Physical Sciences and Mathematics Commons^™

Diagnosis Of The July 6, 2002 Ogallala, Nebraska Flash Flood, David B. Radell, Mark R. Anderson, John W. Stoppkotte, James R. Mccormick

Department of Earth and Atmospheric Sciences: Faculty Publications

During the early morning hours of 6 July 2002, a mesoscale convective system (MCS) traversed southwestern Nebraska and produced more than 40 cm of precipitation, resulting in a flash flood that closed Interstate 80 and caused one fatality near Ogallala, Nebraska. Regional climatology yields that this flash flood ranked first in precipitation amount for a 24 hour period over the past one hundred years. Synoptic and mesoscale features similar to other flash flooding events and conducive to extremely heavy precipitation were in place over the Central Plains, including a weak upper level ridge, high precipitable water values (180% of normal), …

Inconsistencies Between Pangean Reconstructions And Basic Climate Controls, Clinton Rowe, David B. Loope, Robert J. Oglesby, Rob Van Der Voo, Charles E. Broadwater

Department of Earth and Atmospheric Sciences: Faculty Publications

The supercontinent Pangea dominated our planet from the Permian into the Jurassic. Paleomagnetic reconstructions have been used to estimate the latitudinal position of Pangea during this 100-million-year period. Atmospheric circulation, recorded by eolian sandstones in the southwestern United States, shows a broad sweep of northeasterly winds over their northernmost extent, curving to become northwesterly in the south. This evidence is consistent with paleomagnetic reconstructions of the region straddling the equator in the Early Permian but is at odds with its northward movement to about 20°N by the Early Jurassic. At least one of the following scenarios must be true: the …

Retreating To Advance Women Geoscience Faculty, Suzanne O'Connell, Mary Anne Holmes

Department of Earth and Atmospheric Sciences: Faculty Publications

Seventeen women geoscientists from New England, New York, and New Jersey assembled for a writing retreat at Boston College's Connors Family Retreat and Conference Center, set on 80 pastoral acres on the outskirts of Boston. Funded through the National Science Foundation ADVANCE program, the retreat had two objectives: to facilitate writing and to develop a supportive community. It succeeded on both accounts. Although new to science, retreats of this sort have long been a highly sought after experience for writers in other disciplines. The potential benefits for scientists, in particular, women scientists, are great. Writing is a cornerstone of our …

Sedimentology Of The Whiteclay Gravel Beds (Ogallala Group) In Northwestern Nebraska, Usa: Structurally Controlled Drainage Promoted By Early Miocene Uplift Of The Black Hills Dome, Christopher R. Fielding, Hannan E. Lagarry, Leigh Anne Lagarry, Bruce E. Bailey, James B. Swinehart

Department of Earth and Atmospheric Sciences: Faculty Publications

The newly recognized Whiteclay Gravel Beds (WGB) of the Miocene Ogallala Group crop out as a narrow, discontin­uous ribbon of sands and gravels in Dawes and Sheridan Counties, northwestern Nebraska, USA. The WGB are ex­posed in a series of municipal gravel quarries and natural exposures that define a linear trench in underlying strata at least 20 m deep and up to 300 m wide, with short, southeast-trending reaches separating generally longer east-trend­ing sections. This gravel-filled trench can be recognized from the Nebraska–South Dakota border near Whiteclay, Ne­braska southeastward to east of Gordon, Nebraska, a distance of ~ 30 km. The …

Sedimentology And Stratigraphic Architecture Of The Late Permian Betts Creek Beds, Queensland, Australia, Jonathan P. Allen, Christopher R. Fielding

Department of Earth and Atmospheric Sciences: Faculty Publications

The Late Permian Betts Creek Beds form a succession of coal-bearing alluvial-coastal plain sediments in a basin marginal setting within the northeastern Galilee Basin, Queensland, Australia. The unit is ~ 50–60 m in thick­ness at Porcupine Creek National Park where outcrop is laterally continuous for several kilometers. Eight fa­cies have been identified within the formation and can be grouped into 2 facies associations: (A) channel depos­its and (B) floodbasin deposits. The channel association consists of conglomerate (A1) and trough cross-bedded multistorey sandstone facies (A2), both interpreted as deposits of low-sinuosity river systems, tidally influenced fluvial channels (A3), interbedded sandstone and …

