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• 21. [Article] The Ore bin ; Vol. 36 No. 3 (March 1974)

  Wright's Point, a 250-foot-high, sinuous, flat-topped ridge, projects eastward into Harney Basin, Harney County, Oregon. This 6-mile-long feature ranges from 200 to 600 yards wide and merges with a broad ...

  Citation × Citation Citation Abstract Copy Title: The Ore bin ; Vol. 36 No. 3 (March 1974) Author: Niem, Alan R., Oregon. Dept. of Geology and Mineral Industries Wright's Point, a 250-foot-high, sinuous, flat-topped ridge, projects eastward into Harney Basin, Harney County, Oregon. This 6-mile-long feature ranges from 200 to 600 yards wide and merges with a broad mesa at its western end. The nearest topographic highs are Dog Mountain, 2 miles southwest, and foothills of the Blue Mountains near Burns, 12 miles northwest. The point is composed of a fluvial sequence of tuffaceous channel sandstones, mudstones, and conglomerates (Pliocene-Pleistocene Harney Formation) capped by two thin, early Pleistocene diktytaxitic olivine basalt flows. The configuration of the ridge and the paleocurrent pattern, sedimentary structures, fossils, and stratigraphic relations of the rocks to nearby topographic highs suggest that the fluvial sequence and capping basalts were deposited in a narrow valley of an eastward flowing meandering stream(s). The basalts acted as a protective cap while the less-resistant valley walls were eroded away to produce an inverted topography. Remnants of the valley walls consist of a Plio-Pleistocene palagonite tuff ring at Dog Mountain and ignimbrites and tuffaceous sediments of the middle Pliocene Danforth Formation in the Blue Mountain foothills. Reworked palagonite tuff, pumice sands, and Danforth ignimbrite pebbles compose the sandstone and conglomerates of Wright's Point. Measured elevation differences at the base of the lower flow, orientations of filled and open lava tubes, and increasing number of flows to the west suggest that the basalt flowed from west to east down the stream valley. Probable sources of the basalts are several vents 6 miles west of Wright's Point near the Palomino Buttes. Title: The Ore bin ; Vol. 36 No. 3 (March 1974) Author: Niem, Alan R., Oregon. Dept. of Geology and Mineral Industries Wright's Point, a 250-foot-high, sinuous, flat-topped ridge, projects eastward into Harney Basin, Harney County, Oregon. This 6-mile-long feature ranges from 200 to 600 yards wide and merges with a broad mesa at its western end. The nearest topographic highs are Dog Mountain, 2 miles southwest, and foothills of the Blue Mountains near Burns, 12 miles northwest. The point is composed of a fluvial sequence of tuffaceous channel sandstones, mudstones, and conglomerates (Pliocene-Pleistocene Harney Formation) capped by two thin, early Pleistocene diktytaxitic olivine basalt flows. The configuration of the ridge and the paleocurrent pattern, sedimentary structures, fossils, and stratigraphic relations of the rocks to nearby topographic highs suggest that the fluvial sequence and capping basalts were deposited in a narrow valley of an eastward flowing meandering stream(s). The basalts acted as a protective cap while the less-resistant valley walls were eroded away to produce an inverted topography. Remnants of the valley walls consist of a Plio-Pleistocene palagonite tuff ring at Dog Mountain and ignimbrites and tuffaceous sediments of the middle Pliocene Danforth Formation in the Blue Mountain foothills. Reworked palagonite tuff, pumice sands, and Danforth ignimbrite pebbles compose the sandstone and conglomerates of Wright's Point. Measured elevation differences at the base of the lower flow, orientations of filled and open lava tubes, and increasing number of flows to the west suggest that the basalt flowed from west to east down the stream valley. Probable sources of the basalts are several vents 6 miles west of Wright's Point near the Palomino Buttes. Close

• 22. [Article] Seismic stratigraphy of the central South China Sea basin and implications for neotectonics

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/journal/10.1002/%28ISSN%292...

  Citation × Citation Citation Abstract Copy Title: Seismic stratigraphy of the central South China Sea basin and implications for neotectonics Author: Li, Jiabiao, Colwell, Frederick S., Koppers, Anthony A. P., Li, Chun-Feng, Ding, Weiwei, et al. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/journal/10.1002/%28ISSN%292169-9356/. Title: Seismic stratigraphy of the central South China Sea basin and implications for neotectonics Author: Li, Jiabiao, Colwell, Frederick S., Koppers, Anthony A. P., Li, Chun-Feng, Ding, Weiwei, et al. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/journal/10.1002/%28ISSN%292169-9356/. Close

• 23. [Article] Ocean Temperature Variability during the Late Pleistocene

  This dissertation explores one overarching question relevant to the paleoclimate of the latest Pleistocene glacial cycle (approximately the last 130,000 years): “How did spatial and temporal evolution ...

