Faculty Advisers/Collaborators: Karen Havholm and Brian Mahoney
Stratigraphic Variability in the Lone Rock Formation, Dunn and St Croix Counties, WI
The Upper Cambrian Lone Rock Formation is a glauconitic, predominantly fine-grained sandstone that was deposited over Wisconsin in a shallow marine shelf environment. The Lone Rock Formation comprises an overall fining-upwards sequence from the underlying medium- to coarse-grained sandstone of the Wonewoc Formation to the overlying siltstone and shale of the St Lawrence Formation, representing a transgression of the Cambrian sea onto the craton. Recent work in southern Dunn and Trempealeau Counties shows a 30-meter thickness of the Lone Rock formation; grain size and stratification indicate a smaller scale regressive event superimposed on the overall transgressive trend. For this study the Lone Rock Formation was measured and described from exposures north and west of earlier studies. Composite stratigraphic sections 43-46 meters thick were constructed for northern Dunn County and for the Hudson-Afton area. These northern sections show vertical facies variations similar to the southerly sections indicating an initial deepening to near storm wave-base, followed by shallowing to just above fair-weather wave-base before a final deepening. These sections are 50% thicker than the southerly sections, but match well with a core from St Paul, MN and earlier regional studies by Berg (1954) and James (1977), prompting recorrelation of the southerly sections.
Dan Dahlman and Aaron Walczak
Faculty Adviser/Collaborator: J. Brian Mahoney
Geochemical Distinction of Glaciofluvial Sediments in the Puget Lowland
Basin-wide correlation of geologic stratigraphy in the Puget Lowland of Northwestern Washington has been particularly difficult due to the complex intertwining of the glacial and interglacial units. Source regions for the glacial and interglacial sediments in the Lowland have been interpreted as alternating between the Puget Lobe of the Cordilleran Ice Sheet and Cascadian sediments. Cordilleran Ice Sheet sediments consist primarily of gneiss, schist, quartzite, and distinctive heavy metals from granitic and metamorphic terranes of British Columbia. Cascadian sediments typically consist of andesite, basalt, diorite, and granodiorite. Sediment samples are tested for major and trace element chemistry in order to determine relative concentrations from each source region throughout time. Preliminary major element chemistry indicates the samples fall into two distinct geochemical groups: 1) Low silica (< 65% SiO2) with relatively high levels of Al, Ti, Fe, K, and 2) High silica (70%+) with corresponding low values of Al, Ti, Fe, and K. Trace element geochemistry indicates unusually high concentrations of certain transitional metals in the low silica group such as Nb, Th, Y, V, and Zr. These associations suggest that sediment geochemistry is not controlled by bedrock composition alone. We suggest that there are two controls on sediment geochemistry: 1) the primary control is the composition of the source area; and, 2) a secondary control exerted by the intensity of weathering in the source area prior to transport.
Lisa L. Kraft
Faculty Adviser/Collaborator: John R. Tinker
Minimizing Overlap of Septic System Plumes and Capture Zones of Private Water Supply Wells in Unsewered Subdivisions
The Planning and Development Department of Eau Claire County, WI proposed a revision to their subdivision control ordinance which requires information on the direction and rate of groundwater flow and the five-year groundwater capture zone for each well within proposed unsewered subdivisions. The primary concern of Eau Claire County is whether wells within and immediately down gradient of a subdivision will exceed 10 mg/L nitrate-nitrogen. A primary concern of developers of subdivisions is whether it is technically and economically feasible to meet the proposed requirements. A three-dimensional groundwater flow model, MODFLOW estimates the feasibility of designing a subdivision to meet the proposed requirements. Briarwood Subdivision has 97 lots with sandy soils underlain by fluvial/lacustrine sediment and the Mr. Simon sandstone. Input values for hydraulic conductivity, specific storage, specific yield, porosity, and recharge are obtained from published data and from well constructor's reports. Steady-state, water-table elevations are calibrated to known water-table elevations and to the Eau Claire County water-table map. Septic systems are modeled as continuous point sources of 45 mg/L of nitrate-nitrogen. Nitrate-nitrogen plumes from the septic systems are calibrated to known nitrate-nitrogen concentrations in private water-supply wells within the subdivision. The calibrated model for Briarwood Subdivision is used to minimize the overlap of septic system plumes with the five-year capture zones of water-supply wells. Wells and septic systems serving multiple homes and variation in well depth are techniques used to minimize nitrate-nitrogen concentrations.