Quaternary Glaciation And Hydrologic Variation In The South American Tropics As Reconstructed From The Lake Titicaca Drilling Project, Sherilyn C. Fritz, Paul A. Baker, Geoffrey O. Seltzer, Ashley Ballantyne, Pedro Tapia, Hai Cheng, R. Lawrence Edwards

Department of Earth and Atmospheric Sciences: Faculty Publications

A 136-m-long drill core of sediments was recovered from tropical high-altitude Lake Titicaca, Bolivia-Peru, enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370,000 yr. Within the errors of the age model, the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages. Periods of ice advance in the southern tropical Andes generally were periods of positive water balance, as evidenced by deeper and fresher conditions in Lake Titicaca. Conversely, reduced glaciation occurred during periods of negative …

Combined Remote Sensing And Field Investigations Of Hydrocarbon Trap Analogue Structures: Examples From The Zagros Simply Folded Belt, Iran And The Sawtooth Range, Montana [Abstract], Caroline M. Burberry, David Cannon, John W. Cosgrove, Terry Engelder

Department of Earth and Atmospheric Sciences: Faculty Publications

First paragraph of abstract: Structures that outcrop at the surface in fold-thrust belts are frequently good analogues for hydrocarbon traps in compressional environments. Along-strike changes in structure and geometry have important implications for connectivity and fluid flow throughout the petroleum system, e.g. in the Zagros Simply Folded Belt, Iran, and in a surface reservoir analogue in the Sawtooth Range, Montana.

Drainage Diversion Patterns And Landform Morphology As An Indicator Of Deformation Style: Examples From The Zagros Simply Folded Belt, Islamic Republic Of Iran (Abstract), Caroline M. Burberry, John W. Cosgrove, J.-G. Liu

Department of Earth and Atmospheric Sciences: Faculty Publications

First paragraph of abstract: In the NW-SE trending Zagros Simply Folded Belt, landform organisation is shown to be a straightforward response to tectonic forcing processes using remote sensing. Two end-member fold types (detachment folds and fault-bend folds) interact with streams flowing into the Persian Gulf. Using drainage network analysis and geomorphologic methods, the organisation of emergent landform morphologies is mapped and the distribution of different fold types is inferred.

A Diatom Record Of Late Holocene Climate Variation In The Northern Range Of Yellowstone National Park, Usa, Brandi B. Bracht, Jeffery R. Stone, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

The changes in diatom species composition in a sediment core from Crevice Lake, Yellowstone National Park, spanning the past 2550 yr, were used to reconstruct long-term limnological and ecological conditions that may be related to late Holocene climate variability. Planktic forms dominate the fossil diatom assemblages throughout this record, but changes in species dominance indicate varying nutrient levels over time, particularly phosphorus. The changes in the nutrient concentrations in the lake were probably driven by changes in temperature and wind strength that affected the duration of watercolumn mixing and thus the extent of nutrient recycling from deep waters. Prior to …

A 2650-Year-Long Record Of Environmental Change From Northern Yellowstone National Park Based On A Comparison Of Multiple Proxy Data, Cathy Whitlock, Walter Dean, Joseph Rosenbaum, Lora Stevens, Sherilyn C. Fritz, Brandi Bracht, Mitchell Power

Department of Earth and Atmospheric Sciences: Faculty Publications

Geochemical, stable-isotope, pollen, charcoal, and diatom records were analyzed at high-resolution in cores obtained from Crevice Lake, a varved-sediment lake in northern Yellowstone National Park. The objective was to reconstruct the ecohydrologic, vegetation, and fire history of the watershed for the last 2650 years to better understand past climate variations at the forest-steppe transition. The data suggest a period of limited bottom-water anoxia, relatively wet winters, and cool springs and summers from 2650 to 2100 cal yrBP (700–150 BC). Dry warm conditions occurred between 2100 and 850–800 cal yrBP (150 BC and AD 1100–1150), when the lake was anoxic, winter …

