Variation in the composition and partitioning of adsorbed cations at a brine-contaminated crude oil production facility in southeastern Louisiana,USA

The first geological materials impacted by oil field wastes released into near-surface environments in southern Louisiana, USA, are typically clays and silts. Clay minerals within these siliciclastic sediments have the potential for altering the composition of produced water wastes through cation exchange. The general relations between the composition of adsorbed cations and interstitial water salinity in brine-contaminated samples from a site in southeastern Louisiana are consistent with previous studies of multicomponent exchange in groundwater systems of varying salinity. The divalent cations Ca and Mg dominate as adsorbed cations at low salinities (<1200 mg/L), but Na is dominant at moderate to high salinities (up to 53,000 mg/L). The change in the proportions of adsorbed cations is a non-linear function of salinity, and the transition from Ca-dominated adsorption to Na-dominated adsorption occurs over a narrow range of salinities.     

New evidence for high discharge to the Chukchi shelf since the Last Glacial Maximum

Using CHIRP subbottom profiling across the Chukchi shelf, offshore NW Alaska, we observed a large incised valley that measures tens of kilometers in width. The valley appears to have been repeatedly excavated during sea level lowering; however, the two most recent incisions appear to have been downcut during the last sea level rise, suggesting an increase in the volume of discharge. Modern drainage from the northwestern Alaskan margin is dominated by small, low-discharge rivers that do not appear to be large enough to have carved the offshore drainage. The renewed downcutting and incision during the deglaciation and consequent base level rise implies there must have been an additional source of discharge. Paleoprecipitation during deglaciation is predicted to be at least 10% less than modern precipitation and thus cannot account for the higher discharge to the shelf. Glacial meltwater is the most likely source for the increased discharge.     

Heavy metals deposited from the atmosphere on upland Scottish soils: Chemical and lead isotope studies of the association of metals with soil components

Three soil profiles taken from the Hartwood Research Station in Central Scotland have been analyzed using chemical digestion and extraction techniques to investigate the chemical association of heavy metals deposited from the atmosphere. Total digestion, EDTA extraction and the BCR (Bureau Communitaire de Reference) sequential extraction procedure were used. In addition, lead isotope ratios in the whole soils and in the fractions from the sequential extraction procedure were measured using thermal ionisation mass spectrometry. All the digestion and extraction procedures gave clear indication of enhanced concentrations of heavy metals in surface soils, in particular for lead and zinc. Whereas total digestion gave a good indication of the heavy metal status of the soils, the extraction procedures were necessary to provide information on chemical association of the metals with soil components, information needed to understand the soil processes involved in mobilization of metals. Lead isotope analysis of the whole soils revealed a consistent picture of lower ²⁰⁶Pb/²⁰⁷Pb ratios in surface soils (1.140-1.147) than in soils at 20-30 cm depth (1.182-1.190). The steady progression from the lower to higher ratios down the profile was clear indication that anthropogenic lead had penetrated to some degree into the deeper soils. The combination of sequential extraction and lead isotope analysis proved to be a powerful approach to studying this effect in more detail and showed that the fractions extractable from 20 to 30 cm soils contained lead with much lower ²⁰⁶Pb/²⁰⁷Pb ratios (1.174-1.178) than the residual fraction (1.196-1.200). As the extractable fractions contained ≥85% of the lead in the soil, a substantial portion of lead at 20-30 cm depth was of anthropogenic origin. The ²⁰⁶Pb/²⁰⁷Pb ratios of 1.174-1.178 found in the extractable fractions suggested that the mobile component of the anthropogenic lead was that deposited before the introduction of leaded petrol.     

