GSA Abstracts Presented by UC Researchers
Here are the abstracts of the presentations by the University of CIncinnati's Department of Geology at the 2005 GSA annual meeting.
Implications of New Correlation of Middle Devonian Strata in Eastern North America: The Roles of Tectonics vs. Eustasy and a Refined Sea Level Curve for the Givetian Stage
BARTHOLOMEW, Alexander J., BRETT, Carlton, Geology, University of Cincinnati, and BAIRD, Gordon, Dept. of Geoscience, SUNY Fredonia
The well-exposed Givetian age (upper Middle Devonian) rocks of the Appalachian foreland basin (Hamilton Group, Tully Formation, and the Genesee Group of New York State) preserve one of the most detailed records of high-order sea level oscillation cycles for this time period in the world. Detailed examination has revealed that the pattern of high-order sea level oscillations documented in the New York section is not restricted to the New York area, but can be positively identified at all scales in most areas where coeval units are preserved.
Hybrid Eustatic and Flexural Effects Within a Synorogenic Clastic Wedge: Establishing Temporal Links Between the Late Middle Devonian Tully Formation and the Nearshore Gilboa Sandstone in East-Central New York
BAIRD, Gordon, Dept. of Geoscience, SUNY Fredonia, BRETT, Carlton, and BARTHOLOMEW, Alexander J., University of Cincinnati Department of Geology
In central and western New York, the late Middle Devonian is represented, in part, by anomalous shelf carbonate deposits of the late Givetian Tully Formation. This limestone succession, recording key aspects of the global Taghanic Bioevent, contrasts markedly with bounding detrital facies of the syntectonic Catskill Delta Complex.
Recurrent Faunas Revisited: The Upper Devonian Ithaca Shale Tropidoleptus Faunas of Central New York
BRENNAN, Patrick R., Earth and Atmospheric Sciences, Cornell University, BRETT, Carlton E., BARTHOLOMEW, Alexander J., Geology, University of Cincinnati, and ALLMON, Warren D., Paleontological Research Institution, Ithaca
The onset of major deepening in the basal Genesee Formation of the late Middle Devonian in New York marks the second phase of the Acadian Orogeny and a significant change in sedimentation and biostratigraphic sequences. This is the position of the global Taghanic bioevent. At the Tully Limestone/Genesee contact, 6080 percent of the diverse shallow-marine Hamilton fauna is lost from the Appalachian Basin. However, elements of the Hamilton or Tropidoleptus fauna recur in the Upper Devonian, specifically in the Ithaca Formation, long after their apparent extinction near the contact between the Tully Limestone and Geneseo black shales (at the base of the Genesee). These Lazarus faunas in the Upper Devonian, mainly brachiopods and trilobites, are a subset of the complete Tropidoleptus fauna of the Middle Devonian. They do not co-occur with the distinctly Upper Devonian Ithaca fauna, but are normally found with taxa of the Tropidoleptus fauna, or in monotypic assemblages.
Events at the Tully Unconformity were more complex than simple sea-level changes and include major faunal migrations, facies changes, and sedimentation response to orogeny. The presence of 1) flaggy laminated siltstones with sharp erosive bases and flute and groove casts, 2) cyclicity at scales ranging from tens of meters to centimeters, and 3) local interbedding with hummocky bedded to bioturbated siltstones and sandstones are all indicative of more storm-influenced deposition in more normally oxygenated shelf settings. It is these beds that contain the recurring Hamilton faunas. These Lazarus faunas are important as they show that certain biofacies may persist across major disruptions and may return to a local basin briefly during times of ameliorating conditions.
Sequence Stratigraphy and Lagerstätten in the Middle Cambrian, Great Basin, Utah
BRETT, Carlton1, DESANTIS, Michael K.1, ALLISON, Peter A.2, and LIDDELL, W. David3, (1) Department of Geology, Univ of Cincinnati (2) Earth Science and Engineering, Imperial College, South Kensington Campus, London (3) Department of Geology, Utah State University
Ongoing study of high-resolution sequence stratigraphy of the Middle Cambrian Wheeler and Marjum formations in the Drum Mountains and House Range of west-central Utah has revealed recurrent patterns of conditions resulting in the preservation of various types of fossil Lagerstätten. Lagerstätten (from the German meaning deposit place) refers to an area rich in preserved fossils, usually of many types.
Concentration Lagerstätten, represented by spicular and fragmental trilobite hash beds, are associated with sediment-starved conditions, while conservation Lagerstätten occur primarily in the overlying sparsely fossiliferous highstand shales. Obrution Lagerstätten of articulated trilobites and eocrinoids were preferentially preserved by episodic mud tempestites/turbidites on more oxic seafloors during later highstand. Conversely, the combination of lower dysoxic-anoxic conditions, abundant organic detritus, and relatively rapid episodic influx of detrital sediment favored repeated burial and preservation of organic remains, primarily algae, but in rare instances, including soft-bodied animal remains.
