Paleoecology, biogeography, and evolution of reef ecosystems in the Panthalassa Ocean during the Late Triassic: Insights from reef limestone of the Sambosan Accretionary Complex, Shikoku, Japan

- Ten reef limestone outcrops of the Sambosan Accretionary Complex in Shikoku Island, Japan, are investigated.
- Reef biota inventory and relative abundances of reef components allow to identify two types of reef.
- Evolution from microbialite-sponge-microproblematica reefs to sponge-dominated reefs during the Late Triassic.
- Multivariate analyses demonstrate biogeographic affinities with reefs of South Tethys.

Upper Triassic reefs from the Panthalassa Ocean have been understudied in comparison to their Tethyan counterparts and are therefore pivotal to understanding the global reef evolution during the Late Triassic. To fill this gap, Upper Triassic reef limestone from ten localities of the Sambosan Accretionary Complex at Shikoku Island (Japan) has been investigated. Biotic assemblages, quantitative microfacies analysis, and integrated biostratigraphy allow us to characterize two types of reefs, those attributed to the Ladinian?-Early Carnian and those attributed to the Late Carnian-Rhaetian? At the regional scale, our data refine the biostratigraphic framework of the Upper Triassic Sambosan limestone. At the global scale, multivariate analyses support a strong paleobiogeographic affinity of the Western Panthalassa reef biota with those of the South Tethys Ocean during the Ladinian-Carnian and Norian-Rhaetian. Additionally, they indicate connections with East Panthalassa reefs during the Norian-Rhaetian.