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SESSION NO. 12 12-7 3:50 PM Santistevan, Fred [218540] THE ROLE OF THE SIBERIAN TRAPS IN THE PERMIAN-TRIASSIC MASS EXTINCTION: ANALYSIS THROUGH CHEMICAL FINGERPRINTING OF MARINE SEDIMENTS USING RARE EARTH ELEMENTS (REES) SANTISTEVAN, Fred, Geology, University of Cincinnati, 500 Geology/Physics Bldg, Cincinnati, OH 45221, santisfa@mail.uc.edu, ALGEO, Thomas J., Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, HANNIGAN, Robyn, Environmental, Earth, and Ocean Sciences, University of Massachusetts - Boston, 100 Morrissey Boulevard, Boston, MA 02125, and WILLIAMS, Jeremy C., Environmental Earth and Ocean Sciences, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125 The Permian-Triassic boundary (PTB) mass extinction at ~252 Ma was the largest biotic catastrophe in Earth history, resulting in the disappearance of ~90% of marine invertebrate species. Recent work has shown that the most likely trigger for this event was eruption of the Siberian Traps, the largest sub-aerial flood basalt province of the last 500 million years. However, direct evidence linking the Siberian Traps to the marine mass extinction has been lacking. Volcanic units are commonly characterized by unique rare earth element (REE) signatures, and published studies show that the Siberian Traps had an unusual REE chemistry (Lightfoot et al., 1990, 1993; Arndt et al., 1993, 1995, 1998; Federenko et al., 1997, 2000). In this study, we are examining the REE chemistry of eight marine PTB sections having a wide global distribution with the goal of determining whether the characteristic REE signature of the Siberian Traps can be recognized in ash beds or in background sediments of these successions. If recognized, this signature could provide information regarding the geographic dispersal of volcanic ash, its relationship to regional environmental changes, and its effects on marine and terrestrial ecosystems. Our work is currently in progress, but preliminary results suggest that REE signatures potentially characteristic of Siberian Traps source material are present in some, but not all, marine PTB sections. 12-8 4:10 PM Voice, Peter J. [218491] THE GLOBAL DETRITAL ZIRCON DATABASE: AN UPDATE VOICE, Peter J., Department of Geosciences, Western Michigan University, 1903 W. Michigan Ave, MS 5241, Kalamazoo, MI 49008, peter.voice@wmich.edu, KOWALEWSKI, Michal, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, and ERIKSSON, Kenneth A., Department of Geosciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061 A flood of new detrital zircon U-Pb age data has allowed for a rapid growth of the Global Detrital Zircon Database (GDZD). The latest version of the database includes over 284,000 single age determinations from U-Pb dating of detrital zircons. These zircons represent ~5,600 detrital zircon age frequency distributions that come from all continents and range in age from modern sediment samples to Archean metasedimentary rocks. Host rock compositions are dominated by siliciclastics, though a small fraction of the samples are derived from carbonates and other chemical/biochemical sedimentary units. For all age frequency distributions, the GDZD also records a best estimate of the host sediment maximum and minimum age independent of the detrital zircon U-Pb ages. The large amount of data has allowed us to empirically derive relationships between host sediment age and sample size of analyzed zircons. Detrital zircons are an excellent example of the principle of inclusions; they are always as old as, or older than, the host sediment. A simple quantitative metric can be used to measure the offset between the maximum host sediment age and the youngest detrital zircon age recorded. We have found that as a function of tectonic setting, relatively small sample sizes are required to best estimate the age of the host sediment with the smallest offset. Tectonic settings with syn-volcanism tend to require sample sizes of 40 grains or less in order to provide the best constraint on the age of the sample – a grain that is relatively contemporaneous with deposition of the unit. Passive margins and intracratonic basins tend to exhibit much greater offsets between the host sediment age and the youngest detrital zircon and require larger samples of dated zircons to find these young zircons. 