Natural history of biogenic siliceous sedimentary rocks as a paleoceanographical guide

对具有高硅含量特征的沉积岩进行了地质调查，并与古海洋重建相联系。它们出现在环太平洋造山带。在日本列岛，晚古生代和中生代层状燧石岩、第三纪硅质页岩（所谓硬页岩）和硅藻土是硅质沉积岩的代表。它们主要由放射虫遗骸、硅质海绵针状体和硅藻体等硅质微化石组成，不含碎屑粗粒碎屑。这些事实表明，硅质岩具有生物成因，形成于中上层至半中上层环境。而生物区系的含量对于估算海洋水团性质和重建全球海洋环流具有重要意义。三叠纪和早侏罗世燧石岩作为外来块体嵌套在侏罗纪增生杂岩、Chichibu、Ashio和Mino-Tanba带中，被认为是泛海带热带至亚热带海洋硅质浮游生物高产的标志。岛户带白垩纪—第三纪增生杂岩中的白垩纪燧石岩与泛大陆分裂形成的赤道流有关。以中中新世为主的第三系硅质页岩和硅藻土分布在日本海一侧，受冷咸化深水的影响。寒冷的深水与德雷克通道的开通和南极大陆的隔绝所形成的南极环极流有关。硅质沉积岩在地代史上的不均匀分布反映了全球海洋环流的板块重组和变化以及海洋硅质微生物群的生产力。

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.