http://hdl.handle.net/1957/1718 Search the Channel search http://ir.library.oregonstate.edu/dspace/simple-search http://hdl.handle.net/1957/9242 Title: Geology of the Antone district of Wheeler County, Oregon <br/> <br/>Abstract: The area studied in detail, known as the Antone District, is located in the southeast corner of Wheeler County, Oregon, , between longitude 119 37. and 119°54 east, and latitude 44°23 and 44°3O' north. Surface elevations range from 3050 feet above sea level in the northeast corner of the district, to 6M5 feet on Spanish Peak. The Miocene Columbia Biver lavas outcrop over 48 of the 68 square miles in the district. Older rocks exposed include Pre- Cretaoeous mota-sedimente and metamorphosed intrusives, Cretaceous conglomerates and sandstones, a granite porphyry pluton, and the brilliantly colored rooks of the upper 011goe.ne and lower Miocene John Day. The early Tertiary formation known as the Clarno does not outcrop in this district. Younger formations include the gravels and tuffs of the upper Miocene Mascall formation, extensive outcrops of the Pliocone Rattlesnake, and limited accumulations of undifferentiated Quaternary alluvium. A horublende andesite extrusive, which is probably of Pleistocene age, occurs in the western part of the district. Eaoh of the above stratigraphic units is discussed under the following headings: Distribution and Topographic Expression; Lithology; Thickness; Age and Stratigraphic Relations. A section of the "Dayville Quadrangls, issued by the U. S. aeologioal Survey, was used as a base for a detailed map showing the distribution of the various formations. Special attention was devoted to the study of the Pre-Cretaceous rooks. Approximately 8000 feet of ohloritic schist, argillite, caleareous sohist, phyllie, marble, and quartzite are included in this older series. Basic Intrusives, largely altered to serpentine, cut the meta-sediments. The structure of the Antone District is discussed under the following subheadings: John Day Valley Syncline; Ochoco Escarpment and Highland; Pre-Cretaceous Folding and Faulting; Cretaceous Monocline; and, Fracturing and Slumping of the Rattlesnake Formation. Special sections have been devoted to historical and economic geology. The report is adequately illustrated with photomicrographs of representative rooks and with numerous pertinent detail photographs. Also included is a plate showing the structural details of a north-south section through the middle of the Antone District. <br/> <br/>Description: Graduation date: 1949; Presentation date: 1948-06-11 Thu, 10 Jun 1948 22:58:59 GMT http://hdl.handle.net/1957/9234 Title: Crustal structure of the Sulaiman Range, Pakistan, from gravity data <br/> <br/>Abstract: Gravity data along an east-west profile from the Punjab plain of Pakistan to the western border town of Chaman have been incorporated into interpretation of the gross crustal structure underlying the Sulaiman Range. Interpretation of the free-air, Bouguer, and isostatic gravity anomalies suggests that 15 to 25 km thick, transitional crust underlies the 250 km wide fold-and-thrust belt. Thick overlying sediments are compensated by shallow mantle material, which leads to a long wavelength (-200 km) Bouguer gravity high in the area. Free-air and isostatic anomalies suggest that high topography in the eastern Sulaiman Range lacks roots, as the Moho apparently shallows beneath the thick (> 15 km) sediments. In the western Sulaiman Range the topography appears to be compensated by thicker crust. Interpretation of transitional crust in the region suggests that passive margin structures identified along the western edge of the Indo-Pakistani subcontinent continue under the Sulaiman foldbelt, and that the region is at an early stage of continental collision. The crust appears to be deformed under the load of the thrust belt and the influence of horizontal compressive forces resulting from the convergence of the Indian subcontinent against the Afghan Block. Crustal thickening is taking place on the west, as the Indo-Pakistani plate is underthrusting continental crust of this block. <br/> <br/>Description: Graduation date: 1991; Presentation date: 1991-01-24 Wed, 23 Jan 1991 22:58:59 GMT http://hdl.handle.net/1957/9229 Title: Geology of the Elsie-lower Nehalem River area, south-central Clatsop and northern Tillamook counties, northwestern Oregon <br/> <br/>Abstract: The middle Eocene Tillamook