资料报告:阿拉伯海Laxmi盆地U1457地点沉积物的x射线荧光研究

M. Lyle, D. Kulhanek, M. G. Bowen, Annette Hahn
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We report data and acquisition conditions for major and many minor elements. We find large variability in CaCO3 content in the Pleistocene section, from around 14 to 89 wt%. We used discrete shipboard CaCO3 measurements to calibrate the XRF Ca data. CaCO3 has cyclic variability and correlates with light sediment colors. Variation in aluminosilicate elements is largely caused by changes in dilution by CaCO3. The lower part of the spliced section, presumably representing distal Indus Fan deposits, has a distinctive but more uniform composition than the upper part. Introduction Variability in chemical composition of deep-sea sediments provides important data needed to understand changes in primary productivity, the carbon cycle, and sources of aluminosilicates. However, chemical analyses are typically too slow and expensive for high-resolution study of chemical composition covering long intervals of time. They also consume the sediments, so only limited numbers of analyses can be performed. Nondestructive X-ray fluorescence (XRF) core scanning provides the potential to produce high-resolution chemical profiles that can be calibrated with a small number of discrete chemical analyses. XRF is an X-ray optical technique that can measure most major and some minor elements. It is an economical way to extract bulk chemical data over longer sediment/rock profiles where thousands of analyses might be needed to resolve lithostratigraphic changes in the section. The method can be used to gather chemical data at a vertical resolution similar to that of physical property data collection by track systems on the JOIDES Resolution (e.g., Westerhold and Röhl, 2009; Lyle et al., 2012). These chemical measurements can augment physical property measurements to study cyclostratigraphy or rapid changes in sedimentation. If calibrated, the XRF data can be used to understand the long-term evolution of biogeochemical cycles and to identify the provenance of aluminosilicate sediments (Lyle and Baldauf, 2015). Data acquisition methods Data in this report were acquired at the IODP Gulf Coast Repository in College Station, Texas (http://iodp.tamu.edu/labs/xrf) using a third-generation Avaatech XRF core scanner with a Canberra X-PIPS SDD, Model SXD 15C-150-500 150 eV resolution X-ray detector. The XRF scanner is configured to analyze split sediment core M. Lyle et al. Data report: X-ray fluorescence studies of Site U1457 sediments halves for elements between Al and U in the periodic table. The Xray tube and detector apparatus is mounted on a moving track so that multiple spots at different positions along a split core section can be analyzed during each scanning run, and multiple scans with different settings can be automatically programmed (Richter et al., 2006). The operator controls X-ray tube current, voltage, measurement time (live time), X-ray filters used, and area of X-ray illumination. The downcore position step is precise to 0.1 mm. For the Site U1457 (Figure F1) XRF scans, sample spacing was set at 2 cm intervals downcore in each core section, and separate scans at two voltages were used. The X-ray illumination area was set at 1.0 cm in the downcore direction and 1.2 cm in the cross-core direction, and the scan was run down the center of the split core half (6.8 cm total diameter for cores collected using the advanced piston corer [APC]). The first scan was performed at 10 kV, 800 μA, 15 s live time, and no filter for the elements Al, Si, S, Cl, K, Ca, Ti, Mn, and Fe. A second scan was performed at 30 kV, 1000 μA, 20 s live time, and Pd-thick filter for Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb, Mo, Pb, and Bi. Of these elements, Br, Rb, Sr, and Zr had sufficiently large signals to justify further data reduction. Each core section was removed