In situ fossil stumps of Glossopteris are preserved in their original growth position in fluvial deposits of the Upper Buckley Formation (Upper Permian) in the Beardmore Glacier, central Transanctarctic Mountains. Roots radiate shallowly from the stumps into immature paleosols that retain their lamination. Of the 87 stumps found, 74 are in two horizons at Lamping Peak separated vertically by approximately one meter. The stumps represent forests that flourished at polar paleolatitudes (>70°S). Mean maximum tree height (~20 m), density (~2000 trees/ha), and basal area (~175 m²/ha) of the fossil forest are comparable to those of modern temperate forests and greater than those of other Permian and some younger high-paleolatitude forests. Regardless of the strongly seasonal polar light regime, conditions were sufficiently warm and wet to promote growth during the growing season. Large woody debris (LWD) and macerated debris are preserved as imprints and coalified plant material although the wood of most of the stumps has been replaced by magnetite. The LWD and macerated plant material are more abundant in Upper than Lower Permian deposits in which no stumps have been found. Because of the paucity of branches and root stocks, LWD is inferred to have been transported, which is consistent with its preferred orientation. Results from stream table experiments suggest orientation of LWD is controlled by flow direction when transported; therefore, orientation of LWD at Lamping Peak likely indicates paleoflow.

We consider the response of monazite in country rock to magmatic intrusion. Intrusion of the Searchlight pluton at 15.7-17.7 Ma produced extensive hydrothermal ore deposits in overlying units. Later tilting of the pluton has resulted in a cross sectional exposure with deeper levels exposed to the east (Bachl et al. 2001). The top the pluton primarily intrudes Miocene volcanics though in the southern portion of the roof zone it contacts highly altered Proterozoic augen orthogneiss. Along the northern border of the pluton, from shallow to intermediate depth, it is in contact with Proterozoic gneiss with deeper portions in contact with the ~66 Ma Ireteba granite. ten samples of the Proterozoic gneiss were collected, four from the augen orthogneiss in the southern roof area (which yielded no monazite), four along a 0.5 km transect northward from the northern margin into the country rock, one from a large block located in the lower Searchlight zone (XG-12), and one from the north western margin near the roof area (XG-11). Monazites from the Ireteba granite near the contact with the Searchlight display irregular zoning, and LA-ICP-MS Th-Pb dating shows a bimodal age distribution with peaks at ~17 Ma and ~53 Ma (this older age represents mixed zoned analysis rather than a real geologic event). However, oxygen and hydrogen isotope whole rock analyses of these rocks show no pattern of variation related to sample distance from the Searchlight Ireteba contact. This in addition with petrographic evidence suggests that monazite alteration in the Ireteba was caused by some mechanism other than fluid alteration, and calls into question the use of patchy zoning as a diagnostic feature of hydrothermal alteration. The monazites collected in the Proterozoic wall rock transect, display irregular zoning with a unimodal LA-ICP-MS 207Pb/206Pb age of 1656±3.5 Ma. Monazites analyzed from XG-11 and XG-12 display irregular zoning and discordant U-Pb ages. When plotted with samples from the Proterozic wall zone transect samples XG-11 and XG-12 lie on a line of discordia with an upper intercept (defined by the wall zone samples) at 1641±16 Ma and a lower intercept at 134±98 Ma suggesting that these analyses represent mixing between Proterozoic age zones and Cretaceous (Ireteba) or Miocene (Searchlight) ages. Intrusion of the Searchlight pluton appears to have been recorded by the partial recrystallization of monazite in the Ireteba granite, and possibly in portions of the roof zone and in Proterozoic country rock blocks in the lower Searchlight unit. The lack of apparent hydrothermal alteration in the wall zone and the highly altered appearance of rocks in the southern roof zone suggest that fluid release from the Searchlight pluton was highly focused through the roof zone. Bachl et al. (2001) GSA Bulletin v.113 no.9; p.1213-1228.

