Rock Flour Research Articles

Incubation Experiments Characterize Turbid Glacier Plumes as a Major Source of Mn and Co, and a Minor Source of Fe and Si, to Seawater

AbstractGlaciers are a source of fine‐ground rock flour to proglacial and coastal marine environments. In these environments, suspended rock flour may affect light and (micro)nutrient availability to primary producers. Due to high loads of glacier rock flour, the particulate metal load of glacier runoff typically exceeds the dissolved metal load. As glacier rock flour is deposited in downstream environments, short‐term exchange between particulate and dissolved metal phases may have a moderating influence on dissolved metal concentrations. Here we compare the behavior of iron (Fe), manganese (Mn), cobalt (Co) and silica (Si) following the addition of different glacier‐derived sediments into seawater under conditions of varying sediment load (20–500 mg L−1), time (0.5 hr–21 days), temperature (4–11°C) and light exposure (dark/2,500 Lux). Despite a moderately high labile Fe content across all particle types (0.28–3.50 mg Fe g−1 of dry sediment), only 0.27–7.13 μg Fe g−1 was released into seawater, with less efficient release as sediment load increased. Conversely, Si, Mn, and Co exhibited a more constant rate of release, which was less sensitive to sediment load. Dissolved Si release was equivalent to 17% ± 22% of particulate amorphous Si after 1–2 weeks. Dissolved Mn concentrations in most incubations exceeded dissolved Fe concentrations within 1 hr despite labile Mn content being 12‐fold lower than labile Fe content. Our results show the potential for glacier‐derived particles to be a large source of Mn and Co to marine waters and add to the growing evidence that Mn may be the bio‐essential metal most affected by glacier‐associated sources.

Glacial rock flour increases photosynthesis and biomass of natural phytoplankton communities in subtropical surface waters: a potential means of action for marine CO2 removal

Glacial rock flour increases photosynthesis and biomass of natural phytoplankton communities in subtropical surface waters: a potential means of action for marine CO2 removal

Radionuclide intake due to food drying surfaces: implications for individual ingestion effective dose in Ogbomoso, Southwestern Nigeria

Measurement of low-level radionuclide transfer from food drying surfaces is of radiological importance in environmental protection, especially in West Africa where farmers commonly preserve their foodstuffs by a low cost method of sun-drying on surfaces such as rock, asphalt, concrete, wood, metals, or roofing sheets which are reported sources of natural radionuclides. The transfer coefficient of natural radionuclides from drying surfaces into food samples is therefore a concern for dietary intake for the consumers. The radioactivity measurements of commonly used food drying surfaces in Ogbomoso, as well as cassava flour sun-dried on these surfaces were performed via gamma-ray spectrometry. Cassava flour was sun-dried on fabric raised 1 meter above the ground to serve as control sample (CF control ). Activity concentrations of 40 K, 238 U, 232 Th in rock, asphalt, concrete and cassava flour dried on these surfaces were determined using a lead-shielded NaI(Ti) detector crystal. Food consumption data and the measured activity concentrations in dried cassava flour were used to estimate ingestion effective dose of radionuclide intake from cassava flour due to these drying surfaces. Annual ingestion effective doses (mSvy−1) in cassava flour dried on concrete, rock, asphalt and fabric were estimated to be 0.72, 0.59, 0.42 and 0.26, respectively. Radionuclide addition was observed in cassava flour dried on concrete, rock and asphalt with transfer variation maximum in rock surface and minimum in asphalt surface. Result of this study is useful for radiometric data analysis in the study area especially on food safety regulations.

Mountain glaciers influence biogeochemical and ecological characteristics of high‐elevation lakes across the northern Rocky Mountains, USA

