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• 201. [Article] An edaphic study of the Mt. Pisgah Arboretum water garden, Coast Fork of the Willamette River

  Wetlands are widely identified as providing important and fundamental processes valuable for maintaining ecosystem health and diversity. Located in the southern Willamette Valley, the Mt. Pisgah Arboretum ...

  Citation × Citation Citation Abstract Copy Title: An edaphic study of the Mt. Pisgah Arboretum water garden, Coast Fork of the Willamette River Author: Bergen, Cameron Francis Wetlands are widely identified as providing important and fundamental processes valuable for maintaining ecosystem health and diversity. Located in the southern Willamette Valley, the Mt. Pisgah Arboretum contains some valuable remaining wetland habitat along the Coast Fork of the Willamette River. One goal of the Mt. Pisgah Arboretum is "to promote conservation, research, and awareness of ecology". To reach this goal, the Arboretum has identified the importance of maintenance and enhancement activities for onsite native habitats, including riparian and wetland habitats. Before restoration or enhancement activities can begin, it is essential to develop an understanding of current environmental conditions. The purpose of this research was to document both the characteristics and distribution of hydric soils and the hydrology, and to provide insight into the patterns and processes associated with a floodplain wetland. In this study, transect sampling of edaphic features was used to identify the distribution of hydric soils and the hydrologic nature of the Mt. Pisgah Arboretum Water Garden. Soil morphological data for particle size, matrix colors and redox features were evaluated and compared with observations of ground water hydrology, river hydrology and precipitation. Five stratigraphic units were identified underlying the Water Garden. A basalt Bedrock unit underlies the uplands associated with Mt. Pisgah and extends at least part way beneath the floodplain. The Clay unit was formed above the Bedrock unit, with some degree of encroachment onto the floodplain. Below 153 m are floodplain sediments, cobbles at depth, then a sand layer and silty clay loam at the surface. The Cobble unit overlaps the Bedrock unit at its base and is most likely Pleistocene age alluvium. The Sand unit is of Holocene age and is found only in the abandoned thalweg, tapering off laterally in both directions across the ancient channels. Draped above this all and slightly overlapping the upland Bedrock and Clay units, is the SiCL unit. The SiCL unit represents Holocene age alluvium, fine material deposited by slow moving water and overbank deposition. The Water Garden soils reflect this mosaic of parent materials on a complex slope. Water Garden soils sometimes met saturation requirements for hydric soils, but they did not always meet hydric soil indicator requirements. The hydrological data suggest that the soils in depressional areas of the Water Garden occupy a zone where water is exchanged between saturated sediments surrounding the channel of the Coast Fork and the channel itself. The hydrology of depressional areas with both ponded surface water and near surface saturation was principally the result of hyporheic upwelling. The soils in these depressional areas tended to form redox concentrations that met hydric soil indicator criteria. Hillslope soils in concave footslope positions exhibited hydrology indicating two separate zones of saturation, one near surface, the other at depth, related to infiltration and accumulation of precipitation. Few redoximorphic features were observed in hillslope soils, and the one hydric soil indicator that was used at these locations did not require redox. Accurate and detailed delineation of hydric soils on this landscape and clear determination of dominant sources of saturation provided an improved understanding of the complex nature of the Water Garden wetland. Results of this study show that hydric soils occupy both depressional and hillslope positions within the Water Garden. Delineation of a soil as hydric or non hydric was facilitated by the use of hydric soil indicator criteria, morphology and hydrology. This analysis provides the managers of the Mt. Pisgah Arboretum with an accurate representation of where hydric soils currently exist and the respective sources of saturation. With this information, managers are better equipped to develop restoration and enhancement options that better reflect the current environmental conditions in the Water Garden. Title: An edaphic study of the Mt. Pisgah Arboretum water garden, Coast Fork of the Willamette River Author: Bergen, Cameron Francis Wetlands are widely identified as providing important and fundamental processes valuable for maintaining ecosystem health and diversity. Located in the southern Willamette Valley, the Mt. Pisgah Arboretum contains some valuable remaining wetland habitat along the Coast Fork of the Willamette River. One goal of the Mt. Pisgah Arboretum is "to promote conservation, research, and awareness of ecology". To reach this goal, the Arboretum has identified the importance of maintenance and enhancement activities for onsite native habitats, including riparian and wetland habitats. Before restoration or enhancement activities can begin, it is essential to develop an understanding of current environmental conditions. The purpose of this research was to document both the characteristics and distribution of hydric soils and the hydrology, and to provide insight into the patterns and processes associated with a floodplain wetland. In this study, transect sampling of edaphic features was used to identify the distribution of hydric soils and the hydrologic nature of the Mt. Pisgah Arboretum Water Garden. Soil morphological data for particle size, matrix colors and redox features were evaluated and compared with observations of ground water hydrology, river hydrology and precipitation. Five stratigraphic units were identified underlying the Water Garden. A basalt Bedrock unit underlies the uplands associated with Mt. Pisgah and extends at least part way beneath the floodplain. The Clay unit was formed above the Bedrock unit, with some degree of encroachment onto the floodplain. Below 153 m are floodplain sediments, cobbles at depth, then a sand layer and silty clay loam at the surface. The Cobble unit overlaps the Bedrock unit at its base and is most likely Pleistocene age alluvium. The Sand unit is of Holocene age and is found only in the abandoned thalweg, tapering off laterally in both directions across the ancient channels. Draped above this all and slightly overlapping the upland Bedrock and Clay units, is the SiCL unit. The SiCL unit represents Holocene age alluvium, fine material deposited by slow moving water and overbank deposition. The Water Garden soils reflect this mosaic of parent materials on a complex slope. Water Garden soils sometimes met saturation requirements for hydric soils, but they did not always meet hydric soil indicator requirements. The hydrological data suggest that the soils in depressional areas of the Water Garden occupy a zone where water is exchanged between saturated sediments surrounding the channel of the Coast Fork and the channel itself. The hydrology of depressional areas with both ponded surface water and near surface saturation was principally the result of hyporheic upwelling. The soils in these depressional areas tended to form redox concentrations that met hydric soil indicator criteria. Hillslope soils in concave footslope positions exhibited hydrology indicating two separate zones of saturation, one near surface, the other at depth, related to infiltration and accumulation of precipitation. Few redoximorphic features were observed in hillslope soils, and the one hydric soil indicator that was used at these locations did not require redox. Accurate and detailed delineation of hydric soils on this landscape and clear determination of dominant sources of saturation provided an improved understanding of the complex nature of the Water Garden wetland. Results of this study show that hydric soils occupy both depressional and hillslope positions within the Water Garden. Delineation of a soil as hydric or non hydric was facilitated by the use of hydric soil indicator criteria, morphology and hydrology. This analysis provides the managers of the Mt. Pisgah Arboretum with an accurate representation of where hydric soils currently exist and the respective sources of saturation. With this information, managers are better equipped to develop restoration and enhancement options that better reflect the current environmental conditions in the Water Garden. Close

• 202. [Article] Convergent margin magmatism in the central Andes and its near antipodes in western Indonesia : spatiotemporal and geochemical considerations

  This dissertation combines volcanological research of three convergent continental margins. Chapters 1 and 5 are general introductions and conclusions, respectively. Chapter 2 examines the spatiotemporal development ...