12-9 4:30 PM Hayden, Travis G. [218404] ESTIMATING LAST GLACIAL MAXIMUM ICE THICKNESS USING POROSITY AND DEPTH RELATIONSHIPS: EXAMPLES FROM AND-1B, MCMURDO SOUND, ANTARCTICA HAYDEN, Travis G., Department of Geosciences, Western Michigan University, 1187 Rood Hall, 1903 W. Michigan Ave, Kalamazoo, MI 49008, t4hayden@wmich.edu, KOMINZ, Michelle A., Department of Geosciences, Western Michigan University, 1903 W. Michigan Ave, Kalamazoo, MI 49008, and NIESSEN, Frank, Geosciences, Alfred Wegener Institute, Columbusstrasse, Building D-1170, Bremerhaven, D-27568, Germany We have estimated ice thicknesses at the AND-1B drillsite during the Last Glacial Maximum by adapting an existing technique used to calculate eroded overburden. We analyze the porosity as a function of depth and lithology from measurements taken on the AND-1B core, and compare these results to reference data obtained on Ocean Drilling Program Legs 178, Leg 188, and Integrated Ocean Drilling Project Leg 318. These reference datasets are deep marine sediments of similar lithology and have not been overcompacted by overriding ice sheets. Using these reference datasets we estimate the amount of overburden required to compact the sediments to the porosity observed in AND-1B. This analysis is a function of lithology, depth and porosity, and generates sediment-equivalent overburden estimates between 500 and 900 meters. These are translated into ice thickness estimates by accounting for differences in sediment and ice densities. The lithologies analyzed are most likely to compact consistently and predictably, and result in a range of ice thickness between 1,059 – 1,984 meters, with a best-fit estimate of 1,630 meters of ice at Last Glacial Maximum. These values compare well with mass-balance corrected, independently calculated, ice-thicknesses estimates of 1,730 meters based on exposures of Last Glacial Maximum till deposits. While this analysis can only specifically estimate ice thicknesses during Last Glacial Maximum, due to the overprinting effect of Last Glacial Maximum ice on previous ice advances, it also has implications for previous maximum ice thickness during earlier Pleistocene glacial maximums. Lastly, as ice thickness at Last Glacial Maximum is unknown in existing ice sheet reconstructions, this analysis provides constraint on model predictions. 12-10 4:50 PM Cupples, William B. [218372] UPLAND GRAVELS OF THE MISSISSIPPI RIVER VALLEY AND THEIR INSIGHTS TO PREGLACIAL DRAINAGE IN CENTRAL NORTH AMERICA CUPPLES, William B., Department of Earth Sciences, University of Memphis, 1 Johnson Hall, Memphis, TN 38152, wcupples@memphis.edu and VAN ARSDALE, Roy B., Earth Sciences, Univ. of Memphis, 1 Johnson Hall, Memphis, TN 38152 The upland Tertiary gravels of the Mississippi River Valley have puzzled geologists for many decades. These gravels are generally interpreted to be terrace deposits of the pre-glacial Mississippi and Ohio rivers. The gravels are called the Citronelle Formation in Louisiana, Preloess gravels in Mississippi, Upland Complex in Tennessee and Arkansas, and the Mounds and 16 2013 GSA Abstracts with Programs Grover in Illinois and possibly the Windrow in Wisconsin, Iowa, and Minnesota. The base of these predominantly chert gravels are approximately 75 m above the base of the Mississippi River Quaternary alluvium. Previous investigators have identified large wavelength paleo-meanders in the upland gravels of northwestern Mississippi that indicate a discharge as much as 5 to 10 times greater than the modern Mississippi River. This larger river suggests that the drainage basin of the pre-glacial Mississippi River may have been much larger than today and perhaps extended north into Canada. This current study explores that possibility by mapping bedrock surface elevation and gravel data from 99 wells in Illinois and bedrock elevations from 980 wells in Minnesota that we have interpreted to mark the base of the pre-glacial Mississippi River. The distribution of these upland gravels in conjunction with