Discovery and significance of Late Famennian ammonoid faunas in western Junggar, Xinjiang

A number of ammonoids are discovered for the first time from the Late Devonian (late Famennian) in the north of Hoxtolgay of western Junggar, Xinjiang. The Platyclymenia fauna includes Platyclymenia (Pl.) subnautilina (Sandberger), Sporadoceras sp., Prionoceras frechi (Wedekind), and others, which was probably related to the Annulata Event. The cyrtoclymeniid fanua is characterized by spectacularly large-sized Protactoclymenia sp. and Cyrtoclymenia? sp. with a diameter up to ca. 20 cm. These ammonoids can be correlated with the assemblage of the standard Devonian ammonoid Ⅳ Zone of West Europe (conodont Upper trachytera Zone to Lower expansa Zone). The occurrences of the late Famennian cyrtoclymeniid fauna in different sections in the area north of Hoxtolgay can be well correlated. The horizons bearing these fossils can be regarded as a marker layer for stratigraphic correlation in this area.