THE "AGE OF CRINOIDS" BEGAN IN THE LATE DEVONIAN

The Frasnian-Famennian mass extinction event ranks in the top five in taxonomic and ecological severity and particularly devastated tropical marine ecosystems. Famennian strata in Xinjiang Province, China, contain both the F-F boundary, the Kellwasser and Hangenberg Anoxic Events associated with the F-F and D-C Extinctions respectively, but also a Famennian rebound fauna in a highly fossiliferous shallow marine setting associated with an oceanic island arc complex in the Central Asian Orogenic Belt (CAOB). Total faunal diversity reported from the Hongguleleng Formation and the ‘Hebukehe’ Formation is 166 genera and 235 species. Diversity includes 2 genera and species of sponges, 17 genera and 22 species of corals, 1 genus and species of trilobite, 18 genera and 34 species of bryozoans, 48 genera and 57 species of brachiopods, 4 genera and species of cephalopods, 12 genera and 14 species of blastoids, 32 genera and 44 species of crinoids, and 2 genera and 2 species of vertebrates (not including the conodonts). The majority of this faunal diversity is from the Hongguleleng Formation, which is predominantly a shallow marine sequence dating from the latest Frasnian to the middle Famennian (conodont biozones - linguiformis, triangularis, crepida, Late rhomboidea, and marginifera). The ‘Hebukehe’ Formation ranges in age from middle to late Famennian, is a deeper water sequence with radiolarian cherts, and has a lower diversity fauna. The ‘Hebukehe’ Formation does contain a unique deep-water assemblage of crinoids and blastoids that is taxonomically different from the echinoderm fauna in the Hongguleleng Formation.The Hongguleleng crinoid and blastoid faunas are the most diverse Famennian faunas known and have closer affinity with Mississippian faunas than with Devonian faunas. These faunas are morphologically advanced showing many thecal characters rare in Devonian faunas, but common in the Mississippian. The rebound from the F-F Extinction Event was more rapid than previously thought. Estimates of recovery time based on sedimentation rates are on the order of 100,000 years. The rebound fauna was concentrated in NW China particularly for echinoderms and we can conclude that the Age of Crinoids encompassed the Famennian in addition to the stages of the Mississippian.