from refrigeration at least 2 h before scanning and was covered about 15 min before being placed on the scanner with 4 μm thick Ultralene plastic film (SPEX Centriprep, Inc.). The Ultralene film protects the detector face from becoming sediment covered and contaminated during the scan. It is important to wait until the core sections warm to room temperature before putting the film on core sections. Plastic film placed over cool core sections can cause water condensation onto the film, which severely reduces light-element XRF peak areas by absorbing the emitted low-energy X-rays (Lyle et al., 2012). All core sections contained within the continuous spliced section of Site U1457 were analyzed. Where the sediment splice changed from one hole to the other, both sections at the tie point were scanned in their entirety. All of the sections within the revised Site U1457 splice listed in Lyle and Saraswat (2019) were scanned. All data gathered, including the overlaps, are included in Table T1 (Hole U1457A) and Table T2 (Hole U1457B). Table T3 contains the Hole U1457C data, and Table T4 contains the Site U1457 splice data, which represents the data along a continuous sediment section for the upper 125 m CCSF. All tables contain both the raw peak areas and the normalized median-scaled (NMS)-reduced data, described below. Because there is more than one method of data reduction for XRF scan data (Weltje and Tjallingii, 2008; Lyle et al., 2012; Weltje et al., 2015), we report both raw peak area data and processed data in Tables T1, T2, and T3. The raw data thus will allow reprocessing in the future, if warranted. Data reduction methods for later calibration—normalized median-scaled (NMS) data Data reduction was achieved through a simple two-step method, as explained in Lyle et al. (2012): (1) The data were first median scaled by setting the median peak area of each element to a model percent derived from average graywacke (Wedepohl, 1995). The range in the peak area data was then converted into a raw percentage by dividing the peak area of each individual sample by the median peak area and then multiplying the result by the model median elemental abundance. (2) Because the resulting raw data rarely summed to 100% of the major elemental oxides, they were then normalized so that the major rock-forming elemental oxides summed to 100%. The normalization was achieved by dividing the raw sum of the major oxides into 100, and then multiplying each raw oxide by this factor. Minor elements were normalized by the same factor. The normalization step is used to eliminate variability caused by differences in porosity or cracks or by XRF source intensity variation (Lyle et al., 2012). The NMS method of data reduction has a few similarities and several differences to that of Weltje and Tjallingii (2008) and the further elucidation of the method in Weltje et al. (2015). Weltje and Tjallingii (2008) normalize each elemental peak area first by dividing by the sum of the total raw peak areas. They then log transform these ratios to reduce the range between major and minor XRFemitters, like our median-scaling step. Finally, they solve a matrix of XRF element/element ratios for composition. Weltje et al. (2015) investigated the use of various matrix solutions to get final composiFigure F1. Shaded bathymetric map of the Arabian Sea showing the location of Site U1457 (see the Site U1457 chapter [Pandey et al., 2016]). Site U1457 is located near the south coast of India, in the Laxmi Basin of the Arabian Sea. Yellow circles = sites drilled during Expedition 355, red stars = earlier scientific drilling sites, pink line = approximate extent of Indus Fan after Kolla and Coumes (1987), yellow dashed lines with question marks = the speculated locations of the continent/ocean boundary depending on whether Laxmi Basin is floored by oceanic or continental crust, gray lines with numbers = magnetic anomalies from Royer et al. (2002). Ba y o f B en ga l Arabian Sea axmi idge","PeriodicalId":20641,"journal":{"name":"Proceedings of the International Ocean Discovery Program","volume":"1 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2018-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"2","resultStr":"{\"title\":\"Data report: X-ray fluorescence studies of Site U1457 sediments, Laxmi Basin, Arabian Sea\",\"authors\":\"M. Lyle, D. Kulhanek, M. G. 