Earth Sciences Commons^™

Synthesis Of Stratigraphies From Shallow-Water Sequences At Sites 871 Through 879 In The Western Pacific Ocean, Elisabetta Erba, Isabella Premoli Silva, Paul A. Wilson, Malcolm S. Pringle, William V. Sliter, David K. Watkins, Annie Arnaud Vanneau, Timothy J. Bralower, Ann F. Budd, Gilbert F. Camoin, Jean-Pierre Masse, Jörg Mutterlose, William W. Sager

Department of Earth and Atmospheric Sciences: Faculty Publications

This paper discusses the synthesis of bio-, magneto-, and isotope stratigraphies in the shallow-water sediment sequences drilled on guyots in the western Pacific Ocean during Leg 144. Material previously dredged from the slopes of a few guyots and the Cretaceous section recovered at Site 869 are also considered. The integrated stratigraphy along with radiometric ages resulted in the reconstruction of the geological events that produced atolls and guyots.

Integrated Remote Sensing, Structural And Petroleum Systems Modeling Of The Iraqi‐Kurdish Fold Belt, Caroline M. Burberry, Matthias D. Greb, Matthew Laughland, Beth Dudley-Murphy, Gregory Nash, Ministry Of Natural Resources, Iraqi Kurdistan Region

Department of Earth and Atmospheric Sciences: Faculty Publications

An integrated two‐dimensional remote sensing, structural and petroleum systems modeling study was carried out for the Iraqi‐Kurdish Fold Belt to analyze potential trap structures as well as the driving mechanisms of petroleum generation, migration and accumulation in the structural complex thrust belt area.

Processing of Landsat‐7 ETM data has been used to create false color images, highlighting lithological differences, from which geological maps can be generated. Analysis of lineaments in these images is used to generate fault and fracture maps, producing a suite of geological surface maps. In addition, analysis of drainage patterns and erosional features is used to understand …

Modern And Late Holocene Wind Regimes Over The Great Plains (Central U.S.A.), Rebecca L. Schmeisser, David B. Loope, Joseph A. Mason

Department of Earth and Atmospheric Sciences: Faculty Publications

The Great Plains of the central United States contain numerous presently stabilized dune fields that were active during the late Holocene. The most recent period of reactivation occurred about 700–1000 years ago during the Medieval Climatic Anomaly, a period of frequent, severe drought recognized throughout the North American West. Dune orientations and internal bedding preserve information about paleowinds from this time period. We compared paleowind information with modern winds and potential sand transport analyzed from meteorological data. While both reconstructed paleowinds and modern winds include a strong northwesterly component over the northern to central portions of the Great Plains, a …

Coupled Carbon Isotopic And Sedimentological Records From The Permian System Of Eastern Australia Reveal The Response Of Atmospheric Carbon Dioxide To Glacial Growth And Decay During The Late Paleozoic Ice Age, Lauren P. Birgenheier, Tracy D. Frank, Christopher R. Fielding, Michael C. Rygel

Department of Earth and Atmospheric Sciences: Faculty Publications

Proxy geochemical records from high-latitude, ice-proximal deposits have the potential to provide key insights into past icehouse climates, but such records are rare. The Permian System of eastern Australia contains a rich record of environmental and climatic changes that occurred in areas proximal to glaciation during the acme and waning stages of the late Paleozoic ice age. Within this succession, a wealth of fine-grained, organic matter-rich facies provides an opportunity to construct a bulk δ¹³C_org record that records changes in atmospheric CO₂ through the Permian. Fluctuations in δ¹³C_org track changes in climate determined …

Climatic And Environmental Controls On The Occurrence And Distributions Of Long Chain Alkenones In Lakes Of The Interior United States, Jaime L. Toney, Yongsong Huang, Sherilyn C. Fritz, Paul A. Baker, Eric Grimm, Paul Nyren

Department of Earth and Atmospheric Sciences: Faculty Publications

Long chain alkenones (LCA) are temperature-sensitive lipids with great potential for quantitative reconstruction of past continental climate. We conducted the first survey for alkenone biomarkers from 55 different lakes in the Northern Great Plains and Nebraska Sand Hills of the United States. Among those surveyed, we found 13 lakes that contain LCAs in the surface sediments. The highest concentrations of alkenones in sediments are found in cold (mean annual air temperature ~11 °C versus 17 °C in our warmest sites), brackish to mesosaline (salinity = 8.5–9.7 g/L), and alkaline (pH = 8.4–9.0) lakes with high concentrations of sodium and sulfate. …

