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• 1. [Article] Superposed compressional and extensional strain in Lower Paleozic rocks of the northwestern Grant Range, Nevada

  The Grant Range, in east-central Nevada, is a north-east trending range bounded on the west by a west-dipping normal fault system. Rocks within the range record a complex polyphase Mesozoic ductile compressional ...

  Citation × Citation Citation Abstract Copy Title: Superposed compressional and extensional strain in Lower Paleozic rocks of the northwestern Grant Range, Nevada Author: Camilleri, Phyllis A. The Grant Range, in east-central Nevada, is a north-east trending range bounded on the west by a west-dipping normal fault system. Rocks within the range record a complex polyphase Mesozoic ductile compressional and Cenozoic brittle extensional deformational history. The northwestern Grant Range exposes deformed, regionally metamorphosed and unmetamorphosed, Cambrian to Mississippian carbonate and clastic strata, and minor Tertiary granitic and andesitic dikes. Cambrian and Ordovician rocks are ductilely strained and metamorphosed. Metamorphic grade decreases stratigraphically upwards, generally commensurate with the degree of ductile strain. Two Mesozoic compressional events are recorded in the rocks of the northwestern Grant Range. The first event produced mesoscopic, east-vergent folds with spaced axial-planar cleavage. These folds were overprinted by small-scale, west-vergent thrust faults and folds of the second event. Regional metamorphism began during the first folding event, but outlasted deformation. Static metamorphism was followed by west-vergent deformation, which marked the end of metamorphism. The compressional structures may have been part of an east-vergent anticline or the hanging wall of an east-vergent thrust fault. Ductile Mesozoic compressional structures and fabrics are cut by an arched, imbricate stack of Cenozoic low-angle normal faults of a more brittle character. The low-angle normal faults omit stratigraphic section, and each successively structurally higher fault is generally younger than the one below it. Most faults appear to be west-directed. The age of the low-angle normal fault system is constrained only as late Oligocene to Pleistocene, but could be largely Miocene to Pleistocene. Some granitic and andesitic dikes cross-cut or are cut by low-angle normal faults, indicating that igneous activity is at least in part synchronous with extension. The geometry of the low-angle normal faults suggest that these faults could be rotated, extinct fault segments formed as a result of arching of the upper reaches of the high- to moderate-angle west-dipping normal fault system responsible for the uplift of the Grant Range. This would suggest that the low-angle normal faults are products of progressive Basin and Range extension and do not represent a distinct extensional event. Title: Superposed compressional and extensional strain in Lower Paleozic rocks of the northwestern Grant Range, Nevada Author: Camilleri, Phyllis A. The Grant Range, in east-central Nevada, is a north-east trending range bounded on the west by a west-dipping normal fault system. Rocks within the range record a complex polyphase Mesozoic ductile compressional and Cenozoic brittle extensional deformational history. The northwestern Grant Range exposes deformed, regionally metamorphosed and unmetamorphosed, Cambrian to Mississippian carbonate and clastic strata, and minor Tertiary granitic and andesitic dikes. Cambrian and Ordovician rocks are ductilely strained and metamorphosed. Metamorphic grade decreases stratigraphically upwards, generally commensurate with the degree of ductile strain. Two Mesozoic compressional events are recorded in the rocks of the northwestern Grant Range. The first event produced mesoscopic, east-vergent folds with spaced axial-planar cleavage. These folds were overprinted by small-scale, west-vergent thrust faults and folds of the second event. Regional metamorphism began during the first folding event, but outlasted deformation. Static metamorphism was followed by west-vergent deformation, which marked the end of metamorphism. The compressional structures may have been part of an east-vergent anticline or the hanging wall of an east-vergent thrust fault. Ductile Mesozoic compressional structures and fabrics are cut by an arched, imbricate stack of Cenozoic low-angle normal faults of a more brittle character. The low-angle normal faults omit stratigraphic section, and each successively structurally higher fault is generally younger than the one below it. Most faults appear to be west-directed. The age of the low-angle normal fault system is constrained only as late Oligocene to Pleistocene, but could be largely Miocene to Pleistocene. Some granitic and andesitic dikes cross-cut or are cut by low-angle normal faults, indicating that igneous activity is at least in part synchronous with extension. The geometry of the low-angle normal faults suggest that these faults could be rotated, extinct fault segments formed as a result of arching of the upper reaches of the high- to moderate-angle west-dipping normal fault system responsible for the uplift of the Grant Range. This would suggest that the low-angle normal faults are products of progressive Basin and Range extension and do not represent a distinct extensional event. Close

