Abstract
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.
Highlights
China is a complex collage of continental blocks and accretionary belts, as well as several smaller blocks and terranes, including amalgamation of the North China plates and the southern marginal areas of Siberia
This paper focuses on upper lower Cambrian trilobites from the Beishan area, northwestern Gansu Province of China
Of the two known species of Edelsteinaspis with four axial rings in the pygidium, the pygidial border is comparatively narrow in E. gracilis Lermontova, 1940, whereas it is distinctly wider in E. plana
Summary
China is a complex collage of continental blocks and accretionary belts, as well as several smaller blocks and terranes, including amalgamation of the North China plates and the southern marginal areas of Siberia. The axis is strongly convex (tr.), rising steeply from the pleural fields, gently tapered rearwards, rounded posteriorly, almost reaching the border furrow, 88% of the pygidial length and 42% of the pygidial width anteriorly; it is composed of four distinct rings and a very short terminal piece. Edelsteinaspis differs from ‘typical’ dorypygids essentially only in having a more elevated frontal glabellar lobe, more deeply impressed glabellar furrows (which appear strongly arched because of the tilt imposed by the anteriorly elevated glabella) and wider pleural fields, features generally not useful in classification above species or perhaps genus level. Of the two known species of Edelsteinaspis with four axial rings in the pygidium, the pygidial border is comparatively narrow in E. gracilis Lermontova, 1940, whereas it is distinctly wider in E. plana. Poliellina (Politinella) bajanica Ivshin, 1979, from the Bayanaulsk Horizon, central Kazakhstan; by original designation
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