Combined Use Of Frequency-Domain Electromagnetic And Electrical Resistivity Surveys To Delineate Near-Lake Groundwater Flow In The Semi-Arid Nebraska Sand Hills, Usa, John T. Ong, John W. Lane Jr., Vitaly A. Zlotnik, Todd Halihan, Eric A. White

Department of Earth and Atmospheric Sciences: Faculty Publications

A frequency-domain electromagnetic (FDEM) survey can be used to select locations for the more quantitative and labor-intensive electrical resistivity surveys. The FDEM survey rapidly characterized the groundwaterflow directions and configured the saline plumes caused by evaporation from several groundwater-dominated lakes in the Nebraska Sand Hills, USA. The FDEM instrument was mounted on a fiberglass cart and towed by an all-terrain vehicle, covering about 25km/day. Around the saline lakes, areas with high electrical conductivity are consistent with the regional and local groundwater flow directions. The efficacy of this geophysical approach is attributed to: the high contrast in electrical conductivity between various …

Salinity Dynamics Of Discharge Lakes In Dune Environments: Conceptual Model, Vitaly A. Zlotnik, Neville I. Robinson, Craig T. Simmons

Department of Earth and Atmospheric Sciences: Faculty Publications

Lakes of varying salinity are ubiquitous in dune environments with semiarid climates. Often these lakes become solute traps due to specific groundwater flow conditions. Over geological time after emergence of such lakes, the groundwater flow and mass transport processes lead to accumulation of solutes. This salinity increase can result in mineral deposition and free convection from lakes. However, high solute concentrations in these lakes are often not observed. We propose a conceptual model that estimates the lake salinity dynamics and yields concentration profiles beneath the lakes over centennial and millennial scales. Unlike previous approaches, a simple mathematical model is proposed …

Effects Of Irrigated Agroecosystems: 1. Quantity Of Soil Water And Groundwater In The Southern High Plains, Texas, B. R. Scanlon, R. C. Reedy, J. B. Gates

Department of Earth and Atmospheric Sciences: Faculty Publications

Although irrigated agriculture is the primary consumer of global groundwater resources, information on recharge rates and sustainable irrigation is limited. The study objective was to fingerprint irrigation return flow to quantify percolation/recharge and to estimate sustainable irrigation levels. This paper focuses on water quantity; a companion paper addresses water quality. Soil samples from 13 boreholes drilled beneath irrigated agroecosystems in the southern High Plains were analyzed for matric potential and waterextractable Cl and NO₃. Unsaturated zone pore water beneath irrigated agroecosystems can be fingerprinted by higher matric potentials (wetter soils, median mp: −40 m) and higher NO_{3 …}

Effects Of Lightning And Other Meteorological Factors On Fire Activity In The North American Boreal Forest: Implications For Fire Weather Forecasting, David Peterson, Jun Wang, Charles Ichoku, Lorraine Remer

Department of Earth and Atmospheric Sciences: Faculty Publications

The effects of lightning and other meteorological factors on wildfire activity in the North American boreal forest are statistically analyzed during the fire seasons of 2000–2006 through an integration of the following data sets: the MODerate Resolution Imaging Spectroradiometer (MODIS) level 2 fire products, the 3-hourly 32-km gridded meteorological data from North American Regional Reanalysis (NARR), and the lightning data collected by the Canadian Lightning Detection Network (CLDN) and the Alaska Lightning Detection Network (ALDN). Positive anomalies of the 500 hPa geopotential height field, convective available potential energy (CAPE), number of cloud-to-ground lightning strikes, and the number of consecutive dry …

A New Small-Bodied Species Of Palaeonictis (Creodonta, Oxyaenidae) From The Paleocene-Eocene Thermal Maximum, Stephen G. B. Chester, Jonathan I. Bloch, Ross Secord, Doug M. Boyer

Department of Earth and Atmospheric Sciences: Faculty Publications

Oxyaenid creodonts are extinct carnivorous mammals known from the Paleogene of North America, Europe, and Asia. The genus Palaeonictis is represented by three species that together span the late Paleocene to early Eocene of North America, and at least one species from the early Eocene of Europe. Previously, only a single trigonid of Palaeonictis was known from the interval encompassing the Paleocene-Eocene Thermal Maximum (PETM) in North America. We describe Palaeonictis wingi sp. nov. from the PETM in the Cabin Fork drainage, southeastern Bighorn Basin, Wyoming, based on associated right and left dentaries with P₂-M₂. Palaeonictis …