  Citation × Citation Citation Abstract Copy Title: Convergent margin magmatism in the central Andes and its near antipodes in western Indonesia : spatiotemporal and geochemical considerations Author: Salisbury, Morgan J. This dissertation combines volcanological research of three convergent continental margins. Chapters 1 and 5 are general introductions and conclusions, respectively. Chapter 2 examines the spatiotemporal development of the Altiplano-Puna volcanic complex in the Lípez region of southwest Bolivia, a locus of a major Neogene ignimbrite flare- up, yet the least studied portion of the Altiplano-Puna volcanic complex of the Central Andes. New mapping and laser-fusion ⁴⁰Ar/³⁹Ar dating of sanidine and biotite from 56 locations, coupled with paleomagnetic data, refine the timing and volumes of ignimbrite emplacement in Bolivia and northern Chile to reveal that monotonous intermediate volcanism was prodigious and episodic throughout the complex. ⁴⁰Ar/³⁹Ar age determinations of 13 ignimbrites from northern Chile previously dated by the K-Ar method improve the overall temporal resolution of Altiplano-Puna volcanic complex development. Together with new and updated volume estimates, the new age determinations demonstrate a distinct onset of Altiplano-Puna volcanic complex ignimbrite volcanism with modest output rates beginning ~11 Ma, an episodic middle phase with the highest eruption rates between 8 and 3 Ma, followed by a general decline in volcanic output. The cyclic nature of individual caldera complexes and the spatiotemporal pattern of the volcanic field as a whole are consistent with both incremental construction of plutons as well as a composite Cordilleran batholith. Chapter 3 examines the spatiotemporal development of marine tephra deposits in deep sea sediment cores from the Sunda trench near Sumatra, which reveal evidence for seven large (minimum volume 0.6 – 6.3 km³), previously undocumented, explosive eruptions in this region over the last ~110,000 years, presumably sourced from mainland Sumatra. Sediment cores were collected within and adjacent to the Sunda trench from 3.3ºN to 4.6ºS at water depths between 1.8 and 5.5 km and distances of ~200 to 310 km from the active Sumatran volcanic arc. Glass shards within the tephra horizons were analyzed via the electron microprobe and laser ablation ICP-MS and define three compositional groups. Minimum volume estimates for the seven unique units are consistent with volcanic explosivity index (VEI; Newhall and Self, 1982) values of 4 - 5. The most frequent, widespread, and youngest deposits were found in the central region of the study area suggesting the central Sumatran arc as at the highest risk for large explosive eruptions. The first detailed chronological and geochemical data are presented for Tunupa volcano and nearby Huayrana lavas in chapter 4. New ⁴⁰Ar/³⁹Ar age determinations reveal edifice construction at ~1.5 Ma, a duration of ~90-240 k.y., and extrusion rates of 0.43 to 0.93 km³/k.y. Mineralogical compositional and textural data are consistent with shallow crustal storage (~7-18 km) and magma mixing. Volcano morphology, extrusion rates, mineralogy and textures are all similar to the Pleistocene to recent composite cones of the arc front, although new and available age data from the literature indicate that Western Cordilleran volcanism was concomitant with extrusion of both Huayrana (~11 Ma) and Tunupa (~1.5 Ma) lavas in the behind arc region. Arc-related volcanism was either widespread during these eruptive periods, or an additional melting mechanism was involved. Geochemical data, such as lower Ba/Nb ratios and enriched high field strength elemental concentrations, compared to volcanoes of the modern arc front suggest that Huayrana and Tunupa lavas were derived from a different source than the modern arc front. Geophysical and geochemical research in the central Andes indicate local variations in crustal and lithospheric thicknesses and compositions consistent with a dynamic continental lithosphere that has foundered in piecemeal fashion into the underlying asthenosphere throughout the mid to late Cenozoic. The data presented in this chapter for Tunupa and Huayrana indicate a complex petrogenetic origin and more research is necessary to determine the relative roles of arc and non-arc volcanism beneath the central Altiplano. Title: Convergent margin magmatism in the central Andes and its near antipodes in western Indonesia : spatiotemporal and geochemical considerations Author: Salisbury, Morgan J. This dissertation combines volcanological research of three convergent continental margins. Chapters 1 and 5 are general introductions and conclusions, respectively. Chapter 2 examines the spatiotemporal development of the Altiplano-Puna volcanic complex in the Lípez region of southwest Bolivia, a locus of a major Neogene ignimbrite flare- up, yet the least studied portion of the Altiplano-Puna volcanic complex of the Central Andes. New mapping and laser-fusion ⁴⁰Ar/³⁹Ar dating of sanidine and biotite from 56 locations, coupled with paleomagnetic data, refine the timing and volumes of ignimbrite emplacement in Bolivia and northern Chile to reveal that monotonous intermediate volcanism was prodigious and episodic throughout the complex. ⁴⁰Ar/³⁹Ar age determinations of 13 ignimbrites from northern Chile previously dated by the K-Ar method improve the overall temporal resolution of Altiplano-Puna volcanic complex development. Together with new and updated volume estimates, the new age determinations demonstrate a distinct onset of Altiplano-Puna volcanic complex ignimbrite volcanism with modest output rates beginning ~11 Ma, an episodic middle phase with the highest eruption rates between 8 and 3 Ma, followed by a general decline in volcanic output. The cyclic nature of individual caldera complexes and the spatiotemporal pattern of the volcanic field as a whole are consistent with both incremental construction of plutons as well as a composite Cordilleran batholith. Chapter 3 examines the spatiotemporal development of marine tephra deposits in deep sea sediment cores from the Sunda trench near Sumatra, which reveal evidence for seven large (minimum volume 0.6 – 6.3 km³), previously undocumented, explosive eruptions in this region over the last ~110,000 years, presumably sourced from mainland Sumatra. Sediment cores were collected within and adjacent to the Sunda trench from 3.3ºN to 4.6ºS at water depths between 1.8 and 5.5 km and distances of ~200 to 310 km from the active Sumatran volcanic arc. Glass shards within the tephra horizons were analyzed via the electron microprobe and laser ablation ICP-MS and define three compositional groups. Minimum volume estimates for the seven unique units are consistent with volcanic explosivity index (VEI; Newhall and Self, 1982) values of 4 - 5. The most frequent, widespread, and youngest deposits were found in the central region of the study area suggesting the central Sumatran arc as at the highest risk for large explosive eruptions. The first detailed chronological and geochemical data are presented for Tunupa volcano and nearby Huayrana lavas in chapter 4. New ⁴⁰Ar/³⁹Ar age determinations reveal edifice construction at ~1.5 Ma, a duration of ~90-240 k.y., and extrusion rates of 0.43 to 0.93 km³/k.y. Mineralogical compositional and textural data are consistent with shallow crustal storage (~7-18 km) and magma mixing. Volcano morphology, extrusion rates, mineralogy and textures are all similar to the Pleistocene to recent composite cones of the arc front, although new and available age data from the literature indicate that Western Cordilleran volcanism was concomitant with extrusion of both Huayrana (~11 Ma) and Tunupa (~1.5 Ma) lavas in the behind arc region. Arc-related volcanism was either widespread during these eruptive periods, or an additional melting mechanism was involved. Geochemical data, such as lower Ba/Nb ratios and enriched high field strength elemental concentrations, compared to volcanoes of the modern arc front suggest that Huayrana and Tunupa lavas were derived from a different source than the modern arc front. Geophysical and geochemical research in the central Andes indicate local variations in crustal and lithospheric thicknesses and compositions consistent with a dynamic continental lithosphere that has foundered in piecemeal fashion into the underlying asthenosphere throughout the mid to late Cenozoic. The data presented in this chapter for Tunupa and Huayrana indicate a complex petrogenetic origin and more research is necessary to determine the relative roles of arc and non-arc volcanism beneath the central Altiplano. Close

• 203. [Article] Robert Hooke and the foundation of geology : a comparison of Steno and Hooke and the Hooke imprint on the Huttonian theory ; and, The tectonic evolution of the Oregon continental margin : rotation of segment boundaries and possible spacetime relationships in the Central High Cascades

  Based on the principle that the history of a discipline is important to the discipline itself, this thesis devotes two chapters to ROBERT HOOKE AND THE FOUNDATION OF GEOLOGY and two chapters to modern ...

