Products Of Chemical Weathering Research Articles

Patterns and Processes of Salt Efflorescences in the McMurdo region, Antarctica

Evaporite salts are abundant around the McMurdo region, Antarctica (∼78°S) due to very low precipitation, low relative humidity, and limited overland flow. Hygroscopic salts in the McMurdo Dry Valleys (MDVs) are preferentially formed in locations where liquid water is present in the austral summer, including along ephemeral streams, ice-covered lake boundaries, or shallow groundwater tracks. In this study, we collected salts from the Miers, Garwood, and Taylor Valleys on the Antarctic continent, as well as around McMurdo Station on Ross Island in close proximity to water sources with the goal of understanding salt geochemistry in relationship to the hydrology of the area. Halite is ubiquitous; sodium is the major cation (ranging from 70%–90% of cations by meq kg-1 sediment) and chloride is the major anion (>50%) in nearly all samples. However, a wide variety of salt phases and morphologies are tentatively identified through scanning electron microscopy (SEM) and X-ray diffraction (XRD) work. We present new data that identifies trona (Na3(CO3)(HCO3)·2H2O), tentative gaylussite (Na2Ca(CO3)2·5H2O), and tentative glauberite (Na2Ca(SO4)2) in the MDV, of which the later one has not been documented previously. Our work allows for the evaluation of processes that influence brine evolution on a local scale, consequently informing assumptions underlying large-scale processes (such as paleoclimate) in the MDV. Hydrological modeling conducted in FREZCHEM and PHREEQC suggests that a model based on aerosol deposition alone in low elevations on the valley floor inadequately characterizes salt distributions found on the surfaces of the soil because it does not account for other hydrologic inputs/outputs. Implications for the salt distributions include their use as tracers for paleolake levels, geochemical tracers of ephemeral water tracks or “wet patches” in the soil, indicators of chemical weathering products, and potential delineators of ecological communities.

Long-term controls on soil organic carbon with depth and time: A case study from the Cowlitz River Chronosequence, WA USA

Over timescales of soil development (millennia), the capacity of soils to stabilize soil organic carbon (SOC) is linked to soil development through changes in soil mineralogy and other soil properties. In this study, an extensive dataset of soil profile chemistry and mineralogy is compiled from the Cowlitz River Chronosequence (CRC), WA USA. The CRC soils range in age from 0.25 to 1200kyr, spanning a developmental gradient encompassing clear changes in soil mineralogy, chemistry, and surface area. Comparison of these and other metrics of soil development with SOC properties reveal several relationships that may be diagnostic of the long-term coupling of soil development and C cycling. Specifically, SOC content was significantly correlated with sodium pyrophosphate extractable metals emphasizing the relevance of organo-metal complexes in volcanic soils. The depth distributions of organo-metals and other secondary weathering products, including the kaolin and short-range order (SRO) minerals, support the so-called “binary composition” of volcanic soils. The formation of organo-metal complexes limits the accumulation of secondary minerals in shallow soils, whereas in deep soils with lower SOC content, secondary minerals accumulate. In the CRC soils, secondary minerals formed in deep soils (below 50cm) including smectite, allophane, Fe-oxides and dominated by the kaolin mineral halloysite. The abundance of halloysite was significantly correlated with bulk soil surface area and 14C content (a proxy for the mean age of SOC), implying enhanced stability of C in deep soils. Allophane, an SRO mineral commonly associated with SOC storage, was not correlated with SOC content or 14C values in CRC soils. We propose conceptual framework to describe these observations based on a general understanding of pedogenesis in volcanic soils, where SOC cycling is coupled with soil development through the formation of and fate of organo-metal or other mobile weathering products. This framework highlights interactions between SOC and soil development, which may be applicable to other soils where organic inputs interact with the products of chemical weathering.

Study of phyllosilicates and carbonates from the Capri Chasma region of Valles Marineris on Mars based on Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars (MRO-CRISM) observations

Spectral reflectance data from the MRO-CRISM (Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars) of Capri Chasma, a large canyon within Valles Marineris on Mars, have been studied. Results of this analysis reveal the presence of minerals, such as, phyllosilicates (illite, smectite (montmorillonite)) and carbonates (ankerite and manganocalcite). These minerals hint of the aqueous history of Noachian time on Mars. Phyllosilicates are products of chemical weathering of igneous rocks, whereas carbonates could have formed from local aqueous alteration of olivine and other igneous minerals. Four different locations within the Capri Chasma region were studied for spectral reflectance based mineral detection. The study area also shows the spectral signatures of iron-bearing minerals, e.g. olivine with carbonate, indicating partial weathering of parent rocks primarily rich in ferrous mineral. The present study shows that the minerals of Capri Chasma are characterized by the presence of prominent spectral absorption features at 2.31μm, 2.33μm, 2.22μm, 2.48μm and 2.52μm wavelength regions, indicating the existence of hydrous minerals, i.e., carbonates and phyllosilicates. The occurrence of carbonates and phyllosilicates in the study area suggests the presence of alkaline environment during the period of their formation. Results of the study are important to understand the formation processes of these mineral assemblages on Mars, which may help in understanding the evolutionary history of the planet.

