Search

Search Results

• 1. [Article] Geology of the Tillamook Head--Necanicum Junction area, Clatsop County, northwest Oregon

  Five distinct lithologic units compose the Tertiary rocks in the Tillamook Head - Necanicum Junction area of the northern Oregon Coast Range. They are: the late Eocene to early Miocene Oswald West mudstones, ...

  Citation × Citation Citation Abstract Copy Title: Geology of the Tillamook Head--Necanicum Junction area, Clatsop County, northwest Oregon Author: Neel, Robert Holmes Five distinct lithologic units compose the Tertiary rocks in the Tillamook Head - Necanicum Junction area of the northern Oregon Coast Range. They are: the late Eocene to early Miocene Oswald West mudstones, the middle Miocene Angora Peak sandstone and Silver Point mudstone members of the Astoria Formation, and the middle Miocene intrusive and extrusive Depoe Bay and Cape Foulweather basalts. These units are locally overlain by Pleistocene marine terraces and Holocene beach and dune sands, stream alluvium, and landslide deposits. The Oswald West mudstones, Angora Peak sandstones, and Silver Point mudstones are informal stratigraphic names used in this study. The Oswald West mudstones consist of over 2, 000 feet of well-bedded, intensely burrowed, silty mudstones and siltstones interstratified with minor glauconitic sandstones, tuff beds, and thick bedded tuffaceous siltstones Foraminifera, trace fossils, glauconite, and the general fine-grained character of these rocks suggest that deposition occurred in an open marine deep-water environment, possibly as part of a prodelta or on the outer continental shelf. The Angora Peak member is composed of several hundred feet of moderately sorted, medium- to coarse-grained quartzose-feldspathic and lithic sandstones. The sandstones unconformably overlie the Oswald West mudstones and are thick bedded, laminated, and less commonly cross-laminated. Sedimentary structures, sorting, and stratigraphic relationships suggest that the sandstones were deposited in a high energy, wave-dominated environment, possibly as delta sheet sands. The sands were, in part, redistributed by waves and longshore drift to form offshore coastal barrier bars and.linear clastic shoreline deposits. The overlying 650-foot thick Silver Point member consists dominantly of dark gray, micaceous, laminated mudstones and very thin siltstones. Rhythmically interbedded mudstones and fine-grained turbidite sandstones occur in the lower part of the unit. Deposition occurred in cool, low energy, open marine conditions, probably of sublittoral to upper bathyal depths. Oversteepening of Angora Peak sheet sands on the delta front may have resulted in periodic slumping of sands which were transported by turbidity currents into a shelf basin of the deeper water Silver Point delta-slope environment. An east to west paleocurrent pattern in the Salver Point turbidite sandstonesis consistent with this model. Sandstone petrography and heavy mineral suites of the Astoria Formation suggests a dominantly volcanic and sedimentary provenance for these strata, probably the pre-Miocene volcanic rocks of the western Cascades and local Coast Range Eocene basalts and sandstones. Mineralogy and rare rock fragments in the sandstones also suggest that some detritus was derived from the granitic, metamorphic, and Paleozoic sedimentary terrains of eastern Oregon and Washington, and from British Columbia and western Idaho, possibly transported via an "ancestral Columbia River drainage system. Numerous dikes, sills, and irregular-shaped plutons of Depoe Bay Basalt and Cape Foulweather Basalt intruded the Oswald West mudstones and Astoria Formation. The major intrusive body in the area is the 900-foot thick sill that forms Tillamook Head. At Ecola State Park, the forceful intrusion of this sill into the semi-consolidated Silver Point strata at very shallow depths produced local synsedimentary folds. Over 1, 000 feet of extrusive Depoe Bay Basalt palagonitized pillow lavas and breccias and 2.00 feet of very local Cape Foulweather pillow lavas lie with angular unconformity over the Silver Point member. Deformation which accompanied the general Coast Range uplift during the late Miocene to Pleistocene formed four northeast-trending folds in the thesis area and two sets of high angle faults which strike north-south and northwest- southeast through the area. In addition, active landslides are abundant throughout the area, particularly along the coast. Economic