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Articles 3661 - 3690 of 4538

Full-Text Articles in Earth Sciences

Stockwork Tungsten (Scheelite)-Molybdenum Mineralization, Lake George, Southwestern New Brunswick, Robert R. Seal Ii, Alan Clark, Charles Morrissy Jan 1987

Stockwork Tungsten (Scheelite)-Molybdenum Mineralization, Lake George, Southwestern New Brunswick, Robert R. Seal Ii, Alan Clark, Charles Morrissy

United States Geological Survey: Staff Publications

Scheelite-molybdenite stockwork mineralization constitutes one component of the Lake George polymetallic (Sb-W-Mo-Au-base metal) deposit, a complex hydrothermal center of Late Silurian (ca. 412 m.y.) age in the Fredericton trough of the northern Appalachians. The stockwork, hosted by Silurian graywackes, in part calcareous, is spatially and temporally related to a postkinematic cupola of biotite monzogranite, and its formation overlapped in time with the emplacement of monzogranitic porphyry dikes. Mineralogical and textural evidence indicates that contact metamorphism associated with the cupola had ceased before the initiation of W-Mo mineralization and that it occurred, at pressures of less than 1.75 kb, in two …

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15N/14N Variations In Cretaceous Atlantic Sedimentary Sequences: Implication For Past Changes In Marine Nitrogen Biogeochemistry, Greg H. Rau, Michael A. Arthur, Walter E. Dean Jan 1987

15N/14N Variations In Cretaceous Atlantic Sedimentary Sequences: Implication For Past Changes In Marine Nitrogen Biogeochemistry, Greg H. Rau, Michael A. Arthur, Walter E. Dean

United States Geological Survey: Staff Publications

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds ("black shales") were found to have significantly lower δ15N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have δ15N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have …

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Genesis Of Marine Terrace Soils, Barbados, West Indies: Evidence From Mineralogy And Geochemistry, Daniel R. Muhs, Russell C. Crittenden, John N. Rosholt, Charles A. Bush, Kathleen C. Stewart Jan 1987

Genesis Of Marine Terrace Soils, Barbados, West Indies: Evidence From Mineralogy And Geochemistry, Daniel R. Muhs, Russell C. Crittenden, John N. Rosholt, Charles A. Bush, Kathleen C. Stewart

United States Geological Survey: Staff Publications

Well-developed, clay-rich soils dominated by interstratified kaolinite-smectite are found on the uplifted coral reef terraces on the island of Barbados. The reef limestone is unlikely to have been the soil parent material however, because it is 98 per cent CaCO, and geomorphic evidence argues against the 20 m of reef solution required to produce the soils by this process. The mineralogy of the sand, silt, and clay fractions of the soils, and trace element geochemistry, suggest that aeolian materials carried on the trade winds from Africa, volcanic ash from the island of St. Vincent, and quartz from Tertiary bedrock on …

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Mesodictyon, A New Fossil Genus Of The Centric Diatom Family Thalassiosiraceae From The Miocene Chalk Hills Formation, Western Snake River Plain, Idaho, Edward Theriot, J. Platt Bradbury Jan 1987

Mesodictyon, A New Fossil Genus Of The Centric Diatom Family Thalassiosiraceae From The Miocene Chalk Hills Formation, Western Snake River Plain, Idaho, Edward Theriot, J. Platt Bradbury

United States Geological Survey: Staff Publications

Three new centric diatom species assigned to a new genus are described from Miocene lacustrine deposits of Idaho. Species of the new genus, Mesodictyon, have the areola cribrum in the middle of the loculus, strutted processes and radiating, non-fasciculated striae. The strutted processes of M. magnum (diameter 60-150 μm) have long (2-3 μm) tubular extensions. The strutted processes of M. fovis (diameter 14-80 μm) are in distinct pits near the junction of the face and mantle. The valve face of M. undulatum (diameter 10-44 μm) is weakly tangentially undulate. Preliminary evidence indicates that Mesodictyon has a wide geographic distribution …