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We find large variability in CaCO3 content in the Pleistocene section, from around 14 to 89 wt%. We used discrete shipboard CaCO3 measurements to calibrate the XRF Ca data. CaCO3 has cyclic variability and correlates with light sediment colors. Variation in aluminosilicate elements is largely caused by changes in dilution by CaCO3. The lower part of the spliced section, presumably representing distal Indus Fan deposits, has a distinctive but more uniform composition than the upper part. Introduction Variability in chemical composition of deep-sea sediments provides important data needed to understand changes in primary productivity, the carbon cycle, and sources of aluminosilicates. However, chemical analyses are typically too slow and expensive for high-resolution study of chemical composition covering long intervals of time. They also consume the sediments, so only limited numbers of analyses can be performed. Nondestructive X-ray fluorescence (XRF) core scanning provides the potential to produce high-resolution chemical profiles that can be calibrated with a small number of discrete chemical analyses. XRF is an X-ray optical technique that can measure most major and some minor elements. It is an economical way to extract bulk chemical data over longer sediment/rock profiles where thousands of analyses might be needed to resolve lithostratigraphic changes in the section. The method can be used to gather chemical data at a vertical resolution similar to that of physical property data collection by track systems on the JOIDES Resolution (e.g., Westerhold and Röhl, 2009; Lyle et al., 2012). These chemical measurements can augment physical property measurements to study cyclostratigraphy or rapid changes in sedimentation. If calibrated, the XRF data can be used to understand the long-term evolution of biogeochemical cycles and to identify the provenance of aluminosilicate sediments (Lyle and Baldauf, 2015). Data acquisition methods Data in this report were acquired at the IODP Gulf Coast Repository in College Station, Texas (http://iodp.tamu.edu/labs/xrf) using a third-generation Avaatech XRF core scanner with a Canberra X-PIPS SDD, Model SXD 15C-150-500 150 eV resolution X-ray detector. The XRF scanner is configured to analyze split sediment core M. Lyle et al. Data report: X-ray fluorescence studies of Site U1457 sediments halves for elements between Al and U in the periodic table. The Xray tube and detector apparatus is mounted on a moving track so that multiple spots at different positions along a split core section can be analyzed during each scanning run, and multiple scans with different settings can be automatically programmed (Richter et al., 2006). The operator controls X-ray tube current, voltage, measurement time (live time), X-ray filters used, and area of X-ray illumination. The downcore position step is precise to 0.1 mm. For the Site U1457 (Figure F1) XRF scans, sample spacing was set at 2 cm intervals downcore in each core section, and separate scans at two voltages were used. The X-ray illumination area was set at 1.0 cm in the downcore direction and 1.2 cm in the cross-core direction, and the scan was run down the center of the split core half (6.8 cm total diameter for cores collected using the advanced piston corer [APC]). The first scan was performed at 10 kV, 800 μA, 15 s live time, and no filter for the elements Al, Si, S, Cl, K, Ca, Ti, Mn, and Fe. A