http://hdl.handle.net/1957/7890 Collection contains recent scholarly output of student majors in Geology. Search the Channel search http://ir.library.oregonstate.edu/dspace/simple-search http://hdl.handle.net/1957/9482 Title: Stable isotope investigation of a hydrothermal alteration system : Butte porphyry copper deposit <br/> <br/>Abstract: Typical porphyry-type Cu-Mo mineralization predates and underlies the well-known Main Stage polymetallic veins of the Butte district, Montana. This thesis presents the first systematic study of the isotopic characteristics of the pre-Main Stage K-silicate and sericitic wallrock alteration related to the porphyry Cu-Mo stage. Oxygen and hydrogen isotopic compositions were obtained from hydrous and other silicate minerals of sixty-two samples from the unaltered host rock and ores: four Butte Quartz Monzonite; seven samples from K-silicate alteration; twenty samples of K-silicate alteration affected by late argillic alteration; and twenty-seven samples of gray-sericite alteration. These data support current porphyry Cu-Mo models that the associated hydrothermal fluids that produced pre-Main Stage K-silicate and gray sericite were dominantly magmatic in origin. Butte differs from other porphyry Cu-Mo districts because the widespread Main Stage or younger argillic alteration dominated by meteoric water (öD = -100 to -120%) has partly to totally reset the hydrogen isotopic compositions of hornblende (D = -45 to -l26%) and biotite (öD -61 to -l35%) in the fresh Butte Quartz Monzonite host rock, biotite (D = -47 to -131%o) of the early high temperature K-silicate alteration assemblages, and locally reset the öD values (-25 to -1 l7%o) of sericite (muscovite) of gray-sericite alteration assemblages. The effect of argillic alteration on these minerals was to produce D-depleted isotopic composition (öD = -80 to -140%). Sulfur isotope analyses have been applied to sulfides and anhydrite from forty-seven samples selected from deep drill cores. These include sulfate-sulfide assemblages in veinlets associated with K-silicate alteration selvages and slightly younger quartz-pyrite veinlets associated with gray-sericite alteration selvages. The K-silicate and gray-sericite sulfide values (34S = +0.4 to +4.7 %) presented here are similar to those of Main Stage sulfides reported previously and suggest a conventional "magmatic" value (ö345 about 2 %o) for Butte sulfide-sulfur in the hydrothermal fluid. However, the anhydrite from the K-silicate alteration yields a much heavier 634S value (+ 12.9 %o), therefore, total sulfur (&4Szs %) of the early K-silicate assemblage was likely as heavy as 10 per mil, suggesting a possible crustal component to this relatively oxidized system. <br/> <br/>Description: Graduation date: 2000 http://hdl.handle.net/1957/9481 Title: Surface-subsurface geology of the middle to upper Eocene sedimentary and volcanic rock units, western Columbia County, northwest Oregon <br/> <br/>Abstract: The middle to upper Eocene Tillamook Volcanics form the basement in the Rock Creek - Rocky Point area. These tholeiitic to alkalic basalts, basaltic andesites, and andesites were erupted as shield volcanoes seaward of the strandline ontop of an older deep-marine mudstone unit (Yamhill Formation) and an accreted portion of oceanic seafloor (lower Eocene Siletz River Volcanics). The subaerial flows are predominantly aphyric with subordinate plagioclase-augite porphyritic flows with pilotaxitic texture. The overlying Hamlet formation (informal) is composed of three members which document a marine transgression over subsiding islands of Tilamook Volcanics in the middle to late Eocene. The stratigraphically lowest Roy Creek member is composed of basaltic boulder to cobble conglomerate grading upward into fossiliferous pebbly basaltic sandstone deposited around sea stacks and along a high-energy rocky coastline composed of Tillamook Volcanics. Continued subsidence and transgression resulted in deposition of the Sunset Highway member of the Hamlet formation, which conformably overlies the Roy Creek member. The Sunset Highway member consists of interbedded micaceous arkosic sandstone and siltstone with rare basaltic grit beds occurring near the top of the member. Molluscan fauna, faint low-angle cross-bedding, parallel laminations and bioturbation in these sandstones are interpreted to represent deposition in a high-energy inner shelf environment. The upper Narizian (upper Eocene) Sweet Home Creek member conformably overlies the Sunset Highway member in western Columbia and eastern Clatsop counties and is composed of two lithofacies. The dominant lower facies consists of micromicaceous and carbonaceous silty mudstone which contains abundant Foraniinifera indicative of outer neritic to tipper