Pyrite crystals were synthesized with no impurities and doped with As, Co, or Ni to be investigated along with natural samples, using electrochemical techniques, wet chemical kinetic experiments, and solid-state measurements of semiconducting properties to determine the effect of impurity content on pyrites oxidation behavior. Potential step experiments, cyclic voltammetry, AC voltammetry, and electrochemical impedance spectroscopy (EIS) were performed along with mixed-flow-through and batch reactor experiments to measure rates of pyrite oxidation and propose charge transfer mechanisms. A solution near pH 2 containing 1 mM ferric iron, open to atmospheric oxygen, was chosen for all experiments to approximate water affected by acid mine drainage. For the electrochemical experiments van der Pauw/Hall effect measurements determined resistivity, carrier concentration and carrier mobility of pyrite electrodes. Concentration of As, Co, and Ni in pyrite electrodes was determined with laser ablation inductively coupled plasma mass spectroscopy. The anodic dissolution of pyrite and the reduction of ferric iron half-reactions were taken as proxies for natural pyrite oxidation. Pyrite containing no impurities is least reactive. Pyrite with As is more reactive than pyrite with either Ni or Co despite lower dopant concentration. Solid state measurements, AC voltammetry, and EIS data agree with previous studies reporting As, Co and Ni impurity defect states residing at different energy levels within the band gap. The current density generated from potential step experiments increased with increasing As concentration indicating the higher reactivity of As-doped pyrite may be related to p-type conductivity and corrosion by holes. The mixed-flow-through and batch experiments also showed higher rates of oxidation for pyrite with impurities as determined by inductively coupled plasma atomic emission spectroscopy. However, the Co-doped and As-doped pyrite rates were statistically equal. The results indicate that Co and Ni are released to solution as the oxidation reaction progresses while As is not. Evidence from the AC voltammetry and EIS suggests that the higher reactivity of doped pyrite results from introduced defect levels which lead to higher density of occupied surface states at the solid-solution interface and increased metallic behavior. Based on the EIS equivalent circuit model, it is hypothesized that charge transfer occurs directly from the pyrite conduction band but also in a two step recombination process mediated by intra-bandgap defect surface states. .

In the Si&#x00F0;a-Fljotshverfi District of south Iceland, Pleistocene basaltic lava forms flame-like apophyses, dikes, and disaggregation structures that invade overlying hyaloclastite. Apophyses as well as underlying lavas are cube-jointed, indicating rapid cooling due to formation in a wet environment and suggesting that hyaloclastite and lava were emplaced almost concurrently, while hyaloclastite was wet and weak. Thermal modeling suggests that influx of heat from the underlying lava resulted in increased fluid pressure in the hyaloclastite matrix. Fracturing of the chilled rind that had formed atop the lava permitted injection of lava into the overlying hyaloclastite. Diffusion of pressure away from the injection site dragged the matrix apart, facilitating propagation of lava upward to form the apophyses. <p> Most of Aztec Wash, a mid-sized Miocene pluton in the Colorado River Extensional Corridor, is characterized by mafic, intermediate, and felsic rocks that are interspersed on very small to large scale. Field relations suggest that this heterogeneous assemblage is the product of repeated injection of basaltic magma into a variably crystal-rich magma chamber and subsequent mechanical and chemical interactions. The most pristine manifestations of the intruding mafic magma are sheets and discrete pillow-like masses of basaltic material hosted by granite. The petrographic and textural similarity between sheets and pillows suggests that the latter formed from the former by disaggregation while still molten. The goal of this study is to understand how mafic disaggregation into a cooler host works in these two specific settings, with potential application to magmatic systems as a whole.

This study investigates the effects of earthworm burrowing on arsenic mobility and speciation in soil. The use of roxarsone in the poultry industry as a feed supplement is an increasing anthropogenic source of arsenic. Most of the arsenic is excreted in the litter, later used as agricultural fertilizer. With larger pushes for soil conservation, the decrease in tillage allows earthworm populations to increase and burrows to become more permanent. The influence of earthworms on soil mixing is controlled by two main components: physical displacement and earthworm feeding habits. Mesocosm experiments were constructed to test the hypothesis that earthworms and burrows provide means for biotransformation and redistribution of arsenic. By controlling the thickness and location of a contaminated layer within the soil columns, arsenic concentrations can be used to indicate bioturbation rates by fitting depth profiles to a simple 1-D advection/diffusion model with a spatial decay term that varies with depth. Synchrotron X-ray methods reveal small-scale displacement of arsenic near the burrow and in the bulk soil. Microbeam X-ray Absorption Near Edge Structure spectra were collected to determine arsenic speciation. Arsenic initially introduced as roxarsone tended to be in a methylated form after 30 days. Within the earthworm tissue, arsenic-glutathione complexes were formed. Overall implications are that 1) burrows serve as macropores allowing rapid transport to greater depths during infiltration events; 2) bioturbation rates appear to be depth-dependent; and 3) earthworm soil mixing produces potentially mobile forms of arsenic that may become bioavailable as arsenic is transported through the subsurface.

This study examines how coupled geomorphic and biologic processes influence the potential for hillslope soils to store organic carbon. A mass-balance model of soil organic carbon on hillslopes is developed by combining soil transport with biologic carbon production and respiration. The model is compared with soil carbon measurements on three hillslopes that represent various stages of hillslope evolution at Land-Between-the-Lakes National Recreation Area, northwest Tennessee. Both model results and field measurements suggest that locations of soil thickening are able to store more organic carbon than locations of soil thinning. In model simulations of a hillslope relaxing onto a fluvial terrace, locations of soil thickening, which propagate upslope, represent the greatest potential to increase soil organic carbon through time. The downslope increase in soil organic carbon seen in modeling and field measurements arises from the systematic variation in soil thickness associated with soil transport and hillslope evolution. Varying soil transport parameters (e.g. diffusivity, initial soil production) in model simulations reveals that physical soil transport processes exert greater control than biological carbon production and respiration on the change in soil organic carbon storage of a hillslope through time. At locations where thinned soils are converted to locations of soil thickening, the organic carbon storage of the soil increased in model simulations by 5-25%. This study suggests that physical soil processes are more important than biological carbon production and respiration processes in sequestering organic carbon in forested hillslope soils.