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Stable Isotope Compositions Of Fossil Mollusks From Southern California: Evidence For A Cool Last Interglacial Ocean, Daniel R. Muhs, T. Kurtis Kyser Jan 1987

Stable Isotope Compositions Of Fossil Mollusks From Southern California: Evidence For A Cool Last Interglacial Ocean, Daniel R. Muhs, T. Kurtis Kyser

United States Geological Survey: Staff Publications

Stable isotope compositions have been determined for modem mullusks and fossil mollusks collected from uplied marine terraces at three l d t i e s in southern California. By using a paleocliatic model that decouples the temperature and ice-volume signals in ocean water, ocean-water temperatures off southern California are estimated to have been -3.8 °C at ~85 ka, -3.0 °C at ~107 ka, and -2.2 °C at ~125 ka relative to present temperature. These results indicate rather cool conditions during the peak of the last interglacial stage at 125 ka and conflict with results from terrace faunal studies that suggest …

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Lungfish Burrows In The Upper Triassic Chinle And Dolores Formations, Colorado Plateau, Russell F. Dubiel, Robert H. Blodgett, Thomas M. Bown Jan 1987

Lungfish Burrows In The Upper Triassic Chinle And Dolores Formations, Colorado Plateau, Russell F. Dubiel, Robert H. Blodgett, Thomas M. Bown

United States Geological Survey: Staff Publications

Vertical-to-inclined, cylindrical trace fossils that occur in the Upper Triassic Chinle and Dolores Formations on the Colorado Plateau are interpreted to be the casts of lungfish burrows. The casts, which are as much as 11 cm in diameter and as much as 1.6 m long, were formed by passive siliciclastic and carbonate sedimentation into apparently abandoned lungfish burrows. Locally, the burrow fillings are overwhelmingly abundant, and many intersect and have destroyed former burrow fillings. Superposition of bioturbation episodes has obliterated most primary sedimentary structures. This bioturbation has contributed to the mottled coloration and the knobby-weathering texture of the rocks. The …

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Patterns Of Dental Evolution In Early Eocene Anaptomorphine Primates (Omomyidae) From The Bighorn Basin, Wyoming, Thomas M. Bown, Kenneth D. Rose Jan 1987

Patterns Of Dental Evolution In Early Eocene Anaptomorphine Primates (Omomyidae) From The Bighorn Basin, Wyoming, Thomas M. Bown, Kenneth D. Rose

United States Geological Survey: Staff Publications

ABSTRACT--The subfamily Anaptomorphinae contains the oldest and most generalized members of the tarsier-like primates and is the basal group of the extinct family Omomyidae. The best and most continuous record of anaptomorphine history is from rocks of early Eocene (Wasatchian) age in the Bighorn Basin of northwest Wyoming where eight genera and 14 species are recognized. Three of these species are new (Teilhardina crassidens, Tetonius matthewi, Absarokius metoecus), and four other new species are described from elsewhere (Tetonius mckennai, Absarokius gazini, A. australis, Strigorhysis huerfanensis). Teilhardina tenuicula and Absarokius nocerai are …

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Sedimentology Of The Upper Triassic Chinle Formation Southeastern Utah: Paleoclimatic Implications, Russell F. Dubiel Jan 1987

Sedimentology Of The Upper Triassic Chinle Formation Southeastern Utah: Paleoclimatic Implications, Russell F. Dubiel

United States Geological Survey: Staff Publications

The Upper Triassic Chinle Formation in southeastern Utah was deposited in a complex fluvial-deltaic-lacustrine system. The Chinle records the evolution of a continental system in response to variations in climate, tectonics, and sediment supply. Chinle strata represent deposits of fluvial channels and floodplains, lacustrine deltas, lacustrine basins, and lacustrine and playa mudflats. These rocks include a variety of vertebrate, invertebrate, and plant fossils, trace fossils, and paleosols that provide information on depositional environments, water tables, and paleoclimate.