  Citation × Citation Citation Abstract Copy Title: Ocean Temperature Variability during the Late Pleistocene Author: Hoffman, Jeremy Scott This dissertation explores one overarching question relevant to the paleoclimate of the latest Pleistocene glacial cycle (approximately the last 130,000 years): “How did spatial and temporal evolution of ocean temperature, both at the surface and interior, relate to other parts of the climate system in the late Pleistocene?” Results from three studies are presented that seek to address longstanding questions in paleoceanography and paleoclimatology for the late Pleistocene using a combination of novel and accepted statistical and geochemical analysis techniques and leveraging comparisons with available global climate model data. The last interglaciation (LIG; ~129-116 ka) was the most recent period in Earth’s history with higher-than-present global sea level (≥6-9 m) under similar-to-preindustrial concentrations of atmospheric CO₂. This suggests that additional feedbacks related to albedo, insolation, and ocean overturning circulation may have resulted in the apparent warming required to cause the higher sea level. Our understanding of how much warmer the LIG was relative to the present interglaciation remains uncertain, however, with current estimates suggesting that sea-surface temperatures (SSTs) were 0-2°C warmer than late-20th century average global temperatures. We present a global compilation of proxy-based annual SST spanning the LIG. Using Monte Carlo and Bayesian techniques to propagate uncertainties in age-model and proxy-based SST reconstructions, our results quantify the spatial timing, amplitude, and uncertainty in global and regional SST change during the LIG. Our conclusions suggest that the LIG surface ocean was indistinguishable from the average surface ocean temperatures observed for the last two decades (1995-2014). This may ultimately imply that the Earth is currently committed to ≥6-9m of equilibrium sea-level rise. Although the LIG is not an analogue for present and future climate change due to the large differences in seasonal orbital insolation and absence of anthropogenic greenhouse gas radiative forcing, it provides an opportunity to test the ability of global climate models to simulate the mechanisms and climate feedbacks responsible for the warmer climate and higher global mean sea level during the LIG. However, when forced only by LIG greenhouse gas concentrations and insolation changes, climate models suggest that the annual mean temperature response was not significantly different from preindustrial control simulations. We present the first multi-model and multiscenario ensemble of transient and equilibrium global climate modeling results spanning the LIG. We show, using a novel model-data comparison framework, that these scenario-specific model results exhibit regionally independent agreement with ocean basin-specific proxy-based SST stacks. This result ultimately implies structural uncertainties and/or misrepresentations of climate feedbacks in the existing suite of climate model simulations, or underestimations of additional proxy-based SST uncertainties. Our conclusions suggest a new target LIG time period for future model-data comparisons and highlight the need for higher resolution transient climate modeling of the LIG and its dependence on meltwater input to the high latitude oceans during the preceding deglaciation. Few discoveries have stimulated the paleoclimate community more so than Heinrich events. Nevertheless, the cause of Heinrich events, characterized by a large flux of icebergs sourced from the Hudson Strait Ice Stream into the North Atlantic, remains debated. Commonly attributed to internal ice-sheet instability, the occurrence of Heinrich events during the coldest intervals of the last glacial cycle instead suggests an external climate control. We expand on recent studies that have shown that incursions of warm subsurface waters into the intermediate depth North Atlantic Ocean destabilized an ice shelf fronting the Hudson Strait Ice Stream, causing a Heinrich event. We present new surface- and bottom-water stable isotope, trace metal, and sedimentary records from two cores taken along the Labrador margin that further support subsurface warming as a trigger of Hudson Strait Heinrich events. We further relate these changes to other sediment core records from the North Atlantic and transient deglacial climate modeling results to show that subsurface warming was ubiquitous across the intermediate North Atlantic during the early part of the last deglaciation and was most likely caused by a preceding reduction in the Atlantic Meridional Overturning Circulation. Title: Ocean Temperature Variability during the Late Pleistocene Author: Hoffman, Jeremy Scott This dissertation explores one overarching question relevant to the paleoclimate of the latest Pleistocene glacial cycle (approximately the last 130,000 years): “How did spatial and temporal evolution of ocean temperature, both at the surface and interior, relate to other parts of the climate system in the late Pleistocene?” Results from three studies are presented that seek to address longstanding questions in paleoceanography and paleoclimatology for the late Pleistocene using a combination of novel and accepted statistical and geochemical analysis techniques and leveraging comparisons with available global climate model data. The last interglaciation (LIG; ~129-116 ka) was the most recent period in Earth’s history with higher-than-present global sea level (≥6-9 m) under similar-to-preindustrial concentrations of atmospheric CO₂. This suggests that additional feedbacks related to albedo, insolation, and ocean overturning circulation may have resulted in the apparent warming required to cause the higher sea level. Our understanding of how much warmer the LIG was relative to the present interglaciation remains uncertain, however, with current estimates suggesting that sea-surface temperatures (SSTs) were 0-2°C warmer than late-20th century average global temperatures. We present a global compilation of proxy-based annual SST spanning the LIG. Using Monte Carlo and Bayesian techniques to propagate uncertainties in age-model and proxy-based SST reconstructions, our results quantify the spatial timing, amplitude, and uncertainty in global and regional SST change during the LIG. Our conclusions suggest that the LIG surface ocean was indistinguishable from the average surface ocean temperatures observed for the last two decades (1995-2014). This may ultimately imply that the Earth is currently committed to ≥6-9m of equilibrium sea-level rise. Although the LIG is not an analogue for present and future climate change due to the large differences in seasonal orbital insolation and absence of anthropogenic greenhouse gas radiative forcing, it provides an opportunity to test the ability of global climate models to simulate the mechanisms and climate feedbacks responsible for the warmer climate and higher global mean sea level during the LIG. However, when forced only by LIG greenhouse gas concentrations and insolation changes, climate models suggest that the annual mean temperature response was not significantly different from preindustrial control simulations. We present the first multi-model and multiscenario ensemble of transient and equilibrium global climate modeling results spanning the LIG. We show, using a novel model-data comparison framework, that these scenario-specific model results exhibit regionally independent agreement with ocean basin-specific proxy-based SST stacks. This result ultimately implies structural uncertainties and/or misrepresentations of climate feedbacks in the existing suite of climate model simulations, or underestimations of additional proxy-based SST uncertainties. Our conclusions suggest a new target LIG time period for future model-data comparisons and highlight the need for higher resolution transient climate modeling of the LIG and its dependence on meltwater input to the high latitude oceans during the preceding deglaciation. Few discoveries have stimulated the paleoclimate community more so than Heinrich events. Nevertheless, the cause of Heinrich events, characterized by a large flux of icebergs sourced from the Hudson Strait Ice Stream into the North Atlantic, remains debated. Commonly attributed to internal ice-sheet instability, the occurrence of Heinrich events during the coldest intervals of the last glacial cycle instead suggests an external climate control. We expand on recent studies that have shown that incursions of warm subsurface waters into the intermediate depth North Atlantic Ocean destabilized an ice shelf fronting the Hudson Strait Ice Stream, causing a Heinrich event. We present new surface- and bottom-water stable isotope, trace metal, and sedimentary records from two cores taken along the Labrador margin that further support subsurface warming as a trigger of Hudson Strait Heinrich events. We further relate these changes to other sediment core records from the North Atlantic and transient deglacial climate modeling results to show that subsurface warming was ubiquitous across the intermediate North Atlantic during the early part of the last deglaciation and was most likely caused by a preceding reduction in the Atlantic Meridional Overturning Circulation. Close