Attachment, Facies Distribution, and Life History Strategies in Crinoids from the Upper Ordovician of Kentucky
BRETT, Carlton, DELINE, Bradley, and MCLAUGHLIN, Patrick, Department of Geology, Univ of Cincinnati
Late Ordovician crinoids from the Cincinnati Arch region exhibit distinct modes of attachment that may relate to their facies distributions and life history strategies. Certain forms, such as Anomalocrinus, were permanently attached via solid cemented holdfast disks. These crinoids rarely occur in articulated clusters; the lower ends of the columns were frequently partially buried indicating that these crinoids were sufficiently strongly attached that they remained intact through many disruptive events. Such crinoids were hard substrate specialists, but occurred across a range of water depths.
Conversely, Ectenocrinus and Iocrinus were weakly attached to the substrate and mainly relied upon the weight of their columns for temporary anchorage. Such taxa were probably confined to areas below average storm wave base; however, they evidently were subject to major disruption during large storms, as they frequently occur in large, monospecific clusters, with masses of current aligned columns in mudstones. Excellent preservation indicates that the crinoids were preserved near their living site, a paradox, as glyptocrinids, lacking a cemented or radicular holdfast, seemingly could not have survived on shifting skeletal sand shoals. Despite suffering frequent mass mortalities, loosely attached Ordovician crinoids presumably survived because of rapid proliferation as r-selected generalists. Disruptive events were sufficiently rare that they did not provide a significant selective factor for firm attachments.
Middle Cambrian Microbial Communities Along a Bathymetric Gradient
WESTFIELD, Isaac T.1, LIDDELL, W. David1, and BRETT, Carlton E.2, (1) Department of Geology, Utah State University, (2) Department of Geology, University of Cincinnati
Microbial communities within the uppermost part of the Middle Cambrian Wheeler Formation make up a distinctive and laterally-continuous horizon in the Drum Mountains of west-central Utah. The microbial communities in the Drum Mountains display pronounced bathymetric-related changes in morphology and composition.
Can We See the Forest for the Trees? Faunal Stability and Spatio-Temporal Scale in the Devonian Hamilton Group, New York State
BAUGH, Heather L., Department of Earth Sciences, Syracuse University, Heroy Geology Laboratory, Syracuse BRETT, Carlton E., Department of Geology, University of Cincinnati and IVANY, Linda C., Earth Sciences, Syracuse University
Brett and Baird introduced the concept of coordinated stasis about a decade ago after a number of years of field observation of New York Silurian-Devonian sequences. Earlier studies have cast some doubt on the validity of coordinated stasis in the Hamilton Group, but issues of temporal and spatial scale could not be directly addressed with the data available at that time. In this study, we test for taxonomic and ecologic stability within the Hamilton Group at the formation, member, and horizon levels over a broad geographic area. As expected from the results of previous studies, variability within horizons and geographic variation within members allow us to reject the null hypothesis that samples are randomly distributed, suggesting that the assemblages within horizons and members are often distinct geographically. In addition, we tested for ecological stability by coding taxa for their substrate and feeding characteristics and repeating the analysis at various scales.
The results are similar to those of the taxonomic tests in that the formation analysis suggests stability, but the finer-scale tests do not. As the original definition of coordinated stasis describes a regional pattern at the scale of formations, we find no basis to reject it. Perhaps the question should not be does coordinated stasis occur? but rather, at what scale is the pattern apparent? At high temporal and spatial resolutions, fossil assemblages appear to be variable. It is only at the larger scale of regional formations that stability becomes statistically perceptible, reinforcing the field impression that these faunas are stable for millions of years.
Encrusting Biont Guild Distribution on Euphotic to Aphotic Hard Surfaces in the Modern Gulf of Mexico and Bahamas
PARSONS-HUBBARD, Karla, Geology Dept, Oberlin College, WALKER, Sally E., Department of Geology, Univ of Georgia, BRETT, Carlton E., Department of Geology, Univ of Cincinnati, POWELL, Eric N., Haskin Shellfish Research Laboratory, Rutgers University and JONES, Donna Carlson, Biology, University of Cincinnati
Analysis of assemblages of encrusting epibionts has great potential for the interpretation of paleonvironments. (Epibionts are animals such as brachiopods, crinoids or gastropods that live on the surface of other animals.) Patterns of encrustation on hard substrates have been fairly well documented in modern shallow water environments less than 10 meters in depth, but little is known of encrusting communities in deeper water settings. Results presented here are drawn from eight-year experimental deployments of mollusk shell substrates at the sediment water interface in two separate oceanic regimes: (a) carbonate platform, escarpment and basin; depths of 15 to 290m: Lee Stocking Island, Bahamas, and (b) siliciclastic-dominated shelf/slope settings: 72 to 600 m in varied settings from muddy seafloor to petroleum seeps and a brine pool, in the Gulf of Mexico.
Biont guilds with the potential to be preserved in the fossil record (that is, those organisms with hard skeletons or those that leave traces on the substrate) exhibit trends with respect to depth (and light), substrate type, ocean basin and even specific environment (such as petroleum seeps). In areas less than 100m deep, biont community composition was strongly controlled by the substrate upon which the experimental shells were deployed. Shells on hard sea bottoms in the deeper photic (accessible by sunlight) zone (25100m) possessed a large cohort of bionts, including coralline and endolithic algae, varied bryozoans, clionid sponges, serpulids and foraminifera. Corals are also present in the deeper photic zone, but showed no correlation with seafloor type. The deeper dysphotic to aphotic (limited to no sunlight) zone (100600m) regardless of seafloor type, is characterized by a sparse, low diversity assemblage of chitinous ciliates, endolithic fungi, foraminifera and serpulid tubes. These results should have important applications to interpretations of paleoenvironments based on bionts preserved on fossil shell material.