AbstractMountain glaciers are retreating rapidly due to climate change, leading to the formation of downstream lakes. However, little is known about the physical and biogeochemical conditions in these lakes across a range of glacial influence. We surveyed alpine lakes fed by both glacial and snowpack meltwaters and those fed by snowpack alone to compare nutrient concentrations, stoichiometry, water clarity, chlorophyll, and zooplankton communities. Total phosphorus (TP) and soluble reactive phosphorus were two times higher in glacial lakes than in non‐glacial lakes, while nitrate concentrations were three times higher. However, organic carbon concentrations in glacial lakes were two times lower than in non‐glacial lakes. The carbon‐to‐phosphorus ratio and the nitrogen‐to‐phosphorus ratio of lake seston increased with water clarity in glacial lakes, suggesting that turbidity from glacial flour increases light limitation and increases stoichiometric food quality for zooplankton in newly formed lakes. However, chlorophyll a concentrations did not differ between lake types. Through structural equation modeling, we found that glaciers exhibit a bidirectional association with nitrate and TP concentrations, perhaps mediated through landscape vegetation and lake clarity. Zooplankton communities in high‐turbidity glacial lakes were largely composed of cyclopoid copepods and rotifers (i.e., non‐filter feeders), while non‐glacial lakes tended to be dominated by calanoid copepods and cladocerans (i.e., filter feeders). Our results show that glacier‐influenced lakes have biogeochemical and ecological characteristics distinct from snow‐fed mountain lakes. Sustained studies are needed to assess the dynamics of these unique features as the influence of the alpine cryosphere fades under ongoing climate change.

Glacial rock flour reduces the hydrophobicity of Greenlandic cultivated soils

AbstractSoil water repellency (WR) is ubiquitous across Greenlandic cultivated fields, which may constrain agricultural production. Fine‐grained glacial rock flour (GRF) is available in the surrounding landscape, which could serve as a soil amendment. We tested whether the application of GRF (rates of 0, 50, 100, 300, and 500 ton ha−1) reduced the WR across two field trials in South Greenland. The field trials, Upernaviarsuk (UP) and South Igaliku (SI), differed in clay (UP: 0.05–0.11 kg kg−1; SI: 0.03–0.05 kg kg−1) and organic carbon (OC) contents (UP: 0.04–0.13 kg kg−1; SI: 0.01–0.03 kg kg−1). We measured WR across gravimetric water contents (W) from oven‐dry to the W where WR ceased (WNON) to obtain whole WR‐W curves. Most soils became hydrophilic around air‐dry conditions at application rates of ≥300 ton ha−1, likely due to increased clay:OC ratios. Application rates of ≥300 ton ha−1 generally reduced the trapezoidal integrated area of the WR‐W curve (WRAREA), WNON, and WR after heat treatments at 105°C (WR105) and 60°C (WR60). The WR105 was significantly reduced in both fields at 500 ton ha−1, while WR60 was significantly reduced in UP at application rates of ≥300 ton ha−1. The GRF effects were masked by texture and OC variations. Normalizing WRAREA to the water vapor sorption isotherms (utilizing the Campbell‐Shiozawa model) revealed that GRF consistently reduced the normalized WRAREA. The SI field showed the largest reduction in the normalized WRAREA, likely due to its lower OC and clay contents. Thus, GRF could reduce WR across two Greenlandic field trials.

Browning and blueing – what is the fate of polar coasts?

Covered by extensive ice sheets that often terminate as ice shelves or tidewater glaciers, polar coasts are also seasonally surrounded by sea ice. However, this “whitescape” is shrinking rapidly; the years 2012 and 2022 saw sea-ice minima for the Arctic and the Antarctic, respectively. The loss of ice is transforming these coastal areas, especially in the Arctic and West Antarctica. Meltwater transports particles, called glacial flour, from land to ocean, and when intensive enough this discharge creates “brown zones” across fjords in summer. Turbid glacial plumes hinder light penetration and darken coastal waters, thereby limiting photosynthesis, while turbulent mixing induces aggregation of particles and the resulting formation of so-called marine snow (clumps of largely organic matter that coalesce and sink through the water column) (Sci Total Environ 2021; doi.org/10.1016/j.scitotenv.2021.146491). When these particles reach the seabed, they cover benthic organisms such as this macroalga (Himantothallus grandifolius), photographed in Mackellar Inlet (62°S, Antarctic Peninsula) – a glaciomarine fjord that has not “browned” yet. Furthermore, warming intensifies iceberg calving and thus likely increases the risk of ice-scouring to benthic macroalgae in the shallows. However, glacial retreat also exposes new shallow-water habitats; by allowing phytoplankton blooms and seaweed expansion in these newly ice-free areas, this exposure process (“blueing”) increases carbon accumulation in marine systems (“blue carbon”), particularly in fjords, due to their high storage-to-sequestration efficiency (Sci Nat 2021; doi.org/10.1007/s00114-021-01748-8). In polar coastal zones, many climate-change–related feedbacks are anticipated. It is therefore crucial to assess the carbon sinks emerging due to marine ice losses; though little known, these sinks provide important negative feedbacks to climate change that could be recognized as a nature-based solution. To what extent will blueing balance the effects of advancing brown zones?