Sequence Stratigraphic Controls On Synsedimentary Cementation And Preservation Of Dinosaur Tracks: Example From The Lower Cretaceous, (Upper Albian) Dakota Formation, Southeastern Nebraska, U.S.A., Preston Lee Phillips Jr., Greg A. Ludvigson, R. Matthew Joeckel, Luis A. González, Robert L. Brenner, Brian J. Witzke

Department of Earth and Atmospheric Sciences: Faculty Publications

A thin cemented sandstone bed in the Upper Albian Dakota Formation of southeastern Nebraska contains the first dinosaur tracks to be described from the state. Of equal importance to the tracks are stable-isotope (C, O) analyses of cements in the track bed, especially in the context of data derived from generally correlative strata (sandstones and sphaerosiderite-bearing paleosols) in the region. These data provide the framework for interpretations of paleoenvironmental conditions, as well as a novel approach to understanding mechanisms of terrestrial vertebrate track preservation.

High minus-cement-porosity (> 47%) and low grain-to-grain contacts (~2.5) in the track bed indicate early (pre-compaction) …

Leaks In The Pipeline: Why Do Women Remain Curiously Absent From The Ranks Of Academia?, Mary Anne Holmes

Department of Earth and Atmospheric Sciences: Faculty Publications

Family issues can cause women to abandon academia at every rung of the career ladder. Policy-makers have addressed some ways to get more women on to the lower rungs of the ladder. But solutions at the higher steps—tenure and beyond—are proving a little more difficult.

Lacustrine Evidence For Moisture Changes In The Nebraska Sand Hills During Marine Isotope Stage 3, Kimberly C. Jacobs, Sherilyn C. Fritz, James B. Swinehart

Department of Earth and Atmospheric Sciences: Faculty Publications

In the central Great Plains of North America, loess stratigraphy suggests that climate during the late Pleistocene was cold and dry. However, this record is discontinuous, and there are few other records of late-Pleistocene conditions. Cobb Basin, located on the northern edge of the Nebraska Sand Hills, contains lacustrine sediments deposited during Marine Isotope Stage 3, beginning approximately 45,000 cal yr BP and continuing for at least 10,000 yr. The lake was formed by a dune dam blockage on the ancient Niobrara River, and its deposits contain a diatom record that indicates changes through time in lake depth driven by …

Evaluating Climatic And Non-Climatic Influences On Ion Chemistry In Natural And Man-Made Lakes Of Nebraska, Usa, D. M. Bennett, Sherilyn C. Fritz, John C. Holz, Aris A. Holz, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

Conductivity and major ion chemistry data were analyzed for a suite of Nebraska (USA) natural lakes, reservoirs, sand pits, and barrow pits to evaluate the magnitude of climatic versus non-climatic influence on ionic concentration and composition. In both natural lakes and sand and barrow pits, conductivity is positively related to longitude and reflects decreasing effective moisture from east to west. Reservoirs showed no relationship between lake conductivity and location, probably because the reservoirs are very strongly influenced by groundwater and surface water inflow and have shorter residence times relative to the other lake types. At smaller spatial scales, conductivity among …

Co2-Forced Climate And Vegetation Instability During Late Paleozoic Deglaciation, Isabel P. Montañez, Neil J. Tabor, Deb Niemeier, William A. Dimichele, Tracy D. Frank, Christopher R. Fielding, John L. Isbell, Lauren P. Birgenheier, Michael C. Rygel

Department of Earth and Atmospheric Sciences: Faculty Publications

The late Paleozoic deglaciation is the vegetated Earth’s only recorded icehouse-to-greenhouse transition, yet the climate dynamics remain enigmatic. By using the stable isotopic compositions of soil-formed minerals, fossil-plant matter, and shallow-water brachiopods, we estimated atmospheric partial pressure of carbon dioxide (pCO₂) and tropical marine surface temperatures during this climate transition. Comparison to southern Gondwanan glacial records documents covariance between inferred shifts in pCO₂, temperature, and ice volume consistent with greenhouse gas forcing of climate. Major restructuring of paleotropical flora in western Euramerica occurred in step with climate and pCO₂ shifts, illustrating the biotic impact associated …

