Use of Calibrated ITRAX XRF Data in Determining Turbidite Geochemistry and Provenance in Agadir Basin, Northwest African Passive Margin

Abstract

The Agadir Basin is a mixed siliciclastic-volcaniclastic deepwater turbidite system derived from several sedimentary sources. Estimating the influence of these sources requires detailed geochemical profiles of sediment cores. This is achieved using an ITRAX µXRF core scanner that normally produces elemental profiles in units of counts or count rate. Improved insights are achieved if the ITRAX data are calibrated to produce concentration data. Turbidite geochemistry can then be used to more reliably infer the sources of flows and identify primary sediment sources, which are the Moroccan slope for siliciclastic beds and the western Canary Islands for volcaniclastic turbidites. Cross-plots of the geochemical data discriminate variations between different siliciclastic and volcaniclastic beds. For example, differences between two distinctive volcaniclastic marker beds, named A2 and A14, reflect differences in their respective Canary Island sources and indicate a primitive basaltic source for bed A2 and an evolved source for bed A14. Compositional variations between siliciclastic deposits reflect potential variations in the sediment source that failed or the location of the failure on the Moroccan continental slope.

Understanding the impact of millennial to sub-decadal climate and limnological change on the stability of As in lacustrine sediments

“…both observed minor increases in Pearson's R value between XRF-CS and ED-XRF of Ca, whereas inMaclachlan et al (2015) and this study, Ca correlation coefficients decreased slightly after water content correction. Carbonate content in cores examined byTjalingii et al (2007) was high at 30-65 wt %, whereas cores examined by andMaclachlan et al (2015) generally ranged from about 5-15 wt % and carbonate content in Harvey Lake was < 1 wt %. Standards analyzed by Bureau Veritas showed that ICP-MS-measured Ca concentrations are accurate to actual concentrations within the 90% confidence interval, indicating ICP-MS accurately reproduced Ca trends in sediment.…”

“…Comparison of wt % organic matter to Coh/Inc scatter from the Harvey Lake samples did not show a strong correlation (τ = -0.43, n = 61; Figure 3.3). Other researchers have shown that there is negligible impact on the XRF-CS signal if water content or large sediment grains constitute < 25 wt % of a sample (Maclachlan et al 2015). It is possible that a similar relationship is true for organic content, although this was not quantified by Maclachlan et al (2015).…”

“…The use of high-resolution, non-destructive, X-ray fluorescence core scanners (XRF-CS) has become commonplace in the study of paleoenvironments and paleoclimate (Turner et al 2010;Giralt et al 2011;Gregory et al 2015;Profe et al 2016;, sediment provenance (Kujau et al 2010;Hunt et al 2015;Zielhofer et al 2017) and soil and sediment contamination Miller et al 2015;Rodríguez-Germade et al 2015;Lintern et al 2016;Schillereff et al 2016). X-ray fluorescence core scanners are capable of analyzing sediment cores at up to 0.1 mm resolution at < 30 s per interval, offering a major advantage in speed, cost, and resolution over conventional geochemical analysis (ED-or WD-XRF, ICP-MS, INAA).…”

“…X-ray fluorescence core scanners are capable of analyzing sediment cores at up to 0.1 mm resolution at < 30 s per interval, offering a major advantage in speed, cost, and resolution over conventional geochemical analysis (ED-or WD-XRF, ICP-MS, INAA). A consequence of this rapid, high-resolution analysis is loss of geochemical accuracy and precision (Tjallingii et al 2007;Hennekam and de Lange 2012;Maclachlan et al 2015). Traditional XRF analysis uses sediment which is ground to homogenous particle size and either fused to glass beads or compressed into a puck with a smooth surface to minimize matrix and specimen effects (International Atomic Energy Agency 1997; Weltje and Tjallingii 2008).…”

“…Traditional XRF analysis uses sediment which is ground to homogenous particle size and either fused to glass beads or compressed into a puck with a smooth surface to minimize matrix and specimen effects (International Atomic Energy Agency 1997; Weltje and Tjallingii 2008). XRF-CS measurements can be influenced by heterogeneities in the sample surface, such as an uneven topography or variation in particle size (specimen effects), or by reabsorption, reemission and scattering of primary X-radiation by some component of the sediment being analyzed, such as interstitial water content, sediment porosity, or the sediment itself (matrix effects; Tjallingii et al 2007;Maclachlan et al 2015).…”