Weathering, sedimentary and diagenetic controls of mineral and geochemical characteristics of the vertebrate-bearing Silesian Keuper

AbstractMudstones and claystones from the southern marginal area of the European Upper Triassic, midcontinental Keuper basin (Silesia, southern Poland) were investigated using XRD, organic and inorganic geochemistry, SEM, K-Ar of illite-smectite, AFT, and stable isotopes of O and C in carbonates in order to unravel the consequent phases of the geological history of these rocks, known for abundant fossils of land vertebrates, and in particular to evaluate the diagenetic overprint on the mineral composition. The detected and quantified mineral assemblage consists of quartz, calcite, dolomite, Ca-dolomite, illite, mixed-layer illite-smectite, and kaolinite as major components, plus feldspars, hematite, pyrite, chlorite, anatase, siderite, goethite as minor components. Palygorskite, gypsum, jarosite and apatite were identified in places.The K-Ar dates document a post-sedimentary thermal event, 164 Ma or younger, which resulted in partial illitization of smectite and kaolinite. The maximum palaeotemperatures were estimated from illite-smectite as ∼125°C. Apatite fission track data support this conclusion, indicating a 200–160 Ma age range of the maximum temperatures close to 120°C, followed by a prolonged period of elevated temperatures. These conclusions agree well with the available data on the Mesozoic thermal event, which yielded Pb-Zn deposits in the area. Organic maturity indicators suggest the maximum palaeotemperatures <110°C.Palygorskite was identified as authigenic by crystal morphology (TEM), and calcite by its accumulation in soil layers and by its isotopic composition evolving with time, in accordance with the sedimentary and/or climatic changes. Dolomite isotopic composition indicates more saline (concentrated) waters. Palygorskite signals a rapid local change of sedimentary conditions, correlated with algal blooms. This assemblage of authigenic minerals indicates an arid climate and the location at the transition from a distal alluvial fan to mudflat.Fe-rich smectite, kaolinite, and hematite were products of chemical weathering on the surrounding lands and are therefore mostly detrital components of the investigated rocks. Kaolinite crystal morphology and ordering indicates a short transport distance. Hematite also crystallizedin situ, in the soil horizons. A large variation in kaolinite/2:1 minerals ratio reflects hydraulic sorting, except of the Rhaetian, where it probably signals a climatic change, i.e. a shift in the weathering pattern towards kaolinite, correlated with the disappearance of hematite. Quartz, 2M1illite, and minor feldspars and Mg-chlorite were interpreted as detrital minerals. The documented sedimentation pattern indicates that in more central parts of the Keuper playa system, where an intense authigenesis of the trioctahedral clays (chlorite, swelling chlorite, corrensite, sepiolite) took place, illite and smectite were the dominant detrital clay minerals.Cr/Nb and Cr/Ti ratios were found as the best chemostratigraphic tools, allowing for the correlation of all investigated profiles. A stable decrease of these ratios up the investigated sedimentary sequence is interpreted as reflecting changes in the provenance pattern from more basic to more acidic rocks.

On the biogeochemical response of a glacierized High Arctic watershed to climate change: revealing patterns, processes and heterogeneity among micro‐catchments

AbstractOur novel study examines landscape biogeochemical evolution following deglaciation and permafrost change in Svalbard by looking at the productivity of various micro‐catchments existing within one watershed. It also sheds light on how moraine, talus and soil environments contribute to solute export from the entire watershed into the downstream marine ecosystem.We find that solute dynamics in different micro‐catchments are sensitive to abiotic factors such as runoff volume, water temperature, geology, geomorphological controls upon hydrological flowpaths and landscape evolution following sea level and glacial changes. Biotic factors influence the anionic composition of runoff because of the importance of microbial SO42− and NO3− production. The legacy of glaciation and its impact upon sea level changes is shown to influence local hydrochemistry, allowing Cl− to be used as a tracer of thawing permafrost that has marine origins. However, we show that a ‘glacial signal’ dominates solute export from the watershed. Therefore, although climatically driven change in the proglacial area has an influence on local ecosystems, the biogeochemical response of the entire watershed is dominated by glacially derived products of rapid chemical weathering. Consequently, only the study of micro‐catchments existing within watersheds can uncover the landscape response to contemporary climate change. Copyright © 2014 John Wiley & Sons, Ltd.