“An Overview Of The Amazonian Aerosol Characterization Experiment 2008 (Amaze-08)” Published In Atmos. Chem. Phys., 10, 11415-11438, 2010, S. T. Martin, M. O. Andreae, D. Althausen, P. Artaxo, H. Baars, S. Borrmann, Q. Chen, D. K. Farmer, A. Guenther, S. S. Gunthe, J. L. Jimenez, T. Karl, K. Longo, A. Manzi, T. Muller, T. Pauliquevis, M. D. Petters, A. J. Prenni, U. Poschl, L. V. Rizzo, J. Schneider, J. N. Smith, E. Swietlicki, J. Tota, A. Wiedensohler, S. R. Zorn

Department of Earth and Atmospheric Sciences: Faculty Publications

No abstract provided.

Inferring Lake Depth Using Diatom Assemblages In The Shallow, Seasonally Variable Lakes Of The Nebraska Sand Hills (Usa): Calibration, Validation, And Application Of A 69-Lake Training Set, Avery L. C. Shinneman, Danuta M. Bennett, Sherilyn C. Fritz, Jens Schmieder, Daniel R. Engstrom, Aris Efting, John Holz

Department of Earth and Atmospheric Sciences: Faculty Publications

The Nebraska Sand Hills are a distinctive eco-region in the semi-arid Great Plains of the western United States. The water table underlying the Sand Hills is part of the High Plains/ Ogallala aquifer, an important water resource for the central Great Plains. Lake levels are affected directly by fluctuations in the water table, which is recharged primarily by local precipitation and responds quickly to climatically induced changes in regional water balance. Instrumental records are available for only 50–100 years, and paleolimnological data provide important insights into the extremes and variability in moisture balance over longer time scales. A set of …

Zebulon Pike: Great American Explorer Or Climate Spy?, Merlin P. Lawson, Randall Cerveny, Cary Mock

Department of Earth and Atmospheric Sciences: Faculty Publications

Zebulon Pike is known in history books as one of America’s heroes—a great explorer whose adventures in the American West rivaled the Lewis and Clark Expedition and who became the namesake for Colorado’s Pike’s Peak. But what if the history books got it wrong, and Pike was actually not the hero everyone thinks he is? What if he was actually a spy carrying out a secret mission, or a scoundrel interested in overthrowing the American government and helping to carve a new empire out of the North American Southwest? Evidence from Pike’s famed expedition in 1806-1807 points to the possibility …

Collapse Of The Maya: Could Deforestation Have Contributed?, Robert Oglesby, Thomas L. Sever, William Saturno, David J. Erickson Iii, Jayanthi Srikishen

Department of Earth and Atmospheric Sciences: Faculty Publications

The collapse of the Maya civilization during the ninth century A.D. is a major conundrum in the history of mankind. This civilization reached a spectacular peak but then almost completely collapsed in the space of a few decades. While numerous explanations have been put forth to explain this collapse, in recent years, drought has gained favor. This is because water resources were a key for the Maya, especially to ensure their survival during the lengthy dry season that occurs where they lived. Natural drought is a known, recurring feature of this region, as evidenced by observational data, reconstructions of past …

Effects Of Irrigated Agroecosystems: 2. Quality Of Soil Water And Groundwater In The Southern High Plains, Texas, B. R. Scanlon, J. B. Gates, R. C. Reedy, W. A. Jackson, J. P. Bordovsky

Department of Earth and Atmospheric Sciences: Faculty Publications

Trade‐offs between water‐resource depletion and salinization need to be understood when promoting water‐conservative irrigation practices. This companion paper assesses impacts of groundwater‐fed irrigation on soil water and groundwater quality using data from the southern High Plains (SHP). Unsaturated zone soil samples from 13 boreholes beneath irrigated agroecosystems were analyzed for water‐extractable anions. Salt accumulation in soils varies with irrigation water quality, which ranges from low salinity in the north (median Cl: 21 mg/L) to higher salinity in the south (median Cl: 180 mg/L). Large Cl bulges under irrigated agroecosystems in the south are similar to those under natural ecosystems, but …

