Browsing by Author "Tutolo, Benjamin M."
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- ItemOpen AccessA measurement method for U-Th-Sm/He dating of apatite by laser ablation(2018-05-14) Pickering, Julia; Enkelmann, Eva; Matthews, William; Nair, Rajeev; Tutolo, Benjamin M.Thermochronology is a useful tool for dating thermal evolution of rocks in the upper crust. Thermochronometers have the ability to record the cooling of a rock through varying temperature windows. The apatite U-Th/He system is one of the low-temperature thermochronological systems that records cooling temperatures from 45-80°C. Apatite U-Th/He dating is conventionally done through whole grain analysis, where grains are picked and measured and then packed into Nb capsules which are heated in a vacuum to extract and measure the 4He content. Grains are subsequently dissolved and their U, Th, and Sm concentrations are measured by solution ICP-MS. This study addresses a new method of U-Th/He dating using apatite by laser ablation. In the laser ablation method grains are mounted in a vacuum stable medium and then ablated using a laser in a vacuum cell. The laser ablation method has several advantages over whole-grain measurements that limit bias from the grain selection process and improve analytical efficiency. An independently characterised megacryst of Durango apatite is used as a calibration material for the new laser ablation method. The megacryst was characterised at the University of Calgary and the University of Colorado Boulder by conventional whole-grain dating. The analysis yields an age of 32.56 ± 0.34 Ma. The measured age compares well to published ages for Durango apatite. I present here a new method of laser ablation U-Th/He on apatite. The method generally follows previously published laser ablation methodologies for zircon, monazite and titanite with modifications suited for apatite. Grains were mounted using a heated platen press, which pressed samples into FEP bonded to an aluminum backing plate. Samples were loaded into an ultra high vacuum chamber and ablated using a excimer laser and the liberated 4He is measured using an quadrupole mass spectrometer system. The ablated sites were imaged using an optical profilometer and ablated pit volume measured using PitVol, a custom MatLabTM algorithm. After the pit volume measurement, U, Th and Sm concentrations were measured by laser ablation ICP-MS and the U-Th-Sm/He date calculated. The method presented was validated using the characterized Durango apatite megacryst and Fish Canyon Tuff (FCT) apatite reference materials. Weighted average of Durango dates (32.50±0.32 Ma) compare well with conventional whole grain methods for chips of the same Durango crystal. Systematic errors in the method are expected, particularly in the pit measurement and U, Th, Sm measurement to which correction (κ-value) was applied. These Durango dates were used to produce a ҡ-value to correct the secondary reference material and unknown samples. After correction, FCT apatite yields a weighted average age of 28.37 ± 0.96 Ma, which agrees well with published data.
- ItemOpen AccessThe contribution of aqueous catechol-silica complexes to silicification during carbonate diagenesis(J.GCA, 2020-04) Escario Perez, Sofia; Nightingale, Michael; Humez, Pauline; Tutolo, Benjamin M.Pore-filling and carbonate-replacing silica is exceedingly common in carbonates, but the fundamental geochemical mechanisms that drive these silicification reactions during diagenesis remain poorly understood. An existing mode has proposed that carbonate silicification proceeds through an interface-coupled dissolution-precipitation reaction, but it lacks a mechanism that enables pore fluids to reach the requisite level of supersaturation with respect to silica to allow nucleation and growth. Here, we present a sequence of batch experiments ranging in duration from 7 to 49 days designed to test the hypothesis that these reactions are facilitated by the formation and destruction of organo-silica complexes during diagenesis. Our results illustrate that the stability of organo-silica complexes is dependent upon the concentration of organic molecules in solution, as well as pH, 16 salinity, and solution redox state. Together, these results allow us to present the following scheme for organo-silica complex mediation of silicification reactions: Firstly, the breakdown of organic matter in the presence of siliceous material creates organo-silica complexes, leading to silica-enriched pore fluids, a process which is enhanced by the anoxic conditions accompanying sediment burial. Then, as environmental conditions evolve (fO2, salinity, light, fCO2, pH...), the stability of the organo-silica complexes diminishes, and the organo-silica complexes break down. Simultaneously, the pore fluids become intensely silica-supersaturated in direct proportion to the amount of organic material remaining in solution. The resulting supersaturation drives carbonate silicification via the precipitation of silica minerals, a process which is aided by the presence of silica “nuclei” (such as sponge spicules). This study contributes new data and a conceptual model that will aid in the ongoing quest to understand carbonate silicification reactions and their potential applications in hydrocarbon exploitation and geologic CO2 storage. Moreover, it helps to explain the common association between silica precipitates and organic mineral in the sedimentary rock record.
