The Middle and Late Triassic was a time of important reef development. This evolution, which is primarily documented in the Tethys realm, comprised several phases from the Anisian to the Rhaetian. To help elucidate the less constrained reef evolution in the Panthalassa domain, samples of reef limestone were collected from several localities along the Sambosan Accretionary Complex in Shikoku Island, southwest Japan. In this paper, we report a well-preserved and comprehensive reef biota, including several taxonomic groups, such as scleractinian corals, calcified sponges, calcareous algae, foraminifers, and microproblematica. Seventeen species are described for the first time in Japan among the 33 that are identified in this study. The assemblage-based biostratigraphy and index taxa indicate a Ladinian?-Carnian age. This new finding corresponds to an older reef limestone than has been previously identified in the Sambosan Accretionary Complex and may represent the initiation of shallow-water carbonate deposition on western Panthalassa seamounts. This work also provides valuable insights on reef ecosystem biodiversity in the Panthalassa domain during the Middle? to Late Triassic

During the Late Triassic, carbonate platforms expanded on continental shelves and island arcs. They have been studied in detail in the Tethys realm but coeval mid-oceanic shallow-water environments of the Panthalassa domain have received less attention. To fill this gap, we investigated the Upper Triassic limestone of the Sambosan Accretionary Complex (SAC), southwest Japan. A comprehensive sampling of the Upper Triassic limestone has been performed in 16 localities at Shikoku Island. Eight microfacies, ranging from pelagic to lagoonal settings, were identified, including two microfacies that are described in the SAC for the first time. Quantitative microfacies analysis assesses the composition of the SAC limestone and its biostratigraphy is refined. Finally, a speculative depositional model of the SAC carbonate platforms is proposed based on modern and ancient analogues. Instead of a true atoll-type platform with well-defined facies belts as suggested by previous studies, this new model suggests that the typical Sambosan platform was more probably a carbonate bank with submerged margins and a mosaic of microfacies in the platform interior. Special attention is given to the factors that have probably controlled the carbonate sedimentation at the top of the seamount(s)

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

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The Carnian Amphiclina beds of the eastern Southern Alps mostly consist of shale and sandstone deposited in the deep-marine Slovenian Basin, which was located near the western margin of the Meliata Ocean. In the vicinity of Cerkno (Slovenia), blocks of massive or crudely bedded limestone crop out within a succession of clastic rocks that are several hundred meters thick. Sponge-microbialite boundstone and coral pillarstone are the predominant facies within these blocks. Oncoid floatstone-rudstone and moderately sorted peloid packstone form crudely layered parts of the blocks, whereas intraclast-cortoid packstone and poorly sorted peloid packstone occur locally in cross-stratified thin beds, truncated at block margins. Detailed mapping further shows that limestone blocks form units at discrete stratigraphic levels within shale and that these units are variable in thickness. Whereas the largest blocks mostly lie concordant to the bedding, smaller blocks are poorly sorted and randomly oriented. All of this evidence suggests that the limestone blocks are olistoliths, derived from an outer platform margin and/or uppermost slope