• 24. [Article] Data report : composition of clay minerals from hemiplegic sediments at Hydrate Ridge, Cascadia subduction zone

  This report describes the results of semiquantitative analysis of clay mineral composition by X-ray diffraction. The samples consist of hemipelagic mud and mudstone cored from Hydrate Ridge during Leg ...

  Citation × Citation Citation Abstract Copy Title: Data report : composition of clay minerals from hemiplegic sediments at Hydrate Ridge, Cascadia subduction zone Author: Torres, Marta E., Underwood, Michael This report describes the results of semiquantitative analysis of clay mineral composition by X-ray diffraction. The samples consist of hemipelagic mud and mudstone cored from Hydrate Ridge during Leg 204 of the Ocean Drilling Program. We analyzed oriented aggregates of the clay-sized fractions (<2 μm) to estimate relative percentages of smectite, illite, and chlorite (+ kaolinite). For the most part, stratigraphic variations in clay mineral composition are modest and there are no significant differences among the seven sites that were included in the study. On average, early Pleistocene to Holocene trench slope and slope basin deposits contain 29% smectite, 31% illite, and 40% chlorite (+ kaolinite). Late Pliocene to early Pleistocene strata from the underlying accretionary prism contain moderately larger proportions of smectite with average values of 38% smectite, 27% illite, and 35% chlorite (+ kaolinite). There is no evidence of clay mineral diagenesis at the depths sampled. The expandability of smectite is, on average, equal to 64%, and there are no systematic variations in expandability as a function of burial depth or depositional age. The absence of clay mineral diagenesis is consistent with the relatively shallow sample depths and corresponding maximum temperatures of only 24°–33°C. Title: Data report : composition of clay minerals from hemiplegic sediments at Hydrate Ridge, Cascadia subduction zone Author: Torres, Marta E., Underwood, Michael This report describes the results of semiquantitative analysis of clay mineral composition by X-ray diffraction. The samples consist of hemipelagic mud and mudstone cored from Hydrate Ridge during Leg 204 of the Ocean Drilling Program. We analyzed oriented aggregates of the clay-sized fractions (<2 μm) to estimate relative percentages of smectite, illite, and chlorite (+ kaolinite). For the most part, stratigraphic variations in clay mineral composition are modest and there are no significant differences among the seven sites that were included in the study. On average, early Pleistocene to Holocene trench slope and slope basin deposits contain 29% smectite, 31% illite, and 40% chlorite (+ kaolinite). Late Pliocene to early Pleistocene strata from the underlying accretionary prism contain moderately larger proportions of smectite with average values of 38% smectite, 27% illite, and 35% chlorite (+ kaolinite). There is no evidence of clay mineral diagenesis at the depths sampled. The expandability of smectite is, on average, equal to 64%, and there are no systematic variations in expandability as a function of burial depth or depositional age. The absence of clay mineral diagenesis is consistent with the relatively shallow sample depths and corresponding maximum temperatures of only 24°–33°C. Close

