Geology topics

S.R. Poulson

Publications and source records attributed to S.R. Poulson.

5 recordsLinked to original sources

USGS2011

Derivation of S and Pb in phanerozoic intrusion-related metal deposits from neoproterozoic sedimentary pyrite, Great Basin, United States

The thick (≤8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high δ 34 S values (−11.6 to 40.8‰, >70% exceed 10‰; 51 analyses) derived from reduction of seawater sulfate, and by markedly radiogenic Pb isotopes ( 207 Pb/ 204 Pb >19.2; 15 analyses) acquired from clastic detritus eroded from Precambrian cratonal rocks to the east-southeast. In the overlying Paleozoic section, Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions similar to those of TDS sedimentary pyrite, consistent with derivation of deposit S and Pb from TDS pyrite. Minor element abundances in TDS pyrite (e.g., Pb, Zn, Cu, Ag, and Au) compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated, implying that enrichment in source minerals is not a precondition for intrusion-related metal deposits. Three mechanisms for transferring components of TDS sedimentary pyrite to intrusion-related metal deposits are qualitatively evaluated. One mechanism involves (1) decomposition of TDS pyrite in thermal aureoles of intruding magmas, and (2) aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy S, radiogenic Pb, and possibly other sedimentary pyrite and detrital mineral components, as sulfide minerals in intrusion-related metal deposits. A second mechanism invokes mixing and S isotope exchange in thermal aureoles of Pb and S exsolved from magma and derived from decomposition of sedimentary pyrite. A third mechanism entails melting of TDS strata or assimilation of TDS strata by crustal or mantle magmas. TDS-derived or assimilated magmas ascend, decompress, and exsolve a mixture of TDS volatiles, including isotopically heavy S and radiogenic Pb from sedimentary pyrite, and volatiles acquired from deeper crustal or mantle sources. In the central and eastern Great Basin, the wide distribution and high density of small to mid-sized vein, replacement, and skarn intrusion-related metal deposits in lower Paleozoic rocks that contain TDS sedimentary pyrite S and Pb reflect (1) prolific Jurassic, Cretaceous, and Tertiary magmatism, (2) a regional, substrate reservoir of S and Pb in permeable and homogeneous siliciclastic strata, and (3) relatively small scale concentration of substrate and magmatic components. Large intrusion-related metal deposits in the central and eastern Great Basin acquired S and most Pb from thicker lithospheric sections.

Economic Geology↗

USGS2009

Assessment of diel chemical and isotopic techniques to investigate biogeochemical cycles in the upper Klamath River, Oregon, USA

The upper Klamath River experiences a cyanobacterial algal bloom and poor water quality during the summer. Diel chemical and isotopic techniques have been employed in order to investigate the rates of biogeochemical processes. Four diel measurements of field parameters (temperature, pH, dissolved oxygen concentrations, and alkalinity) and stable isotope compositions (dissolved oxygen-?? 18 O and dissolved inorganic carbon-?? 13 C) have been performed between June 2007 and August 2008. Significant diel variations of pH, dissolved oxygen (DO) concentration, and DO-?? 18 O were observed, due to varying rates of primary productivity vs. respiration vs. gas exchange with air. Diel cycles are generally similar to those previously observed in river systems, although there are also differences compared to previous studies. In large part, these different diel signatures are the result of the low turbulence of the upper Klamath River. Observed changes in the diel signatures vs. sampling date reflect the evolution of the status of the algal bloom over the course of the summer. Results indicate the potential utility of applying diel chemical and stable isotope techniques to investigate the rates of biogeochemical cycles in slow-moving rivers, lakes, and reservoirs, but also illustrate the increased complexity of stable isotope dynamics in these low-turbulence systems compared to well-mixed aquatic systems. ?? 2009 Elsevier B.V.

Chemical Geology↗

USGS2008

Photoreduction fuels biogeochemical cycling of iron in Spain's acid rivers

A number of investigations have shown that photoreduction of Fe(III) causes midday accumulations of dissolved Fe(II) in rivers and lakes, leading to large diel (24-h) fluctuations in the concentration and speciation of total dissolved iron. Less well appreciated is the importance of photoreduction in providing chemical energy for bacteria to thrive in low pH waters. Diel variations in water chemistry from the highly acidic (pH 2.3 to 3.1) Río Tinto, Río Odiel, and Río Agrio of southwestern Spain (Iberian Pyrite Belt) resulted in daytime increases in Fe(II) concentration of 15 to 66 µM at four diel sampling locations. Dissolved Fe(II) concentrations increased with solar radiation, and one of the stream sites showed an antithetic relationship between dissolved Fe(II) and Fe(III) concentrations; both results are consistent with photoreduction. The diel data were used to estimate rates of microbially catalyzed Fe(II) oxidation (1 to 3 nmol L − 1 s − 1 ) and maximum rates of Fe(III) photoreduction (1.7 to 4.3 nmol L − 1 s − 1 ). Bioenergetic calculations indicate that the latter rates are sufficient to build up a population of Fe-oxidizing bacteria to the levels observed in the Río Tinto in about 30 days. We conclude that photoreduction plays an important role in the bioenergetics of the bacterial communities of these acidic rivers, which have previously been shown to be dominated by autotrophic Fe(II)-oxidizers such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans . Given the possibility of the previous existence of acidic, Fe(III)-rich water on Mars, photoreduction may be an important process on other planets, a fact that could have implications to astrobiological research.

