The effect of fluid composition on the behavior of well cemented, quartz-rich sandstone during faulting

Previous studies [O'Kane, A., Onasch, C.M., Farver, J., 2007. The role of fluids in low-temperature, fault-related deformation of quartz arenite. Journal of Structural Geology 29, 819--836; Cook, J., Dunne, W.M., Onasch, C.M., 2006. Development of a dilatant damage zone along a thrust relay in a low-porosity quartz arenite, Journal of Structural Geology 28, 776–792] found that quartz arenite within two fault zones in the Appalachian foreland thrust belt displays very different structural styles and histories despite deforming at similar pressures and temperatures during the Alleghanian orogeny. A comparison of the grain-scale deformation and fluid histories using transmitted and cathodoluminescence microscopy and fluid inclusion microthermometry, shows that fluid composition was a controlling factor for causing these differences. The Cove fault zone deformed in the presence of aqueous fluids, first a CaCl₂ brine and then an iron-rich fluid. The precipitation of quartz cement from the brine kept pace with brittle deformation, maintaining overall rock cohesion in the fault zone. The introduction of iron-rich fluids caused a switch from precipitation to dissolution of quartz, along with precipitation of goethite. In a damage zone along a backthrust in the Cave Mountain anticline, early deformation occurred in the presence of an aqueous fluid from which quartz was precipitated. The latest deformation, however, occurred in the presence of a methane-rich fluid, which inhibited the precipitation of quartz cement producing porous breccias and open fractures despite deformation at 6 km depth. Fluid composition not only affected cementation in the fault zones, but also the selection of grain-scale deformation mechanisms. Therefore, it is a controlling factor in determining the behavior and strength of these fault zones.     

Water quality assessment of Wei River, China using fuzzy synthetic evaluation

Wei River is the major source of water for the urban residents, industrial production and agricultural activities in the central Shaanxi plain of China. Water quality of the Wei River was determined by collecting water samples from 25 locations along the Baoji Xi’an reach and analyzing for pH, EC, BOD₅, DO, COD, F, Se, As, and Hg. Fuzzy synthetic evaluation with the entropy method for weight determination was used to assess the water quality of the river. Results indicate that the water quality of 23 sampling sites fall into the fifth grade (bad level), whereas two sampling sites are in the fourth grade (poor level). The comparison of this method with the typical fuzzy synthetic evaluation shows that it is effective in water quality assessment. The assessment results indicate that the Wei River is heavily polluted at most of the sampling locations, with mercury as the major pollutant. Strict enforcement of the regulations for domestic and industrial wastewater discharges is vital to avoid damage to the water environment and to protect human and ecological health.     

Watershed geochemistry: The control of aqueous solutions by soil materials in a small watershed

Laboratory and field data indicate that the aqueous geochemistry of a small watershed in siliceous materials is largely determined by reactions between soil and water. For dissolved SiO₂, Ca⁺², K⁺, Na⁺, a reversible steady state is achieved in the soil within hours. The solute concentrations are in equilibrium with kaolinite, the end-product in the local weathering sequence. The processes occur in a drainage basin in which solution activities are the predominant form of erosion.     

Dynamic response by large step integration

A family of unconditionally stable algorithms for the economical computation of large linear dynamic systems is described and applied. Possible application to divergent systems is considered and some of the difficulties of extending the use of the algorithms to non-linear systems are discussed. In the Appendix a previously developed conditionally stable algorithm is applied to the non-linear gust response of a prestressed cable roof structure over the Munich Olympic Stadium. The idealization involves 1,164 degrees of freedom.     

Evaluation of the Johnson and Ettinger Model for Prediction of Indoor Air Quality

