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1. Data report: 87Sr/86Sr in pore fluids from IODP Expeditions 372 and 375, Hikurangi margin

   https://doi.org/10.14379/iodp.proc.372B375.202.2020  

   Ayres, C.; Torres, M.E.; Haley, B.; Luo, M. (March 2020, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   We report on the Sr isotopic compositions of pore fluids recovered during International Ocean Discovery Program (IODP) Expeditions 372 and 375. Pore fluid samples were acidified and loaded directly onto columns containing EICHROM Sr spec resin, followed by analyses using a NU multicollector inductively coupled plasma–mass spectrometer (MC-ICP-MS). The strontium systematics in this margin point to a series of processes that include carbonate diagenesis, ash alteration, and diffusive exchange with the underlying oceanic crust. The role of ash alteration is evidenced at all drilled sites by a decrease in the 87Sr/86Sr ratio in the upper 130 m of the sediment column to values as low as 0.70846. In the calcareous early Paleocene to late Miocene sediment from Site U1520, the pore fluid strontium concentration shows a marked increase to 1280 µM at 647.3 meters below seafloor (mbsf), but the corresponding 87Sr/86Sr ratios do not show a significant change is this unit. In the early Late Cretaceous sediment at this site, there is an increase in dissolved strontium concentration with a corresponding decrease in 87Sr/86Sr ratios to 0.706312 at the bottom of the cored section. 

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2. Data report: 87Sr/86Sr in pore fluids from Expedition 362

   https://doi.org/10.14379/iodp.proc.362.201.2019  

   McCarthy, M.; Zirkle, B.; Torres, M.E.; Haley, B.A. (January 2019, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   We report on the Sr isotopic composition of pore fluids recovered from Sites U1480 and U1481 drilled during International Ocean Discovery Program Expedition 362, which sampled the incoming sedimentary section of North Sumatra to investigate the causes of shallow seismogenesis in the Sumatra-Andaman margin. Sr isotope data are valuable in identifying diagenetic alteration of the incoming sequence, which can alter mechanical properties of the sedimentary wedge and subsequently affect its seismogenic behavior. Site U1480 recovered input sediment to ~1420 meters below seafloor (mbsf), and sediment was sampled from 1150 to 1500 mbsf at Site U1481. To determine the Sr isotopic composition, acidified pore fluid samples recovered at sea were loaded directly onto columns containing EICHROM Sr-Spec resin and followed by analyses using a NU multicollector inductively coupled plasma–mass spectrometer (MC-ICPMS). We observed a marked increase in 87Sr/86Sr ratios to 0.71376 in the Sr contribution from alteration of terrigenous material from the Bengal-Nicobar Fan. This trend is reversed in the deeper sequence, where 87Sr/86Sr ratios decrease to 0.70820 in the deepest sample analyzed (1300 mbsf). Only the deepest sediment was recovered at Site U1481, and the pore fluids also show a decrease in 87Sr/86Sr ratios from 0.71296 at 1172 mbsf to 0.70913 at 1495 mbsf. 

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3. Tracing the Environmental Effects of Mineral Fertilizer Application with Trace Elements and Strontium Isotope Variations

   https://doi.org/10.1021/acs.estlett.4c00170  

   Hill, Robert C; Williams, Gordon_D Z; Wang, Zhen; Hu, Jun; El-Hasan, Tayel; Duckworth, Owen W; Schnug, Ewald; Bol, Roland; Singh, Anjali; Vengosh, Avner (May 2024, Environmental Science & Technology Letters)

   Fertilizer utilization is critical for global food security. This study examines the occurrence of trace elements (TEs) and Sr isotope (87Sr/86Sr) variations in phosphate rocks and mineral fertilizers from a sample collection representative of major phosphate producing countries. We show high concentrations of several TEs in phosphate rocks (n=76) and their selective enrichment in phosphate fertilizers (n=40) of specific origin. Consistent with the concentrations in parent phosphate rocks, phosphate fertilizers from the U.S. and Middle East have substantially higher concentrations of U, Cd, Cr, V, and Mo than in fertilizers from China and India. Yet, fertilizers from China and India generally have higher concentrations of As. The 87Sr/86Sr in phosphate fertilizers directly mimic the composition of their source phosphate rocks, with distinctive higher ratios in fertilizers from China and India (0.70955–0.71939) relative to phosphate fertilizers from U.S. and Middle East (0.70748–0.70888). Potash fertilizers have lower Sr and TEs and higher 87Sr/86Sr (0.72017–0.79016), causing higher 87Sr/86Sr in mixed NPK-fertilizers. Selective extraction (Mehlich III) of soils from an experimental agricultural site shows relative enrichment of potentially plant-available P, Sr, and TEs in topsoil, which is associated with Sr isotope variation towards the 87Sr/86Sr of the local utilized phosphate fertilizer. 

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4. Reconstructing the depositional environment and diagenetic modification of global phosphate deposits through integration of uranium and strontium isotopes

   https://doi.org/10.1016/j.chemgeo.2024.122214  

   Hill, Robert C; Wang, Zhen; Williams, Gordon DZ; Polyak, Victor; Singh, Anjali; Kipp, Michael A; Asmerom, Yemane; Vengosh, Avner (September 2024, Chemical Geology)