• 25. [Article] Geology of Babyshoe Ridge Area, Southern Cascades, Washington

  The thesis area consists of approximately thirty square miles in the Southern Cascades of Washington near Mount Adams. The oldest exposed rocks are sedimentary volcanic clastics and pyroclastic flows of ...

  Citation × Citation Citation Abstract Copy Title: Geology of Babyshoe Ridge Area, Southern Cascades, Washington Author: Harle, David Sig The thesis area consists of approximately thirty square miles in the Southern Cascades of Washington near Mount Adams. The oldest exposed rocks are sedimentary volcanic clastics and pyroclastic flows of late-Oligocene age that form a homocline in the northwest corner of the area. A thick pile of younger Tertiary lavas, mudflows, and volcanic clastics unconformably overlie the Oligocene rocks, and contain two hydrothermally altered zones. Andesitic lavas from Mount Adams lap onto older rocks and are of Recent to Pleistocene age. Two glacial till deposits and two airfall pyroclastic layers are present throughout the area. One major fault and two broad folds are present in the area. The geothermal potential is not believed to be great, because genetic relationships indicate the hydrothermal systems that produced the two alteration zones were active only in pre- Pleistocene time. There are no external manifestations of a presently active hydrothermal system with geothermal potential. Title: Geology of Babyshoe Ridge Area, Southern Cascades, Washington Author: Harle, David Sig The thesis area consists of approximately thirty square miles in the Southern Cascades of Washington near Mount Adams. The oldest exposed rocks are sedimentary volcanic clastics and pyroclastic flows of late-Oligocene age that form a homocline in the northwest corner of the area. A thick pile of younger Tertiary lavas, mudflows, and volcanic clastics unconformably overlie the Oligocene rocks, and contain two hydrothermally altered zones. Andesitic lavas from Mount Adams lap onto older rocks and are of Recent to Pleistocene age. Two glacial till deposits and two airfall pyroclastic layers are present throughout the area. One major fault and two broad folds are present in the area. The geothermal potential is not believed to be great, because genetic relationships indicate the hydrothermal systems that produced the two alteration zones were active only in pre- Pleistocene time. There are no external manifestations of a presently active hydrothermal system with geothermal potential. Close

• 26. [Article] Late Pleistocene lithic technological organization on the southern Oregon coast : investigations at Indian Sands (35-CU-67C)

  Excavations conducted at Indian Sands (35-CU-67C), located along Oregon's southern coast, during 2002 and 2003 identified two discreet, artifact-bearing stratigraphic units. The uppermost unit is a deflated ...