Dissolved inorganic carbon in the Xijiang River: concentration and stable isotopic composition

Dissolved inorganic carbon (DIC) is one the major products of chemical weathering of the land, and it is also one of the most active components in the riverine carbon species. Concentration and stable isotopic composition of DIC in the mainstream of the Xijiang River (XJR) and its two tributaries (the Guijiang and Hejiang rivers) were investigated during a hydrological year and a massive flooding. DIC concentration of most selected sections of the XJR system varied from 750 to 2,400 μM with an average of (1,630 ± 390) μM. DIC was significantly diluted in the massive flooding period. The stable isotopic composition of DIC (δ13CDIC) varied from −14.75 to −8.25 ‰ [with an average of (−11.19 ± 1.18) ‰], from 17.22 to −10.65 ‰ [with an average of (−13.00 ± 1.86) ‰], and from −15.94 to −9.71 ‰ [with an average of (−12.68 ± 1.28) ‰] in the mainstream of the XJR, the Guijiang River and the Hejiang River, respectively. This is jointly determined by the outcrop area of carbonate rocks and the properties of soil organic carbon within the catchments. δ13CDIC is less negative in the dry season because of the increasing contribution from karst groundwater and more negative in the wet season because of the increasing contribution from surface soil water. Calcite was saturated sometimes at the mainstream sections of the XJR. Carbonate-sourced DIC contributes 10.32–43.95 % with an average of about (27.69 ± 6.03) % of the riverine DIC for the XJR. The XJR exports about 4.27 × 1012 g of DIC in the surveyed year, of which about 83 % occurred in the wet season.

Increased river alkalinization in the Eastern U.S.

The interaction between human activities and watershed geology is accelerating long-term changes in the carbon cycle of rivers. We evaluated changes in bicarbonate alkalinity, a product of chemical weathering, and tested for long-term trends at 97 sites in the eastern United States draining over 260,000 km(2). We observed statistically significant increasing trends in alkalinity at 62 of the 97 sites, while remaining sites exhibited no significant decreasing trends. Over 50% of study sites also had statistically significant increasing trends in concentrations of calcium (another product of chemical weathering) where data were available. River alkalinization rates were significantly related to watershed carbonate lithology, acid deposition, and topography. These three variables explained ~40% of variation in river alkalinization rates. The strongest predictor of river alkalinization rates was carbonate lithology. The most rapid rates of river alkalinization occurred at sites with highest inputs of acid deposition and highest elevation. The rise of alkalinity in many rivers throughout the Eastern U.S. suggests human-accelerated chemical weathering, in addition to previously documented impacts of mining and land use. Increased river alkalinization has major environmental implications including impacts on water hardness and salinization of drinking water, alterations of air-water exchange of CO2, coastal ocean acidification, and the influence of bicarbonate availability on primary production.

A granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins

A review of published literature was undertaken to determine if there was a fingerprint of chemical weathering in regoliths subjected to periglacial conditions during their formation. If present, this fingerprint would be applied to the question of when blockfields in periglacial landscapes were initiated. These blocky diamicts are usually considered to represent remnants of regoliths that were chemically weathered under a warm, Neogene climate and therefore indicate surfaces that have undergone only a few metres to a few 10s of metres of erosion during the Quaternary. Based on a comparison of clay and silt abundances and secondary mineral assemblages from blockfields, other regoliths in periglacial settings, and regoliths from non-periglacial settings, a fingerprint of chemical weathering in periglacial landscapes was identified. A mobile regolith origin under, at least seasonal, periglacial conditions is indicated where clay(%) ≤ 0.5*silt(%) + 8 across a sample batch. This contrasts with a mobile regolith origin under non-periglacial conditions, which is indicated where clay(%) ≥ 0.5*silt(%) − 6 across a sample batch with clay(%) ≥ 0.5*silt(%) + 8 in at least one sample. A range of secondary minerals, which frequently includes interstratified minerals and indicates high local variability in leaching conditions, is also commonly present in regoliths exposed to periglacial conditions during their formation. Clay/silt ratios display a threshold response to temperature, related to the freezing point of water, but there is little response to precipitation or regolith residence time. Lithology controls clay and silt abundances, which increase from felsic, through intermediate, to mafic compositions, but does not control clay/silt ratios. Use of a sedigraph or Coulter Counter to determine regolith granulometry systematically indicates lower clay abundances and intra-site variability than use of a pipette or hydrometer. In contrast to clay/silt ratios, secondary mineral assemblages vary according to regolith residence time, temperature, and/or precipitation. A microsystems model is invoked as a conceptual framework in which to interpret the concurrent formation of the observed secondary mineral ranges. According to the fingerprint of chemical weathering in periglacial landscapes, there is generally no evidence of blockfield origins under warm Neogene climates. Nearly all blockfields appear to be a product of Quaternary physical and chemical weathering. A more dominant role for periglacial processes in further bevelling elevated, low relief, non-glacial surface remnants in otherwise glacially eroded landscapes is therefore indicated.

