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Lower tertiary stratigraphy in Katmai National Park, Alaska: a lithologic and petrographic study




Houston, William S., author
Ethridge, Frank G., advisor
Lee, Robert E., committee member
Flores, Romeo M., committee member

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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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Geology, Stratigraphic -- Tertiary
Geology -- Alaska -- Katmai National Park and Preserve


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