Thomas Robert McManus
Faculty Adviser/Collaborator: Bradford R. Burton
Textural transition from plastic to brittle strain, Ruby Mountains, northeast Nevada
The Ruby Mountains of northeast Nevada are a major mountain range in the US Basin and Range extensional province that has undergone large-magnitude crustal extension. The Ruby Mountains shear zone (RMSZ) is exposed for more than 100 km along the western flank of the range. Radiometric dating of minerals in the RMSZ and adjacent footwall show that extension occurred in the Late Eocene to Oligocene (ca 22-36 Ma), when the RMSZ evolved from plastic to brittle deformation mechanisms. Plastic deformation is indicated by the development of mylonitic rocks showing crystal plastic strain, whereas brittle deformation is manifested in cataclasite including gouge, microbreccia and breccia. The mylonitic-to-cataclastic textures of the RMSZ were studied in the central Ruby Mountains using detailed geologic mapping (summer of 1998), and petrographic analysis of a suite of 70 fault rock samples. These studies show that the RMSZ consists of five distinct textural zones: 1) a footwall of granitic rocks which show some crystal plastic and cataclastic strain, 2) a mylonitic shear zone in which crystal plastic strain was the dominant deformation mechanism, but was accompanied by cataclasis of feldspar, 3) a basal chloritic cataclasite zone in which mylonitic textures are overprinted by cataclasite, 4) a complex zone of moderately to intensely hydrothermally altered fault rocks. and 5) a hanging wall of intensely altered chert breccia and microbreccia formed from a protolith of chert and argillite. The textural transition is interpreted to reflect cooling of the exhumed crust during extension and fault attitudes support a rolling-hinge model of extensional fault evolution.
Faculty Adviser/Collaborator: J. Brian Mahoney
Petrographic Analysis of the Late Cretaceous Nanaimo Group of the Georgia Basin
The Nanaimo Group is comprised of sedimentary rocks deposited in the Georgia Basin in the Upper Cretaceous and deformed by an Eocene compression event. The Nanaimo Group is approximately 4 km thick and consists of a succession of conglomerate-sandstone-mudstone units. This study focuses on the upper six formations (Cedar District, De Courcy, Northumberland, Geoffrey, Spray, Gabriola) located in the northern Gulf Islands (Denman and Hornby) and north-eastern Vancouver Island encompassing 1.5-2 km of the Group. The rocks are primarily fine to medium-grained feldspathic arenites with varying amounts of mica and lithic fragment compositions suggesting erosion from different sources. The purpose of this study is to assess the vertical and lateral stratigraphic variability in sedimentary petrography in the upper Nanaimo Group. Sedimentary petrography provides information, through detailed thin-section analysis, about the erosional history of source rocks through time. The Nanaimo Group has an apparent increase in metamorphic lithic fragments, biotite, and muscovite upward in the section. It also appears to have a corresponding decrease in volcanic lithics. This suggests that the source rocks are changing through time and is concurrent with the uplift and erosion of the volcanic, plutonic, and metamorphic rocks of the Coast Belt to the east of the Georgia Basin.
Christine D. Pint
Faculty Advisers/Collaborators: J. Brian Mahoney and Lori D. Snyder
Stratigraphic and Structural Analysis of the Middle Jurassic Hazelton Group, Nechako Plateau, North Central British Columbia
Analysis of the stratigraphy and structure of the Middle Jurassic Hazelton Group will constrain the Jurassic through Cretaceous history of north central British Columbia. The oldest rocks found on the Nechako Plateau are volcaniclastic rocks correlative to the Hazelton Group. These rocks are intruded by the Late Cretaceous Skins Lake Pluton and overlain by Eocene and younger volcanic rocks. The Hazelton group is penetratively deformed and is believed to form the upper plate of a northeast trending thrust fault. The Hazelton Group in this area is composed of polymictic cobble conglomerate, red pebbly mudstone, and feldspathic lithic greywacke. Exposure in the area is poor, with the Hazelton Group found in low relief areas. The outcrop pattern consists of ribs of conglomerate encased in finer grained strata. The rocks commonly dip moderately to the north, but are locally folded about a northwest trending fault axis. The rocks display two well-defined cleavages: S1 cleavage is closely spaced, dipping moderately to the southeast; S2 cleavage is less well developed and dips steeply to the west. Geometric relationships between these structural features suggest multiple episodes of deformation affected the Hazelton Group between the Middle Jurassic and Late Cretaceous.