  Citation × Citation Citation Abstract Copy Title: Late Pleistocene lithic technological organization on the southern Oregon coast : investigations at Indian Sands (35-CU-67C) Author: Willis, Samuel C. Excavations conducted at Indian Sands (35-CU-67C), located along Oregon's southern coast, during 2002 and 2003 identified two discreet, artifact-bearing stratigraphic units. The uppermost unit is a deflated surface containing burnt shell and lithic artifacts associated with early Holocene ¹⁴C dates, while the underlying unit contained only lithic tools and debitage, some of which were associated with a ¹⁴C date of 10,430 ± 150 RCYBP. The late Pleistocene lithic assemblage at 35-CU-67C provides the earliest evidence for human presence on the Oregon coast to date. Analysis performed on the late Pleistocene assemblage addresses the validity of existing hypotheses regarding the nature of early Oregon coastal hunter-gatherer technological and subsistence strategies. These hypotheses are focused on whether early populations on the Oregon coast practiced a generalist-forager or collector subsistence strategy. Using theoretical approaches that deal with the organization of hunter-gatherer technology, analyses were conducted on the lithic tool and debitage assemblages at 35-CU- 67C in order to infer past hunter-gatherer behavior. Through the implementation of multiple tool and debitage analysis methodologies, issues of hunter-gatherer mobility, raw material procurement, stages of lithic reduction, tool production, and site function are presented. The data generated by the late Pleistocene lithic assemblage at 35-CU-67C are compared with the overlying surficial assemblage, additional early sites along the North American Pacific coast, and to contemporaneous sites located further inland within the Pacific Northwest region. Results of the lithic analyses at 35-CU-67C show distinct similarities in debitage trends between the assemblages of each stratigraphic unit. However, when tool assemblages from these units are compared, discrepancies in the types and amount of tools are found. Reasons for intra-site variability and similarity are explained through raw material studies and site function at 35-CU-67C. Additionally, similarities between the early tool assemblage at 35-CU-67C and those found in early tool assemblages on the extended Pacific coast and interior Pacific Northwest regions are discussed. This thesis demonstrates that early southern Oregon coastal populations had a tendency towards high mobility and used a generalized toolkit organization. Early lithic technology used at 35-CU-67C emphasized multidirectional core technology and biface manufacture in the form of preforms and leaf-shaped projectile-points. This type of technological organization is to be expected from hunter-gatherers practicing a generalist-forager subsistence strategy. Based on the 10,430 ± 150 RCYBP date and technological organization at 35-CU-67C, early Oregon coastal occupation is seen as encompassing a generalist-forager subsistence strategy most likely adapted to both coastal and terrestrial environments. Title: Late Pleistocene lithic technological organization on the southern Oregon coast : investigations at Indian Sands (35-CU-67C) Author: Willis, Samuel C. Excavations conducted at Indian Sands (35-CU-67C), located along Oregon's southern coast, during 2002 and 2003 identified two discreet, artifact-bearing stratigraphic units. The uppermost unit is a deflated surface containing burnt shell and lithic artifacts associated with early Holocene ¹⁴C dates, while the underlying unit contained only lithic tools and debitage, some of which were associated with a ¹⁴C date of 10,430 ± 150 RCYBP. The late Pleistocene lithic assemblage at 35-CU-67C provides the earliest evidence for human presence on the Oregon coast to date. Analysis performed on the late Pleistocene assemblage addresses the validity of existing hypotheses regarding the nature of early Oregon coastal hunter-gatherer technological and subsistence strategies. These hypotheses are focused on whether early populations on the Oregon coast practiced a generalist-forager or collector subsistence strategy. Using theoretical approaches that deal with the organization of hunter-gatherer technology, analyses were conducted on the lithic tool and debitage assemblages at 35-CU- 67C in order to infer past hunter-gatherer behavior. Through the implementation of multiple tool and debitage analysis methodologies, issues of hunter-gatherer mobility, raw material procurement, stages of lithic reduction, tool production, and site function are presented. The data generated by the late Pleistocene lithic assemblage at 35-CU-67C are compared with the overlying surficial assemblage, additional early sites along the North American Pacific coast, and to contemporaneous sites located further inland within the Pacific Northwest region. Results of the lithic analyses at 35-CU-67C show distinct similarities in debitage trends between the assemblages of each stratigraphic unit. However, when tool assemblages from these units are compared, discrepancies in the types and amount of tools are found. Reasons for intra-site variability and similarity are explained through raw material studies and site function at 35-CU-67C. Additionally, similarities between the early tool assemblage at 35-CU-67C and those found in early tool assemblages on the extended Pacific coast and interior Pacific Northwest regions are discussed. This thesis demonstrates that early southern Oregon coastal populations had a tendency towards high mobility and used a generalized toolkit organization. Early lithic technology used at 35-CU-67C emphasized multidirectional core technology and biface manufacture in the form of preforms and leaf-shaped projectile-points. This type of technological organization is to be expected from hunter-gatherers practicing a generalist-forager subsistence strategy. Based on the 10,430 ± 150 RCYBP date and technological organization at 35-CU-67C, early Oregon coastal occupation is seen as encompassing a generalist-forager subsistence strategy most likely adapted to both coastal and terrestrial environments. Close

• 27. [Article] Millennial-scale surface and deep water oscillations in the N.E. Pacific : implications for late pleistocene climate change

  Citation × Citation Citation Abstract Copy Title: Millennial-scale surface and deep water oscillations in the N.E. Pacific : implications for late pleistocene climate change Author: Lund, David Charles Title: Millennial-scale surface and deep water oscillations in the N.E. Pacific : implications for late pleistocene climate change Author: Lund, David Charles Close

• 28. [Article] Constraints of the origin of the middle Pleistocene transition from the glacial sedimentary record of the north-central United States

  This dissertation focuses on the role of ice sheets in the transition during the middle Pleistocene (-1.2 Ma) from 41-kyr glacial cycles to 100-kyr glacial cycles. This research evaluates the hypothesis ...

