Smear slide grain counts from IODP Site 323-U1342

Here we present new grain count data from from Integrated Ocean Drilling Program (IODP) Expedition 323 Site U1342 Holes A, C, and D. New records of sediment composition from laminated and non-laminated were determined from smear slide (quantitative grain counts) and particle size analyses. A subset of samples from three laminated intervals (672-697 ka, 826-836 ka, and 847-851 ka) and four adjacent massive intervals (668-671 ka, 822-825 ka, 803-845 ka, and 853-856 ka) were selected for analyses. Sediment smear slides were examined with a transmitted light petrographic microscope equipped with a standard eyepiece micrometer. Biogenic (pennate and centric diatoms, silicoflagellates, sponge spicules, foraminifers, and coccolithophores), mineral (clay minerals, silt- to sand-size siliciclastics), and volcaniclastic components were identified and their percentage abundances were visually determined under a petrographic microscope using a 40X objective and 10X eyepiece. For each sample, 3 counts were done on different parts of a smear slide using a random walk, and the average value of the 3 counts was used. Particle size analyses on the same samples were carried out with a Beckman-Coulter LS 13 320 laser particle size analyzer (LPSA) attached to an aqueous module equipped with a pump and a built-in ultrasound unit. Size distributions were analyzed from 0.04 µm to 2 mm. Measurements of such a wide particle size range are possible because the particle sizer is composed of two units: a laser beam for conventional (Fraunhofer) diffraction (from 0.4 µm to 2 mm) and a polarized intensity differential scatter (PIDS) unit, which measures particles based on the Mie theory of light scattering (0.04 µm). The samples for the analyses were subsampled and dispersed in the deionized water of the aqueous module of the particle sizer until obscuration values of 10%–15% and PIDS obscuration values of 48%–52% were obtained. The optical model chosen for the grain size determination is the default Fraunhofer model, based on the Fraunhofer theory of light scattering. Data interpolation and statistical analyses were calculated with the laser particle sizer proprietary software (56). Because all samples analyzed tend to log-normal grain size distributions in the 0.04 µm to 2 mm spectrum, geometric rather than arithmetic statistics were applied to the values obtained by the logarithmically spaced size channels of the particle sizer. Smear slide analyses show that laminated sediments contain significantly more diatomaceous biogenic material relative to siliciclastic grains. Laminated samples contain a higher percentage of total diatoms compared to non-laminated samples (72 versus 30%) and a higher percentage of well-preserved (i.e. whole, non-fragmented) diatoms (29 versus 9%), indicative of a high siliceous flux rate. Laminated sediments also display higher proportions of other biogenic particles (including silicoflagellates, sponge spicules, foraminifera, and coccolithophores).

本研究提供了综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）323航次U1342站位A、C、D孔的全新粒级计数数据。本研究通过涂片镜检（定量粒级计数）与粒度分析，获取了纹层状与非纹层状沉积物的全新组分记录。本次分析选取了3个纹层沉积段（672~697 ka、826~836 ka及847~851 ka）与4个相邻的块状沉积段（668~671 ka、822~825 ka、803~845 ka及853~856 ka）的样品子集。沉积物涂片样品采用配备标准目镜测微尺的透射光岩石显微镜进行观测。在40倍物镜与10倍目镜的配置下，通过岩石显微镜目视识别并统计了生物组分（羽纹纲与中心纲硅藻、硅鞭藻、海绵骨针、有孔虫及颗石藻）、矿物组分（黏土矿物、粉砂-砂级硅质碎屑）与火山碎屑组分的百分含量。每个样品均通过随机游走法在涂片的不同区域完成3次计数，并取3次计数的平均值作为最终结果。对上述样品的粒度分析采用贝克曼库尔特LS 13 320激光粒度分析仪（Laser Particle Size Analyzer, LPSA）完成，该设备搭载了配备泵体与内置超声单元的湿法进样模块。分析覆盖的粒径分布范围为0.04 μm至2 mm。该粒度分析仪可实现如此宽量程的粒径测量，原因在于其由两个单元组成：用于常规夫琅禾费衍射（量程0.4 μm~2 mm）的激光光路，以及基于米氏光散射理论的偏振强度差散射（Polarized Intensity Differential Scatter, PIDS）单元（量程0.04 μm）。分析样品经二次取样后，被分散至粒度分析仪的湿法进样模块的去离子水中，直至遮光率达到10%~15%，且PIDS遮光率达到48%~52%。本次粒度测定选用的光学模型为默认的夫琅禾费模型，其基于夫琅禾费光散射理论。数据插值与统计分析均通过激光粒度分析仪的专属软件完成（参考文献56）。由于所有待测样品在0.04 μm~2 mm量程内的粒径分布均符合对数正态分布，因此针对粒度分析仪对数间隔粒径通道获取的测量值，采用几何统计而非算术统计方法进行处理。涂片镜检结果表明，与硅质碎屑颗粒相比，纹层状沉积物中富含硅藻源生物组分。相较于非纹层状样品，纹层状样品的总硅藻占比更高（72% vs 30%），且保存完好（即完整无破碎）的硅藻占比亦更高（29% vs 9%），这指示了较高的硅质通量速率。纹层状沉积物中其他生物颗粒（包括硅鞭藻、海绵骨针、有孔虫及颗石藻）的占比同样更高。