Stratigraphy and sedimentation of the Onion Peak area, Clatsop County, Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/j3860b07d

Descriptions

Attribute NameValues
Creator
Abstract or Summary
  • Six Tertiary units are exposed in the Onion Peak area near the town of Cannon Beach., Oregon. The units consist of: late Eocene to early Miocene Oswald West mudstones (informal), middle Miocene Astoria Formation (Angora Peak sandstone and Silver Point mudstone members.-informal), middle Miocene basalts of intrusive and extrusive Depoe Bay Basalt, and intrusive Cape Foulweather Basalt. Beach sands, Pleistocene marine terraces, and stream alluvium unconformably overlie these Tertiary units. The Oswald West mudstones consist of more than 1600 feet of well-bedded, burrowed, tuffaceou siltstones and mudstones with sub ordinate tuff and glauconitic sandstone beds. Foraminiferal and trace fossil evidence suggest that these mudstones were deposited in marine waters of upper bathyal depths. The overlying 1700-foot thick Astoria Formation is divided into two informal mappable members: the 1100-foot thick Angora Peak sandstone and the 600-foot thick Silver Point mudstone (proposed informally in this study). The Angora Peak sandstone member is composed of several hundred feet of thickly laminated feldspathic sandstones with local cross-bedded lithic conglomerates and carbonaceous siltstones. The overlying Silver Point mudstone member consists of rhythmically interbedded mudstones and graded turbidite sandstones, overlain by bedded mudstones, thin siltstones, and local conglomerate lenses. Conglomerate clast lithologies and heavy mineral suites of the Silver Point and Angora. Peak members are similar to the sediment carried by the Columbia River today and may be an ancient deposit of that river system. The provenances for these strata were pre-Miocene andesitic and dacitic rocks of the western Cascades, the Coast Range Eocene Tillamook basalts, and plutonic, metamorphic, and sedimentary contributions from eastern Oregon and Washington, Idaho, Montana, and Canada, Channel fluvial sandstones, conglomerates, and well-bedded shallow marine sandstones of the Angora Peak member, probably interfingering with interbedded, deeper marine (600 feet-outer shelf) mudstones and turbidite sndstones of the Silver Point member, are interpreted to have been deposited near the mouth of a river, adjacent to the ocean as a delta. Dikes, sills, peperites, and irregular intrusive bodies of middle Miocene Depoe Bay Basalt intruded Oswald West mudstones and the Astoria Formation. These aphanitic to finely crystalline equigranular basaltic intrusives locally fed over 2000 feet of palagonitized pillow lavas and basaltic breccias which now form the highest peaks in the area. The intrusives locally penecontemporaneously deformed the Astoria strata into a series of large-scale soft sediment deformation folds and sedimentary breccias. Cape Foulweather Basalt intrudes all sedimentary units and cuts the Depoe Bay Basalts. The basalt is recognized by sparse, large plagioclase phenocrysts. The area is cut by several east-west and north-south trending high angle faults with up to 500 feet displacement A large north-south syncline in the central part of the thesis area delineates a structural and depositional basin. A smaller north-plunging anticline is present near the coast. Recent landslides in the Silver Point member have been particularly destructive along the coast and inland; they have been caused by wave, stream action, and by man over-steepening unstable slopes. Crushed basalt quarry rock and potential petroleum reservoirs in the Angora Peak sandstones in stratigraphic and structural tra traps, particularly in nearby offshore areas, are the main geological economic resources of the area.
Resource Type
Date Available
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Academic Affiliation
Non-Academic Affiliation
Subject
Rights Statement
Language
Digitization Specifications
  • Master files scanned at 600 ppi (256 Grayscale, 24-bit Color) using Capture Perfect 3.0 on a Canon DR-9080C in TIF format. PDF derivative scanned at 300 ppi (256 B&W, 24-bit Color), using Capture Perfect 3.0, on a Canon DR-9080C. CVista PdfCompressor 3.1 was used for pdf compression and textual OCR.
Replaces
Additional Information
  • description.provenance : Made available in DSpace on 2008-08-21T13:12:41Z (GMT). No. of bitstreams: 1 Smith_Thomas_N_1974.pdf: 5540830 bytes, checksum: 033840cfef9c83dc592bb54b1f83bcec (MD5)
  • description.provenance : Submitted by Anna Opoien (aoscanner@gmail.com) on 2008-08-20T20:11:22Z No. of bitstreams: 1 Smith_Thomas_N_1974.pdf: 5540830 bytes, checksum: 033840cfef9c83dc592bb54b1f83bcec (MD5)
  • description.provenance : Approved for entry into archive by Linda Kathman(linda.kathman@oregonstate.edu) on 2008-08-21T13:12:40Z (GMT) No. of bitstreams: 1 Smith_Thomas_N_1974.pdf: 5540830 bytes, checksum: 033840cfef9c83dc592bb54b1f83bcec (MD5)
  • description.provenance : Approved for entry into archive by Linda Kathman(linda.kathman@oregonstate.edu) on 2008-08-21T13:10:48Z (GMT) No. of bitstreams: 1 Smith_Thomas_N_1974.pdf: 5540830 bytes, checksum: 033840cfef9c83dc592bb54b1f83bcec (MD5)

Relationships

In Administrative Set:
Last modified: 08/19/2017

Downloadable Content

Download PDF
Citations:

EndNote | Zotero | Mendeley

Items