Series 2, Beishan, Gansu Province, China. On kirjeldatud Hiina Gansu provintsi Beishani piirkonna kolme Alam-Kambriumi labiloike Shuangyingshani kihistu trilobiidid. Nende hulgas domineerivad eodiscoidsed ja 'corynexochiidsed' trilobiidid kokku vahemalt kumne perekonna esindajatega (Serrodiscus, Tannudiscus, Calodiscus, Pagetides, Kootenia, Edelsteinaspis, Ptarmiganoides?, Politinella, Dinesus ning Subeia). See trilobiidikooslus viitab elustiku samasusele pigem Siberi laamaga kui Gondwanaga, millest on jareldatud, et antud piirkonna ehk Alam-Kambriumi Kesk-Tian Shani--Beishani laam paiknes toenaoliselt Siberi laamale usna lahedal.