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Showing papers by "ExxonMobil published in 2019"


Journal ArticleDOI
TL;DR: This paper provides an introduction to Reinforcement Learning technology, summarizes recent developments in this area, and discusses their potential implications for the field of process control, and more generally, of operational decision-making.

171 citations


Journal ArticleDOI
TL;DR: It is demonstrated that this reaction is catalyzed by a [Cu-O-Cu]2+ motif that forms via a hypothesized proton-aided diffusion of hydrated Cu ions within the cages of SSZ-13 zeolites, the primary active site for selective partial methane oxidation.
Abstract: Copper-exchanged zeolites can continuously and selectively catalyze the partial oxidation of methane to methanol using only oxygen and water at low temperatures, but the genesis and nature of the active sites are currently unknown. Herein, we demonstrate that this reaction is catalyzed by a [Cu-O-Cu]2+ motif that forms via a hypothesized proton-aided diffusion of hydrated Cu ions within the cages of SSZ-13 zeolites. While various Cu configurations may be present and active for methane oxidation, a dimeric Cu motif is the primary active site for selective partial methane oxidation. Mechanistically, CH4 activation proceeds via rate-determining C-H scission to form a surface-bound C1 intermediate that can either be desorbed as methanol in the presence of H2O/H+ or completely oxidized to CO2 by gas-phase O2. High partial oxidation selectivity can be obtained with (i) high methane and water partial pressures and (ii) maximizing Cu dimer formation by using zeolites with high Al content and low Cu loadings.

158 citations


Journal ArticleDOI
01 Apr 2019
TL;DR: In this article, the authors provide a framework for understanding how to convert ethanol into distillate-range molecules and the key research problems to be addressed, including thermodynamics, kinetics, process integration and catalyst development.
Abstract: Ethanol is presently the most common liquid fuel derived from biomass. One way of meeting the growing demand for heavier middle-distillate fuels — diesel and jet fuels comprising hydrocarbons of typically 8–22 carbon atoms — is to derive these from ethanol. This Review describes the chemistries and processes involved in the conversion of ethanol into diesel and jet fuel drop-in replacements and blendstocks. This conversion of ethanol relies on reactions including dehydration (to olefins), dehydrogenation (to aldehydes), hydrogenation (of C=C and C=O bonds), acid-catalysed olefin oligomerization, metal-catalysed olefin oligomerization, aldolization and ketonization. We discuss the thermodynamics, kinetics, process integration and catalyst development of different approaches. Some routes, particularly those based on olefin oligomerization, have been realized on the pilot scale. Other routes are currently in laboratory stages. This Review provides a framework for understanding how to convert ethanol into distillate-range molecules and the key research problems to be addressed. Ethanol has emerged as a potential alternative feedstock for the synthesis of middle-distillate transportation fuels. This Review describes the chemistry of ethanol-to-distillate processes and challenges associated with improving current technologies and implementing new ones.

108 citations


Journal ArticleDOI
TL;DR: The importance of considering gas-fired power plants alongside coal-fired plants in future analyses of carbon capture materials is emphasized, and specific challenges and opportunities related to adsorptive carbon capture from the emissions of gas- Fired plants are addressed.
Abstract: In recent years, the power sector has shown a growing reliance on natural gas, a cleaner-burning fuel than coal that emits approximately half as much CO2 per kWh of energy produced. This rapid growth in the consumption of natural gas has led to increased CO2 emissions from gas-fired power plants. To limit the contribution of fossil fuel combustion to atmospheric CO2 levels, carbon capture and sequestration has been proposed as a potential emission mitigation strategy. However, despite extensive exploration of solid adsorbents for CO2 capture, few studies have examined the performance of adsorbents in post-combustion capture processes specific to natural gas flue emissions. In this perspective, we emphasize the importance of considering gas-fired power plants alongside coal-fired plants in future analyses of carbon capture materials. We address specific challenges and opportunities related to adsorptive carbon capture from the emissions of gas-fired plants and discuss several promising candidate materials. Finally, we suggest experiments to determine the viability of new CO2 capture materials for this separation. This broadening in the scope of current carbon capture research is urgently needed to accelerate the deployment of transformational carbon capture technologies.

