Sarah Gordee and Carter Dettloff
Faculty Advisor/Collaborator: Bradford Burton
Recipient of First Place Award in Natural and Physical Sciences
Geologic and Geochemical Comparison of Late Eocene and Oligocene Volcanic and Intrusive Rocks, Carlin-Range and Central Ruby Mountains, Elko County, Nevada
The central Ruby Mountains and the Carlin-Range, northeast Nevada, are separated by a major northwest-dipping fault zone that accommodated large magnitude extension beginning in the late Eocene (~35 Ma). The Harrison Pass pluton is a composite granodiorite and monzogranite body that was emplaced at mid-to-upper crustal levels ~36.6 My. b.p. and is exposed in the footwall of the fault zone. Volcanic rocks of similar age and composition are exposed in the hanging wall of the fault near Robinson Mountain, 30 km to the west-northwest of Harrison Pass pluton. This study tested the hypothesis that the volcanic rocks in the Carlin-Piñon Range are the extrusive equivalents of Harrison Pass pluton. Proof of this relationship would provide piercing points to measure slip on the fault zone, and have important implications for the tectonic reconstruction of northeastern Nevada. Detailed geologic mapping was conducted to establish volcanic units, and geochemical analyses were used to compare the petrogenetic history of the rocks. Major and trace element compositional trends show strong similarities between the intrusive and extrusive suites, as do modal mineralogy and plagioclase zoning. The data are non-unique, but support a genetic relationship that should be further investigated using isotope geology.
Faculty Advisor/Collaborator: Karen Havholm
Documenting Sand Dune Stratigraphy Through Ground-Penetrating Radar, Flintstone Hill, SW Manitoba
Geoarchaeological study of Flintstone Hill, a stabilized parabolic dune in Glacial Lake Hind Basin (SW Manitoba) is ongoing. Previous studies of sediments in and below the dune in a Souris River cut-bank determined that glacial Lake Hind occupied the site and was replaced first by closed basin lake/wetland conditions by 9250 BP, then by eolian deposition by 6700 BP. Multiple thin sand sheet beds capped by soils were deposited between 5500 BP and 3250 BP. The lower condensed zone includes carbonate enrichment, indicating maximum aridity prior to 4000 BP when a flood truncated the section and deposited a silt layer. The upper condensed zone lacks carbonate but contains clay bands. The parabolic dune then migrated in, since experiencing deflation and soil formation. To determine the 3-D internal stratigraphy of dune and underlying sand sheet strata, five ground-penetrating radar (GPR) transects were collected, but only penetrated five meters. A prominent sub-horizontal reflection was imaged four meters below the highest point on the dune. Profiles and cores indicate this reflection corresponds to the condensed zone. Above this, concave upward and southward-dipping reflections are present locally; these indicate soil-capped deflation scours and locally preserved dune cross-strata. GPR data from below the prominent reflector are very limited. However, profiles and cores expose angle-of-repose dune cross-strata up to 1.5 m thick below the condensed zone indicating migrating eolian dunes rather than sand sheets initially buried the wetland.
Faculty Advisor/Collaborator: Karen Havholm
Documenting the Paleoenvironment of the Proterozoic Hinckley Sandstone
The Proterozoic Hinckley Sandstone, a late-stage sediment deposit in the Mid-Continent Rift, is exposed in east-central Minnesota. This mature, quartz-rich sandstone was previously interpreted as a shallow lacustrine system, but new evidence (Beaster and Kohn, 2000) indicates that it was deposited in a fluvial and eolian environment. This interpretation is based on recognition of two different types of cross-strata, trough and planar, that each displays a distinct paleocurrent direction. The unimodal trough orientation of trough cross-strata is consistent with southeastward bed form migration in a fluvial environment. Northeast-dipping planar cross-strata containing adhesion structures, which are indicative of wind blown sediment adhering to a damp surface, indicate wind-blown dunes migrating perpendicular to the adjacent streams. For this study, four additional stratigraphic sections were measured, described, and correlated to previously measured sections. New sections to the north and south of the previous study area show little difference in overall facies type or distribution. Overall, fluvial facies dominate over eolian. Detailed lateral tracing of beds demonstrates that locally thick eolian cross-strata thin and disappear laterally by downward cutting of fluvial basal scour surfaces over distances of 200m. Four types of deformation have been identified within the Hinckley Sandstone: upturned and broken laminations, flame structures, convolute bedding, and small-scale faults. Analysis of deformed strata to determine the cause(s) of the deformation is ongoing.
