Sedimentary facies from Upper Triassic reefal limestone of the Sambosan accretionary complex in Japan: mid-ocean patch reef development in the Panthalassa Ocean

Abstract

Microfacies of the Early to Middle Norian reefal limestone of the Sambosan Accretionary Complex (SAC) at Kamase locality, southwest Japan, are classified into seven major facies types in stratigraphic order: peloidal grainstone-packstone, unfossiliferous lime-mudstone, tubular problematica-rich wackestone, sponge-coral floatstone, sponge bafflestone, coral rudstone, and peloidal-bioclastic packstone-grainstone. The SAC records patch reef development on a mid-oceanic seamount in the Panthalassa Ocean. Because most examples of Triassic reefs come from the former Tethys, counterparts such as those from the SAC are pivotal in resolving paleogeographic issues as well as clarifying the depositional patterns between the eastern Tethys and adjacent western Pacific (Panthalassa). We also reveal that the primary stratigraphy of the reefal limestone was disrupted by submarine landslides of the seamount in an open-ocean realm during the late Middle to Late Jurassic time.