Silica- and sulfate-bearing rock coatings in smelter areas: Products of chemical weathering and atmospheric pollution I. Formation and mineralogical composition

Black rock-coatings occur in proximity to smelters and roast yards of the Greater Sudbury area, Ontario, Canada and contain information about the past interactions between surface minerals, and gaseous and particulate atmospheric components, many of which were pollutants. Rock-coatings were collected from various locations within the Sudbury area and are characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron microprobe analysis, infrared spectroscopy and X-ray photoelectron spectroscopy. Acidic fumigations and rain, the result of vast quantities of SO2 released from smelting, increased the chemical weathering rate of exposed rocks in the Sudbury area. Non-stoichiometric dissolution of the silicate minerals under acidic conditions resulted in the accumulation of silicic acid and the subsequent formation of a silica–gel type coating. The silica gel transformed overtime into amorphous silica, opal (opal C and opal-CT) and cristobalite. Dissolution of the underlying rock and also of metal-bearing particles by sulfuric acid resulted in the in situ formation of metal–sulfate-rich layers on the interfaces between the atmosphere and the silica-rich coating (atmosphere–coating interface, ACI) and between the silica-rich coating and the underlying rock (rock–coating interface, RCI). These metal–sulfate-rich layers contain nanometer aggregates of Fe–Cu–sulfate–hydroxide, goldichite, mereiterite, guildite, butlerite and antlerite. The silica-rich matrix also contains a mix of detrital grains from adjacent rocks and soils (feldspar, quartz, hematite, chlorite, montmorillonite) and non-dissolved smelter-derived nano- to micro-size particulates (metal–silicates, metal–oxides, C-spheres). The apparent disequilibrium between the embedded particles and the Fe–Cu-sulfates suggests that trapped nanoparticles were encapsulated into pores which prevented their equilibration with acidic metal–sulfate-bearing fluids. An XPS depth profile indicates a gradual transition from lower to higher concentrations of metals from the coating surface towards the metal–sulfate-rich layer on the ACI, which suggests that the outer surface of the coatings is currently leached on an angstrom scale by surface waters.

Geophysical analysis of the soils for civil (Geotechnical) engineering and urban planning purposes: Some case histories from Turkey

The aim of this study is to review the geophysical investigations in civil engineering and urban planning by some case histories in Turkey. Geophysics deals with a wide array of earth phenomena, including the temperature distribution of the earth's interior (the source, configuration and variations of the geomagnetic field) and the large-scale features of the terrestrial crust, such as rifts, continental sutures and mid-oceanic ridges. From the geophysical point of view, civil engineering and urban planning includes several geophysical topics used to investigate the physical properties, the physical techniques for regional and local land use planning or micro-zonation, the natural disaster risk estimation studies, etc. In this study, the geophysical approach, regarding civil engineering and urban planning against the natural or artificial disaster risk in macro (human/nature) and micro (society/earth) scales, is given. Geophysical methods provide solutions to a wide range of geotechnical problems: Slope stability, soil liquefaction and amplification studies, site investigations and testing, water works, subways, etc. In this study, an evaluation of the geophysical methods applied to geotechnical problems related to the soils is presented. Soils consist of the products of physical and chemical weathering of the rocks of the earth’s crust. As a part of the engineering design, the aim of a site/soil investigation is to provide the basic data to evaluate the interaction of the natural environment with the proposed structure. As it is known, using physical measurements in geophysics, it is studied as the natural and artificially generated physical fields of the earth. Key words: Geotechnical engineering, geophysics, earthquake engineering, soils, soil dynamics.

