PLIO-PLEISTOCENE GLACIAL DEPOSITS IN NORTHEASTERN NEBRASKA: NEW EXPOSURES AND INTERPRETATIONS

Recent interpretation of oxygen isotopic data for benthic and planktonic foraminifera recovered during ocean drilling programs suggest that world ice volume was greater than the ice volume of 18 thousand years ago (Late Wisconsinan) approximately 2.5 million years ago (Prentice and Matthews, Geology, November, 1988). This agrees well With biostratigraphic and paleoecologic interepretations drawn from sediment cores obtained from the Arctic Ocean Basin. The latter data suggest complete ice cover of the basin during the period 2.2-2.4 million years ago (Scott et at., G.S.A. Bulletin, February, 1989)

Pamphlet to Accompany Geologic Map GMC-34: Geologic Map of the O’Neill 1º x 2º Quadrangle, Nebraska, with Configuration Maps of Surfaces of Formations

This map is necessarily generalized. It is based primarily on data from 7.5’ surficial geologic quadrangle maps of the map area prepared by the authors principally from 1991 to 2000, from Voorhies (unpub. data, 1974), as well as data from test-hole drilling done across the quadrangle by the Conservation and Survey Division, University of Nebraska, and its cooperators over many years since the 1930s. For more detailed information, consult the geologic data files of the Conservation and Survey Division, School of Natural Resources, University of Nebraska-Lincoln. The quadrangle is mostly covered by vegetation and Holocene sediments. Limited good exposures of older sediments and bedrock occur usually in road cuts, in quarry and pit excavations, on valley sides, on stream and river cut banks, and in isolated erosional remnants on uplands. Users of this map should remember that the scale of the map is small and allows only a general picture of the geology of the quadrangle to be depicted. Users should check with the authors regarding specific sites and, if necessary, do field checks of these sites. As new data become available the authors intend to update the data sets used in preparation of this quadrangle text and maps and to issue refined versions, if necessary. The earliest geologic map that included part of the study area was published by Charles Lyell in 1845 (Diffendal, 1993). Other geologic maps at different scales that include all or parts of the map area are by Darton (1899, 1905), Condra (1908), Schulte (1952), Mendenhall (1953), Lampshire (1956), Burchett (1986), Weeks and Gutentag, (1981), Weeks and others (1988), Swinehart and others (1994), and Diffendal and Voorhies (1994). Geologic maps of adjacent areas in Nebraska and South Dakota include Burchett and others (1975), Burchett and others (1988), Diffendal (1991), and Souders (2000) for Nebraska and Stevenson and Carlson (1950, 1951), Baker and others (1952), Collins and French (1958), Schoon and Sevon (1958), Stevenson and others (1958), and Stevenson and others (1959) for parts of South Dakota. Detailed groundwater investigations and associated stratigraphic test drilling (of parts or all of the map area) were done by Darton (1905), Condra (1908), Reed (1944), Keech and Schreurs (1953, 1954), Cronin and Newport (1956), Reed (1957), Smith (1958), Newport (1959), Souders and Shaffer (1969), Souders (1976), Gutentag and Weeks (1980), Luckey and others (1981), Lawton and Hiergesell (1988), Weeks and others (1988), Pierce (1989), Rahn and David (1989), Burchett and Smith (1992), and Lackey and others (1995, 1998a, 1998b, 2000)

Ashfall Tephra in the Ogallala Group of the Great Plains: Characteristics and Significance

The Miocene Ogallala Group blankets the Great Plains east of the Rocky Mountains. This sheet of largely fluvial deposits, lying downwind of major silicic volcanic fields to the west, was ideally located to receive and preserve tephra from these fields. This investigation brings modern methods of tephrochronlogy to bear on the age and identity of Ogallala tephra. Results indicate that ~40 separate tephra layers, ranging in age from ~16.5–5.0 Ma, in the Ogallala. Most tephra came from Yellowstone hotspot sources. The relative frequency of hotspot tephra in the Ogallala matches that in more proximal regions to the west with peak intensities in the intervals ~16.5−15 Ma nd ~13.0−8.5 Ma. About 30 of the Ogallala tephra are correlated with tephra of known age the the Basin and Range to the west. Using the ages of correlative tephra to the west insight into the age of the Ogallala, the correlation of Ogallala tephra from region to region in the Great Plains, and sedimentation rates within the Ogallala. In the Ogallala sedimentation rates vary. The rates are lowest (3–9 m/Ma) in the Cap Rock Mbr. of the Ash Hollow Fm. along the Niobrara River and in undifferentiated Ogallala strata and in the undifferentiated Ogalala Gp. in NW Kansas. Rates of 40–80 m/Ma characterize the Valentine Fm. beneath the Cap Rock Mbr. Finally, one tephra, the 11.37 Ma Cougar Point Tuff XI, is recognized at 6 localies. This key horizon provides the first detailed structure contours within the Ogallala. These contours show a sharply increasing slope of the Ogallala west of 101° W that reflects the post–6 Ma tilt along the western edge of the Ogallala. East of 101º W the gradients mirror the gradients of the major rivers (1.3 to 1.6 m/km.). West of 101º W gradients increase and reach a maximun of 4.6 m/km at the crest of the Gangplank

