Search

Search Results

• 1. [Article] The Littlefield Rhyolite, Eastern Oregon: Distinct Flow Units and Their Constraints on Age and Storage Sites of Grande Ronde Basalt Magmas

  The Littlefield Rhyolite consists of widespread, high-temperature, hotspot-related rhyolitic lavas that erupted in eastern Oregon contemporaneous to late-stage Grande Ronde Basalt lavas. The estimated ...

  Citation × Citation Citation Abstract Copy Title: The Littlefield Rhyolite, Eastern Oregon: Distinct Flow Units and Their Constraints on Age and Storage Sites of Grande Ronde Basalt Magmas Author: Webb, Brian McCulloch Year: 2017 The Littlefield Rhyolite consists of widespread, high-temperature, hotspot-related rhyolitic lavas that erupted in eastern Oregon contemporaneous to late-stage Grande Ronde Basalt lavas. The estimated total volume of erupted rhyolites is ~100 km3 covering ~850 km2. The focus of this study has been to investigate the stratigraphy and petrology of the Littlefield Rhyolite and whether field and geochemical relationships exist to help constrain the timing and storage sites of Grande Ronde Basalt magmas. Although often indistinguishable in the field, our data reveal that the Littlefield Rhyolite consists of two geochemically distinct rhyolite flow packages that are designated here as lower and upper Littlefield Rhyolite, according to stratigraphic relationships in the Malheur River Gorge. Rarely viewed in sequence, these rhyolites are distinguished by Zr, Ba, Nb, TiO2 and FeO contents and 40Ar/39Ar ages (16.12±0.04 and 16.16±0.10 Ma versus 16.01±0.06 and 16.05±0.04 Ma). Rhyolites known either as ‘rhyolite of Cottonwood Mountain’ or ‘rhyolite of Bully Creek Canyon’, and which are exposed around Cottonwood Mountain, northwest of Vale, have compositions similar to samples of lower Littlefield Rhyolite. Additionally, single crystal 40Ar/39Ar ages of two samples (16.12±0.07, 16.20±0.08) are statistically indistinguishable. Among units sandwiched between the lower and upper Littlefield Rhyolite are several lava flows and a one-meter thick agglutinated spatter deposit of Hunter Creek Basalt. The spatter deposit thickens to 10s of meters over a distance of 800 m where the deposit is strongly welded. We recognize this as a venting site of Hunter Creek Basalt, and that Hunter Creek Basalt is geochemically and petrographically similar to, and contemporaneous with, late-stage Grande Ronde Basalt. Ages of Littlefield Rhyolite flow units constrain the timing of eruption of Hunter Creek Basalt to an age span of ~100k years, between 16.05 – 16.12 Ma. One local variant of late-stage Grand Ronde Basalt is icelanditic (~62 wt. % SiO2) and is found at a number of places including a location near the southern extent of the upper Littlefield Rhyolite. Geochemical modeling strongly suggests that icelandite lavas resulted from mixing of Grande Ronde and upper Littlefield Rhyolite magmas, thereby tying a Grande Ronde magma storage site to within the greater Malheur River Gorge area, and indicating contemporaneity of rhyolitic and Grande Ronde magma reservoirs. Title: The Littlefield Rhyolite, Eastern Oregon: Distinct Flow Units and Their Constraints on Age and Storage Sites of Grande Ronde Basalt Magmas Author: Webb, Brian McCulloch Year: 2017 The Littlefield Rhyolite consists of widespread, high-temperature, hotspot-related rhyolitic lavas that erupted in eastern Oregon contemporaneous to late-stage Grande Ronde Basalt lavas. The estimated total volume of erupted rhyolites is ~100 km3 covering ~850 km2. The focus of this study has been to investigate the stratigraphy and petrology of the Littlefield Rhyolite and whether field and geochemical relationships exist to help constrain the timing and storage sites of Grande Ronde Basalt magmas. Although often indistinguishable in the field, our data reveal that the Littlefield Rhyolite consists of two geochemically distinct rhyolite flow packages that are designated here as lower and upper Littlefield Rhyolite, according to stratigraphic relationships in the Malheur River Gorge. Rarely viewed in sequence, these rhyolites are distinguished by Zr, Ba, Nb, TiO2 and FeO contents and 40Ar/39Ar ages (16.12±0.04 and 16.16±0.10 Ma versus 16.01±0.06 and 16.05±0.04 Ma). Rhyolites known either as ‘rhyolite of Cottonwood Mountain’ or ‘rhyolite of Bully Creek Canyon’, and which are exposed around Cottonwood Mountain, northwest of Vale, have compositions similar to samples of lower Littlefield Rhyolite. Additionally, single crystal 40Ar/39Ar ages of two samples (16.12±0.07, 16.20±0.08) are statistically indistinguishable. Among units sandwiched between the lower and upper Littlefield Rhyolite are several lava flows and a one-meter thick agglutinated spatter deposit of Hunter Creek Basalt. The spatter deposit thickens to 10s of meters over a distance of 800 m where the deposit is strongly welded. We recognize this as a venting site of Hunter Creek Basalt, and that Hunter Creek Basalt is geochemically and petrographically similar to, and contemporaneous with, late-stage Grande Ronde Basalt. Ages of Littlefield Rhyolite flow units constrain the timing of eruption of Hunter Creek Basalt to an age span of ~100k years, between 16.05 – 16.12 Ma. One local variant of late-stage Grand Ronde Basalt is icelanditic (~62 wt. % SiO2) and is found at a number of places including a location near the southern extent of the upper Littlefield Rhyolite. Geochemical modeling strongly suggests that icelandite lavas resulted from mixing of Grande Ronde and upper Littlefield Rhyolite magmas, thereby tying a Grande Ronde magma storage site to within the greater Malheur River Gorge area, and indicating contemporaneity of rhyolitic and Grande Ronde magma reservoirs. Close