  Citation × Citation Citation Abstract Copy Title: Robert Hooke and the foundation of geology : a comparison of Steno and Hooke and the Hooke imprint on the Huttonian theory ; and, The tectonic evolution of the Oregon continental margin : rotation of segment boundaries and possible spacetime relationships in the Central High Cascades Author: Drake, Ellen T. Based on the principle that the history of a discipline is important to the discipline itself, this thesis devotes two chapters to ROBERT HOOKE AND THE FOUNDATION OF GEOLOGY and two chapters to modern geology, viz. THE TECTONIC EVOLUTION OF THE OREGON CONTINENTAL MARGIN. The first part of this abstract covers the historical section of the thesis and the second part the scientific section. Robert Hooke was much more than the originator of Hooke's Law or an inventor who invented or perfected meteorological instruments and who pioneered equipment design for sounding the depths of the ocean and collecting ocean water samples at various depths. He supplied Isaac Newton with the concept of centripetal force which allowed Newton to formulate his Laws of Gravitation; he was the first to demonstrate the pressure and volume relationships of gases which were called Boyle's Law. His geological contributions had a profound influence on the development of geology, but they have been largely ignored by modern historians and geologists. The 17th-century Dane Nicolaus Steno has been honored by geologists as a founder of geology and the 18th-century Scotsman James Hutton is widely recognized as the father of modern geology. In a comparison of Steno's geological contributions with those of Hooke, the latter emerges as having made a more extensive and profound contribution. Furthermore, Hooke's system of the earth as presented in his Cutlerian Lectures, published posthumously as Discourse of Earthquakes in 1705, is almost identical to the theory James Hutton announced to the Royal Society of Edinburgh in 1785. This similarity is not a coincidence. That Hutton was thoroughly aware of Hooke's writings is shown not only by the extent to which the intelligentsia of the 18th century cited, quoted and adopted Hooke's ideas, but also by Hutton's own text in both his Abstract of 1785 and his Theory of the Earth in 1788. In the few places where Hutton disagreed with Hooke, Hutton's style became polemical. He seemed to argue against specific points originated by Hooke, which then act as a Hookian signature on the Huttonian Theory. Hooke's influence in the development of geological thought and especially on the foundation of the pre-continental-drift paradigm was a significant one. Robert Hooke, therefore, like Steno, deserves recognition by geologists as a founder of their science. The tectonic evolution of the Oregon continental margin centers around the process of subduction of the Juan de Fuca plate. Models have been advanced to explain the complex tectonic history of this area. The imbricate thrust model seems to test well at the Oregon margin. This model, however, is complicated by the additional processes of segmentation and rotation. This synthesized scenario of the Cenozoic tectonic evolution of the Oregon margin considers the subduction process, including volcanism in the Cascades, as a near-extinction system. This area presently could be experiencing a period of transition from compressional underthrusting to strike-slip motions resulting from extensional forces as the Juan de Fuca plate is coupled with the North America plate. A model involving the rotation of segment boundaries is proposed which may shed some light on time-space and petrologic relationships in the Cascades. The positions of these segment boundaries are supported by bathymetric data on the continental shelf and by the deformation of marine terraces along the Oregon and Washington coasts. Plane vector triangle solutions calculated by Riddihough (1977) for point interactions between the Juan de Fuca plate and the America plate show that the direction of convergence has not been constant over the last 8.5 m.y. The data suggest that the subducted slab had rotated at least 9° in a clockwise direction during the last 1.5 m.y. The model suggests that the arrival of a segment boundary in coincidence with conditions favorable for eruptions may have built the high Central Cascade peaks during the Pleistocene. Title: Robert Hooke and the foundation of geology : a comparison of Steno and Hooke and the Hooke imprint on the Huttonian theory ; and, The tectonic evolution of the Oregon continental margin : rotation of segment boundaries and possible spacetime relationships in the Central High Cascades Author: Drake, Ellen T. Based on the principle that the history of a discipline is important to the discipline itself, this thesis devotes two chapters to ROBERT HOOKE AND THE FOUNDATION OF GEOLOGY and two chapters to modern geology, viz. THE TECTONIC EVOLUTION OF THE OREGON CONTINENTAL MARGIN. The first part of this abstract covers the historical section of the thesis and the second part the scientific section. Robert Hooke was much more than the originator of Hooke's Law or an inventor who invented or perfected meteorological instruments and who pioneered equipment design for sounding the depths of the ocean and collecting ocean water samples at various depths. He supplied Isaac Newton with the concept of centripetal force which allowed Newton to formulate his Laws of Gravitation; he was the first to demonstrate the pressure and volume relationships of gases which were called Boyle's Law. His geological contributions had a profound influence on the development of geology, but they have been largely ignored by modern historians and geologists. The 17th-century Dane Nicolaus Steno has been honored by geologists as a founder of geology and the 18th-century Scotsman James Hutton is widely recognized as the father of modern geology. In a comparison of Steno's geological contributions with those of Hooke, the latter emerges as having made a more extensive and profound contribution. Furthermore, Hooke's system of the earth as presented in his Cutlerian Lectures, published posthumously as Discourse of Earthquakes in 1705, is almost identical to the theory James Hutton announced to the Royal Society of Edinburgh in 1785. This similarity is not a coincidence. That Hutton was thoroughly aware of Hooke's writings is shown not only by the extent to which the intelligentsia of the 18th century cited, quoted and adopted Hooke's ideas, but also by Hutton's own text in both his Abstract of 1785 and his Theory of the Earth in 1788. In the few places where Hutton disagreed with Hooke, Hutton's style became polemical. He seemed to argue against specific points originated by Hooke, which then act as a Hookian signature on the Huttonian Theory. Hooke's influence in the development of geological thought and especially on the foundation of the pre-continental-drift paradigm was a significant one. Robert Hooke, therefore, like Steno, deserves recognition by geologists as a founder of their science. The tectonic evolution of the Oregon continental margin centers around the process of subduction of the Juan de Fuca plate. Models have been advanced to explain the complex tectonic history of this area. The imbricate thrust model seems to test well at the Oregon margin. This model, however, is complicated by the additional processes of segmentation and rotation. This synthesized scenario of the Cenozoic tectonic evolution of the Oregon margin considers the subduction process, including volcanism in the Cascades, as a near-extinction system. This area presently could be experiencing a period of transition from compressional underthrusting to strike-slip motions resulting from extensional forces as the Juan de Fuca plate is coupled with the North America plate. A model involving the rotation of segment boundaries is proposed which may shed some light on time-space and petrologic relationships in the Cascades. The positions of these segment boundaries are supported by bathymetric data on the continental shelf and by the deformation of marine terraces along the Oregon and Washington coasts. Plane vector triangle solutions calculated by Riddihough (1977) for point interactions between the Juan de Fuca plate and the America plate show that the direction of convergence has not been constant over the last 8.5 m.y. The data suggest that the subducted slab had rotated at least 9° in a clockwise direction during the last 1.5 m.y. The model suggests that the arrival of a segment boundary in coincidence with conditions favorable for eruptions may have built the high Central Cascade peaks during the Pleistocene. Close

• 204. [Article] Valley fill and channel incision in Meyer's Canyon, northcentral Oregon

  Meyer's Canyon, a tributary of Bridge Creek in the John Day Basin, is a deeply incised valley fill in northcentral Oregon. The current channel is incised to the Cretaceous and Tertiary bedrock. To determine ...