Chemical Geology↗

USGS2006

Isotope sourcing of prehistoric willow and tule textiles recovered from western Great Basin rock shelters and caves - proof of concept

Isotope and trace-metal analyses were used to determine the origin of plants used to manufacture prehistoric textiles (basketry and matting) from archaeological sites in the western Great Basin. Research focused on strontium (87Sr/86Sr) and oxygen (18O/16O) isotope ratios of willow (Salix sp.) and tule (Schoenoplectus sp.), the dominant raw materials in Great Basin textiles. The oxygen-isotope data indicated that the willow and tule used to produce the textiles were harvested from the banks of rivers or in marshes characterized by flowing water and not from lakes or sinks. The strontium-isotope data were useful in showing which plants came from the Humboldt River and which came from rivers headed in the Sierra Nevada.

Journal of Archaeological Science↗

USGS1998

Oxalate adsorption at a plagioclase (An47) surface and models for ligand-promoted dissolution

Previous work on adsorption of oxalate at aluminosilicate surfaces suggests that maximum adsorption occurs through a bidentate attachment of the organic ligand, at near-neutral pH. Rates of ligand-promoted dissolution are expected to be greatest at this pH as well. We tested this model by measuring oxalate adsorption on the surface of andesine (An47), in solutions of pH 3- 5 and total oxalate concentrations of 0-8 mM. Contrary to expectation, the greatest adsorption density of 24 ??mol m-2 total oxalate was observed at pH 3 and 8 mM total oxalate. Adsorption is dependent upon the activities of both oxalate (C2O42-) and bioxalate (HC2O4-) in solution and can be modeled with either a two-term Langmuir or a two-term Freundlich isotherm. A Freundlich adsorption model provided the best fit to rate data because it was not constrained to a finite number of adsorption sites, as was the Langmuir model. The two-term ligand adsorption model was incorporated into a rate model: R(tot) = k(H-)[H(ads)/+](L) + k(HOx-)[HOx(ads)/-] + k(Ox2- )[Ox2(ads)/-] where R(tot) is the net dissolution rate of the feldspar, [i(ads)] is the concentration of species i adsorbed to the surface, and k(i) is the rate constant for release of the surface complex. The model was fit to data for oxalate-promoted dissolution of andesine, resulting in estimates for the rate constants of k(HOx-) = 1.16 x 10-12, k(Ox2-) = 1.05 x 10-12, and k(H-) = 9.61 x 10-13 mol of feldspar (??mol of i) (??mol of i)-1 s-1.Previous work on adsorption of oxalate at aluminosilicate surfaces suggests that maximum adsorption occurs through a bidentate attachment of the organic ligand, at near-neutral pH. Rates of ligand-promoted dissolution are expected to be greatest at this pH as well. We tested this model by measuring oxalate adsorption on the surface of andesine (An47), in solutions of pH 3-5 and total oxalate concentrations of 0-8 mM. Contrary to expectation, the greatest adsorption density of 24 ??mol m-2 total oxalate was observed at pH 3 and 8 mM total oxalate. Adsorption is dependent upon the activities of both oxalate (C2O42-) and bioxalate (HC2O4-) in solution and can be modeled with either a two-term Langmuir or a two-term Freundlich isotherm. A Freundlich adsorption model provided the best fit to rate data because it was not constrained to a finite number of adsorption sites, as was the Langmuir model. The two-term ligand adsorption model was incorporated into a rate model: Rtot = kH(+)[Hads+]L +kHOx(-) [HOxads-]+kOx(2-) [Oxads 2-] where Rtot is the net dissolution rate of the feldspar, [iads] is the concentration of species i adsorbed to the surface, and ki is the rate constant for release of the surface complex. The model was fit to data for oxalate-promoted dissolution of andesine, resulting in estimates for the rate constants of kHOx(-) = 1.16??10-12, kOx(2-) = 1.05??10-12, and kH(+) = 9.61??10-13 mol of feldspar (??mol of i)-1 s-1.

Environmental Science & Technology↗