Greenlandic glacial rock flour improves crop yield in organic agricultural production

The application of mechanically crushed silicate minerals to agricultural soils has been proposed as a method for both improving crop yields and sequestering inorganic carbon through enhanced mineral weathering. In Greenland, large quantities of finely grained glacial rock flour (GRF) are naturally produced by glacial erosion of bedrock and deposited in easily accessible lacustrine and marine deposits, without the need for energy-intensive grinding. To determine if this material can improve crop yields, we applied 10 and 50 t GRF ha−1 to a sandy, organic agricultural field in Denmark. Two field trials were carried out to test the first-year yield response to GRF in both maize and potatoes, residual effects on potato yields in the year after application, and second and third-year residual effects on spring wheat. Reference-K treatments were included for comparison to determine if the beneficial effects of GRF were primarily due to its K content (3.5% K2O). This alternative source of silicate minerals improved crop yields in the year of application. Though there was no improvement in yield with the reference-K treatments, for each additional ton of GRF applied, maize dry yield increased by 59 kg ha−1 and potato tuber yield by an additional 90 kg ha−1. No residual effects on crop yields were observed in the following years, but we suspect that benefits might persist over multiple seasons at sites with lower initial fertility. The increase in yields achieved with GRF could offset some of the costs of applying silicate minerals as a CO2 sequestration scheme.

Mechanisms Governing 90Sr Removal and Remobilisation in a VLLW Surface Disposal Concept

Flow-through columns were used to assess potential long-term trends in 90Sr biogeochemistry and transport in a Finnish near-surface very low-level waste (VLLW) repository concept. Experiments simulated the effects of water intrusion and flow through the repository barrier and backfill materials, examining impacts on 90Sr migration. Artificial rainwater containing 2.0 mg/L stable Sr (as a proxy for 90Sr) was pumped through column systems that had varying compositions from a matrix of rock flour (backfill material), bentonite (backfill/sealing material), and carbon steel (waste encapsulation material), for 295 days. Effluent geochemistry was monitored throughout. Sr retention behaviour in all column systems was broadly similar. Sr removal from influent rainwater was marked (~95% removed) at the beginning of the experiments, and this degree of removal was maintained for 20 days. Thereafter, Sr concentrations in the effluents began to rise, reaching ~2 mg/L by 295 days. Further, 56%–67% of added Sr was retained in the repository materials over the 295-day reaction period. Analysis of the effluents indicated that colloids did not form; as such, Sr output was likely to be aqueous Sr2+. Upon completion of the experiment, solid-associated Sr distribution and speciation in the columns were assessed through column sectioning and post-mortem analyses, which encompassed the following: total acid digests, sequential extractions, and XAS analysis. The total acid digests and sequential extractions showed that Sr was evenly distributed throughout the columns and that the majority (68%–87%) of solid-associated Sr was in the exchangeable fraction (MgCl2). This suggested that a major part of the solid-phase Sr was weakly bound to the column materials via outer-sphere sorption. Interestingly, a smaller amount of Sr (7%–23%) could only be extracted by aqua regia, suggesting that a proportion of Sr may bind more strongly to the barrier materials. XAS analysis of select samples confirmed that the dominant Sr phase was sorbed to the rock flour and bentonite, but not corroded carbon steel. Columns were also subject to remobilisation experiments using artificial rain- and seawater without added Sr. While rainwater remobilised Sr slowly, high-ionic strength seawater remobilised Sr at much higher rates in the systems containing bentonite. Interestingly, Sr was well retained in the rock flour-only system following rain and seawater intrusion. Overall, the results indicate that the column materials provide reactive surfaces for Sr removal should it be released from waste packages; however, the backfill and barrier materials have limited retention capacity, and the dominant sorption interaction is relatively weak. The safety case for the shallow disposal of radioactive waste should consider the possibility of seawater intrusion and that the bentonite-bound Sr was significantly more susceptible to remobilisation following seawater, despite retaining slightly more Sr during sorption experiments.

