Late Paleozoic Radiolaria from the Upper Triassic sedimentary mélange in Shangrila, Southwest China and its geological significance

Moderately well-preserved radiolarians were collected recently from the exotic siliceous blocks within the sedimentary mélange of the Upper Triassic Hagong Formation exposed in Shangrila, southwestern China. These radiolarians, characterized by high diversity, include spumellarians, entactinarians, latentifistularians, and albaillellarians. Among them, 28 species of Albaillellaria belonging to 3 genera are taxonomically analyzed. Most species recorded are correlated with coeval radiolarian assemblages from Germany and Japan. Thirteen albaillellarian assemblages are discriminated, ranging in age from Early Carboniferous to Middle Permian. Because the siliceous blocks within the sedimentary mélange originated in the Garze-Litang tectonic belt, the successful recovery of the well-preserved datable albaillellarians provides the age constraints necessary for the interpretation of the tectonic development of the Garze-Litang tectonic belt. On the basis of the deep-water settings indicated by the albaillellarian fauna, we suggest that the sedimentary basin, represented by the Garze-Litang tectonic belt, became a deep-water basin during Early Carboniferous to Middle Permian and, hence, the Dege-Zhongdian microplate must have been gradually separated by rifting from the Yangtze Plate before the Early Carboniferous.