96 citations


Journal ArticleDOI
01 Aug 2019-Energy
TL;DR: In this article, the authors used several renewable energy penetration scenarios to determine when an electric grid might be more vulnerable to frequency contingencies, such as a generator outage, and used unit commitment and dispatch modeling to quantify system inertia.

86 citations


Journal ArticleDOI
TL;DR: The work presented here moves for-ward design principles for amidoxime-functionalized ligands and provides scope for strategies to enhance the capture of uranium as a sustainable nuclear fuel source.
Abstract: To move nuclear as a primary energy source, uranium resources must be secured beyond what terrestrial reserves can provide. Given the vast quantity of uranium naturally found in the ocean, adsorbent materials have been investigated to recover this vital fuel source. Amidoxime (AO) has been found to be the state-of-the-art functional group for this purpose, however, improvements must still be made to overcome the issues with selectively capturing uranium at such a low concentration found in the ocean. Herein, we report PAF-1 as a platform to study the effects of two amidoxime ligands. The synthesized adsorbents, PAF-1-CH2NHAO and PAF-1-NH(CH2)2AO, with varying chain lengths and grafting degrees, were investigated for their uranium uptakes and kinetic efficiency. PAF-1-NH(CH2)2AO was found to outperform PAF-1-CH2NHAO, with a maximum uptake capacity of 385 mg/g and able to reduce a uranium-spiked solution to ppb level within 10 min. Further studies with PAF-1-NH(CH2)2AO demonstrated effective elution for multiple adsorption cycles and showed promising results for uranium recovery in the diverse composition of a spiked seawater solution. The work presented here moves forward design principles for amidoxime-functionalized ligands and provides scope for strategies to enhance the capture of uranium as a sustainable nuclear fuel source.

83 citations


Journal ArticleDOI
TL;DR: It is demonstrated that functionalization of the metal-organic framework Mg2(dobpdc) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO2 capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements.
Abstract: Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO2 emissions. However, the separation of CO2 from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO2 partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO2 strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO2. High partial pressures of O2 (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO2 capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO2 capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO2 by a cooperative mechanism that enables access to a large CO2 cycling capacity with a small temperature swing (2.4 mmol CO2/g with ΔT = 100 °C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO2 capture in 2-ampd-Mg2(dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO2 adsorption, thereby increasing the thermodynamic driving force for CO2 binding. In light of the exceptional thermal and oxidative stability of 2-ampd-Mg2(dobpdc), its high CO2 adsorption capacity, and its high CO2 capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation.

82 citations


Journal ArticleDOI
TL;DR: It is found that ecosystem functions and services increase with the age of the structure and vary with geographical setting, such that decommissioning decisions need to take an ecosystem approach that considers their broader habitat and biodiversity values.

66 citations


Journal ArticleDOI
TL;DR: Multistakeholder consensus was obtained that it is unlikely that the presence of microplastic in the environment currently represents a risk, which implies that research that directly addresses the development and application of methods that strengthen the quality of data should be given the highest priority.
Abstract: Emissions of plastic waste to the environment and the subsequent degradation into microplastic particles that have the potential to interact with biological organisms represent a concern for global society. Current understanding of the potential impacts on aquatic and terrestrial population stability and ecosystem structure and function associated with emissions of microplastic particles is limited and insufficient to fully assess environmental risks. Multistakeholder discussions can provide an important element in helping to identify and prioritize key knowledge gaps in assessing potential risks. In the present review, we summarize multistakeholder discussions from a 1-d International Council of Chemical Associations-sponsored symposium, which involved 39 scientists from 8 countries with representatives from academia, industry, and government. Participants were asked to consider the following: discuss the scientific merits and limitations of applying a proposed conceptual environmental risk assessment (ERA) framework for microplastic particles and identify and prioritize major research needs in applying ERA tools for microplastic particles. Multistakeholder consensus was obtained with respect to the interpretation of the current state of the science related to effects and exposure to microplastic particles, which implies that it is unlikely that the presence of microplastic in the environment currently represents a risk. However, the quality and quantity of existing data require substantial improvement before conclusions regarding the potential risks and impacts of microplastic particles can be fully assessed. Research that directly addresses the development and application of methods that strengthen the quality of data should thus be given the highest priority. Activities aimed at supporting the development of and access to standardized reference material were identified as a key research need. Environ Toxicol Chem 2019;38:2087-2100. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