Sedimentologic and paleontologic interpretations both support an interpretation of abundant lakes, streams, and marshes with high, but fluctuating water tables for all but …

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Conservation And Survey Division. 1987. Significant Rises And Declines In Nebraska Groundwater Levels (From Pre-Development As Of Fall 1985)/Registered Irrigation Wells In Nebraska (As Of January 1, 1986), Conservation Survey Division, U.S. Geological Survey Jan 1987

Conservation And Survey Division. 1987. Significant Rises And Declines In Nebraska Groundwater Levels (From Pre-Development As Of Fall 1985)/Registered Irrigation Wells In Nebraska (As Of January 1, 1986), Conservation Survey Division, U.S. Geological Survey

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Nebraska Mineral Operations Review, 1986, Raymond R. Burchett, Duane A. Eversoll Jan 1987

Nebraska Mineral Operations Review, 1986, Raymond R. Burchett, Duane A. Eversoll

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Analysis And Interpretation Of Ice-Deformed Sediments From Harrison Bay, Alaska, Steven A. Fischbein Jan 1987

Analysis And Interpretation Of Ice-Deformed Sediments From Harrison Bay, Alaska, Steven A. Fischbein

Department of Earth and Atmospheric Sciences: Faculty Publications

The surficial sediments present on the continental shelf off the north coast of Alaska in the vicinity of Harrison Bay consist dominantly of fine grained sand, silt, and mud that were deposited during Holocene time. Depositional environments in Harrison Bay range from outer shelf to prodelta and delta front. Ice sediment interaction has overprinted structural deformation on many of the sediments present in Harrison Bay, and has in some cases obliterated the original lithologic continuity of the sediments. Ice related deformation ranges from simple loading features to more complex folded and faulted structures. A hypothetical model has been proposed which …

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Chemical, Physical And Mineralogical Properties Of Mitchell And Tripp Soils In The Nebraska Panhandle, G. A. Uzochukwu, D. T. Lewis Oct 1986

Chemical, Physical And Mineralogical Properties Of Mitchell And Tripp Soils In The Nebraska Panhandle, G. A. Uzochukwu, D. T. Lewis

Nebraska Agricultural Experiment Station: Historical Research Bulletins

Mitchell and Tripp soils are some of the most important agricultural soils in the Nebraska Panhandle. Yet, they have received little attention in terms of their basic chemical, physical, and mineral properties. Management decisions can be made on a more informed basis if this kind of information is available. This study was to acquire the information, with special emphasis on mineralogical properties of the soils and their parent materials. This emphasis was given because it is known that other soils in the region contain volcanic ash in measurable amounts. The presence of volcanic ash in soils has been associated with …

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Cliff-Height And Slope-Angle Relationships In A Chronosequence Of Quaternary Marine Terraces, San Clemente Island, California, Russell Crittenden, Daniel R. Muhs Sep 1986

Cliff-Height And Slope-Angle Relationships In A Chronosequence Of Quaternary Marine Terraces, San Clemente Island, California, Russell Crittenden, Daniel R. Muhs

United States Geological Survey: Staff Publications

Zusammenfassung. Eine Abfolge quartarer Strandterrassen auf ~an Clemente Island, Kalifornien, liefert einen Rahmen fur die quantitative Analyse der Anderungen an vom Meer verlassenen Kustenkliffen als Funktion der Zeit. Es wurde eine Abschatzung der Anwendbarkeit von BUCKNAM & ANDERSON (1979) log-lin~arer Beziehung zwischen Wandhohe und Hangwinkel durchgefuhrt, indem Brandungskliffhohe und maximale Hangwinkel verwendet wurden. Die Ergebnisse zeigen eine regelhafte Zunahme des Hangwinkels mit dem Logarithmus der Kliffhohe, und Kliffe einer bestimmten Hohe zeigen m,it der Zeit eine Abnahmedes maximalen Hangwinkels. 1m ganzen waren die Relationen schwacher als fur FluBterrassen und Bruchstufen in unverfestigten Materialen, aber die Methode kann wahrscheinlich verwendet werden, …

