Geological and Geographical Characteristics of Limestone and Karst Landforms in Japan: Insights from Akiyoshidai, Seiyo (Shikoku), and Okinoerabu Island

Limestone in Japan exhibits distinct distribution patterns and associated lithologies compared to limestone found in most other parts of the world. These differences reflect contrasting depositional settings and formation processes. While the majority of the world’s limestones originate from reefs and their detritus deposited on continental shelves adjacent to continents, most limestones in Japan are derived from atoll reefs formed on oceanic island basalts. The remainder developed as reefs and associated detritus along the margins of island arcs underlain by continental crust. In this study, we refer to the former as Accreted Oceanic Reef (AOR) Limestones and the latter as Autochthonous Arc-Shelf (AAS) Limestones. These two types not only differ in origin and depositional environment, but also in the development of karst landforms, including cave systems. AOR Limestones, typified by the Akiyoshi Limestone of Akiyoshidai and the Shikoku Karst, partly distributed in Seiyo (Shikoku), and Pre-Cenozoic AAS Limestones such as Torinosu Limestone of Seiyo (Shikoku) exhibit complex three-dimensional structures that contrast with various caves common worldwide. In contrast, Cenozoic AAS Limestones are exemplified by the Pleistocene Ryukyu Limestone of Okinoerabu Island, where caves, though relatively small, develop parallel to bedding planes. While differing in scale from many caves worldwide, their fundamental structures are comparable. These contrasting characteristics provide new insights into the geological and geomorphological diversity of limestone and karst landforms in Japan.