previous studies allows a partial reconstruction of the course of the pre-glacial Mississippi River system and its elevation from central Minnesota to Memphis, Tennessee. The elevation of this pre-glacial Mississippi River profile allows us to test the hypothesis that the ancestral (Pliocene) Mississippi River flowed south from Canada. SESSION NO. 13, 1:30 PM Thursday, 2 May 2013 T6. Quaternary Time Machine: Methods and Analyses of Soils and Sediments to Reveal Secrets of Past Environments Fetzer Center, Room 1040/1050 13-1 1:35 PM Sipola, Maija E. [218640] MINERALOGICAL CHARACTERIZATION OF SOLO RIVER TERRACE DEPOSITS AT NGANDONG, CENTRAL JAVA, INDONESIA SIPOLA, Maija E., Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, maija-sipola@uiowa.edu The Ngandong Homo erectus site in Central Java, Indonesia is of great interest to paleoanthropologists and geoarchaeologists. The morphology of the H. erectus crania first discovered there in the 1930’s suggests those fossils may be of the most recently-living Homo erectus known in the world, yet numerous studies have been unable to confidently date the age of the fossils or the timing of site formation. In addition, thousands of fossils of non-hominin macrofauna have been collected during early excavations of the Ngandong site without a comprehensive geoarchaeological assessment of their relationship to the terrace stratigraphy, preventing an understanding of the depositional processes responsible for site formation. Recently, a thorough excavation of the site was undertaken by a team of Indonesian and American scientists with special focus on documenting and analyzing the site stratigraphy. In this study I summarize the results of a mineralogical analysis of the stratigraphic layers present at the site in an effort to delineate possible depositional facies boundaries based on different sediment sources. I combine these mineralogical data with results of grain-size and grain-shape analyses to characterize the sediment source(s) and depositional conditions that produced the fossil-bearing terrace deposits present at Ngandong. This information improves our understanding of the Solo River fluvial dynamics at the time of site formation and may potentially inform as to the location and condition of other fossil-bearing deposits in the region. 13-2 1:55 PM Miao, Xiaodong [218408] USING OSL AND RADIOCARBON DATING TO CONSTRAIN THE TIME OF SOIL DEVELOPMENT MIAO, Xiaodong1 , WANG, Hong1 , HANSON, Paul R. 2 , MASON, Joseph A. 3 , and LIU, Xiaodong4 , (1) Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, 615 E. Peabody Dr, Champaign, IL 61820, miao@ illinois.edu, (2) School of Natural Resources, University of Nebraska-Lincoln, Lincoln, 68588, (3) Department of Geography, University of Wisconsin-Madison, 550 N. Park St, 160 Science Hall, Madison, WI 53706, (4) SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, 710075 Time, one of the five factors in soil development along with climate, parent material, organisms, and topography, is theoretically defined as the time elapsed since the parent materials were deposited and subaerially exposed, according to Jenny’s model. Soil time was estimated previously based on the degree of soil development, but in many environments the soil ages have not been practically calculated. We propose that the best method for estimating the time of soil development is subtraction of the Pyrolysis-Volatile (Py-V) 14C dates of soil’s uppermost A horizon from OSL dates of C horizon of parent material. The Py-V 14C dates represent most mobile soil organic carbon that is least resistant to biodegradation in soil environment, therefore yielding youngest ages potentially, while OSL dating on the C horizon estimates the depositional time of the parent material. We tested this new approach in four scenarios: 1. Modern soil developed downward in loess; 2. Cumulative Soil formed upward in loess; 3. Soil formed in dune sand; 4. A counterexample to show that simple subtraction is not always appropriate. This approach constrains soil time more reasonably than using either OSL or radiocarbon dates alone. If no old carbon contamination is assumed, the difference between the Py-V ages