Investigating How Ontogeny and Environment Influence Morphological Variation Within Species of the Bivalve Genus Cucullaea
BUICK, Devin P., Geology, University of Cincinnati
Throughout its 200 million-year history, the bivalve genus Cucullaea has remained morphologically conservative at a synoptic level, despite exhibiting significant temporal variation in its biogeographic and environmental distribution. However, individual species often exhibit significant variation, which has had an impact on species-level taxonomic classifications and the evolutionary inferences drawn from them. A major goal of this research is to address two important causes of morphological variation within Cucullaea species: ontogenetic changes exhibited by individuals during their lifetimes, and variations among individuals as a function of environment. To accomplish these objectives, museum type and bulk collections for well-preserved populations of various cucullaeid species are being digitized, allowing these morphological relationships to be investigated in detail.
By understanding the causes and degree of morphological variation seen within species of Cucullaea, variations between species and the features that define these taxonomic units may be defined more clearly, permitting their assessment within a biogeographic, ontogenetic and environmental framework for an improved understanding of Cucullaea's evolutionary history.
Timing and Style of Glaciation on the Gurla Mandhata Massif: A Test for Synchroneity of Semi-Arid Tibetan Glaciers with Global Climate Change
DAVIS, Nicole K., OWEN, Lewis A., Geology, University of Cincinnati, and YI, Chaolu, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing
The driving forces behind Quaternary glaciations in the Himalaya and Tibet have not been resolved despite the climatic importance of the region. In particular, it has not been determined if Quaternary glaciation was synchronous throughout the orogen and whether changes in glacier ice volume were contemporaneous with global climate fluctuations. Recently, glacial chronologies defined by numerical dating have suggested that the south Asian summer monsoon is important in delivering moisture to Himalayan-Tibetan glaciers in monsoon-influenced regions, allowing them to advance most effectively in times of low latitude insolation maxima when the monsoon is most intense. This work suggests that glaciation was generally synchronous in monsoon-dominated regions of the Himalaya and Tibet.
However, the importance of the mid-latitude westerlies in delivering moisture to Himalayan-Tibetan glaciers has not been determined, and may be particularly significant in semi-arid areas that are distal to the monsoon influence, such as southwestern Tibet. To examine the nature of glaciation in a semi-arid region of Tibet and to test the possible dominance of the mid-latitude westerlies in forcing glaciation, we have examined the glacial geology of Gurla Mandhata (Naimona'nyi), a 7,728 m-high massif in southernmost SW Tibet. In this region, glacial landforms record a progression from expanded ice cap glaciation, to piedmont, and, ultimately, to entrenched valley glaciation. Using cosmogenic surface exposure dating we are developing a glacial chronology for the massif. This allows us to compare the glacial chronologies and style of glaciation with other proxies, including ice core and deep sea sediment records, to test for regional and global glacial synchroneity.
The Appearance of Change: Searching for an Environmental Transition in an Accumulating Subfossil Assemblage
FERGUSON, Chad Allen, Department of Geology, University of Cincinnati
Organisms and their environments are invariably linked, and understanding their interrelationships is of great interest to paleontologists. If a habitat is altered, then a change in the associated community of organisms is expected, but, despite years of research on subfossil assemblages, the extent to which rapid environmental changes can be recorded in the fossil record remains uncertain. In this investigation, I assess the impact of a well-constrained, anthropogenic, environmental change on a marine molluscan death assemblage.
Previous experiments on Cross Bank, in southeastern Florida Bay, altered the local seagrass community through nutrient enrichment, prompting a temporal transition from the wide-bladed seagrass Thalassia to the needle-bladed seagrass Halodule. During the present study, two 1200m transects were established along the crest of Cross Bank with stations at 200m increments.
Quantitative analyses of the subsamples demonstrate marked differences between altered and control sites in the rank orders and relative abundances of major molluscan taxa. These differences are tied to the physical characteristics of the two seagrasses and the suitability of these habitats to the fauna. Large-bodied grazing gastropods and infaunal bivalves suited to life in a Thalassia-habitat, such as Cerithium muscarum and Pitar fulminatus, decrease in relative abundance in the Halodule-rich habitat, while smaller bodied gastropods and epifaunal bivalves like Bittiolum varium and Brachiodontes exustus increase in abundance. Whether a similar differentiation can be recognized stratigraphically within cores from altered, Halodule-rich sites is currently being evaluated.
New Science LibrariansIs There a Future?
GOODEN, Angela M., Geology-Mathematics-Physics Library, University of Cincinnati
The objective of this study is to determine how many opportunities are actually available for new science librarians. As a result of forecasts stating that there will soon be a shortage of librarians, several recruitment efforts are under way to grow more librarians. At the same time, budget cuts and hiring freezes occur daily and threaten the pool of jobs available.