Influence Of The Arctic Oscillation On Central United States Summer Rainfall, Qi Hu, Song Feng

Department of Earth and Atmospheric Sciences: Faculty Publications

Effects of the Arctic oscillation (AO) on summer rainfall variability in the central United States are examined in order to improve understanding and prediction of the interannual variation in the summer rainfall. Major results show persistent AO effects that resulted in less summer rainfall in the central United States during the positive phase of the AO and more rainfall during the negative AO phase. These effects are most prominent at the interannual time scale. The key physical processes connecting the AO with the rainfall variations are shown in changes in latitudinal location of the midlatitude upper tropospheric westerly jet over …

Response Of River‐Dominated Delta Channel Networks To Permanent Changes In River Discharge, Doug Edmonds, Rudy Slingerland, Jim Best, Dan Parsons, Norman D. Smith

Department of Earth and Atmospheric Sciences: Faculty Publications

Using numerical experiments, we investigate how river‐dominated delta channel networks are likely to respond to changes in river discharge predicted to occur over the next century as a result of environmental change. Our results show for a change in discharge up to 60% of the initial value, a decrease results in distributary abandonment in the delta, whereas an increase does not significantly affect the network. However, an increase in discharge beyond a threshold of 60% results in channel creation and an increase in the density of the distributary network. This behavior is predicted by an analysis of an individual bifurcation …

Collapse Of The Maya: Could Deforestation Have Contributed?, Robert J. Oglesby, Thomas L. Sever, William Saturno, David J. Erickson Iii, Jayanthi Srikishen

Department of Earth and Atmospheric Sciences: Faculty Publications

The collapse of the Maya civilization during the ninth century A.D. is a major conundrum in the history of mankind. This civilization reached a spectacular peak but then almost completely collapsed in the space of a few decades. While numerous explanations have been put forth to explain this collapse, in recent years, drought has gained favor. This is because water resources were a key for the Maya, especially to ensure their survival during the lengthy dry season that occurs where they lived. Natural drought is a known, recurring feature of this region, as evidenced by observational data, reconstructions of past …

Response Of River‐Dominated Delta Channel Networks To Permanent Changes In River Discharge, Doug Edmonds, Rudy Slingerland, Jim Best, Dan Parsons, Norm Smith

Department of Earth and Atmospheric Sciences: Faculty Publications

Using numerical experiments, we investigate how river‐dominated delta channel networks are likely to respond to changes in river discharge predicted to occur over the next century as a result of environmental change. Our results show for a change in discharge up to 60% of the initial value, a decrease results in distributary abandonment in the delta, whereas an increase does not significantly affect the network. However, an increase in discharge beyond a threshold of 60% results in channel creation and an increase in the density of the distributary network. This behavior is predicted by an analysis of an individual bifurcation …

Synthesis Of Satellite (Modis), Aircraft (Icartt), And Surface (Improve, Epa‐Aqs, Aeronet) Aerosol Observations Over Eastern North America To Improve Modis Aerosol Retrievals And Constrain Surface Aerosol Concentrations And Sources, Easan Drury, Daniel J. Jacob, Robert J. D. Spurr, Jun Wang, Yohei Shinozuka, Bruce E. Anderson, Antony D. Clarke, Jack Dibb, Cameron Mcnaughton, Rodney Weber

Department of Earth and Atmospheric Sciences: Faculty Publications

We use an ensemble of satellite (MODIS), aircraft, and ground‐based aerosol observations during the ICARTT field campaign over eastern North America in summer 2004 to (1) examine the consistency between different aerosol measurements, (2) evaluate a new retrieval of aerosol optical depths (AODs) and inferred surface aerosol concentrations (PM_2.5) from the MODIS satellite instrument, and (3) apply this collective information to improve our understanding of aerosol sources. The GEOS‐Chem global chemical transport model (CTM) provides a transfer platform between the different data sets, allowing us to evaluate the consistency between different aerosol parameters observed at different times and …

Melting Alpine Glaciers Enrich High-Elevation Lakes With Reactive Nitrogen, Jasmine E. Saros, Kevin C. Rose, David W. Clow, Verlin C. Stevens, Andrea B. Nurse, Heather A. Arnett, Jeffery R. Stone, Craig E. Williamson, Alexander P. Wolfe