Faculty Advisers/Collaborators: J. Brian Mahoney and Peter Mustard
Clastic Dikes as Paleoslope Indicators in the Nanaimo Group, Hornby Island, British Columbia
The Upper Cretaceous (89-71 Ma) Nanaimo group on the western edge of the Canadian Cordillera is composed of eleven main stratigraphic units, which represent a series of stacked submarine fan sequences deposited in a foreland basin. The Northumberland Formation is a thinly bedded medium brown mudstone. Near the top of this unit, on the southeastern side of Hornby Island, are numerous clastic sandstone dikes and synsedimentary folds that are interbedded with turbidite deposits. These clastic dikes and sedimentary folds are formed from a partially lithified unit cracking and pulling apart as it slides down a slope. Orientations of these structures are good indicators of paleoslope direction. The synsedimentary fold axes trend shallowly to the northwest (19/336, n=27), which suggests that the paleoslope direction would strike northwest, dip southwest and flow is to the southwest. Dike orientations, which are nearly vertical but have a general northeast strike (209/86, n=60), are perpendicular to the paleoslope. The axial planes of the synsedimentary folds strike northeast and dip southeast (063/47,n=27). Clastic dike and axial plane orientations suggest paleoslope is to the southeast, not to the southwest as suggested by fold axes. This means that clastic dikes would be parallel to paleoslope. This contrasting data indicates that either the use of axial planes or fold axes are unreliable in the interpretation of paleoslope direction. Comprehension of the paleoslope data of these units will constrain the geography and geometry of the formation of submarine fan facies in the Nanaimo basin.
Carrie Rowe and Jean Morrison
Faculty Advisers/Collaborators: J. Brian Mahoney and Robert Hooper
Speciation and Transport of Heavy Metals in the Coeur d'Alene River Valley, Northern Idaho
Heavy metal contamination has become a major environmental problem in historic mining districts like Leadville, Colorado; Butte, Montana; and Coeur d'Alene, Idaho. The current remediation protocol in these situations consists of stripping the contaminated sediments and piling them onto an impermeable membrane that will "contain" the sediment and "stop" the transport of the contaminated materials. This may be a reasonable solution in small, contained areas, but the spread of contaminated sediments by normal fluvial processes in most mining districts can cover both the mining district and a large area down stream. Environmental conditions (Eh, pH, water characteristics, biology) within fluvial subenvironments (levee, wetlands and bedload) vary widely, resulting in complex heavy metal speciation through out the fluvial system. Sequential Extraction, is a digestive process which determines whether heavy metals are bound in exchangable, carbonate, oxidized, organic or residual fractions. It has established that levee environments are characterized by large portions of lead in an oxidized form with minute portions in the residual fraction. The zinc in these samples seems to be contained mostly in the exchangable and residual fractions. Wetlands, which are primarily reducing environments, are characterized by high lead levels in the exchangable fraction, which is easily mobile, and high zinc in the exchangable and oxidizing fraction. Scanning Electron Microscopy has shown that microbes may be important in fixing easily mobile metals into a less bioavailable form. The complexity of heavy metal speciation in the Coeur d'Alene River Valley is represented by vertical and horizontal variability in all subenvironments. Documentation of heavy metal speciation, mobility and bioavialability is critical for the remediation of this and for other historic mining districts.
Faculty Adviser/Collaborator: J. Brian Mahoney
Comparative Geochemistry of the Spences Bridge Group and Coeval Volcanic Rocks of South-Central British Columbia
The Spences Bridge Group is a subduction related volcanic arc system divided into two formations. The Pimanus Formation, which has a composition ranging from basaltic to rhyolitic, containing a significant volume of epiclastic and volcaniclastic sediments. Conformably overlying the Pimanus Formation is the Spius Formation, which is a series of vesicular, basaltic to andesitic flows lacking epiclastic and volcaniclastic deposits. The Spences Bridge arc is a ~215 km long and 50 km wide Mid-Cretaceous (ca. 100 Ma.) volcanic arc with a general northwest southeast trend which is truncated by the Fraser Fault at its north end. Movement along this fault has apparently resulted in translation of the Spences Bridge Group to the northwest. The purpose of this study is to geochemically characterize the Spences Bridge Group and compare its geochemical signature with that of coeval volcanic rocks in the Churn Creek and Empire Valley area located 115 km to the northwest on the opposite side of the Fraser Fault. Preliminary geochemical results show both suites are predominantly medium K subalkalic, calc-alkaline basalts to basaltic-andesite with a distinct subduction related signature. Samples from the main arc appear to form two distinct geochemical groups with one group's signature enriched in P2S05, Nb, Zr, and Y. The two distinct geochemical populations appear to correspond to the Spius and Pimanus Formation of the Spences Bridge Group. When geochemical results from Churn Creek and Empire Valley samples were compared to results from the main arc they appeared to form two distinct groups that overlap with groups of the Spius and Pimanus Formations. This suggests volcanics from Churn Creek and Empire Valley are geochemically related to Spences Bridge Group volcanics.