One of the hottest topics in the literature today is about the graying or aging of the profession. Much has been written about the education needs for new catalogers. Black studied the socialization needs of employed entry-level librarians. Martindale discussed opportunities for entry-level librarians in the geographic information systems field. After discovering an increase in the number of positions that require three or more years of experience, Russell alluded that entry-level positions are becoming rarer. However, there appears to be a dearth of literature concerning the specific topic of permanent jobs available to a wider range of new librarians interested in science librarianship.
For this study, a content analysis of job advertisements from 2000-2005 issues of American Libraries was conducted. American Libraries was selected because it is the official magazine of the American Library Association and it lists advertisements for academic, public and special libraries. In addition, it has a subscriber list of 64,000 and a readership greater than that.
Did Alpha Diversity Triple Between the Paleozoic and Cenozoic?
ALROY, John, Paleobiology Database, University of California, Santa Barbara and HENDY, Austin J.W., Department of Geology, Univ of Cincinnati
Sampling-standardized analyses using Paleobiology Database data have shown that Cenozoic global diversity was never clearly greater than early Paleozoic diversity. However, other sampling-standardized analyses claim to show a tripling or even quadrupling of alpha diversity (variation in the number of taxa within a community). The discrepancy is very problematic because global diversity is just alpha times beta diversity. (Beta diversity is the change in species diversity between ecosystems or communities. Beta diversity is a combination of species that are unique to each of the ecosystems being compared.) There is no reason to think that beta was three times higher in the Paleozoic.
A possible solution is taphonomic, or looking at the conditions by which organisms become fossils. Lithification makes collection of small and fragile shells difficult, and may co-occur with diagenetic removal of aragonitic shells. Samples from lithified sediments are extraordinarily common in the Paleozoic, but less so in the Cenozoic.
Meanwhile, it has been argued that observed Cenozoic values should be doubled to correct for high diversity in the tropics. However, only about 37% of modern shelf area is tropical, and many "temperate" Cenozoic samples are from diverse subtropical regions like the Gulf Coast, so a downward correction for temperate environments also should be made. The net effect is therefore likely to be quite small, and hardly enough to cause a serious problem for estimates of global diversity.
What Is a K-Bentonite?
MARKER, Patrick Grady, and HUFF, Warren D., Department of Geology, Univ of Cincinnati
Questions frequently arise as to whether a particular clay-rich bed might be an altered volcanic ash fall in the form of a bentonite or K-bentonite. These beds are often datable using fission track and U/Pb dating of zircons, K/Ar, and Ar/Ar of amphibole, biotite and sanidine. Due to their unique composition, they provide an indispensable tool when correlating sections. The criteria for recognizing such beds are varied, but fall into two broad categories, field criteria and laboratory criteria. Ideally, one would want both, but often that is not possible. However, there are key features to look for in each case that can aid in reliable identification and we present a summary of them here.
Field Criteria: K-bentonites can be different colors when wet (blue, green, red, yellow) but are characteristically yellow when weathered. Due to their clay rich nature, they will feel slippery and waxy when wet. Some K-bentonites contain euhedral to anhedral volcanogenic biotite, quartz, feldspar, amphibole, zircon and apatite. The typical appearance of a K-bentonite bed in outcrop is that of a fine-grained clay-rich band ranging between 1 mm 2m in thickness that has been deformed by static load from the enclosing siliciclastic or carbonate sequence. Accelerated weathering of K-bentonites causes them to be recessed into the outcrop face. For thicker K-bentonites there is often a zone of nodular or bedded chert in the adjacent strata at both the base and the top of the bed.
Laboratory Criteria: Most bentonites and K-bentonites are smectite- or illite/smectite-rich, although some may contain a considerable amount of kaolinite, and those that have undergone low-grade metamorphism may be dominated by R3 I/S and/or sericite plus chlorite/smectite (corrensite) and/or chlorite.
So initial steps should begin with separation and x-ray diffracion analysis of the clay fraction. Wet sieving the sample is important to separate the clay portion from the volcanic crystals that could possibly be present in the sample. Bentonites may contain volcanic phenocrysts and volcanic glass. Study of the non-clay fraction under a high quality optical microscope is satisfactory to determine what types of crystals are present in the sample. Thin section study may also be used. We illustrate with seven examples that were thought to be bentonites. Only one was positively confirmed.
A Comparison of Numerical Dating Techniques at a Late Quaternary Spit-Shoreline Complex, Northern End of Silver Lake, Mojave Desert, California
OWEN, Lewis A., Geology, University of Cincinnati, FINKEL, Robert, Lawrence Livermore National Laboratory, Center for Accelerator Mass Spectrometry KAUFMAN, Darrell, Geology and Environmental Sciences, Northern Arizona University, SHARP, Warren D., Berkeley Geochronology Center, and SINGHVI, Ashok, Planetary and Geosciences Division, Physical Research Lab, Ahmedabad, India
Quantifying rates of Quaternary landscape evolution and paleoenvironmental change, and establishing Quaternary stratigraphic frameworks in drylands has been difficult mainly because radiocarbon dating cannot be readily applied in environments with sparse organic material. The development of optically stimulated luminescence (OSL), cosmogenic radionuclide (CRN) surface exposure, and new technical advances in amino acid racemization (AAR) and U-series dating, however, now allow successions of sediments and landforms to be dated to define the timing and durations of various phases of development of a sedimentary record. Yet few studies provide comparisons between these techniques to test the validity and applicability of newly evolving methods, as well as established radiocarbon dating.
