Physical properties, mineral and chemical compositions, and accumulation rates of Holocene and Upper Pleistocene bottom sediments from the Sea of Okhotsk

Mineral and chemical compositions and physical properties of diatomaceous clayey-siliceous sediments from the Sea of Okhotsk are studied. Accumulation rates of silica are determined. Their compositional model based on silica content is similar to that of Late Jurassic and Olenekian-Middle Anisian cherts from the Sikhote Alin region. Thickness of Holocene siliceous unit and accumulation rates of siliceous deposits depended on bioproductivity in the upper water layer and seafloor topography. Accumulation rates of amorphous SiO2 (0.05-5.7 g/cm**2/ka) and free SiO2 (0.5-11.6 g/cm**2/ka) are minimal on seamounts and maximal in depressions near foothills. These values match accumulation rates of free SiO2 in Triassic and Late Jurassic basins of the Sikhote Alin region (0.33-3 g/cm**2/ka). Comparison of composition and accumulation rates of silica shows that Triassic and Late Jurassic siliceous sequences of Sikhote Alin could accumulate in a marginal marine basin near a continent.

本研究对鄂霍次克海（Sea of Okhotsk）产出的硅藻质黏土硅质沉积物的矿物组成、化学成分及物理性质开展了系统研究，并测定了其中硅质组分的堆积速率。基于硅质含量建立的组分模型，与锡霍特阿林（Sikhote Alin）地区晚侏罗世及奥伦尼克期-中安尼西期燧石的组分模型具有相似性。全新世硅质单元的厚度与硅质沉积物的堆积速率，受上层水体生物生产力及海底地形共同调控。其中无定形二氧化硅（amorphous SiO₂，0.05~5.7 g/cm²/ka）与游离二氧化硅（free SiO₂，0.5~11.6 g/cm²/ka）的堆积速率在海山处最低，在山麓附近的海底凹陷区域达到最大值。该数值范围与锡霍特阿林地区三叠纪及晚侏罗世盆地内游离二氧化硅的堆积速率（0.33~3 g/cm²/ka）相一致。通过对比硅质组分的组成与堆积速率，可推断锡霍特阿林地区的三叠纪及晚侏罗世硅质沉积序列形成于近大陆的边缘海盆地环境中。