at the uppermost and lowermost sola of a soil almost certainly underestimates the time of soil development, and the difference between OSL ages taken from above and below a soil most likely overestimates it. Combination of OSL and radiocarbon can best constrain soil development time. 13-3 2:15 PM Reinhardt, Jason [218513] INVESTIGATING THE INFLUENCE OF LAND USE HISTORY ON SAVANNA SOILS IN LOWER MICHIGAN: IMPLICATIONS FOR MANAGEMENT, RESTORATION, AND CONSERVATION REINHARDT, Jason1 , HOBBS, Trevor2 , and NAGEL, Linda M. 1 , (1) School of Forest Resources and Environmental Science, Michigan Technological University, 1400 Townsend Dr, Houghton, MI 49931, jrreinha@mtu.edu, (2) Huron-Manistee National Forest, GeoCorps Participant, 1755 S. Mitchell St, Cadillac, MI 49601 Prior to European settlement, mixed oak savanna was a naturally occurring ecosystem in Michigan’s Lower Peninsula. Maintained by wildfire, these savanna openings likely migrated over space and time on excessively-drained sandy soils. Most of this plant community type has been lost due to early land management practices, especially agriculture and timber. Decades of fire suppression have led to degradation of what remains. Remnant examples are an important part of the ecological landscape and provide refuge for a multitude of early-successional species, most notably the Federally-Endangered Karner Blue Butterfly (KBB; Lycaeides melissa samuelis).
Because of this, the US Forest Service implements a variety of management techniques, such as controlled burns, bulldozing, masticating, and partial harvesting, to restore and maintain oak savanna ecosystems. However, attainment of desirable levels of plant species diversity and abundance following restoration activity has proven difficult. We hypothesized that land use history and its influence on soils play a significant role in the potential for restoration success, especially with respect to resultant floristic composition. The purpose of this research was to 1) establish site-specific historic land use and 2) determine impacts on soil morphology, soil chemistry, and current savanna communities in the southern Manistee National Forest. Preliminary results suggest that land use history helps explain variation in soil A horizon thickness, and the presence/absence of important savanna plants such as wild lupine (Lupinus perennis). Preliminary results support our hypothesis that historic land use and its influence on soil morphology significantly impact floristic diversity and abundance in savanna ecosystems. This insight has the potential to help prioritize potential management and habitat restoration sites, and can be incorporated into existing savanna ecosystem management techniques by land managers and government agencies. Soil sample processing is currently underway in the laboratory, and analysis of the effects of land use history on further soil morphological characteristics and soil chemistry will follow. 13-4 2:35 PM Rovey, Charles W. [218231] PALEOSOLS WITHIN THE PRE-ILLINOIAN TILL SEQUENCE IN NORTHERN MISSOURI RECORD CHANGES IN PLEISTOCENE CLIMATE ROVEY, Charles W. II, Geography, Geology, and Planning, Missouri State University, 901 S. National, Springfield, MO 65897, charlesrovey@missouristate.edu Exposures in northern Missouri preserve the Sangamon Geosol developed in Loveland Silt above the Yarmouth Geosol in till. Reasons for the distinctive red coloration within these two paleosols (temperature vs. time) have been debated for many years, but previous workers did not have a sequence of older paleosols for comparison. Here, four pre-Yarmouth paleosols are also preserved locally within the Pre-Illinoian till sequence, and cosmogenic isotope dates for these tills also provide the age of the soils along with the duration of soil development. Generally, the older paleosols formed over a much longer time than the younger. For example, the oldest till (Atlanta Formation) was deposited at ~2.4 Ma and was buried by the overlying Moberly Formation at ~1.3 Ma. Thus, the Atlanta paleosol developed over ~1.1 myr, compared to no more than ~0.1 myr for the Sangamon. The oldest paleosols rarely developed hues redder than 10YR, but