Reduction of bedrock blocks as corestones in the weathering profile: Observations and model

Blocks of metavolcaniclastic rock exposed at the surface in upland catchments of the Espiritu Santo and Mameyes rivers within the Luquillo Experimental Forest (Puerto Rico) are interpreted as corestones, reduced from initial joint-bounded bedrock blocks by subsurface weathering. Maximum corestone size, expressed as the geometric mean of the three dimensions, S = \(\sqrt[3]{\mathit{abc}}\) , shows a smooth envelope when plotted against elevation. We postulate that, for each catchment, they represent in situ corestones within a stratified weathering profile, many tens of meters in thickness, that has been subsequently exhumed by younger erosion. We formulate a simplified one-dimensional model for reduction in corestone size within a steady-state weathering profile that incorporates: (i) vertical fluid transport of the reactant and the soluble products of chemical weathering; (ii) linear kinetics of corestone reduction; and, subsequently, (iii) erosion. The rate of advance of a steady-state weathering profile is a statement of the mass balance between entering reactants and weathering components, here idealized as H+ and albite. The mathematical relations, \[\frac{1}{2}\frac{k{\upsilon}{\lambda}}{f_{AB}}({\gamma}c_{R})^{N}{=}K({\gamma}c_{R})^{N}{=}V \left(\frac{S_{0}}{6L{\ast}}\right),\] tie the laboratory-determined rate constant for dissolution of albite (k) to a generalized kinetic constant for the rate of decrease (K) in corestone diameter to the advance rate of the weathering profile (V). The last parentheses contain an effective roughness at the scale of the weathering profile, where S0 is the maximum size of initial bedrock blocks, inferred to be set by initial bedrock fracture spacing, and 3L* is the profile thickness. The laboratory scale roughness value, λ, is the ratio of the surface area accessed by BET analysis to that of the corestone grain scale. In the model, erosion is not coupled with weathering, although the presence of corestones of finite size, SE > 0, exiting at the erosional surface may be postulated to affect the erosional flux. The thickness of the corestone weathering profile derived for the model for the distance between bedrock and a corestone-free saprolite cap is approximately \[3L{\ast}{=}\frac{({\beta}qc_{R}) \left(\frac{M_{ab}}{f_{ab}{\rho}_{ab}}\right)S_{0}}{2{[}K({\gamma}c_{R})^{N}{]}}.\] This expression is the product of the effective pH buffering-adjusted input reactant flux per unit area times a stoichiometeric factor linking this to net albite dissolution, divided by the rate of corestone size reduction at the input concentration of protons. Further, the profile thickness scales with the input “particle” size, S0. The model fit, which yields the ratio \[\frac{S_{0}}{3L{\ast}}{\approx}0.02,\] is consistent with a rate constant for albite dissolution that lies between laboratory-measured and field-estimated values. Sensitivity to the reaction order of albite dissolution with respect to H+, N, is small, except near the base of the profile. This model yields insights into the relationship between fracture spacing and the evolution of particle size and chemistry in weathering profiles.

Long term changes of chemical weathering products in rivers heavily impacted from acid mine drainage: Insights on the impact of coal mining on regional and global carbon and sulfur budgets

The long term impacts of acid mine drainage (AMD) on stream chemistry and regional carbon and sulfur budgets were explored using watersheds of Pennsylvania underlain by extensive coal deposits. Areas of these watersheds have been mined for 200 yr, yet mining activity decreased to < 2% of peak by the late 1900s. A unique aspect of this study was the coupling of 100 yr of data on stream chemistry measurements with detailed coal mining data, which allowed for new budgets of the impact of mining on regional and global budgets. The Lackawanna River and upper Schuylkill River, both ~ 900 km 2 watersheds, witnessed dramatic changes in pH, alkalinity, calcium, magnesium and sulfate. Sulfate fluxes from these watersheds, for instance, were 4–12 times higher in the 1940s than they are currently. Fluxes of sulfate and magnesium from the Susquehanna River at Danville, the major tributary to the Chesapeake Bay, are currently 32 and 70% of what they were in the 1940s, while alkalinity fluxes have doubled and pH has recovered 0.8 pH units. The direct impact on regional carbon budgets through the degassing of CO 2 from carbonates was intense during the height of AMD but the long term regional impact is modest, resulting in the loss of ~ 3.1 Tg of carbon to the atmosphere over the last century. During the 1940s, the export of AMD derived sulfate to the 29,000 km 2 portion of the Susquehanna River studied here was twice as large as the current input from SO x deposition to the entire 71,000 km 2 Susquehanna watershed. This is surprising, comparing the small spatial footprint of AMD to the large footprint of the entire Susquehanna watershed. Normalizing these export rates to coal production data we estimate that global sulfur releases from AMD could account for 28–40% of riverine sulfate derived from pyrite oxidation, and be equal to ~ 20% of anthropogenic S from atmospheric deposition. This study emphasizes the potential importance of AMD to global S budgets, particularly since coal mining is predicted to increase by 50% in the coming century.