Dinosaur Tectonics: A Structural Analysis Of Theropod Undertracks With A Reconstruction Of Theropod Walking Dynamics, Ole Graversen, Jesper Milán, David B. Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

A dinosaur trackway in the Middle Jurassic eolian Entrada Sandstone of southern Utah, U.S.A., exposes three undertracks that we have modeled as isolated tectonic regimes showing the development of fold-thrust ramp systems induced by the dinosaur’s feet. The faulted and folded sequence is comparable to crustal-scale tectonics associated with plate tectonics and foreland fold-thrust belts. A structural analysis of the dinosaur tracks shows the timing and direction of the forces exercised on the substrate by the animal’s foot during the stride. Based on the structural analysis, we establish a scenario for foot movements and weight distribution in the feet. During …

Burrows Dug By Large Vertebrates Into Rain-Moistened Middle Jurassic Sand Dunes: A Reply, David B. Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

Odier (2007) is concerned with two issues: (1) I did not cite his work on burrows in the Navajo Sandstones of southeastern Utah in my article (Loope 2006), and (2) he believes I amwrong in interpreting the structures preserved in the Entrada Sandstone as burrows. On the first issue, I failed to cite both his 2004 abstract and the newly published book that he sent me in October 2006. My article was accepted on June 12, 2006; I returned the proofs on August 23; and the issue was published online on October 4, 2006. The timing of these events makes …

Stream Network Characteristics Used To Infer The Distribution Of Fold Types In The Zagros Simply Folded Belt, Iran, Caroline M. Burberry, John W. Cosgrove, Jian Guo Liu

Department of Earth and Atmospheric Sciences: Faculty Publications

Progressive deformation at a convergent margin (the Zagros Simply Folded Belt) was analysed using satellite images, digital elevation models, contour maps and artificially generated stream networks. Two end-member fold types (fault-bend folds and detachment folds) interact with streams flowing from the High Zagros Mountains into the Persian Gulf. Growing folds divert streams and create wind or water gaps in characteristic patterns which are related to the uplift histories of the two fold types. Additionally, the symmetry of minor channels reflects the inherent symmetry of the folds. The distribution of fold types is shown for the region N27°- N30°, E50°-E54° at …

Observational Analysis Of The 27 May 1997 Central Texas Tornadic Event. Part Ii: Tornadoes, Adam L. Houston, Robert B. Wilhelmson

Department of Earth and Atmospheric Sciences: Faculty Publications

The 27 May 1997 central Texas tornadic event has been investigated in a two-part observational study. As demonstrated in Part I, the 1D environment associated with this event was unfavorable for significant (≥F2) tornadoes. Yet, the storm complex produced at least six significant tornadoes, including one rated F5 (the Jarrell, Texas, tornado). The purpose of this article is to examine the spatiotemporal interrelationships between tornadoes, preexisting boundaries, antecedent low-level mesocyclones, convective cells, and midlevel mesocyclones. It is shown that each of the six observed tornadoes that produced greater than F0 damage formed along the storm-generated gust front, not along preexisting …

Decadal Variation Of The Southwest U.S. Summer Monsoon Circulation And Rainfall In A Regional Model, Q. Steven Hu, Yongjun Zheng

Department of Earth and Atmospheric Sciences: Faculty Publications

Previous studies have identified several major causes for summer rainfall variations over the southwest United States, for example, land memory (i.e., relationships between antecedent winter season precipitation and snow cover anomalies and subsequent summer rainfall anomalies over the southwest United States; these anomalies are likely most important in the northwest United States, although antecedent anomalies in the southwest United States also may be important in determining summer rainfall variations) and sea surface temperature (SST) anomalies in the North Pacific. Atmospheric responses to these “boundary forces” interact with moisture flows from the Gulf of Mexico and from the Gulf of California …

An Improved Qc Process For Temperature In The Daily Cooperative Weather Observations, Kenneth Hubbard, Nathaniel B. Guttman, Jinsheng You, Zhirong Chen