西安地区地热水和渭北岩溶水同位素特征及相互关系

依据采自西安地区300到3000米深地热井中地热水的水化学成分和同位素成分,确定出地热水的主要补给源和循环路径。地热水δ~(18)O 值变化于-11.8‰～-3.1‰VSMOW 之间,而δD 值变化幅度很小,在-87～-80‰VSMOW 之间,与西安市区现代大气降水的δD 值(～-60‰VSMOW)明显不同。在δ~(18)O～δD 关系图上,浅层地热水(〈1500米〉落在大气降水线上,而深层地热水(>1500米)向右侧偏离了大气降水线,呈现显著的氧同位素正向漂移现象。氧同位素由秦岭山前向盆地内部逐渐富集,在盆地内部随井深成正相关。据此判断,西安地热水的补给区位于秦岭山区。~(14)C 值表现为与氧同位素相反的变化趋势,~(14)C 年龄值在6,000～30,000年之间,表明地热水的地下循环时间很长。由井间~(14)C 年龄差异估算出从南到北地热水平均流速为1.7米/年,从西到东为2.5米/年。这些特征与渭北岩溶水截然不同,表明西安地区地热水与渭北岩溶水之间,虽然在空间上有密切联系,但分属于不同的水文地质单元,有各自独立的补径排系统。     

Monte Ollasteddu, a new gold discovery in the Variscan basement of Sardinia (Italy): first isotopic (40Ar−39Ar, Pb) and fluid inclusion data

The Monte Ollasteddu deposit represents a major gold discovery in the Variscan basement of southeastern Sardinia. Gold occurs in late-Variscan extensional brittle structures hosted by meta-volcanic, and subordinately meta-sedimentary, rocks. The vein mineralogy is dominated by quartz; arsenopyrite is the main sulphide. Reconnaissance ⁴⁰Ar–³⁹Ar dating gives ages around ∼260 Ma on K-feldspar from mineralized veins, whereas metamorphic white mica from the host rock gives ages clustering at ∼307 Ma. The best age estimate for biotite from a nearby leucogranite body is 286.3±2.2 Ma. The Pb isotope signature of ore and gangue minerals is entirely consistent with literature data for Variscan deposits of Sardinia, and for European Variscan gold deposits. Fluid inclusion data point to the presence of both CO₂-bearing and CO₂-free fluids, with homogenization temperatures ranging from 220 to 415°C, with low-to-moderate salinities (0.4–6.2 wt% NaCl equivalent). Monte Ollasteddu shows several features similar to European Variscan gold deposits; however, the age of mineralization might post-date granitoid intrusion by as much as 30 Ma, being instead coeval with very late calc-alkaline basaltic dykes, marking the transition to a post-orogenic, pre-Tethyan geodynamic setting. Electronic Supplementary Material Supplementary material is available for this article at     

Mercury content of the Springfield coal, Indiana and Kentucky

With pending regulation of mercury emissions in United States power plants, its control at every step of the combustion process is important. An understanding of the amount of mercury in coal at the mine is the first step in this process. The Springfield coal (Middle Pennsylvanian) is one of the most important coal resources in the Illinois Basin. In Indiana and western Kentucky, Hg contents range from 0.02 to 0.55 ppm. The variation within small areas is comparable to the variation on a basin basis. Considerable variation also exists within the coal column, ranging from 0.04 to 0.224 ppm at one Kentucky site. Larger variations likely exist, since that site does not represent the highest whole-seam Hg nor was the collection of samples done with optimization of trace element variations in mind. Estimates of Hg capture by currently installed pollution control equipment range from 9–53% capture by cold-side electrostatic precipitators (ESP) and 47–81% Hg capture for ESP + flue-gas desulfurization (FGD). The high Cl content of many Illinois basin coals and the installation of Selective Catalytic Reduction of NO_x enhances the oxidation of Hg species, improving the ability of ESPs and FGDs to capture Hg.     

Migration pathways in the Central North Slope foreland basin, Alaska USA: solute and thermal constraints on fluid flow simulations