  Citation × Citation Citation Abstract Copy Title: Constraints of the origin of the middle Pleistocene transition from the glacial sedimentary record of the north-central United States Author: Roy, Martin This dissertation focuses on the role of ice sheets in the transition during the middle Pleistocene (-1.2 Ma) from 41-kyr glacial cycles to 100-kyr glacial cycles. This research evaluates the hypothesis that the middle Pleistocene transition (MPT) was related to the glacial erosion of a regolith mantle and the subsequent exposure of fresh crystalline bedrock. This issue is addressed through the study of glacial sedimentary sequences in Iowa, Nebraska, Kansas, and Missouri. Testing the hypothesis first required the establishment of a stratigraphic framework for pre-Illinoian glacial sequences. A chronology developed around till compositional data and chronological constraints provided by paleomagnetic measurements on glacigenic sediments, and three volcanic ashes, indicate that the midcontinent tills can be grouped under three categories representing at least seven ice advances: two older groups of reverse-polarity tills containing a low and intermediate proportion of clasts and minerals derived from crystalline bedrock, respectively, and one younger group of normal-polarity tills enriched in crystalline materials. The bulk geochemistry of the silicate fraction of the midcontinent tills was then used to evaluate the character of the rock source eroded by ice sheets. The results show a general trend in which geochemical indices, from oldest to youngest tills, fall parallel to a mixing line defined by the composition of a weathered and fresh crystalline rock sources, respectively. The content in meteoric 10Be of tills also supports the existence of a regolith and its glacial erosion by -1.3 Ma, thus concordant with the onset of the MPT. Marine records of strontium, hafnium, and osmium isotopes provide additional support for the hypothesis. The nature of the till compositional changes was further addressed through a provenance study based on 504 40Ar/39Ar ages measured on individual K-feldspar grains retrieved from tills that span the last 2 Myr. Most samples yielded ages identical to those of numerical ages of the Churchill Province, thereby constraining deposition by ice from the western (Keewatin) sector of the Laurentide ice sheet. These results rule out a change in provenance, and thus show support for a change in the composition of the Churchill bedrock source during the late Cenozoic. Title: Constraints of the origin of the middle Pleistocene transition from the glacial sedimentary record of the north-central United States Author: Roy, Martin This dissertation focuses on the role of ice sheets in the transition during the middle Pleistocene (-1.2 Ma) from 41-kyr glacial cycles to 100-kyr glacial cycles. This research evaluates the hypothesis that the middle Pleistocene transition (MPT) was related to the glacial erosion of a regolith mantle and the subsequent exposure of fresh crystalline bedrock. This issue is addressed through the study of glacial sedimentary sequences in Iowa, Nebraska, Kansas, and Missouri. Testing the hypothesis first required the establishment of a stratigraphic framework for pre-Illinoian glacial sequences. A chronology developed around till compositional data and chronological constraints provided by paleomagnetic measurements on glacigenic sediments, and three volcanic ashes, indicate that the midcontinent tills can be grouped under three categories representing at least seven ice advances: two older groups of reverse-polarity tills containing a low and intermediate proportion of clasts and minerals derived from crystalline bedrock, respectively, and one younger group of normal-polarity tills enriched in crystalline materials. The bulk geochemistry of the silicate fraction of the midcontinent tills was then used to evaluate the character of the rock source eroded by ice sheets. The results show a general trend in which geochemical indices, from oldest to youngest tills, fall parallel to a mixing line defined by the composition of a weathered and fresh crystalline rock sources, respectively. The content in meteoric 10Be of tills also supports the existence of a regolith and its glacial erosion by -1.3 Ma, thus concordant with the onset of the MPT. Marine records of strontium, hafnium, and osmium isotopes provide additional support for the hypothesis. The nature of the till compositional changes was further addressed through a provenance study based on 504 40Ar/39Ar ages measured on individual K-feldspar grains retrieved from tills that span the last 2 Myr. Most samples yielded ages identical to those of numerical ages of the Churchill Province, thereby constraining deposition by ice from the western (Keewatin) sector of the Laurentide ice sheet. These results rule out a change in provenance, and thus show support for a change in the composition of the Churchill bedrock source during the late Cenozoic. Close

• 29. [Article] The case for NE-SW extension in northeast Oregon

  A zone of diffuse deformation -600 km-wide extending from northern California to Washington has developed resulting from the oblique subduction of the Juan de Fuca plate beneath North America, and the ...