Department of Earth and Atmospheric Sciences: Faculty Publications

TempVal is a spatial component of data quality assurance algorithms applied by the National Climatic Data Center (NCDC), and it has been used operationally for about 4 yr. A spatial regression test (SRT) approach was developed at the regional climate centers for climate data quality assurance and was found to be superior to currently used quality control (QC) procedures for the daily maximum and minimum air temperature. The performance of the spatial quality assessment procedures has been evaluated by assessing the rate with which seeded errors are identified. A complete dataset with seeded errors for the year 2003 for the …

Modeling Annual Extreme Precipitation In China Using The Generalized Extreme Value Distribution, Song Feng, Saralees Nadarajah, Qi Hu

Department of Earth and Atmospheric Sciences: Faculty Publications

Extreme precipitation events are the major causes of severe floods in China. In this study, four time series of daily, 2-day, 5-day, and 10-day annual maximum precipitation from 1951 to 2000 at 651 weather stations in China were analyzed. The generalized extreme value (GEV) distribution was used, to model the annual extreme precipitation events at each station. The GEV distribution was also modified to explore the linear temporal trends in the extreme events. The results showed that more than 12% of the stations have significant (p-value < 0.10) linear trends. Decreasing trends are mainly observed in northern China, and increasing trends are observed in the Yangtze River basin and northwestern China. The return periods of extreme participation have changed stations with significant temporal trends. The 50-year event observed in parts of the Yangtze River basin, and northwestern China during the 1951-60, has become a more frequent 25-year event in the 1990s. The spatial distribution of the return levels of the 651 stations are closely related to the climatic mean precipitation, and are influenced by the East Asian summer monsoon system (return levels are measures of extremity – for example, a 10 year return level is the value that can be expected to be exceeded on average once in every 10 years). The return period of extreme precipitation, that caused the 1998 severe floods in the Yangtze River basin, was also evaluated from a probabilistic perspective.

A Novel Over-Sea-Ice Seismic Reflection Survey In Mcmurdo Sound, Antarctica, S. J. Betterly, M. A. Speece, R. H. Levy, David M. Harwood, S. A. Henrys

Department of Earth and Atmospheric Sciences: Faculty Publications

During the austral spring of 2005, approximately 28 km of over-sea-ice seismic reflection data were recorded over McMurdo Sound, Antarctica, in support of the ANtarctic geological DRILLing Program (ANDRILL). The 2005 ANDRILL Southern McMurdo Sound Project (SMS) seismic survey incorporated techniques that improved the quality of over-sea-ice seismic data. Previous over-sea-ice seismic experiments have had limited success because of poor source coupling caused by thin sea ice and source bubble-pulse effects caused by explosive seismic sources placed in the water column. To mitigate these problems, a Generator-Injector (GI) air gun was used as the seismic source. The GI air gun …

Metastable Equilibria Among Dicarboxylic Acids And The Oxidation State During Aqueous Alteration On The Cm2 Chondrite Parent Body, Jason A. Mcalister, Richard M. Kettler

Department of Earth and Atmospheric Sciences: Faculty Publications

Linear saturated dicarboxylic acids are present in carbonaceous chondrite samples at concentrations that suggest aqueous alteration under conditions of metastable equilibrium. In this study, previously published values of dicarboxylic acid concentrations measured in Murchison, Yamato-791198, and Tagish Lake carbonaceous chondrites are converted to aqueous activities during aqueous alteration assuming water:rock ratios that range from 1:10 to 10:1. Logarithmic plots of the aqueous activities of any two dicarboxylic acids are proximal to lines whose slope is fixed by the stoichiometry of reactions describing the oxidation–reduction equilibrium between the two species. The precise position of any line is controlled by the equilibrium …

Quantitative Analysis Of The Calcareous Nannofossil Assemblages From Ciros-1, Victoria Land Basin, Antarctica, David K. Watkins

Department of Earth and Atmospheric Sciences: Faculty Publications

The lower portion of the CIROS-1 core (McMurdo Sound, Antarctica) has been cited as evidence for Late Eocene continental glaciation on Antarctica. A reassessment of this age determination is warranted in the face of mounting evidence from multiple proxies that continental glaciation was initiated by rapid ice-growth during the earliest Oligocene. Examination of calcareous nannofossil assemblages from this section confirmed very low fossil abundance, low species richness, and the presence of reworked taxa. A minimum of 37% of the total species richness in the section comprises reworked forms, including Late Cretaceous and latest Paleocene to Middle Eocene species. Quantitative analysis …