- ItemOpen AccessEstablishing High-Resolution Hydrogeological, Geochemical and Isotopic Baseline Conditions of the Fresh Water Zone at a Field Research Site Near Brooks, Alberta, Canada(2019-12-20) Cheung, Terri Tze-Man; Mayer, Bernhard; Lawton, Don C.; Cey, Edwin E.; Tutolo, Benjamin M.A high-resolution baseline characterization of dissolved gases in groundwater at the CMC field research site from 25.0 to 106.3 m depths was conducted. Data was collected from a continuously cored 106.3 m deep borehole, a 100.0 m deep Westbay® multi-level system and a 67.1 m deep domestic well. The multi-level well with 26 ports revealed variability and stratification in hydrogeology and hydrochemistry. Ports completed in coals had high flow rates and yielded sodium bicarbonate water type, water isotope compositions resembling local meteoric water, elevated methane and ethane concentrations, and biogenic d13C-CH4 values of <-82‰. Below the coals, ports were characterized by lower flow rates, higher d18O and d2H values of water and variable water types. Methane and ethane concentrations were lower compared to samples obtained from coals and d13C-CH4 values ranged between -75‰ and -60‰. The domestic well yielded groundwater with chemical and isotopic compositions resembling groundwater from only the high-flowing coal-containing aquifer portions.
- ItemOpen AccessEvaluation of nitrate in groundwater under long-term manure application(2018-08-27) Kyte, Emily; Cey, Edwin E.; Ryan, M. Cathryn; Tutolo, Benjamin M.Over-application of manure to agricultural fields can contaminate groundwater resources through the leaching of nitrogen below the root zone. The goal of this study was to evaluate the factors affecting the spatial and temporal distribution of nitrate in groundwater following 44 years of manure application. The sampling of 26 wells over an 18-month period revealed that nitrate concentrations ranged from <10 mg-N/L to 1350 mg-N/L and isotopic analysis of 15N-NO3 and 18O-NO3 showed that denitrification occurred in 16 well locations. Generalized additive mixed models (GAMM’s) confirmed that cumulative manure loading had the largest control on the current spatial distribution of groundwater nitrate, while a decrease in groundwater nitrate with sampling date and an increase with dissolved organic carbon (DOC) and were also significant relationships. Evidence for the leaching of nitrogen into groundwater was found in well locations where manure was applied within the past 16 years. The groundwater nitrate trends observed in this long-term study suggest that historical management practices will affect groundwater quality for many decades to come.
- ItemOpen AccessGeochemical and Petrophysical Characterization of Canadian Low-Permeability Oil and Liquid-Rich Gas Reservoirs using Drill Cuttings(2020-12-16) Yang, Zhengru; Clarkson, Christopher R.; Spencer, Ronald J.; Tutolo, Benjamin M.Significant technology development has aided gas and oil production from Canadian ultra-low permeability (unconventional) reservoirs during the past twenty years. Multi-fractured horizontal wells (MFHWs) in particular have enabled commercial production from these reservoirs. However, hydraulic fracturing in MFHWs is commonly performed without consideration for reservoir quality variability along the lateral section of MFHWs. Identification of “sweet spots” along the lateral can help to target hydraulic fracture stages. Drill cuttings are, however, often the only reservoir samples collected from MFHWs. This thesis addresses the limitations of the currently available drill cuttings characterization techniques, and proposes new methods to estimate geochemical and petrophysical properties from this sample type. A predictive algorithm is developed for quantification of mineralogical composition from elemental data obtained using portable energy dispersive X-ray fluorescence (pXRF) and inductively coupled plasma mass spectrometry (ICP-MS) techniques. The development of this technique allows operators to acquire high-resolution mineralogical compositions along the length of MFHWs by conducting inexpensive, time-efficient, non-destructive elemental analysis. Another important contribution of this thesis is the establishment of an integrated experimental and modeling approach to estimate surface diffusion coefficients and permeability of porous media, including synthetic porous materials and drill cuttings collected from unconventional reservoirs. Currently, the commonly-used empirical methods for estimation of surface diffusion cannot incorporate the complexity of rock fabrics in unconventional reservoirs. To address this limitation, in this thesis, surface diffusion coefficients of the gas/solid system are estimated by history-matching adsorption rate data collected on small amounts of porous materials using a newly-developed rate-of-adsorption (ROA) model. Simulation results demonstrate the importance of surface diffusion under the applied experimental conditions. Finally, the impact of organic matter on 1) matrix permeability and 2) gas transport properties in macro-/meso-/micropores of Duvernay shale samples is investigated. The proposed ROA model is applied to 1) extract gas (N2/CO2) apparent permeability, and 2) investigate gas transport mechanisms. The evolution of pore attributes, permeability and flow regimes of shale samples are determined by subjecting shale samples to an Extended Slow Heating (ESH) Rock-Eval thermal treatment and measuring the properties after each treatment stage.