bathyal water depths. Thin-bedded micaceous arkosic turbidite sandstones in nested channels of the upper facies are locally present near the top of the unit and represent deposits of a channelized shelf-slope break. Abrupt sea level regression coupled with increased sedimentation rates due to tectonic unroofing in source areas in Idaho and Washington resulted in abrupt shallowing of sedimentation before deposition of the overlying Cowlitz Formation (C & W sandstone member). The C & W sandstone in cores from the Mist Gas Field and outcrops in the Rock Creek - Rocky Point area in Columbia County consists of massive to hummocky bedded sandstone with some bioturbated siltstone and coal formed in a delta front complex ranging from brackish-water swamps to storm-wave-dominated lower shoreface environments. Sandstone onlaps basement highs of Tillamook Volcanics (Nehalem arch), resulting in a complicated facies geometry with some intrabasinal basaltic detritus. Sedimentary structures, statistical grain size analysis, and lithofacies associations suggest that strong wave processes reworked the delta front sands during a transgression at the seaward edge of the system. Thickening-upward and shallowing-upward sequences record periods of westward deltaic progradation and increasing storm-wave energy. C & W gas reservoirs consist of well-sorted, friable, fine-grained arkose to lithic arkose. Sandstone reservoir porosity and permeability average 31% and 1200 md, respectively. Porosity is dominated by primary intergranular pores which have been reduced by (1) compaction of ductile grains, (2) formation of minor mixed-layer clay rim cement, sparry calcite cement and authigenic pyrite, and (3) late stage precipitation of plagioclase, K-feldspar, and quartz overgrowths. However, partial dissolution of plagiociase feldspar has created some secondary porosity. Although arkosic sandstones have high porosities and correspondingly high permeabilities, chioritic cement in volcaniclastic-rich sandstones significantly reduces permeability without concomitant reduction in porosity. The Cole Mountain basalt (informal) locally intnides and overlies the Cowlitz Formation. These basalts to basaltic andesites have calc-alkaline affinities and consist of hypabyssal sills, submarine lava flows, and local peperites which are lithologically, chemically, and petrographically distinct from the slightly older Tillamook Volcanics. The uppermost Narizian to Refugian (latest Eocene) Keasey Formation unconfonnably overlies the Cowlitz Formation in the study area. Volcanic and glauconitic sandstones at the base of the Keasey Formation mark the unconformity and reflect a period of slow sedimentation under slightly reducing conditions. The Keasey Formation predominantly consists of stractureless, tuffaceous fossiliferous mudstone deposited by hemipelagic sedimentation on the middle to upper slope. The informal Miocene (?) Ivy Creek formation locally disconformably overlies the Keasey Formation in the study area. The fluvially deposited Ivy Creek formation consists of a friable upper trough cross-bedded pebbly sand fades which overlies 9 m of blue organic-rich overbank clay. Local pebbly grits in matrix-support with buried flow-oriented rooted tree stems suggest that some debris flows entered the fluvial system from surrounding highlands. The unit may correspond to the middle Miocene Scappoose Formation. Northwest-trending down-to-the-northeast high-angle faults, some with oblique offset, and a subordinate set of older east-trending faults are the dominant structural features of the Rock Creek - Rocky Point area. The faulting produces a dissected structural high or upthrown basement block of middle to upper Eocene Tillamook Volcanics. Upper Eocene sedimentary units flank the north and south sides with occasional perched sedimentary outliers along the volcanic crest. Although source rock evaluations from this study indicate that the upper Eocene samples are thermally immature, it is possible that thermogenic "thy" gas at Mist migrated updip from more deeply buried Cowlitz shales and coals or equivalent Eocene strata in the adjacent Tualatin and Astoria basins. <br/> <br/>Description: Graduation date: 1990; Presentation date: 1990-03-02 http://hdl.handle.net/1957/9478 Title: The oligocene and miocene geology of the Tillamook embayment Tillamook County, northwest Oregon <br/> <br/>Abstract: Eleven sedimentary and volcanic rock units are mapped and described in the thesis area, and chronicle the dynamic geologic history of the Tillamook embayment from the Oligocene through the middle Mlocene. The oldest unit is the Zemorrian to early Saucesian Smuggler Cove formation, a bathyal tuffaceous mudstone with some thin- to thick-bedded tuff layers deposited on the middle