21 results match your criteria Chemical Geology[Journal]

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Effect of Bicarbonate and Oxidizing Conditions on U(IV) and U(VI) Reactivity in Mineralized Deposits of New Mexico.

Chem Geol 2019 Oct 8;524:345-355. Epub 2019 Jul 8.

Department of Chemical and Biological Engineering, MSC01 1120, University of New Mexico, Albuquerque, New Mexico 87131, USA.

We investigated the effect of bicarbonate and oxidizing agents on uranium (U) reactivity and subsequent dissolution of U(IV) and U(VI) mineral phases in the mineralized deposits from Jackpile mine, Laguna Pueblo, New Mexico, by integrating laboratory experiments with spectroscopy, microscopy and diffraction techniques. Uranium concentration in solid samples from mineralized deposit obtained for this study exceeded 7000 mg kg, as determined by X-ray fluorescence (XRF). Results from X-ray photoelectron spectroscopy (XPS) suggest the coexistence of U(VI) and U(IV) at a ratio of 19:1 at the near surface region of unreacted solid samples. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2019.07.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6690612PMC
October 2019
1 Read

Reactivity of As and U co-occurring in Mine Wastes in northeastern Arizona.

Chem Geol 2019 Sep 20;522:26-37. Epub 2019 May 20.

Department of Civil Engineering MSC01 1070, University of New Mexico, Albuquerque, NM 87131, USA.

The reactivity of co-occurring arsenic (As) and uranium (U) in mine wastes was investigated using batch reactors, microscopy, spectroscopy, and aqueous chemistry. Analyses of field samples collected in proximity to mine wastes in northeastern Arizona confirm the presence of As and U in soils and surrounding waters, as reported in a previous study from our research group. In this study, we measured As (< 0. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2019.05.024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6675030PMC
September 2019
1 Read

Determinants of blood water O variation in a population of experimental sheep: implications for paleoclimate reconstruction.

Chem Geol 2018 May 26;485:32-43. Epub 2018 Mar 26.

Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA.

Mammalian body, blood and hard tissue oxygen isotope compositions (O values) reflect environmental water and food sources, climate, and physiological processes. For this reason, fossil and archaeological hard tissues, which originally formed in equilibrium with body chemistry, are a valuable record of past climate, landscape paleoecology, and animal physiology and behavior. However, the environmental and physiological determinants of blood oxygen isotope composition have not been determined experimentally from large herbivores. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2018.03.034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6261537PMC
May 2018
1 Read

Simultaneously Quantifying Ferrihydrite and Goethite in Natural Sediments Using the Method of Standard Additions with X-ray Absorption Spectroscopy.

Chem Geol 2018 Jan 21;476:248-259. Epub 2017 Nov 21.

Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY 10964, USA.

The presence of ferrihydrite in sediments/soils is critical to the cycling of iron (Fe) and many other elements but difficult to quantify. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to speciate Fe in the solid phase, but this method is thought to have difficulties in distinguishing ferrihydrite from goethite and other minerals. In this study, both conventional EXAFS linear combination fitting (LCF) and the method of standard-additions are applied to the same samples in attempt to quantify ferrihydrite and goethite more rigorously. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2017.11.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5771421PMC
January 2018
4 Reads

Determination of Cr(III) solids formed by reduction of Cr(VI) in a contaminated fractured bedrock aquifer: Evidence for natural attenuation of Cr(VI).

Chem Geol 2017 Dec;474:1-8

National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, U.S. Environmental Protection Agency, United States.

Hexavalent chromium Cr(VI) is toxic and can be highly mobile in many aquifer systems. Redox reactions with naturally occurring minerals and organic compounds can reduce Cr(VI) to Cr(III), forming labile Cr(III) oxyhydroxide precipitates, which is a natural attenuation process. In fractured bedrock aquifers, reduction of Cr(VI) in the rock matrix can enhance attenuation beyond that from matrix diffusion only, and potentially reduce back diffusion if concentrations in fractures decline following source reduction via natural processes or engineered remediation. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2017.10.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7252521PMC
December 2017

nanoscale observations of gypsum dissolution by digital holographic microscopy.

Chem Geol 2017 Jun 17;460:25-36. Epub 2017 Apr 17.

Materials and Structural Systems Division, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.

Recent topography measurements of gypsum dissolution have not reported the absolute dissolution rates, but instead focus on the rates of formation and growth of etch pits. In this study, the absolute retreat rates of gypsum (010) cleavage surfaces at etch pits, at cleavage steps, and at apparently defect-free portions of the surface are measured in flowing water by reflection digital holographic microscopy. Observations made on randomly sampled fields of view on seven different cleavage surfaces reveal a range of local dissolution rates, the local rate being determined by the topographical features at which material is removed. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2017.04.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5562293PMC
June 2017
21 Reads

Uptake of nickel by synthetic mackinawite.