Ashfall Tephra in the Ogallala Group of the Great Plains: Characteristics and Significance

The Miocene Ogallala Group blankets the Great Plains east of the Rocky Mountains. This sheet of largely fluvial deposits, lying downwind of major silicic volcanic fields to the west, was ideally located to receive and preserve tephra from these fields. This investigation brings modern methods of tephrochronlogy to bear on the age and identity of Ogallala tephra. Results indicate that ~40 separate tephra layers, ranging in age from ~16.5–5.0 Ma, in the Ogallala. Most tephra came from Yellowstone hotspot sources. The relative frequency of hotspot tephra in the Ogallala matches that in more proximal regions to the west with peak intensities in the intervals ~16.5−15 Ma nd ~13.0−8.5 Ma. About 30 of the Ogallala tephra are correlated with tephra of known age the the Basin and Range to the west. Using the ages of correlative tephra to the west insight into the age of the Ogallala, the correlation of Ogallala tephra from region to region in the Great Plains, and sedimentation rates within the Ogallala. In the Ogallala sedimentation rates vary. The rates are lowest (3–9 m/Ma) in the Cap Rock Mbr. of the Ash Hollow Fm. along the Niobrara River and in undifferentiated Ogallala strata and in the undifferentiated Ogalala Gp. in NW Kansas. Rates of 40–80 m/Ma characterize the Valentine Fm. beneath the Cap Rock Mbr. Finally, one tephra, the 11.37 Ma Cougar Point Tuff XI, is recognized at 6 localies. This key horizon provides the first detailed structure contours within the Ogallala. These contours show a sharply increasing slope of the Ogallala west of 101° W that reflects the post–6 Ma tilt along the western edge of the Ogallala. East of 101º W the gradients mirror the gradients of the major rivers (1.3 to 1.6 m/km.). West of 101º W gradients increase and reach a maximun of 4.6 m/km at the crest of the Gangplank

Caenorhabditis elegans Genomic Response to Soil Bacteria Predicts Environment-Specific Genetic Effects on Life History Traits

With the post-genomic era came a dramatic increase in high-throughput technologies, of which transcriptional profiling by microarrays was one of the most popular. One application of this technology is to identify genes that are differentially expressed in response to different environmental conditions. These experiments are constructed under the assumption that the differentially expressed genes are functionally important in the environment where they are induced. However, whether differential expression is predictive of functional importance has yet to be tested. Here we have addressed this expectation by employing Caenorhabditis elegans as a model for the interaction of native soil nematode taxa and soil bacteria. Using transcriptional profiling, we identified candidate genes regulated in response to different bacteria isolated in association with grassland nematodes or from grassland soils. Many of the regulated candidate genes are predicted to affect metabolism and innate immunity suggesting similar genes could influence nematode community dynamics in natural systems. Using mutations that inactivate 21 of the identified genes, we showed that most contribute to lifespan and/or fitness in a given bacterial environment. Although these bacteria may not be natural food sources for C. elegans, we show that changes in food source, as can occur in environmental disturbance, can have a large effect on gene expression, with important consequences for fitness. Moreover, we used regression analysis to demonstrate that for many genes the degree of differential gene expression between two bacterial environments predicted the magnitude of the effect of the loss of gene function on life history traits in those environments

Male Mating Rate Is Constrained by Seminal Fluid Availability in Bedbugs, Cimex lectularius

Sexual selection, differences in reproductive success between individuals, continues beyond acquiring a mating partner and affects ejaculate size and composition (sperm competition). Sperm and seminal fluid have very different roles in sperm competition but both components encompass production costs for the male. Theoretical models predict that males should spend ejaculate components prudently and differently for sperm and seminal fluid but empirical evidence for independent variation of sperm number and seminal fluid volume is scarce. It is also largely unknown how sperm and seminal fluid variation affect future mating rate. In bedbugs we developed a protocol to examine the role of seminal fluids in ejaculate allocation and its effect on future male mating rate. Using age-related changes in sperm and seminal fluid volume we estimated the lowest capacity at which mating activity started. We then showed that sexually active males allocate 12% of their sperm and 19% of their seminal fluid volume per mating and predicted that males would be depleted of seminal fluid but not of sperm. We tested (and confirmed) this prediction empirically. Finally, the slightly faster replenishment of seminal fluid compared to sperm did not outweigh the faster decrease during mating. Our results suggest that male mating rate can be constrained by the availability of seminal fluids. Our protocol might be applicable to a range of other organisms. We discuss the idea that economic considerations in sexual conflict research might benefit from distinguishing between costs and benefits that are ejaculate dose-dependent and those that are frequency-dependent on the mating rate per se