Effects of physical erosion on chemical denudation rates: A numerical modeling study of soil-mantled hillslopes

Many biogeochemical and Earth surface processes depend critically on chemical weathering. The immediate products of chemical weathering are present as solutes and secondary minerals in groundwater, soils, and streams, and form the nutritional foundation for terrestrial biogeochemistry. Chemical weathering also contributes to physical erosion by weakening bedrock and producing easily erodible regolith, and as the primary long-term sink for atmospheric CO 2 it modulates Earth's long-term climate via the greenhouse effect. Long-term chemical denudation rates on soil-mantled hillslopes can be estimated from cosmogenic radionuclide (CRN) concentrations in soil-borne quartz and the enrichment of a chemically inert tracer in soil relative to its parent bedrock, a technique that inherently assumes steady physical erosion over the timescale of CRN accumulation. We present a numerical model that computes changes in soil mineralogy and CRN concentrations under time-varying physical erosion rates, and we use this model to assess the accuracy of the CRN-based technique for estimating chemical denudation rates in non-steady conditions. Our modeling results suggest that CRN-based estimates of chemical denudation rates closely resemble actual chemical denudation rates averaged over the timescale of CRN accumulation, even during large-amplitude and long-period oscillations in physical erosion rates. For example, this model predicts that when physical erosion rates fluctuate sinusoidally by 50% of their mean over any period in time, CRN-based estimates of chemical denudation rates should differ from actual chemical denudation rates by less than 15%. Our model also implies that chemical denudation rates should approach zero both when physical erosion rates approach zero (because soluble minerals become depleted in the soil) and when physical erosion rates approach the maximum soil production rate (because soil thickness approaches zero). Modeled chemical denudation rates thus reach a maximum at intermediate physical erosion rates. If this relationship holds in nature, it implies that in rapidly eroding regions, further increases in physical erosion rates (e.g., due to increases in tectonic uplift rates) may not necessarily lead to faster chemical denudation on soil-mantled hillslopes.

Lithology and geochemistry of Triassic deposits in the southwest of the West Siberian geosyneclise

Sedimentological and geochemical studies of a Triassic volcanosedimentary section of the Tura Group on the southern margin of the Koltogory-Urengoi Rift have shown a wide occurrence of fine- and very fine-clastic turbidites with admixtures of glauconite and basic and acid pyroclastic material. According to petrographic and geochemical data, the section sandstones are mainly graywackes and partly litharenites, and the mudstones are montmorillonite clayey rocks with admixtures of chlorite, hydromica, and kaolinite. The sourcelands of the peneplaned plateau abound in basic volcanics, which suggests (by analogy with the Triassic strata of the Siberian Platform) a wider occurrence of flood basalts in the past. Most of these basalts were, most likely, eroded, which resulted in a predominance of rift basalts on the pre-Jurassic weathering surface. Along with tephra and volcanoclastics, the clastic rocks are dominated by products of chemical weathering developed after basic volcanics. Marine deposits revealed in the Koltogory-Urengoi Rift section suggest the inflow of sea waters from the northern (in the modern frame of reference) ocean basin localized north of the modern Severnaya Zemlya Archipelago. The sedimentation basin of the rift was a narrow but extended bay of the Red Sea type, where the formation of marine deposits was accompanied by the eruption of basalts in the area of Nikol'skaya BH-1 lasting up to the late Middle Triassic.

Strontium stable isotopes fractionate in the soil environments?

This study shows that the stable isotopic composition of strontium (the 88Sr/ 86Sr ratio expressed as δ 88/86Sr value relative to the NBS987 standard) varies significantly in sedimentary terrestrial environments. The abundances of 86Sr, 88Sr isotopes were analyzed by MC-ICP-MS “Nu Plasma”. All studied rocks and waters show δ 88/86Sr values that are distinctly different from the measured NBS987 standard (yielding 0.01 ± 0.05‰, all errors are reported as 2 σ). Modern corals from the northern Gulf of Aqaba, Red Sea yielded significantly different value than seawater (δ 88/86Sr = 0.22 ± 0.07‰, compared to 0.35 ± 0.06‰, respectively), in an excellent correlation with the δ 88/86Sr analyses reported by Fietzke and Eisenhauer [Fietzke, J., Eisenhauer, A., 2006. Determination of temperature-dependent stable strontium isotopes ( 88Sr/ 86Sr) fractionation via bracketing standard MC-ICP-MS. Geochm. Geophys. Geosyst. 7 (no. 8)] on other coral samples. All carbonate samples that originated in the marine environment: corals ( porites and acropora from the northern Gulf of Aqaba); Cretaceous limestone and runoff from the Judea Mountains as well as lacustrine evaporitic aragonite (Dead Sea); and Red Sea and Atlantic seawater yield an average δ 88/86Sr value of 0.26 ± 0.1‰. On the other hand, secondary materials (products of chemical weathering) from the terrestrial environment of the Judea Mountain such as terra rossa soil and speleothem calcite (that derives its Sr from the above-lying soil) yielded significantly lower δ 88/86Sr value of − 0.17 ± 0.06‰. This indicates that strontium isotopes fractionate in the soil environment calling for a possible development of strontium isotopes as a tracer for processes of chemical weathering and pedogenesis.