  Citation × Citation Citation Abstract Copy Title: Valley fill and channel incision in Meyer's Canyon, northcentral Oregon Author: Peacock, Kathi A. Meyer's Canyon, a tributary of Bridge Creek in the John Day Basin, is a deeply incised valley fill in northcentral Oregon. The current channel is incised to the Cretaceous and Tertiary bedrock. To determine the precedence of the current incision and the variation and timing of depositional sequences, the sediments exposed by incision were examined for clues. The incision evaluated in this study occurs along the length of the lower valley fill, approximately 2300 meters, with a maximum depth of about 22 meters near the medial section of the valley. The incision occurred near the beginning of the 20th century and widened from 1951 to 1979, after which tributary headward cutting only is occurring at one location. Colluvial aprons and aggradation within and at the margins of alluvial fans indicate depositional processes again dominate. Fill sediments date from the early Holocene. Volume of the fill prior to incision was estimated to be about 10.8 mcm (million cubic meters), of which 1.2 mcm (11%) was removed by the incision. Fill sediments are contributed by coalescing alluvial fans and alluvial plain sedimentation. The Upper Drainage and Permian Tributary could potentially donate 67% of the Lower Valley fill sediments though these portions of the drainage were not studied. Early sedimentation is dominated by coarse-grained fluvial transport, followed by numerous thick fine-grained sequences, topped by debris flow/mud drape couplets where proximal fan processes dominate. Sediment size decreases and sorting increases toward the fan margins. Valley plain deposition is currently and was, within the Holocene, enhanced and influenced by thick vegetation due to perennial groundwater saturation. Aggradation throughout the Lower Valley fill has dominated over the course of the Holocene, with only one previous episode of incision coincident with the Mt. Mazama eruption, about 6900 yrs BP. Rates of accumulation have changed over the course of the Holocene. Volume rate of accumulation was 140 m3/yr prior to the Mazama eruption and 210 m3/yr following the eruption at a proximal fan location. Within the alluvial fans and plains, sediment characteristics change with distance from source of sediment. At more distal fan and alluvial plain locations, an average volume accumulation rate of 260 m3/yr was estimated prior to the Mazama eruption, and 130 m3/yr following the eruption. These rates indicate that input at the proximal locations has been increasing in the late Holocene and that aggradation may again be dominating Meyer's Canyon sedimentation. Recurrence intervals of debris flows (proximal locations) or events capable of transporting matrix-supported gravels (distal and alluvial plain locations) show an average recurrence interval of 600 yrs pre-Mazama and 1500 yrs post-Z4azama. At proximal locations, the shortest interval is after about 1200 yrs before present (BP) when debris flows occurred about every 500 years. Shorter intervals also generally occurred in all pre-Mazama locations when coarse-sediment input was rapid, probably from the Pleistocene-Holocene climate shift from cool/wet to warmer/drier. Following the Z4azama eruption, the medial section of the Lower Valley fill had rapid input of coarse debris, while proximal fan locations had massive fine-grained input. This is interpreted as a complex response, i.e., rapid runoff reworked previously deposited sediments at proximal locations and sediments were deposited at more distal locations. Fine-grained sediment accumulation followed this period until about 1200 yrs BP. The strongest evidence for a causal mechanism for incision is a complex response at the previously saturated wet-meadow, medial portion of the Lower Valley fill due to loss of riparian vegetation which maintained an oversteepend alluvial slope. The previously saturated portion of the Lower Valley fill shows an increasing transportation slope over time. This slope was probably maintained by the hydrophytic vegetation, but loss of that vegetation due to Euroamerican influence could have led to a geomorphic threshold being crossed on the oversteepened slope and channel incision ensued. The incision is widest at this point and, if width is used as a surrogate for length of time of exposure, it is likely that incision began here. Title: Valley fill and channel incision in Meyer's Canyon, northcentral Oregon Author: Peacock, Kathi A. Meyer's Canyon, a tributary of Bridge Creek in the John Day Basin, is a deeply incised valley fill in northcentral Oregon. The current channel is incised to the Cretaceous and Tertiary bedrock. To determine the precedence of the current incision and the variation and timing of depositional sequences, the sediments exposed by incision were examined for clues. The incision evaluated in this study occurs along the length of the lower valley fill, approximately 2300 meters, with a maximum depth of about 22 meters near the medial section of the valley. The incision occurred near the beginning of the 20th century and widened from 1951 to 1979, after which tributary headward cutting only is occurring at one location. Colluvial aprons and aggradation within and at the margins of alluvial fans indicate depositional processes again dominate. Fill sediments date from the early Holocene. Volume of the fill prior to incision was estimated to be about 10.8 mcm (million cubic meters), of which 1.2 mcm (11%) was removed by the incision. Fill sediments are contributed by coalescing alluvial fans and alluvial plain sedimentation. The Upper Drainage and Permian Tributary could potentially donate 67% of the Lower Valley fill sediments though these portions of the drainage were not studied. Early sedimentation is dominated by coarse-grained fluvial transport, followed by numerous thick fine-grained sequences, topped by debris flow/mud drape couplets where proximal fan processes dominate. Sediment size decreases and sorting increases toward the fan margins. Valley plain deposition is currently and was, within the Holocene, enhanced and influenced by thick vegetation due to perennial groundwater saturation. Aggradation throughout the Lower Valley fill has dominated over the course of the Holocene, with only one previous episode of incision coincident with the Mt. Mazama eruption, about 6900 yrs BP. Rates of accumulation have changed over the course of the Holocene. Volume rate of accumulation was 140 m3/yr prior to the Mazama eruption and 210 m3/yr following the eruption at a proximal fan location. Within the alluvial fans and plains, sediment characteristics change with distance from source of sediment. At more distal fan and alluvial plain locations, an average volume accumulation rate of 260 m3/yr was estimated prior to the Mazama eruption, and 130 m3/yr following the eruption. These rates indicate that input at the proximal locations has been increasing in the late Holocene and that aggradation may again be dominating Meyer's Canyon sedimentation. Recurrence intervals of debris flows (proximal locations) or events capable of transporting matrix-supported gravels (distal and alluvial plain locations) show an average recurrence interval of 600 yrs pre-Mazama and 1500 yrs post-Z4azama. At proximal locations, the shortest interval is after about 1200 yrs before present (BP) when debris flows occurred about every 500 years. Shorter intervals also generally occurred in all pre-Mazama locations when coarse-sediment input was rapid, probably from the Pleistocene-Holocene climate shift from cool/wet to warmer/drier. Following the Z4azama eruption, the medial section of the Lower Valley fill had rapid input of coarse debris, while proximal fan locations had massive fine-grained input. This is interpreted as a complex response, i.e., rapid runoff reworked previously deposited sediments at proximal locations and sediments were deposited at more distal locations. Fine-grained sediment accumulation followed this period until about 1200 yrs BP. The strongest evidence for a causal mechanism for incision is a complex response at the previously saturated wet-meadow, medial portion of the Lower Valley fill due to loss of riparian vegetation which maintained an oversteepend alluvial slope. The previously saturated portion of the Lower Valley fill shows an increasing transportation slope over time. This slope was probably maintained by the hydrophytic vegetation, but loss of that vegetation due to Euroamerican influence could have led to a geomorphic threshold being crossed on the oversteepened slope and channel incision ensued. The incision is widest at this point and, if width is used as a surrogate for length of time of exposure, it is likely that incision began here. Close

• 205. [Article] I. Direction of maximum horizontal compression in western Oregon determined by borehole breakouts. II. Structure and tectonics of the northern Willamette Valley, Oregon

  Elliptical borehole enlargements or "breakouts" caused by systematic spalling of a borehole wall due to regional maximum horizontal stresses were identified in 18 wells drilled in the Coast Range and Willamette ...

