Estimation of the Biogenic Silica Content in Lacustrine Bottom Silicate Sediments by X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF)

In paleoenvironmental work, X-ray diffraction (XRD) and X-ray fluorescence (XRF) are commonly used to quantify the main rock-forming mineral phases and elements in lacustrine deposits. The amorphous phase information of biogenic silica content as an important indicator of environmental change is of special interest in paleoecological investigations. We present the range evaluation technique of amorphous biogenic silica content in lacustrine bottom silicate sediments by integrating XRD and XRF measurements. The technique is based on the rock-forming elemental contents obtained by XRF and crystalline quartz contents determined by XRD and includes a procedure of searching for minimum and maximum silica oxide contents as a component with compliance to the balance of mineral composition and elements content in a sample. The amorphous phase of biogenic silica is defined to be the difference between the content of available silica oxide and that of crystalline quartz. The results are in agreement with the results obtained by wet chemistry digestion. The correlation coefficient between the calculated and determined by wet chemistry values of biogenic silica contents is 0.90. The lower limit of quantitative assessment is approximately 2 wt. %. Although the calculated range of biogenic silica content is larger than its uncertainty obtained by the wet chemistry method, the proposed technique is useful for estimating the variation of biogenic silica content throughout the sediment core depth when XRD and XRF measurements are available.