resources of the area include basalt quarry rock for rip-rap and road base, basalt stream gravels for road aggregate, and potential petroleum resources may occur in the adjacent offshore area. Title: Geology of the Tillamook Head--Necanicum Junction area, Clatsop County, northwest Oregon Author: Neel, Robert Holmes Five distinct lithologic units compose the Tertiary rocks in the Tillamook Head - Necanicum Junction area of the northern Oregon Coast Range. They are: the late Eocene to early Miocene Oswald West mudstones, the middle Miocene Angora Peak sandstone and Silver Point mudstone members of the Astoria Formation, and the middle Miocene intrusive and extrusive Depoe Bay and Cape Foulweather basalts. These units are locally overlain by Pleistocene marine terraces and Holocene beach and dune sands, stream alluvium, and landslide deposits. The Oswald West mudstones, Angora Peak sandstones, and Silver Point mudstones are informal stratigraphic names used in this study. The Oswald West mudstones consist of over 2, 000 feet of well-bedded, intensely burrowed, silty mudstones and siltstones interstratified with minor glauconitic sandstones, tuff beds, and thick bedded tuffaceous siltstones Foraminifera, trace fossils, glauconite, and the general fine-grained character of these rocks suggest that deposition occurred in an open marine deep-water environment, possibly as part of a prodelta or on the outer continental shelf. The Angora Peak member is composed of several hundred feet of moderately sorted, medium- to coarse-grained quartzose-feldspathic and lithic sandstones. The sandstones unconformably overlie the Oswald West mudstones and are thick bedded, laminated, and less commonly cross-laminated. Sedimentary structures, sorting, and stratigraphic relationships suggest that the sandstones were deposited in a high energy, wave-dominated environment, possibly as delta sheet sands. The sands were, in part, redistributed by waves and longshore drift to form offshore coastal barrier bars and.linear clastic shoreline deposits. The overlying 650-foot thick Silver Point member consists dominantly of dark gray, micaceous, laminated mudstones and very thin siltstones. Rhythmically interbedded mudstones and fine-grained turbidite sandstones occur in the lower part of the unit. Deposition occurred in cool, low energy, open marine conditions, probably of sublittoral to upper bathyal depths. Oversteepening of Angora Peak sheet sands on the delta front may have resulted in periodic slumping of sands which were transported by turbidity currents into a shelf basin of the deeper water Silver Point delta-slope environment. An east to west paleocurrent pattern in the Salver Point turbidite sandstonesis consistent with this model. Sandstone petrography and heavy mineral suites of the Astoria Formation suggests a dominantly volcanic and sedimentary provenance for these strata, probably the pre-Miocene volcanic rocks of the western Cascades and local Coast Range Eocene basalts and sandstones. Mineralogy and rare rock fragments in the sandstones also suggest that some detritus was derived from the granitic, metamorphic, and Paleozoic sedimentary terrains of eastern Oregon and Washington, and from British Columbia and western Idaho, possibly transported via an "ancestral Columbia River drainage system. Numerous dikes, sills, and irregular-shaped plutons of Depoe Bay Basalt and Cape Foulweather Basalt intruded the Oswald West mudstones and Astoria Formation. The major intrusive body in the area is the 900-foot thick sill that forms Tillamook Head. At Ecola State Park, the forceful intrusion of this sill into the semi-consolidated Silver Point strata at very shallow depths produced local synsedimentary folds. Over 1, 000 feet of extrusive Depoe Bay Basalt palagonitized pillow lavas and breccias and 2.00 feet of very local Cape Foulweather pillow lavas lie with angular unconformity over the Silver Point member. Deformation which accompanied the general Coast Range uplift during the late Miocene to Pleistocene formed four northeast-trending folds in the thesis area and two sets of high angle faults which strike north-south and northwest- southeast through the area. In addition, active landslides are abundant throughout the area, particularly along the coast. Economic resources of the area include basalt quarry rock for rip-rap and road base, basalt stream gravels for road aggregate, and potential petroleum resources may occur in the adjacent offshore area. Close