  Citation × Citation Citation Abstract Copy Title: The case for NE-SW extension in northeast Oregon Author: Essman, Jim E. A zone of diffuse deformation -600 km-wide extending from northern California to Washington has developed resulting from the oblique subduction of the Juan de Fuca plate beneath North America, and the northwestward migration of the Pacific plate. This zone is marked by a change in structural style from transtension in the southern Oregon and western Nevada to transpression in southern and western Washington. The transition occurs across a relatively inactive zone in northeastern Oregon. New geologic mapping near the northern edge of this transitional zone suggests that extensional deformation persists into northeastern Oregon. The study area on the Oregon-Idaho border, is a complex zone characterized by NNWtrending primarily sinistral-oblique normal faults linking the NW-trending Halfway and Sturgill Peak (both down to the NE) normal faults to the NW and SE, respectively. The Halfway fault, -20 km-long - 730 m dip-slip separation, marks the southern boundary of a half-graben; whereas the Sturgill Peak fault, - 10 to 15 km long and not associated with a half-graben, has a minimum dip-slip separation of - 660 m. In contrast, the transfer zone informally named the Powder River Peninsula Fault Zone, or PRPFZ, houses numerous -NNW-striking, 2 to 3 km-long normal and sinistral-oblique normal faults with dip-slip separations of < 130 m. Evidence of late Pleistocene-Holocene deformation within the transfer zone is found in at least four places, and at two of those involves sinistral-oblique normal faults (-10-15 m vertical separation on a bedrock scarp) cutting late Pleistocene Bonneville flood gravels, -14 ka, with flood gravels both entrained in the fault plane and interbedded with Holocene colluvium implying significant activity in the late Pleistocene and possibly the early Holocene. Additionally, one fault in the PRPFZ cuts Holocene (?) soils/clays and deforms Pleistocene ash beds. Slip rates calculated from slickenlines and separations in the PRPFZ range from 0.01 mm/yr to possibly as high as 2.8 mm/yr to. This detailed slip data for the PRPFZ can be used as a proxy for the more regional deformational styles. Although the Halfway and Sturgill Peak faults have been interpreted to represent the southeastern extension of the Olympic-Wallowa Lineament (OWL), the tectonic and structural significance of the OWL remains poorly understood. It is suggested here that these structures reflect the continuation of Basinand-Range style deformation into northeastern Oregon, and western Idaho, and any connection to the OWL to be circumstantial. Furthermore, the presence of these structures poses a potential seismic hazard to local hydroelectric facilities. Title: The case for NE-SW extension in northeast Oregon Author: Essman, Jim E. A zone of diffuse deformation -600 km-wide extending from northern California to Washington has developed resulting from the oblique subduction of the Juan de Fuca plate beneath North America, and the northwestward migration of the Pacific plate. This zone is marked by a change in structural style from transtension in the southern Oregon and western Nevada to transpression in southern and western Washington. The transition occurs across a relatively inactive zone in northeastern Oregon. New geologic mapping near the northern edge of this transitional zone suggests that extensional deformation persists into northeastern Oregon. The study area on the Oregon-Idaho border, is a complex zone characterized by NNWtrending primarily sinistral-oblique normal faults linking the NW-trending Halfway and Sturgill Peak (both down to the NE) normal faults to the NW and SE, respectively. The Halfway fault, -20 km-long - 730 m dip-slip separation, marks the southern boundary of a half-graben; whereas the Sturgill Peak fault, - 10 to 15 km long and not associated with a half-graben, has a minimum dip-slip separation of - 660 m. In contrast, the transfer zone informally named the Powder River Peninsula Fault Zone, or PRPFZ, houses numerous -NNW-striking, 2 to 3 km-long normal and sinistral-oblique normal faults with dip-slip separations of < 130 m. Evidence of late Pleistocene-Holocene deformation within the transfer zone is found in at least four places, and at two of those involves sinistral-oblique normal faults (-10-15 m vertical separation on a bedrock scarp) cutting late Pleistocene Bonneville flood gravels, -14 ka, with flood gravels both entrained in the fault plane and interbedded with Holocene colluvium implying significant activity in the late Pleistocene and possibly the early Holocene. Additionally, one fault in the PRPFZ cuts Holocene (?) soils/clays and deforms Pleistocene ash beds. Slip rates calculated from slickenlines and separations in the PRPFZ range from 0.01 mm/yr to possibly as high as 2.8 mm/yr to. This detailed slip data for the PRPFZ can be used as a proxy for the more regional deformational styles. Although the Halfway and Sturgill Peak faults have been interpreted to represent the southeastern extension of the Olympic-Wallowa Lineament (OWL), the tectonic and structural significance of the OWL remains poorly understood. It is suggested here that these structures reflect the continuation of Basinand-Range style deformation into northeastern Oregon, and western Idaho, and any connection to the OWL to be circumstantial. Furthermore, the presence of these structures poses a potential seismic hazard to local hydroelectric facilities. Close

• 30. [Article] Soil solution chemistry, profile development, and mineral authigenesis in several western Oregon soils

  Clay mineral genesis was studied in soils representative of several different geomorphic surfaces in western Oregon, ranging in age from Pliocene-early Pleistocene to late Pleistocene. Soil solution studies, clay ...

