Darriwilian (Middle Ordovician) chitinozoans from the Qaidam Paleoplate, northwest China

The Qaidam Paleoplate is a microcontinent that is currently part of central Asia. Its position during the Ordovician is uncertain, with paleogeographic reconstructions placing it either near South China or near North China. Ordovician microfossils such as chitinozoans have not previously been reported from the Qaidam Paleoplate. In this paper, a chitinozoan microfauna from the middle part of the Shihuigou Formation in the Dameigou section, South Qilian Mountains, Qinghai Province, northwest China is documented. The assemblage is dated as Darriwilian (Undulograptus austrodentatus and Archiclimacograptus confertus graptolite biozones) on the basis of associated graptolites. The chitinozoan fauna is well-preserved and includes several biostratigraphically and paleogeographically important chitinozoan species, such as Lagenochitina langei, L. pirum, Rhabdochitina magna, R. usitata, Conochitina turgida, C. subcylindrica, C. decipiens, Clavachitina poumoti, Belonechitina nevillensis, B. cf. uniformipunctata and B. chydaea. The assemblage contains a specimen in which the collarette of a specimen of Desmochitina sp. is attached to the aboral pole of a specimen of Lagenochitina sp., possibly indicating that a single organism could produce more than one chitinozoan morphospecies. The Conochitina turgida-C. subcylindrica Biozone is indicated by the recovered chitinozoan assemblage. Biostratigraphically important species from the Qaidam microfauna suggest faunal affinities with Laurentia (North America), eastern Gondwana (Australia) and the peri-Gondwana area (southeast China). The chitinozoan paleogeographic data indicate that the Qaidam region was at low latitude during the Middle Ordovician, and that the area was near South China. The paleogeographic information deduced from chitinozoans is consistent with that obtained from graptolites and paleomagnetic analysis in previous studies.