This study illustrates that each of the geochronological methods contributes to an estimate of the timing and duration of a physical/geochemical event in the history of the spit-beach. Detailed studies at key sites such as this will help refine methods and will provide insights into new ways of utilizing numerical dating techniques to provide details on chemical and physical processes within arid and semi-arid environments.
Fault Slip Rates on the Northern Death Valley Fault Zone and Eastern California Shear Zone Kinematics
FRANKEL, Kurt L., Department of Earth Sciences, Univ of Southern California, DOLAN, James F., Department of Earth Sciences, Univ of Southern California, FINKEL, Robert C., Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, OWEN, Lewis A., Department of Geology, Univ of Cincinnati, KNOTT, Jeffrey R., Department of Geological Sciences, California State Univ, BELMONT, Patrick W., Earth and Environmental Sciences, Lehigh University, and LEE, Jeffrey, Geological Sciences, Central Washington Univ
The Northern Death Valley fault zone is thought to accommodate 38 mm/yr of the approximately 9 mm/yr of relative Pacific-North America plate boundary motion in the eastern California shear zone, north of the Garlock fault. Although slip rates in the region are well constrained geodetically, there has been limited quantitative geochronology with which to compare the short-term geodetic rates to intermediate- and long-term geologic slip rates along the fault system. As a consequence, the Northern Death Valley fault zone remains as the largest major missing piece to the geologic versus geodetic slip rate puzzle in the northern-half of the eastern California shear zone.
Determining a slip rate budget north of the Garlock fault has implications for the occurrence and locations of strain transients along major plate boundaries, such as those suggested for the Mojave section of the eastern California shear zone. Once we know precise slip rates on all major faults we can identify whether transient strain accumulation is characteristic of the entire plate boundary or alternatively, the result of local complexities such as the Big Bend of the San Andreas fault.
Stability (?) of the Matanuska Glacier over the Last 14.5 Cal Ka and Younger Dryas Cooling in South-Central Alaska
EVENSON, E.B.1, YU, Z.C.1, WALKER, K.N.1, HAJDAS, I.2, ALLEY, R.B.3, LAWSON, D.E.4, LARSON, G.L.5, and LOWELL, T.V.6, (1) Lehigh University, Bethlehem, (2) ETH, Zurich (3) Pennsylvania State University (4) CRREL, (5) Michigan State University and (6) University of Cincinnati
Multi-proxy data from two cores at Hundred Mile Lake in the Matanuska Valley of south-central Alaska were used to investigate climate and vegetation change over the last 13,500 cal years. Here we discuss the implications of the HML cores with respect to the deglaciation history of the Matanuska Valley. HML is located in a series of well-developed, nested end moraines, 5 km from the terminus of the modern Matanuska Glacier. The timing of deglaciation and the Younger Dryas (YD) cooling is controlled by six AMS dates one on organic-rich sediment, one on a terrestrial macrofossil and four on Pisidium mollusk shells. The 14C dates on shells were corrected for the old carbon effect, and all dates were calibrated using INTCAL 98 dataset. An age model was developed based on linear interpolation of five accepted dates. Extrapolation of the age-depth model, 0.5m, to the base of the lacustrine sediment provides a minimum deglaciation age of 14.5 ka (1 ka = 1000 cal yr BP).
Perhaps the most surprising and important conclusion to be derived from this study is that the terminus of Matanuska Glacier was located only 5 km down valley of its present position 14.5 ka. This would also require that the YD ice margin and end moraine, if there is one, is located between HML and the modern Matanuska Glacier margin, or up-glacier of the modern margin, and that the Matanuska did not advance far enough down valley during the YD to overrun the HML site. The up-glacier scenario is consistent with the emerging picture of early post-glacial warmth in high northern latitudes far from the melting ice sheets, including peak temperatures before YD in parts of Alaska (Kaufman et al., 2004, Quat. Sci. Rev.), in response to peak summer insolation near YD time. Any YD re-advance of Matanuska Glacier may have been muted both because the YD signal was small so far from the north Atlantic center of action, and because YD cooling in widespread regions was concentrated in wintertime and glaciers respond primarily to summer temperatures.
