Radiographic study of the distribution of boron in recent mollusc shells     

Marian Furst  H.A Lowenstam  D.S Burnett 《Geochimica et cosmochimica acta》1976,40(11):1381-1386

Studies have been made of the boron content and distribution in recent Mytilus edulis shells by mapping the alpha particle distribution produced by the ¹⁰B (n,α)⁷Li reaction using cellulose nitrate track detectors. Boron is concentrated in the inorganic parts of the shell matrix and is enriched in aragonite relative to calcite by a factor of 1.5–2. The B contents in different parts of individual shells and in different specimens from a given locality are well defined, particularly for the aragonite layer. A correlation was found between the B in the aragonite layer and the salinity of the water in which the shells grew. The method shows promise as a means of using the boron content of fossil shells to determine paleosalinity.  相似文献   

Growth rates of Pacific manganese nodules as deduced by uranium-series and hydration-rind dating techniques     

William C. Burnett  Maury Morgenstein 《Earth and Planetary Science Letters》1976,33(2):208-218

Growth rates of four Pacific ferromanganese deposits have been determined by uranium-series and hydration-rind dating techniques. This represents the first time these two methods have been applied to the same samples. Of the four samples analyzed, two agree in both techniques and two show a wide disparity. The samples that do not agree have uranium-series rates which are low compared to those deduced by the hydration-rind techniques. The same samples also display steep²³²Th activity gradients in the outer layers of the ferromanganese material. Since the half-life of²³²Th is extremely long (10¹⁰ yr), these gradients could not be due to radioactive decay. This suggests that the distribution of²³⁰Th, at least in these cases, may also be a result of some process other than radioactive decay.One of our samples which has a steep²³²Th gradient produces a²³⁰Th “exposure age” which is indistinguishable to the calculated hydration age within the analytical uncertainty. The rate of growth calculated on the basis of the slope of the decline of²³⁰Th within the deposit, however, is low by over one order of magnitude when compared to the rate determined by the hydration-rind method. Although previous results indicate that the distribution of²³²Th is usually quite random within ferromanganese deposits, our results indicate that caution should be exercised when assessing their growth rates on the basis of uranium-series results.  相似文献   

The lateral and vertical growth of laterite weathering profiles,Hawaiian Islands,USA     

S.T. Nelson  B. Barton  M.W. Burnett  J.H. McBride  L. Brown  I. Spring 《地球表面变化过程与地形》2020,45(12):2940-2953

The Hawaiian Islands permit investigation of tropical chemical weathering rates and processes on a single rock type, basalt. Chronosequences are investigated as a function of rainfall due to the varying age of each island, including Kauai (~4 Ma), Oahu (~2 Ma), and Hawaii's Kohala Peninsula (~0.3 to 0.17 Ma). Understanding tropical critical zone (CZ) development is vital given the large populations in developing countries that rely on it. HVSR (horizontal-to-vertical spectral ratio) seismic soundings on Kauai indicate that ~60% of the variability in laterite thickness is due to gradients in precipitation, with errors in erosion corrections and variability in the original permeability structure of the volcanic sequence playing important roles. Basalts have higher horizontal than vertical hydraulic conductivity (K_h > K_v) , and local variability in likely drives much of the remaining differences in laterite thickness. HVSR is well suited for estimating laterite thickness as it has been shown to reliably detect the base of the weathering profile, is rapid (20 min/sounding), highly portable, and occupies a very small footprint. Comparison of Kauai and Oahu weathering profiles suggests that the Oahu laterites are fully or nearly fully formed, despite being half the age of Kauai. By contrast, the young laterites on Kohala (~170 to ~300 ka) exhibit greatly contrasting thicknesses, where coastal laterites are thick and interior laterites are thin, suggesting that early weathering on shield volcanoes produces wedge-shaped laterites near the coast. With time, the thick (coastal) end of the wedge propagates upslope such that a fully developed, constant-thickness laterite carapace can form in ~2 Ma or less. The development of thickened coastal laterites on young substrates depends on greater water–rock ratios as vertically infiltrating water upslope is diverted laterally. This view of laterite development is very different compared to endmember models of continental weathering and CZ development. © 2020 John Wiley & Sons, Ltd.  相似文献   

Nannofossils and their applications. Proceedings of the International Nannofossil Association Conference, London 1987 : J. A. Crux & S. E. van Heck (editors). 1989, xiii + 356 pp. Ellis Horwood/British Micropalaeontological Society, £69.50, ISBN 0-7458-0237-0     

Jackie Burnett  Alan Lord 《Cretaceous Research》1989,10(4)

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Enhanced production of stratospheric OH from methane oxidation at elevated reactive chlorine levels in northern midlatitudes   总被引：1，自引：0，他引：1  

Elizabeth B. Burnett  Clyde R. Burnett 《Journal of Atmospheric Chemistry》1995,21(1):13-41

Examination of odd-hydrogen production and loss processes in the lower stratosphere reveals that the large abundances of midlatitude ClO recently measured requires a reassessment of the OH yield from methane oxidation due to a more rapid initiation of the methane oxidation sequence by atomic chlorine. Using a steady state calculation for OH and an iterative procedure for evaluating odd-hydrogen production from the methane oxidation sequence, we demonstrate that both OH and reactive chlorine are amplified below 25 km. The amplified values of OH and ClO are found to be consistent with recent measurements of ClO concentrations and of OH column abundances.  相似文献   