Quantification of CO2 uptake by enhanced weathering of silicate minerals applied to acidic soils

The application of ground silicate minerals to agricultural soils has been proposed as a method for taking up CO2 by enhancing the weathering rate of these minerals through their exposure to soil acids. Alternatively, glacial rock flour, a finely grained material which is abundantly available without the need for energy-intensive grinding, could be used. However, simple and inexpensive methods for determining the amount of CO2 taken up as a result of weathering of applied minerals are still needed, and the impact of non-carbonic acids on CO2 uptake has yet to be accounted for. Here, we present a protocol for correcting estimates of CO2 uptake due to enhanced mineral weathering to account for weathering by non-carbonic soil acids. We determine that soils with a pH below 6.3 need correction for weathering by other acids than carbonic acid and that, given the impact of non-carbonic acids, soils with a pH below 5.2 may not be ideal candidates for mineral applications aimed at CO2 uptake, depending on the pCO2. We report an estimated CO2 uptake of 728 kg CO2 ha−1 after the application of 50 tons ha−1 of Greenlandic glacial rock flour to an acidic, sandy soil in Denmark over 3 years.

Geophysical–geotechnical methodology for assessing the spatial distribution of glacio‐lacustrine sediments: The case history of Lake Seracchi

AbstractProglacial lakes are distinctive features of deglaciated landscapes and often act as sediment sinks, collecting solid material from subglacial erosion or washout of deglaciated areas. The solid transport flow, strongly linked to the glaciers and periglacial landforms, may rise due to the rapid changes driven by climate warming, causing deep transformations in the basin hydrology, and even the appearance or disappearance of lakes at a decadal timescale.The goal of this study was to present a geophysical–geotechnical approach that integrates several techniques, to quantify the sediment distribution in a proglacial lake. A geophysical survey is performed with ground‐penetrating radar (GPR) installed on a boat, whereas a time‐domain reflectometer (TDR) measures the electrical conductivity and permittivity of the lakebed sediments. Unperturbed samples are collected and analyzed to measure the main geotechnical properties of the sediment: grain‐size distribution, plastic limit, and liquid limit. Such properties support the interpretation of the GPR data and the detection of spatial variations of the sediment facies.To validate the proposed methodology, field tests were carried out at Lake Seracchi, the largest lake of the Rutor glacier, Italian Alps. It formed around 1880 because of the recent glacier shrinkage, as chronicled by valuable historical documents. Its greyish waters carry a significant amount of suspended sediment recognized as glacial flour, which gradually accumulates on the bottom of the lake.The obtained bathymetry and sediment thickness maps of Lake Seracchi show the strength of the approach: from only a few manual samples, it is possible to extrapolate the geotechnical properties of interest, such as friction angle or hydraulic conductivity, to wider areas, surveyed by the geophysical techniques. This is achieved by investigating the spatial distribution of key geophysical properties linked to the geotechnical properties of interest.

Erfahrungen beim Tunnelbau in durchlässigem glazialen Lockergestein: offener Kies

AbstractGlacial soil deposits are present in Europe on both sides of the Alps, in Scandinavia, Northern Germany, Poland and in North America. There are typical names of the stages of the glaciation, however, the geotechnical characteristics of glacial deposits are similar in all regions; but are very heterogeneous locally. Glacial deposits extend from boulders to invisible silt particle (rock flour) and to clay particles, both of similar grain size. In this paper the focus will be on clean gravel without fines, so‐called open gravel and the challenges and solutions for tunnelling.Face support by pure bentonite slurry is insufficient in open gravel. Different techniques have been used in practice: clogging the pore channels with fines of appropriate gradation by controlling the content fines in the slurry. Use of high viscous slurry with increased clay or bentonite content. In another solution lime powder and polymers were added in the excavation chamber of an earth‐pressure shield to modify the ground. Other aspects such as muck disposal will be evaluated.

The Flims rock avalanche: structure and consequences

The Flims rock avalanche has a gliding surface that cuts down section in a limestone sequence and does not follow a weak horizon. The gliding surface is parallel to bedding and/or to the penetrative Alpine foliation in the limestone that is characterized by a shape-preferred orientation of calcite grains. Predisposition was governed by structural weaknesses in form of sub-vertical fault zones within solid limestone. Faults controlled the orientation of lateral scarps of the rock avalanche. The main body of the rock avalanche behaved as semi-coherent mass, which preserved the original overall structure. The internal deformation occurred by dynamic fragmentation, which was distributed rather heterogeneously. Fragmentation starts by the formation of veins consisting of comminuted limestone. In a later stage crosscutting veins coalesce to form a texture with entirely comminuted limestone (“rock flour”) containing angular shattered fragments of limestone of variable sizes. The involvment of the post-glacial water-saturated substrate contributed to the long-runout of the Flims rock avalanche. The substrate was plowed bulldozer-wise at the front of the rock avalanche and escaped upward through the moving rock avalanche as clastic dikes and blow-out pipes. Bulldozing raised the valley floor in front of the rock avalanche by more than 100 m and, on the margins, entrained pieces of the valley flank and the neighboring, older Tamins rock avalanche deposit. The liquefied substrate breached the Tamins rock avalanche at Reichenau and entrained fragments thereof down the valley. The fragments now form the famous tumas of Domat/Ems, Felsberg and Chur. Lake Ilanz, dammed the by Flims rock avalanche, experienced a first major outburst shortly after its formation.