A Chronology of Mountain Glaciation and Associated Paleotemperature Records from the Scoresby Sund Region, East Greenland
KELLY, Meredith A.1, HALL, Brenda L.2, LOWELL, Thomas V.3, SCHAEFER, Joerg M.1, DENTON, George H.2, and BROECKER, Wallace S.1, (1) Geochemistry, Lamont-Doherty Earth Observatory, (2) Climate Change Institute and Department of Earth Sciences, University of Maine, Bryand Global Science Center, Orono, (3) Department of Geology, University of Cincinnati
The surface exposure dating method is applied to develop a chronology of mountain glaciation in the Scoresby Sund region of East Greenland. At least twenty 10Be dates of glacially transported boulders from atop moraines and kames indicate that valley glaciers likely existed during the last glacial maximum (LGM) and the last glacial-interglacial transition. Radiocarbon dates of shells from raised marine terraces deposited subsequent to deglaciation are minimum ages for the moraines. These radiocarbon dates provide rates of post-glacial isostatic uplift based upon terrace elevations which are important for an accurate determination of 10Be production rates.
Equilibrium line altitudes (ELAs) of former valley glaciers are estimated based on field evidence and map data. ELAs associated with former glacial extents are compared to the ELA from a historic glacial advance. The surface exposure dates, coupled with ELA depressions, enable a calculation of the temperature signals underlying the respective glacial advances and a comparison of these data with other paleoclimatic records.
Of particular interest is a comparison of paleotemperature records from mountain glaciers in East Greenland with paleotemperatures recorded by nearby Greenland ice cores, such as Renland and GISP2. Paleotemperature records from Greenland ice cores show a cooling during abrupt cold events within the last glacial period that is one order of magnitude greater than paleotemperatures determined from ELA depressions of mountain glaciers in mid- and high-latitude regions elsewhere. The data will rigorously test whether a similar discrepancy exists between paleotemperatures as recorded by Greenland ice cores and those derived from ELA depressions of mountain glaciers in East Greenland. The existence of such a discrepancy would suggest that Greenland ice cores and mountain glaciers recorded different climatic signals.
Population Structure and Orientation Patterns of Uintacrinus in the Upper Cretaceous (Santonian) of the Western Interior USA
WEBBER, Andrew J., Department of Geology, Miami University, MEYER, David L., Dept of Geology, Univ of Cincinnati, and MILSOM, Clare V., School of Biological & Earth Sciences, Liverpool John Moores University, England
The stemless crinoid Uintacrinus socialis Grinnell occurs in dense aggregations of many individuals preserved in thin, compacted beds. Taphonomic evidence indicates that these aggregations resulted from mass mortality followed by surficial disarticulation and microbial sealing, rather than by gradual accumulation. Therefore we treated aggregations as snapshots of Uintacrinus life assemblages from which we could derive information about population structure. We examined 25 Uintacrinus slabs in U.S. and European museums as well as newly collected material from the Niobrara Formation of Kansas and the Mancos Shale of western Colorado. Calyx diameters were measured for populations on 10 slabs having the best preservation. Size frequency diagrams revealed close similarity in mean diameter and size range for all populations except one from the Niobrara in which individual size is significantly smaller. All histograms are unimodal and bell-shaped. Cumulative frequency vs. size diagrams confirmed that distributions are normal and unclustered. These size distributions suggest that aggregations most likely represent single age-cohorts. Although specimens are preserved in a variety of orientations, most lie parallel to bedding. Orientation of horizontal specimens on 12 slabs was measured by dividing each aggregation into quadrants. Significant directional trends in one or more quadrants were found on 10 slabs, and on five slabs there was a tendency for a spokelike alignment of crowns with arms directed towards the center of the aggregation. Eddy currents may have produced these centripetal patterns; other slabs show alignments indicative of unidirectional flow. Bottom currents are consistent with passive filtration feeding by Uintacrinus, and may also have been related to processes of mass mortality that introduced lethal conditions.
Glacier Advances Since the MIS3b(?) In Tibet and Neighboring Mountains Based on Radiocarbon Datings
YI, Chaolu, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, OWEN, Lewis A., Geology, University of Cincinnati, LIU, Kexin, Institute of Heavy Ion Physics, Peking Univ & Key Lab of Heavy Ion, Beijing and CUI, Zhijiu, Department of Urban Planning and Environmental Sciences, Peking University
More numerical dating data of Quaternary glaciations in wide areas of Tibetan plateau are necessary to understand the paleoglacial climatic dynamic in the plateau. We have dated and collected 67 data of radiocarbon dating and found five Quaternary glacier advances at 40~56ka, 24~16ka, 11.5~10.4ka, 3.1ka, 2.8~2.5ka and Little Ice Age. Few data suggest MIS3b was present in southwestern Tibet, indicating that there might be a strong wet current flowing from the India Ocean to southwestern Tibet.
High-Resolution Sequence Stratigraphy and Event Bed Correlations of the Upper Ordovician Black River and Trenton Groups in Central Pennsylvania: Unraveling (Adding To?) a Century of Controversy
CORNELL, Sean R., MCLAUGHLIN, Patrick, and BRETT, Carlton E., Department of Geology, Univ of Cincinnati, H.N. Fisk Laboratory of Sedimentology
Despite their proximity to type sections of the Black River (BR) and Trenton (TR) Groups in NY, Mohawkian strata of central PA have been difficult for establishing precise regional correlations. These difficulties are promulgated by the general facies change to deeper water carbonates and the difficult identification of key lithologic units and time-rock intervals of the type region (e.g., Rocklandian, Kirkfieldian, Shermanian). In spite of this problem, previous researchers established correlations on the biostratigraphic occurrence of key TR taxa: the occurrence of Maclurites, Hesperorthis, Doleroides within the Centre Hall (L Nealmont Fm) and Echinosphaerites sp within the Rodman (U Nealmont): Rockland-Kirkfield of NY; and the occurrence of Cryptolithus in the overlying Salona Fm: Sugar River of NY (E Shermanian). Early qualitative K-bentonite assessments were utilized to help firm up these time-rock classifications. However, as many of these taxa are now known to be facies controlled and fairly long-ranging within the Mohawkian, these correlations have been challenged.