rubification increases within the younger sola, despite shorter durations of weathering, culminating in bright red hues near 5YR within the Yarmouth and Sangamon Geosols. Thus, these paleosols record increasing interglacial temperatures, beginning in the Middle Pleistocene. Caliche is nearly always present within the older weathering profiles, but is absent within the modern and Sangamon soils in this area. Thus, the older paleosols developed under drier conditions than the more recent climates. The depth to the top of caliche also increases systematically with younger age, recording increases in mean annual precipitation during the Early and Middle Pleistocene. In summary the paleosol sequence in northern Missouri records a trend toward warmer and moister climates during the Pleistocene. 13-5 2:55 PM Kerr, Phillip J. [218759] THROUGH A WOOLY LENS: INVESTIGATIONS FROM A MAMMOTH BURIAL IN IOWA KERR, Phillip J. 1 , BETTIS, E. Arthur III1 , and BAKER, Richard G. 2 , (1) Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, phillip-kerr@ uiowa.edu, (2) Department of Geoscience, University of Iowa, Iowa City, IA 52242 Investigations sponsored by the Iowa Museum of Natural History have discovered the remains of three mammoths eroding from alluvium in a small tributary of the South Skunk River in southern Iowa. Coring, examination of excavation walls, radiocarbon dating, and macrofossil analyses are providing a preliminary picture of the paleoenvironment occupied by the mammoths and the processes responsible for formation of the fossil deposit. Excavations to date have recovered fossils from early Holocene alluvium that filled a plunge pool cut into an older terrace fill that apparently contains in-situ mammoth remains. The pristine condition of bone recovered to date and a lack of size or density sorting suggests a very short transport distance. An exposure of the older terrace fill and cores from the terrace surface adjacent to the excavation show a sequence of fine-grained late glacial alluvium separated from sand and gravel by an organic-rich zone that yielded a radiocarbon date of 13,120+50 B.P. Plant macrofossils recovered from the organic zone indicate a marshy area within a spruce forest. On-going investigations are focused on refining a sedimentary model for the site and determining the location of the in-place deposition of the mammoth remains. 13-6 3:30 PM Harrison, Jeffrey M. [218615] LINKING 2,000 YEARS OF SEDIMENTATION IN THE WESTERN ARCTIC OCEAN TO AN ATMOSPHERIC TEMPERATURE PROXY RECORD FROM A GLACIAL LAKE IN THE BROOKS RANGE, AK HARRISON, Jeffrey M. 1 , ORTIZ, Joseph D. 1 , ABBOTT, Mark B. 2 , BIRD, Broxton W. 3 , HACKER, David B. 1 , GRIFFITH, Elizabeth M. 1 , and DARBY, Dennis A. 4 , (1) Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44242, jharri72@kent.edu, (2) Department of Geology and Planetary Science, Univ of Pittsburgh, Pittsburgh, PA 15260, (3) Department of Earth Sciences, Indiana University-Purdue University, Indianapolis, IN 46202, (4) Department of Ocean, Earth, & Atmospheric Sciences, Old Dominion University, Norfolk, VA 23529 The delivery of sediment to the Alaskan continental shelf is largely associated with ice drift and wind driven Arctic Ocean circulation patterns that have varied during the Holocene. This study presents a comparison of two continuous, high-resolution proxy records from the western Arctic over the past 2,000 years. Direct correlations were made between marine grain size, related to shifts in depositional mechanisms, and terrestrial atmospheric climate in northern Alaska. To provide variations of sedimentation patterns in the Arctic Ocean (e.g., sea-ice transport, density flows, ocean currents), the grain size distributions were measured in a piston core (HLY02-04 JPC16) from the eastern Chukchi Sea at a higher resolution than previously reported. A revised JPC16 age-depth model was used in this analysis (Darby et al., 2012). The sediment core, collected on the east flank of Barrow Canyon (72.1555°N, 153.50817°W), preserves a record of local variations in sedimentation mechanisms in the Chukchi-Beaufort Seas. A Varimax-rotated Principle Component Analysis (VPCA) was conducted on