James D. Gleason

Early Gondwanan connection for the Argentine Precordillera terrane

Abstract The Precordillera of Argentina is widely accepted as an exotic terrane of Laurentian (North American) affinity. Newly acquired U/Pb ages on individual detrital zircons from Lower Cambrian and Upper Ordovician quartz sandstone beds in the Argentine Precordillera indicate a Gondwanan provenance not associated with any known part of Laurentia. Accordingly, the Precordillera terrane is likely underlain by basement rock of Gondwanan affinity. In addition, detrital zircons from the Upper Ordovician sandstone bed provide no evidence for a Mid Ordovician position against the inboard Famatina arc. These results demand critical re-evaluation of widely held assumptions regarding the paleogeography of the Argentine Precordillera.

Mercury isotopic evidence for multiple mercury sources in coal from the Illinois basin.

Coal combustion is the largest source of anthropogenic mercury (Hg) emissions to the atmosphere and, thus, has vast environmental implications. Recent developments in Hg stable isotope geochemistry offer a new tool for tracing sources and chemical transformations of anthropogenic Hg in the environment. We present here the first isotopic study of mercury in organic and inorganic constituents of four Pennsylvanian-age coal seams in the Illinois Basin, one of the main coal-producing areas in the USA. We report mass dependent isotopic variations relative to the NIST 3133 standard as δ(202)Hg and mass independent fractionation as Δ(199)Hg and Δ(201)Hg values. The data for Illinois coals show a wide range of δ(202)Hg (-0.75 to -2.68‰), Δ(201)Hg (0.04 to -0.22‰), and Δ(199)Hg (0.02 to -0.23‰). In contrast, vein pyrite from two coal seams is isotopically unfractionated relative to NIST 3133. Collectively, these data suggest that isotopically distinct Hg sources contributed to the organic and inorganic fractions of Illinois coals. The Δ(201)Hg/ Δ(199)Hg ratio of Illinois coals is 1:1, consistent with isotopic fractionation by photochemical reduction of Hg(2+) prior to deposition in coal-forming environments. The isotopic composition of Hg in pyrite is more likely derived from hydrothermal fluids that precipitated reduced sulfur in Illinois coal seams. These results demonstrate, for the first time, the potential of Hg isotopes to discriminate between syngenetic (depositional) and epigenetic (hydrothermal) sources of Hg in coal. Our findings may be useful in distinguishing among various geological processes controlling the distribution of Hg in coal and monitoring the fractions of Hg in emissions associated with organic versus inorganic components of coal.

Paleotectonic Implications of a Mid‐ to Late‐Ordovician Provenance Shift, as Recorded in Sedimentary Strata of the Ouachita and Southern Appalachian Mountains

North American Ordovician strata record a large shift in their neodymium isotopic composition ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Antarctic environmental variability since the late Miocene: ODP Site 745, the East Kerguelen sediment drift

\Delta \epsilon _{\mathrm{Nd}\,}=\sim 7

Broad region of no sediment in the southwest Pacific Basin

\end{document} ) at around 450 Ma. As part of a continuing effort to understand this phenomenon, we studied the provenance of Middle and Upper Ordovician clastic sedimentary rocks along a transect through the southern Appalachian and Ouachita Mountains using a combination of high‐resolution graptolite‐neodymium isotopic analysis and U‐Pb dating of detrital zircon. Taconian (Blountian)‐age clastic sediment (ca. 465 Ma) in the southern Appalachians ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Isotopic signatures of mercury contamination in latest Permian oceans

\epsilon _{\mathrm{Nd}\,}=-8