61 citations


Journal ArticleDOI
TL;DR: This critical review evaluated SQGs for use in screening‐level risk assessments to identify sediments that may pose a risk to the benthic community and recommended the use of SQGs in screening evaluations and enhancements to current approaches.
Abstract: Polycyclic aromatic hydrocarbons (PAHs) in sediments can pose harm to the benthic community. Numerous sediment quality guidelines (SQGs) for the protection of benthic life are available to assess the risk of individual PAHs and PAH mixtures in sediments. Sediment quality guidelines are derived using empirical or mechanistic approaches. Empirically based guidelines are derived using databases of paired sediment chemistry and biological responses and relating sediment concentration to the frequency of an adverse response. Mechanistically based SQGs are derived by considering the inherent aqueous toxicity of the chemical to different biota coupled with site-specific sediment characteristics (i.e., organic C) known to influence PAH bioavailability. Additionally, SQGs are derived to be either protective or predictive of adverse effects in benthic organisms. The objective of this critical review was to evaluate SQGs for use in screening-level risk assessments to identify sediments that may pose a risk to the benthic community. SQGs for PAHs were compiled and compared, and performance evaluated for predicting the presence and absence of toxicity using an extensive field data set. Furthermore, a 2-carbon equilibrium partitioning model and direct measurement of porewater via passive sampling were evaluated for improved performance in higher tiered risk assessments. Recommendations for the use of SQGs in screening evaluations, enhancements to current approaches, and opportunities to refine site risk estimate assessments using passive sampling measurements are discussed. Integr Environ Assess Manag 2019;15:505-518. © 2019 SETAC.

59 citations


Journal ArticleDOI
TL;DR: In this article, a copper porous metal oxide catalyst was used for supercritical methanol depolymerization and hydrodeoxygenation (SCM-DHDO) of maple wood and lignin extracted with GVL from maple wood.

Journal ArticleDOI
TL;DR: In this article, the authors examined the potential for global detection of methane plumes from individual point sources with the new generation of spaceborne imaging spectrometers (EnMAP, PRISMA, EMIT, SBG, CHIME) scheduled for launch in 2019-2025.
Abstract: . We examine the potential for global detection of methane plumes from individual point sources with the new generation of spaceborne imaging spectrometers (EnMAP, PRISMA, EMIT, SBG, CHIME) scheduled for launch in 2019–2025. These instruments are designed to map the Earth's surface at high spatial resolution ( 30 m×30 m ) and have a spectral resolution of 7–10 nm in the 2200–2400 nm band that should also allow useful detection of atmospheric methane. We simulate scenes viewed by EnMAP (10 nm spectral resolution, 180 signal-to-noise ratio) using the EnMAP end-to-end simulation tool with superimposed methane plumes generated by large-eddy simulations. We retrieve atmospheric methane and surface reflectivity for these scenes using the IMAP-DOAS optimal estimation algorithm. We find an EnMAP precision of 3 %–7 % for atmospheric methane depending on surface type. This allows effective single-pass detection of methane point sources as small as 100 kg h −1 depending on surface brightness, surface homogeneity, and wind speed. Successful retrievals over very heterogeneous surfaces such as an urban mosaic require finer spectral resolution. We tested the EnMAP capability with actual plume observations over oil/gas fields in California from the Airborne Visible/Infrared Imaging Spectrometer – Next Generation (AVIRIS-NG) sensor ( 3 m×3 m pixel resolution, 5 nm spectral resolution, SNR 200–400), by spectrally and spatially downsampling the AVIRIS-NG data to match EnMAP instrument specifications. Results confirm that EnMAP can successfully detect point sources of ∼100 kg h −1 over bright surfaces. Source rates inferred with a generic integrated mass enhancement (IME) algorithm were lower for EnMAP than for AVIRIS-NG. Better agreement may be achieved with a more customized IME algorithm. Our results suggest that imaging spectrometers in space could play an important role in the future for quantifying methane emissions from point sources worldwide.