Retention of ion-implanted-xenon in olivine: Dependence on implantation dose     

C.L. Melcher  T.A. Tombrello  D.S. Burnett 《Geochimica et cosmochimica acta》1983,47(10):1707-1712

The diffusion of Xe in olivine, a major mineral in both meteorites and lunar samples, was studied. Xe ions were implanted at 200 keV into single-crystal synthetic-forsterite targets and the depth profiles were measured by alpha particle backscattering before and after annealing for 1 hour at temperatures up to 1500°C. The fraction of implanted Xe retained following annealing was strongly dependent on the implantation dose. Maximum retention of 100% occurred for an implantion dose of 3 × 10¹⁵ Xe ions/cm². Retention was less at lower doses, with ≥ 50% loss at 1 × 10¹⁴ Xe ions/cm². Taking the diffusion coefficient at this dose as a lower limit, the minimum activation energy necessary for Xe retention in a 10 μm layer for 10⁷ years was calculated as a function of metamorphic temperature. For example, an activation energy of 50 kcal/mole implies Xe retention may be possible for metamorphic temperatures below 500°C.  相似文献   

Early diagenesis of organic matter in Peru continental margin sediments: Phosphorite precipitation     

P.N Froelich  M.A Arthur  W.C Burnett  M Deakin  V Hensley  R Jahnke  L Kaul  K.-H Kim  K Roe  A Soutar  C Vathakanon 《Marine Geology》1988,80(3-4):309-343

Pore water chemistry (total dissolved CO₂, NH₄, NO₃, NO₂, PO₄, Si(OH)₄, Ca, Mg, Fe, Mn, SO₄, H₂S and F, and titration alkalinity), solid phase chemistry (C_org, P_org, C_TOT, N_TOT, F, Si_OPAL and S_II), and sediment characteristics (porosity, dry bulk density and formation factors) were determined on a centimeter-scale spacing in the upper 20–40 cm of sediments under intense upwelling areas on the Peru continental shelf. These data demonstrate that carbonate fluorapatite (CFA) is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content (up to 20% C_org), very high porosity ( > 0.96 ml cm⁻³) and very low dry bulk density (< 0.1 g cm⁻³). Dissolved phosphate concentrations at the sediment-water interface range from 20 to 100 μM, orders of magnitude higher than bottom-water concentrations, and much higher than predicted from regeneration of organic matter. The mechanism of this interfacial phosphate release is unclear, but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments. Fluoride is incorporated into CFA by diffusion from the overlying seawater, and carbonate ions are provided from pore-water alkalinity. Magnesium concentrations in this reaction zone are not significantly different from those of seawater, suggesting that magnesium depletion is not a necessary prerequisite for CFA precipitation.

The environment of precipitation is interface-linked rather than driven by organic diagenesis of phosphorus deeper in the sediment. Most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region, but almost all show the precipitation signature near the interface. This interface-linked early diagenetic porewater environment for the precipitation of CFA explains many of the geochemical characteristics of phosphorites and provides a “testable” model to compare the modern phosphogenic analog with ancient phosphorite deposits. Two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites.  相似文献   

Properties of dune topographic state space for six barrier islands of the U.S. southeastern Atlantic coast     

Jackie A. Monge 《自然地理学》2016,37(6):452-475

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Electron Microprobe/SIMS Determinations of Al in Olivine: Applications to Solar Wind,Pallasites and Trace Element Measurements     

Julie M. Paque  Amy E. Hofmann  Donald S. Burnett  Yunbin Guan  Amy J.G. Jurewicz  Dorothy S. Woolum  Chi Ma  George R. Rossman 《Geostandards and Geoanalytical Research》2020,44(3):473-484

Electron probe microanalyser measurements of trace elements with high accuracy are challenging. Accurate Al measurements in olivine are required to calibrate SIMS implant reference materials for measurement of Al in the solar wind. We adopt a combined EPMA/SIMS approach that is useful for producing SIMS reference materials as well as for EPMA at the ~ 100 µg g^?1 level. Even for mounts not polished with alumina photoelectron spectroscopy shows high levels of Al surface contamination. In order to minimise electron beam current density, a rastered 50 × 100 µm electron beam was adequate and minimised sensitivity to small Al‐rich contaminants. Reproducible analyses of eleven SIMS‐cleaned spots on San Carlos olivine agreed at 69.3 ± 1.0 µg g^?1. The known Al mass fraction was used to calibrate an Al implant into San Carlos. Accurate measurements of Al were made for olivines in the pallasites: Imilac, Eagle Station and Springwater. Our focus was on Al in olivine, but our technique could be refined to give accurate electron probe measurements for other contamination‐sensitive trace elements. For solar wind, it is projected that the Al/Mg abundance ratio can be determined to 6%, a factor of 2 more precise than the solar spectroscopic ratio.  相似文献   

Bioremediation of 1,4-Dioxane: Successful Demonstration of In Situ and Ex Situ Approaches     

John F. Horst  Caitlin H. Bell  Andrew Lorenz  Monica Heintz  Yu Miao  Jackie Saling  David Favero  Shaily Mahendra 《Ground Water Monitoring & Remediation》2019,39(4):15-24

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