- ItemOpen AccessInvestigating groundwater recharge rates and seasonality under irrigated and dryland conditions at two agricultural sites near Lethbridge, Alberta(2019-08-09) Hughes, Alexandra Therese; Cey, Edwin E.; Hayashi, Masaki; Tutolo, Benjamin M.In order to better understand the impacts of land use on groundwater resources, this study investigated the effects of irrigation on groundwater recharge at two study sites near Lethbridge, Alberta. Depression-focused and diffuse recharge rates were quantified beneath uplands, flatlands and depressions under irrigated and dryland conditions using the chloride mass balance, water table fluctuation and water balance methods. Seasonality of recharge was also considered (i.e., summer vs. overwinter). Results show long-term recharge rates of 88 ± 26 to 113 ± 31 mm/yr beneath depressions, 50 ± 21 to 29 ± 44 mm/yr beneath flatlands and -4 ± 5 to 4 ± 2 mm/yr beneath uplands. Overwinter (November 2017-April 2018) snowmelt recharge was the same for irrigated and dryland flatlands (between 33 ± 7 and 68 ± 113 mm). Recharge during the 2018 growing season was 42 ± 141 and 21 ± 122 mm beneath the irrigated and dryland flatlands, respectively. Numerical model simulations showed 3.1 times more summer recharge under irrigated versus dryland flatland conditions. Irrigation was shown to affect both the rate and seasonality of recharge at the two study sites.
- ItemOpen AccessNaturally Derived Silicate-based Nanoparticles for Enhanced Oil Recovery in Sandstone Reservoirs(2020-11-16) Sagala, Farad; Nassar, Nashaat N.; Hassanzadeh, Hassan; Maini, B. B.; Dong, Mingzhe; Tutolo, Benjamin M.; Poitzsch, Martin E.Chemical enhanced oil recovery (C-EOR) is a commonplace method used extensively to extract trapped oil with reasonable recovery percentages during the tertiary stage of oil production. Besides, new technologies have emerged and have been tested for their efficiency to increase oil recovery after the conventional primary and secondary recovery techniques. Nanoparticles as a branch of nanotechnology are emerging as a new alternative technology for C-EOR and recovery processes of trapped oil. Tunable silicate-based nanoparticles as nanofluids can be injected into the reservoir at the secondary/tertiary stage as a standalone or when coupled with some other existing conventional techniques to enhance the recovery of the remaining trapped oil. Nanofluids can be introduced into the reservoir at a typical chemical flood configuration to produce more oil by changing the geochemical properties of the reservoir such as wettability, disjoining pressure, IFT etc. In the first phase of this study, silicate-based nanoparticles were synthesized, then partially altered their functionality by anchoring various agents such as silanes and polymers, generating various forms of functionalized silicate-based nanoparticles. Characterization techniques, such as scanning electron microscope (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), dynamic light scattering (DLS), and zeta potential were conducted for the produced nanoparticles to confirm their surface identity, functionality, stability, and morphology. The EOR performance was investigated by mainly interfacial tension (IFT), contact angle, spontaneous imbibition, relative permeability measurements, conducting aggregation experiments and displacement tests using Berea sandstone cores at reservoir conditions. Results showed that the synthesized nanoparticles either alone or when integrated with existing conventional techniques can recover substantial trapped oil at the tertiary stage. Furthermore, a considerable improvement of oil recovery was achieved by combining silicate-based nanoparticles with low salinity water flooding. Subsequently, using silicate-based nanoparticles as EOR agents provides a prospect of being applied in EOR.