second scan was performed at 30 kV, 1000 μA, 20 s live time, and Pd-thick filter for Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb, Mo, Pb, and Bi. Of these elements, Br, Rb, Sr, and Zr had sufficiently large signals to justify further data reduction. Each core section was removed from refrigeration at least 2 h before scanning and was covered about 15 min before being placed on the scanner with 4 μm thick Ultralene plastic film (SPEX Centriprep, Inc.). The Ultralene film protects the detector face from becoming sediment covered and contaminated during the scan. It is important to wait until the core sections warm to room temperature before putting the film on core sections. Plastic film placed over cool core sections can cause water condensation onto the film, which severely reduces light-element XRF peak areas by absorbing the emitted low-energy X-rays (Lyle et al., 2012). All core sections contained within the continuous spliced section of Site U1457 were analyzed. Where the sediment splice changed from one hole to the other, both sections at the tie point were scanned in their entirety. All of the sections within the revised Site U1457 splice listed in Lyle and Saraswat (2019) were scanned. All data gathered, including the overlaps, are included in Table T1 (Hole U1457A) and Table T2 (Hole U1457B). Table T3 contains the Hole U1457C data, and Table T4 contains the Site U1457 splice data, which represents the data along a continuous sediment section for the upper 125 m CCSF. All tables contain both the raw peak areas and the normalized median-scaled (NMS)-reduced data, described below. Because there is more than one method of data reduction for XRF scan data (Weltje and Tjallingii, 2008; Lyle et al., 2012; Weltje et al., 2015), we report both raw peak area data and processed data in Tables T1, T2, and T3. The raw data thus will allow reprocessing in the future, if warranted. Data reduction methods for later calibration—normalized median-scaled (NMS) data Data reduction was achieved through a simple two-step method, as explained in Lyle et al. (2012): (1) The data were first median scaled by setting the median peak area of each element to a model percent derived from average graywacke (Wedepohl, 1995). The range in the peak area data was then converted into a raw percentage by dividing the peak area of each individual sample by the median peak area and then multiplying the result by the model median elemental abundance. (2) Because the resulting raw data rarely summed to 100% of the major elemental oxides, they were then normalized so that the major rock-forming elemental oxides summed to 100%. The normalization was achieved by dividing the raw sum of the major oxides into 100, and then multiplying each raw oxide by this factor. Minor elements were normalized by the same factor. The normalization step is used to eliminate variability caused by differences in porosity or cracks or by XRF source intensity variation (Lyle et al., 2012). The NMS method of data reduction has a few similarities and several differences to that of Weltje and Tjallingii (2008) and the further elucidation of the method in Weltje et al. (2015). Weltje and Tjallingii (2008) normalize each elemental peak area first by dividing by the sum of the total raw peak areas. They then log transform these ratios to reduce the range between major and minor XRFemitters, like our median-scaling step. Finally, they solve a matrix of XRF element/element ratios for composition. Weltje et al. (2015) investigated the use of various matrix solutions to get final composiFigure F1. Shaded bathymetric map of the Arabian Sea showing the location of Site U1457 (see the Site U1457 chapter [Pandey et al., 2016]). Site U1457 is located near the south coast of India, in the Laxmi Basin of the Arabian Sea. 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引用次数: 2

摘要