  Citation × Citation Citation Abstract Copy Title: I. Direction of maximum horizontal compression in western Oregon determined by borehole breakouts. II. Structure and tectonics of the northern Willamette Valley, Oregon Author: Werner, Kenneth Stefan Elliptical borehole enlargements or "breakouts" caused by systematic spalling of a borehole wall due to regional maximum horizontal stresses were identified in 18 wells drilled in the Coast Range and Willamette Valley of western Oregon. The breakouts generally indicate a NNW to NNE orientation of maximum horizontal compression (oH[subscript max]) that agrees with the predominant direction of Gllmax determined from earthquake focal mechanisms, from post-middle Miocene structural features, and from alignments of Holocene volcanic centers in the Pacific Northwest. However, this orientation is inconsistent with the N50°E convergence between the Juan de Fuca and North American plates determined by Riddihough [1984] from Juan de Fuca plate magnetic lineations as young as 730 ka (the Brunhes-Matuyama boundary). The predominant NNW to NNE orientation of Gllmax may be due to the complex interaction of a northwestward-moving Pacific plate driving into the Gorda and Juan de Fuca plates and indirectly transmitting N-S compression across the strongly coupled Cascadia subduction zone into the overriding North American plate [Spence, 1989]. Alternatively, the predominant NNW to NNE orientation of cillmax may be due to a landward counterclockwise rotation of the direction of oHmax from N50°E compression offshore to N-S compression in the Coast Range. The northern Willamette Valley lies on the eastern flank of the broad northnortheast- trending Oregon Coast Range structural arch. Eocene to Oligocene marine sedimentary rocks crop out along the western side of the northern Willamette Valley and form a gently eastward dipping homocline. However, beneath the center of the Willamette Valley, Eocene to Oligocene strata are structurally warped up. During the Eocene several major volcanic centers subdivided the Coast Range forearc region into shallow to deep marine basins. Several such volcanic centers occur adjacent to the northern Willamette Valley and are associated with residual gravity anomaly highs and lineations. The top of basalt in the northern Willamette Valley (middle Miocene Columbia River basalt except near the valley margins) is contoured based on petroleum exploration wells, water wells, and seismic-reflection data. It is structurally downwarped to an altitude of less than -500 m just north of Woodburn. The downwarp is bounded to the south by the NE-trending Waldo Hills range-front fault and in part to the north by the NE-trending Yamhill River-Sherwood fault zone. The NW-trending Mt. Angel fault extends across the northern Willamette Valley between Mt. Angel and Woodburn and deforms middle Miocene Columbia River basalt and overlying Pliocene and Miocene fluvial and lacustrine deposits. The top of Columbia River basalt is vertically separated, NE side up, roughly 100 m based on seismic-reflection data near Woodburn, and 250+ m based on water-well data near Mt. Angel. The Mt. Angel fault is part of a NW-trending structural zone that includes the Gales Creek fault west of the Tualatin basin; however, a connection between the Gales Creek and Mt. Angel faults does not occur through Willamette River alluvial deposits. A series of small earthquakes (6 events with me = 2.0, 2.5, 2.4, 2.2, 2.4, 1.4) occurred on August 14, 22, and 23, 1990 with epicenters near the northwest end of the Mt. Angel fault. Routine locations indicate a depth of about 30 km. The preferred composite focal mechanism is a right-lateral strike-slip fault with a small normal component on a plane striking north and dipping steeply to the west. Both recent mapping of the Mt. Angel fault and the recent seismicity suggest that the Gales Creek-Mt. Angel lineament is similar to the Portland Hills-Clackamas River lineament found to the north. Together, these two lineaments may take up right-lateral strike-slip motions imposed on the upper plate by oblique subduction. Boring Lava appears to occur extensively in the subsurface of the northeastern portion of the northern Willamette Valley based on seismic data. Many of the faults in the area are interpreted to be largely caused by doming from influx of Boring magma or subsidence associated with evacuation of Boring magma. Such faults occur at Petes Mountain, at Parrett Mountain, along the Molalla River, and possibly near Curtis. The fault along the Molalla River appears to offset the Pleistocene (?) Rowland Formation 1 m (Glenn, 1965). Title: I. Direction of maximum horizontal compression in western Oregon determined by borehole breakouts. II. Structure and tectonics of the northern Willamette Valley, Oregon Author: Werner, Kenneth Stefan Elliptical borehole enlargements or "breakouts" caused by systematic spalling of a borehole wall due to regional maximum horizontal stresses were identified in 18 wells drilled in the Coast Range and Willamette Valley of western Oregon. The breakouts generally indicate a NNW to NNE orientation of maximum horizontal compression (oH[subscript max]) that agrees with the predominant direction of Gllmax determined from earthquake focal mechanisms, from post-middle Miocene structural features, and from alignments of Holocene volcanic centers in the Pacific Northwest. However, this orientation is inconsistent with the N50°E convergence between the Juan de Fuca and North American plates determined by Riddihough [1984] from Juan de Fuca plate magnetic lineations as young as 730 ka (the Brunhes-Matuyama boundary). The predominant NNW to NNE orientation of Gllmax may be due to the complex interaction of a northwestward-moving Pacific plate driving into the Gorda and Juan de Fuca plates and indirectly transmitting N-S compression across the strongly coupled Cascadia subduction zone into the overriding North American plate [Spence, 1989]. Alternatively, the predominant NNW to NNE orientation of cillmax may be due to a landward counterclockwise rotation of the direction of oHmax from N50°E compression offshore to N-S compression in the Coast Range. The northern Willamette Valley lies on the eastern flank of the broad northnortheast- trending Oregon Coast Range structural arch. Eocene to Oligocene marine sedimentary rocks crop out along the western side of the northern Willamette Valley and form a gently eastward dipping homocline. However, beneath the center of the Willamette Valley, Eocene to Oligocene strata are structurally warped up. During the Eocene several major volcanic centers subdivided the Coast Range forearc region into shallow to deep marine basins. Several such volcanic centers occur adjacent to the northern Willamette Valley and are associated with residual gravity anomaly highs and lineations. The top of basalt in the northern Willamette Valley (middle Miocene Columbia River basalt except near the valley margins) is contoured based on petroleum exploration wells, water wells, and seismic-reflection data. It is structurally downwarped to an altitude of less than -500 m just north of Woodburn. The downwarp is bounded to the south by the NE-trending Waldo Hills range-front fault and in part to the north by the NE-trending Yamhill River-Sherwood fault zone. The NW-trending Mt. Angel fault extends across the northern Willamette Valley between Mt. Angel and Woodburn and deforms middle Miocene Columbia River basalt and overlying Pliocene and Miocene fluvial and lacustrine deposits. The top of Columbia River basalt is vertically separated, NE side up, roughly 100 m based on seismic-reflection data near Woodburn, and 250+ m based on water-well data near Mt. Angel. The Mt. Angel fault is part of a NW-trending structural zone that includes the Gales Creek fault west of the Tualatin basin; however, a connection between the Gales Creek and Mt. Angel faults does not occur through Willamette River alluvial deposits. A series of small earthquakes (6 events with me = 2.0, 2.5, 2.4, 2.2, 2.4, 1.4) occurred on August 14, 22, and 23, 1990 with epicenters near the northwest end of the Mt. Angel fault. Routine locations indicate a depth of about 30 km. The preferred composite focal mechanism is a right-lateral strike-slip fault with a small normal component on a plane striking north and dipping steeply to the west. Both recent mapping of the Mt. Angel fault and the recent seismicity suggest that the Gales Creek-Mt. Angel lineament is similar to the Portland Hills-Clackamas River lineament found to the north. Together, these two lineaments may take up right-lateral strike-slip motions imposed on the upper plate by oblique subduction. Boring Lava appears to occur extensively in the subsurface of the northeastern portion of the northern Willamette Valley based on seismic data. Many of the faults in the area are interpreted to be largely caused by doming from influx of Boring magma or subsidence associated with evacuation of Boring magma. Such faults occur at Petes Mountain, at Parrett Mountain, along the Molalla River, and possibly near Curtis. The fault along the Molalla River appears to offset the Pleistocene (?) Rowland Formation 1 m (Glenn, 1965). Close

• 206. [Article] Changing landscape, climate, and life during the age of mammals: interpreting paleontology, evolving ecosystems, and climate change in the Cenozoic fossil parks

  This thesis develops a manual for interpreters at six National Park Service areas established to preserve and interpret fossils of the Cenozoic Era: Fossil Butte National Monument (Wyoming), John Day Fossil ...