Volcanics form the oldest rock unit in the Elsie-lower Nehalem River area. K-Ar age determinations and age constraints imposed by foraminiferal and calcareous nannofossil assemblages of overlying sedimentary strata indicate an absolute age of about 42 Ma for the uppermost Tillamook Volcanics. Major oxide values indicate that the upper Tillamook Volcanics are highly fractionated high Fe-Ti tholeiitic basalts and basaltic andesites. These volcanics were erupted in a developing forearc under an extensional plate tectonic setting and formed a moderately large oceanic island. These subaerial flows are predominantly aphyric to plagioclase-augite porphyritic and have a pilotaxitic flow texture. Epochs of both normal and reverse magnetic polarity are recorded. Thermal subsidence related to the end of the volcanism resulted in deposition of the transgressive late Eocene Hamlet formation over the "Tillamook island". The informal Hamlet formation consists of three members. From oldest to youngest they are: the Roy Creek member, the Sunset Highway member, and the Sweet Home Creek member. Three lithofacies are present in the Roy Creek member. The stratigraphically lowest of these consists of basaltic boulder-pebble conglomerate and locally fossiliferous pebbly basaltic sandstones which were deposited in a high energy nearshore environment around rocky basaltic headlands and sea stacks of the Tillamook Volcanics. Molluscan fossils in this lithofacies are correlative to the middle to late Eocene "CowlitzCoaledo" fauna. Successively overlying lithofacies are a very coarseto coarse-grained shallow marine basaltic sandstone lithofacies and a medium- to fine-grained basaltic sandstone lithofacies. This fining upward sequenced documents progressive deepening of the depositional basin. Framework clasts in all three Roy Creek member lithofacies were predominantly derived from the Tillamook Volcanics. Pore-filling diagenetic chlorite, smectite (nontronite), calcite, and zeolite (clinoptilolite and heulandite) cements severely reduce the porosity of Roy Creek member sandstones. The Sunset Highway member of the Hamlet formation conformably overlies the Roy Creek member in eastern Clatsop and western Columbia counties and pinches out to the west at about the longitude of the Nehalem River in T. 4 N., R. 8 W.. The Sunset Highway member is predominantly composed of interbedded micaceous arkosic sandstone, lithic arkose, and muddy micaceous arkosic siltstone with a few beds of basaltic sandstone and basaltic debris flow breccias. The dominant micaceous arkosic composition of the Sunset Highway member reflects a distant extrabasinal granitic-metamorphic provenance and contrasts with that of the locally derived underlying basaltic Roy Creek member. Low angle trough cross-bedding, hummocky bedding, and microcross-laminations in fine to medium-grained arkosic sandstones are interpreted to have been produced by large storm-generated waves and on a high energy inner shelf. Thin interbeds of bioturbated mudstone and mollusc-bearing bioturbated sandstones formed during periods of fairweather conditions and during lower sedimentation rates. Rare matrix supported, basaltic debris-flow breccias and basaltic sandstones were derived from nearby basaltic headlands and by rivers draining the Tillamook Volcanics. Minor secondary intraparticle porosity occurs with some primary intergranular porosity in relatively matrix-free Sunset Highway member arkosic sandstones. However, much of the porosity and permeability of these potential sandstones has been reduced by diagenetic smectite coatings on framework grains and potassium feldspar overgrowths of feldspars. The mudstone-dominated Sweet Home Creek member was conformably deposited on the Sunset Highway member in eastern Clatsop and western Columbia counties. In western Clatsop County the Sweet Home Creek member directly and conformably overlies the Roy Creek member due to pinch out of the Sunset Highway member. Upper Narizian to lowermost Refugian benthic foraminiferal assemblages from this unit indicate outer shelf to upper slope sedimentation and continued subsidence of the depositional (Astoria) basin. Micromicaceous and carbonaceous silty mudatone dominates this unit but thin-bedded micaceous arkosic turbidite sandstones are present in the lower part, and rare, thin basaltic turbidites are present in the upper half. X-ray diffraction analysis shows that the dominant clay