Natural history of biogenic siliceous sedimentary rocks as a paleoceanographical guide

对以高硅含量为特征的沉积岩进行了与古海洋重建有关的地质研究。它们产于环太平洋造山带。在日本群岛，晚古生代和中生代层状硅质岩、第三系硅质页岩(所谓的硬页岩)和硅藻土是硅质沉积岩的代表。它们主要由放射虫遗迹、硅质海绵针状体和硅藻小锥等硅质微体化石组成，不含碎屑粗颗粒碎屑。这些事实表明，硅质岩具有生物成因，形成于远洋-半远洋环境。在地质史上，生物群的含量对于判断海洋水团的性质和重建全球海洋环流是最重要的。三叠纪和早侏罗世硅质岩作为外来块体嵌入在侏罗纪吸积杂岩、赤部、阿西奥和米诺-坦巴带中，被认为是可能位于潘塔拉萨热带-亚热带的海洋硅质浮游生物高生产力的标志。岛户带白垩纪-第三纪增生杂岩中的白垩纪硅质岩与超大陆联合大陆解体形成赤道流有关。日本海一侧分布的第三系主要为中中新世硅质页岩和硅藻土，受冷咸水深水的影响而成藏。冰冷的深水与德雷克海峡的开放和南极大陆的孤立形成南极绕极流有关。地史上硅质沉积岩的不均匀分布反映了全球大洋环流和海相硅质微生物生产力的板块重组和变化。

Sedimentary rocks characterized by high silica content were geologically investigated in relation to paleoceanographical reconstruction. They occur in the circum-Pacific orogenic belts. In Japanese Islands, late Paleozoic and Mesozoic bedded chert, Tertiary siliceous shale (so-called hard shale), and diatomite are the representatives of the siliceous sedimentary rocks. They consist mostly of such siliceous microfossils as radiolarian remains, siliceous sponge spicules and diatom frustules and contain no detrital coarse-grained clastics. These facts show that the siliceous rocks are of biogenic origin and were formed in pelagic to hemi-pelagic environment. And the contents of biota are most important for estimation of nature of ocean water-mass and for reconstruction of global ocean circulation in geohistory. Triassic and early Jurassic cherts embedded as exotic blocks in the Jurassic accretion complex, Chichibu, Ashio, and Mino-Tanba belts, are regarded as a sign of high productivity of marine siliceous plankton possibly in tropical to subtropical zone of the Panthalassa. Cretaceous chert in the Cretaceous to Tertiary accretion complex, Shimato Belt, is related to the formation of equatorial current as a result of the breakup of supercontinent Pangaea. Tertiary, mainly middle Miocene, siliceous shale and diatomite distributed in Sea of Japan side were accumulated under the influence of cold saline deep water. The cold deep water was related to the formation of Antarctic circumpolar current due to the opening of Drake passage and the isolation of the Antarctic Continet. Uneven distribution of siliceous sedimentary rocks in geohistory is considered to reflects plate reorganization and change in global ocean circulation and in productivity of marine siliceous microbiota.