Reef-Building Corals and Stromatoporoids as Witnesses: Tracking the Late Jurassic Palaeogeographic Evolution of Central Tibet"

The Dongqiao area, situated within the Bangong–Nujiang Suture Zone in central Tibet, harbors a ~2.8 m-thick scleractinian coral–stromatoporoid reef within the Upper Jurassic Dongqiao Formation. This fossil assemblage stands as a key witness, offering a unique window into the Late Jurassic depositional environment and palaeogeographic configuration of the Dongkaco microcontinent. This study focuses on the Zigetangco section, employing these fossil builders to unravel the reef's composition, microfacies, palaeoecology, and profound palaeogeographic significance. A diverse community of 15 genera and 22 species of scleractinian corals, and 7 genera and 11 species of stromatoporoids have been identified, including three potential new scleractinian coral species. The reef is characterized as a small patch reef, and microfacies analysis paints a vivid picture of its habitat: a shallow-marine carbonate platform within the subtidal zone, under warm, normal-salinity conditions and moderate hydrodynamic energy, indicating a stable ecological setting. The coral assemblage, dominated by colonial forms, exhibits strong Tethyan affinities, further testifying to its connection to the broader oceanic realm. Palaeogeographic comparison, guided by these fossil witnesses, reveals a high similarity to Late Jurassic coral assemblages from the northern margin of the Neo-Tethys, with clear links to the South Qiangtang Terrane, but weaker affinities to the Lhasa and Himalayan terranes. These results strongly suggest that the Dongkaco microcontinent had already amalgamated with the South Qiangtang Terrane by the Late Jurassic, while the western Dongqiao Ocean remained a gateway to the Neo-Tethys. Thus, these reef-building organisms act as key witnesses, providing compelling new biostratigraphic and palaeoecological constraints on the complex closure history of the Bangong–Nujiang Ocean and refining the Late Jurassic stratigraphic framework of the region.