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SESSION NO. 23 imagination, even when abundant subsurface data are readily available. In practice, subsurface information is usually sparse, and evaluating model uncertainty constitutes a significant challenge. This study employs hybrid models incorporating stochastic variability within a deterministic hydrostratigraphic framework to model spatial variability of physical hydrogeologic properties and assess contaminant transport prediction uncertainty in a complex glacial aquifer system. The approach is illustrated with a case study in Ann Arbor, Michigan, USA, where plumes of groundwater containing 1,4-dioxane have migrated several kilometers in different directions through 80m of underlying glacial drift. The deepest known plume appears to be advancing toward the Huron River beneath a groundwater Prohibition Zone established in 2005. 1,4-Dioxane is readily soluble in water but resistant to microbial degradation and adsorption to soil particles. Thus, it provides a tracer-like record of solute transport. More than 130 monitoring wells and 20 extraction wells have been drilled to detect, trace, and remediate 1,4-dioxane in the area. These wells form the basis of an allostratigraphic interpretation of the three-dimensional distribution of aquifer and aquitard units, constrained by available hydraulic head and contaminant concentration data, that is described in this presentation. Stochastic modeling of aquifer and aquitard properties within that deterministic hydrogeologic framework is described in a companion presentation. 23-5 9:35 AM Pappas, Lena K. [218547] ADDING THE SPOTS: STOCHASTIC MODELING WITHIN A DETERMINISTIC HYDROSTRATIGRAPHIC FRAMEWORK TO ACCOUNT FOR SMALL-SCALE VARIABILITY AND UNCERTAINTY IN A COMPLEX GLACIAL AQUIFER SYSTEM PAPPAS, Lena K., Dept. of Geology, Wayne State University, 0224 Old Main, 4841 Cass, Detroit, MI 48202, lkpappas@wayne.edu and LEMKE, Lawrence D., Department of Geology, Wayne State University, 0224 Old Main, 4841 Cass, Detroit, MI 48202 Glacial sediments contain variable and complex textures and sedimentary structures that can impede attempts to predict field scale subsurface groundwater flow or contaminant transport behavior. Refinement of deterministic hydrostratigraphic models to account for small-scale variability using stochastic modeling provides a means to assess flow and transport uncertainty. This study illustrates the application of a hybrid modeling approach integrating deterministic and stochastic components to assess uncertainty in selected contaminant transport metrics. The site is located in central Washtenaw County, Michigan, USA, where monitoring wells have been installed in more than 130 locations as part of an ongoing remediation effort. Natural gamma radiation counts were recorded in monitoring well logs located throughout the site. Measurement intervals in each well were classified as aquifer or aquitard based on their position within a deterministic allohydrostratographic interpretation. Sequential Gaussian simulation was used to create an ensemble of realizations of gamma values conditioned to gamma well log measurements within a 14km2 area of a regional groundwater model. Aquifer and aquitard simulations were generated separately and merged into a single 3D model honoring the original allohydrostratographic interpretation. Hydraulic conductivity was then assigned in each 30x30x3m MODFLOW model cell based on an experimentally determined exponential relationship between hydraulic conductivity and gamma count values. 100 stochastic realizations were ranked a priori using harmonic mean K values for flow paths along the primary migration direction between the source area and the Huron River, a potential groundwater discharge location at the site. Relevant transport metrics (e.g., first arrivals and breakthrough times at the river calculated using MODPATH and MT3D) were compared among realizations to evaluate the degree to which stochastic variability influences transport and whether a priori rankings can be used to identify realizations representing the range of transport behavior uncertainty predicted using the full ensemble. 