Petrochemistry of metapsammitic rocks from the Patom Highland: Reconstruction of the protolith composition

Precambrian psammitic rocks of the Patom Highland as constituents of metasedimentary groups belong to the quartz-polymictic family, which is divided in each group into the following five petrochemical types: (A) highly silicic quartz sandstones, (B) silicic quartz sandstones, (C) alkali silicic quartz sandstones, (D) Fe-Si polymictic sandstones, and (E) Fe-Al-Si polymictic sandstones. The mineralogic-petrographic classification elaborated by Shutov (1967) may be applied to the calculated quantitative mineral and component compositions of metasandstone protoliths. According to this classification, the petrochemical types A–E may be correlated with monomictic (A′), oligomictic (B′), and mesomictic (C′) sandstones, feldspar-quartz graywacke (D′) and graywacke proper (E′), respectively. Quartz-polymictic sandstones make up the direct petrographic (mineralogic-petrographic) series A′-B′-C′-D′-E′ and the almost mirror inverse series E′-D′-C′-B′. The direct series A′-E′ represent the transgressive branches of sedimentary cycles that begin with the crustal redeposited products of chemical weathering, including high-Al schists and monomictic (A′) and oligomictic (B′) quartz sandstones. As the humid climate became arid, the sandstones gave way to the mesomictic sandstones C′ and to the polymictic sandstones D′ and E′ in the middle sections of sedimentary cycles. The polymictic sandstones mark culminations of tectonic activity that led to the formation of high mountains. The inverse series E′-B′ begin from the periods of mountainous topography and characterize regressive branches of sedimentary cycles that mark the decreasing tectonic activity. Polymictic sandstones E′ and D′ are replaced by oligomictic sandstones B′ in these branches. Thus, petrographic or mineralogic-petrographic series reflect the compositional evolution of psammitic rocks between epochs of peneplanation. The termination of these epochs and resumption of orogenic movements are documented by deposition of the Teptorgo-Mama, Kadalikan, and Bodaibo sedimentary groups. The onset of tectonic events fell on the terminal Paleoproterozoic, Early Riphean, and the Middle-Late Riphean. The composition of sedimentary rocks underwent progressive changes during the tectonic evolution of the continental margin of the Siberian Craton and the concomitant variation of paleoclimate.

Investigation of the performance of a coring bit in frozen mud under Martian conditions of low temperature and pressure

A diamond‐impregnated bit will be the most probable choice for Mars drilling applications. This is because it can be used to drill or cut the hardest rocks, including the most common rocks on Mars, i.e., basalt and andesite (Bandfield et al., 2000). Recent results suggest a possibility of the Martian regolith containing clay minerals (Webster and Savage, 2004; Ruff, 2003), products of chemical weathering of certain minerals such as, for example, olivine (Hoefen et al., 2003) in the presence of water. Thus, in addition to volcanic rocks, the bit might also have to drill through other geological formations, including, for example, clay‐rich soils commonly known as mud. This argument supposes that the Martian drill will have no option for changing bits. Thus the question exists, whether a bit of the diamond‐impregnated type can also be used successfully in frozen mud. It was found that mud exhibits three different physical conditions, depending on its temperature. The bit can effectively drill and the entire core can be successfully recovered provided that the mud is kept in the temperature region between approximately −8°C and 0°C. Above 0°C the mud becomes sticky. Below −8°C the mud is hard frozen and the bit cannot penetrate it successfully. Measurement of the electrical resistance of the mud directly below the bit while drilling was used together with the bit temperature to assess the physical state of the mud below the bit.