Screening level models are now commonly used to estimate vapor intrusion for subsurface volatile organic compounds (VQCs). Significant uncertainty is associated with processes and models and, to date, there has been only limited field-based evaluation of models for this pathway. To address these limitations, a comprehensive evaluation of the Johnson and Ettinger (J&E) model is provided through sensitivity analysis, comparisons of model-predicted to measured vapor intrusion for 11 petroleum hydrocarbon and chlorinated solvent sites, and review of radon and flux chamber studies. Significant intrusion was measured at five of 12 sites with measured vapor attenuation ratios (α_m's) (indoor air/source vapor) ranging from ∼1 × 10⁻⁶ to 1 × 10⁻⁴. Higher attenuation ratios were measured for studies using radon, inert tracers, and flux chambers; however, these ratios are conservative owing to boundary conditions and tracer properties that are different than those at most VOC-contaminated sites. Reasonable predictions were obtained using the J&E model with comparisons indicating that model-predicted vapor attenuation ratios (α_p's) were on the same order, or less than the α_m's. For several sites, the α_m were approximately two orders of magnitude less than the α_p's indicating that the J&E model is conservative in these cases. The model comparisons highlight the importance in using appropriate input parameters for the J&E model. The regulatory implications associated with use of the J&E model to derive screening criteria are also discussed.     

Organic carbon to Th ratios of marine organic matter

Uncertainties in the determinations of particulate organic carbon flux from measurements of the disequilibrium between ²³⁴Th and its mother isotope uranium depend largely on the determination of the organic carbon to ²³⁴thorium (OC : ²³⁴Th) ratio. The variability of the OC : ²³⁴Th ratio in different size fractions of suspended matter, ranging from the truly dissolved (< 3 or 10 kDa) fraction to several millimeter sized marine snow, as well as from sediment trap material was assessed during an eight-day cruise off the coast of California in Spring 1997. The affinity of polysaccharide particles called TEP (transparent exopolymer particles) and inorganic clays to ²³⁴Th was investigated through correlations. The observed decrease in the OC : ²³⁴Th ratio with size, within the truly dissolved to small particle size range, is consistent with concepts of irreversible colloidal aggregation of non-porous nano-aggregates. No consistent trend in the OC : ²³⁴Th ratio was observed for particles between 1 or 10 to 6000 μm. Origin and fate of marine particles belonging to this size range are diverse and interactions with ²³⁴Th too complex to expect a consistent relationship between OC : ²³⁴Th ratio and size, if all categories of particles are included. The relationship between OC and ²³⁴Th was significant when data from the truly dissolved fraction were excluded. However, variability was very large, implying that OC flux calculations using different collection methods (e.g. sediment trap, Niskin bottles or pumps) would differ significantly. Therefore a large uncertainty in OC flux calculations based on the ²³⁴Th method exist due to individual decisions as to which types or size classes of particles best represent sinking material in a specific area. Preferential binding of ²³⁴Th to specific substance classes could explain the high variability in the relationship between OC and ²³⁴Th. At 15 m, in the absence of lithogenic material, the OC : ²³⁴Th ratio was a function of the fraction of TEP or TEP-precursors in OC, confirming that acidic polysaccharides have a high affinity for ²³⁴Th and that TEP carry a ligand for ²³⁴Th. Preferential binding to TEP might change distribution patterns of ²³⁴Th considerably, as TEP may sink when included in large aggregates, or remain suspended or even ascend when existing as individual particles or microaggregates. In the presence of lithogenic matter, at depths below 30 m, the ratio between ²³⁴Th and OC was linearly related to the ratio between alumino silicates and C. The affinity of inorganic substances to ²³⁴Th is known to be relatively low, suggesting that a coating of acidic polysaccharides was responsible for the apparently high affinity between ²³⁴Th and lithogenic material. Overall, OC : ²³⁴Th ratios of all material collected during this investigation can best be explained by differential binding of ²³⁴Th to both TEP and TEP-precursors, as well as to lithogenic minerals, which were very abundant in an intermediate nepheloid layer between 50 and 90 m.     

Effect of organic matter and selected heavy metals on sorption of acenaphthene,fluorene and fluoranthene onto various clays and clay minerals

The effects of organic matter (80% humic and 15% fulvic acid) and coexistence of heavy metals (Ni, Pb and Zn) on sorption of three polycyclic aromatic hydrocarbons (PAHs)—acenaphthene, fluorene and fluoranthene—were examined for kaolinite, 60% kaolinite?+?40% sand, and 43% kaolinite?+?42% sand?+?15% bentonite. In total 108 batch sorption tests of PAHs were conducted for three types of clay mineral mixtures in six possible combinations of soil organic matter and heavy metal contents from no heavy metals and organic matter added to maximum organic matter added with spiked heavy metals. Results showed that the existence of metals increased the sorption of PAHs onto kaolinite from 4.7% for acenaphthene to 17.9% for fluoranthene. Organic matter in a kaolinite-sand-bentonite matrix could increase PAH sorption by up to 140% for fluoranthene. In all cases, increases were greater for fluoranthene, a larger PAH molecule. Heavy metals coexisting with organic matter led to enhanced sorption of PAHs compared to clay minerals without organic matter. Synergistic effects of organic matter and heavy metals on PAH sorption increments in the mixtures studied were such that the overall sorption could be 10–41% higher than that based on summation of the separate effects of metals and organics.     