Preservation And Erosion Of Theropod Tracks In Eolian Deposits: Examples From The Middle Jurassic Entrada Sandstone, Utah, U.S.A., Jesper Milán, David B. Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

The Middle Jurassic Entrada Sandstone, exposed near the town of Escalante, southern Utah, consists of large-scale cross-bedded eolian deposits that are interbedded with horizontally laminated sand sheets and thin sets of eolian cross-strata, representing periods with a moister climate. The flat-bedded units contain numerous tracks and trackways from small to large-sized theropod dinosaurs. These tracks are today exposed in several distinct erosional states, allowing detailed studies of track and undertrack formation in eolian deposits. Tracks that originally were emplaced on sloping surfaces show, in their present-day erosional state, a morphology distinct from those originally emplaced on horizontal surfaces. Further, the …

Evaluation Of The Streambed Leakage Concept In Analytical Models Using Data From Three Pumping Tests, Sefan J. Kollet, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

Two-dimensional analytical models of pumping induced drawdown and stream depletion account for the streambed properties and stream geometry. Using data from three pumping tests performed under various hydrologic conditions, the following hypotheses were tested: (1) a partially penetrating stream at a certain distance from the pumping well can be represented by the streambed leakage term in the analytical models; (2) in the streambed leakage term, the streambed conductance coefficient λ=(WK′)/m′ accounts for the average stream width W, the streambed thickness m′, and hydraulic conductivity K′. The first hypothesis was tested by comparing results from tests under flow and no-flow stream …

Polarimetric Signatures And Microphysical Processes In Tornadic Southern And High Plains Classic Supercells, Matthew S. Van Den Broeke

Department of Earth and Atmospheric Sciences: Faculty Publications

Preliminary schematics of polarimetric signatures are developed for classic, tornadic supercells at low, mid, and upper levels for the Southern and High Plains. Schematics are developed for pre-tornado, tornado, and tornado demise times from a small collection of cases, most of which were cyclically tornadic. Characteristic signatures and patterns are identified for reflectivity factor (Z_HH), differential reflectivity (Z_DR), correlation coefficient (ρ_hv), specific differential phase (K_DP), and linear depolarization ratio (LDR_VH), and signatures likely related to the tornado lifecycle are discussed.

Additionally, observed changes in four polarimetric variables (Z_HH, …

High-Resolution Evidence For Dynamic Transitional Geomagnetic Field Behaviour From A Miocene Reversal, Mcmurdo Sound, Ross Sea, Antarctica, Andrew P. Roberts, Anisch Bakrania, Fabio Florindo, Christopher J. Rowan, Christopher R. Fielding, Ross D. Powell

Department of Earth and Atmospheric Sciences: Faculty Publications

We report a high-resolution record of a Miocene polarity transition (probably the Chron C6r-C6n transition) from glacimarine sediments in McMurdo Sound, Ross Sea, Antarctica, which is the first transition record reported from high southern latitudes. The transition is recorded in two parallel cores through a 10.7 m stratigraphic thickness. The sediments are interpreted as having been deposited in a marine environment under the influence of floating ice or seaward of a glacier terminus from which a large sediment load was delivered to the drill site. The core was recovered using rotary drilling, which precludes azimuthal orientation of the core and …

The Sensitivity Of Convective Initiation To The Lapse Rate Of The Active Cloud-Bearing Layer, Adam L. Houston, Dev Niyogi

Department of Earth and Atmospheric Sciences: Faculty Publications

Numerical experiments are conducted using an idealized cloud-resolving model to explore the sensitivity of deep convective initiation (DCI) to the lapse rate of the active cloud-bearing layer [ACBL; the atmospheric layer above the level of free convection (LFC)]. Clouds are initiated using a new technique that involves a preexisting airmass boundary initialized such that the (unrealistic) adjustment of the model state variables to the imposed boundary is disassociated from the simulation of convection. Reference state environments used in the experiment suite have identical mixed layer values of convective inhibition, CAPE, and LFC as well as identical profiles of relative humidity …