23-6 10:25 AM Keefer, Donald A. [218826] SEDIMENTOLOGIC MODELING AND TRANSMISSIVITY MAPPING TO SUPPORT GROUNDWATER FLOW AND CONTAMINANT TRANSPORT MODELING IN GLACIAL SEDIMENTS KEEFER, Donald A., THOMASON, Jason F., and BROWN, Steven E., Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, 615 E. Peabody Dr, Champaign, IL 61820, dkeefer@illinois.edu Over the past decade, geologists and hydrogeologists at the Illinois State Geological Survey (ISGS) have been trying to provide users with maps and accompanying information that better support decisions about groundwater quantity and quality problems. Recent advances within the ISGS into new methods in 3-D geologic and hydrogeologic mapping have provided opportunities to push out new map products that further benefit hydrogeologic problem solving. A strategy is evolving at the ISGS where sedimentologic models of varying complexity are used with 3-D maps of sand/gravel aquifer distribution and thickness to produce sets of transmissivity maps that provide insight on the predicted ranges and distributions of hydraulic conductivity. The complexity of the sedimentologic models are based on the quantity and quality of available data, confidence in the conceptual models governing the overall glacial framework, and the objectives being addressed by the mapping efforts. On one end, transmissivity maps reflect general sedimentologic shifts, such as proximal to distal relationships based on distance from ice margins, together with broad ranges in hydraulic conductivity from published table-based sources. This approach results in generalized maps reflecting broad zonation of estimated maximum and minimum transmissivity values. At the other end of the complexity spectrum, geostatistical methods are used with the traditionally-developed 3-D maps to simulate a number of possible distributions of sediment lithotypes or facies within aquifers. Then these lithotype distributions are populated with geostatistically-simulated values of porosity and permeability to create a range of possible 3-D models of the aquifer hydraulic properties. These can be ranked and upscaled as appropriate for the groundwater problem at hand. 23-7 10:50 AM Mulligan, Riley P.M. [218370] DETERMINING THE 3-D GLACIAL SEDIMENTOLOGY AND HYDROSTRATIGRAPHY OF THE SOUTHERN PART OF THE COUNTY OF SIMCOE, SOUTHERN ONTARIO MULLIGAN, Riley P.M., School of Geography and Earth Science, McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1, Canada, mulligrp@mcmaster.ca, EYLES, Carolyn H., School of Geography and Earth Sciences, McMaster University, Hamilton, ON L8S 4K1, and BAJC, Andy F., Ontario Geological Survey, 933 Ramsey Lake Road, Sudbury, ON P3E 6B5, Canada Increasing urban expansion and agricultural growth are placing growing stresses on existing groundwater reserves hosted within Quaternary sediments in southern Ontario. Preserving the quality of groundwater resources requires a detailed knowledge of the three-dimensional distribution of subsurface geologic units. In the South Simcoe region of Ontario this is made possible through integration of data from fully-cored boreholes and sediment outcrops. 54 2013 GSA Abstracts with Programs Analysis of 56 outcrop exposures in cutbanks along the Nottawasaga River and 6 fully-cored boreholes within the former Lake Algonquin plain have led to the identification of six lithofacies associations (FA1–6). The stratigraphy is floored by the late Wisconsin Newmarket Till (FA1) which is locally overlain by ice-proximal debris flows (FA2). These glacial sediments are overlain by glaciolacustrine silt rhythmites (FA3) that pass upwards into deltaic sand (FA4) and channelized fluviodeltaic sand and gravel (FA5). Lying above the fluvial deposits are widespread sand and silt rhythmites (FA6), which coarsen up-section toward the ground surface. Qualitative observations of groundwater discharge through these FAs at outcrop faces has yielded important data on the internal heterogeneity of subsurface units, as well as possible preferential groundwater flow pathways through both aquifer and aquitard units within the region. The sand-rich surficial layers (FAs 4-6) within the Lake Algonquin plain form an unconfined aquifer system that permits extensive infiltration of surface water. The lower aquitard units (FAs 1 and 3) form a regionally significant hydraulic barrier for surficial water sources, directing shallow groundwater laterally into the Nottawasaga River. Coarse-grained interbeds are observed within the lower aquitard units and create layers or conduits of high hydraulic conductivity that permit transport of shallow groundwater. The potential connection of coarse-grained layers could create hydraulic windows through the aquitards, allowing surficial water sources to reach more deeply buried aquifer units. Understanding the geometry and interconnectedness of these subsurface sediments is essential for planning drinking water supply for growing urban communities in the region and for the prediction of contaminant migration pathways. 