利用国际海洋发现计划(IODP)墨西哥湾沿岸储存库的x射线荧光(XRF)岩心扫描仪,沿着国际海洋发现计划(IODP)站点U1457的岩心,以2厘米分辨率测量了大块沉积物的化学性质。对U1457A孔和U1457B孔组装的更新世剪接剖面进行了整体扫描,构建了海底下125 m岩心复合深度(CCSF)近连续的沉积物体化学剖面。U1457C孔的部分剖面也进行了扫描:(1)上中新世半深海剖面和(2)下古新世30 m直接覆盖玄武岩剖面。在更新世拼接剖面中,2 cm间距代表150-300 y的采样分辨率,而在中新世上部剖面中,样品之间的间距约为500 y。我们报告主要元素和许多次要元素的数据和获取条件。我们发现更新世剖面的CaCO3含量变化很大,从14%到89%不等。我们使用离散的船载CaCO3测量来校准XRF Ca数据。CaCO3具有循环变异性,并与浅沉积物颜色相关。铝硅酸盐元素的变化主要是由CaCO3稀释度的变化引起的。拼接剖面的下半部分可能代表远端印度河扇沉积,其组成比上半部分独特但更均匀。深海沉积物化学成分的变化为了解初级生产力、碳循环和铝硅酸盐来源的变化提供了重要的数据。然而,化学分析对于长时间的高分辨率化学成分研究来说通常过于缓慢和昂贵。它们也会消耗沉积物,因此只能进行有限数量的分析。非破坏性x射线荧光(XRF)核心扫描提供了产生高分辨率化学剖面的潜力,可以通过少量离散化学分析进行校准。XRF是一种可以测量大多数主要元素和一些次要元素的x射线光学技术。这是一种经济的方法,可以从较长的沉积物/岩石剖面中提取大量化学数据,因为可能需要数千次分析才能解决剖面中的岩石地层变化。该方法可用于收集垂直分辨率的化学数据,类似于JOIDES分辨率上的跟踪系统收集的物理性质数据(例如,Westerhold和Röhl, 2009;Lyle et al., 2012)。这些化学测量可以增强物理性质测量,以研究旋回地层学或沉积的快速变化。如果经过校准,XRF数据可用于了解生物地球化学循环的长期演变,并确定铝硅酸盐沉积物的来源(Lyle和Baldauf, 2015)。本报告中的数据是在德克萨斯州大学城的IODP墨西哥湾沿岸储存库(http://iodp.tamu.edu/labs/xrf)使用第三代Avaatech XRF核心扫描仪与堪培拉X-PIPS SDD,型号SXD 15C-150-500 150 eV分辨率x射线探测器获得的。XRF扫描仪配置用于分析分裂沉积物岩心。数据报告:对U1457站点沉积物的x射线荧光研究,发现元素周期表中Al和U之间的元素。x射线管和探测器装置安装在移动轨道上,以便在每次扫描运行时,可以沿分割的岩心剖面分析不同位置的多个点,并且可以自动编程不同设置的多个扫描(Richter et al., 2006)。操作者控制x射线管电流、电压、测量时间(活时间)、使用的x射线滤光片和x射线照射面积。下芯位置步进精确到0.1毫米。对于Site U1457(图F1) XRF扫描,在每个岩心切片中,样品间距设置在岩心下方2厘米的间隔,并在两个电压下进行单独扫描。x射线照射区域设置为下岩心方向1.0 cm和交叉岩心方向1.2 cm,扫描沿劈开岩心一半的中心向下进行(采用先进活塞盖[APC]收集的岩心总直径为6.8 cm)。第一次扫描在10 kV, 800 μA, 15 s寿命下进行,对Al, Si, s, Cl, K, Ca, Ti, Mn和Fe元素不加滤波。第二次扫描在30 kV, 1000 μA, 20 s寿命下进行,使用pd厚滤波器对Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb, Mo, Pb和Bi进行扫描。在这些元素中,Br、Rb、Sr和Zr有足够大的信号来证明进一步的数据缩减是合理的。每个核心切片在扫描前至少2小时从冰箱中取出,覆盖约15分钟,然后用4 μm厚的Ultralene塑料薄膜(SPEX Centriprep, Inc.)放在扫描仪上。Ultralene薄膜保护探测器表面在扫描过程中不被沉积物覆盖和污染。重要的是要等到核心部分温暖到室温,然后再把胶片放在核心部分。 在冷却的核心部分上放置塑料薄膜会导致水凝结在薄膜上,通过吸收发射的低能x射线,严重减少轻元素XRF峰面积(Lyle et al., 2012)。对Site U1457连续拼接截面内的所有核心截面进行分析。当沉积物拼接从一个孔改变到另一个孔时,连接点的两个剖面都被完整扫描。扫描了Lyle和Saraswat(2019)中列出的修订后的Site U1457剪接中的所有部分。收集到的所有数据,包括重叠部分,如表T1 (U1457A孔)和表T2 (U1457B孔)所示。表T3包含U1457C孔数据,表T4包含U1457站点拼接数据,它们代表了上部125 m CCSF连续沉积物剖面的数据。所有表都包含原始峰值面积和标准化的中位数缩放(NMS)减少的数据,如下所述。因为对于XRF扫描数据有不止一种数据约简方法(Weltje和Tjallingii, 2008;Lyle et al., 2012;Weltje et al., 2015),我们在表T1、T2和T3中报告了原始峰面积数据和处理数据。因此,如果有必要,原始数据将允许在将来进行再处理。后期校准的数据约简方法-归一化中位数缩放(NMS)数据数据约简是通过简单的两步法实现的,如Lyle等人(2012)所述:(1)首先通过将每个元素的中位数峰面积设置为平均graywacke的模型百分比(Wedepohl, 1995)来对数据进行中位数缩放。然后将每个样品的峰面积除以中位数峰面积,然后将结果乘以模型中位数元素丰度,将峰面积数据中的范围转换为原始百分比。(2)由于所得到的原始数据很少能达到主要元素氧化物的100%,因此对它们进行归一化处理,使主要造岩元素氧化物的总和达到100%。标准化是通过将主要氧化物的原始和除以100,然后将每个原始氧化物乘以这个因子来实现的。次要元素被同一因子归一化。归一化步骤用于消除孔隙度或裂缝差异或XRF源强度变化引起的可变性(Lyle et al., 2012)。数据约简的NMS方法与Weltje和Tjallingii(2008)的方法以及Weltje et al.(2015)对该方法的进一步阐述有一些相似之处,也有一些不同之处。Weltje和Tjallingii(2008)首先通过除以总原始峰面积的总和来标准化每个元素峰面积。然后,他们对这些比率进行对数变换,以减少主要和次要xrfemter之间的范围,就像我们的中位数缩放步骤一样。最后,他们求解了组成的XRF元素/元素比例矩阵。Weltje et al.(2015)研究了使用各种矩阵解来获得最终组合(图F1)。阿拉伯海阴影水深图显示了Site U1457的位置(参见Site U1457章节[Pandey et al., 2016])。U1457遗址位于印度南海岸附近,位于阿拉伯海的拉克西米盆地。黄色圆圈=第355次科考期间钻探的地点,红色星星=更早的科学钻探地点,粉色线=在Kolla和Coumes(1987)之后印度河扇的大致范围,黄色带问号的虚线=根据拉克西米盆地是由海洋地壳还是大陆地壳覆盖而推测的大陆/海洋边界位置,灰色带数字的线= Royer等人(2002)的磁异常。它位于阿拉伯海的边缘
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Data report: X-ray fluorescence studies of Site U1457 sediments, Laxmi Basin, Arabian Sea
Bulk sediment chemistry was measured at 2 cm resolution along cores from International Ocean Discovery Program (IODP) Site U1457 using the X-ray fluorescence (XRF) core scanner at the IODP Gulf Coast Repository. The Pleistocene splice section assembled from Holes U1457A and U1457B was scanned in its entirety, and nearly continuous sediment bulk chemistry profiles were constructed to a depth of 125 m core composite depth below seafloor (CCSF). Some sections of Hole U1457C were also scanned: (1) an upper Miocene hemipelagic section and (2) a 30 m lower Paleocene section directly overlying basalt. In the Pleistocene spliced sections, 2 cm spacing represents a sampling resolution of 150–300 y, whereas in the upper Miocene section this spacing represents about 500 