The North Slope foreland basin, Alaska, USA is an east–west asymmetrical trough‐shaped basin adjacent to the Brooks Range fold‐thrust mountain belt. Lower Cretaceous age rocks make up much of the sediment fill, including flysch‐like marine turbidites and shales of the Torok and Fortress Mountain formations and marine and sandstones, shales and conglomerates of the overlying Nanushuk group. Lower Cretaceous age rocks were deposited on top of a Palaeozoic and Mesozoic age passive margin sequence. We have conducted numerical simulations of fluid flow driven by topographic recharge in the Central North Slope foreland basin. These simulations are constrained by salinity estimates from well logs, location of oil and gas fields, vitrinite reflectance and heat flow measurements. Our model results indicate that there are two south to north pathways for fluid migration. The primary pathway for fluid movement is downward through the Fortress Mountain formation, then upwards along the interface between the Fortress Mountain and Torok Formation and finally northward through the permeable Nanushuk group. A smaller mass of groundwater moves along sands below the Torok formation and into offshore sediments north of Alaska. Very little meteoric water enters the underlying Palaeozoic rocks in our simulations, which could explain the presence of deep saline pore waters. Our results also show that permafrost is a primary control on the pathway and rate of fluid flow by controlling the distribution of surface recharge and discharge. For example, areas of high heat flow and low saline waters along the arctic coast may represent upward groundwater discharge because of the absence of permafrost. As surface temperatures were warmer in the Miocene, the absence of permafrost would produce a more local fluid circulation pattern and less transfer of heat energy from south to north.     

Resolving the Geometry of Hydraulic Fractures from Tilt Measurements

This paper discusses the resolution of geometrical characteristics of pressurized fractures from tiltmeter data. The quasi-static deformation and tilt field induced by such fractures can be modeled by superposition of displacement discontinuity (DD) singularities. Despite the relatively common use of such measurements to infer fracture characteristics, there is a widespread misunderstanding of what can be accurately determined, depending on the relative distance between the tiltmeter array and the fracture. We investigate in detail the resolution of the dimensions and orientation of hydraulic fractures or faults from tilt measurements. In particular, we formally prove that at a distance larger than about twice the characteristic length of the fracture, elastostatic measurements such as those measured by tiltmeters are not able to resolve independently all the dimensions of the fracture, although the fracture volume can be robustly inverted from the data. The resolution of fracture orientation is also discussed using an analysis based on a spatial Fourier Transform of the tilt field. The relative angle between the plane where the measurements are located and the fracture plane plays a major role in the accuracy of this estimation. In an illustrative field example, where the measurements are located in the far-field of the fracture deformation field, we show how a single DD singularity can be used to model tiltmeter data and efficiently obtain the fracture orientation and volume.     

Raman spectroscopic carbonaceous material thermometry of low-grade metamorphic rocks: Calibration and application to tectonic exhumation in Crete, Greece

We present new Raman spectra data of carbonaceous material (CM) to extend the range of the Raman spectra of CM thermometer (RSCM) to temperatures as low as 100 °C. Previous work has demonstrated that Raman spectroscopy is an excellent tool to describe the degree of graphitization of CM, a process that is independent of pressure but strongly dependent on metamorphic temperature. A linear relationship between temperature and the Raman parameter R2 (derived from the area of the defect band relative to the ordered graphite band) forms the basis of a previous thermometer. Because R2 shows little variability in low-temperature samples, 330 °C serves as a lower limit on the existing thermometer. Herein, we present Raman spectra from a suite of low-temperature (100 to 300 °C) samples from the Olympics Mountains and describe other aspects of the Raman spectra of CM that vary over this range. In particular, the Raman parameter R1 (the ratio of heights of the disordered peak to ordered peak) varies regularly between 100 and 350 °C. These data, together with published results from higher-temperature rocks, are used to calibrate a modified RSCM thermometer, applicable from 100 to 700 °C. Application to low-grade metasediments in the Otago region in the South Island of New Zealand gives temperatures consistent with previous estimates, demonstrating the reliability of the modified RSCM thermometer.We apply the modified RSCM thermometer to 53 samples from Crete to evaluate the role of the Cretan detachment fault in exhuming Miocene high pressure/low-temperature metamorphic rocks exposed there. The metamorphic rocks below the detachment (the Plattenkalk and Phyllite-Quartzite units) give metamorphic temperatures that range from 250 to 400 °C, consistent with previous petrologic estimates. We also demonstrate that the Tripolitza unit, which lies directly above the detachment, gives an average metamorphic temperature of about 260 °C. The modest break in metamorphic temperature in central Crete indicates that the Cretan detachment accounts for only 5 to 7 km of exhumation of the underlying HP-LT metamorphic rocks, which were initially accreted at ∼ 35 km. We argue that the bulk of the exhumation (∼ 28 km out of 35 km total) occurred by pervasive brittle stretching and erosion of structural units above the detachment.