JPC16. We inferred three principal components (PCs) of sediment deposition at the core site related to anchor ice, nepheloid flows, and suspension freezing based on variations in grain-size distributions. This interpretation is consistent with previous downcore analysis by Darby et al. (2009). A fourth, less significant mode, is related to resuspension and deposition connected to intermittent suspension. While all components showed increased variability since 200 yr BP, factors related to sea-ice showed the highest positive loadings between 2000-1300 cal yr BP. The high-resolution record of sediment deposition in the Arctic Ocean allowed for direct correlation SESSION NO. 13 with the atmospheric climate proxy as recorded by varve thickness in the Brooks Range (Bird et al., 2009). The time interval investigated here shows a significant relationship of marine sea-ice sedimentation with variability in atmospheric temperature (r = 0.7). Additionally, marine sedimentation appears to lag the atmospheric temperature proxy, indicating that temperature is a primary forcing mechanism in sea-ice variation. This analysis suggests that warmer intervals are likely correlated with greater sea-ice melt and favor sedimentation of entrained sediments. 13-7 3:50 PM Matzke, Jeffrey A. [218043] A NEW VIEW OF THE STONE ZONE ON THE IOWA EROSION SURFACE MATZKE, Jeffrey A. 1 , BETTIS, E. Arthur III2 , WEIRICH, Frank1 , and VOGELGESANG, Jason3 , (1) Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, jeffrey-matzke@uiowa.edu, (2) Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, (3) Iowa Geological and Water Survey, Iowa Department of Natural Resources, 109 Trowbridge Hall, Iowa City, IA 52242 The processes that generated the distinctive landscape of the Iowa Erosion Surface (IES) of northeastern Iowa have been debated for over a century. A number of researchers have concluded that the IES experienced a periglacial environment and was underlain by continuous permafrost during the last glacial maximum. Ubiquitous throughout the IES is a stone zone that lies 60-100cm below the surface. Several explanations for the genesis of the stone zone have been proposed, including a lag concentrate, biomantle processes, and cryogenesis. We utilized a combination of coring and trenching, ground penetrating radar and resistivity to investigate the 3D distribution of the stone zone, overlying “pedisediment” and the underlying contact with dense till across a 100 m2 area on a typical IES hillslope in east-central Iowa . Our preliminary results indicate that the stone zone occurs in the basal few decimeters of pedisediment that rests uncomformably and abruptly on eroded, dense till. Ice wedge casts extend from the stone zone into the underlying till. The depth of the stone zone below the modern surface increases downslope and the stone zone dissipates and eventually is replaced by relatively thick loamy sand beneath the footslope. These relationships argue against the stone zone being of biogenic origin. The occurrence of ice wedge casts associated with the stone zone and systematic changes in the thickness and texture of the pedisediment suggest to us that stone zone on the IES was formed by a combination of cryogenic and active zone erosive processes during the full glacial period. 13-8 4:10 PM Artz, Joe Alan [218799] MULTI-PROXY MID-HOLOCENE FLUVIAL PROCESSES AT TWO LOCALITIES IN CENTRAL IOWA ARTZ, Joe Alan, Earthview Environmental, LLC, 310 Second Street, Coralville, IA 522411, joe@earthviewenvironmental.com The Palace site (13PK966) is a buried Middle Archaic site in the Des Moines River valley near the city of Des Moines in central Iowa. Several relatively tightly stratified and stratigraphically separated occupation surfaces were inhabited ca. 7,000 BP. Houses were present, and a human burial was also encountered. The archaeological deposits are buried in a silty clay loam overbank facies that veneers a former point bar. The overbank veneer grades laterally to a clay to silty clay channel-fill that was perhaps a wetland, occupying a nearly-filled-in paleochannel at the time of occupation. Other than an occasional coarse-textured splay or chute deposit, the