minerals in the Sweet Home Creek member niudstone are smectite (montmorillonite), kaolinite, and illite. The Cole Mountain basalt (informal) intrudes and locally overlies the Sweet Home Creek member. This caic-alkaline basaltic andesite is thought to have formed in a compressional plate tectonic regime and been emplaced on the outer shelf and upper slope as shallow irregular sills and dikes and minor submarine pillow basalt-hyaloclastite complexes. Siliceous nodules associated with pillowed units locally contains a few per cent pyrite and are associated with small areas of high-grade supergene copper-silver mineralization. The normally polarized Cole Mountain basalt is chemically, petrographically, and lithologically distinct from the Tillamook Volcanics and Grande Ronde Basalt of the Columbia River Basalt Group. The uppermost Narizian and Refugian (late Eocene) Jewell member of the Keasey Formation disconformably overlies the Cole Mountain basalt and Sweet Home Creek member. A thin basal glauconitic sandstone-siltstone reflects a period of reduced sedimentation under slightly reducing conditions and marks the disconformity. The unit primarily consists of laminated to thin bedded tuffaceous mudstone with a few thin tuff beds, small micaceous arkosic sandstone channels and clastic dikes. Clay minerals in the Jewell member are dominated by smectite (montmorillonite), with minor kaolinite and illite (degraded mica) in the lower part of the unit. Benthic foraminiferal assemblages in the unit indicate bathyal or slope depths and have been assigned to the lower Refugian to upper Narizian stages. In the middle Miocene, irregular dikes and sills of the Grande Ronde Basalt of the Columbia River Basalt Group intruded the late Eocene sedimentary strata in the thesis area. Two magneto-chemical types of Grande Ronde Basalt, N2/low MgO-low Ti02 and N2/ high MgO, were identified in the thesis area. These were geochemically and magnetically correlated to subaerial flows of magneto-chemical types IA and 5A of Mangan and others (1986) on the Columbia Plateau. The intrusions or invasive flows are interpreted to have been derived from voluminous plateau eruptions by invasion into soft, unconsolidated Neogene sediments at the marine/coast interface and then into the more brittle but ductile Paleogene strata of the area as first proposed by Beeson and others (1979). Uplift of the Coast Range was initiated in the late Miocene as a result of rapid offshore underthrusting in the subduction zone (Snavely and others, 1983). This has resulted in subaerial erosion and exposure of the faulted and gently folded forearc ridge and deposition of Quaternary alluvial gravels and sands along major rivers and creek in the thesis area. The dominant structural features of the Elsie-lower Nehalem River area are generally down-to-the-north, east-west-trending high angle faults with oblique offset and a conjugate set of oblique slip northwest-trending right-lateral and northeast-trending left-lateral faults. Folds are broad and relatively minor. The major east-west-trending fault pattern may have been initially produced by extensional stresses related to subsidence of the "Tillamook island". The conjugate strike-slip fault pattern may have been created by partial coupling of the forearc basin with oblique subduction of the Farallon plate. Other than timber, locally used rock aggregate from small quarries is the only resource that has been realized in the thesis area. Most quarries are developed in dikes and sills of Grande Ronde Basalt and the aggregate is used to macadamize logging roads. Diagenetic events have resulted in significant loss of porosity and permeability of potential reservoir sandstones in the area. The most favorable targets are relatively matrix-free micaceous arkosic sandstones in the Sunset Highway member, but these have been breached by erosion in the eastern part of the thesis area and pinch out in the western part of the area where potential mudstone cap rocks (e.g., Hamlet and Keasey formations) are present. Mudstones in the area contain woody-structured kerogen and average about 1% total organic carbon. These potential source rocks are generally thermally immature but have locally been baked by basaltic intrusions. This results in elevated vitrinite reflectance values (in the oil window and beyond) and, therefore, the mudstones may be potential source rocks for methane generation. Mineralized fault