23-8 11:10 AM Weaver, Laura K. [218660] EXAMINING THE INFLUENCE OF ENHANCED HYDROGEOLOGIC KNOWLEDGE ON STRUCTURAL UNCERTAINTY IN THREE-DIMENSIONAL RECONSTRUCTIONS OF GLACIGENIC SEDIMENT WEAVER, Laura K. 1 , ARNAUD, Emmanuelle2 , ABBEY, Daron1 , SHIKAZE, Steven1 , MEYER, Jessica R. 3 , and PARKER, Beth L. 3 , (1) Matrix Solutions Inc, 31 Beacon Point Court, Breslau, ON N1B 1M0, Canada, lweaver@matrix-solutions.com, (2) G360 Centre for Applied Groundwater Research, School of Environmental Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada, (3) G360 Centre for Applied Groundwater Research, School of Engineering, University of Guelph, 50 Stone Rd E, Guelph, ON N1G 2W1, Canada Three-dimensional (3D) hydrogeologic representations of the subsurface focus on the spatial distribution and interconnectedness of hydrogeologic units inferred from lithology, primary and secondary structures, fluid chemistry, hydraulic head, and hydraulic conductivity data, in addition to other data sources. These conceptual models are guided by a hydrogeologic framework developed from depositional environment interpretations and may form the basis for numerical groundwater flow modeling. Although sophisticated 3D interpolation software and numerical efficient of modeling codes enable parameterization and simulation of complex systems, the availability and quality subsurface data limits the modeled complexity. Uncertainty in the distribution and geometries of subsurface units between field data points may be reduced through the inclusion of stratigraphic knowledge in the interpolation process. To explore the influence of enhanced (hydro)geologic understanding on framework development, three conceptual block models were constructed for glacial sediment associated with ice marginal deposition. Unit volumes were generated using: 1) associations based on sediment texture, b) an imposed conceptual framework on genetically-linked, texturally similar sediment, and 3) an imposed framework on genetically-linked, texturally similar sediment with the addition of control points. Increasing amounts of “expert” knowledge is incorporated into each model, moving from a model developed solely on the available data, through the inclusion of regional stratigraphic knowledge, and furthered with additional inferences based on expected facies associations. The distribution and interconnectedness of sediment were interpolated across the study area using interpolation algorithms in a 3D software environment. The resulting hydrogeologic unit geometries were evaluated for plausibility given the established glacial history of the area and error associated with the interpolation. The influence of hydrogeologic knowledge on output unit distributions and the resulting structural uncertainty was investigated by comparison of unit distributions and geometries, relative unit volumes, and fit of the top of unit elevations to borehole observations across the three conceptual block models. 23-9 11:30 AM Dogan, Mine [218733] INTEGRATING 3D GPR FACIES ANALYSIS AND HIGH RESOLUTION HYDRAULIC CONDUCTIVITY DATA: IMPLICATIONS FOR TRANSPORT MODELING IN HETEROGENEOUS MEDIA DOGAN, Mine1 , VAN DAM, Remke L. 1 , HYNDMAN, David W. 1 , and BUTLER, James J. Jr2 , (1) Department of Geological Sciences, Michigan State University, 206 Natural Science Building, East Lansing, MI 48824, minedoga@msu.edu, (2) Kansas Geological Survey, University of Kansas, 1930 Constant Ave, Lawrence, KS 66047 The transport of solutes through aquifers is primarily controlled by the spatial distribution of hydraulic conductivity (K). With limited availability of K data, as is common in many field studies, it is not possible to accurately simulate transport using the classical advection-dispersion equation, particularly in heterogeneous deposits. Although alternative approaches for simulating transport through such deposits may provide reasonable representations of average plume behavior, they do not replicate observed concentration histories at observation wells. We postulate that a suite of novel high-resolution characterization methods may provide the necessary subsurface data to significantly improve flow and transport simulations through heterogeneous porous media. To this end, we combined 3D ground-penetrating radar (GPR) data with high-resolution K (HRK) and electrical conductivity (EC) data from direct-push profiles, at a heterogeneous fluvial deposit in northeastern Mississippi. The full-resolution GPR data cubes, collected using standard field equipment, were used to generate 3D facies models, which include information on major bounding surfaces, dip angles and directions, and connectivity. The HRK and EC profiles, collected using equipment mounted on Geoprobe drilling rigs, provided information on vertical distribution of hydraulic and electric properties at intervals of a few centimeters. Comparative analysis of the geophysical and drilling data reveals a good correlation at the major facies boundaries. Data integration has enabled construction of hydrostratigraphic models of these heterogeneous deposits and realistic modeling of flow and transport.