• 2. [Article] The Deschutes Formation-- High Cascade transition in the Whitewater River area, Jefferson County, Oregon

  The Whitewater River area is located directly east of Mt. Jefferson in the Cascades of central Oregon. Approximately 90 mi2 (230 km2) were mapped (scale 1/24,000) and four new K-Ar ages and 151 major element ...

  Citation × Citation Citation Abstract Copy Title: The Deschutes Formation-- High Cascade transition in the Whitewater River area, Jefferson County, Oregon Author: Yogodzinski, Gene M. The Whitewater River area is located directly east of Mt. Jefferson in the Cascades of central Oregon. Approximately 90 mi2 (230 km2) were mapped (scale 1/24,000) and four new K-Ar ages and 151 major element analyses were obtained in a study of the stratigraphic and magmatic transition from the Miocene - Pliocene Deschutes Formation on the east to the Pliocene - Pleistocene High Cascades on the west. Deschutes strata in the Whitewater River area overlie late Miocene (8-11+ m.y.) andesites, dacites, and rhyodacites along an erosional unconformity. The oldest Deschutes rocks exposed in the Whitewater River area are approximately 6 m.y. old, and the youngest are probably between 4.5 and 5 m.y. old. The oldest High Cascade rocks exposed in the Whitewater River area are approximately 4.3 m.y. old. There is no evidence for a hiatus in volcanic activity between Deschutes and High Cascade time in the Whitewater River area. Late Pleistocene explosive volcanism, probably free Mt. Jefferson, is evidenced in a hornblende rhyodacite pyroclastic-flow deposit which occurs within the glacial stratigraphy and is tentatively thought to be between approximately 60,000 and 20,000 years old. Deschutes strata are dominated by pyroclastic lithologies (mostly ash-flow tuffs) with some lava flows and minor epiclastic sediment. Compositions range mostly between basaltic andesite and dacite. Many Deschutes-age rocks are aphyric, high in Fed, TiO2, and alkalies, and low in MgO, CaO, and A12O3. They define a tholeiitic trend extending at least from basaltic andesite to dacite that can largely be derived through fractional crystallization of plagioclase, olivine, magnetite, and clinopyroxene from a parent magma, probably of basaltic composition. These rocks are compositionally similar to "tholeiitic anorogenic andesites" that are most commonly associated with areas of crustal extension. Rocks of High Cascade age in the Whitewater River area are mostly lava flaws that range in composition from basalt (high-alumina, olivine tholeiite) to rhyodacite. The High Cascade suite forms a calc-alkalic association that is typical of subduction-related magmatic arcs. Fractional crystallization of the basalts leads to iron-enrichment. Fractional crystallization of the basaltic andesites might lead to calc-alkalic compositions, but the mineral phases necessary to deplete the magmas in FeO, TiO2, and CaO (magnetite and clinopyroxene) are not common phenocryst phases in the basaltic andesites or andesites. Two northwest-trending, down-to-the-west normal faults with sane possible strike-slip motion have been mapped in the upper Whitewater River area, directly west of Lion's Head. Motion on these faults occurred after approximately 4 m.y. ago, but probably began prior to that time. There is between 200 and 400 ft (60-120 m) of apparent vertical separation on the western side of these faults. There may be a large, northwest-trending fault running from the south end of Green Ridge, through Bald Peter and the Whitewater River area, but this structure is largely buried by younger volcanic rocks. There is no evidence for a northern extension of the north-trending Green Ridge faults, and there is no evidence for large structural displacement in the lower Whitewater River along north- or northwest-trending structures. The Deschutes Formation - High Cascade transition in the Whitewater River area is marked by a switch in the eruptive style and in the dominant magmatic compositions during Deschutes and High Cascade times. Volcanism in the Whitewater River area does not appear to have been episodic with respect to volume and/or intensity; rather, the character of magmatism has varied with time and with the tectonic style through the period immediately prior to and following the formation