Abstract

Late Ordovician rocks of the Qilang and Yingan formations from the Kalpin area in the Tarim region of western Xinjiang, China (Tarim palaeoplate) contain a moderately diverse graptolite fauna. The fauna from the Qilang Formation contains Corynoides calicularisNicholson, 1867; Dicranograptus clingani resicisWilliams and Bruton, 1983; Lasiograptus costatusLapworth, 1873; Pseudoclimacograptus scharenbergi (Lapworth, 1876); and Glossograptus sp. among other species. This assemblage most likely corresponds to the upper Climacograptus (Climacograptus) bicornis Zone? to lower C. (Diplacanthograptus) lanceolatus Zone of Australia. The Qilang Formation also yields the new taxon, Amplexograptus maxwelli spinousus new subspecies. The overlying Yingan Formation yields a more diverse assemblage that includes Climacograptus (Diplacanthograptus) spiniferusRuedemann,1912; C. (D.) lanceolatusVandenBerg, 1990; Orthograptus quadrimucronatus (Hall, 1865); Amplexograptus praetypicalisRiva,1987; Dicellograptus pumilusLapworth,1876; and D. morrisiHopkinson, 1871. This assemblage most likely corresponds to the Corynoides americanus Zone through the C. (D.) spiniferus Zone of eastern Laurentia, or to the D. clingani Zone of Scotland and central Newfoundland. The presence of a C. (D.) lanceolatus and C. (D.) spiniferus succession in the Yingan Formation also suggests correlation with the Eastonian 1 and 2 of Australasia. The Yingan Formation faunas represent an offshore Pacific Province assemblage dominated by cosmopolitan epipelagic species. The fauna is most similar, both in terms of species composition and relative abundance patterns, to those of the Appalachian Basin. The Yingan faunas differ from the latter in the absence of Laurentian endemic species (except for Amplexograptus praetypicalis), and in the common occurrence of dicellograptids.

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