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Moving Under, Around, And Through The Miocene Reconstruction Of Southern California, John Barron Aug 1986

Moving Under, Around, And Through The Miocene Reconstruction Of Southern California, John Barron

United States Geological Survey: Staff Publications

Modern southern California is fragmented by faults that juxtapose blocks with contrasting topographies and differing geologic histories. Many of the tectonic events that have shaped southern California were initiated during the Miocene, as subduction along the ancient trench margin off southern California was replaced by transform (strikeslip) faulting, such as that along the San Andreas fault.

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Effect Of Pre-Burn Artificial Litter And Prescribed Burning On Smooth Brome (Bromus Inermis Leyss), Patricia R. Boehner Aug 1986

Effect Of Pre-Burn Artificial Litter And Prescribed Burning On Smooth Brome (Bromus Inermis Leyss), Patricia R. Boehner

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Paleoclimates In Southwestern Tasmania During The Last 13,000 Years, Vera Markgraf, J. Platt Bradbury, J.R. Busby Aug 1986

Paleoclimates In Southwestern Tasmania During The Last 13,000 Years, Vera Markgraf, J. Platt Bradbury, J.R. Busby

United States Geological Survey: Staff Publications

Plant-sociological and climatic classification of the Australian Nothofagus cunninghamii rain forest provides the basis for a new, semiquantitative approach to interpretations of late-Quaternary paleoclimates from four pollen sequences in southwestern Tasmania. Varying proportions of rain-forest pollen types in the records were related to different modern rain-forest alliances and their specifc climatic regimes, such as Eastern Rain Forest, Leatherwood Rain Forest, and sclerophyllous, Subalpine Rain Forest. According to this interpretation, early Holocene climates were characterized by 1,600 mm annual precipitation and 10°C annual temperature, conditions substantially warmer and drier than previously thought. Maximum precipitation levels of 2,500 mm annually were not …

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Late Pleistocene And Holocene Paleolimnology Of Two Mountain Lakes In Western Tasmania, J. Platt Bradbury Aug 1986

Late Pleistocene And Holocene Paleolimnology Of Two Mountain Lakes In Western Tasmania, J. Platt Bradbury

United States Geological Survey: Staff Publications

The analysis of diatoms from two lake-sediment cores from southwestern Tasmania that span the Pleistocene-Holocene boundary provides insight about paleolimnological and paleoclimatic change in this region. Both Lake Vera (550 m elevation), in west-central Tasmania, and Eagle Tarn (1,033 m elevation), in south-central Tasmania, have lacustrine records that begin about 12,000 years ago. Despite significant differences in location, elevation, and geologic terrane, both lakes have, had similar, as well as synchronous, limnological histories. Each appears to have been larger and more alkaline 12,000 years ago than at present, and both became shallower through time. Fossil diatom assemblages about 11,500 years …

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Improving Nebraska's Near-Real Time Weather-Based Products Through User Interaction, Steven J. Meyer Jul 1986

Improving Nebraska's Near-Real Time Weather-Based Products Through User Interaction, Steven J. Meyer

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Groundwater Levels In Nebraska, 1985, Michael J. Ellis, Darryll T. Pederson Jul 1986

Groundwater Levels In Nebraska, 1985, Michael J. Ellis, Darryll T. Pederson

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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The Population Biology Of Oak Middle Creek Structure 58-B After An Experimental Stocking With Adult Fish: A Three Year Evaluation, Donn A. Rodekohr Jun 1986

The Population Biology Of Oak Middle Creek Structure 58-B After An Experimental Stocking With Adult Fish: A Three Year Evaluation, Donn A. Rodekohr

