Investigation of the thermal history of the Delaware Basin (West Texas,USA) using carbonate clumped isotope thermometry

We utilized carbonate clumped isotope thermometry to explore the thermal history of the Delaware Basin, West Texas, USA. Carbonate wellbore cuttings from five oil/gas wells across the basin yielded clumped isotope temperatures (T(Δ₄₇)) ranging from 27°C to 307°C, interpreted to reflect a combination of initial precipitation/recrystallization temperature and solid-state C-O bond reordering during burial. Dolomite samples generally record lower apparent T(Δ₄₇)s than calcite, reflecting greater resistance to reordering in dolomite. In all five wells, clumped isotope temperatures exceed modern downhole temperature measurements, indicating higher heat flow in the past. Using modelled burial curves based on sedimentological history, we created unique time-temperature histories by linearly applying a geothermal gradient. Applying two different thermal history reordering models, we modelled the extent of solid-state C–O bond reordering to iteratively find the time-averaged best-fit geothermal gradients for each of the five wells. Results of this modelling suggest that the shallower, southwestern portion of the study area experienced higher geothermal gradients throughout the sediment history (~45°C/km) than did the deeper, southeastern portion (~32°C/km), with the northern portion experiencing intermediate geothermal gradients (~35–38°C/km). This trend is in agreement with the observed gas/oil ratios of the Delaware Basin, increasing from east to west. Furthermore, our clumped isotope temperatures agree well with previously published vitrinite reflectance data, confirming previous observations and demonstrating the utility of carbonate clumped isotope thermometry to reconstruct basin thermal histories.     

Simple Spectrophotometric Determination of Ferrous Iron in Twelve French Geochemical Reference Standards

Iron (II) oxide in silicate rocks can readily be measured after digestion with HF and HCl by reaction with KI and KIO₃. The iodine produced during the digestion is trapped in CCl₄ and measured at 512 nm spectrophotometrically. Results for ten accepted and two new geochemical reference standards are presented.     

A Donnan potential model for metal sorption onto Bacillus subtilis

In this study, we conducted electrophoretic mobility, potentiometric titration, and metal sorption experiments to investigate the surface charge characteristics of Bacillus subtilis and the electrostatic interactions between metal cations and the cell surface electric field. Electrophoretic mobility experiments performed as a function of pH and ionic strength show an isoelectric point of pH 2.4, with the magnitude of the electrokinetic potential increasing with increasing pH, and decreasing with increasing ionic strength. Potentiometric titration experiments conducted from pH 2.4 to 9 yield an average surface charge excess of 1.6 μmol/mg (dry mass). Corresponding cell wall charge density values were used to calculate the Donnan potential (Ψ_DON) as function of pH and ionic strength. Metal sorption experiments conducted with Ca(II), Sr(II), and Ba(II) exhibit strong ionic strength dependence, suggesting that the metal ions are bound to the bacterial cell wall via an outer-sphere complexation mechanism. Intrinsic metal sorption constants for the sorption reactions were determined by correcting the apparent sorption constant with the Boltzmann factor. A 1:2 metal-ligand stoichiometry provides the best fit to the experimental data with log K₂^int values of 5.9 ± 0.3, 6.0 ± 0.2, 6.2 ± 0.2 for Ca(II), Sr(II), and Ba(II) respectively. Electrophoretic mobility measurements of cells sorbed with Ca(II), Sr(II), and Ba(II) support the 1:2 sorption stoichiometry. These results indicate that electrical potential parameters derived from the Donnan model can be applied to predict metal binding onto bacterial surfaces over a wide range of pH and ionic strength conditions.     

Mud consolidation during a short time interval

Flume observations of the consolidation of mud beds deposited from an unsteady flow show that 10-mm layer undergoes considerable consolidation during the time of deposition and within the first hour after deposition ceases, but little additional consolidation during the next 24 hr. A certain minimum thickness, between 3 and 10 mm, is required for any consolidation to occur. The results support the hypothesis that thick mud layers may form in nearshore subtidal areas as the result of accumulation of thinner layers deposited during successive tidal cycles, but only if each individual layer is able to withstand erosion during the subsequent cycle.     

Equity in the distribution of urban environmental amenities: the case of Washington,D.C.