• 2. [Article] Stratigraphy and sedimentation of the Onion Peak area, Clatsop County, Oregon

  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 ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy and sedimentation of the Onion Peak area, Clatsop County, Oregon Author: Smith, Thomas N. 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. Title: Stratigraphy and sedimentation of the Onion Peak area, Clatsop County, Oregon Author: Smith, Thomas N. 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. Close

• 3. [Article] Stratigraphy and sedimentation of the Neahkahnie Mountain - Angora Peak area, Tillamook and Clatsop Counties, Oregon

  Four distinct lithologic units compose the Tertiary rocks of the Neahkahnie Mountain - Angora Peak area, located along the northwest Oregon coast near the town of Nehalem. The Tertiary units are the late ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy and sedimentation of the Neahkahnie Mountain - Angora Peak area, Tillamook and Clatsop Counties, Oregon Author: Cressy, Frank Beecher Four distinct lithologic units compose the Tertiary rocks of the Neahkahnie Mountain - Angora Peak area, located along the northwest Oregon coast near the town of Nehalem. The Tertiary units are the late Oligocene to early Miocene Oswald West mudstones, the middle Miocene Angora Peak sandstone member of the Astoria Formation, and middle Miocene intrusive and extrusive rocks of the Depoe Bay Basalt. These units are unconformably overlain by Pleistocene and Recent beach and dune sands, alluvium, and tidal flat muds. The Oswald West mudstones and the Angora Peak sandstone member are informal stratigraphic units proposed in this study. The Oswald West mudstones consist of over 1600 feet of well-bedded, highly burrowed, tuffaceous siltstones and silty mudstones interbedded with minor amounts of graded turbidite sandstones and submarine slump deposits. Foraminifera and trace fossils suggest deposition occurred in marine waters of upper bathyal depths. The Angora Peak sandstone consists of over 1800 feet of thin- to thick-bedded, locally cross-bedded, fine- to coarse-grained arkosic sandstones, pumiceous and basaltic conglomerates, carbonaceous and micaceous siltstones, and local coal beds. The inter-fingering shallow marine and fluvial sandstones are interpreted to have been deposited in a high-energy, wave dominated, deltaic environment which reworked the sediments into extensive delta-front sheet sands similar to those observed in the modern Niger and Rhone deltas. Mineralogy, heavy minerals, and conglomerate clast lithologies indicate that most of the sediments were derived from local uplifted areas of Eocene basalts and early Tertiary sediments and from the Oligocene Little Butte Volcanics in the western Cascades. Rare metamorphic and plutonic clasts, sedimentary quartzite, heavy minerals, and sandstone mineralogy suggest that metamorphic, igneous, and Paleozoic sedimentary terranes in eastern Oregon and Washington, British Columbia, Idaho, and Montana supplied some of the sediments, possibly via an ancestral Columbia River. Dikes, sills, and plugs of aphanitic to finely crystalline Depoe Bay Basalt intrude the older sedimentary rocks and locally are feeders for palagonitized pillow breccias which unconformably overlie the Angora Peak sandstone. The major intrusive body is a 1200-foot thick diabasic sill referred to as the Neahkahnie sill. The extrusive basalts formed in a subsiding marine basin in which over 1600 feet of pillow lavas, pillow breccias, and minor basalt flows were locally extruded. The area is cut by a series of west-northwest and north-trending faults. Two synclines and an anticline strike subparallel to the west-northwest trending faults. Title: Stratigraphy and sedimentation of the Neahkahnie Mountain - Angora Peak area, Tillamook and Clatsop Counties, Oregon Author: Cressy, Frank Beecher Four distinct lithologic units compose the Tertiary rocks of the Neahkahnie Mountain - Angora Peak area, located along the northwest Oregon coast near the town of Nehalem. The Tertiary units are the late Oligocene to early Miocene Oswald West mudstones, the middle Miocene Angora Peak sandstone member of the Astoria Formation, and middle Miocene intrusive and extrusive rocks of the Depoe Bay Basalt. These units are unconformably overlain by Pleistocene and Recent beach and dune sands, alluvium, and tidal flat muds. The Oswald West mudstones and the Angora Peak sandstone member are informal stratigraphic units proposed in this study. The Oswald West mudstones consist of over 1600 feet of well-bedded, highly burrowed, tuffaceous siltstones and silty mudstones interbedded with minor amounts of graded turbidite sandstones and submarine slump deposits. Foraminifera and trace fossils suggest deposition occurred in marine waters of upper bathyal depths. The Angora Peak sandstone consists of over 1800 feet of thin- to thick-bedded, locally cross-bedded, fine- to coarse-grained arkosic sandstones, pumiceous and basaltic conglomerates, carbonaceous and micaceous siltstones, and local coal beds. The inter-fingering shallow marine and fluvial sandstones are interpreted to have been deposited in a high-energy, wave dominated, deltaic environment which reworked the sediments into extensive delta-front sheet sands similar to those observed in the modern Niger and Rhone deltas. Mineralogy, heavy minerals, and conglomerate clast lithologies indicate that most of the sediments were derived from local uplifted areas of Eocene basalts and early Tertiary sediments and from the Oligocene Little Butte Volcanics in the western Cascades. Rare metamorphic and plutonic clasts, sedimentary quartzite, heavy minerals, and sandstone mineralogy suggest that metamorphic, igneous, and Paleozoic sedimentary terranes in eastern Oregon and Washington, British Columbia, Idaho, and Montana supplied some of the sediments, possibly via an ancestral Columbia River. Dikes, sills, and plugs of aphanitic to finely crystalline Depoe Bay Basalt intrude the older sedimentary rocks and locally are feeders for palagonitized pillow breccias which unconformably overlie the Angora Peak sandstone. The major intrusive body is a 1200-foot thick diabasic sill referred to as the Neahkahnie sill. The extrusive basalts formed in a subsiding marine basin in which over 1600 feet of pillow lavas, pillow breccias, and minor basalt flows were locally extruded. The area is cut by a series of west-northwest and north-trending faults. Two synclines and an anticline strike subparallel to the west-northwest trending faults. Close