y between samples. We report data and acquisition conditions for major and many minor elements. We find large variability in CaCO3 content in the Pleistocene section, from around 14 to 89 wt%. We used discrete shipboard CaCO3 measurements to calibrate the XRF Ca data. CaCO3 has cyclic variability and correlates with light sediment colors. Variation in aluminosilicate elements is largely caused by changes in dilution by CaCO3. The lower part of the spliced section, presumably representing distal Indus Fan deposits, has a distinctive but more uniform composition than the upper part. Introduction Variability in chemical composition of deep-sea sediments provides important data needed to understand changes in primary productivity, the carbon cycle, and sources of aluminosilicates. However, chemical analyses are typically too slow and expensive for high-resolution study of chemical composition covering long intervals of time. They also consume the sediments, so only limited numbers of analyses can be performed. Nondestructive X-ray fluorescence (XRF) core scanning provides the potential to produce high-resolution chemical profiles that can be calibrated with a small number of discrete chemical analyses. XRF is an X-ray optical technique that can measure most major and some minor elements. It is an economical way to extract bulk chemical data over longer sediment/rock profiles where thousands of analyses might be needed to resolve lithostratigraphic changes in the section. The method can be used to gather chemical data at a vertical resolution similar to that of physical property data collection by track systems on the JOIDES Resolution (e.g., Westerhold and Röhl, 2009; Lyle et al., 2012). These chemical measurements can augment physical property measurements to study cyclostratigraphy or rapid changes in sedimentation. If calibrated, the XRF data can be used to understand the long-term evolution of biogeochemical cycles and to identify the provenance of aluminosilicate sediments (Lyle and Baldauf, 2015). Data acquisition methods Data in this report were acquired at the IODP Gulf Coast Repository in College Station, Texas (http://iodp.tamu.edu/labs/xrf) using a third-generation Avaatech XRF core scanner with a Canberra X-PIPS SDD, Model SXD 15C-150-500 150 eV resolution X-ray detector. The XRF scanner is configured to analyze split sediment core M. Lyle et al. Data report: X-ray fluorescence studies of Site U1457 sediments halves for elements between Al and U in the periodic table. The Xray tube and detector apparatus is mounted on a moving track so that multiple spots at different positions along a split core section can be analyzed during each scanning run, and multiple scans with different settings can be automatically programmed (Richter et al., 2006). The operator controls X-ray tube current, voltage, measurement time (live time), X-ray filters used, and area of X-ray illumination. The downcore position step is precise to 0.1 mm. For the Site U1457 (Figure F1) XRF scans, sample spacing was set at 2 cm intervals downcore in each core section, and separate scans at two voltages were used. The X-ray illumination area was set at 1.0 cm in the downcore direction and 1.2 cm in the cross-core direction, and the scan was run down the center of the split core half (6.8 cm total diameter for cores collected using the advanced piston corer [APC]). The first scan was performed at 10 kV, 800 μA, 15 s live time, and no filter for the elements Al, Si, S, Cl, K, Ca, Ti, Mn, and Fe. A second scan was performed at 30 kV, 1000 μA, 20 s live time, and Pd-thick filter for Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb, Mo, Pb, and Bi. Of these elements, Br, Rb, Sr, and Zr had sufficiently large signals to justify further data reduction. Each core section was removed from refrigeration at least 2 h before scanning and was covered about 15 min before being placed on the scanner with 