Electron Transfer Function versus Oxygen Delivery: A Comparative Study for Several Hexacoordinated Globins Across the Animal Kingdom

Caenorhabditis elegans globin GLB-26 (expressed from gene T22C1.2) has been studied in comparison with human neuroglobin (Ngb) and cytoglobin (Cygb) for its electron transfer properties. GLB-26 exhibits no reversible binding for O2 and a relatively low CO affinity compared to myoglobin-like globins. These differences arise from its mechanism of gaseous ligand binding since the heme iron of GLB-26 is strongly hexacoordinated in the absence of external ligands; the replacement of this internal ligand, probably the E7 distal histidine, is required before binding of CO or O2 as for Ngb and Cygb. Interestingly the ferrous bis-histidyl GLB-26 and Ngb, another strongly hexacoordinated globin, can transfer an electron to cytochrome c (Cyt-c) at a high bimolecular rate, comparable to those of inter-protein electron transfer in mitochondria. In addition, GLB-26 displays an unexpectedly rapid oxidation of the ferrous His-Fe-His complex without O2 actually binding to the iron atom, since the heme is oxidized by O2 faster than the time for distal histidine dissociation. These efficient mechanisms for electron transfer could indicate a family of hexacoordinated globin which are functionally different from that of pentacoordinated globins

Demographic History of Indigenous Populations in Mesoamerica Based on mtDNA Sequence Data

The genetic characterization of Native American groups provides insights into their history and demographic events. We sequenced the mitochondrial D-loop region (control region) of 520 samples from eight Mexican indigenous groups. In addition to an analysis of the genetic diversity, structure and genetic relationship between 28 Native American populations, we applied Bayesian skyline methodology for a deeper insight into the history of Mesoamerica. AMOVA tests applying cultural, linguistic and geographic criteria were performed. MDS plots showed a central cluster of Oaxaca and Maya populations, whereas those from the North and West were located on the periphery. Demographic reconstruction indicates higher values of the effective number of breeding females (Nef) in Central Mesoamerica during the Preclassic period, whereas this pattern moves toward the Classic period for groups in the North and West. Conversely, Nef minimum values are distributed either in the Lithic period (i.e. founder effects) or in recent periods (i.e. population declines). The Mesomerican regions showed differences in population fluctuation as indicated by the maximum Inter-Generational Rate (IGRmax): i) Center-South from the lithic period until the Preclassic; ii) West from the beginning of the Preclassic period until early Classic; iii) North characterized by a wide range of temporal variation from the Lithic to the Preclassic. Our findings are consistent with the genetic variations observed between central, South and Southeast Mesoamerica and the North-West region that are related to differences in genetic drift, structure, and temporal survival strategies (agriculture versus hunter-gathering, respectively). Interestingly, although the European contact had a major negative demographic impact, we detect a previous decline in Mesoamerica that had begun a few hundred years before

PLIO-PLEISTOCENE GLACIAL DEPOSITS IN NORTHEASTERN NEBRASKA: NEW EXPOSURES AND INTERPRETATIONS

Recent interpretation of oxygen isotopic data for benthic and planktonic foraminifera recovered during ocean drilling programs suggest that world ice volume was greater than the ice volume of 18 thousand years ago (Late Wisconsinan) approximately 2.5 million years ago (Prentice and Matthews, Geology, November, 1988). This agrees well With biostratigraphic and paleoecologic interepretations drawn from sediment cores obtained from the Arctic Ocean Basin. The latter data suggest complete ice cover of the basin during the period 2.2-2.4 million years ago (Scott et at., G.S.A. Bulletin, February, 1989)

Geologic Framework of the Niobrara River Drainage Basin and Adjacent Areas in South Dakota Generally East of the 100th Meridian West Longitude and West of the Missouri River

General geology and stratigraphy of the Niobrara River drainage basin in Nebraska and adjacent parts of South Dakota generally west of the Missouri River is reviewed. Of particular importance are the correlation of the Long Pine Formation of Pliocene age in Nebraska with the Herrick Gravels in South Dakota, the recognition of the members of the Ogallala Group named by Skinnner, Skinner and Gooris (1968) and by Skinner and Johnson (1984) in the basin, the acceptance of the relationships of the Miocene and older Tertiary units in the basin to those in the part of the study area in South Dakota as proposed by Skinner and Taylor (1967), Skinner, Skinner and Gooris (1968) and by Skinner and Johnson (1984), and the recognition of the Rosebud Formation of the Arikaree Group (Skinner, Skinner, and Gooris, 1968) in the basin. Rocks now included in the Rosebud were placed previously in the White River Group by the Conservation and Survey Division (Burchett , 1986). A refined geologic map of the area shows the currently known distributions of all of the major units, including the Long Pine/Herrick, the Rosebud, and the Chadron formations. none of which has been shown on a map of the study area previously