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1. Data report: clay mineral assemblages within biocalcareous and volcaniclastic inputs to the Hikurangi subduction zone, IODP Expedition 372B/375 Sites U1520 and U1526, offshore New Zealand

   https://doi.org/10.14379/iodp.proc.372B375.207.2021  

   Underwood, M.B. (October 2021, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   Inputs to the Hikurangi subduction zone, offshore North Island, New Zealand, include volcaniclastic conglomerates that were deposited during the Late Cretaceous on the flanks of the subducting basement of Hikurangi Plateau. The overlying succession of pelagic carbonates is early Paleocene to early Pleistocene in age and ranges in composition from calcareous mudstone to muddy chalk and chalk. A thick wedge of Quaternary trench sediments occupies the top of the stratigraphic succession. International Ocean Discovery Program Expedition 375 cored those subduction inputs at two sites. Site U1520 is located on the distal edge of the trench, and Site U1526 is located near the crest of Tūranganui Knoll, where a highly condensed section of pelagic-hemipelagic sediment covers the basalt basement. This report provides the results of 128 X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical settling equivalent), where smectite + illite + undifferentiated (chlorite + kaolinite) + quartz = 100%. Clay minerals in the altered volcaniclastic conglomerates and basalt consist almost exclusively of smectite. At Site U1520, the normalized abundance of smectite in overlying biocalcareous sediments ranges from 28.3 to 72.9 wt% (mean = 54.2 wt%), whereas the abundance of illite ranges from 16.1 to 49.0 wt% (mean = 32.0 wt%). The range for undifferentiated chlorite + kaolinite is 0.3–17.8 wt% (mean = 7.4 wt%), and the range for clay-sized quartz is 2.7–20.5 wt% (mean = 6.4 wt%). Upsection depletion of smectite in those sediments is balanced by upsection enrichment of illite. That same age-dependent trend is evident in coeval biocalcareous drift sediments from Ocean Drilling Program Sites 1123 (North Chatham drift) and 1124 (Rekohu drift). Moving downsection at Site U1520, indicators of clay diagenesis are inconsistent. Values of illite crystallinity index increase (i.e., peak broadening), whereas the proportion of illite within illite/smectite mixed-layer clays increases with depth. 

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2. Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy

   https://doi.org/10.3390/min13070889  

   Varner, Thomas S.; Kulkarni, Harshad V.; Bhuiyan, Mesbah Uddin; Cardenas, M. Bayani; Knappett, Peter S.; Datta, Saugata (July 2023, Minerals)

   Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained deposits that are rich in organic matter (OM), clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a useful indicator of pore water As concentrations. The pore waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment were extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment collected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concentrations of sedimentary As and Fe were measured by X-ray fluorescence, and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treatment, sediment samples were placed in a preheated furnace at 600 °C for 3 h. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change in color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicate that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40%, whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals. 

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3. Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treat-ment and Spectroscopy

   Thomas S. Varner, Harshad V. (September 2023, Minerals)

   Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained de-posits rich in organic matter, clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a use-ful indicator of pore-water As concentrations. The pore-waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment have been extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment col-lected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concen-trations of sedimentary As and Fe were measured by X-Ray Fluorescence and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treat-ment, sediment samples were placed in a preheated furnace at 600C for 3 hours. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change of color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicat-ed that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40% whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals. 

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4. Data report: clay mineral assemblages in hemipelagic sediments entering the Sumatra subduction zone, IODP Sites U1480 and U1481, Expedition 362

   https://doi.org/10.14379/iodp.proc.362.204.2020  

   Rosenberger, K.; Underwood, M.B.; Vrolijk, P.; Haines, S. (July 2020, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   This report documents the results of X-ray diffraction analyses of 132 mud and mudstone samples collected offshore Sumatra during International Ocean Discovery Program Expedition 362. The clay-size mineral assemblage consists of smectite, illite, chlorite, kaolinite, and quartz. The relative abundance of smectite at Site U1480 decreases downsection from a mean value of 33 wt% in Unit I to a mean of 19 wt% in Unit II; illite increases from a mean of 49 wt% to a mean of 59 wt%. Smectite in Unit III increases to a mean of 73 wt%, and illite decreases to a mean of 19 wt%. Mean values are subordinate (<16 wt%) for undifferentiated chlorite + kaolinite and <7 wt% for quartz in all units. A significant compositional discrepancy occurs between Subunit IIIA at Site U1480 (mean smectite = 64 wt%) and Unit III at Site U1481 (mean smectite = 36 wt%). At Site U1480, the expandability of illite/smectite mixed-layer clays increases downsection, which is opposite to the trend expected with burial diagenesis. The maximum value is 88% within smectite-rich samples from Unit III. Values of the illite crystallinity index are between 0.42Δ°2θ and 0.76Δ°2θ, with most data straddling the generic boundary between advanced diagenesis and anchimetamorphism. Illite (060) reflections yield bo values of 8.988 to 9.000, which are indicative of low phengite contents. Smectite (060) reflections display peak apex positions of 61.998°–61.798°2θ, which are consistent with the mineral structure of montmorillonite. The detrital illite fraction contains 46%–60% 2M1 polytype, and the remainder is 1M/1Md. 

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5. Data for "Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy"

   https://doi.org/10.4211/hs.f78bac856a1c420b924a9582b1a4ff8e  

   Varner, Thomas; Kulkarni, Harshad; Bhuiyan, Mesbah; Cardenas, M; Knappett, Peter; Datta, Saugata (May 2024, HydroShare)

   This repository contains all the sediment and experimental data used in this study. Study Abstract Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained deposits that are rich in organic matter (OM), clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a useful indicator of pore water As concentrations. The pore waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment were extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment collected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concentrations of sedimentary As and Fe were measured by X-ray fluorescence, and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treatment, sediment samples were placed in a preheated furnace at 600 °C for 3 h. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change in color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicate that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40%, whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals. 

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