Sedimentation rate, bulk density, accumulation rate of terrigenous material and grain sizes of ODP Leg 167 sites

The terrigenous mineral fraction of sediments recovered by drilling during Ocean Drilling Program Leg 167 at Sites 1018 and 1020 is used to evaluate changes in the source and transport of fine-grained terrigenous sediment and its relation to regional climates and the paleoceanographic evolution of the California Current system during the late Pleistocene. Preliminary time scales developed by correlation of oxygen isotope stratigraphies with the global SPECMAP record show average linear sedimentation rates in excess of 100 m/m.y., which provide an opportunity for high-resolution studies of terrigenous flux, grain size, and mineralogy. The mass flux of terrigenous minerals at Site 1018 varies from 5 to 30 g/(cm**2 x k.y.) and displays a general trend toward increased flux during glacials. The terrigenous record at Site 1020 shows a similar pattern of increased glacial input, but overall accumulation rates are significantly lower. Spectral analysis demonstrates that most of this variability is concentrated in frequency bands related to orbital cycles of eccentricity, tilt, and precession. Detailed grain-size analysis performed on the isolated terrigenous mineral fraction shows that sediments from Site 1018 are associated with higher energy transport and depositional regimes than those found at Site 1020. Grain-size data are remarkably uniform throughout the last 500 k.y., with no discernible difference observed between glacial and interglacial size distributions within each site. X-ray diffraction analysis of the <2-µm clay component suggests that the deposition of minerals found at Site 1020 is consistent with transport from a southern source during intervals of increased terrigenous input.

本研究利用大洋钻探计划（Ocean Drilling Program，ODP）第167航次在1018和1020站位钻取的沉积物陆源矿物组分，评估晚更新世期间细粒陆源沉积物的物源与搬运过程变化，及其与区域气候和加利福尼亚海流系统古海洋演化的关联。前期通过氧同位素地层学与全球SPECMAP记录对比建立的年代标尺显示，两处站位的平均线性沉积速率均超过100米/百万年，为开展陆源物质通量、粒度与矿物学的高分辨率研究提供了条件。1018站位的陆源矿物质量通量介于5至30克/(平方厘米·千年)，整体呈现冰期通量升高的趋势。1020站位的陆源沉积记录也呈现出冰期输入量升高的相似模式，但整体沉积积累速率显著更低。频谱分析表明，该类变化的绝大多数信号集中于与轨道周期（偏心率、倾角与岁差）相关的频带内。对分离出的陆源矿物组分开展的详细粒度分析显示，1018站位沉积物的搬运与沉积动力环境能量高于1020站位。过去50万年以来的粒度数据整体极为均一，两处站位的冰期与间冰期粒度分布均未出现可识别的差异。对<2微米黏土组分的X射线衍射（X-ray diffraction，XRD）分析表明，1020站位的矿物沉积模式与陆源输入升高时段来自南部物源的搬运过程相一致。