Marine sediments preserve archives of glacier behavior from many proxies, with lithofacies analysis providing direct evidence of glacial extent and dynamics. Many of these lithofacies have corresponding physical and geochemical properties that may be identified through quantitative, nondestructive logging properties. This study applies supervised and unsupervised classification to downcore logging data to attempt to model temperate glacimarine facies, which are independently identified via visual lithofacies analysis based on core photographs, digital X-radiography, and computed tomography scans. We test the limits of these methods by modeling both broad glacial and interglacial and small-scale variations in Late Pleistocene (<60,000 yr) glacier extent leading into the Holocene deglaciation for a temperate ice stream at Integrated Ocean Drilling Program Site U1419 in the Gulf of Alaska. Multi-meter-scale mud and diamict lithofacies interpreted as non-glacial versus glacial conditions can be modeled with both methods using downcore physical property logging data (b* color reflectance, magnetic susceptibility, and natural gamma-ray activity) augmented with scanning X-ray fluorescence (XRF) elemental abundance (Ca, Zr, Si, K, Rb, and Al). Physical properties are most useful for delineating decimeter-meter-scale variations in composition and clay content, whereas scanning XRF elements best capture differences in sand versus clay content and composition at decimeter-centimeter scales. Neither classification technique can model the observed small-scale variations in diamict facies using elemental abundance from higher-resolution scanning XRF or from physical properties. Comparison of unsupervised cluster model results with observed lithofacies allows for identification of three different glacial conditions at Site U1419-ice-proximal, fluctuating, and retreating. For small-scale variations in glacial extent, cluster model results are best used as complementary data to image-based lithofacies identification rather than as a replacement.
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Semiquantitative elemental results from X-ray fluorescence (XRF) scanning of sediment cores from Integrated Ocean Drilling Program (IODP) Site U1419 in the Gulf of Alaska are presented. This site contains varying lithofacies that have been previously correlated with glacial-interglacial changes in sedimentation and water-column productivity. XRF scanning was conducted to aid in interpretation of sedimentation during the last glacial period.Crossplots of elements often interpreted as detrital and biogenically sourced show positive correlations between Ca and Al, Si, Ti, Sr, and Si with Al, with no correlation between Ca and Ba. When detrital elements were compared with volume-corrected shipboard magnetic susceptibility (MS), Fe and Ti appear to positively covary, whereas Al inversely covaries. K shows a similar downhole pattern to Fe and Ti, whereas Si is similar to Al. Zr alternates between positively and negatively covarying with Fe, Ti, and K. Mn, Rh, Rb, and Pb intensities 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 intensities are inversely related to Al, Si, and Zr. S roughly mirrors trends displayed by Ca. Mo, Nb, Y, Ga, Ge, P, Ba, Bi, As, and Cu intensities show little to no downhole variation, and changes in Br and Cl intensities are most likely related to water content. IntroductionSite U1419, drilled during Integrated Ocean Drilling Program (IODP) Expedition 341, is located on the upper continental slope in the northern Gulf of Alaska (Fig. F1) (see the "Site U1419" chapter [Jaeger et al., 2014b]). Previous results from the site reveal a high-resolution, heterolithic, deglacial-modern sedimentary record (Davies et al., 2011;Addison et al., 2012). The drilling objectives of Site U1419 were to extend this record of glacial dynamics and paleoceanography into the late Pleistocene. The primary objectives were to constrain the timing of modern to late Pleistocene glacial events of the northwestern Cordilleran ice sheet. The secondary objectives were to document the influence of North Pacific sea-surface temperatures as a control on the regional glacial dynamics and to address the dynamics of productivity and intermediate water circulation on hypoxia in the region.Previous work done at this site revealed the link between the varied sedimentary lithofacies and the water column and glacima- The periodic correspondence of the Gulf of Alaska paleoclimate with events in the North Atlantic suggests that strata accumulating at Site U1419 prior to the deglacial could contain stadial and interstadial periods with varied productivity and glacigenic sedimentation (Praetorius and Mix, 2014). Lithofacies and sediment composition are expected to follow these potential changes. To create a high spatial resolution elemental data set to capture these changes, scanning X-ray fluorescence (XRF) analyses were performed on core sections within the stratigraphically continuous spliced composite record (see the "Site U1419" chapter [Jaeger et al., 2014b]). E...
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