of the High cascade graben. Title: The Deschutes Formation-- High Cascade transition in the Whitewater River area, Jefferson County, Oregon Author: Yogodzinski, Gene M. The Whitewater River area is located directly east of Mt. Jefferson in the Cascades of central Oregon. Approximately 90 mi2 (230 km2) were mapped (scale 1/24,000) and four new K-Ar ages and 151 major element analyses were obtained in a study of the stratigraphic and magmatic transition from the Miocene - Pliocene Deschutes Formation on the east to the Pliocene - Pleistocene High Cascades on the west. Deschutes strata in the Whitewater River area overlie late Miocene (8-11+ m.y.) andesites, dacites, and rhyodacites along an erosional unconformity. The oldest Deschutes rocks exposed in the Whitewater River area are approximately 6 m.y. old, and the youngest are probably between 4.5 and 5 m.y. old. The oldest High Cascade rocks exposed in the Whitewater River area are approximately 4.3 m.y. old. There is no evidence for a hiatus in volcanic activity between Deschutes and High Cascade time in the Whitewater River area. Late Pleistocene explosive volcanism, probably free Mt. Jefferson, is evidenced in a hornblende rhyodacite pyroclastic-flow deposit which occurs within the glacial stratigraphy and is tentatively thought to be between approximately 60,000 and 20,000 years old. Deschutes strata are dominated by pyroclastic lithologies (mostly ash-flow tuffs) with some lava flows and minor epiclastic sediment. Compositions range mostly between basaltic andesite and dacite. Many Deschutes-age rocks are aphyric, high in Fed, TiO2, and alkalies, and low in MgO, CaO, and A12O3. They define a tholeiitic trend extending at least from basaltic andesite to dacite that can largely be derived through fractional crystallization of plagioclase, olivine, magnetite, and clinopyroxene from a parent magma, probably of basaltic composition. These rocks are compositionally similar to "tholeiitic anorogenic andesites" that are most commonly associated with areas of crustal extension. Rocks of High Cascade age in the Whitewater River area are mostly lava flaws that range in composition from basalt (high-alumina, olivine tholeiite) to rhyodacite. The High Cascade suite forms a calc-alkalic association that is typical of subduction-related magmatic arcs. Fractional crystallization of the basalts leads to iron-enrichment. Fractional crystallization of the basaltic andesites might lead to calc-alkalic compositions, but the mineral phases necessary to deplete the magmas in FeO, TiO2, and CaO (magnetite and clinopyroxene) are not common phenocryst phases in the basaltic andesites or andesites. Two northwest-trending, down-to-the-west normal faults with sane possible strike-slip motion have been mapped in the upper Whitewater River area, directly west of Lion's Head. Motion on these faults occurred after approximately 4 m.y. ago, but probably began prior to that time. There is between 200 and 400 ft (60-120 m) of apparent vertical separation on the western side of these faults. There may be a large, northwest-trending fault running from the south end of Green Ridge, through Bald Peter and the Whitewater River area, but this structure is largely buried by younger volcanic rocks. There is no evidence for a northern extension of the north-trending Green Ridge faults, and there is no evidence for large structural displacement in the lower Whitewater River along north- or northwest-trending structures. The Deschutes Formation - High Cascade transition in the Whitewater River area is marked by a switch in the eruptive style and in the dominant magmatic compositions during Deschutes and High Cascade times. Volcanism in the Whitewater River area does not appear to have been episodic with respect to volume and/or intensity; rather, the character of magmatism has varied with time and with the tectonic style through the period immediately prior to and following the formation of the High cascade graben. Close

• 3. [Article] Subsurface geology of the southeastern Cuyama Valley, southern Coast Ranges, California

  The southeastern Cuyama Valley is located in the southern Coast Ranges, west of Bakersfield, California. Subsurface geologic mapping using data from 62 prospect wells was integrated with surface mapping to ...

