Late Permian radiolarians from the ‘Middle‐UpperDevonian’ in the Paqiu area of theChangning‐MenglianBelt, western Yunnan, China and their bearings on analysing the remains of thePalaeo‐Tethys

Abstract

The Changning‐Menglian Belt in western Yunnan, China, is one of the key regions to decode the evolution of Palaeo‐Tethys. However, the work has been hampered considerably by the loose definition and composite nature of some stratigraphic units in the belt. These units normally have varied lithological components (slices of sequences), most of which yield scarce fossils. An example is the ‘Middle‐Upper Devonian (D2‐3)’ unit, which was established to accommodate a series of cherts, shales, siltstones and sandstones, occurring rather frequently in the central zone of the Belt. Its age assignment was mainly based on the Late Devonian conodonts from some siliceous shale intervals. However, the ‘D2‐3’ unit contains strata of ages other than Middle‐Late Devonian, as has been indicated by a few studies in the Chahe‐Manxin area. The Late Permian radiolarians have been obtained from bedded cherts of the ‘D2‐3’ in Paqiu area which provided the first solid evidence for the presence of Late Permian beds in the ‘D2‐3’ in this area. Radiolarians from two chert outcrops about 3 km apart can be assigned to two Wuchiapingian‐Changhsingian assemblages, namely, theAlbaillella levisandAlbaillella protolevisassemblages, respectively, with the former being slightly younger than the latter. Statistical analysis of Permian radiolarians from different localities in the Belt shows that Late Permian radiolarians are much commoner than Middle Permian radiolarians and Early Permian radiolarians. A review of the taxonomical composition of Late Permian radiolarians of the Belt shows that faunas from different localities can be classed into three groups, according to their contents of albaillellaians, latentifistularians, entactinarians and spumellarians, whose depositional environments correspond respectively to deep water (>500 m), intermediate water (200–500 m), and shallow water depths (<200 m). Such a composition indicates that the Late Permian radiolarian‐bearing siliceous rocks in the Changning‐Menglian Belt are slices from various palaeogeographic settings.