Experimental determination of synthetic NdPO4 monazite end-member solubility in water from 21°C to 300°C: implications for rare earth element mobility in crustal fluids

The solubility of synthetic NdPO₄ monazite end-member has been determined experimentally from 21 to 300°C in aqueous solutions at pH = 2, and at 21°C and pH = 2 for GdPO₄. Measurements were performed in batch reactors, with regular solution sampling for pH measurement, rare earths and phosphorous analysis by inductively coupled plasma mass spectrometry (ICP-MS) coupled with a desolvation system. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to check that no reprecipitation of secondary phases occurred and that the mineral surfaces remained those of a monazite. Coupled with speciation calculations, measured solution compositions permitted the determination of NdPO₄ and GdPO₄ solubility products which are in general agreement with previous experimental determination on rhabdophane at 25°C, but showing that monazite is more than two orders of magnitude less soluble than inferred on the basis of previous thermodynamic estimates. The temperature evolution from 21 to 300°C of the equilibrium constant (K) of the NdPO₄ monazite end-member dissolution reaction given by:

     

Piezometric levels as possible indicator of aquifer structure: analysis of the data from Maknassy basin aquifer system (Central Tunisia)

The knowledge of piezometric data is of vast interest in many applications, such as assessing groundwater flow direction and identifying recharge zone of the aquifer. In this paper, a methodology is presented as a complementary approach to characterize multilayered aquifer system structure and functioning using piezometric data and the cartography of the hydraulic charge difference. The methodology is presented to gradually discriminate the aquifer system levels and to evaluate the spatial distribution of hydraulic heads. The hydraulic charge difference mapping permits to track spatial evolution of the impermeable levels. The methodology has been applied over the Maknassy basin aquifer system, located in central Tunisia. The obtained results, showing the multilayered aquifer structure, are validated using hydrochemical approach and piezometric data not considered in the reasoning.     

Onset of Hydraulic Fracture Initiation Monitored by Acoustic Emission and Volumetric Deformation Measurements

In this paper, the results of laboratory studies of fracture initiation, early propagation and breakdown are reported. Three experiments were conducted on a low permeability sandstone block, loaded in a polyaxial test frame, to representative effective in situ stress conditions. The blocks were instrumented with acoustic emission (AE) and volumetric deformation sensors. In two experiments, fluids of different viscosity were injected into the wellbore, fluid injection was interrupted soon after the breakdown pressure had been reached. This allowed us to investigate hydraulic fracture initiation. In the third test, fracture initiation criteria were applied to stop hydraulic fracture propagation significantly earlier, prior to breakdown, and as it propagated a short distance from the wellbore. The analysis of AE results shows an increase in AE activity and a change in the AE spatial correlation, during the fracture initiation. This early stage of fracturing correlates strongly with the onset of rock volumetric deformation, and is confirmed by the analysis of ultrasonic transmission monitoring. The rock microstructure, after the test, was investigated by analysis of scanning electron microscope images. These indicated the development of leak-off zone near the wellbore and a dry hydraulic fracture at the farther distance from the wellbore.     

Preliminary estimates of regolith generation and mobility in the Susquehanna Shale Hills Critical Zone Observatory,Pennsylvania, using meteoric 10Be

This study seeks to quantify the rate and timing of regolith generation in the Critical Zone at the Susquehanna Shale Hills Critical Zone Observatory (SSHO). Meteoric ¹⁰Be depth profiles were determined using measurements from 30 hillslope soil and bedrock core samples in an effort to constrain ¹⁰Be inventories. The SSHO is located in the temperate climate zone of central Pennsylvania and comprises a first-order watershed developed entirely on a Fe-rich, organic-poor, Silurian-aged shale. Two major perturbations to the landscape have occurred at SSHO in the geologically recent past, including significant and sustained periglacial activity until after the retreat of the Laurentide ice sheet (～21 ka) and deforestation during early colonial land-use. Bulk soil samples (n = 16) were collected at three locations along a planar hillslope on the southern ridge of the catchment, representing the ridge top, mid-slope and valley floor. Rock chip samples (n = 14) were also collected from a 24 m deep core drilled into the northern ridge top. All meteoric ¹⁰Be concentration profiles show a declining trend with depth, with most of the ¹⁰Be retained in the uppermost decimeters of the soil. Meteoric ¹⁰Be inventories are higher at the mid-slope and valley floor sample sites, at 3.71 ± 0.02 × 10¹⁰ at/cm² and 3.69 ± 0.02 × 10¹⁰ at/cm², than at the ridge top site (1.90 ± 0.01 × 10¹⁰ at/cm²). The ¹⁰Be inventory at the convex ridge top site implies a minimum residence time of ～10.6 ka, or if erosion is steady, an erosion rate of 19.4 ± 0.2 m/My.     