  Citation × Citation Citation Abstract Copy Title: Subsurface geology of the southeastern Cuyama Valley, southern Coast Ranges, California Author: Spitz, Herbert M. The southeastern Cuyama Valley is located in the southern Coast Ranges, west of Bakersfield, California. Subsurface geologic mapping using data from 62 prospect wells was integrated with surface mapping to determine the depositional and deformational history of this part of the Neogene Cuyama basin. The northwest-trending Russell fault system was active from late Oligocene to Pliocene time. Deformation along this major wrench system began during deposition of the late Oligocene to early Miocene Soda Lake Shale Member of the Vaqueros Formation and ended prior to deposition of the Plio-Pleistocene Morales Formation. The southern extension of this fault system remains uncertain, but it probably joins the Ozena fault southeast of the South Cuyama oil field. Removal of 16 to 18 miles of right-lateral offset on the Russell fault system restores the Ozena fault to a position directly east of the La Panza fault. These two faults were probably a single fault, designated the La Panza-Ozena fault, which was active, north-side down, during the Oligocene. Nonmarine conglomerates of the Simmler and lower Caliente formations were deposited north of this fault during the Oligocene, prior to the initiation of notion on the Russell fault system. Three major faults of the Cox fault zone on the west and the Lundstrom-Becker and Becker-Heller faults on the east define the margins of the Cox trough, a complex north- to northeast-trending graben north of the Russell fault which was active from Saucesian through Relizian time (early Miocene). The Saltos Shale Member of the Monterey Formation increases in thickness by 3 to 7 times across the margins of the trough. Growth faulting associated with the Cox trough ended prior to deposition of the middle Johnston sand on all faults except the Cox 46-5 fault, which was active through deposition of the Branch Canyon Sandstone. Post-Pliocene tectonism in the Cuyama basin was limited to folding and reverse-faulting in response to regional north-south compression. The Central Cuyama dome and associated north-dipping reverse faults formed during an early episode of this deformation. Subsequent deformation occurred on the Morales fault, the South Cuyama fault, and the rejuvenated Ozena fault. This Quaternary thrusting obscured the structures of the older wrench-tectonic regime and resulted in the formation of the Caliente and Sierra Madre Ranges and the present-day Cuyama Valley. Title: Subsurface geology of the southeastern Cuyama Valley, southern Coast Ranges, California Author: Spitz, Herbert M. The southeastern Cuyama Valley is located in the southern Coast Ranges, west of Bakersfield, California. Subsurface geologic mapping using data from 62 prospect wells was integrated with surface mapping to determine the depositional and deformational history of this part of the Neogene Cuyama basin. The northwest-trending Russell fault system was active from late Oligocene to Pliocene time. Deformation along this major wrench system began during deposition of the late Oligocene to early Miocene Soda Lake Shale Member of the Vaqueros Formation and ended prior to deposition of the Plio-Pleistocene Morales Formation. The southern extension of this fault system remains uncertain, but it probably joins the Ozena fault southeast of the South Cuyama oil field. Removal of 16 to 18 miles of right-lateral offset on the Russell fault system restores the Ozena fault to a position directly east of the La Panza fault. These two faults were probably a single fault, designated the La Panza-Ozena fault, which was active, north-side down, during the Oligocene. Nonmarine conglomerates of the Simmler and lower Caliente formations were deposited north of this fault during the Oligocene, prior to the initiation of notion on the Russell fault system. Three major faults of the Cox fault zone on the west and the Lundstrom-Becker and Becker-Heller faults on the east define the margins of the Cox trough, a complex north- to northeast-trending graben north of the Russell fault which was active from Saucesian through Relizian time (early Miocene). The Saltos Shale Member of the Monterey Formation increases in thickness by 3 to 7 times across the margins of the trough. Growth faulting associated with the Cox trough ended prior to deposition of the middle Johnston sand on all faults except the Cox 46-5 fault, which was active through deposition of the Branch Canyon Sandstone. Post-Pliocene tectonism in the Cuyama basin was limited to folding and reverse-faulting in response to regional north-south compression. The Central Cuyama dome and associated north-dipping reverse faults formed during an early episode of this deformation. Subsequent deformation occurred on the Morales fault, the South Cuyama fault, and the rejuvenated Ozena fault. This Quaternary thrusting obscured the structures of the older wrench-tectonic regime and resulted in the formation of the Caliente and Sierra Madre Ranges and the present-day Cuyama Valley. Close