A camerate-rich Late Carboniferous (Moscovian) crinoid fauna from volcanic conglomerate, Xinjiang, People's Republic of China

Abstract

A low-diversity camerate-rich crinoid fauna from the Qijiagou Formation, Taoshigo Valley near Turpan, Xinjiang-Uygar Autonomous Region, China was collected during field work in May, 1993. The crinoid fauna is dominated by species of Platycrinites. Other camerate crinoids include a species in the Paragaricocrinidae, Actinocrinites, a hexacrinitid, and an acrocrinoid. The only other non-North American occurrence of this latter family is Springeracrocrinus from the Moscovian of Russia. In addition to the camerates, there are several advanced cladid inadunates more typical of Upper Carboniferous crinoid faunas, including an erisocrinoid (possibly Sinocrinus), Graphiocrinus, ?Cromyocrinus, and an agassizocrinoid (Petschoracrinus) represented by partly fused infrabasal cones. A single radial plate with angustary facet may represent a cyathocrinoid. There also is a catillocrinoid, assigned here to Paracatillocrinus. The fauna, which resembles Moscovian crinoids described from Russia, is preserved in graded volcanic conglomeratic debris flows that overlie a carbonate mound and contain clasts up to 3 m in dimension. The crinoids are fragmentary, with many calyces seemingly torn into two or three pieces and dumped in with the pyroclastic debris. Camerates are represented by large thecal scraps consisting of numerous plates, or by large individual plates or circlets. Other fossils include rare solitary rugose corals, tabular bryozoans, Neospirifer, and other fragmentary brachiopods. We suspect that the crinoids may have been swept off of a nearby carbonate mound and deposited as debris-flow bedload.