Journal ArticleDOI
TL;DR: It is found that the cellulose-degrading anaerobe Clostridium cellulolyticum exhibits slow, near-equilibrium glycolysis due to the use of pyrophosphate rather than ATP for fructose-bisphosphate production, resulting in enhanced per-glucose ATP yield.
Abstract: Glycolysis plays a central role in producing ATP and biomass. Its control principles, however, remain incompletely understood. Here, we develop a method that combines 2H and 13C tracers to determine glycolytic thermodynamics. Using this method, we show that, in conditions and organisms with relatively slow fluxes, multiple steps in glycolysis are near to equilibrium, reflecting spare enzyme capacity. In Escherichia coli, nitrogen or phosphorus upshift rapidly increases the thermodynamic driving force, deploying the spare enzyme capacity to increase flux. Similarly, respiration inhibition in mammalian cells rapidly increases both glycolytic flux and the thermodynamic driving force. The thermodynamic shift allows flux to increase with only small metabolite concentration changes. Finally, we find that the cellulose-degrading anaerobe Clostridium cellulolyticum exhibits slow, near-equilibrium glycolysis due to the use of pyrophosphate rather than ATP for fructose-bisphosphate production, resulting in enhanced per-glucose ATP yield. Thus, near-equilibrium steps of glycolysis promote both rapid flux adaptation and energy efficiency.

Journal ArticleDOI
TL;DR: The Geological Orrery is a network of geological records of orbitally paced climate designed to address the inherent limitations of solutions for planetary orbits beyond 60 million years ago and lays out an empirical framework to map the chaotic evolution of the Solar System.
Abstract: The Geological Orrery is a network of geological records of orbitally paced climate designed to address the inherent limitations of solutions for planetary orbits beyond 60 million years ago due to the chaotic nature of Solar System motion. We use results from two scientific coring experiments in Early Mesozoic continental strata: the Newark Basin Coring Project and the Colorado Plateau Coring Project. We precisely and accurately resolve the secular fundamental frequencies of precession of perihelion of the inner planets and Jupiter for the Late Triassic and Early Jurassic epochs (223-199 million years ago) using the lacustrine record of orbital pacing tuned only to one frequency (1/405,000 years) as a geological interferometer. Excepting Jupiter's, these frequencies differ significantly from present values as determined using three independent techniques yielding practically the same results. Estimates for the precession of perihelion of the inner planets are robust, reflecting a zircon U-Pb-based age model and internal checks based on the overdetermined origins of the geologically measured frequencies. Furthermore, although not indicative of a correct solution, one numerical solution closely matches the Geological Orrery, with a very low probability of being due to chance. To determine the secular fundamental frequencies of the precession of the nodes of the planets and the important secular resonances with the precession of perihelion, a contemporaneous high-latitude geological archive recording obliquity pacing of climate is needed. These results form a proof of concept of the Geological Orrery and lay out an empirical framework to map the chaotic evolution of the Solar System.


Journal ArticleDOI
TL;DR: In this paper, the authors studied the rheology of powder incorporation in the conching of chocolate, and found that the input of mechanical energy and staged addition of surfactants combine to increase the jamming volume fraction of the system, thus increasing the maximum flowable solid content.
Abstract: The mixing of a powder of 10- to 50-μm primary particles into a liquid to form a dispersion with the highest possible solid content is a common industrial operation. Building on recent advances in the rheology of such “granular dispersions,” we study a paradigmatic example of such powder incorporation: the conching of chocolate, in which a homogeneous, flowing suspension is prepared from an inhomogeneous mixture of particulates, triglyceride oil, and dispersants. Studying the rheology of a simplified formulation, we find that the input of mechanical energy and staged addition of surfactants combine to effect a considerable shift in the jamming volume fraction of the system, thus increasing the maximum flowable solid content. We discuss the possible microscopic origins of this shift, and suggest that chocolate conching exemplifies a ubiquitous class of powder–liquid mixing.