Brent Kabat and Katie Thornburg
Faculty Advisor/Collaborator: J. Brian Mahoney and Robert Hooper
Swan Lake Transect: Insight into Metal Speciation in the Lower Couer d'Alene River Valley, Idaho
Toxic metals (especially lead and zinc) are widely distributed throughout the lower Coeur d'Alene River Valley. Variations in the hydrologic regime, redox conditions, porosity/permeability, organic content and microbial activity results in complicated metal transport pathways. Documentation of these pathways is a prerequisite to effective remediation, and requires accurate analysis of lateral and vertical variations. We have sampled a detailed transect of fluvial sediments in the Swan Lake area of the lower river valley. Sediment cores were retrieved from river channel, levee, back levee, marsh and lacustrine environments. An analytical approach combining sequential extraction, electron microscopy, and microanalysis provides a comprehensive assessment of particulate speciation in these varied environments. Flood redistribution of oxide, sulfide and carbonate phases results in periodic contaminant recharge generating a complex system of metal dissolution, mobilization, migration and precipitation. In levee environments, authigenic sulfides from flood scouring are quickly oxidized resulting in development of oxide coated grain surfaces. Stability of detrital minerals on the levee is variable depending on sediment permeability, grain size and mineralogy resulting in a complex stratigraphy of oxide zones (multiple Zn-Pb-Mn-Fc oxyhydroxide phases) mottled with zones dominated by detrital and authigenic carbonate and sulfide phases. Marshes subjected to periodic subaerial exposure/flooding are dominated by authigenic and biogenic mineralization. Lacustrine environments are dominated by colloidal inorganic and biogenic sulfide minerals.
Faculty Advisor/Collaborator: Phillip Ihinger
Geology at Oregon Caves National Monument
Oregon Caves National Monument is a unique and complex geologic area. The main feature in this park is the unusual occurrence of a marble cave, which is intruded by plutonic dikes and locally as well as regionally metamorphosed. Through an internship sponsored by the Geological Society of America and the National Parks Service, I spent the summer of 2000 on the interpretation staff of this park. The formal duties of the internship included preparing and presenting an educational program to the public regarding the impacts of humans on the regional geology, rewriting the geological section of the tour guide handbook to include accurate geologic information, and continuing a water quality project which required collection of water samples within the cave for later analysis and interpretation. The water quality project included taking measurements in various locations in the cave for temperature, pH, conductivity, and taking samples to be geochemically analyzed for ionic concentrations. Based on the data, interpretations can be made regarding the creation and evolution of this distinctive cave.
Faculty Advisor/Collaborator: J. Brian Mahoney
Provenance Signature of Glaciofluvial Sediments, Puget Lowland, Washington
Quaternary sediments in the Puget Lowland comprise a complex succession of intercalated glacial, glaciofluvial, and glaciomarine sediments derived from two distinct source regions. Sedimentation patterns were alternately dominated by 1) the Puget Lobe of the Cordilleran Ice Sheet, which provided detritus rich in metamorphic and plutonic debris from southern British Columbia, and 2) smaller alpine glaciers to the east, which provided detritus dominated by volcanic detritus from Tertiary to Recent volcanism in the Cascade Range. Each source region provided sediment with distinctive petrologic and geochemical characteristics. Complex patterns of glacial and interglacial sedimentation have led to a complicated stratigraphy that varies widely across the region. This investigation attempts to fingerprint individual source regions in order to provide baseline data applicable to modeling sediment distribution in the Puget Lowland. Stream sediment samples from modern-day rivers have been acquired from four general areas. the Northern Cascades and Coast Mountains, the Central Cascades, the Southern Cascades, and the Olympic Mountains. Major and trace element geochemistry is being used to identify geochemical markers from each region in an attempt to identify distinctive characteristics that can be used to model temporal and spatial variations in sediment supply to the Lowland.
Faculty Advisor/Collaborator: Robert Hooper and Kent Syverson
Clay Mineralogy of Till Units in Western Wisconsin
Semi-quantitative till clay mineralogy of the < 1m fraction has been examined to determine if clay mineralogy can be used to differentiate the various till units in western Wisconsin. Older, calcareous till units of the Pierce and Marathon Fms. and the overlying, reddish-brown, sandy till units of the River Falls, Lincoln, Copper Falls Fms. and an unnamed till unit in Chippewa County, WI have been analyzed using the standardized laboratory procedures of Moore and Reynolds (1997). Methods include vacuum mounting clays, deconvolution of peak areas using JADE (v. 3.1), and determining mineral intensity factors (MIFs) from NEWMOD. Eighty basal till samples have been processed and the clay minerals quantified based on illite (I), kaolinite (K), vermiculite (V), and mixed layer illite/smectite (I/S).