Geochemical processes in the Onyx River, Wright Valley, Antarctica: Major ions, nutrients, trace metals

We present data on major ions, nutrients and trace metals in an Antarctic stream. The Onyx River is located in Wright Valley (77–32 S; 161–34 E), one of a group of ancient river and glacier-carved landforms that comprise the McMurdo Dry Valleys of Antarctica. The river is more than 30 km long and is the largest of the glacial meltwater streams that characterize this relatively ice-free region near the Ross Sea. The complete absence of rainfall in the region and the usually small contributions of glacially derived tributaries to the main channel make this a comparatively simple system for geochemical investigation. Moreover, the lack of human impacts, past or present, provides an increasingly rare window onto a pristine aquatic system. For all major ions and silica, we observe increasing concentrations with distance from Lake Brownworth down to the recording weir near Lake Vanda. Chemical weathering rates are unexpectedly high and may be related to the rapid dissolution of ancient carbonate deposits and to the severe physical weathering associated with the harsh Antarctic winter. Of the nutrients, nitrate and dissolved reactive phosphate appear to have quite different sources. Nitrate is enriched in waters near the Lower Wright Glacier and may ultimately be derived from stratospheric sources; while phosphate is likely to be the product of chemical weathering of valley rocks and soils. We confirm the work of earlier investigations regarding the importance of the Boulder Pavement as a nutrient sink. Dissolved Mn, Fe, Ni, Cu, and Cd are present at nanomolar levels and, in all cases, the concentrations of these metals are lower than in average world river water. We hypothesize that metal uptake and exchange with particulate phases along the course of the river may serve as a buffer for the dissolved load. Concurrent study of these three solute classes points out significant differences in the mechanisms and sites of their removal from the Onyx River.

On the Development of Autochthonous Blockfields in the Grey Basalts of Sub-Antarctic Marion Island

Sub-Antarctic Marion Island has experienced a periglacial climate since the Last Glacial Maximum. Post-glacial allochthonous openwork accumulations appear to be well developed below 750 m a.s.l., although basalt surfaces exhibit only poorly developed autochthonous blockfields. Bedrock disintegration appears to be confined to a single layer of detritus, probably formed by pressure release on deglaciation. Holocene environmental conditions have not produced chemical weathering products and have preserved the layer of mechanically derived residuals. At altitudes above 750 m a.s.l., blockfield formation appears to be limited by former permanent snow cover. Given the ideal conditions for frost action throughout the Holocene, the absence of well-developed mechanically derived detritus supports the argument for longer time intervals of formation and the non-periglacial origins of autochthonous blockfields.

Dust production and deposition in Asia and the north Pacific Ocean over the past 12 Myr

The silicate fractions of recent pelagic sediments in the central north Pacific Ocean are dominated by eolian dust derived from central Asia. An 11 Myr sedimentary record at ODP Sites 885/886 at 44.7°N, 168.3°W allows the evaluation of how such dust and its sources have changed in response to late Cenozoic climate and tectonics. The extracted eolian fraction contains variable amounts (>70%) of clay minerals with subordinate quartz and plagioclase. Uniform Nd isotopic compositions ( ϵ Nd=−8.6 to −10.5) and Sm/Nd ratios (0.170–0.192) for most of the 11 Myr record demonstrate a well-mixed provenance in the basins north of the Tibetan Plateau and the Gobi Desert that was a source of dust long before the oldest preserved Asian loess formed. ϵ Nd values of up to −6.5 for samples <2.9 Ma indicate ≤35 wt% admixture of a young, Kamchatka-like volcanic arc component. The coherence of Pb and Nd in the erosional cycle allows us to constrain the Pb isotopic composition of Asian loess devoid of anthropogenic contamination to 206Pb/ 204Pb=18.97±0.06, 207Pb/ 204Pb=15.67±0.02, 208Pb/ 204Pb=39.19±0.11. 87Sr/ 86Sr (0.711–0.721) and Rb/Sr ratios (0.39–1.1) vary with dust mineralogy and provide an age indication of ∼250 Ma. 40Ar/ 39Ar ages of six dust samples are uniform around 200 Ma and match the K–Ar ages of modern dust deposited on Hawaii. These data reflect the weighted age average of illite formation. Changes from illite≥smectite with significant kaolinite to illite- and chlorite-rich, kaolinite-free assemblages since the late Pliocene document changes in the intensity of chemical weathering in the source region. Such weathering evidently did not disturb the K–Ar systematics, and only induced scatter in the Rb–Sr data. We propose that when smectite forms at the expense of illite, K and Ar are quantitatively lost from what becomes smectite, but are quantitatively retained in adjacent illite layers. 40Ar/ 39Ar age data, therefore, are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite, the major K-bearing phase in the dust. Over the past 12 Myr, the dust flux to the north Pacific increased by more than an order of magnitude, documenting a substantial drying of central Asia. This climatic change, however, did not alter the ultimate source of the dust, and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern Asia and the Pacific Ocean.