Stephen M. Sellwood
Faculty Advisers/Collaborators: Lori Snyder and Bob Anderson
Geochemistry of Two Tertiary Plutons, North-Central British Columbia
During July, 1998, two felsic plutonic bodies were mapped and systematically sampled for geochemical analysis and U-Pb age dating. Initial field results indicate that these plutons are texturally and compositionally similar to each other and may be related to the Eocene Ootsa Lake Group felsic volcanic and volcaniclastic rocks widely exposed in the area. This study documents the geochemical signatures of two felsic plutons of probable Eocene age in north central British Columbia. Approximately 15 samples were processed to fused disks and pressed pellets. Major and minor element compositions were determined using the X-Ray Fluorescence Spectrometer in the Department of Geology. Geochemical data collected during this study were compared to existing geochemical data from the Ootsa Lake Group rocks to help establish possible petrogenetic linkages.
Faculty Adviser/Collaborator: Kent Syverson
Surficial Glacial Geology of the Albertville Quadrangle, Chippewa County, West-Central Wisconsin
The Albertville Quadrangle is located in west-central Wisconsin, approximately 20-30 km southwest and south of the outermost Late Wisconsinan end moraines. The lack of glacial landforms, the deep incision of the landscape, and the high degree of sediment weathering suggest a pre-Late Wisconsinan age for much of the sediment in the area. This summer 1998 field study was initiated to understand more about the pre-Late Wisconsinan glacial history of western Wisconsin. Reconnaissance mapping was conducted for one introductory week in the field area. Then aerial photographs, 7.5' topographic maps, well logs, and the Chippewa County soil survey were interpreted to make a preliminary 1:24,000-scale surficial geology map for the Albertville Quad. Seven weeks were spent in the field verifying and modifying contacts, including one week boring holes with the 13-ton Wisconsin Geological and Natural History Survey [WGNHS] truck. High areas south of Elk Creek generally are underlain by Cambrian sandstone and/or weathered outwash < 5 m thick. The sandy gravel outwash contains clasts up to 25 cm in diameter, is weathered to depths of 5 m, is deeply eroded by streams, and commonly is located on the shoulders of hills. In some areas yellowish-red pedogenic clay nearly lithifies the sediment, and many of these soils are misinterpreted as till units in the soil survey. One site high in the landscape contains reddish-brown (5YR 4/4) till 4 m thick, with mean sand:silt:clay percentages of 64:27:9 (n=5). This till may be associated with the River Falls or Lincoln Formations and has been the only till discovered in the study area. Outwash north of Elk Creek is less weathered and thinner than to the south, and is located at intermediate elevations in the bedrock-controlled landscape. Late Wisconsinan outwash of the Chippewa River is up to 50 m thick in the Wissota Terrace in the southeastern part of the Albertville Quad. Sandy silt loess is up to 3 m thick on the western bank of the Chippewa River valley and thins toward the west.
We thank the WGNHS, the Chippewa County Land Conservation Dept., and the UW-Eau Claire Summer Research Experiences for Undergraduates program for funding this project.
Faculty Advisers/Collaborators: Robert L. Hooper and Kent M. Syverson
Clay Minerology of Pre-Late Wisconsinan Till Units, West-Central Wisconsin
This study uses standardized analytical methods to determine if the clay mineralogies of pre-Late Wisconsinan till units are distinctive and useful for identifying till units in west-central Wisconsin. Older, gray, calcareous till units and the overlying younger, reddish-brown, sandy pre-Late Wisconsinan till units are being analyzed. Analyses are being conducted using the < 1m clay size fraction and clay treatments/mounting methods described by Moore and Reynolds (1997). Twenty-four clay samples have been separated, vacuum-mounted on filter paper, and scanned using CuKa radiation and a 1¡ divergence slit. Qualitative clay mineral determinations have been made using glycolation, K-saturation, acid treatments, and heat treatments. Quick scans from 2-50¡2q have provided generalized diffraction patterns, and slow scans between 14-20¡ and 23-30¡2q have produced detailed peaks for quantitative analysis. Peak areas have been deconvoluted using JADE (v. 3.1). Clay mineral MIFs have been calculated using NEWMOD (v. 2.02). Peak areas and MIFs have been used to calculate clay mineral percentages, which then have been normalized to 100%. Initial mean clay mineral percentages have been calculated for three reddish-brown till units:
Merrill Mbr. of the Lincoln Fm.: I=42%, S=35%, K+V=12%, C=11% (n=7)
Bakerville Mbr. of the Lincoln Fm.: I=41% , S=42%, K+V=5%, C=12% (n=2)
River Falls Fm.: I=41%, S=36%, K+V=18%, C=5% (n=5)
(where I=illite, S=smectite, K=kaolinite, V=vermiculite, C=chlorite, and n=number of samples).