- ItemOpen AccessOrganic Sulfur-Bearing Species as Subsurface Carbon Storage Vectors(2019-09-12) Yim, Calista; Larter, S. R.; Huang, Haiping; Snowden, L. R.; Tutolo, Benjamin M.To tackle climate change issues, this study investigates whether residual biomass can be converted to a suitable form for permanent subsurface sequestration. Natural sulfurization processes in sedimentary organic matter are investigated as mechanisms to generate biologically refractory water-soluble organic molecules. Such molecular vectors could be sequestered in shallow, saline, contaminated aquifers through solubility trapping. Sulfur-rich oils were analyzed with gas chromatography mass spectrometry and Fourier transform ion cyclotron resonance mass spectrometry to reveal molecular compositions of complex organosulfur compounds in such oils. Sulfurized compounds including C20-28, C35 and C40 species were detected with double bond equivalent values suggesting the occurrence of sulfurized lipids. Laboratory sulfurization experiments on lipids yielded products with up to 7 sulfur atoms, which suggests labile biomolecules can be altered to biologically refractory molecules. Biodegradation resistance and water solubility estimates of various model compounds show sulfinyl functional groups improves water solubility and biodegradation resistance of molecules.
- ItemOpen AccessA rate law for sepiolite growth at ambient temperatures and its implications for early lacustrine diagenesis(2020-01) Arizaleta, Maria L.; Nightingale, Michael; Tutolo, Benjamin M.
- ItemOpen AccessThe Evolution of Petrophysical Properties During Thermal Maturation, as a Function of Various Hydrocarbon Fractions Comprising the Total Organic Carbon Content(2018-05-16) Clarke, Katherine; Pedersen, Per; Clarkson, Christopher R.; Pedersen, Per Kent; Sanei, Hamed; Meyer, Rudi; Tutolo, Benjamin M.Rock Eval pyrolysis is a standard industry technique used to evaluate the hydrocarbon-generating potential of a formation by quantifying its total organic matter content and thermal maturity. By utilizing a new Rock Eval procedure (ESH Rock Eval), in which the heating rate is slowed down over an extended temperature range, different hydrocarbon components are more easily distinguished due to enhanced peak resolution. The impacts of these various hydrocarbon types on reservoir quality is evaluated by observing the evolution of organic matter and petrophysical properties during pyrolysis. With the elution of the free hydrocarbons in the sample (S1 peak in Rock Eval), petrophysical properties do not notably change. However, significant changes occur after the S2a and S2b peaks, which correspond to the pyrolysis of pervasive, fluid-like hydrocarbon residue (FHR) which coats mineral grains, and the remaining organic matter (solid bitumen) that resides in the larger pore spaces in the samples, respectively. This work was evaluated utilizing core and drill cuttings samples from the Montney, Duvernay and Doig Formations from the Western Canadian Sedimentary Basin.
