Graptolites from the Qilang and Yingan formations (Caradoc, Ordovician) of Kalpin, western Tarim, Xinjiang, China

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 containsCorynoides calicularisNicholson, 1867;Dicranograptus clingani resicisWilliams and Bruton, 1983;Lasiograptus costatusLapworth, 1873;Pseudoclimacograptus scharenbergi(Lapworth, 1876); andGlossograptussp. among other species. This assemblage most likely corresponds to the upperClimacograptus (Climacograptus) bicornisZone? to lowerC. (Diplacanthograptus) lanceolatusZone of Australia. The Qilang Formation also yields the new taxon,Amplexograptus maxwelli spinoususnew subspecies. The overlying Yingan Formation yields a more diverse assemblage that includesClimacograptus (Diplacanthograptus) spiniferusRuedemann, 1912;C. (D.) lanceolatusVandenBerg, 1990;Orthograptus quadrimucronatus(Hall, 1865);Amplexograptus praetypicalisRiva, 1987;Dicellograptus pumilusLapworth, 1876; andD. morrisiHopkinson, 1871. This assemblage most likely corresponds to theCorynoides americanusZone through theC. (D.) spiniferusZone of eastern Laurentia, or to theD. clinganiZone of Scotland and central Newfoundland. The presence of aC. (D.) lanceolatusandC. (D.) spiniferussuccession 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 forAmplexograptus praetypicalis), and in the common occurrence of dicellograptids.