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Browsing by Author "Ethridge, Frank G., advisor"

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    Lower tertiary stratigraphy in Katmai National Park, Alaska: a lithologic and petrographic study
    (Colorado State University. Libraries, 1994) Houston, William S., author; Ethridge, Frank G., advisor; Lee, Robert E., committee member; Flores, Romeo M., committee member
    Seacliff s in Katmai National Park have been mapped by prior workers as the Eocene(?) West Foreland Formation and the Oligocene(?) Hemlock Conglomerate and/or equivalents. The outcrops comprise a thick sequence of non-marine conglomerates, sandstones, siltstones, shales and coals that were deposited in low to high sinuosity fluvial channels and associated floodplain environments. The sediments were deposited in a fore-arc basin developed during the evolution of the Mesozoic-Cenozoic arc-trench system of the northeast Pacific region. Lithic arenites, the dominant sandstone type, have major framework constituents of quartz, volcanic and metamorphic rock fragments, chert, and plagioclase. Minor constituents include polycrystalline quartz, potassium feldspars, micas and accessory minerals. The majority of samples are texturally sub mature to mature. Sediment from proximal source terrains largely dictated sandstone texture and composition. Systematic vertical trends in texture or composition were not observed. The dominant source terrain for both formations was the paleo-Alaska Range volcanic arc to the west. Metamorphic sediments were derived from subduction complexes to the east, however, that source was commonly masked by an overwhelming influx of volcanic material. Authigenic minerals include calcite, phyllosilicates and iron oxides. All three are pore-filling, but only phyllosilicates and iron oxides are pore-lining. The most abundant phyllosilicate is chlorite which occurs as grain coats and in radiating and microcrystalline pore-fill phases. Compaction and/or cementation has completely occluded all primary pore space. Minimal secondary porosity has been created by dissolution of detrital grains and cements, and by micro fractures. A progressive sequence of diagenetic features resembles that of paragenetic sequences developed for formations in other arc-related basins. This suggests a main-line diagenetic sequence for volcanic-rich sediments deposited in fore-arc basins. The sequence appears to be independent of whether the depositional setting is marine or non-marine, and comprises: (1) compaction and development of clay coats; (2) calcite cementation; (3) cementation by chlorite and/or other phyllosilicates; and (4) complex replacement and alteration.
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    Sequence stratigraphic framework for top seal development: examples from the Skull Creek and Graneros shales, Denver basin
    (Colorado State University. Libraries, 1999) Edwards, Kimberly, K., author; Sutton, Sally J., advisor; Ethridge, Frank G., advisor; Almon, William R., committee member
    In general, the distal open marine shelf setting, typified by the Graneros Shale produces a rock with a greater and more uniform seal capacity relative to the rocks of a proximal open marine shelf setting, such as those of the Skull Creek Shale. A distal setting, which usually corresponds to the time of maximum transgression, may produce better seals because there is less coarse clastic sediment input, which allows slow deposition of clays from suspension to be the dominant depositional process. In this study, the higher capacity seal rocks occur in the upper parts of the TST, either within the condensed section or below it. The Skull Creek locations show seal occurrence to be stratigraphically higher on depositional topographic highs, and lower in areas that were topographically low at the time of deposition. Top seal capacity was quantified with mercury injection capillary pressure (MICP) analysis. Other physical characteristics of these marine shales were studied but only porosity, permeability, total clay, and hydrogen index consistently demonstrated a significant correlation with seal capacity in both units. Shales that are well laminated with a high percentage of total clay and/or total organic carbon with a type I-II (marine) kerogen may or may not qualify as the best seal. Top seal capacity may be more a function of rock fabric rather than mineralogy. For example, two samples may have exactly the same amount of quartz, as shown by XRD analysis, but thin section examination reveals that the majority of quartz in one sample is present as grains and in the other sample as cement. Samples with cement usually provide a better seal because they decrease the pore throat diameter, thus increasing the amount of hydrocarbons that can be trapped. Seal quality in both the Skull Creek and Graneros Shales is quite variable throughout each of the facies within the TST deposits.