- ItemOpen AccessTransitioning an Alkaliphilic and Photosynthetic Microbial Consortium from Laboratory to Outdoor Demonstration Scale(2023-10-05) Haines, Marianne Victoria; Strous, Marc; Strous, Marc; Tutolo, Benjamin M.; Dunfield, Peter F.; De la Hoz Siegler, Hector; Kleinegris, Dorinde M.M.The 21st century’s challenges—climate change, growing population, resource decline, habitat and species loss—mean that current practices must be replaced, redesigned, and improved. Phytoplankton, reliant on water, light, nutrients, and CO2, offer versatile applications in nutritional supplements, agricultural feed, bioplastics, wastewater treatment, and bioenergy production. Currently, the most successful commercial ventures center on select taxa like Spirulina and Chlorella and produce high-value products for human consumption. Expanding the scope of viable commercial taxa and their applications hinges on overcoming critical challenges in cultivation, notably biomass productivity, robustness, and resource use. Inspiration can be drawn from natural environments where phytoplankton flourish, like alkaline soda lakes. These lakes are characterized by elevated pH and high carbonate alkalinity. Growing phytoplankton in high pH (10+), high carbonate alkalinity medium (0.5 M) increases the driving force for CO2 capture into solution and helps exclude competitors and predators which can cause biomass instability. This thesis chronicles the transition of biomass from alkaline soda lakes, dominated by the cyanobacterium Sodalinema alkaliphilum, from laboratory to large-scale outdoor demonstration. Chapter 2 explores the microbes inhabiting such lakes and their societal applications. Chapter 3 describes the design, construction, and operation of laboratory photobioreactors with programmable lighting and online growth measurements. Chapter 4 follows outdoor biomass cultivation in a 1,000 L photobioreactor, demonstrating sustained growth at a pH sufficient for CO2 capture from air. In Chapter 5, cultivation in a 3,000 L open raceway pond (ORP) reports long-term medium re-use, water requirements, and CO2 capture from air, although optimisation is necessary. Operational seasons ranged 70–140 days—160 being the maximum possible in Calgary’s temperate climate. Average daily yields were ∼ 3–4 g/m2/day (ash-free) with modeling predicting productivity could reach 6 g/m2/day by reducing biomass density. Finally, Chapter 6 quantifies ORP biomass losses, with stable isotope probing unveiling insights into S. alkaliphilum physiology and ecology. In conclusion, this research explores the feasibility of growing S. alkaliphilum biomass at scale for extended durations and has generated baseline data and operational insights which can be used to inform and refine the sustainability and productivity of future iterations of this technology.
- ItemOpen AccessUse of Imaging Techniques to Quantify Fluid-Rock Interaction and Petrophysical Properties in Low Permeability Hydrocarbon Reservoirs(2018-11-01) Deglint, Hanford John; Clarkson, Christopher R.; Spencer, Ronald J.; Tutolo, Benjamin M.; Bryant, Steven L.; Mohanty, Kishore K.Low permeability (‘tight’) reservoirs have become a viable source of hydrocarbons in North America because of horizontal drilling and multi-stage hydraulic fracturing. While commercial production continues for these unconventional resources, recovery of the available hydrocarbons (particularly liquids) remains low. This is due impart to the lack of understanding of the basic reservoir properties. Without advancing characterization methods for petrophysical and geomechanical properties, we can expect these inefficiencies in resource development to persist. This thesis begins to address this lapse in knowledge by using imaging techniques to quantify fluid-rock interaction and characterize petrophysical properties. In tight reservoirs, most of the hydrocarbon resource resides within the matrix nanopore structure. However, conventional characterization methods are not usually performed at this scale. Ultra-small-angle neutron scattering is employed to probe geological samples for determining the connected and unconnected porosity, including porosity at the nanoscale. This information can be used in tandem with 2D scanning electron microscope (SEM) images to populate pore network models which in turn are used to derive petrophysical properties. An important contribution of this thesis is the development of techniques to enable the imaging and quantification of wettability at the micro- and nanoscale. While imaging of rock nanopore pore structure is now routine, imaging of fluid-rock interaction at this scale, which is necessary for quantifying multi-phase fluid distribution and flow, is not. Using an environmental SEM, three approaches are employed: 1) condensation and evaporation, 2) cryogenic, and 3) micro-injection. Using a parametrized Young-Laplace model, contact angles (advancing/receding) and spontaneous imbibition rates are calculated. Fluid distributions in preserved core are determined. Macro- and micro-contact angles for the same sample are compared, revealing that contact angle variance in a small sample is large, even within sites a few millimetres apart. This suggests that macro-scale measurements do not appropriately capture the heterogeneity of low-permeability samples. Finally, using a combination of X-ray, SEM, and cathodoluminescence, a variety of rock petrophysical properties are determined from drill cuttings. Custom written software using advanced image processing techniques is used to automatically measure mineralogical composition, cementation, and porosity.