overbank deposits exhibit no macroscopically visible stratigraphy. Soil thin sections, however, reveal micromorphological evidence for sedimentary bedding in the form of changes in size and sorting of sand grains, for short-lived periods of surface stability in the form of channel microstructures created by bioturbation. d13C ratios for the 250 cm thick overbank facies are primarily between -23 and -20 o/oo, values that are intermediate between warm- and cool- season plants. There is, however, a significant excursion in C4 grasses in a 50-cm-thick zone, with ratios of -15 to -17 o/oo. This zone immediately overlies the 7,000-year-old cultural horizon. It may therefore, be the signature of a mid-Holocene warming episode. Pollen records from other central-Iowa sites indicate that the prairie expanded across central Iowa in this approximate time range. Other recent work by the author on the Middle Raccoon River, about 50 km west of the Palace site, show evidence of a major fluvial discontinuity at ca. 7,000 BP, based on radiocarbon ages from channel and channel-fill facies at the bottom of a 4-5 m thick upward-fining sequence. Largescale sedimentary structures observe in core and cutbank profiles indicate high energy deposition between ca. 7,000 and 6,500 BP. 13-9 4:30 PM Grimley, David A. [218205] PLEISTOCENE MOLLUSCAN ASSEMBLAGES TO AID UNDERSTANDING OF PALEOENVIRONMENT, PALEOCLIMATE AND CHRONOLOGY: EXAMPLES FROM ILLINOIS GRIMLEY, David A., Illinois State Geological Survey, Prairie Research Institute, University of Illinois, 615 E. Peabody Dr, Champaign, IL 61820, dgrimley@illinois.edu and OCHES, Eric A., Department of Natural & Applied Sciences, Bentley University, 175 Forest St, Waltham, MA 02452 Across the southern Midwest region, Pleistocene mollusks are locally found in relatively unaltered loess or lacustrine sediment (particularly slackwater deposits) synchronous with central U.S.A. glaciations. More rarely, molluscan faunas are preserved in interglacial lake deposits. The assemblage of gastropods and bivalves provides important information about past environments, climate, and ecology that complements other paleoenvironmental data. In addition, the shell material can be used in chronological studies. Paleoenvironmental interpretations aided by molluscan occurrences include differentiation of terrestrial vs. aquatic conditions; seasonal vs. perennial lake; deep vs. shallow water; and flowing vs. quiet water. Faunas tend to vary spatially and stratigraphically between distal and ice-proximal environments. Such observations can complement or refine interpretations from sedimentological, geomorphic, and other fossil records (e.g., pollen, ostracodes), thus providing a clearer picture of the paleoenvironment. In some cases, such as in oxidized sediments, molluscan assemblages are preserved where other records are lacking or poorly preserved. Some species of minute terrestrial gastropod genera (Vertigo, Pupilla, Columella, Gastrocopta) have climatic sensitivity and, by comparisons with modern distribution patterns (Nekola and Coles, 2010), can aid in general paleoclimate estimations. Aquatic species are generally less affected by climate but some species have sensitivity. Carbon and oxygen isotopic analyses of shell carbonate can aid with interpretations of paleovegetation, paleotemperature, or paleohumidity, though other factors should be considered. Chronologically, radiocarbon dating of Wisconsin Episode terrestrial mollusks in loess or lakeshore records are more precise and considered by many to be more accurate than luminescence dating. With the development of multiple amino acid assays in recent years, amino acid geochronology (using terrestrial or aquatic species) is proving valuable in differentiating Wisconsin, Illinois, and pre-Illinois episode deposits in Illinois, as was initially suggested in western Indiana (Miller et al. 1987). Comparisons of glutamic and aspartic acid D/L ratios with Succinea and Hendersonia are most fruitful thus far. 2013 GSA North-Central Section Meeting 17
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Crane, Renee 21-5* Crisp, Alexis A.
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