  Citation × Citation Citation Abstract Copy Title: Changing landscape, climate, and life during the age of mammals: interpreting paleontology, evolving ecosystems, and climate change in the Cenozoic fossil parks Author: Kenworthy, Jason P. This thesis develops a manual for interpreters at six National Park Service areas established to preserve and interpret fossils of the Cenozoic Era: Fossil Butte National Monument (Wyoming), John Day Fossil Beds National Monument (Oregon), Badlands National Park (South Dakota), Florissant Fossil Beds National Monument (Colorado), Agate Fossil Beds National Monument (Nebraska), and Hagerman Fossil Beds National Monument (Idaho). The manual will help interpreters place their park’s story into the context of three components of paleoecosystems preserved in each park: changes in geologic landscapes, global climate, and the evolution of mammals. It also provides context for interpreting modern climate change. The colorful landscapes of the Cenozoic fossil parks preserve evidence of changing landscapes, climates, and life as well as clues about change affecting our future. Because the six parks are nationally and globally significant paleontological sites, they also offer interpretive opportunities to connect visitors to the science of paleontology. The manual is written for interpreters with a variety of geology, other science and humanities backgrounds. The first three chapters provide a basic foundation of paleontological knowledge and interpretive resources applicable to all of the parks. Chapter 1 is an introduction to the scope and significance of the fossils and paleoecosystems preserved in each of the Cenozoic fossil parks. Chapter 2 outlines NPS interpretive theory and offers practical information for developing paleontology interpretation and interpreting longterm paleoecosystem evolution. Chapter 3 provides geologic content and interpretive methods for answering three common questions visitors ask: How old are these fossils? What is a fossil? and Were all these fossils found here? Interpretive responses to these questions allow visitors to connect with the Cenozoic Era, fossilization processes, and the profound sense of place afforded by the fossil parks. Chapters 4, 5, and 6 summarize how the major components of ecosystems changed between the extinction of dinosaurs 65 million years ago and the beginning of the Pleistocene “ice ages” 2.6 million years ago. Chapter 4 details the active geologic processes—mountain building and volcanic activity—of the American West during this time period and how these processes helped form and preserve the paleoecosystems of the parks. Chapter 5 places the parks’ paleoecosystems in chronological order and relates them to the global climate transition from the “greenhouse” world (nearly-tropical forests and lakes at Fossil Butte NM, John Day Fossil Beds NM, Badlands NP, and Florissant Fossil Beds NM) of 65 to 34 million years ago, to the “icehouse” world (cooler and drier woodlands, savannahs, and grasslands at John Day Fossil Beds NM, Badlands NP, Agate Fossil Beds NM, and Hagerman Fossil Beds NM) beginning 34 million years ago and continuing today. Chapter 6 traces the evolution of the horse during this time of global change from a four-toed, dog-sized browser to a hoofed, zebra-sized grazer on the grasslands of the American West. Chapter 7 describes the “ice ages” that followed the stories of the Cenozoic fossil parks. It also places the global climatic and ecosystem changes told by the Cenozoic fossil parks in the context of modern, rapid, anthropogenic climate changes. Each chapter includes “Digging Deeper” boxes that provide more detailed geologic content, or interpretive suggestions. Title: Changing landscape, climate, and life during the age of mammals: interpreting paleontology, evolving ecosystems, and climate change in the Cenozoic fossil parks Author: Kenworthy, Jason P. This thesis develops a manual for interpreters at six National Park Service areas established to preserve and interpret fossils of the Cenozoic Era: Fossil Butte National Monument (Wyoming), John Day Fossil Beds National Monument (Oregon), Badlands National Park (South Dakota), Florissant Fossil Beds National Monument (Colorado), Agate Fossil Beds National Monument (Nebraska), and Hagerman Fossil Beds National Monument (Idaho). The manual will help interpreters place their park’s story into the context of three components of paleoecosystems preserved in each park: changes in geologic landscapes, global climate, and the evolution of mammals. It also provides context for interpreting modern climate change. The colorful landscapes of the Cenozoic fossil parks preserve evidence of changing landscapes, climates, and life as well as clues about change affecting our future. Because the six parks are nationally and globally significant paleontological sites, they also offer interpretive opportunities to connect visitors to the science of paleontology. The manual is written for interpreters with a variety of geology, other science and humanities backgrounds. The first three chapters provide a basic foundation of paleontological knowledge and interpretive resources applicable to all of the parks. Chapter 1 is an introduction to the scope and significance of the fossils and paleoecosystems preserved in each of the Cenozoic fossil parks. Chapter 2 outlines NPS interpretive theory and offers practical information for developing paleontology interpretation and interpreting longterm paleoecosystem evolution. Chapter 3 provides geologic content and interpretive methods for answering three common questions visitors ask: How old are these fossils? What is a fossil? and Were all these fossils found here? Interpretive responses to these questions allow visitors to connect with the Cenozoic Era, fossilization processes, and the profound sense of place afforded by the fossil parks. Chapters 4, 5, and 6 summarize how the major components of ecosystems changed between the extinction of dinosaurs 65 million years ago and the beginning of the Pleistocene “ice ages” 2.6 million years ago. Chapter 4 details the active geologic processes—mountain building and volcanic activity—of the American West during this time period and how these processes helped form and preserve the paleoecosystems of the parks. Chapter 5 places the parks’ paleoecosystems in chronological order and relates them to the global climate transition from the “greenhouse” world (nearly-tropical forests and lakes at Fossil Butte NM, John Day Fossil Beds NM, Badlands NP, and Florissant Fossil Beds NM) of 65 to 34 million years ago, to the “icehouse” world (cooler and drier woodlands, savannahs, and grasslands at John Day Fossil Beds NM, Badlands NP, Agate Fossil Beds NM, and Hagerman Fossil Beds NM) beginning 34 million years ago and continuing today. Chapter 6 traces the evolution of the horse during this time of global change from a four-toed, dog-sized browser to a hoofed, zebra-sized grazer on the grasslands of the American West. Chapter 7 describes the “ice ages” that followed the stories of the Cenozoic fossil parks. It also places the global climatic and ecosystem changes told by the Cenozoic fossil parks in the context of modern, rapid, anthropogenic climate changes. Each chapter includes “Digging Deeper” boxes that provide more detailed geologic content, or interpretive suggestions. Close

• 207. [Article] Fault behavior over geomorphic time scales in the Pakistan Himalaya, Kashmir Himalaya, and California

  The state of the knowledge for fault behavior in the northwest Himalaya and California varies dramatically. In the Pakistan and Kashmir Himalaya, few data constrain the role that individual active faults ...

