A facies model of contourites

通过对博索半岛晚新生代深海层序和其他晚新生代沉积盆地(如Kakegawa、Miyazaki和Kumano盆地)的详细露头分析，研究了受底流影响的砂质沉积(砂质等值线)的岩相特征。砂质等值线以平行层理、波纹交错层理等牵引构造为特征，并伴有少量逆级配和波纹层理。具体地说，波纹交错层理通常与泥浆褶皱、冲击波和透镜状层理联系在一起。这些沉积构造一般不表现出任何规则的垂直层序，如浊积岩中的Bouma层序。一般而言，砂质等深岩比伴生的浊积岩分选得更好，与下伏的浊积岩或半长角岩具有尖锐的或渐变的底部接触，而与上覆的半长角岩具有尖锐的上部接触。在合同中，砂质等深岩的骨架成分与伴生浊积岩的骨架成分基本相当。砂质等值线的古水流在时间和空间上是可变的，浊流-等深岩连续体类型的时空变化反映了晚新生代沉积盆地深海底流的不同强度。现代黑潮及其相关深海环境下的深水水流速度和方向的变化在日本群岛附近被记录下来。因此，类似的过程似乎是导致日本西南部晚新生代沉积盆地中砂质等高线沉积的原因。

Lithofacies characteristics of bottom-current-influenced sandy deposits (sandy contourites) were studies based on detailed outcrop analyzes of late Cenozoic deep-sea successions in the Boso Peninsula and those from some other late Cenozoic sedimentary basins, such as the Kakegawa, Miyazaki, and Kumano Basins. Sandy contourites are characterized by traction structures, such as parallel lamination and ripple cross-lamination, together with minor inverse grading and wave ripple-lamination. In particular, ripple cross-lamination is commonly associated with mud drapes and flaser and lenticular bedding. These sedimentary structures, in general, do not show any regular vertical sequences, such as the Bouma sequence in turbidites.In general, sandy contourites are better sorted than associated turbidites and have sharp or gradational basal contacts with underlying turbidites or hemipelagites, and sharp upper contacts with overlying hemipelagites. Framework composition of sandy contourites, in contracts, is largely equivalent to that of associated turbidites. Paleocurrents of sandy contourites are variable in time and space and spatial and temporal variations intypes of turbidite-to-contourites continuums suggests varying intensity of deep-sea bottom currents in the late Cenozoic sedimentary basins.Variations in speed and direction of deep-water currents under the modern Kuroshio Current and its associated deep-sea environments have been documented off the Japanese Islands. Thus, analogous processes appear to have been responsible for the deposition of sandy contourites in the late Cenozoic sedimentary basins in Southwest Japan.