Building on previous and ongoing research, studies of the BR to TR interval in NY/Ontario and KY/OH have been successful in establishing a framework of depositional sequences constrained by K-bentonites, disturbed horizons, epibole horizons, hardgrounds, isotopic shifts and biostratigraphic correlations. This framework provides many opportunities to establish litho, bio, and chronostratigraphic position of these Mohawkian sequences in the intervening region of central PA. We recognize 6 large-scale depositional sequences (M1-M6 of Holland & Patzkowsky) and 6 smaller-scale sequences (M5: A-C, M6: A-C) within the BR to TR interval of PA. Our studies in PA have adjusted previous time-rock correlations. It is suggested that the base of the M5A sequence (base Watertown of NY), be placed at the SB at the base of the Centre Hall and the M5A MFS be placed at the top of the Rodman (top Selby of NY). This correlation is consistent with conodont correlations, and recent carbon isotopic studies. This correlation, however, is at odds with earlier quantitative K-bentonite correlations which suggest the placement of the M4-M5A SB within the Salona. More recent chemical fingerprinting methods are now being employed to test these correlations.
Late Quaternary Glaciations of Mushtagata and Mt. Kongur in Semi-Arid Region of Northwestern Tibet from Cosmogenic 10be Exposure Dating
SEONG, Yeong Bae and OWEN, Lewis A., Geology, University of Cincinnati, 45221, FINKEL, Robert, Lawrence Livermore National Laboratories, Center for Accelerator Mass Spectrometry, and YI, Chaolu, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing
The glaciation in Tibet and the Himalaya is essentially controlled by two major climatic systems; the mid-latitude westerlies and south Asian summer monsoon. To help resolve the relative importance of these climatic systems, we studied two massifs in northwestern Tibet, Mushtagata and Mt. Kongur, of which present day climates are influenced solely by the mid-latitude westerlies and is beyond the influence of the monsoon. Remote sensing, geomorphic mapping and cosmogenic Be-10 surface exposure dating of boulders on the moraines indicates that the glaciers of Mushatagata at 41-125ka, 17-71Ka, 17.8ka, 13.7ka, 10.5 ka, 8.2ka 6.5 ka, 4.5 ka, 1.8 ka and Little Ice Age. The temporal variations of glaciations of in this region are not in phase with other areas of the Tibetan Plateau that are dominantly affected by Indian Summer Monsoon, but are broadly synchronous with Northern Hemisphere. Interestingly, our data show that glaciations in the semi-arid northwestern Tibet since Last Glacial Maximum are likely linked to Northern Hemisphere cooling events (Rapid Climate Changes) by Mid-latitude Westerlies.
Deglaciation in Northwestern Ontario: Implications for the Beginning of the Moorhead Phase of Glacial Lake Agassiz
FISHER, Timothy G.1, LOWELL, Thomas V.2, LOOPE, Henry M.1, and HENRY, Tammy1, (1) Department of Earth, Ecological & Environmental Sciences, Univ of Toledo, (2) Dept of Geology, Univ of Cincinnati
The presence of glacial lake sediment above the sub-continental drainage divide (between the Superior and Agassiz basins) northwest of Thunder Bay, Ontario, records a paleo lake at elevations higher than previously mapped. A series of hydraulically assisted Livingston cores from small basins and channels penetrated the organic and inorganic contact. Numerous radiocarbon ages from terrestrial macrofossils at the base of the organic sediment indicate evolution of small ponds dominated by peat and gyttja between 10,200 and 10,000 14C yrs BP. Beneath the dated contact, approximately 200 rhythmites (possibly varves) indicate passage of the ice margin up to perhaps 200 years earlier.
The location of the coring sites atop the drainage divide requires dams to the east and west. To the east, both the Rainy and Superior lobes were likely close to the Dog Lake and Marks Moraines, respectively. To the west there is greater uncertainly as to what held the water in at this elevation. One possibility is that it was glacial Lake Agassiz, but this would require a waterplane to be ~50 m higher than previously suggested, and without independent dating control on strandlines, a difficult hypothesis to test. Alternatively, the dam to the west was the St. Louis sublobe, an eastern offshoot of the Des Moines lobe, and a lake was trapped in the Rainy River basin between the receding glaciers. Presumably this lake was glacial Lake Johnston (Antevs, 1951) in which 1250 varves were counted, but whether it is the same lake as glacial Lake Koochiching, as described by Hobbs in northern Minnesota, remains to be verified. Until ice retreated north of the McIntosh channel in west-central Minnesota, Lake Agassiz (Climax) could not have merged with Lake Koochiching, and sometime after that the lake dropped to the Moorhead low phase. At the Snake Curve section just north of the McIntosh channel fluvial gravel between lake clays dates at 9900 14C yr BP. Lake lowering at our coring sites in northwestern Ontario did not begin until ~10,100 14C BP and most of the 42 radiocarbon dates associated with the Moorhead Phase range in age from 10,2009900 14C yrs BP. Reworking of some older material in Moorhead-aged deposits may explain the old age given to the Moorhead Phase and it is suggested that the Moorhead Phase is younger than previously supposed.