  Citation × Citation Citation Abstract Copy Title: Fault behavior over geomorphic time scales in the Pakistan Himalaya, Kashmir Himalaya, and California Author: Madugo, Christopher Lee Madden The state of the knowledge for fault behavior in the northwest Himalaya and California varies dramatically. In the Pakistan and Kashmir Himalaya, few data constrain the role that individual active faults play in accommodating Indo-Eurasian convergence and the relative earthquake hazard across the region. By contrast, the San Andreas fault in California is one of the best-studied fault systems in the world, although seismic hazard models have yet to incorporate certain available geologic data, such as measurements of slip-in-the-last-event. This dissertation addresses the sparsity of earthquake hazard data in the northwest Himalaya, and the problem of how best to utilize available data in hazard models for California by (1) Providing the first quantitative constraints on the latest Pleistocene slip rate and earthquake potential for the thrust front Pakistan; (2) Characterizing the rate and style of upper plate faulting in Kashmir over geomorphic (10⁴ year) time scales; and (3) Creating a standardized database of fault offsets to help test time-dependent and time-independent seismic hazard models for the Uniform California Rupture Forecast. The Himalayan thrust front in Pakistan is defined by the Salt Range thrust (SRT), the up-dip extension of the plate boundary décollement, the Main Himalayan thrust (MHT). We constrain the convergence rate across the SRT by determining the slip rate for the Kalabagh fault (KF), a tear fault that is linked with the SRT at depth. Based on the age and offset of two alluvial fan apexes from their source canyons, we estimate a slip rate of between 9 and 27 mm/yr (~12-17 mm/yr best estimate) for the KF-SRT fault system. This rate matches well with the geodetically-constrained creep rate for the MHT at depth, suggesting the entire slip budget for the Pakistan Himalaya is accommodated at the thrust front. Because the SRT is cored by salt, the earthquake potential for the fault is inferred to be low, although evidence for seismogenic Holocene rupture on the Kalabagh fault, which is also locally lined with salt, suggests that the frontal fault ruptures in plate boundary earthquakes on the MHT. The primary implications of these findings are that convergence in the Pakistan Himalaya is focused at the thrust front rather than distributed between different faults across the plate boundary. In the Kashmir Himalaya, multiple active faults along the plate boundary suggest that Indo-Eurasian convergence is partitioned between the thrust front and faults to the north. To test how much deformation occurs within the overriding plate, we characterized deformation for the Balapora fault, a high-angle reverse fault on the southwest side of the Kashmir Valley. Based on dated offset stream terraces and alluvial fans, the slip rate for the Balapora fault is consistently between 0.3 and 0.5 mm/yr over time scales varying by an order magnitude between about 40 ka and 400 ka. These slip rates translate to shortening rates of 0.1 mm/yr, or less than 1% of the convergence rate across the Kashmir Himalaya. Earthquake recurrence for the Balapora fault is several thousand years, which is consistent with the low slip rate for the fault. The inference is thus that, the majority of convergence in the Kashmir Himalaya is accommodated near the thrust front, as in the Pakistan Himalaya. For California, a new database was created from thousands of measurements of slip resulting from one or more historical to prehistoric earthquakes for use in seismic hazard models. A new rating scheme characterizes the quality of the offsets. Multiple methods to estimate slip during the last event, average slip and slip-per-event are used to analyze the data. These data provide a first order check for models of earthquake behavior. With the advent of high resolution topographic datasets such as LiDAR, the new methodology serves as a template for inclusion of rapidly-accumulating topographic and paleoseismic data in California as well as to regions such as the Himalayan front, as those types of data are adopted. Title: Fault behavior over geomorphic time scales in the Pakistan Himalaya, Kashmir Himalaya, and California Author: Madugo, Christopher Lee Madden The state of the knowledge for fault behavior in the northwest Himalaya and California varies dramatically. In the Pakistan and Kashmir Himalaya, few data constrain the role that individual active faults play in accommodating Indo-Eurasian convergence and the relative earthquake hazard across the region. By contrast, the San Andreas fault in California is one of the best-studied fault systems in the world, although seismic hazard models have yet to incorporate certain available geologic data, such as measurements of slip-in-the-last-event. This dissertation addresses the sparsity of earthquake hazard data in the northwest Himalaya, and the problem of how best to utilize available data in hazard models for California by (1) Providing the first quantitative constraints on the latest Pleistocene slip rate and earthquake potential for the thrust front Pakistan; (2) Characterizing the rate and style of upper plate faulting in Kashmir over geomorphic (10⁴ year) time scales; and (3) Creating a standardized database of fault offsets to help test time-dependent and time-independent seismic hazard models for the Uniform California Rupture Forecast. The Himalayan thrust front in Pakistan is defined by the Salt Range thrust (SRT), the up-dip extension of the plate boundary décollement, the Main Himalayan thrust (MHT). We constrain the convergence rate across the SRT by determining the slip rate for the Kalabagh fault (KF), a tear fault that is linked with the SRT at depth. Based on the age and offset of two alluvial fan apexes from their source canyons, we estimate a slip rate of between 9 and 27 mm/yr (~12-17 mm/yr best estimate) for the KF-SRT fault system. This rate matches well with the geodetically-constrained creep rate for the MHT at depth, suggesting the entire slip budget for the Pakistan Himalaya is accommodated at the thrust front. Because the SRT is cored by salt, the earthquake potential for the fault is inferred to be low, although evidence for seismogenic Holocene rupture on the Kalabagh fault, which is also locally lined with salt, suggests that the frontal fault ruptures in plate boundary earthquakes on the MHT. The primary implications of these findings are that convergence in the Pakistan Himalaya is focused at the thrust front rather than distributed between different faults across the plate boundary. In the Kashmir Himalaya, multiple active faults along the plate boundary suggest that Indo-Eurasian convergence is partitioned between the thrust front and faults to the north. To test how much deformation occurs within the overriding plate, we characterized deformation for the Balapora fault, a high-angle reverse fault on the southwest side of the Kashmir Valley. Based on dated offset stream terraces and alluvial fans, the slip rate for the Balapora fault is consistently between 0.3 and 0.5 mm/yr over time scales varying by an order magnitude between about 40 ka and 400 ka. These slip rates translate to shortening rates of 0.1 mm/yr, or less than 1% of the convergence rate across the Kashmir Himalaya. Earthquake recurrence for the Balapora fault is several thousand years, which is consistent with the low slip rate for the fault. The inference is thus that, the majority of convergence in the Kashmir Himalaya is accommodated near the thrust front, as in the Pakistan Himalaya. For California, a new database was created from thousands of measurements of slip resulting from one or more historical to prehistoric earthquakes for use in seismic hazard models. A new rating scheme characterizes the quality of the offsets. Multiple methods to estimate slip during the last event, average slip and slip-per-event are used to analyze the data. These data provide a first order check for models of earthquake behavior. With the advent of high resolution topographic datasets such as LiDAR, the new methodology serves as a template for inclusion of rapidly-accumulating topographic and paleoseismic data in California as well as to regions such as the Himalayan front, as those types of data are adopted. Close

• 208. [Article] Paleoceanography of the Eastern Equatorial Pacific during the Neogene : synthesis of Leg 138 drilling results

  The primary objective of Leg 138 was to provide detailed information about the ocean's response to global climate change during the Neogene. Two north south transects were drilled (95° and 110°W) within ...