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Hydrogeology Of Water-Quality Monitoring Transects In An Irrigated Area Of The Eastern Sand Hills, Nebraska, Dennis R. Lawton May 1986

Hydrogeology Of Water-Quality Monitoring Transects In An Irrigated Area Of The Eastern Sand Hills, Nebraska, Dennis R. Lawton

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Environmental And Physiological Effects On Water Use Of Cereal Crops, Joon Kim Mar 1986

Environmental And Physiological Effects On Water Use Of Cereal Crops, Joon Kim

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Interspecific Interactions Of Green Sunfish (Lepomis Cyanellus) And (Creek Chub (Semotilus Atromaculatus) In Small Streams In Southeast Nebraska, Steve L. Schleiger Mar 1986

Interspecific Interactions Of Green Sunfish (Lepomis Cyanellus) And (Creek Chub (Semotilus Atromaculatus) In Small Streams In Southeast Nebraska, Steve L. Schleiger

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Environmental And Physiological Effects On Water Use Of Cereal Crops, Joon Kim Mar 1986

Environmental And Physiological Effects On Water Use Of Cereal Crops, Joon Kim

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Policy Issue Study On Integrated Management Of Surface Water And Groundwater Report, Dayle E. Williamson, Bob Kuzelka Feb 1986

Policy Issue Study On Integrated Management Of Surface Water And Groundwater Report, Dayle E. Williamson, Bob Kuzelka

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Identification And Analysis Of Climatic Fields Through Dot-Density Shading, Stephen J. Lavin, Randall S. Cerveny Jan 1986

Identification And Analysis Of Climatic Fields Through Dot-Density Shading, Stephen J. Lavin, Randall S. Cerveny

Department of Earth and Atmospheric Sciences: Faculty Publications

Gridded matrices of climatic data can be mapped by computer with a variety of symbolization methods, all of which have some shortcomings. A new mapping procedure, dot-density shading, is herein proposed as an alternative mapping form. Dot-density shading produces continuous-appearing dot patterns whose density is proportional to the data. Significant algorithms are those for computing dot numerosity and quasi-random dot placement. A number of application including data error detection and anomaly recognition are discussed.

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Diatom Stratigraphy Of The Lower Pliocene Part Of The Sisquoc Formation, Harris Grade Section, California, John A. Barron, Jack G. Baldau Jan 1986

Diatom Stratigraphy Of The Lower Pliocene Part Of The Sisquoc Formation, Harris Grade Section, California, John A. Barron, Jack G. Baldau

United States Geological Survey: Staff Publications

Lower Pliocene diatoms were studied from the Sisquoc Formation and lowermost Foxen Mudstone, exposed along Hams Grade north of Lompoc, California, to refine the diatom biostratigraphy of post-Monterey Formation sediments in California. Sixty-seven diatom taxa were identified in the 25 samples examined from the 790-m thick (2950-ft) section. The diatoms are assignable to the uppermost Nitzschia reinholdii Zone and Thalassiosira oestrupii Zone of Damn (1981), and five tentative subzones for local correlation are proposed. Regional correlations and taxon occurrence are discussed, and the base of the Nitzschia reinholdii Zone is redefined as at the last occurrence of Thalassionema schraderi.

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Development Of Oriented Lakes In The Eastern Rainbasin Region Of South Central Nebraska, James P. Krueger Jan 1986

Development Of Oriented Lakes In The Eastern Rainbasin Region Of South Central Nebraska, James P. Krueger

School of Natural Resources: Dissertations, Theses, and Student Research

The Eastern Rainbasin region is located on a relatively flat-lying, loess-covered plain. The gently sloping land surface is poorly drained and in places local drainage is toward basins which lack external drainage. In the spring, excell precipitation collects in these basins, forming small lakes and marshes. It is these ephemeral lakes that give the region its name.

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Resource Notes-Spring 1986 Jan 1986

Resource Notes-Spring 1986

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Resource Notes-Summer 1986 Jan 1986

Resource Notes-Summer 1986

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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