Journal ArticleDOI
TL;DR: In this paper, two field examples from the Alpine Tethys margins in the Eastern and Southern Alps (SE Switzerland and N Italy) were selected to characterize: (1) the pre-rift architecture of the continental lithosphere, (2) the localization of rift-related deformation in distinct portions of the lithosphere; and (3) the interaction between pre-existing mechanical heterogeneities representing the initial prerift architecture.

Journal ArticleDOI
TL;DR: Model results suggest that knowledge of droplet sizes and improved estimation of pseudo-component biodegradation rates and lag times would enhance prediction of the fate and transport of subsurface oil.

Journal ArticleDOI
TL;DR: In this paper, the authors reported the analysis of heavy mineral populations and the ages of detrital zircons from Gondwana diamictite deposits from eight landmasses: Africa (5 samples), Antarctica (5), Australia (8), the Ellsworth Mountains terrane (1, Antarctica), the Falkland Islands (2, diamictites plus U-Pb SHRIMP ages on granite clasts), India (1), Madagascar (1).

Journal ArticleDOI
TL;DR: Evidence is found that one or a few β hydrogens are present in petroporphyrins of low carbon numbers using a combination of ultraviolet–visible spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and non-contact atomic force microscopy.
Abstract: Determination of the molecular structures of petroporphyrins has been crucial to understand the diagenetic pathways and maturation of petroleum. However, these studies have been hampered by their s...

Journal ArticleDOI
12 Jul 2019-Science
TL;DR: This work controlled the charge state of organic molecules and resolved their structures in neutral, cationic, anionic, and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using carbon monoxide–functionalized tips.
Abstract: The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity, and aromaticity, with implications for on-surface synthesis, catalysis, photoconversion, and applications in molecular electronics. On insulating, multilayer sodium chloride (NaCl) films, we controlled the charge state of organic molecules and resolved their structures in neutral, cationic, anionic, and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using carbon monoxide (CO)–functionalized tips. We detected changes in conformation, adsorption geometry, and bond-order relations for azobenzene, tetracyanoquinodimethane, and pentacene in multiple charge states. Moreover, for porphine, we investigate the charge state–dependent change of aromaticity and conjugation pathway in the macrocycle. This work opens the way to studying chemical-structural changes of individual molecules for a wide range of charge states.

Journal ArticleDOI
TL;DR: In this article, it is shown that Heteroatoms are essential for functional groups in organic structures and are complementary to hydrocarbon molecules in reactivities and properties, but it is still a challenge to quickly iden...
Abstract: Heteroatoms are essential for functional groups in organic structures and are complementary to hydrocarbon molecules in reactivities and properties. However, it is still a challenge to quickly iden...

Posted ContentDOI
TL;DR: In this article, the charge state of a molecule governs its physicochemical properties, such as conformation, reactivity and aromaticity, with implications for on-surface synthesis, catalysis, photo conversion and applications in molecular electronics.
Abstract: The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity and aromaticity, with implications for on-surface synthesis, catalysis, photo conversion and applications in molecular electronics. On insulating, multilayer NaCl films we control the charge state of organic molecules and resolve their structures in neutral, cationic, anionic and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using CO functionalized tips. We detect changes in conformation, adsorption geometry and bond-order relations for azobenzene, tetracyanoquinodimethane and pentacene in multiple charge states. Moreover, for porphine we investigate the charge-state-dependent change of aromaticity and conjugation pathway in the macrocycle. This work opens the way to studying chemical-structural changes of individual molecules for a wide range of charge states.