Effects of Glacial Flour on Marine Micro-plankton: Evidences from Natural Communities of Greenlandic Fjords and Experimental Studies

Meltwater runoff from glaciers carries particles, so-called glacial flour that may affect planktonic organisms and the functioning of marine ecosystems. Protist microplankton is at the base of marine food webs and thus plays an important role in sustaining important ecosystem services. To assess the effect of glacial flour on photoautotrophic, heterotrophic and mixotrophic microplankton, the spatial distribution of these trophic groups was studied in four Greenlandic fjords during summer. The results suggest that the abundance of the autotrophic microplankton was affected by the glacier meltwater due to reduced light penetration and nutrient availability. The abundance of heterotrophic and mixotrophic microplankton were not apparently affected by the glacier meltwater. Incubation experiments were conducted on the natural population and in laboratory cultures of two mixoplanktonic ciliate species. The experiments on the natural population revealed that none of the trophic groups were affected by the suspended material at concentrations up to 50mg L-1. The experiments on cultures gave no indication that glacial flour was ingested by the mixoplanktonic ciliates. Growth rates of cultured ciliates were not affected by the glacial flour addition. These results suggest that heterotrophic and mixotrophic microplankton are not affected by glacial flour as much as autotrophic microplankton.

Can silicon in glacial rock flour enhance phosphorus availability in acidic tropical soil?

Can silicon in glacial rock flour enhance phosphorus availability in acidic tropical soil?

A mineralogical study of glacial flour from Three Sisters, Oregon: An analog for a cold and icy early Mars

Geomorphic and mineralogical data from the martian surface indicate liquid water was abundant on the martian surface and near subsurface ∼3.5 to 4 Gyr ago, but whether early Mars had a warm and wet climate or whether it was cold and icy with punctuated periods of warmth is still unknown. Mineral assemblages of sedimentary rocks on Mars help determine past aqueous conditions and sediment sources. Here, we report on the primary and secondary mineral and amorphous assemblage of glacial flour from Collier Glacier valley on the northern flank of North Sister in Oregon, U.S.A. to identify mineralogical characteristics of mafic sediments altered under cold, wet conditions. Collier glacial flour is dominated by primary igneous minerals (plagioclase is dominant, with lesser amounts of pyroxene and olivine) and comprises 10-40 wt.% X-ray amorphous materials. Crystalline secondary phases (e.g., phyllosilicates, zeolite) are not significant contributors to the authigenic alteration assemblage. High-resolution transmission electron microscopic observations of the <2 μm size fraction of the flour demonstrate that the X-ray amorphous materials are both primary (i.e., volcanic glass) and secondary in nature. The secondary X-ray amorphous materials are enriched in Si, Al, and Fe, and we observe incipient phyllosilicate formation associated with primary and secondary amorphous materials. Our results indicate chemical weathering on a cold and icy early Mars would have produced X-ray amorphous materials, but not crystalline secondary phases. We suggest that the abundant X-ray amorphous materials recognized from orbit and in situ on Mars could have formed under cold and periodically wet conditions similar to those on North Sister today. Furthermore, the lack of volumetrically significant phyllosilicate formation in Collier Glacier flour indicates phyllosilicates on Mars did not form in a cold and wet climate.