• 2. [Article] Historical Vegetation of Three Salmon-Bearing Watersheds in the Interior Columbia River Basin

  Land use practices can be a contributing factor to environmental degradation and have been the focus of many ecological studies. One aspect that is less addressed is land use history and the effects that ...

  Citation × Citation Citation Abstract Copy Title: Historical Vegetation of Three Salmon-Bearing Watersheds in the Interior Columbia River Basin Author: Smith, Tyanna Year: 2014 Land use practices can be a contributing factor to environmental degradation and have been the focus of many ecological studies. One aspect that is less addressed is land use history and the effects that past practices, such as logging and grazing, can have on the current landscape. This paper describes research and the synthesis of material on the environmental history and watershed characteristics for three watersheds located within spawning and rearing areas for Chinook salmon in the Grande Ronde River Basin in Northeast Oregon: upper Grande Ronde River, Catherine Creek, and Minam River. The Grande Ronde Basin is critical spawning and rearing habitat for salmonids listed under the Endangered Species Act. The primary historical data sources for reconstructing 19th century stream and riparian conditions are the General Land Office township survey notes from 1863 - 1901. Data about the habitat conditions of the landscape were extracted from notes of each township survey source regarding vegetation, stream crossings, and other features found on the landscape in tabular and spatial forms. Data were organized to describe common stream and riparian conditions for the historical time period using a geographic information system. Watershed basin, Chinook salmon life history, ecoregion and surveyor were analyzed using multivariate techniques to determine which parameters were strongly connected to historical vegetation. Ecoregion had the strongest correlation with plant communities. For future research, these historical data could be compared to current habitat survey data, such as the Oregon Department of Fish & Wildlife’s Aquatic Habitat Inventories, to evaluate the degree of change over time of stream and riparian conditions. Title: Historical Vegetation of Three Salmon-Bearing Watersheds in the Interior Columbia River Basin Author: Smith, Tyanna Year: 2014 Land use practices can be a contributing factor to environmental degradation and have been the focus of many ecological studies. One aspect that is less addressed is land use history and the effects that past practices, such as logging and grazing, can have on the current landscape. This paper describes research and the synthesis of material on the environmental history and watershed characteristics for three watersheds located within spawning and rearing areas for Chinook salmon in the Grande Ronde River Basin in Northeast Oregon: upper Grande Ronde River, Catherine Creek, and Minam River. The Grande Ronde Basin is critical spawning and rearing habitat for salmonids listed under the Endangered Species Act. The primary historical data sources for reconstructing 19th century stream and riparian conditions are the General Land Office township survey notes from 1863 - 1901. Data about the habitat conditions of the landscape were extracted from notes of each township survey source regarding vegetation, stream crossings, and other features found on the landscape in tabular and spatial forms. Data were organized to describe common stream and riparian conditions for the historical time period using a geographic information system. Watershed basin, Chinook salmon life history, ecoregion and surveyor were analyzed using multivariate techniques to determine which parameters were strongly connected to historical vegetation. Ecoregion had the strongest correlation with plant communities. For future research, these historical data could be compared to current habitat survey data, such as the Oregon Department of Fish & Wildlife’s Aquatic Habitat Inventories, to evaluate the degree of change over time of stream and riparian conditions. Close