Site selectivity of the boring Rogerella isp. infesting Cardiaster granulosus (Goldfuss) (Echinoidea) in the type Maastrichtian (Upper Cretaceous,Belgium)

A burrowing spatangoid echinoid (heart urchin), Cardiaster granulosus (Goldfuss), from the type area of the Maastrichtian Stage (Upper Cretaceous) in Belgium, was infested only in the plates of the ambulacral petals by acrothoracian barnacle borings, Rogerella isp. This infestation was after the death and exhumation of the echinoid. The distribution of Rogerella may indicate the azimuth of current flow at the time of exhumation prior to final burial. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental studies of equilibrium iron isotope fractionation in ferric aquo-chloro complexes

Here we compare new experimental studies with theoretical predictions of equilibrium iron isotopic fractionation among aqueous ferric chloride complexes (Fe(H₂O)₆³⁺, FeCl(H₂O)₅²⁺, FeCl₂(H₂O)₄⁺, FeCl₃ (H₂O)₃, and FeCl₄^-), using the Fe-Cl-H₂O system as a simple, easily-modeled example of the larger variety of iron-ligand compounds, such as chlorides, sulfides, simple organic acids, and siderophores. Isotopic fractionation (⁵⁶Fe/⁵⁴Fe) among naturally occuring iron-bearing species at Earth surface temperatures (up to ∼3‰) is usually attributed to redox effects in the environment. However, theoretical modeling of reduced isotopic partition functions among iron-bearing species in solution also predicts fractionations of similar magnitude due to non-redox changes in speciation (i.e., ligand bond strength and coordination number). In the present study, fractionations are measured in a series of low pH ([H⁺] = 5 M) solutions of ferric chloride (total Fe = 0.0749 mol/L) at chlorinities ranging from 0.5 to 5.0 mol/L. Advantage is taken of the unique solubility of FeCl₄^- in immiscible diethyl ether to create a separate spectator phase, used to monitor changing fractionation in the aqueous solution. Δ⁵⁶Fe_aq-eth = δ⁵⁶Fe (total Fe remaining in aqueous phase)−δ⁵⁶Fe (FeCl₄^- in ether phase) is determined for each solution via MC-ICPMS analysis.Both experiments and theoretical calculations of Δ⁵⁶Fe_aq-eth show a downward trend with increasing chlorinity: Δ⁵⁶Fe_aq-eth is greatest at low chlorinity, where FeCl₂(H₂O)₄⁺ is the dominant species, and smallest at high chlorinity where FeCl₃(H₂O)₃ is dominant. The experimental Δ⁵⁶Fe_aq-eth ranges from 0.8‰ at [Cl^-] = 0.5 M to 0.0‰ at [Cl^-] = 5.0 M, a decrease in aqueous-ether fractionation of 0.8‰. This is very close to the theoretically predicted decreases in Δ⁵⁶Fe_aq-eth, which range from 1.0 to 0.7‰, depending on the ab initio model.The rate of isotopic exchange and attainment of equilibrium are shown using spiked reversal experiments in conjunction with the two-phase aqueous-ether system. Equilibrium under the experimental conditions is established within 30 min.The general agreement between theoretical predictions and experimental results points to substantial equilibrium isotopic fractionation among aqueous ferric chloride complexes and a decrease in ⁵⁶Fe/⁵⁴Fe as the Cl^-/Fe³⁺ ion ratio increases. The effects on isotopic fractionation shown by the modeling of this simple iron-ligand system imply that ligands present in an aqueous environment are potentially important drivers of fractionation, are indicative of possible fractionation effects due to other speciation effects (such as iron-sulfide systems or iron bonding with organic ligands), and must be considered when interpreting iron isotope fractionation in the geological record.     

