Norian (upper Triassic) Microfossils of the Nadanhada Terrane: Conodont, Radiolarian, and Foraminifera from Raohe, Heilongjiang Province, Northeast China

The Nadanhada Terrane of Northeast China preserves a Late Triassic pelagic succession that accreted from the Panthalassa Ocean to the East Asian margin, serves as a key archive for understanding Mesozoic oceanic biostratigraphy and paleoenvironments. New microfossils of conodont, radiolarian, and foraminifera are collected at the Chigang and Huxianshan sections in the Raohe of Heilongjiang Province, Northeast China. Based on this, a robust conodont biostratigraphic framework is established, identifying three successive zones: the Parvigondolella andrusovi Zone, Parvigondolella lata Zone, and Misikella hernsteiniZone, which enable precise correlation with Tethyan sequences. The co-occurrence of the cosmopolitan conodont genus Epigondolella and the typically cooler, higher-latitude conodont genus Norigondolella suggest the influence of cooler deep-water masses at this low paleolatitude site. The recovered low-diversity radiolarian and foraminifera assemblages, dominated by deep-water, cooler-water taxa and lacking warm-water indicators, collectively point to a pelagic seamount setting bathed in cool, dysoxic deep waters. Due to unique ecological conditions and evolutionary refugia offered by isolated Panthalassic seamount ecosystems, microfossil of the Nadanhada Terrane during the late Norian are composed by cosmopolitan species, endemic species and some “relicts” with much shorter ranges in surrounding epeiric seas.