SESSION NO. 24, 8:00 AM Friday, 3 May 2013 T5. Quaternary Research in the Great Lakes Region II: The Holocene, Part I Fetzer Center, Putney Auditorium 24-1 8:00 AM Hladyniuk, Ryan [218332] THE N-ALKANE AND CARBON-ISOTOPE SIGNATURES OF ORGANIC CARBON IN LAKE ONTARIO SINCE 14,000 CAL YR BP HLADYNIUK, Ryan, DILDAR, Nadia, and LONGSTAFFE, Fred J., Department of Earth Sciences, The University of Western Ontario, 1151 Richmond Street, Biological and Geological Sciences Building, London, ON N6A5B7, Canada, rhladyni@uwo.ca The n-alkane abundances and carbon-isotope compositions of organic matter (OM) from Lake Ontario sediments reveal a complex history of variation in both source and lacustrine productivity over the last 14,000 cal yr BP. Glacial sediments containing ~0.2-0.3 % organic carbon (OC) are dominated by C23 through C29 n-alkanes. These compositions most likely represent allochtonous contributions of peat, higher terrestrial plant matter and clay-associated OM delivered by glacial meltwaters from the periglacial environment. Subordinate amounts of C17-C19 n-alkanes may indicate limited primary lacustrine productivity at this time. Transition from glacial to postglacial conditions in the Lake Ontario basin was marked by a lowering of water levels, rising OC contents, and increased abundances of C17-19 n-alkanes. Little systematic carbon isotopic variation was found for individual n-alkanes in the glacial and transitional sediments: C17-C19, –30 per mil; C21, –33 to –30 per mil; and C23+, –33 to –32 per mil, which likely reflects wellmixed, multiple OM sources. Hydraulic closure of Lake Ontario beginning at about 12,300 cal yr BP produced its lowest recorded levels. Approximately equal abundances of C17-C19, C23-C25, and C27+ n-alkanes at this time are tentatively interpreted to indicate lacustrine, (submergent) macrophyte and terrestrial OM contributions. C17-C19 n-alkanes showed little carbon isotopic variation from the older sediments. However, a 2 per mil decrease in carbon-13 for C23 and enrichments of ≤8 per mil for C25+ n-alkanes (C25> C27> C29) occurred by the end of hydraulic closure. Increased littoral zone productivity may have been favoured by low lake levels. Warming beginning at 8,300 cal yr BP triggered a transition from cold/dry to warm/wet conditions, during which water levels gradually rose. OC in associated lake sediments reaches 2 % and contains the highest fraction of C27+ n-alkanes, which have carbon isotopic compositions of –33 to –30 per mil. These data suggest that Lake Ontario received significant terrestrial OM from its catchment at this time. The progressive 5 per mil depletion of carbon-13 in C17 and C25 n-alkanes upwards through this interval remains to be explained. 24-2 8:20 AM Loope, Walter L. [218627] CAN PALEOECOLOGICAL PROXIES ADEQUATELY FORECAST SURFACE COVER ACROSS NORTH CENTRAL NORTH AMERICA? (A CAUTIONARY TALE) LOOPE, Walter L., United States Geological Survey, N8391 Sand Point Road, P.O. Box 40, Munising, MI 49862, wloope@usgs.gov Pollen stratigraphy provides the core body of paleoecological perspective across north central North America. Pollen based methodologies have matured over nearly a century and are now joined by a vast and vetted literature focused on paleolimnology, wetland dynamics, soil stratigraphy and landscape ecology. The COHMAP project of the 1970s and 80s placed these data sets in spatial context across the continent and more recent updates and refinements of these maps have been developed. The utility and importance of paleoecological models are more apparent given recognition of anthropogenic climate forcing. Concurrent with their adoption and broad use in discussions of such forcing, however, caveats and limitations of paleoecological data, prominently voiced by their authors, must be honored. Linda Brubaker, a pioneer in the application of pollen stratigraphy to Upper Michigan, recognized in 1975 that patchy habitats often impose permanent control on vegetation pattern on varying spatial scales. The scale of patchiness varies across landscapes and greatly complicates their classification as well as any assessment of their projected behavior. In broad and roughly uniform landscapes these complications may be minimal; in patchy landscapes, they may defy intuition and interpretation. As Brubaker pointed out, some of the more obvious drivers of patchiness in the upper Midwest are differences in soil texture and development and in the nature of regolith. These differences are invisible in broad pattern but detectable on a local level. Pollen-based maps of surface cover in eastern Upper Michigan prove inadequate in detecting the major climatic anomaly that drove hydrologic closure of the Upper Great Lakes ~10-8 ka. In contrast, an intensive study of 2 ponds within a small sandy tract in Alger County clearly identifies this and other major droughts at that time, albeit on different scales. Maps of Quaternary vegetation at sub-continental scales are useful across uniform environments but may fail to portray important local and even regional differences. This has long been recognized and expressed by pollen practitioners but may be glossed over by modelers who need to summarize projected change across the continent. 