テクトニクスと動物群に基づく前期白亜紀の日本の古地理 Early Cretaceous Paleogeography of Japan, based on tectonic and faunal data

西南日本のジュラ紀から前期白亜紀付加体の重複配列分布は, 付加体の放散虫化石と付加体の堆積物に不整合で覆う非海成ないし浅海成の堆積物に含まれる軟体動物化石の化石層序と時代論に基づき, オーテリビアン期に形成されたと解釈される。一方, 日本を含む東アジアの浅海成堆積物から後期ジュラ紀〜前期白亜紀のアンモナイトが産出し, それらが低緯度地域と高緯度地域の種を含む。これは, この地域が二つの異なる海流の影響を受けたことを示し, 現在の下部白亜系の分布位置と堆積当時の分布位置がほぼ同じであったと解釈できる。特に, 前期白亜紀の手取地域は高緯度地域からの海流の影響を受けたことが示唆される。これらの解釈は, この時期のテクトニクスの考察による日本列島の位置の解釈と化石による解釈の両者がともに整合性のあることを示す。

Tectonic duplication of Jurassic to early Early Cretaceous accretionary complexes occurred during the Hauterivian in Southwest Japan. Then, Lower Cretaceous sedimentation in the Outer Zone of Southwest Japan began in the Late Hauterivian to Early Barremian. Lower Cretaceous strata on the Jurassic accretionary complexes include Barremian ammonite faunas that contain both northern and southern elements. This provides important evidence for the existence of oceanic currents from both the high latitudes and the equatorial regionsal this time. The Outer Zone of Southwest Japan was situated approximately in its present position (latitude), based on theevidence from those currents configuration. In the Inner Zone of Southwest Japan at this time, radiolarian chert conglomerates originaled from the Mino-Tamba-Ashio Belt in the upper part of the Tetori Group as signed to approximately Hauterivian to Aptian suggest an upheaval of the eastern highland of the Tetori Basin. A resultant gulf with a north-opening mouth is interpreted to have developed in the Tetori Basin, influenced by a current from northern latitudes.