This study examines equity issues in access to urban environmental amenities using Washington, D.C. as a case study. The amenities that are the focus of this study, urban trees and urban parks, have a range of social and health benefits for city dwellers, and Washington, D.C. is a major city with a large, diverse population and long-standing geographic divisions by race and class. Using spatial regression techniques, the study examines disparities in access to these amenities by race, ethnicity, and socioeconomic status at citywide and sub-city scales. Mixed evidence is found for disparities in access across amenities and across scales. The results emphasize the need for studies of access to urban environmental amenities to pay closer attention to the differences between amenities and to issues of scale.     

A four-dimensional variational system for skillful operational prediction of convective storms

正Forecasting convective storms using NWP models is an important goal and a highly active area of ongoing research.Skillful and reliable NWP of convective storms could allow for severe weather warnings with longer lead times,as operational forecasters begin to incorporate convective-scale forecasts into severe weather forecast operations(Stensrud et al.,2009,2013).This would then provide vulnerable individuals and industries with more time to seek shelter and/or mitigate     

A Predictive Geospatial Exploration Model for Mississippi Valley Type Pb–Zn Mineralization in the Southeast Missouri Lead District

The Pb–Zn sulfide concentrations hosted by dolomitized Cambrian carbonates in Southeast Missouri are world-class Mississippi Valley Type (MVT) deposits. These deposits commonly are in sites where local Precambrian basement highs resulted in depositional pinchouts of the basal Cambrian sandstones that served as a regional aquifer for basinal fluid migration driven by late Paleozoic Ouachita deformation. Mineralization also appears to be spatially related to regional faults that probably served as local fluid conduits. Understanding spatial associations between sites of known mineralization and regional geology, geochemistry, and geophysics in Southeast Missouri will be a useful guide in future exploration efforts in this region and for similar geologic settings globally. The weights-of-evidence method is used to evaluate regional geology, geochemistry, and geophysical datasets and produce favorability maps for MVT deposits in Southeast Missouri. Host rock characteristics, regional structural controls, stream sediment geochemistry, and proximity to basement highs appear to be the most useful data for predicting the location of the major deposits. This work illustrates the potential utility of mineral potential modeling to prioritize areas for exploration and identify permissive areas for undiscovered MVT mineralization.

     

Metal-silicate partitioning of cesium: Implications for core formation

Here we present the first set of metal-silicate partitioning data for Cs, which we use to examine whether the primitive mantle depletion of Cs can be attributed to core segregation. Our experiments independently varied pressure from 5 to 15 GPa, temperature from 1900 to 2400 °C, metallic sulfur content from pure Fe to pure FeS, silicate melt polymerization, expressed as a ratio of non-bridging oxygens to tetrahedrally coordinated cations (nbo/t) from 1.26 to 3.1, and fO₂ from two to four log units below the iron-wüstite buffer. The most important controls on the partitioning behavior of alkalis were the metallic sulfur content, expressed as X_S, and the nbo/t of the silicate liquid. Normalization of X_S to 0.5 yielded the following expressions for D-values as a function of nbo/t: log D_Na = −2.0 + 0.44 × (nbo/t), log D_K = −2.4 + 0.67 × ( nbo/t), and log D_Cs = −3.2 + 1.17 × (nbo/t). Normalization of nbo/t to 2.7 resulted in the following equations for D-values as a function of S content: log D_Na = −4.1 + 6.4 × X_S, log D_K = −7.7 + 13.9 × X_S, and log D_Cs = −12.1 + 23.3 × X_S.There appears to be a negative pressure effect up to 15 GPa, but it should be noted that this trend was not present before normalization, and is based on only two measurements. There is a positive trend in cesium’s metal-silicate partition coefficient with increasing temperature. D_Cs exhibits the largest change and increased by a factor of three over 500 °C. The effect of oxygen fugacity has not been precisely determined but in general, lowering fO₂ by two log units resulted in a rise in all D-values of approximately an order of magnitude. In general, the sensitivity of partition coefficients to changing parameters increased with atomic number.The highest D-value for Cs observed in this study is 0.345, which was obtained at nbo/t of 2.7 and a metal phase of pure FeS. This metallic composition has far more S than has been suggested for any credible core-forming metal. We therefore conclude that the depletion of Cs in Earth’s mantle is either caused by radically different behavior of Cs at pressures higher than 15 GPa or is not related to core formation. Even so, we have shown that a planet with a sufficient S inventory may incorporate significant amounts of alkali elements into its core.