Chem Geol 2017 Jun;462:15-29

U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, 919 Kerr Research Drive, Ada, OK 74820, United States.

The uptake of aqueous Ni(II) by synthetic mackinawite (FeS) was examined in anaerobic batch experiments at near-neutral pH (5.2 to 8.4). Read More

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http://dx.doi.org/10.1016/j.chemgeo.2017.04.023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6145480PMC
June 2017
2 Reads

Platinum stable isotope analysis of geological standard reference materials by double-spike MC-ICPMS.

Chem Geol 2014 Jan;363:293-300

Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark.

We report a method for the chemical purification of Pt from geological materials by ion-exchange chromatography for subsequent Pt stable isotope analysis by multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) using a Pt-Pt double-spike to correct for instrumental mass bias. Double-spiking of samples was carried out prior to digestion and chemical separation to correct for any mass-dependent fractionation that may occur due to incomplete recovery of Pt. Samples were digested using a NiS fire assay method, which pre-concentrates Pt into a metallic bead that is readily dissolved in acid in preparation for anion-exchange chemistry. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2013.11.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4326679PMC
January 2014

Single crystal U-Pb zircon age and Sr-Nd isotopic composition of impactites from the Bosumtwi impact structure, Ghana: Comparison with country rocks and Ivory Coast tektites.

Chem Geol 2010 Aug;275(3-4):254-261

Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.

The 1.07 Myr old Bosumtwi impact structure (Ghana), excavated in 2.1-2. Read More

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http://dx.doi.org/10.1016/j.chemgeo.2010.05.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2949568PMC
August 2010
5 Reads

Accretion of Moon and Earth and the emergence of life.

Chem Geol 2000 Aug;169(1-2):69-82

Scripps Institution of Oceanography, University of California, La Jolla, San Diego 92093-0220, USA.

The discrepancy between the impact records on the Earth and Moon in the time period, 4.0-3.5 Ga calls for a re-evaluation of the cause and localization of the late lunar bombardment. Read More

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http://dx.doi.org/10.1016/s0009-2541(00)00333-8DOI Listing
August 2000
3 Reads

Accretion and differentiation of carbon in the early Earth.

Authors:
T N Tingle

Chem Geol 1998 May;147(1-2):3-10

Department of Geological and Environmental Sciences, Stanford University, CA 94305-4045, USA.

The abundance of C in carbonaceous and ordinary chondrites decreases exponentially with increasing shock pressure as inferred from the petrologic shock classification of Scott et al. [Scott, E.R. Read More

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http://dx.doi.org/10.1016/s0009-2541(97)00168-xDOI Listing
May 1998
33 Reads

Productivity-induced sulphur enrichment of hydrocarbon-rich sediments from the Kimmeridge Clay Formation.

Chem Geol 1997 ;134:277-88

URA 724-FR 09 CNRS, Universite d'Orleans, France.

This work aims to highlight the relationship between primary productivity, sulphate reduction and organic carbon preservation in cyclic marine sediments from the Kimmeridge Clay Formation. A concomitant increase of the total sulphur content with the preserved organic content (TOC), shows the progressive supply of both metabolisable organic matter and resistant organic matter is linked to primary productivity. However, variations in sulphate reduction efficiency, based on elemental abundance and isotopic composition of sulphur, reveal that the proportion of metabolisable vs. Read More

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http://dx.doi.org/10.1016/s0009-2541(96)00093-9DOI Listing
December 1998
1 Read

Stable isotopic compositions of carbonates from the Mesoproterozoic Bangemall Group, northwestern Australia.

Chem Geol 1995 Jun;123(1-4):153-71

Botanical Museum, Harvard University, Cambridge, MA 02138, USA.

Marine carbonate rocks from the Mesoproterozoic Bangemall Group of northwestern Australia show little deviation (+/-1.3%) in whole-rock delta 13C(carb)-values about a mean of -0.5%. Read More

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http://dx.doi.org/10.1016/0009-2541(95)00049-rDOI Listing
June 1995
5 Reads

A comparison of iron extraction methods for the determination of degree of pyritisation and the recognition of iron-limited pyrite formation.

Chem Geol 1994 ;111:101-10

Department of Earth Sciences, Leeds University, UK.

Measurements of degree of pyritisation require an estimate of sediment iron which is capable of reaction with dissolved sulphide to form pyrite, either directly or indirectly via iron monosulphide precursors. Three dissolution techniques (buffered dithionite, cold 1 M HCl, boiling 12 M HCl) were examined for their capacity to extract iron from a variety of iron minerals, and iron-bearing sediments, as a function of different extraction times and different grain sizes. All the iron oxides studied are quantitatively extracted by dithionite and boiling HCl (but not by cold HCl). Read More

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http://dx.doi.org/10.1016/0009-2541(94)90084-1DOI Listing
October 1997

Factors influencing organic carbon preservation in marine sediments.