The brittlestar, Ophionotus victoriae, is the third most abundant epifaunal animal in Explorers Cove (EC; mouth of Taylor Valley). However its ossicles, composed of high-Mg calcite, rarely occur in either short cores of recent EC sediment or long cores of Cenozoic deposits in McMurdo Sound (e.g. MIS-ANDRILL 1B). To identify taphonomic processes we analyzed 1) ossicle abundance and microstructural damage in EC cores, 2) ossicle dissolution in a 27-day, in situ experiment using ossicles freed from organic matter, and 3) soft-tissue decay and ossicle dissolution over a 2-year in situ experiment where whole dead brittlestars were suspended above or shallowly buried in the sediment within the taphonomically active zone (TAZ). Seafloor experiments showed a greater maximum percent silhouette area loss (max: 68%) and greater microstructural damage than those suspended (max: 24% loss). From 7,775cm3 of sediment searched from EC, one highly dissolved ossicle was found. Scanning electron microscopy shows the highest levels of dissolution textures, as well as the greatest degradation of the distal portions. During the 27-day experiment ossicles lost between 0.07wt% and 1.31wt%. At observed rate of dissolution and continued exposure in the TAZ it would take between 6 and 110 years for vertebral ossicles to completely dissolve. These results suggest that dissolution affects ossicles soon after death and that the stratigraphic record does not accurately reflect the presence and abundance of ophiuroids, which are major components of shallow Antarctic epifaunal communities.

Sediment core and seismic data was collected and analyzed in order to study the late Holocene geologic history in the Great South Bay estuary, Long Island, New York. The data reveals a distinct and anomalous deposit whose sedimentological characteristics and distribution are shown to be consistent with a modest tsunami striking the New York and New Jersey coast between 2200 and 2400 yr BP. In addition, core and radiocarbon date information are used to reconstruct the chronostratigraphy of the estuary during this period. The timing of the tsunami event coincides with an abrupt transition into the modern estuarine depositional regime of the bay. Such a sudden shift in depositional patterns had not been seen prior and has not been seen since. With significant human population and real estate located in the region, the stability and susceptibility to potentially recurring events is a prompt for understanding such influences or response of the modern coastal system.

This study attempts to define the early to mid-Holocene paleoenvironment at Huaca Prieta, an archaeological site on the north coast of Peru, through a combination of sedimentological, paleoecological, and stable isotope analyses. This research is part of a larger collaborative study drawing on many disciplines, and the interpretations of the results presented here are solely from a geological perspective. Multiple studies point to a severely diminished or even absent El Niño in the region during the mid-Holocene, but the Chicama River valley is a relatively unstudied location. Sediment coring from the upper 6 m reveals laminated to thinly bedded carbonates, organic sediments, and fine-grained clays deposited within larger intervals of sands and silts. These finer-grained sediments evidence a coastal lagoon 3 km in length which existed approximately 7300-6200 cal ybp. Stratigraphic analysis of the upper 6 m of sediments reveals a marked decrease in siliciclastic material delivered to the floodplain during this time, with potential implications for the mid-Holocene El Niño frequency debate and human-environment linkages during this time.

This study employs combined U-Th radiometric age and trace element analyses of zircon from rocks of the Swift Creek stage (16 to 10 ka) of Mount St. Helens in order to obtain time-temperature-composition records of the melts from which these crystals grew. Results illustrate that the Mount St. Helens magmatic system has been constructed over hundreds of thousands of years by repeated intrusion of new magma batches that stall and crystallize within the crust to produce a crystal storage zone (or zones). Zircon trace element signatures primarily record the long-term magmatic conditions and interactions within this active intrusive body and do not record conditions immediately preceding eruption. Pulses of ascending magma rejuvenate and interact with existing intrusions, mixing zircon crystal populations and inducing new phases of zircon growth and melt fractionation, while magmas that do not stall in the crust entrain and mix zircon crystals from the crystal storage zone(s) and carry them to eruption. Geochemical trends with time suggest that the deep-seated magmatic system of Mount St. Helens has been strongly influenced by input of hot, relatively primitive melt since ~100 to 60 ka. This study documents the existence of an intrusive complex beneath an active arc volcano and records a clear connection between Mount St. Helens volcanism and an underlying plutonic magmatic system. It also suggests that, similar to large-scale batholiths, small-scale volcanic systems accumulate in small increments over prolonged periods of time.