Ideas and perspectives: Emerging contours of a dynamic exogenous kerogen cycle

Abstract. Growing evidence points to the dynamic role that kerogen is playing on Earth's surface in controlling atmospheric chemistry over geologic time. Although quantitative constraints on the weathering of kerogen remain loose, its changing weathering behavior modulated by the activity of glaciers suggests that this largest pool of reduced carbon on Earth may have played a key part in atmospheric CO2 variability across recent glacial–interglacial cycles and beyond. This work enunciates the possibility of kerogen oxidation as a major driver of atmospheric CO2 increase in the wake of glacial episodes. This hypothesis of centennial- and millennial-timescale relevance for this chemical weathering pathway is substantiated by several lines of independent evidence synthesized in this contribution, including the timing of atmospheric CO2 increase, atmospheric CO2 isotope composition (13C and 14C), kerogen oxidation kinetics, observations of kerogen reburial, and modeling results. The author hypothesizes that the deglaciation of kerogen-rich lithologies in western Canada contributed to the characteristic deglacial increase in atmospheric CO2, which reached an inflection point ≤ 300 years after the Laurentide Ice Sheet retreated into the kerogen-poor Canadian Shield. To reconcile the release of isotopically light carbon via kerogen oxidation with Earth surface carbon pool constraints, major oceanic degassing and biospheric regrowth must have acted in concert across glacial–interglacial transitions. Additionally, a process such as a strong shift in the ratio of C3 to C4-derived organic matter must be invoked to maintain isotope mass balance, a point key for reconciling the hypothesis with the carbon isotope record of marine dissolved inorganic carbon. In order to test this hypothesis, quantitative constraints on the contribution of kerogen oxidation to CO2 rise at glacial terminations are needed through systematic studies on (1) CO2 fluxes emanating from the weathering of different lithologies, (2) oxidation kinetics of kerogen along glacial chronosequences, and (3) high-resolution temporal changes in the aerial extent of glacially exposed lithological units and glacial flour.

Physical characterization of glacial rock flours from fjord deposits in South Greenland–Toward soil amendment

AbstractGreenlandic fjords contain vast amounts of glacially derived mineral material (glacial rock flour [GRF]), which may be used to amend structureless, low‐clay, and water‐repellent agricultural soils in South Greenland and elsewhere. In this study, we investigate key physical amendment properties of GRF from 16 different deposits in South Greenland. The clay‐sized fraction varied largely (range, 0.11–0.57 kg kg−1), and the particles were mostly angular. The specific surface area (SSA) determined by either ethylene glycol monomethyl ether (EGME, polar liquid) (range, 13.32–88.06 m2 g−1) or water‐vapor adsorption (range, 10.62–63.82 m2 g−1) agreed well (r = .90) and were comparable to kaolinitic‐clay dominated cultivated soils (KA‐soils) with clay content similar to the GRFs. The cation exchange capacities (CECs) (range, 4.25–21.91 cmol kg−1) were similar to or higher than those of the KA‐soils. The water content at the permanent wilting point (PWP) for the GRFs were considerably lower than those of the KA‐soils. The addition of 5% GRF to a sandy soil from Greenland showed a tendency (although not statistically significant) to increase plant available water (PAW). However, very high GRF addition (10 and 15%) significantly decreased the PAW. The specific surface charge (CEC/SSA) of the GRFs were higher than for comparable KA‐soils, suggesting a good soil amendment potential. The results from this study are valuable toward designing sustainable GRF amendment strategies, matching a given cultivated soil with the right amount and type of GRF.

Provenance of Baker River sediments (Chile, 48°S): Implications for the identification of flood deposits in fjord sediments

AbstractFloods are among the most destructive natural hazards on Earth. In paleohydrology, sediments are generally considered as one of the best archives to extend flood records to pre‐historical timescales. Doing so requires being able to identify flood deposits from sediment archives and decipher between flood types. The latter is particularly important in glacierized regions, where meteorological floods frequently co‐occur with glacial lake outburst floods (GLOFs). In Patagonia, results from a recent study suggest that GLOFs are recorded in downstream fjord sediments as fine‐grained and organic‐poor layers, representing the high amount of glacier rock flour transported during lake outbursts, whereas meteorological floods are represented by coarser and more organic deposits. However, not all fine‐grained organic‐poor deposits could be associated with historical GLOFs. Here, we reconstruct the provenance of these Baker River flood deposits using 87Sr/86Sr and εNd, taking advantage of the clear lithological differences that exist between both sides of the watershed. Our results show that both 87Sr/86Sr and εNd are suited to reconstruct sediment provenance in the Baker River watershed but that εNd is the most effective and the least affected by grain‐size variations. Our provenance results confirm that the 21st‐century fine‐grained and organic‐poor deposits represent GLOFs and that the largest winter meteorological flood on record has a distinct coarse and organic‐rich signature. However, our results show that rain‐on‐snow events that occur in summer, and therefore primarily affect the western glacierized part of the watershed, have the same fine‐grained organic‐poor signature as GLOFs. Therefore, this study shows that the sedimentary signature of rain‐on‐snow floods in partially glacierized watersheds depends on the season during which they occur. We anticipate that our findings will contribute to a better interpretation of flood records from partially glacierized watersheds.

