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Articles 1 - 11 of 11
Full-Text Articles in Physical Sciences and Mathematics
Neogene And Quaternary Lacustrine Diatom Biochronology, Western Usa, William Krebs, J. Platt Bradbury, Edward Theriot
Neogene And Quaternary Lacustrine Diatom Biochronology, Western Usa, William Krebs, J. Platt Bradbury, Edward Theriot
United States Geological Survey: Staff Publications
Neogene and Quaternary lacustrine diatomaceous deposits are numerous in the western United States, particularly in the Great Basin. Some of these sediments are interbedded with volcanic rocks that have been dated radiometrically or by the fssion track method. Fossil lacustrine diatom floras can thus be arranged in geochronological order. By this means, a biochronological pattern of lacustrine diatom evolution has emerged: obligate nonmarine Actinocyclus Ehrenberg (Family Hemidiscaceae) appeared in the early Miocene and attained maximum diversity in the middle middle Miocene. A single species of non-marine Actinocyclus persisted to the end of the middle Miocene. Only two species of marine …
Diatoms And Tonsteins As Paleoenvironrnental And Paleodepositional Indicators In A Miocene Coal Bed, Costa Rica, J. David Sanchez, J. Platt Bradbury, Bruce F. Bohor, Donald A. Coates
Diatoms And Tonsteins As Paleoenvironrnental And Paleodepositional Indicators In A Miocene Coal Bed, Costa Rica, J. David Sanchez, J. Platt Bradbury, Bruce F. Bohor, Donald A. Coates
United States Geological Survey: Staff Publications
Fresh-water diatoms are present in coal, and tonsteins (altered volcanic ash) are interbedded with the coal, in the Miocene Venado Formation on the southwest margin of the Limon Basin, in Provincia Alajuela, northern Costa Rica. The Venado Formation is composed of more than 300 m of mudstone, siltstone, sandstone, limestone, volcaniclastics, and coal beds. The coal beds are of unknown lateral extent and mainly occur in the middle part of the formation. The Pataste coal bed occurs near the middle of the formation and is divided into three parts by two tonstein layers. The abundance of biogenic opaline material (diatoms) …
Patterns Of Dental Evolution In Early Eocene Anaptomorphine Primates (Omomyidae) From The Bighorn Basin, Wyoming, Thomas M. Bown, Kenneth D. Rose
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 …
Integration Of Channel And Floodplain Suites, Developmental Sequence And Lateral Relations Of Alluvial Paleosols, Thomas M. Bown, Mary J. Krause
Integration Of Channel And Floodplain Suites, Developmental Sequence And Lateral Relations Of Alluvial Paleosols, Thomas M. Bown, Mary J. Krause
United States Geological Survey: Staff Publications
The lower Eocene Willwood Formation of the Bighorn Basin, northwest Wyoming, consists of about 770 m of alluvial rocks that exhibit extensive mechanical and geochemical modifications resulting from Eocene pedogenesis. Willwood paleosols vary considerably in their relative degrees of maturity; maturity is defined as stage of development as a function of the amount of time required to form. Five arbitrary stages are proposed to distinguish these soils of different maturities in the Willwood Formation. Stage 1 soils, the least mature, are entisols; stage 2 and stage 3 soils are intermediate in maturity and are probably alfisols; and stage 4 and …
Sedimentology Of The Upper Triassic Chinle Formation Southeastern Utah: Paleoclimatic Implications, Russell F. Dubiel
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 …
Lungfish Burrows In The Upper Triassic Chinle And Dolores Formations, Colorado Plateau, Russell F. Dubiel, Robert H. Blodgett, Thomas M. Bown
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 …
Stable Isotope Compositions Of Fossil Mollusks From Southern California: Evidence For A Cool Last Interglacial Ocean, Daniel R. Muhs, T. Kurtis Kyser
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 …
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
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 …
Stockwork Tungsten (Scheelite)-Molybdenum Mineralization, Lake George, Southwestern New Brunswick, Robert R. Seal Ii, Alan Clark, Charles Morrissy
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 …
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
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 …
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
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 …