Authors:
D E Canfield

Chem Geol 1994 ;114:315-29

School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta 30332-0340, USA.

The organic matter that escapes decomposition is buried and preserved in marine sediments, with much debate as to whether the amount depends on bottom-water O2 concentration. One group argues that decomposition is more efficient with O2, and hence, organic carbon will be preferentially oxidized in its presence, and preserved in its absence. Another group argues that the kinetics of organic matter decomposition are similar in the presence and absence of O2, and there should be no influence of O2 on preservation. Read More

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http://dx.doi.org/10.1016/0009-2541(94)90061-2DOI Listing
October 1997
2 Reads

Tectonic control of the crustal organic carbon reservoir during the Precambrian.

Authors:
D J Des Marais

Chem Geol 1994 ;114:303-14

Ames Research Center, Moffett Field, CA 94035-1000, USA.

Carbon isotopic trends indicate that the crustal reservoir of reduced, organic carbon increased during the Proterozoic, particularly during periods of widespread continental rifting and orogeny. No long-term trends are apparent in the concentration of organic carbon in shales, cherts and carbonates. The age distribution of 261 sample site localities sampled for well-preserved sedimentary rocks revealed a 500-700-Ma periodicity which coincided with tectonic cycles. Read More

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http://dx.doi.org/10.1016/0009-2541(94)90060-4DOI Listing
June 1997
1 Read

A much warmer Earth surface for most of geologic time: implications to biotic weathering.

Chem Geol 1993 ;107:221-3

Department of Biology, Howard University, Washington, DC, USA.

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http://dx.doi.org/10.1016/0009-2541(93)90178-lDOI Listing
September 1997
1 Read

Stable isotopic biogeochemistry of carbon and nitrogen in a perennially ice-covered Antarctic lake.

Chem Geol 1993 ;107:159-72

Desert Research Institute, University of Nevada System, Reno 89506, USA.

Lake Hoare (77 degrees 38' S, 162 degrees 53' E) is an amictic, oligotrophic, 34-m-deep, closed-basin lake in Taylor Valley, Antarctica. Its perennial ice cover minimizes wind-generated currents and reduces light penetration, as well as restricts sediment deposition into the lake and the exchange of atmospheric gases between the water column and the atmosphere. The biological community of Lake Hoare consists solely of microorganisms -- both planktonic populations and benthic microbial mats. Read More

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http://dx.doi.org/10.1016/0009-2541(93)90108-uDOI Listing
June 1997
4 Reads

Metal dynamics in Lake Vanda (Wright Valley, Antarctica).

Chem Geol 1989 ;76:85-94

School of Interdisciplinary Studies, Miami University, Oxford, OH 45056, USA.

Data are reported for Mn, Fe, Co, Ni, Cu and Cd in the Onyx River, and for Mn, Co, Ni, Cu and Cd in Lake Vanda, a closed-basin Antarctic lake. Oxic water concentrations for Co, Ni, Cu and Cd were quite low and approximate pelagic ocean values. Scavenging of these metals by sinking particles is strongly indicated. Read More

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http://dx.doi.org/10.1016/0009-2541(89)90129-0DOI Listing
October 1997
2 Reads

Carbon isotope geochemistry of hydrocarbons in the Cerro Prieto geothermal field, Baja California Norte, Mexico.

Chem Geol 1988 ;71:159-67

Ames Research Center, Moffett Field, CA 94035, USA.

Hydrocarbon abundances and stable-isotopic compositions were measured in wells M5, M26, M35 and M102, which represent a range of depths (1270-2000 m) and temperatures (275-330 degrees C) in the field. In order to simulate the production of the geothermal hydrocarbons, gases were collected from the pyrolysis of lignite in the laboratory. This lignite was obtained from a well which sampled rock strata which are identical to those occurring in the field, but which have experienced much lower subsurface temperatures. Read More

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http://dx.doi.org/10.1016/0009-2541(88)90112-xDOI Listing
September 1999
2 Reads

Extended hopanoids in peat environments.

Chem Geol 1984 ;42:25-43

Organic Geochemistry Unit, University of Bristol, Great Britain.

Detailed results are presented for the distributions of triterpenoid alkanes, acids and alcohols of the hopane family in ten samples of peat from three environments, and of contributing organisms in the case of Lyne of Skene, Scotland. Extended hopanoids of the beta alpha and alpha beta configuration appear at the very earliest stage of diagenesis. Such environments appear to be characterised by particular distributions of C32 hopanoid acids and alcohols, and a high preponderance of the C31 alpha beta hopane. Read More

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http://dx.doi.org/10.1016/0009-2541(84)90003-2DOI Listing
September 1999
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