24-3 8:40 AM Yansa, Catherine H. [218716] A 8500-YEAR RECORD OF LAKE-EFFECT CLIMATE FROM MINER LAKE, SOUTHWESTERN LOWER MICHIGAN YANSA, Catherine H., Department of Geography, Michigan State University, 227 Geography Building, East Lansing, MI 48824-1117, yansa@msu.edu and RAWLING, J. Elmo III, Geography/Geology, University of Wisconsin Platteville, 1 University Plaza, Platteville, WI 53818 Miner Lake (42.7°N, 85.8°W) in Allegan County, southwestern Lower Michigan, is located 30 km east of Lake Michigan. Today, the local vegetation is comprised of primarily beech-maple forest and has a lake-mediated climate characterized by higher snowfall and warmer winter temperatures than inland locations. The objective of our research was to test whether the lakeeffect climate in the past was a more dominant influence on the local climate of the Miner Lake area than regional paleoclimate patterns. We did this by analyzing sediment cores from Miner Lake for pollen, plant macrofossils and sedimentology (particle size, % organic matter (OM), and % calcium carbonate (CaCO )), and compared these data to paleoclimate data from two lakes 3 from inland locations with similar latitudes. Over the past 8500 cal yr BP, the sedimentology and paleobotany of Miner Lake indicate that there has been little environmental change in the area. In general, the %OM increases from ~25 to 40%, %CaCO decreases from ~20 to 10% and the median grain size ranges from ~10 to 25 3 microns. The high %OM and CaCO , and fine median grain size in the sediments of Miner Lake 3 SESSION NO. 24 suggest that this lake received little influx of clastic material. The pollen and plant macrofossil records indicate four intervals of vegetation change. A pine-oak forest characterizes Zone I (~8500 to 7000 cal yr BP), prior to the arrival of beech in the region. Zone II (~7000-3200 cal yr BP) is that of a beech-maple forest with oak patches. Percentages of beech and maple are higher than in the two comparative pollen records, indicating that moisture provided by the lake-effect climate prevailed in the Miner Lake area during the peak Holocene warmth. Zone III (~3200-200 cal yr BP) is characterized by cooler and moister conditions, as suggested by expansion of the beech-maple forest. Median grain size is most variable in Zone III. Zone IV (last 200 years) is distinguished by a spike in disturbance weeds, a sharp decrease in %OM, a dramatic increase in %CaCO 3 , and a sharp decrease in median grain size, likely resulting from agriculture. In summary, the paleoclimate record of Miner Lake was, for the most part, invariant during the past several millennia, which suggests that a “lake effect” climate induced by nearby Lake Michigan was a more dominant control than the regional climate for this site. 24-4 9:00 AM Sonnenburg, Elizabeth [218504] PALEOENVIRONMENTAL RECONSTRUCTION OF THE ALPENA-AMBERLEY RIDGE SUBMERGED LANDSCAPE DURING THE LAKE STANLEY LOWSTAND (CA. 8.4-9 KA CAL BP), LAKE HURON SONNENBURG, Elizabeth, Museum of Anthropology, University of Michigan, Ruthven Museums Building 4016, 1109 Geddes Avenue, Ann Arbor, MI 48109, esonnenb@umich.edu The Great Lakes basin has high potential for submerged archaeological sites due to considerable water level changes during deglaciation and as a result of Holocene climate change. The Holocene period in the Great Lakes basin (ca. last 12,000 years) was marked by several phases of drier climate and low lake levels (lowstands) including major events between ca. 11,300-8,400 cal BP recorded in sediments in Lake Huron and Georgian Bay (Lake Hough and Lake Stanley lowstands). During the Lake Stanley phase water levels in the Lake Huron basin were up to 70-100 m below present and large areas of the lake bed were exposed terrestrial landscapes. In 2007 and 2008, a 300 meter-long series of boulders was discovered on the Alpena-Amberley Ridge in 30 m of water in Lake Huron during a side-scan sonar survey. The boulders, when mapped, resembled caribou drive lanes which are well-documented in the Arctic. During the Lake Stanley lowstand phase, the Ridge was a sub-aerially exposed causeway separating the lake into two basins, and the discovery of the potential drive lanes provides compelling albeit circumstantial evidence that the Ridge supported human habitation during the early Holocene. Little is known about the paleogeography and environment of the Ridge since there is limited sedimentation, and most lake-level and paleoenvironmental research in Lake Huron has focused on the more sediment loaded basins of the Georgian and Saginaw Bays. In 2011 and 2012, a total