- ItemEmbargoWeathering-driven porosity generation in altered oceanic peridotites(Elsevier, 2023-01) Pujatti, Simone; Plümper, Oliver; Tutolo, Benjamin M.Ultramafic rocks exposed at slow and ultra-slow spreading mid-ocean ridges represent a significant and extremely reactive portion of the oceanic lithosphere. Thus, mechanistic understanding of the processes by which seawater infiltrates into and reacts with these rocks is essential for constraining their contribution to the chemistry of the oceans and the coupled carbonate-silicate cycle. Recent observations indicate that nanoscale processes contribute to seawater-driven alteration of ultramafic rocks, but conventional petrographic and tomographic observations of the associated physical features are challenging to link to these nanoscale features. Moreover, multiple generations and varying conditions of fluid infiltration often obscure the relative roles of higher-temperature serpentinization, where reactions are mostly isochemical, and lower-temperature weathering reactions, where observations suggest the release of massive amounts of magnesium. Here we bridge these scales and investigate the specific role of weathering processes in dissolution-driven porosity generation by integrating focused ion beam scanning electron microscopy nanotomography and micro-computed X-ray tomography imaging of the pore structures preserved in drill cores of serpentinized oceanic peridotites. Relict olivine crystals in all imaged samples contain abundant etch pits, and those in the higher-resolution FIB-SEM imagery show the presence of channel-like dissolution structures. The pore channels preferentially affect olivine along grain boundaries and show anisotropic distribution likely controlled by crystallographic features. The pores formed via olivine dissolution are interpreted to result from dissolution of serpentinized peridotite at conditions where serpentine and carbonate precipitation are kinetically inhibited, i.e., at weathering conditions. Importantly, the calculated connectivity of the imaged pore structures increases as the scale of investigation increases, suggesting that weathering-driven olivine dissolution facilitates further seawater infiltration and olivine dissolution, a positive feedback that can sustain continued magnesium extraction until the rocks are ultimately cut off from seawater circulation via sedimentation. Thus, while much attention has been directed towards constraining geochemical fluxes from the higher-temperature alteration of ultramafic rocks, our results support literature studies suggesting that mineral dissolution, and hence elemental fluxes, are significant at the lower temperatures of seafloor weathering. Our data thus provide mechanistic evidence of the physical process contributing to the observed elemental loss from weathered oceanic peridotites.
- ItemOpen AccessWeathering-driven porosity generation in altered oceanic peridotites(Elsevier, 2023-01-23) Pujatti, Simone; Plümper, Oliver; Tutolo, Benjamin M.Ultramafic rocks exposed at low and ultra-slow spreading mid-ocean ridges represent a significant and extremely reactive portion of the oceanic lithosphere. Thus, mechanistic understanding of the processes by which seawater infiltrates into and reacts with these rocks is essential for constraining their contribution to the chemistry of the oceans and the coupled carbonate-silicate cycle. Recent observations indicate that nanoscale processes contribute to seawater-driven alteration of ultramafic rocks, but conventional petrographic and tomographic observations of the associated physical features are challenging to link to these nanoscale features. Moreover, multiple generations and varying conditions of fluid infiltration often obscure the relative roles of higher-temperature serpentinization, where most chemical constituents are essentially immobile, and lower-temperature weathering reactions, where observations suggest the release of massive amounts of magnesium. Here we bridge these scales and investigate the specific role of weathering processes in dissolution-driven porosity generation by integrating focused ion beam scanning electron microscopy (FIB-SEM) nanotomography and micro-computed X-ray tomography (μ-CT) imaging of the pore structures preserved in drill cores of serpentinized oceanic peridotites. Relict olivine crystals in all imaged samples contain abundant etch pits, and those in the higher-resolution FIB-SEM imagery show the presence of channel-like dissolution structures. The pore channels preferentially affect olivine along grain boundaries and show anisotropic distribution likely controlled by crystallographic features. The pores formed via olivine dissolution are interpreted to result from dissolution of serpentinized peridotite at conditions where serpentine and carbonate precipitation are kinetically inhibited, i.e., at weathering conditions. Importantly, the calculated connectivity of the imaged pore structures increases as the scale of investigation increases, suggesting that weathering-driven olivine dissolution facilitates further seawater infiltration and olivine dissolution, a positive feedback that can sustain continued magnesium extraction until the rocks are ultimately cut off from seawater circulation via sedimentation. Thus, while much attention has been directed towards constraining geochemical fluxes from the higher-temperature alteration of ultramafic rocks, our results suggest that mineral dissolution, and hence elemental fluxes, are significant at the lower temperatures of seafloor weathering. Our data thus provide mechanistic evidence of the physical process contributing to the observed Mg loss from weathered oceanic peridotites.