We thank the Wisconsin Geological and Natural History Survey, the Chippewa County Land Conservation Department, and the UW-Eau Claire Summer Research Experiences for Undergraduates program for funding this continuing research project.
Sarah Tietz and Lauren Buchholz
Faculty Advisers/Collaborators: Bradford R. Burton and J. Brian Mahoney
Geochemical Characterization and Uplift History of the Okanogan Range Batholith, Washington
The Okanogan Range Batholith (ORB) is located in north-central Washington along the western edge of the Intermontane Belt. It is an elongate north-northwest trending plutonic complex that is separated by the Pasayten Fault (PF) from rocks of the Coast Belt farther west. The tectonic interpretation of this relationship is controversial, but key to our understanding of the tectonic history of the region. Paleomagnetic data suggest that Coast Belt rocks formed more than 1000 km south of their current location, and have been translated northward by large-magnitude slip along the PF. Alternately, geologic data show that sedimentary rocks to the west of the Pasayten Fault received much of their sediment load from erosion of the ORB. These data argue against large-magnitude translation on the fault system. To help resolve this paradox, our study focused on the chemical and petrologic evolution of the ORB, to help characterize the geochemistry and mineralogy of the suspected sediment source terrane, for comparison with Coast Belt sedimentary basins. We are also processing 12 samples for thermochronologic analysis using apatite fission track dating. These data will constrain the thermal history of rocks on both sides of the Pasayten Fault, thus providing an additional test of the large-magnitude translation hypotheses.
History of Active Back-Barrier Coastal Dunes, Northeastern North Carolina and Southeastern Virginia: A Progress Report
Coastal barrier features in North Carolina and Virginia host a number of active and stable eolian back-barrier dunes. Effective management of active dunes and preservation of the unique ecosystems of stabilized dune fields in the face of rapid economic development requires knowledge of geomorphic systems. A first step towards understanding coastal back-barrier dunes is to determine their history and identify whether local or regional factors have influenced dune formation, migration and stabilization. In four representative active crescentic dunes distributed over 100 km of the North Carolina-Virginia coast, ground-penetrating radar (GPR) delineated subsurface sedimentary structures and paleosols. Interpretations were confirmed with trenches and auger-holes. Packages of foreset beds dominate the interior of all dunes studied. The two smaller (10-15 m high) northern dunes have no buried paleosols; paleosols are preserved within the larger (20-25 m high) dunes to the south. Rooted stumps and wood fragments from soil horizons give two radiometric ages; the younger date for soils on both southern dunes is 1650 cal AD or later, indicating that the most recent phases of dune activity occurred since European settlement. Jockeys Ridge has an older soil dated at 1260-1410 cal AD, indicating two phases of dune activity prior to the current phase. Dune depositional dates will be further constrained by Optically Stimulated Luminescence dating. Each dune studied lies south of a closed tidal inlet; the larger, more complex southern dunes are also adjacent to the Albemarle River paleochannel. These features likely provided the sand supply needed to overwhelm vegetation and form dunes in this humid environment.
Faculty Advisers/Collaborators: Karen Havholm and Harry Jol
Ground Penetrating Radar Study of Dunes and Beach Ridges at Cape Henry, Virginia
The coastal strand plain at Cape Henry, Virginia exhibits beach ridges and eolian dunes that have evolved in the late Holocene (< 4000 years) in response to minor climate and associated sea-level fluctuations. Understanding the geomorphic response to such fluctuations is key to predicting coastal response to expected global warming. The purpose of this project is to perform a reconnaissance study to see if Ground Penetrating Radar (GPR) will adequately reveal internal structures within the geomorphic features at Cape Henry to reveal the complex sequence of events that shaped this region. For this project, we developed a GPR sampling strategy to collect data on representative geomorphic features throughout Cape Henry. At each locality this involved calibrating the GPR and performing topographic surveys. The data were processed to incorporate topographic features on the originally flat GPR profiles and processing parameters were varied to produce optimal data quality. Geological analysis indicates that dunes are not composed of simple foreset strata. Some profiles have patterns that reveal sea-ward progradation of beach ridge features. Where higher-resolution (200 MHz) data were taken, resolution was not optimal because transmitter voltage was too high; this indicates that a lower voltage transmitter be used in future work, which will also enhance quality of lower-resolution data in clean sandy conditions. Surveying GPR transects to actual elevation above mean sea level will also aid in data interpretation.