of sixtyseven core, sediment and rock samples were collected by divers and ponar sampler on an ROV. Thirty-six surface sediment grab samples and six short (10-25 cm) cores were obtained for analysis of microdebitage, microfossils, grain size, and organic content. Cores were subsampled at 2 cm intervals for analysis, lithofacies logged in detail and photographed. Preliminary paleoenvrionmental reconstructions based on results from these samples indicate that during the last Lake Stanley phase, the Ridge was a relatively stable landscape with sub-artic vegetation, small shallow ponds, sphagnum bogs, wetlands and rivers, and would have provided numerous potential resources for both caribou and pre-historic hunter-gathers. 24-5 9:40 AM Thompson, Todd A. [218327] THE ELEVATION OF THE PEAK NIPISSING PHASE (MID HOLOCENE) AT OUTLETS OF THE UPPER GREAT LAKES THOMPSON, Todd A., Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405-2208, tthomps@indiana.edu, JOHNSTON, John W., Department of Physical and Chemical Sciences, University of Toronto Mississauga, 3359 Mississauga Road N, Mississauga, ON L5L 1C6, Canada, and LEPPER, Kenneth, Department of Geosciences, North Dakota State University, P.O. Box 6050, Dept. #2745, Fargo, ND 58108-6050 The Nipissing phase of ancestral Lakes Michigan, Huron, and Superior was the last pre-modern highstand of the upper Great Lakes. Reconstructions of past lake-level change and glacial isostatic adjustment (GIA), as well as activation and abandonment of outlets is dependent on an understanding of the elevation of the lake at each outlet. More than one hundred years of study has established the gross elevation of the Nipissing phase at each outlet, but the mixing of geomorphic and sedimentologic data has produced interpreted outlet elevations varying by least several meters. Vibracore facies, optically stimulated luminescence and radiocarbon age control, and ground-penetrating radar transects from new and published studies were collected to determine peak Nipissing water-level elevations for the Port Huron (Lake Huron), Chicago (Lake Michigan), and Sault (Lake Superior) outlets. These data and published relative hydrographs were combined to produce one residual hydrograph for the Port Huron outlet from 6,000 to 3,500 calendar years ago that best defines the rise, peak, and rapid fall of the Nipissing phase. Establishing accurate elevations at the only present-day unregulated outlet of the Great Lakes and the only ancient outlet that has played a critical role in draining the upper Great Lakes since the middle Holocene is a critical step to better understand GIA and water-level change geologically and historically. The geologic context may provide the insight required for water managers to make informed decisions to best manage the largest freshwater system in the world. 24-6 10:00 AM Hanson, Paul R. [218692] IMPACT OF THE NIPISSING AND ALGOMA HIGH LAKE PHASES FROM OSL DATING OF BAYMOUTH BARRIER SYSTEMS IN THE DOOR PENINSULA, WISCONSIN HANSON, Paul R., School of Natural Resources, University of Nebraska-Lincoln, 3310 Holdrege Street, Lincoln, NE 68583, phanson2@unl.edu and RAWLING, J.E. III, Geography and Geology Program, University of Wisconsin-Platteville, Platteville, WI 53818 This study focuses on the geomorphology and geochronology of three baymouth barrier systems at Clark, Europe and Kangaroo Lakes in the Door Peninsula of Wisconsin. The Lake Michigan shoreline in the peninsula contains abundant evidence for fluctuations in lake level as evidenced by strandplains and beach ridges that lie up to ~ 7 m above the present shoreline. Our study was conducted on three baymouth barriers that contain beach ridges that were buried by varying depths of eolian sand in the form of sandsheets, as well as parabolic and transverse dunes with relief of up to 21 m. The purpose of this study was to document when the barriers were deposited and when the subsequent eolian activity occurred. Our chronology for barrier emplacement and dune development is based on 65 OSL samples which were collected from lacustrine sediment within the barrier fills (n = 17) and the overlying eolian sand (n = 48). Sediment samples were collected using bucket augers or a vibracoring device at depths ranging from 0.5 to 4.1 m below the ground surface. Our OSL ages show that baymouth barriers in each of our study sites were constructed between ~ 5.9 to 3.9 ka, and most of our ages correspond closely to the Nipissing high lake level phase. Both geomorphic and geochronological evidence from the Kangaroo Lake site shows portions of this barrier were re-occupied after the Nipissing phase. Our OSL ages from lacustrine sediment taken from within the barrier suggest this occurred at 3.3 to 2.5 ka, 2013 GSA North-Central Section Meeting 55
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