- Chapter contents
- Abstract
- Introduction
- Methods
- Results
- Acknowledgments
- References
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Figures - PDF file
doi:10.2204/iodp.proc.341.203.2017
Results
The scanning XRF data in this report provide a high-resolution record of the geochemistry at Site U1419. Crossplots of elements often associated with detrital and biogenic sources in marine sediments are shown in Figure F2 (Rothwell and Croudace, 2015). Weak positive covariance is seen for Ca and Al and for Ca and Si, with the increased amount of scatter most likely due to increased effects of water content on the low atomic mass and weakly fluorescing Al and Si atoms (Tjallingii et al., 2007). Positive covariance is observed between Ca and Ti, Ca and Sr, and Si and Al. However, a slight negative relationship is observed at extremely high Ca counts between Ca and Ti. There appears to be no relationship between Ca and Ba.
Downhole element distributions of Al, Ca, Fe, K, Si, Ti, and Zr are plotted along with volume-corrected magnetic susceptibility (MS) in Figure F3 (Walczak et al., 2015). All plots are on a core composite depth below seafloor (CCSF-B) depth scale in meters, which is the composite depth scale corrected for compaction (see the “Methods” chapter [Jaeger et al., 2014a]). When comparing detrital elements Al, Fe, and Ti with MS, Al appears to inversely covary, whereas Ti and Fe appear to positively covary. Si exhibits similar downhole variability to Al, and K appears to covary with Fe and Ti. Zr inversely covaries with Ti, Fe, and K shallower than 27 m CCSF-B and deeper than 65 m CCSF-B but positively covaries between 27 and 65 m CCSF-B. Ca displays the strongest downhole variability, with the degree of variation increasing downhole.
Downhole plots of measured elements not shown in Figure F3 along with box and whisker plots of all measured elements are available in DOWNHOLE and BOXPLOTS in “Supplementary material.” Of these elements, Mn, Rh, Rb, and Pb show patterns similar to K, Ti, and Fe, whereas Sr is similar to Ca, and Cr is similar to Al and Si. Ni and Zn are inversely related to Al, Si, and Zr. S roughly mirrors trends displayed by Ca and is characterized by a large peak at 36 m CCSF-B. Mo, Nb, Y, Ga, Ge, P, Ba, Bi, As, and Cu show little to no downhole variation. Mo, Nb, Y, Ga, As, and Cu have been previously measured in the Gulf of Alaska by inductively coupled plasma–mass spectrometry (ICP-MS) at concentrations of a few parts per million (Barron et al., 2009), which most likely falls below the detection limit of the XRF scanner at the GCR, and thus their downhole values likely represent noise. Ba and P have been measured via ICP-MS at concentrations higher than the AVAATECH XRF scanner detection limit (Richter et al., 2006). Bi and Ge are typically found in extremely low concentrations of <2 ppm in continental crust (Rudnick and Gao, 2003) and are assumed to be below the detection limit of the GCR XRF scanner. Changes in Br and Cl intensities are most likely related to water content (Tjallingii et al., 2007). Positive Ar values indicate measurements where X-rays were transmitted through air due core disturbance (i.e., cracks) or bubbles underneath the plastic film.