   The geochemistry of phosphate rocks can provide valuable information on their depositional environment and the redox condition of global oceans through time. Here we examine trace metal concentrations and uranium (δ238U, δ234U) and strontium (87Sr/86Sr) isotope variations of marine sedimentary phosphate rocks and the phosphate-bearing carbonate fluorapatite (CFA) mineral phase, originating from Precambrian to mid-Miocene aged major global phosphate deposits. We find elevated concentrations of several trace elements (Al, V, Cr, Cd, U, Mn, Co, Cu, As, and Rb) in the CFA mineral phase of young phosphate rocks (Miocene to Late Cretaceous) relative to those of older (Devonian to Precambrian) rocks. The δ238U of phosphate rocks of Mid-Miocene to Permian age range from −0.311‰ to 0.070‰, exhibiting a positive fractionation relative to modern seawater (−0.38‰). This is similar to the isotope fractionation reported for carbonate and shale sediments, likely resulting from the reduction of uranium in porewaters during CFA precipitation. Cambrian to Precambrian phosphate rocks have lower δ238U of −0.583‰ to −0.363‰, indicating different depositional redox conditions likely resulting from seafloor anoxia and/or diagenetic modification. The 87Sr/86Sr ratios of phosphate rocks of Cretaceous to Mid-Miocene age generally follow the secular 87Sr/86Sr seawater curve. Phosphate rocks with 87Sr/86Sr that deviate from this curve have characteristic trace metal trends, such as lower Sr/Ca and Sr concentrations, suggesting later diagenetic modification. Older phosphate rocks of Precambrian age are systematically more radiogenic than the expected secular Sr seawater composition at the time of deposition, possibly due to the greater influence of terrestrial input in peritidal zones and/or more pervasive diagenetic modification. Overall, our study reveals connections between U and Sr isotope variations for reconstructing the depositional and diagenetic conditions of global phosphate rock formation through Earth history and the transition to an oxic ocean following the Paleozoic Oxygenation Event. 

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5. Expedition 355 summary

   https://doi.org/10.14379/iodp.proc.355.101.2016  

   Pandey, DK; Clift, PD; Kulhanek, DK; Andò, S; Bendle, JAP; Bratenkov, S; Griffith, EM; Gurumurthy, GP; Hahn, A; Iwai, M; et al (August 2016, Proceedings of the International Ocean Discovery Program Expedition reports)

   The Indian (southwest) summer monsoon is one of the most intense climatic phenomena on Earth, with its long-term development possibly linked to the growth of high topography in South and Central Asia. The Indian continental margin, adjoining the Arabian Sea, offers a unique opportunity to investigate tectonic–climatic interactions and the net impact of these processes on weathering and erosion of the western Himalaya. During International Ocean Discovery Program Expedition 355, two sites (U1456 and U1457) were drilled in Laxmi Basin in the eastern Arabian Sea to document the coevolution of mountain building, weathering, erosion, and climate over a range of timescales. In addition, recovering basement from the eastern Arabian Sea provides constraints on the early rifting history of the western continental margin of India with special emphasis on continental breakup between India and the Seychelles and its relationship to the plume-related volcanism of the Deccan Plateau. Drilling and coring operations during Expedition 355 recovered sediment from Sites U1456 and U1457 in Laxmi Basin, penetrating 1109.4 and 1108.6 m below seafloor (mbsf), respectively. Drilling reached sediment dated to 13.5–17.7 Ma (late early to early middle Miocene) at Site U1456, although with a large hiatus between the lowermost sediment and overlying deposits dated at <10.9 Ma. At Site U1457, a much longer hiatus occurs near the base of the cored section, spanning from ~10.9 to ~62 Ma. At both sites, hiatuses span ~8.2–9.2 and ~3.6–5.6 Ma with a possible condensed section spanning ~2.0–2.6 Ma, although the total duration for each hiatus is slightly different between the two sites. A major submarine fan probably draining the western Himalaya and Karakoram must have been supplying sediment to the eastern Arabian Sea since at least ~17 Ma. Sand mineral assemblages indicate that the Greater Himalayan Crystalline Sequence was fully exposed to the surface by this time. Most of the recovered sediment appears to be derived from the Indus River and includes minerals that are unique to the Indus Suture Zone, in particular glaucophane and hypersthene, most likely originating from the structural base of the Kohistan arc (i.e., within the Indus Suture Zone). Pliocene sandy intervals at Site U1456 were deposited in lower fan “sheet lobe” settings, with intervals of basin–plain turbidites separated by hemipelagic muddy sections deposited during the Miocene. Site U1457 is more distal in facies, reflecting its more marginal setting. No major active lobe appears to have affected Laxmi Basin since the late early Pleistocene (~1.2–1.5 Ma). We succeeded in recovering sections spanning the 8 Ma climatic transition, when monsoon intensity is believed to have changed strongly, although the nature of this change awaits postcruise analysis. We also recovered sediment from large mass transport deposits measuring ~330 and ~190 m thick at Sites U1456 and U1457, respectively. These sections include an upper sequence of slump-folded muddy and silty rocks, as well as underlying calcarenites and limestone breccias, together with smaller amounts of volcanic clasts, all of which are likely derived from the western Indian continental shelf. Identification of similar facies on the regional seismic lines in Laxmi Basin suggests that these deposits form parts of one of the world’s largest mass transport deposits. Coring of igneous basement was achieved at Site U1457. Recovery of massive basalt and associated volcaniclastic sediment at this site should address the key questions related to rifting and volcanism associated with formation of Laxmi Basin. Geochemical analysis indicates that these are low-K, high-Mg subalkaline tholeiitic basalts and do not represent a typical mid-ocean-ridge basalt. Other observations made at the two sites during Expedition 355 provide vital constraints on the rift history of this margin. Heat flow measurements at the two drill sites were calculated to be ~57 and ~60 mW/m2. Such heat flow values are compatible with those observed in average oceanic crust of 63–84 Ma age, as well as with the presence of highly extended continental crust. Postcruise analyses of the more than ~1722 m of core will provide further information about the nature of tectonic–climatic interactions in this global type area for such studies. 

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