The Deglaciation Chronology of the Fort McMurray Area, Alberta: Implications for Meltwater Drainage
WATERSON, Nicholas J.1, LOWELL, Thomas V.1, FISHER, Timothy2, LOOPE, Henry2, and HAJDAS, Irka3, (1) Geology, University of Cincinnati, (2) EEES, University of Toledo, (3) ETH Hoenggerberg, Zurich
New radiocarbon ages and analyses of DEM data from the Fort McMurray, Alberta, area provide insight into deglaciation and meltwater drainage events in the area. From the analyses of DEMs and aerial views from a helicopter, a series of five ice margin positions have been identified and show a stair-step retreat pattern. Chronology is assigned to these ice margin positions from a network of 41 core sites from small lakes associated with moraines in the region. Five key sites document the retreat of an ice lobe emanating from the Lake Athabasca lowland. Preliminary radiocarbon dating results, pending additional analysis still in progress, indicate that deglaciation was later than originally supposed by Dyke et al., and Tarasov and Peltier Chronology of the moraines is presented from oldest (furthest to the southwest) to the youngest (northernmost). The oldest dated ice margin is from Don's Lake located on a moraine just south of the Birch Mountains and west of the Athabasca River, which indicates that this moraine formed prior to about 10,460 +/- 65 14C B.P. (ETH-30586). The next oldest ice margin, south of Fort McMurray, named the Stony Mountain Moraine has a minimum date of 10,030+/- 75 14C BP (ETH-30177). The next ice margin with very lobate moraines just west of the Athabasca River, and is dated at 9,860 +/- 65 14C B.P. (ETH-30594) with a second date of 9,850 +/- 65 14C BP (ETH-30593) from a lake further up on the moraine. The next ice margin known informally as the Firebag Moraine, which also includes the Fort Hills, has a minimum date of 9,595 +/- 70 14C BP (ETH-30174). The youngest ice margin yields a date of 9,510 +/- 70 14C B.P (ETH-30587) from a lake located on the crest of the moraine. Ice margin recession in the study area consists of moraines spanning 1000 radiocarbon years. No evidence of a re-advance was observed. The ice margin geometry when at the Firebag Moraine would have dammed the Athabasca valley, preventing any meltwater drainage through the Clearwater Spillway, catastrophic or otherwise until about 9,595 +/- 70 14C BP. The well-dated, sequential, ice margin chronology in northeast Alberta constrains the timing of potential meltwater drainage through the Clearwater Spillway, indicating that it is too late for it to be a source of freshwater to trigger the Younger Dryas cold period.
Toward an Assessment of Phanerozoic Trends in Beta Diversity: The Importance of Environmental and Geographic Scale
MILLER, Arnold I., BUICK, Devin P., BULINSKI, Katherine V., FERGUSON, Chad A., and HENDY, Austin J.W., Department of Geology, Univ of Cincinnati
Recent assessments of Phanerozoic diversity appear to confirm that alpha (within-community) diversity increased significantly through the Phanerozoic. It has also been suggested that, in aggregate, global diversity during the same interval did not increase as substantially as once envisaged. This raises an important question: was there a trend in beta (between-community) diversity through the Phanerozoic? The answer to this question is essential for determining the aggregate, global trend, because, if the increase in alpha diversity outpaced the aggregate increase, the only way to accommodate this difference is with a DECREASE in beta diversity. On the other hand, if beta diversity remained unchanged or even increased, and assuming that alpha diversity also increased, it would follow that recent suggestions of a muted Phanerozoic global increase may be in error.
In our presentation, we will discuss our initial efforts to assess the Phanerozoic history of beta diversity, starting with a comparison of two exemplars: the Caradocian stage of the Ordovician and the Eocene epoch of the Paleogene. In this context, it is important to consider the geographic or environmental scale at which the compositions of collections are compared to one another (the heart of any assessment of beta diversity). While it might be argued that beta diversity during any interval should be analyzed with samples collected from paleocommunities arrayed along local environmental gradients, there are clearly much broader spatial scales at which biotic turnover is also meaningful, including the degree of differentiation among major, paleocontinent-scale regions of the world. With this in mind, we are investigating the nature of biotic differentiation at multiple geographic and environmental scales, to determine: a) whether, during a given interval, the degree of biotic differentiation did, indeed, vary as a predictable function of geographic or environmental scale; and b) whether, for a given scale, the degree of biotic differentiation varies significantly between the intervals under investigation. This will permit a more sophisticated assessment of beta diversity trends than would be possible by focusing on just a single scale, or by attempting to summarize beta diversity for a given interval with a single approximation.