to upper continental slope during a period of explosive silicic volcanism in the Western Cascade arc. Uppermost Smuggler Cove strata are coarser grained, grading upward to arkosic turbidite sandstone and mudstone and thick bloturbated silty sandstone deposited on the outer shelf during marine regression. This regression heralded the progradation of the overlying shallow-marine Bewley Creek formation (informal) depositional system. The Bewley Creek formation (informal) is proposed in this study for a sequence of pumiceous, volcaniclastic-rich lower Miocene feldspathic litharenites and lithic arkoses deposited during the Pillarlan-stage near the mouth of an ancestral Columbia River. The unit grades from bioturbated silty sandstone to fine-grained hummocky cross-stratified and coarser grained channelized sandstones deposited within, or peripheral to a wave-dominated delta or ebb tidal-delta channel complex. Progradatlon of the Bewley Creek formation may have been caused, in part, by increased volcaniclastic sedimentation attending a pulse of explosive volcanism in the adjacent Western Cascade arc. Reduced volcanic activity, possibly coupled with basin subsidence or eustatic sea level rise, resulted in deposition of mudstones of the Sutton Creek member (informal; proposed) of the Nye Mudstone. The Saucesian Sutton Creek member consists of bathyal, laminated, carbonaceous, and moderately tuffaceous mudstone deposited in an upper continental slope basin. The upper part of the unit contains common lithic to arkosic turbidite sandstone interbeds within nested channel-fill deposits. These strata represent a channelized shelf-slope break environment adjacent to the shallow-marine Angora Peak member of the Astoria Formation depositlonal system. Subsequent marine regression resulted in progradation of the Pillarian- to Newportian-stage arkosic-micaceous sandstone-rich Angora Peak member into the Tillamook embayment. Grainsize analysis, sandstone petrography, scanning electron microscopy, and heavy mineral analyses suggest these lower to middle Miocene mollusk-bearing, fine- to medium-grained sandstones were predominantly deposited near the mouth of an ancestral Columbia River. They accumulated on a high-energy Inner shelf within or down drift of a wave-dominated delta or ebb-tidal delta complex, evidenced by paleocurrent analyses, hummocky cross-stratification and trough cross-stratified submarine channel-fill sequences. The Angora Peak member disconformably overlies Zemorrian mudstones of the Smuggler Cove formation at Cape Kiwanda suggesting local uplift and erosion in that area, followed by Newportian stage transgression in the Tillamook embayment. Exotic cobbles and boulders of two mica granite and sedimentary quartzite at Cape Kiwanda were probably derived from the Idaho Batholith and Precambrian sandstone terrains in Montana, transported via an ancestral Columbia River and longshore current to the shelf possibly bound within tree root bundles. The Netarts Bay member (informal) of the Astoria Formation Is proposed In this study for a late Sauceslan package of fine-grained to pebbly amalgamated and interbedded turbidite, grainflow, and fluldized flow friable thick-bedded lithic arkoses. These massive sandstones contain large penecontemporaneously emplaced channel wall-blocks and naller slltstone rip-ups. These lower to middle Miocene strata were deposited in a submarine canyon head and channel complex offshore of the shallow-marine Angora Peak member depositlonal system. Netarts Bay strata cut Into the underlying Angora Peak shelf strata, and cut and Interfinger with bathyal slope mudstones of the Cannon Beach member of the Astoria Formation. The overlying lower Cannon Beach member Is composed of laminated bathyal mudstones with rare turbidite sandstone interbeds deposited in a coarse clastic-starved slope environment. Upper Cannon Beach member strata In the Tillamook area are characterized by micaceous arkosic and lithic arkosic turbidite sandstones that underlie and occur within nested channel-fill sequences. Bloturbated carbonaceous cross-bedded sandstone In the upper Cannon Beach member records shallowing of the Tillamook embayment to a channelized upper slope to shelf environment. The Tillamook embayment was uplifted and dissected prior to the arrival of six to ten Intracanyon subaerial and submarine lava flows of the Columbia River Basalt Group. These middle Miocene flows, delineatedon the basis of geochemical composition and magnetic polarity, Include (in stratigraphic order) the Grouse Creek (R2 low MgO-low T102), Winterwater (N2 low MgO-low Ti02), and Sentinel Bluffs (high MgO) units of the Grande Ronde Basalt, and the Ginkgo unit of the Frenchman Springs member of the Wanapum Basalt. Orientation of Grande