Physical properties and sedimentology of 4 profiles fom the South Atlantic

Ultrasonic P wavc transmission seismograms recorded on sediment cores have been analyzed to study the acoustic and estimate the clastic properties of marine sediments from different provinces dominated by terrigenous, calcareous, amI diatomaceous sedimentation. Instantaneous frequencies computed from the transmission seismograms are displayed as gray-shaded images to give an acoustic overview of the lithology of each core. Ccntirneter-scale variations in the ultrasonic waveforms associated with lithological changes are illustrated by wiggle traces in detail. Cross-correlation, multiple-filter, and spectral ratio techniques are applied to derive P wave velocities and attenuation coefficients. S wave velocities and attenuation coefficients, elastic moduli, and permeabilities are calculated by an inversion scheme based on the Biot-Stoll viscoelastic model. Together wilh porosity measurements, P and S wave scatter diagrams are constructed to characterize different sediment types by their velocity- and attenuation-porosity relationships. They demonstrate that terrigenous, calcareous, and diatomaceous sediments cover different velocity- and attenuation-porosity ranges. In terrigcnous sediments, P wave vclocities and attenuation coefficients decrease rapidly with increasing porosity, whereas S wave velocities and shear moduli are very low. Calcareous sediments behave similarly at relatively higher porosities. Foraminifera skeletons in compositions of terrigenous mud and calcareous ooze cause a stiffening of the frame accompanied by higher shear moduli, P wave velocities, and attenuation coefficients. In diatomaceous ooze the contribution of the shear modulus becomes increasingly important and is controlled by the opal content, whereas attenuation is very low. This leads to the opportunity to predict the opal content from nondestructive P wave velocity measurements at centimeter-scale resolution.

本研究对沉积岩芯获取的超声纵波（P wave）透射地震记录开展分析，旨在探究不同沉积域海洋沉积物的声学特性并估算其碎屑组分属性；这些沉积域分别以陆源沉积、钙质沉积和硅藻沉积为主。通过透射地震记录计算得到的瞬时频率以灰度阴影图形式展示，可直观呈现各岩芯的岩性声学特征概览。与岩性变化相关的超声波形厘米级差异，通过摆动迹线得到了详细展示。本研究采用互相关、多滤波以及频谱比技术，求解纵波速度与衰减系数。基于比奥-斯托尔（Biot-Stoll）粘弹性模型的反演方法，可计算得到横波（S wave）速度与衰减系数、弹性模量以及渗透率。结合孔隙度实测数据，本研究构建了纵波、横波相关的散点图，通过速度-衰减-孔隙度关系对不同类型沉积物进行分类表征。结果表明，陆源沉积物、钙质沉积物与硅藻沉积物分别覆盖不同的速度-衰减-孔隙度区间。在陆源沉积物中，纵波速度与衰减系数随孔隙度升高快速降低，而横波速度与剪切模量极低。钙质沉积物在孔隙度较高时表现出相似的变化规律。陆源泥与钙质软泥组分中的有孔虫壳体可使沉积物骨架变硬，伴随更高的剪切模量、纵波速度与衰减系数。在硅藻软泥中，剪切模量的贡献愈发显著，且受蛋白石含量调控，而其衰减系数极低。这为通过厘米级分辨率的非破坏性纵波速度测量来预测蛋白石含量提供了可行途径。