Proceedings ArticleDOI
15 Sep 2019
TL;DR: This paper presents a novel Neural Architecture Search (NAS) framework to improve keyword spotting and spoken language identification models and demonstrates that this approach can automatically design DNNs with an order of magnitude fewer parameters that achieves better performance than the current best models.
Abstract: In this paper we present a novel Neural Architecture Search (NAS) framework to improve keyword spotting and spoken language identification models. Even with the huge success of deep neural networks (DNNs) in many different domains, finding the best network architecture is still a laborious task and very computationally expensive at best with existing searching approaches. Our search approach efficiently and robustly finds better model sequences with respect to hand-designed systems. We do this by constructing architectures incrementally, using a custom mutation algorithm and leveraging the power of parameter transfer between layers. We demonstrate that our approach can automatically design DNNs with an order of magnitude fewer parameters that achieves better performance than the current best models. It leads to significant performance improvements: up to 4.09% accuracy increase for language identification (6.1% if we allow an increase in the number of parameters) and 0.3% for phoneme classification in keyword spotting with half the size of the model.

Journal ArticleDOI
TL;DR: A method for modeling the economic competition between different advanced technologies in multi-region multi-sector dynamic energy-economic models based on a markup approach, which represents the measure of the cost of a technology relative to the price received for electricity generation.