Characterisation of natural and remoulded Onsøy clay with focus on the influence of mica

Loss of strength caused by the destructuration of sensitive soils has been identified as the trigger of numerous landslides, some of them of devastating proportions. Norwegian sensitive clay deposits are typically found with a mineralogical composition of inert rock flour, including clay-sized chlorite and dioctahedral mica. The present paper presents a cross-scale study conducted on a sensitive clay from Norway with special focus on the role of mica on the material characteristics. Block samples of Onsøy clay obtained from different depths (4–10 m) were characterised and studied in terms of their mechanical properties, fabric and mineralogy. Oedometer compression tests were carried out in a high-pressure oedometer, applying stress up to 25 MPa on samples in an undisturbed and remoulded state. Microstructural investigations were carried out on undisturbed and remoulded samples using cryo-broadionbeam scanning electron microscopy (cryo-BIB-SEM). Mineral composition was analysed using X-ray diffraction on the bulk samples and the fraction ≤2 μm confirming absence of expandable clay minerals (smectites) and kaolinite. Coarse silt sized and irregular shaped particles were dominated by Na-rich and Ca-rich feldspar, quartz, and framboidal pyrite aggregates. A comparison with data sets from several Norwegian sensitive clay deposits showed that the plasticity index of these clays showed a tendency to decrease with an increasing amount of mica when the salinity is lower than 10 g/l. In contrast, for deposits with a salt concentration of more than 10 g/l, a significant increase in the plasticity index was observed with increasing amount of mica. The formation of aggregates was discussed with relation to its impact on the soil mechanical behaviour-

Recognizing subsurface breccias in Archean terranes: Implications for district scale metallogeny

Breccias are common in ancient and modern volcanic terranes, where they form at and below surface through volcanic, hydrovolcanic, magmatic, or tectonic mechanisms. They are critical for volcanic reconstruction as stratigraphic markers and indicators of geodynamic change and since they can be associated with mineralization their genesis is also important from an exploration perspective. Their origin can be difficult to ascertain in ancient terranes that have undergone polyphase deformation and associated metamorphism. The Joliet Breccia is a subeconomic Cu-Ag prospect within the Neoarchean Rouyn-Noranda mining district, in the Abitbi greenstone belt, Canada. It was previously interpreted as a phreatic breccia formed on the seafloor. This study presents new data indicating that the Joliet Breccia is a subsurface magmatic-hydrothermal breccia. Specifically, the recognition of gradational contacts with host rocks and between internal breccia domains, lack of sedimentary features and the spatial and temporal association with a tonalite intrusion strongly supports this interpretation. The angular, poorly sorted, lithic clasts derived from the immediate host rocks, hydrothermal cement, complete absence of a rock flour matrix, and presence of a radial and concentric fracture pattern extending into the host rocks, further support a subsurface magmatic-hydrothermal emplacement mechanism.A new TIMS U-Pb zircon age of 2698.0 ± 0.9 Ma (2σ) for a tonalite block within the breccia constrains the maximum age of brecciation. Four LA-ICP-MS U-Pb dates on hydrothermal monazite (2693.7 ± 1.0/8.9 Ma; 2696.9 ± 0.45/8.9 Ma; 2698.7 ± 1.4/8.9 Ma; 2701.2 ± 0.33/8.9 Ma; 2 s/2ssys) found in the cement of the Breccia indicate brecciation and mineralization occurred shortly after the emplacement of the tonalite. Similarly, the ca. 2697 Ma St. Jude intrusive breccia indicates a localized ca. 2699–2695 Ma magmatic-hydrothermal event superimposed on ca. 2704–2701 Ma strata. These breccias are temporally correlative with the youngest units of the Blake River Group strata and associated ca. 2698–2695 Ma volcanogenic massive sulfide (VMS) deposits, which suggests an indirect genetic link between these two hydrothermal systems. The VMS deposits may represent the near surface, distal manifestations of a deeper magmatic-hydrothermal system akin to the porphyry-intermediate sulfidation epithermal continuum in modern subaerial volcanic arcs.