Depositional environment of the upper Jurassic-lower Cretaceous reef limestone in western Yamaguchi Prefecture, Southwest Japan

山口県豊浦郡豊浦町室津に分布する豊西層群（上部ジュラ系～下部白亜系）には現地性のサンゴに富む礁性石灰岩が存在する．サンゴは上方に成長し，フレームワークを形成している石灰岩層のみならず，泥岩優勢層でも認められる．サンゴには二つの成長形態が認められ，塊状のものは比較的高エネルギー環境を示し，枝状のものは低エネルギー環境を示す．浅く穏やかな環境から多く報告されているカサノリ類は，枝状サンゴと同じ層準で見られる．本石灰岩は1）石灰質砂岩から明瞭な境界をもって礁性のframestoneに変化し，2）層孔虫・石灰海綿・ヒドロ虫類・被覆微生物・ウーイドが見られない点で，日本に分布する他の上部ジュラ系～下部白亜系炭酸塩岩（例えば，鳥巣石灰岩）と異なる特徴をもつ．

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