Holocene Climate in the Northern Great Plains Inferred from Sediment Stratigraphy, Stable Isotopes, Carbonate Geochemistry, Diatoms, and Pollen at Moon Lake, North Dakota

Seismic stratigraphy, sedimentary facies, pollen stratigraphy, diatom-inferred salinity, stable isotope (δ¹⁸O and δ¹³C), and chemical composition (Sr/Ca and Mg/Ca) of authigenic carbonates from Moon Lake cores provide a congruent Holocene record of effective moisture for the eastern Northern Great Plains. Between 11,700 and 9500¹⁴C yr B.P., the climate was cool and moist. A gradual decrease in effective moisture occurred between 9500 and 7100¹⁴C yr B.P. A change at about 7100¹⁴C yr B.P. inaugurated the most arid period during the Holocene. Between 7100 and 4000¹⁴C yr B.P., three arid phases occurred at 6600–6200¹⁴C yr B.P., 5400–5200¹⁴C yr B.P., and 4800–4600¹⁴C yr B.P. Effective moisture generally increased after 4000¹⁴C yr B.P., but periods of low effective moisture occurred between 2900–2800¹⁴C yr B.P. and 1200–800¹⁴C yr B.P. The data also suggest high climatic variability during the last few centuries. Despite the overall congruence, the biological (diatom), sedimentological, isotopic, and chemical proxies were occassionally out of phase. At these times the evaporative process was not the only control of lake-water chemical and isotopic composition.     

The Low Compaction Grading Technique on Steep Reclaimed Slopes: Soil Characterization and Static Slope Stability

Since the Surface Mining and Control Reclamation Act of 1977, US coal mining companies have been required by law to restore the approximate ground contours that existed prior to mining. To ensure mass stability and limit erosion, the reclaimed materials have traditionally been placed with significant compaction energy. The Forest Reclamation Approach (FRA) is a relatively new approach that has been successfully used to facilitate the fast establishment of native healthy forests. The FRA method specifies the use of low compaction energy in the top 1.2–1.5 m of the contour, which may be in conflict with general considerations for mechanical slope stability. Although successful for reforestation, the stability of FRA slopes has not been fully investigated and a rational stability method has not been identified. Further, a mechanics-based analysis is limited due to the significant amount of oversize particles which makes the sampling and measurement of soil strength properties difficult. To investigate the stability of steep FRA slopes (steeper than 20°), three reclaimed coal mining sites in the Appalachian region of East Tennessee were investigated. The stability was evaluated by several methods to identify the predominant failure modes. The infinite slope method, coupled with the estimation of the shear strength from field observations, was shown to provide a rational means to evaluate the stability of FRA slopes. The analysis results suggest that the low compaction of the surface materials may not compromise the long-term stability for the sites and material properties investigated.     

Seasonal Occurrence of Cownose Rays (Rhinoptera bonasus) in North Carolina’s Estuarine and Coastal Waters

The seasonal occurrence of cownose rays (Rhinoptera bonasus) within North Carolina’s estuarine and coastal waters was examined from aerial surveys conducted during 2004–2006. Generalized linear models were used to assess the influence of several variables (month, year, habitat type, sea surface temperature, and turbidity) on predicted counts of cownose rays. The spatial distributions of rays were compared by season, and differences in group size were tested as a function of season and habitat. Cownose ray data associated with the North Carolina Division of Marine Fisheries (NCDMF) fishery independent gill net sampling program in Pamlico Sound was also examined as a function of season and year, and compared with aerial observations. Rays immigrated into the region in mid-spring (April), dispersed throughout the estuary in the summer (June–August), and emigrated by late autumn (November). Predicted counts were highest in the spring (April, May) and autumn (September–November) for coastal habitats and highest in the summer for estuarine habitats. Predicted counts were also higher in the coastal region than estuarine and higher when sea surface temperatures were above average. Comparison of group size by habitat type revealed substantially larger group sizes in the coastal habitat than the estuarine. In addition, for the estuary, spring surveys had larger group sizes than summer surveys; for the coastal habitat, autumn group sizes were significantly larger than spring or summer group sizes. The NCDMF gill net sampling surveys indicated similar trends in monthly migration patterns as well as increased ray abundance in 2008 and 2009 compared with 2003–2007. These results suggest that North Carolina’s waters serve as important habitat during the seasonal migration of cownose rays, as well as during the summer when the species may utilize the estuarine region as a nursery and/or for foraging.