Department of Earth and Atmospheric Sciences: Faculty Publications

Alpine glaciers have receded substantially over the last century in many regions of the world. Resulting changes in glacial runoff not only affect the hydrological cycle, but can also alter the physical (i.e., turbidity from glacial flour) and biogeochemical properties of downstream ecosystems. Here we compare nutrient concentrations, transparency gradients, algal biomass, and fossil diatom species richness in two sets of high-elevation lakes: those fed by snowpack melt alone (SF lakes) and those fed by both glacial and snowpack meltwaters (GSF lakes). We found that nitrate (NO₃^-) concentrations in the GSF lakes were 1-2 orders of magnitude …

Centennial Eolian Cyclicity In The Great Plains, Usa: A Dominant Climate Pattern Of Wind Transport Over The Past 4000 Years?, Antje Schwalb, Walter E. Dean, Sherilyn C. Fritz, Christoph E. Geiss, Bernd Kromer

Department of Earth and Atmospheric Sciences: Faculty Publications

Proxy evidence at decadal resolution from Late Holocene sediments from Pickerel Lake, northeastern South Dakota, shows distinct centennial cycles (400-700 years) in magnetic susceptibility; contents of carbonate, organic carbon, and major elements; abundance in ostracodes; and δ¹⁸O and δ¹³C values in calcite. Proxies indicate cyclic changes in eolian input, productivity, and temperature. Maxima in magnetic susceptibility are accompanied by maxima in aluminum and iron mass accumulation rates (MARs), and in abundances of the ostracode Fabaeformiscandona rawsoni. This indicates variable windy, and dry conditions with westerly wind dominance, including during the Medieval Climate Anomaly. Maxima in …

Millennial-Scale Climate Variability During The Last Glacial Period In The Tropical Andes, Sherilyn C. Fritz, P. A. Baker, E. Ekdahl, G. O. Seltzer, L. R. Stevens

Department of Earth and Atmospheric Sciences: Faculty Publications

Millennial-scale climate variation during the Last Glacial period is evident in many locations worldwide, but it is unclear if such variation occurred in the interior of tropical South America, and, if so, how the low-latitude variation was related to its high-latitude counterpart. A high-resolution record, derived from the deep drilling of sediments on the floor of Lake Titicaca in the southern tropical Andes, is presented that shows clear evidence of millennial-scale climate variation between ~60 and 20 ka BP. This variation is manifested by alternations of two interbedded sedimentary units. The two units have distinctive sedimentary, geochemical, and paleobiotic properties …

Groundwater Recharge In Natural Dune Systems And Agricultural Ecosystems In The Thar Desert Region, Rajasthan, India, Bridget Scanlon, Abhijit Mukherjee, John B. Gates, Robert C. Reedy, Amarendra K. Sinha

Department of Earth and Atmospheric Sciences: Faculty Publications

Water and nutrient availability for crop production are critical issues in (semi)arid regions. Unsaturated-zone Cl tracer data and nutrient (NO₃ and PO₄) concentrations were used to quantify recharge rates using the Cl mass balance approach and nutrient availability in the Thar Desert, Rajasthan, India. Soil cores were collected in dune/interdune settings in the arid Thar Desert (near Jaisalmer) and in rain-fed (nonirrigated) and irrigated cropland in the semiarid desert margin (near Jaipur). Recharge rates were also simulated using unsaturated zone modeling. Recharge rates in sparsely vegetated dune/interdune settings in the Jaisalmer study area are 2.7-5.6 mm/year (2-3% …

Stratigraphic Signature Of The Late Palaeozoic Ice Age In The Parmeener Supergroup Of Tasmania, Se Australia, And Inter-Regional Comparisons, Christopher R. Fielding, Tracy D. Frank, John L. Isbell, Lindsey C. Henry, Eugene W. Domack

Department of Earth and Atmospheric Sciences: Faculty Publications

Recent research in eastern Australia has established that rather than being a single, long-lived epoch, the late Palaeozoic Ice Age comprised a series of glacial intervals each 1–8 million years in duration, separated by non-glacial intervals of comparable duration. In order to test whether the glacial events recognized in New South Wales and Queensland have broader extent, we conducted a reappraisal of the Parmeener Supergroup of Tasmania, southeast Australia. A facies analysis of the Pennsylvanian to Permian section was carried out, allowing rationalization of the succession into four recurrent facies associations: a) glacigenic facies association, restricted to the basal Pennsylvanian/earliest …

