Permian radiolarians from the A’nyemaqen mélange zone in the Huashixia area of Madoi County, Qinghai Province, Western China, and their implications on regional tectonism

The Huashixia area in the Madoi County, Qinghai Province, western China is one of the most important areas for the studies of the formation and evolution of the A’nyemaqen mélange zone due to the well exposed, relatively complete tectonostratigraphic successions. However, the timing and evolutionary process of the A’nyemaqen paleo-ocean has long been poorly understood. Recently, we obtained abundant radiolarians from the siliceous rocks of the Maerzheng Formation of this mélange zone in Huashixia. Total 19 species in 10 radiolarian genera have been identified. They belong mainly to the Albaillellaria, Spumellaria, Entactinaria, and Latentifistularia. Four radiolarian assemblage zones are established, including: the Pseudoalbaillella rhombothoracata, Pseudoalbaillella scalprata, Ruzhencevispongus uralicus , and Follicucullus bipartitus-Follicucullus sp. cf. F. ventricosus zones. Radiolarian faunal correlations suggest a late Artinskian–early Kungurian age and late Capitanian–early Wuchiapingian age for the first two zones from the lower part and the last two zones from the upper parts of the Maerzheng Formation, respectively. All radiolarians are typical of deep water elements living in deep oceans in low latitudes during the Permian. Previously, the radiolarians of Early Carboniferous to Early Permian age and fusulinids of Early–Middle Permian age have also been reported from the A’nyemaqen mélange successions. The combination of the newly found radiolarians with the previously reported faunal and microfloral assemblages as well as radiometric ages obtained from the same stratigraphic units indicates that the A’nyemaqen paleo-ocean may have opened initially during the Early Carboniferous, expanded from the Early–Middle Permian, reached its acme in the early Late Permian, shrunk during the latest Permian to Early Triassic, and eventually was closed in the Middle Triassic.