Physical properties of sediment cores of the Bengal Fan@en

We examined geophysical data from a Multi-Sensor Core Logger (MSCL), a logging device providing continuous measurements of gamma-ray attenuation, p-wave travel time, and magnetic susceptibility on marine sediment cores. In the first part we focused on the gamma-ray system and compared two different calibration methods. From the gamma-ray attenuation, we calculated densities and porosities by incorporating mass weighted attenuation coefficients. The application of an iteration method reduces the error of the density and porosity estimates compared to GRAPE data. In addition, we derived equations to calculate water content and dry bulk density from gamma-ray attenuation measurements. Comparison with physical properties determined on discrete samples revealed a very good correlation of both data sets (r = 0.99). This correlation is valid for sediments from substantially different geological settings (e.g., turbidites, hemipelagic muds, and opal-rich sediments). In the second part we applied our data to marine geological questions. For sediments from the Antarctic Polar Frontal Zone, there is indication that the content of biogenic opal can be assessed using a correlation of density and p-wave velocity. For sediments from the Bengal Fan, the relationship between the MSCL acoustic impedance (the product of density and p-wave velocity) and the grain-size distribution in discrete samples can be used to predict clay and sand/silt ratios for sediment cores from the shelf and upper continental slope.本研究分析了多传感器岩心记录仪（Multi-Sensor Core Logger, MSCL）获取的地球物理数据——该测井设备可对海洋沉积物岩心开展连续测量，获取伽马射线衰减、纵波走时与磁化率数据。第一部分聚焦伽马射线测量系统，对比了两种不同的校准方法。基于伽马射线衰减数据，结合质量加权衰减系数计算得到沉积物密度与孔隙度。相较于GRAPE数据，迭代法的应用可降低密度与孔隙度的估算误差。此外，本研究推导了基于伽马射线衰减测量值计算含水量与干体积密度的公式。将计算结果与离散样品实测的物理性质对比发现，两套数据具有极强的相关性（r=0.99）。该相关性适用于多种截然不同地质环境下的沉积物，例如浊积岩、半远洋泥质沉积物及富蛋白石沉积物。第二部分将本研究获取的数据应用于海洋地质问题研究。针对南极极锋带的沉积物，研究表明可通过密度与纵波速度的相关性评估生物成因蛋白石含量。针对孟加拉扇沉积物，利用MSCL声阻抗（密度与纵波速度的乘积）与离散样品粒度分布之间的关系，可预测陆架与上大陆坡沉积物岩心的黏土、砂/粉砂占比。