zones have substantial width and length but do not appear to carry anomalous concentrations of any metals other than arsenic. High-grade supergene copper-silver mineralization associated with Cole Mountain basalt intrusions has been documented but appears to be very localized and is not thought to be a viable exploration target. <br/> <br/>Description: Graduation date: 1989; Presentation date: 1988-05-27 Thu, 26 May 1988 22:58:59 GMT http://hdl.handle.net/1957/9226 Title: Petrography of pre-Tertiary rocks of the Blue Mountains, Umatilla County, northeast Oregon <br/> <br/>Abstract: Nine small Mesozoic plutons in TJmatilla County, northeast Oregon, crop out within an area of 58 sq km in the Blue Mountains. The plutons are divided into an earlier series of probable Permian-Triassic age and a later intrusive series of probable Late Jurassic to Middle Cretaceous age. The earlier rocks show effects of regional metamorphism whereas the later plutons are unmetamorphosed. The five units of the earlier intrusive series probably are Early to Middle Triassic in age. They correlate in age and general petrologic type with the Canyon Mountain ophiolite complex. Rock types, whcch may vary within individual plutons, are serpentinized peridotite, quartz-hornblende metagabbro, hornblende metatonalite, and hornblende metatrondhjemite The elongation of several plutons suggests that emplacement was guided by northeast-trending zones of weakness. All plutons were intruded as magmas except the peridotite which was probably tectonically emplaced. Intrusion of these units into the country rock produced a hornblende gneiss and thermal metamorphism up to the sillimanite-cordieritemuscovite-almandine subfacies of Abukuma-type facies series metamorphism. Permian-Triassic regional metamorphism of greenschist grade produced a pronounced northeast foliation in the older series of plutons and associated country rocks. The remaining four plutons are included within a later intrusive episode and are probably Late Jurassic to Middle Cretaceous in age. Age and petrologic type are typical of the Wallowa and Bald Mountain intrusive series. Rock types, in the order of intrusion, are pyroxene-hornblende melagabbronorite; quartz-pyroxene-hornblende gabbronorite; biotite -bearing, quartz-hornblende gabbro; hornblende trondhjemite, and granodiorite. Country rocks are metavolcanic dacitic and andesitic flows and pelitic metasedimentary schists, interbedded on a large scale. They presumably correlate with portions of the Elkhorn Ridge Argillite and/or the Clover Creek Greenstone on the basis of lithologic similarities. Staurolite, not found in pre-Tertiary rocks elsewhere in northeast Oregon, is common in the metasediment A series of interbedded sediments and flows unconformably overlies the pre-Tertiary rocks. The sediment ranges from carbonaceous shale to arkose. Abundant leaf fossils indicate an early or middle Eocene age. Foreset beds, angular grains, and the occurrence of staurolite suggest that the sediment is locally derived from outcrops to the southeast and deposited under fluvial conditions. Most flows are andesitic and commonly contain 30 to 40 percent large phenocrysts of piagioclase, mica, quartz, and hornblende, Post-Eocene deformation has tilted the sediments eastward as much as 37 degrees. Columbia River Basalt unconformably overlies the tilted Eocene strata. Only Yakima-type basalt was found. One prominent flow contains small phenocrysts of plagioclase and is sufficiently distinctive to serve as a marker unit. Gentle northeast-trending folds and small, inconspicuous northwest faults are the chief structural characteristics of the basalt. Quaternary sediments include the loessial Palouse Formation, reworked deposits of Mount Mazama ash, and stream gravels. Chemical analyses of the major oxides, trace elements, and rare earths show consistently low amounts of Ti02 and K2O and depletion in the light rare earths. These chemical data combined with petrologic similarities to known ophiolite complexes suggest that the Permian-Triassic (?) units in the thesis area represent a dismembered ophiolite assemblage. The sialic metasediment suggests a continental provenance; the source of the metavolcanic unit is possibly from an island arc. Together they suggest deposition in a Permian-Triassic back-arc environment. <br/> <br/>Description: Graduation date: 1975; Presentation date: 1975-05-08 Wed, 07 May 1975 22:58:59 GMT