Journal ArticleDOI
01 Jun 2019-Geology
TL;DR: Fildani et al. as discussed by the authors used the U-Pb detrital zircon (DZ) geochronology from the Pleistocene Amazon submarine fan (n = 1352 grains), integrated with on-shore DZ age data, to propose a sedimentary model for sea level-modulated and hydroclimate-modified sediment transfer in Earth's largest source-to-sink system.
Abstract: We use new U-Pb detrital zircon (DZ) geochronology from the Pleistocene Amazon submarine fan (n = 1352 grains), integrated with onshore DZ age data, to propose a sedimentary model for sea level–modulated and hydroclimate-modulated sediment transfer in Earth’s largest source-to-sink system. DZ ages from the modern Amazon River sediment display a progressive downstream dilution by older cratonic zircons, leading to the expectation of a submarine fan with high proportions of craton-derived sediment. Our new DZ age data from the submarine fan and mixture modeling suggest that higher proportions of sediment were supplied from the distant central Andes to the Amazon fan during the last two glacioeustatic lowstands, and thus the observed DZ age spectra of the modern lower Amazon River indicate a relative increase in craton-derived sediment during the Holocene. We interpret that during interglacials, when sea level was high and the submarine fan inactive, the lower Amazon River did not efficiently transfer sand-sized sediment to the margin and thus became enriched in craton-derived sediment. During sea-level lowstands, increased gradients and incision in the lower Amazon River due to base-level lowering resulted in enhanced connectivity and transfer of Andes-sourced zircons to the deep sea. These results are also consistent with interpreted patterns of Andean-Amazon hydroclimate anti-phasing (enhanced precipitation in the central Andes and increased aridity in the northern Amazon Basin) during the Last Glacial Maximum. Our results suggest that sand-sized sediment in the Amazon submarine fan records multi-millennial patterns of sea level and South American hydroclimate. INTRODUCTION The dynamics of fluvial to deep-sea sediment transfer in response to climate and sea-level fluctuations over multi-millennial time scales is complex and nonlinear (Blum and Törnqvist, 2000; Clift, 2006; Blum and Hattier-Womack, 2009). Early research on major fluvial systems focused on the role of base level (Vail et al., 1977) in the context of climate change (Fisk, 1944), while subsequent research modified conceptual models in recognition of the influence of upstream climate-modulated sediment supply and hydrology (Saucier, 1996). Other studies have considered the controls on the timing of submarine fan activity (Covault and Graham, 2010; Maslin, 2009), sediment caliber and volumes delivered to submarine fans (Sweet and Blum, 2016), as well as sediment exhumation and transit rates and the role of river avulsions in sediment transfer to the deep sea (Blum et al., 2018). Provenance techniques applied to major river–to–submarine fan systems are a valuable tool to improve models for the controls on source-to-sink sediment routing system behavior over multi-millennial time scales (Fildani et al., 2018). The Amazon River and deep-sea fan represent a globally important end-member system for understanding land-to-sea sediment dynamics. Submarine fans have been shown to archive histories of output fluxes and onshore environmental change (Normark and Reid, 2003; Fildani et al., 2016; Hessler et al., 2018), and have been used to invert up-system climate forcings in glaciated continent-scale rivers (Clift et al., 2008; Fildani et al., 2016, 2018; Mason et al., 2017; Li et al., 2019). The Amazon catchment straddles equatorial latitudes and has distinct sediment and detrital zircon (DZ) source terranes and physiography (Fig. 1), and the modern fluvial system is characterized by published DZ U-Pb data (Fig. 1B) (Campbell and Allen, 2008; Mapes, 2009; Pepper et al., 2016). We present 1352 new U-Pb DZ ages from 10 samples from cores recovered in the deep-sea Amazon Fan (Sites 936, 945, 946) during Ocean Drilling Program (ODP) Leg 155 (Flood et al., 1995). We integrate our data and results with published U-Pb DZ data from the modern onshore Amazon fluvial system and perform mixture modeling of DZ age spectra to elucidate effects of changing sea level and hydroclimate on temporal patterns of sediment provenance over multi-millennial time scales (marine isotope stages 6–2; MIS 6–MIS 2) within Earth’s largest fluvial to deep-sea sediment routing system. THE AMAZON SOURCETO-SINK SYSTEM The Amazon River represents Earth’s largest freshwater discharge to the ocean (15%–20% of global total) and largest total sediment load (~1200 Mt/yr), and is the largest fluvial system in terms of drainage basin area (~7 × 106 km2) (Milliman and Farnsworth, 2011). Amazon Basin hydroclimate controls water and sediment discharge to the sea and is influenced by the South American monsoon system and the locations of the Intertropical Convergence Zone and South Atlantic Convergence Zone (Novello et al., 2017). Hydroclimate in the central and northern Amazon Basin was overall more arid during the Last Glacial Maximum (LGM) (Häggi et al., 2017), while precipitation increased for the central Andes and the southeastern Amazon craton (Cheng et al., 2013; Baker and Fritz, 2015). Amazon floodplain incision during the LGM significantly altered the eleCITATION: Mason, C.C., et al., 2019, Detrital zircons reveal sea-level and hydroclimate controls on Amazon River to deep-sea fan sediment transfer: Geology, v. 47, p. 1–5, https:// doi .org /10 .1130 /G45852.1 Manuscript received 12 November 2018 Revised manuscript received 2 March 2019 Manuscript accepted 31 March 2019 https://doi.org/10.1130/G45852.1 © 2019 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online XX Month 2019 Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G45852.1/4678806/g45852.pdf by Univ West Georgia user on 17 April 2019 2 www.gsapubs.org | Volume 47 | Number 6 | GEOLOGY | Geological Society of America vation and slope of the river bed in the lower Amazon River (i.e., from ~0.7 to ~7 cm/km) (Mertes and Dunne, 2007). The degree of upstream propagation of incision is uncertain, but may have influenced bed elevations as far as 1700 km from the modern coast (Mertes and Dunne, 2007). The Amazon submarine fan is a late Miocene through Pleistocene accumulation of mainly terrigenous siliciclastic sediment as much as 4–5 km thick (Figueiredo et al., 2009). During highstands, coarse-grained sediment is deposited and stored in floodplains in the lower Amazon River valley and on the shallow continental shelf. When sea levels fall by >40 m relative to Holocene sea level, river water and sediment is transferred across the continental shelf and through the Amazon canyon to the submarine fan (Damuth et al., 1995). The modern onshore Amazon system is partially constrained by existing detrital geochronology (Figs. 1A and 1B) (Campbell and Allen, 2008; Mapes, 2009; Pepper et al., 2016). DZ age data from the Solimões (upper Amazon) and lower Amazon Rivers (Fig. 1A) display a progressive dilution of young zircon age modes (<1.3 Ga) by older craton age modes (Fig. 1B). Given the observed pattern of downstream dilution by cratonic zircon sources, we might expect a submarine fan enriched in a cratonic DZ signature. METHODS AND RESULTS We collected 10 samples of fineto mediumgrained sand from turbidite beds in cores recovered during ODP Leg 155 (Flood et al., 1995), Sites 936, 945, and 946, in the lower Amazon Fan (Fig. 1A for locations; Data File DR1 in the GSA Data Repository1). All sample preparation, analyses, and data reduction were conducted at the UTChron facility at the University of Texas at Austin (USA), where we used standard techniques of mineral separation, and applied laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of zircon grains (methods of Thomson et al. [2017] and references therein). Resultant DZ ages are presented within their composite stratigraphic context (Fig. 2A) as kernel density estimates (KDEs; Figs. 2B and 2C) and plotted using a multidimensional scaling (MDS) map (Fig. 2D). Full isotopic measurements are reported in Data File DR2. The MDS map (Fig. 2D) indicates that the Amazon Fan is a mixture of Andean and cratonic sources, and is most closely related to the central Andes, lower Amazon, and craton sources in MDS space. Sample KDEs from the Amazon Fan (Fig. 2B) show little evidence for systematic stratigraphic trends, but display variable proportions of Phanerozoic and Pan-African–Brasiliano age modes (Fig. 2B). KDE cross-correlation coefficients for all Amazon Fan samples (see Table DR2 in the Data Repository) have a mean and standard deviation (1σ) of 0.45 ± 0.08, which is similar to or slightly less than coefficients for synthetic subsamples drawn from the same parent sample (Saylor and Sundell, 2016). Collectively, Amazon Fan DZ samples (Fig. 2C) have age modes nearly identical to those of published samples from the Amazon River (Mapes, 2009; Campbell and Allen, 2008) (Fig. 2C). However, (1) fan samples are qualitatively more homogenous than modern samples from the length of Amazon River, and (2) Amazon Fan DZ age spectra contain higher proportions of Phanerozoic through Sunsás orogeny–aged zircons (76% U-Pb ages <1.3 Ga) than samples from the lower Amazon (64% <1.3 Ga) (Figs. 1B and 2D; Table DR1), while the modern lower Amazon contains higher proportions of >1.3 Ga zircons derived from the craton (Fig. 1B). To further explore this observed variability in provenance signature between Holocene river and Pleistocene submarine fan samples, we applied a top-down unmixing algorithm (sensu Sharman and Johnstone, 2017; after Mason et al., 2017; Fildani et al., 2018) to quantify the relative contributions of zircons from tributary river components (parents) present in composite (daughter) mixtures, or the lower Amazon River and Amazon Fan. We selected published DZ samples (Campbell and Allen, 2008; Mapes, 2009; Pepper et al., 2016) based on their geographic locations within the Amazon drainage basin, with the goal of characterizing broad swaths of DZ terranes using modern river sands. Results can be viewe