A Study Of Fold Characteristics And Deformation Style Using The Evolution Of The Land Surface: Zagros Simply Folded Belt, Iran, Caroline M. Burberry, John W. Cosgrove, Jian-Guo Liu

Department of Earth and Atmospheric Sciences: Faculty Publications

Deformation styles within a fold-thrust belt can be understood in terms of the spatial organization and geometry of the fold structures. In young fold-thrust belts such as the Zagros, this geometry is reflected topographically by concordant landform morphology. Thus, the distribution of deformation structures can be characterized using satellite image analysis, digital elevation models, the drainage network and geomorphological indicators. The two distinct fold types considered in this study (fault-bend folds and detachment folds) both trending NW-SE, interact with streams flowing NE-SW from the High Zagros Mountains into the Persian Gulf. Multiple abandoned stream channels cross fault-bend folds related to …

Tetrapod Fauna Of The Lowermost Usili Formation (Songea Group, Ruhuhu Basin) Of Southern Tanzania, With A New Burnetiid Record, Christian A. Sidor, Kenneth D. Angielczyk, D. Marie Weide, Roger M. H. Smith, Sterling J. Nesbitt, Linda A. Tsuji

Department of Earth and Atmospheric Sciences: Faculty Publications

Vertebrate fossils from the Ruhuhu Basin of southern Tanzania have been known for over 75 years, but the details of their stratigraphic distribution remain imperfectly understood. Recent fieldwork in the Upper Permian Usili Formation (Songea Group) has led to the discovery of a tetrapod assemblage in a conglomeratic unit at its base. The fossils are concentrated in matrix-supported intraformational clay pebble conglomerates interpreted as mass flow deposits in wide, shallow channels in the distal reaches of an alluvial fan. Included in this new collection are fossils representing the first record of a burnetiid therapsid from Tanzania. The anatomy of the …

Improved Algorithm For Modis Satellite Retrievals Of Aerosol Optical Thickness Over Land In Dusty Atmosphere: Implications For Air Quality Monitoring In China, Jun Wang, Xiaoguang Xu, R. Spurr, Yuxuang Wang, Easan Drury

Department of Earth and Atmospheric Sciences: Faculty Publications

A new algorithm, using the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite reflectance and aerosol single scattering properties simulated from a chemistry transport model (GEOS-Chem), is developed to retrieve aerosol optical thickness (AOT) over land in China during the spring dust season. The algorithmfirst uses a “dynamic lower envelope” approach to sample theMODIS dark-pixel reflectance data in lowAOT conditions, to derive the local surface visible (0.65 μm)/near infrared (NIR, 2.1 μm) reflectance ratio. Joint retrievals of AOT at 0.65 μm and surface reflectance at 2.1 μm are then performed, based on the time, location, and spectraldependent single scattering properties of the …

Coupled Collaborative In-Class Activities And Individual Follow-Up Homework Promote Interactive Engagement And Improve Student Learning Outcomes In A College-Level Environmental Geology Course, Leilani Arthurs, Alexis Templeton

Department of Earth and Atmospheric Sciences: Faculty Publications

Interactive engagement pedagogies that emerge from a constructivist model of teaching and learning are often a challenge to implement in larger classes for a number of reasons including the physical layout of the classroom (e.g. fixed chairs in an amphitheater-style room), the logistics of organizing a large number of students into small peer-learning groups, the ability of a single instructor to personally interact with each of many small groups, and the design of small group activities that are engaging and facilitate student learning. For a large introductory-level Environmental Geology college course, 5 coupled collaborative class-long in-class activities and individual follow-up …

Evolution Of The Cretaceous Calcareous Nannofossil Genus Eiffellithus And Its Biostratigraphic Significance, J. L. Shamrock, David K. Watkins

Department of Earth and Atmospheric Sciences: Faculty Publications

The calcareous nannofossil genus Eiffellithus is an important taxon of mid- to Upper Cretaceous marine sediments in biostratigraphy and paleoceanography. The definition of species within Eiffellithus have been both broadly interpreted and variably applied by nannofossil workers. This is particularly true for the Eiffellithus eximius plexus. While the taxonomy of mid-Cretaceous Eiffellithus species has recently been well-defined, the remaining 35 m.y. history of the genus has not been closely examined. Our investigation of Cenomanian to Maastrichtian sediments from the Western Interior Seaway, Gulf of Mexico, and Western Atlantic gives rise to six new species of Eiffellithus that can be reliably …