Browsing Geology by Issue Date
Now showing items 1-20 of 171
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The Kinetics and Mechanism of Sedimentary Iron Sulfide Formation
(1976)The reaction between goethite, ∝-FeOOH, and aqueous bisulfide ion, HS, was studied under conditions representative of estuarine sediments. The concentration-time curves of the following species were determined by ... -
Impact of Isotopic Heterogeneity in Shallow Systems on Modeling of Stormflow Generation
(1993)A major uncertainty in hydrologic and geochemical modeling of stormflow generation in watersheds has been quantification of the contributions of water and solutes from different sources and hydrologic pathways to streamwater. ... -
A PETROLOGIC, GEOCHEMICAL AND OSMIUM ISOTOPIC STUDY OF SELECTED PRECAMBRIAN KOMATIITES
(2004-11-17)The major and trace elements, and Re-Os isotope systematics of the ca. 2.7-Ga komatiites from the Alexo and Dundonald Beach areas in the Abitibi greenstone belt, Canada, and ca. 2.0-Ga komatiites from Jeesiörova, Finnish ... -
ROCK FABRIC ANALYSIS OF THE SIERRA CREST SHEAR ZONE SYSTEM, CALIFORNIA: IMPLICATIONS FOR CRUSTAL-SCALE TRANSPRESSIONAL SHEAR ZONES
(2004-12-08)Crustal-scale tabular shear zones are common features of transpressional orogens and arcs. Though foliation development in shear zones is well understood, the development of another rock fabric element, lineation, is not. ... -
Characterization of the spatial differences in hydrological functioning in a tidal marsh, Patuxent River, MD: A framework for understanding nutrient dynamics
(2004-12-08)This study investigates spatial variations in sediment hydraulic conductivity (K), network channel shape and horizontal groundwater flux magnitude toward tidal network channels in a freshwater tidal marsh. Results showed ... -
Kinematics and Deformation History of the Cross Lake Greenstone Belt
(2004-12-17)Greenstone belts are a common feature of Archean terrains. However, the tectonic environment for Archean earth remains in hot debate: did vertical or horizontal crustal movement dominate the Archean Eon? Small-scale ... -
Examination of the Thermal Decomposition of Chrysotile
(2005-04-22)The decomposition of pure chrysotile from Thetford, Quebec heated at constant temperature in air from 200-1000°C for 4 to 720 hours was studied by using X-ray diffraction and optical microscopy techniques. No morphological ... -
DETERMINATION OF SULFUR ISOTOPE COMPOSITION IN SULFATE FROM TWO HIGH ELEVATION SNOWPITS BY MULTI-COLLECTOR THERMAL IONIZATION MASS SPECTROMETRY USING A DOUBLE SPIKE
(2005-05-12)The variability of stable sulfur isotopes in nature provides a chemical tool for tracing the various sources of sulfur and a useful tool for understanding the sulfur cycle. It is also well established that snow and ice ... -
A CHEMICAL AND ISOTOPIC COMPARISON OF TWO 1ST-ORDER AGRICULTURAL TRIBUTARIES, KENT COUNTY, MARYLAND
(2005-05-27)Nitrate derived predominantly from agricultural fertilizers results in algal blooms and wide-spread anoxia in estuarine environments. Roughly half the nitrate delivered to the Chesapeake Bay is derived from groundwater ... -
An experimental study of silver partitioning in sulfide-oxide-melt systems at 800 degrees C
(2005-06-01)Silver solubility, and partitioning of silver between pyrrhotite and magnetite at a(Ag) = 0.13 ± 0.04 (1σ) has been determined at 800°C, and a range of fS2 between -4.06 and -0.18 and fO2 between -14.90 and ... -
Terrestrial Alteration of CM2 Chondritic Carbonates in a Suite of Paired Antarctic Meteorites.
(2005-06-01)The δ18O, δ17O, δ13C, and δ14C compositions of carbonate grains were measured from paired Antarctic CM2 chondrites (EET96006, EET96016, EET96017, and EET96019). Oxygen isotopic compositions ... -
TRACING SULFUR SOURCES IN AN ARCHEAN HYDROTHERMAL SYSTEM USING SULFUR MULTIPLE ISOTOPES - A CASE STUDY FROM THE KIDD CREEK VOLCANOGENIC MASSIVE SULFIDE DEPOSIT
(2005-07-07)Mass-independent fractionation of sulfur isotopes in the Archean atmosphere resulted in surface sulfur reservoirs with distinct isotopic signatures. These signatures are used to trace the movement of sulfur through an ... -
A Stable Isotope Investigation of Precipitation Nitrate
(2005-08-15)The isotopic composition of precipitation nitrate reflects the processes involved in its formation. Silver nitrates prepared from Maryland precipitation were thermally decomposed to gases for mass spectrometric analyses. ... -
LITHIUM ISOTOPIC SYSTEMATICS OF THE CONTINENTAL CRUST
(2005-12-05)In order to fully utilize Li isotopes as a geochemical tracer, it is necessary to characterize the Li isotopic compositions of different geological reservoirs, and quantify the magnitude of isotopic fractionations for ... -
Rhenium-Osmium Age Determinations of Glaciogenic Shales from the Mesoproterozoic Vazante Formation, Brazil
(2006-12-12)The Vazante Group is a sedimentary package of carbonate interbedded with diamictite and organic-rich shale, potentially representing a Pleistocene-style glacial cycle of Proterozoic age in Brazil. Lacking volcanic ashes, ... -
Stable Isotopic Evidence for the Rise of Oxygen and Reorganization of the Sulfur Cycle from the ca. 2.3 Ga Duitschland Formation, South Africa
(2006-12-13)Metasedimentary rocks from the Transvaal Supergroup, South Africa, were used in a stable isotopic study to investigate the evolution of the Earth's early atmosphere and early biogeochemical cycles. Sulfur isotopic evidence ... -
A Geochemical and Osmium Isotopic Study of Group IVB Irons and Ungrouped Irons Chinga, Tishomingo and Willow Grove
(2007-01-23)Re-Os isotopic and highly siderophile element (HSE) systematics of IVB irons and ungrouped iron meteorites Chinga, Tishomingo and Willow Grove are presented. IVB iron composition has been constrained by HSE (Re, Os, Ru, ... -
Isotopic systematics of ultramafic and mafic rocks of the Taitao ophiolite, southern Chile
(2007-03-14)A variety of ultramafic and mafic rocks from a well-mapped sampling of the ~6 Ma Taitao Ophiolite, Chile, have been examined. Calculated initial 187Os/188Os ratios of the peridotitic rocks range from 0.1168 to 0.1282. ... -
Sulfur isotope fractionations in biological systems: insight into the Proterozoic biosphere
(2007-03-26)This study focuses on developing a framework for interpreting isotopic fractionations in the four stable sulfur isotopes, with a special focus on microbial effects. Calculations of low temperature equilibrium fractionations ... -
Isotope and Organic Geochemistry of a Unique Proterozoic, Postglacial Succession: The Lapa Formation, Vazante Group, Brazil
(2007-05-09)This study is the second to investigate biological characteristics associated with Proterozoic glaciation via molecular fossils from organic matter preserved in shale. In the Vazante Group, Minas Gerais, Brazil, the Serra ...