|Copper Falls Fm. (n=12)||37.5±10.8||6.9±5.6||33.9±10.6||21.7±5.7|
|Lincoln Fm. (n=14)||32.1±6.6||5.2±2.0||37.2±6.2||25.5±6.0|
|River Falls Fm. (n=12)||31.3±9.3||15.1±5.8||33.8±8.2||19.7±7.2|
|Unnamed Till Unit (n=16)||26.8±7.7||18.7±6.0||37.9±7.1||16.6±7.1|
|Trade River Fm. (n=4)||42.6±8.9||6.3±2.1||39.5±11.2||11.7±7.1|
|Pierce Fm. (n=13)||25.3±5.9||23.3±3.5||39.3±4.6||12.2±1.6|
|Marathon Fm. (n=5)||26.3±11.2||6.3±1.0||50.3±11.3||17.1±4.9|
Based on these results we conclude that the Illinoian River Falls Fm. has more kaolinite than the Wisconsinan Lincoln and Copper Falls Fms., which have low kaolinite and look very similar. The unnamed reddish-brown till in western Chippewa County is very similar to the River Falls Fm. and probably will be mapped as River Falls Fm. The pre-Illinoian, calcareous Pierce Fm. has much more kaolinite than the pre-Illinoian Marathon Fm. and the Late Wisconsinan Trade River Fm.
Faculty Advisor/Collaborator: Robert Hooper
Transmission Electron Microscopy of Grain and Biocoatings from Lead and Zinc Contaminated Sediments in the Lower Coeur D'Alene River Valley
Significant lead and zinc contamination occurs downstream from the Coeur d'Alene mining district. Prior sequential extractions and SEM examination of materials collected from different environments demonstrate complex mineralogical relationships dependent on physical dispersion, local redox conditions, and biologic controls. A substantial amount of the total metals in the lower Coeur d'Alene valley are held as sub-micron grain or bio-coatings that defy adequate characterization using SEM and XRD analysis. Analytical electron microscopy using a transmission electron microscope (TEM) has proven very useful in determining metal speciation in these problematic materials. A new technique for examining heterogeneous grains was applied to unconsolidated samples from different fluvial subenvironments in the lower Coeur d'Alene river valley. TEM analysis has resulted in identification of several new phases and better constraints on the chemistry of many other phases. In oxidized river levee samples, Zn is strongly partitioned into siliceous ferri-hydrite with typical zinc concentrations of 0.5-3 oxide wt%. Lead occurs in a wide variety of ferro-manganese/oxy-hydroxide phases that are typically non-stoichiometric and nano-crystalline. In samples from transitional and reduced redox environments, a wide variety of lead phases were identified including microcrystalline galena and amorphous biocoatings with variable sulfide compositions. Siliceous, ferro-phosphatic spherules occur in one transitional redox sample and contain up to 30 wt% PbO. Zinc is largely constrained to microcrystalline sphalerite or mixed nano-crystalline sulfides in the transitional and reducing fluvial subenvironments. TEM analysis has demonstrated that particulate speciation is far more complex than expected from conventional SEM/XRD analysis of the same samples.
GPS Mapping in Rugged Terrain: The Geronimo Frisbee Course, Kingston, New Mexico
A world-class 20-hole Extreme Frisbee Golf Course, known as Geronimo Golf, is located on the eastern edge of the Black Range, on the western flank of the Rio Grande rift near Kingston, New Mexico. The course is specifically designed to host two yearly professional Frisbee Golf tournaments in April and September. The course is located in the scenic Percha Creek drainage, a rugged area characterized by steep cliffs, rocky hill slopes and thick desert vegetation. The course is extremely challenging due to the aggressive vegetation and extreme elevation changes encountered on the resistant crystal tuff found in the area. The Geronimo Frisbee Golf course is legendary among hardcore frisbee golf players and enthusiasts. The course was mapped in January, 2001, with two different global positioning systems (GPS), including both Trimble and Garmin models. The Trimble provided waypoint information that describes the centerline of each fairway. The Garmin was used to collect data necessary for accurate elevation mapping of each individual tee and pin and for accurate distance measurements between holes. Two separate maps of the course are being developed. A map that superimposes the course layout over a detailed topographic map will give players a good concept of the elevation changes (up to 300 ft from tee to fairway) and challenging hiking they will be encountering on the course. A map that superimposes the course layout over an aerial photograph will give players a realistic overview of the entire course, allowing them to assess potential trouble areas and the best access routes.