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Reports were provided for lithofacies and a depositional setting on the “Kanagaso-ishi” Tuff which were quarried from the Kanagaso Stone Quarry in Kanagaso Town in eastern Komatsu City (in Ishikawa Prefecture, northern central Japan). Stone from the “Kanagaso-ishi” Tuff was once a popular stone material which was widely used in the interior and exterior of buildings in Japan. The cultural value of the stone and its quarry are described in a tourism promotion website page entitled “The Story of Komatsu's Gems-A Stone Culture Polished in the Flow of Time”, which was approved by the Japanese government’s Agency for Cultural Affairs in 2016. The “Kanagaso-ishi” Tuff is regarded to be lithologically correlated to the Lower Miocene (Burdigalian) Akahotani Formation. This is one of the pyroclastic deposits left during the formation of the Sea of Japan in the time from the Oligocene epoch to the middle Miocene epoch. As such, by researching the “Kanagaso-ishi” Tuff, we can provide clearer details regarding the geological history of Japan during the Neogene period. The lithofacies of the “Kanagaso-ishi” Tuff are classified into the following four categories: Lithofacies 1 (massive, poorly sorted pumiceous lapilli tuff made up of the thick lower interval of the quarry); Lithofacies 2 (massive to laminated fine tuff which contains patch-like pumiceous lapilli tuff and polymictic gravel from volcanic rocks); Lithofacies 3 (an alternation of thinly and indistinctly bedded pumiceous lapilli tuff and fine tuff with plane horizontal and low-angle cross-stratification, predominantly in the upper interval of the quarry); and Lithofacies 4 (deformed pumiceous lapilli tuff-fine tuff alternations with slump folds, load casts and water escape structures, accompanied with Lithofacies 3). The above lithofacies are not very likely to be “hot-state” pyroclastic flow nor fluvial to shallow-water deposits but rather are regarded to be primary or resedimented pyroclastic deposits that had accumulated on the middle to lower slope settings as slumped and “cold” volcaniclastic gravity flow deposits. Providing data on the lithofacies of the stone materials also contributes to a deeper understanding of the unique stone culture of Komatsu city. For example, the “striped” and “honeycomb” patterns that are recognized in the tuffs are identified as the Lithofacies 1, and Lithofacies 3 and/or 4, respectively. This geological approach to the study of the stone materials that include the “Kanagaso-ishi” Tuff, are expected to shed new light on the stone culture of the city. |
