Geochemistry and mineralogy of the Oligo-Miocene sediments of the Valley of Lakes, Mongolia

Chemical weathering and progressing alteration as possible controlling factors for creeping landslides

Landslides can behave as dynamic processes, which emerge from the complex interplay of tectonics, erosion, weathering and gravitational influences, triggered by various hydrological, mineralogical, biological and geotechnical factors. Integral studies to assess the mechanisms underlying landslide initiation and progression are mainly focussed on specific cases with high geohazard potential. The landslide near Stadtschlaining (Austria) represents a key study site to elucidate the impacts of pelitic sediment composition, weathering regime, alteration patterns and hydrochemistry on recurrent damage progression in the local infrastructure. Based on field work, soil-mechanical logging (Atterberg limits, undrained strength, friction angles), water chemistry (ICP-OES, IC, hydrochemical modeling), solid-phase characterization (XRD, XRF, SEM) and sorption experiments we establish a conceptual model for initiating and progressing of landslides: Infiltration of low mineralized meteoric water (EC: <200 μS/cm) in permeable limonitic gravels triggers chemical weathering of greenschist-derived detritus and promotes its transformation into kaolinite and smectite. The clayey strata (>50 wt% of clay minerals) create zones of mechanical and chemical weakness in the underground (~4-6 m below ground level), which are characterized by particle disintegration/delamination, slip bedding and deformations, and development of porous layers depicting water flow paths. Subsequent Na⁺ exchange for bivalent ions in the smectite interlayer delivered by percolating, highly mineralized water (EC: 1600-5100 μS/cm) is caused by de-icing salt and fertilizer applications during winter and late summer, and yield in i) decohesion and physical breakdown of the particle aggregates and ii) swelling of the clay matrix in early spring and autumn. These processes reduce the shear strength of the pelitic sediments, resulting in failure and initiation of landslides (deformation: ~500 mm within a month) and subsequent steady creeping motion (deformation: ~100 mm in 6 months). Customized engineered solutions to prevent landslides in this area are presented, which can be conveyed to analogous landslide-affected areas worldwide.

Removal of Barium from Solution by Natural and Iron(III) Oxide-Modified Allophane, Beidellite and Zeolite Adsorbents

Efficient capture of barium (Ba) from solution is a serious task in environmental protection and remediation. Herein, the capacity and the mechanism of Ba adsorption by natural and iron(III) oxide (FeO) modified allophane (ALO), beidellite (BEI) and zeolite (ZEO) were investigated by considering the effects of contact time, temperature, pH, Ba2+ concentration, adsorbent dosage, the presence of competitive ions and adsorption-desorption cycles (regenerability). Physicochemical and mineralogical properties of the adsorbents were characterized by XRD, FTIR, SEM with EDX and N2 physisorption techniques. The Ba2+ adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium conditions were reached within <30 min. BEI, ALO and ZEO with(out) FeO-modification yielded removal efficiencies for Ba2+ of up to 99.9%, 97% and 22% at optimum pH (pH 7.5-8.0). Adsorption isotherms fitted to the Langmuir model, which revealed the highest adsorption capacities for BEI and FeO-BEI (44.8 mg/g and 38.6 mg/g at 313 K). Preferential ion uptake followed in the order: Ba2+ > K+ > Ca2+ >> Mg2+ for all adsorbents; however, BEI and FeO-BEI showed the highest selectivity for Ba2+ among all materials tested. Barium removal from solution was governed by physical adsorption besides ion exchange, intercalation, surface complexation and precipitation, depending mainly on the absorbent type and operational conditions. BEI and FeO-BEI showed a high regenerability (>70-80% desorption efficiency after 5 cycles) and could be considered as efficient sorbent materials for wastewater clean-up.

Removal of Barium, Cobalt, Strontium, and Zinc from Solution by Natural and Synthetic Allophane Adsorbents

The capacity and mechanism of the adsorption of aqueous barium (Ba), cobalt (Co), strontium (Sr), and zinc (Zn) by Ecuadorian (NatAllo) and synthetic (SynAllo-1 and SynAllo-2) allophanes were studied as a function of contact time, pH, and metal ion concentration using kinetic and equilibrium experiments. The mineralogy, nano-structure, and chemical composition of the allophanes were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and specific surface area analyses. The evolution of adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium between aqueous metal ions and allophane was reached within <10 min. The metal ion removal efficiencies varied from 0.7 to 99.7% at pH 4.0 to 8.5. At equilibrium, the adsorption behavior is better described by the Langmuir model than by the Dubinin–Radushkevich model, yielding sorption capacities of 10.6, 17.2, and 38.6 mg/g for Ba 2 + , 12.4, 19.3, and 29.0 mg/g for HCoO 2 − ; 7.2, 15.9, and 34.4 mg/g for Sr 2 + ; and 20.9, 26.9, and 36.9 mg/g for Zn 2 + , by NatAllo, SynAllo-2, and SynAllo-1, respectively. The uptake mechanism is based on a physical adsorption process rather than chemical ion exchange. Allophane holds great potential to effectively remove aqueous metal ions over a wide pH range and could be used instead of other commercially available sorbent materials such as zeolites, montmorillonite, carbonates, and phosphates for special wastewater treatment applications.

Oligocene stratigraphy across the Eocene and Miocene boundaries in the Valley of Lakes (Mongolia)

Cenozoic sediments of the Taatsiin Gol and TaatsiinTsagaan Nuur area are rich in fossils that provide unique evidence of mammal evolution in Mongolia. The strata are intercalated with basalt flows. 40Ar/39Ar data of the basalts frame the time of sediment deposition and mammal evolution and enable a composite age chronology for the studied area. We investigated 20 geological sections and 6 fossil localities of Oligocene and early Miocene deposits from this region. Seventy fossil beds yielded more than 19,000 mammal fossils. This huge collection encompasses 175 mammal species: 50% Rodentia, 13% Eulipotyphla and Didelphomorphia, and 12% Lagomorpha. The remaining 25% of species are distributed among herbivorous and carnivorous large mammals. The representation of lower vertebrates and gastropods is comparatively poor. Several hundred SEM images illustrate the diversity of Marsupialia, Eulipotyphla, and Rodentia dentition and give insight into small mammal evolution in Mongolia during the Oligocene and early Miocene. This dataset, the radiometric ages of basalt I (∼31.5 Ma) and basalt II (∼27 Ma), and the magnetostratigraphic data provide ages of mammal assemblages and time ranges of the Mongolian biozones: letter zone A ranges from ∼33 to ∼31.5 Ma, letter zone B from ∼31.5 to ∼28 Ma, letter zone C from ∼28 to 25.6 Ma, letter zone C1 from 25.6 to 24 Ma, letter zone C1-D from 24 to ∼23 Ma, and letter zone D from ∼23 to ∼21 Ma.