Journal ArticleDOI
TL;DR: In this article, the authors highlight the occurrence of two major decoupling horizons controlling the structural and magmatic evolution of distal magma-poor rifted margins and suggest that during final rifting the strain distribution is controlled first by hydration and then by magmatic processes in the domain of exhumed mantle.

Journal ArticleDOI
TL;DR: Detailed analysis of soNRB-induced corrosion at initial nitrate-to-sulfide (N/S) ratios relevant to oil field operations found biogenic zero-valent sulfur and nitrite as the main causes of corrosion under the experimental conditions.
Abstract: Ambiguous reports of corrosion problems associated with the injection of nitrate for souring control necessitate a deeper understanding of this frequently applied bioengineering strategy. Sulfide-oxidizing, nitrate-reducing bacteria have been proposed as key culprits, despite the underlying microbial corrosion mechanisms remaining insufficiently understood. This study provides a comprehensive characterization of how individual metabolic intermediates of the microbial nitrogen and sulfur cycles can impact the integrity of carbon steel infrastructure. The results help explain the dramatic increases seen at times in corrosion rates observed during nitrate injection in field and laboratory trials and point to strategies for reducing adverse integrity-related side effects of nitrate-based souring mitigation.

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TL;DR: In this article, the authors investigate deactivation mechanisms for a rhenium-promoted titania-supported cobalt catalyst during Fischer-Tropsch (FT) synthesis.

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15 Mar 2019-Wear
TL;DR: In this article, the use of small concentrations of hydrocarbon additives to drilling fluid has shown significant positive effects on these properties, and improvements in friction and wear properties of drilling fluid were analyzed using a four-ball experimental configuration.