Fluvial incision and coarse gravel redistribution across the modern Dead Sea shelf as a result of base-level fall

Global eustatic lowstands can expose vast areas of continental shelves, and occasionally the shelf edge and the continental slope. The degree of fluvial connectivity to receding shores influences the redistribution of sediments across these emerging landscapes. Shelf and slope emergence in the Dead Sea since the middle of the 20th century, offers a rare opportunity to examine evolution of stream connectivity in response to continuous base-level decline. We characterize the connectivity evolution of two streams, using high-resolution time series of aerial imagery and elevation models, field mapping, and grain-size analyses. Our rich spatiotemporal dataset of evolving channel geomorphology, sediment transport conditions, and sediment redistribution, allows calculating potential coarse sediment mobility in response to base level decline. Following shelf emergence, alluvial fans first prograded onto the low-gradient shelf under unfavourable conditions for transporting coarse sediment to the regressing shoreline. Then, with shelf and slope emergence, the two adjacent streams evolved differently. The smaller, more arid watershed still maintains its highstand delta progradation on the shelf and is practically disconnected from the receding lake. The larger catchment, heading in wetter environments and having a narrower shelf, has incised the shelf and renewed and gradually intensified the sediment transport from the highstand to the lowstand delta. Sediment mobilization to lowstand shorelines is controlled by the evolution of the channel profile and by the average speed of gravel transport (10s-100s m yr^-1). These findings from the Dead Sea are relevant to fluvial processes operating on continental shelves during glacial maxima. Streams would have commonly stored high proportions of their coarse sediment on the continental shelves rather than efficiently connecting with the lowstand level. Additionally, differences in sediment routing patterns should exist among nearby streams, primarily due to continental margin geometry and watershed hydrology. © 2019 John Wiley & Sons, Ltd.     

Thirty years of tephra erosion following the 1980 eruption of Mount St. Helens

Repeated measurement of tephra erosion near Mount St. Helens over a 30-year period at steel stakes, installed on 10 hillslopes in the months following the 1980 eruption, provides a unique long-term record of changing processes, controls and rates of erosion. Intensive monitoring in the first three post-eruption years showed erosion declined rapidly as processes shifted from sheetwash and rilling to rainsplash. To test predictions about changes to long-term rates and processes made based on the 3-year record, we remeasured sites in 1992, 2000 and 2010. Average annual erosion from 1983 to 1992 averaged 3.1 mm year⁻¹ and ranged from 1.4 to 5.9 mm year⁻¹, with the highest rate on moderately steep slopes. Stakes in rills in 1983 generally recorded deposition as the rills became rounded, filled and indistinct by 1992, indicating a continued shift in process dominance to rainsplash, frost action and bioturbation. Recovering plants, where present, also slowed erosion. However, in the second and third decades even unvegetated hillslopes ceased recording net measurable erosion; physical processes had stabilized surfaces from sheetwash and rill erosion in the first few years, and they appear to have later stabilized surfaces against rainsplash erosion in the following few decades. Comparison of erosion rates with suspended sediment flux indicates that within about 6 years post-eruption, suspended sediment yield from tephra-covered slopes was indistinguishable from that in forested basins. Thirty years after its deposition, on moderate and gentle hillslopes, most tephra remained; in well-vegetated areas, plant litter accumulated and soil developed, and where the surface remained barren, bioturbation and rainsplash redistributed and mixed tephra. These findings extend our understanding from shorter-term studies of the evolution of erosion processes on freshly created substrate, confirm earlier predictions about temporal changes to tephra erosion following eruptions, and provide insight into the conditions under which tephra layers are preserved. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.