Ponde Basalt foreset-bedded pillow palagonite complexes and lava delta sequences indicate that these Columbia River Basalt units flowed westward into the Tillainook embayment, possibly through a saddle in the ancestral Oregon Coast Range. Marine transgression and deposition of hummocky cross-stratified arkosic marine strata of the Sandstone of Whale Cove followed emplacement of the last Grande Ronde flows. This was succeeded by a regression, as Indicated by the overlying subaerial plagioclase-phyric Ginkgo Unit flow of the Frenchman Springs Basalt. Locally, Winterwater and Sentinel Bluffs unit basalt occur as brecciated peperitic sills and dikes. These were emplaced through the process of "auto-invasion" when dense lava injected downward Into semi-lithifled Tertiary strata under the influence of both a pressure head augmented by flashing steam, and steam blasting. The thesis area is crossed by a complex network of high-angle northwest- and northeast-tending normal and reverse faults, and both low and high-angle east-trending reverse and thrust faults. These faults may have developed through a north-south compressional tectonic regime, a dextral shear couple, or a combination of these two tectonic regimes. Many faults cut Columbia River Basalt units and are thus middle Miocene or younger in age. Tertiary strata including the Columbia River Basalts are also folded within a broad westward-plunging syncline which suggests a middle Miocene or younger compressional event. Source rock analyses indicate that the mudstones of the Cannon Beach member, Sutton Creek member, and Smuggler Cove formation contain type III kerogen capable of generating natural gas only. Although these rocks have thermally innature vitrinite reflectance values, they contain sufficiently high total organic carbon content to be considered potential lean source rocks. Arkosic sandstones of the Angora Peak and Netarts Bay members have fair to good reservoir rock characteristics, and may represent reservoirs offshore for matured hydrocarbons generated from deeply buried source rocks. <br/> <br/>Description: Graduation date: 1991; Presentation date: 1990-03-27 http://hdl.handle.net/1957/9477 Title: Past climate variability in southwestern Oregon and relationships with regional and hemispheric climate <br/> <br/>Abstract: This dissertation presents the results of three studies that assessed climate variability on short and long timescales in western United States. The growth of carbonate formations in caves (speleothems) is used to infer the timing and amplitude of past climate variability. We first assess the controls on speleothem growth for the past 380 000 years by combining high-density U-Th dating with a regional climate model and an energy balance model. The majority of speleothem growth occurred overwhelmingly during interglacial periods and glacial periods were characterized by little or no growth. We assess the mechanisms responsible for growth cessation during the peak of the last glaciation (LGM), 21 000 years ago, with a regional climate model and determine that a combination of drier LGM conditions with a change in the seasonal cycle of the surface water balance provides a feedback mechanism that limited recharge to the deeper soil and reduced or eliminated drip water in the cave. The energy balance model supports this mechanism by indicating that cave temperatures did not drop below the freezing point of water at any time during the last glaciation. We then evaluate the climatic significance of stable isotopes of oxygen in rainwater collected in southwestern Oregon in order to accurately interpret the isotopic record of speleothems. We establish that temperature plays an important role in controlling the distribution of oxygen isotopes in rainwater and therefore speleothems in southwestern Oregon can preserve a record of temperature changes through time. Finally, we present a high-resolution paleoclimate record using speleothems from a cave in Oregon that grew during the last 9000 years and during the middle of the last interglaciation. We find the winter temperatures were sensitive to winter solar insolation and varied in a quasi-cyclical pattern on millennial timescales. This pattern was characteristic of both regional and hemispheric variability as indicated by similarities of our record with other regional and hemispheric climate reconstructions. It appears that higher climate variability in the past was associated with warming trends, with the implication that global warming may make the climate more unstable in the future. Climate variability during the last interglacial period was characterized by different scales of millennial and centennial climate variability compared with the Holocene. <br/> <br/>Description: Graduation date: 2009