• 3. [Article] A Geospatial Tool for Wetland Prioritization at the Watershed Scale

  There is an increasing demand for assessing ecosystem functions for freshwater wetlands, especially when comparing or prioritizing among wetlands at the watershed scale. We estimated the relative potential ...

  Citation × Citation Citation Abstract Copy Title: A Geospatial Tool for Wetland Prioritization at the Watershed Scale Author: Blackmore, Debra Sue, Chang, Heejun Year: 2015 There is an increasing demand for assessing ecosystem functions for freshwater wetlands, especially when comparing or prioritizing among wetlands at the watershed scale. We estimated the relative potential of selected ecosystem functions for freshwater wetlands within a watershed using widely available geospatial data. We developed four functions to estimate 1) flood storage, 2) late season flow, 3) sediment retention and 4) temperature control in four pilot watersheds in Oregon (Tualatin, Coquille, Upper Grande Ronde and Sprague). These watersheds are geographically separated from each other representing diverse ecoregion environments. Spatial analysis and geographic information system (GIS) were designed for maximum re-use, based on publicly-available data, commonly-used software, semi-automated techniques and wetland characterizations that attempt to capture fundamental wetland processes. Our data sources include 30-meter digital elevation models, NRCS soil survey extracts, USGS National Land Cover Data, USGS HUC8 boundaries (polygons) and statewide wetland delineations (polygons) processed within ArcGIS 10.2 and Python 2.7.5 software. Model parameters were compiled using multiple proxy values for size, slope, aspect, proximity, flow path distance, hydrologic gradient, shade, and soil characteristics. WPT characterizations emphasize the multi-faceted value of freshwater wetlands, relating potential within a watershed as well as providing model-based characterizations between watersheds. Our wetland prioritization tool (WPT) provides useful information to estimate and compare the relative potential for selected wetland functions, thereby improving success in wetland conservation, restoration, and mitigation efforts. Title: A Geospatial Tool for Wetland Prioritization at the Watershed Scale Author: Blackmore, Debra Sue, Chang, Heejun Year: 2015 There is an increasing demand for assessing ecosystem functions for freshwater wetlands, especially when comparing or prioritizing among wetlands at the watershed scale. We estimated the relative potential of selected ecosystem functions for freshwater wetlands within a watershed using widely available geospatial data. We developed four functions to estimate 1) flood storage, 2) late season flow, 3) sediment retention and 4) temperature control in four pilot watersheds in Oregon (Tualatin, Coquille, Upper Grande Ronde and Sprague). These watersheds are geographically separated from each other representing diverse ecoregion environments. Spatial analysis and geographic information system (GIS) were designed for maximum re-use, based on publicly-available data, commonly-used software, semi-automated techniques and wetland characterizations that attempt to capture fundamental wetland processes. Our data sources include 30-meter digital elevation models, NRCS soil survey extracts, USGS National Land Cover Data, USGS HUC8 boundaries (polygons) and statewide wetland delineations (polygons) processed within ArcGIS 10.2 and Python 2.7.5 software. Model parameters were compiled using multiple proxy values for size, slope, aspect, proximity, flow path distance, hydrologic gradient, shade, and soil characteristics. WPT characterizations emphasize the multi-faceted value of freshwater wetlands, relating potential within a watershed as well as providing model-based characterizations between watersheds. Our wetland prioritization tool (WPT) provides useful information to estimate and compare the relative potential for selected wetland functions, thereby improving success in wetland conservation, restoration, and mitigation efforts. Close