4 μm thick Ultralene plastic film (SPEX Centriprep, Inc.). The Ultralene film protects the detector face from becoming sediment covered and contaminated during the scan. It is important to wait until the core sections warm to room temperature before putting the film on core sections. Plastic film placed over cool core sections can cause water condensation onto the film, which severely reduces light-element XRF peak areas by absorbing the emitted low-energy X-rays (Lyle et al., 2012). All core sections contained within the continuous spliced section of Site U1457 were analyzed. Where the sediment splice changed from one hole to the other, both sections at the tie point were scanned in their entirety. All of the sections within the revised Site U1457 splice listed in Lyle and Saraswat (2019) were scanned. All data gathered, including the overlaps, are included in Table T1 (Hole U1457A) and Table T2 (Hole U1457B). Table T3 contains the Hole U1457C data, and Table T4 contains the Site U1457 splice data, which represents the data along a continuous sediment section for the upper 125 m CCSF. All tables contain both the raw peak areas and the normalized median-scaled (NMS)-reduced data, described below. Because there is more than one method of data reduction for XRF scan data (Weltje and Tjallingii, 2008; Lyle et al., 2012; Weltje et al., 2015), we report both raw peak area data and processed data in Tables T1, T2, and T3. The raw data thus will allow reprocessing in the future, if warranted. Data reduction methods for later calibration—normalized median-scaled (NMS) data Data reduction was achieved through a simple two-step method, as explained in Lyle et al. (2012): (1) The data were first median scaled by setting the median peak area of each element to a model percent derived from average graywacke (Wedepohl, 1995). The range in the peak area data was then converted into a raw percentage by dividing the peak area of each individual sample by the median peak area and then multiplying the result by the model median elemental abundance. (2) Because the resulting raw data rarely summed to 100% of the major elemental oxides, they were then normalized so that the major rock-forming elemental oxides summed to 100%. The normalization was achieved by dividing the raw sum of the major oxides into 100, and then multiplying each raw oxide by this factor. Minor elements were normalized by the same factor. The normalization step is used to eliminate variability caused by differences in porosity or cracks or by XRF source intensity variation (Lyle et al., 2012). The NMS method of data reduction has a few similarities and several differences to that of Weltje and Tjallingii (2008) and the further elucidation of the method in Weltje et al. (2015). Weltje and Tjallingii (2008) normalize each elemental peak area first by dividing by the sum of the total raw peak areas. They then log transform these ratios to reduce the range between major and minor XRFemitters, like our median-scaling step. Finally, they solve a matrix of XRF element/element ratios for composition. Weltje et al. (2015) investigated the use of various matrix solutions to get final composiFigure F1. Shaded bathymetric map of the Arabian Sea showing the location of Site U1457 (see the Site U1457 chapter [Pandey et al., 2016]). Site U1457 is located near the south coast of India, in the Laxmi Basin of the Arabian Sea. Yellow circles = sites drilled during Expedition 355, red stars = earlier scientific drilling sites, pink line = approximate extent of Indus Fan after Kolla and Coumes (1987), yellow dashed lines with question marks = the speculated locations of the continent/ocean boundary depending on whether Laxmi Basin is floored by oceanic or continental crust, gray lines with numbers = magnetic anomalies from Royer et al. (2002). Ba y o f B en ga l Arabian Sea axmi idge
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