  Citation × Citation Citation Abstract Copy Title: Soil solution chemistry, profile development, and mineral authigenesis in several western Oregon soils Author: Glasmann, Joseph Reed Clay mineral genesis was studied in soils representative of several different geomorphic surfaces in western Oregon, ranging in age from Pliocene-early Pleistocene to late Pleistocene. Soil solution studies, clay mineralogy, and soil raicromorphology were employed to provide evidence of clay mineral synthesis and interpret soil genesis. Soils at each study area were characterized by distinct differences in soil solution chemistry, clay mineralogy, plasmic fabric, and genetic history, although parent material compositions between sites were often similar. Soil solution studies suggested that clay mineral synthesis from solution does not occur in soils representing the oldest geomorphic surface. The cxic soil properties at this location were developed during a prior weathering cycle and the soils are at a genetic endpoint in the present environment. Soil solutions from Ultisols on remnants of Pleistocene surfaces in the Oregon Coast Range were in equilibrium with respect to kaolinite in the solum, but stable with respect to Mg-montmorillonite in the zone characterizing active bedrock weathering. Microraorphological, clay mineralogical, and chemical evidence suggested that alteration of Mgchlorite in sedimentary rocks leads to smectite genesis in the Cr horizon of the Ultisols, followed by conversion of smectite to halloysite and chloritic intergrade in the solum. Alteration of basalt in these soils also leads to the formation of smectite, which is unstable with respect to halloysite in well-drained microenvironments within soil profiles. Soil solutions from soils characteristic of silt-mantled late Pleistocene surfaces on the western margins of the Willamette Valley showed compositional variation from pedon to pedon and horizon to horizon within individual pedons, reflecting the influence of soil parent material compositional variation. Soil solutions were generally in equilibrium with respect to kaolinite, although solutions from horizons developed in tuffaceous sediments were in equilibrium with Mg-montmorillonite. Both kaolinite and smectite were observed as products of mineral authigenesis in these soils. Authigenic clay showed delicate honeycomb or hexagonal morphology in contrast to the parallel oriented appearance of illuvial clays. Andesite alteration in wet, unstable soils of Oregon's western Cascades also resulted in the formation of smectite. The sequence of mineral alteration in andesites is similar to that described for basalts; however, the final products of mineral authigenesis are distinctly microenvironment dependent. Morphologic evidence suggests that chemical properties of bulk soil solutions can not always be considered to represent the solution conditions at the site of mineral authigenesis. In the absence of reliable in situ micro-chemical analytical techniques, detailed micromorphological studies can aid'in interpreting soil microchemical properties at weathering surfaces by revealing the identity of neoformed secondary phases. Title: Soil solution chemistry, profile development, and mineral authigenesis in several western Oregon soils Author: Glasmann, Joseph Reed Clay mineral genesis was studied in soils representative of several different geomorphic surfaces in western Oregon, ranging in age from Pliocene-early Pleistocene to late Pleistocene. Soil solution studies, clay mineralogy, and soil raicromorphology were employed to provide evidence of clay mineral synthesis and interpret soil genesis. Soils at each study area were characterized by distinct differences in soil solution chemistry, clay mineralogy, plasmic fabric, and genetic history, although parent material compositions between sites were often similar. Soil solution studies suggested that clay mineral synthesis from solution does not occur in soils representing the oldest geomorphic surface. The cxic soil properties at this location were developed during a prior weathering cycle and the soils are at a genetic endpoint in the present environment. Soil solutions from Ultisols on remnants of Pleistocene surfaces in the Oregon Coast Range were in equilibrium with respect to kaolinite in the solum, but stable with respect to Mg-montmorillonite in the zone characterizing active bedrock weathering. Microraorphological, clay mineralogical, and chemical evidence suggested that alteration of Mgchlorite in sedimentary rocks leads to smectite genesis in the Cr horizon of the Ultisols, followed by conversion of smectite to halloysite and chloritic intergrade in the solum. Alteration of basalt in these soils also leads to the formation of smectite, which is unstable with respect to halloysite in well-drained microenvironments within soil profiles. Soil solutions from soils characteristic of silt-mantled late Pleistocene surfaces on the western margins of the Willamette Valley showed compositional variation from pedon to pedon and horizon to horizon within individual pedons, reflecting the influence of soil parent material compositional variation. Soil solutions were generally in equilibrium with respect to kaolinite, although solutions from horizons developed in tuffaceous sediments were in equilibrium with Mg-montmorillonite. Both kaolinite and smectite were observed as products of mineral authigenesis in these soils. Authigenic clay showed delicate honeycomb or hexagonal morphology in contrast to the parallel oriented appearance of illuvial clays. Andesite alteration in wet, unstable soils of Oregon's western Cascades also resulted in the formation of smectite. The sequence of mineral alteration in andesites is similar to that described for basalts; however, the final products of mineral authigenesis are distinctly microenvironment dependent. Morphologic evidence suggests that chemical properties of bulk soil solutions can not always be considered to represent the solution conditions at the site of mineral authigenesis. In the absence of reliable in situ micro-chemical analytical techniques, detailed micromorphological studies can aid'in interpreting soil microchemical properties at weathering surfaces by revealing the identity of neoformed secondary phases. Close