4:25 PM - 4:40 PM
[MIS07-04] Estimation of dry bulk density of core sediments using an XRF core scanner
Keywords:XRF core scanner, ITRAX, dry bulk density, Japan Sea
XRF core scanner is equipment for X-ray fluorescence analysis of sediment core samples, which has the advantages of high-resolution and non-destructive determination of elemental compositions of cored sediments. From the XRF spectra, it is possible to read Rayleigh and Compton scattering peaks caused by the interaction between incident X-rays and samples, and it has been reported that Compton scattering intensity and the ratio of Compton and Rayleigh scattering are negatively correlated with the bulk density of the samples (Croudace et al., 2006; Fortin et al., 2013).
Using the dry bulk density (DBD), the sedimentation rate, and the elemental content in the sediment, the material flux of each element can be calculated. In other words, if high-resolution DBDs could be obtained at the same areas as elemental composition, we could calculate the material flux with higher resolution and precision. In this study, we investigated a method to quantitatively estimate the DBD of sediment core samples using the XRF core scanner with high precision and resolution.
We chose hemipelagic sediments collected from three different depths in the Japan Sea (Sites U1424, U1425, U1426) during IODP Exp. 346. The Quaternary hemipelagic sediments of the Japan Sea consist mainly of clay and silty clay with varying contributions of biogenic silica and biogenic calcareous material, and their composition is expected to cover a major part of the compositions of hemipelagic and pelagic sediments. Surfaces of half-split cores stored at 2-4 degrees C at the Kochi Core Center (KCC) were scraped to make them flat and smooth, covered with thin plastic film, then analyzed with an XRF core scanner (ITRAX, Mo tube) at KCC. The results were compared to DBDs measured by Moisture and Density (MAD) analyses onboard (Tada et al., 2015).
Wide variability in grain composition of the Japan Sea sediments significantly affects their DBD and elemental composition. For example, the increase in water content (seawater in pores) causes the decrease in DBD and the increase in Cl peak intensity. The increase in biogenic silica content causes the decrease in DBD due to its high intraskeletal porosity and increase Si peak intensity. Fe, which is a major heavy metal, makes grain density higher, and organic material, which is composed of light elements such as C, H, and O, makes grain density lower. Br content tends to increase with the increase in marine organic matter.
By taking account of these relationships, multiple regression analysis was conducted between MAD-based DBD as a response variable and various combinations of ITRAX outputs such as scattering X-ray intensities and peak intensities of Si, Cl, Fe, Br as explanatory variables. The result of multiple regression analysis suggests that the introduction of Cl intensity in addition to the intensity of X-rays scattering improves the accuracy of the DBD estimation.
By estimating the DBD of each sediment sample only from the results of XRF core scanner, we could obtain the DBDs from exactly the sample areas where element compositions were determined. This will enable us to estimate material flux more precisely and with higher resolution, which will expand our ability for more precise reconstruction of geochemical cycles in the past.
Using the dry bulk density (DBD), the sedimentation rate, and the elemental content in the sediment, the material flux of each element can be calculated. In other words, if high-resolution DBDs could be obtained at the same areas as elemental composition, we could calculate the material flux with higher resolution and precision. In this study, we investigated a method to quantitatively estimate the DBD of sediment core samples using the XRF core scanner with high precision and resolution.
We chose hemipelagic sediments collected from three different depths in the Japan Sea (Sites U1424, U1425, U1426) during IODP Exp. 346. The Quaternary hemipelagic sediments of the Japan Sea consist mainly of clay and silty clay with varying contributions of biogenic silica and biogenic calcareous material, and their composition is expected to cover a major part of the compositions of hemipelagic and pelagic sediments. Surfaces of half-split cores stored at 2-4 degrees C at the Kochi Core Center (KCC) were scraped to make them flat and smooth, covered with thin plastic film, then analyzed with an XRF core scanner (ITRAX, Mo tube) at KCC. The results were compared to DBDs measured by Moisture and Density (MAD) analyses onboard (Tada et al., 2015).
Wide variability in grain composition of the Japan Sea sediments significantly affects their DBD and elemental composition. For example, the increase in water content (seawater in pores) causes the decrease in DBD and the increase in Cl peak intensity. The increase in biogenic silica content causes the decrease in DBD due to its high intraskeletal porosity and increase Si peak intensity. Fe, which is a major heavy metal, makes grain density higher, and organic material, which is composed of light elements such as C, H, and O, makes grain density lower. Br content tends to increase with the increase in marine organic matter.
By taking account of these relationships, multiple regression analysis was conducted between MAD-based DBD as a response variable and various combinations of ITRAX outputs such as scattering X-ray intensities and peak intensities of Si, Cl, Fe, Br as explanatory variables. The result of multiple regression analysis suggests that the introduction of Cl intensity in addition to the intensity of X-rays scattering improves the accuracy of the DBD estimation.
By estimating the DBD of each sediment sample only from the results of XRF core scanner, we could obtain the DBDs from exactly the sample areas where element compositions were determined. This will enable us to estimate material flux more precisely and with higher resolution, which will expand our ability for more precise reconstruction of geochemical cycles in the past.