Isotopic composition of diagenetic silica and associated pore waters of Japan Sea sediments@en

Over a broad region of the eastern Japan Sea, Neogene opaline diatomaceous sediments alter with depth to hard porcellanites and cherts composed of opal-CT and quartz. We examined the oxygen isotopic compositions of these diagenetic silica minerals at four widely spaced sites occupied during ODP Leg 127 in order to investigate the thermal history of the region. Formation temperatures computed from these isotopic data range from 22° to 68°C for opal-CT and from 44° to 92°C for diagenetic quartz, quite similar to temperature ranges estimated from the extrapolated modern gradients, 36°-43°C and 49°-64°C, respectively. At each site the isotopic temperature values cluster near the extrapolated ambient sediment temperatures. As a first approximation, the similarities suggest that the positions of the silica transformations in the basin are controlled by the present thermal regime. […]在日本海东缘的广阔区域内，新近纪蛋白硅质硅藻沉积物随埋藏深度逐渐转化为由CT型蛋白石（opal-CT）和石英组成的致密瓷岩与燧石。为探究该区域的热历史，我们对大洋钻探计划（Ocean Drilling Program, ODP）第127航次所钻探的4个间距较大的站位中的成岩硅质矿物开展了氧同位素组成分析。基于同位素数据计算得到的形成温度范围为：CT型蛋白石22℃至68℃，成岩成因石英44℃至92℃，这与通过外推现代地温梯度得到的温度区间（分别为36℃-43℃与49℃-64℃）高度相似。各站位的同位素温度值均集中于外推得到的沉积物原位环境温度附近。作为一级近似，二者的相似性表明，盆地内硅质矿物转化的位置受当前热体制控制。[…]