  Citation × Citation Citation Abstract Copy Title: Paleoceanography of the Eastern Equatorial Pacific during the Neogene : synthesis of Leg 138 drilling results Author: Mayer, Larry A., Pisias, Nicklas G., Mix, Alan C. The primary objective of Leg 138 was to provide detailed information about the ocean's response to global climate change during the Neogene. Two north south transects were drilled (95° and 110°W) within the region of equatorial divergence driven upwelling (and thus high accumulation rates and resolution) and spanning the major equatorial ocean current boundaries (and thus recording a high amplitude signal of the response of the sediment to climatically and/or tectonically driven changes in ocean circulation). The Neogene is marked by a number of well known climatic and tectonic events (the closing of the Isthmus of Panama, the onset of North Atlantic Deep Water (NADW), the rapid uplift of the Himalayas, the major intensification of Northern Hemisphere glaciation), and the response of the ocean before and after these events was a key focus of Leg 138 drilling. To address these objectives at the highest resolution possible, the Leg 138 scientific staff developed a number of new shipboard strategies and analytical procedures. These included the real time analysis of the near continuous gamma ray attenuation porosity evaluator (GRAPE) and susceptibility profiles produced by the multisensor track (MST) on unsplit cores to monitor core recovery and, if necessary, to modify the drilling strategy to ensure proper offset of coring gaps; the collection of near continuous color reflectance data on split cores; the logging of the first hole drilled at each site to optimize drilling and sampling strategies for subsequent holes; and the use of multiple continuous records to unambiguously construct complete composite sections for each site. The complete, continuous records provided by the GRAPE (with a temporal resolution of often yr), in conjunction with an excellent microfossil stratigraphy and often excellent magnetostratigraphy, allowed for astronomical tuning of the stratigraphic record and resulted in a set of internally consistent, high resolution age models that provide a secure, absolute time scale for the past 6 m.y. For the period before 6 m.y., the absolute time calibration is less secure, but it is still better than any previously offered. The high resolution stratigraphic framework of Leg 138 provided new insight into the previously ambiguous tectonic history of the region. By assuming that maximum sedimentation rates along the north south transect would be expected at the equator, the Leg 138 stratigraphy supports the 1985 work of Cox and Engerbretson, which calls for two different poles of rotation of the Pacific Plate during the interval 0-20 Ma. The Leg 138 plate reconstructions also support several previously hypothesized ridge crest jumps and a slowing of the absolute motion of the Nazca Plate at about 5 Ma. Although Leg 138 data that predates about 13 Ma is limited, the impression that one can gain from these data is that the eastern equatorial Pacific was characterized by relatively high carbonate concentrations and accumulation rates before about 11 Ma. This pattern was interrupted occasionally by rapid massive outpourings of near monospecific laminated diatom oozes that probably represent the formation of massive mats along strong surface water fronts. The laminated diatom oozes (LDO) continue to be present in the Leg 138 record (many of them being expressed as seismic reflections) until about 4.4 Ma. Carbonate accumulation rates begin to decline slowly between 11 and 9.8 Ma, when, at about 9.5 Ma, a near complete loss of carbonate (the "carbonate crash") takes place everywhere in the Leg 138 region (and beyond), except at the westernmost sites close to the equator. The "carbonate crash" was a time of fundamental change for the eastern equatorial Pacific, and perhaps for most of the ocean basins. Unlike many of the carbonate variations that precede and postdate it, this "crash" represents a major dissolution event whose effects can be traced seismically in the central and western Pacific. The changes in bottom water chemistry associated with this event (or series of events) appear to be related to the early phases of the closing of the Panama Gateway. The role of NADW initiation and intensification for controlling carbonate accumulation in the eastern equatorial Pacific is still not resolved; however, ocean modeling demonstrates that the closing of the Panama Gateway may also have a direct influence on NADW production. Therefore, the effects of changes in the Panama Gateway sill depth and the production of NADW may be manifested in the history of eastern equatorial Pacific sedimentation. The "carbonate crash" was followed by a recovery of the carbonate system (except in the Guatemala and Peru basins, which never recovered) that led up to the late Miocene/ early Pliocene sedimentation rate maxima, during which equatorial sedimentation rates are as much as five times greater than those of the late Pliocene or Pleistocene. Examination of modern productivity/ preser vation relationships implies that the sedimentation rate maximum was the result of enhanced productivity. The distribution of eolian sediments and isotopic gradients, along with an analysis of the modes of variance in carbonate deposition over the last 6 m.y., suggest a more northerly position of the Intertropical Convergence Zone (ITCZ), a stronger north south gradient across the equator, and a more zonal circulation focused along the equator during the time of maximum sedimentation. The mechanisms suggested for these changes in circulation patterns include the response of the eastern equatorial Pacific to the closing of the Isthmus of Panama, as well as a global increase in the flux of Ca and Si into the oceans, a possible response to evolution of the Himalayas and the Tibetan Plateau. In an effort to understand the response of the climate system to external (orbital) forcing, 6-m.y.-long, continuous records of carbonate (derived from GRAPE), δ¹⁸O and insolation were analyzed and compared. Evolutionary spectral calculations of the variance and coherence among these records indicate that the insolation record is dominated by precessional frequencies, but that the relative importance of the two precessional frequencies has changed significantly over the last 6 m.y. In general, precessional forcing is not found in the carbonate or isotopic records. In the tilt band, however, a linear response is present between solar forcing and the carbonate and isotope records over some intervals. The carbonate record appears to be tightly coupled to the tilt component of insolation before about 1.9 Ma; however, the isotope record does not begin to show sensitivity to orbital tilt until about 4.5 Ma, the time of significant changes in sedimentation patterns in the eastern equatorial Pacific. Only during the last 500,000 yr do all frequencies respond in a similar manner; we also see a marked increase in the response of the isotopic record to orbital forcing (including 100,000- and 400,000-yr periods). Title: Paleoceanography of the Eastern Equatorial Pacific during the Neogene : synthesis of Leg 138 drilling results Author: Mayer, Larry A., Pisias, Nicklas G., Mix, Alan C. The primary objective of Leg 138 was to provide detailed information about the ocean's response to global climate change during the Neogene. Two north south transects were drilled (95° and 110°W) within the region of equatorial divergence driven upwelling (and thus high accumulation rates and resolution) and spanning the major equatorial ocean current boundaries (and thus recording a high amplitude signal of the response of the sediment to climatically and/or tectonically driven changes in ocean circulation). The Neogene is marked by a number of well known climatic and tectonic events (the closing of the Isthmus of Panama, the onset of North Atlantic Deep Water (NADW), the rapid uplift of the Himalayas, the major intensification of Northern Hemisphere glaciation), and the response of the ocean before and after these events was a key focus of Leg 138 drilling. To address these objectives at the highest resolution possible, the Leg 138 scientific staff developed a number of new shipboard strategies and analytical procedures. These included the real time analysis of the near continuous gamma ray attenuation porosity evaluator (GRAPE) and susceptibility profiles produced by the multisensor track (MST) on unsplit cores to monitor core recovery and, if necessary, to modify the drilling strategy to ensure proper offset of coring gaps; the collection of near continuous color reflectance data on split cores; the logging of the first hole drilled at each site to optimize drilling and sampling strategies for subsequent holes; and the use of multiple continuous records to unambiguously construct complete composite sections for each site. The complete, continuous records provided by the GRAPE (with a temporal resolution of often yr), in conjunction with an excellent microfossil stratigraphy and often excellent magnetostratigraphy, allowed for astronomical tuning of the stratigraphic record and resulted in a set of internally consistent, high resolution age models that provide a secure, absolute time scale for the past 6 m.y. For the period before 6 m.y., the absolute time calibration is less secure, but it is still better than any previously offered. The high resolution stratigraphic framework of Leg 138 provided new insight into the previously ambiguous tectonic history of the region. By assuming that maximum sedimentation rates along the north south transect would be expected at the equator, the Leg 138 stratigraphy supports the 1985 work of Cox and Engerbretson, which calls for two different poles of rotation of the Pacific Plate during the interval 0-20 Ma. The Leg 138 plate reconstructions also support several previously hypothesized ridge crest jumps and a slowing of the absolute motion of the Nazca Plate at about 5 Ma. Although Leg 138 data that predates about 13 Ma is limited, the impression that one can gain from these data is that the eastern equatorial Pacific was characterized by relatively high carbonate concentrations and accumulation rates before about 11 Ma. This pattern was interrupted occasionally by rapid massive outpourings of near monospecific laminated diatom oozes that probably represent the formation of massive mats along strong surface water fronts. The laminated diatom oozes (LDO) continue to be present in the Leg 138 record (many of them being expressed as seismic reflections) until about 4.4 Ma. Carbonate accumulation rates begin to decline slowly between 11 and 9.8 Ma, when, at about 9.5 Ma, a near complete loss of carbonate (the "carbonate crash") takes place everywhere in the Leg 138 region (and beyond), except at the westernmost sites close to the equator. The "carbonate crash" was a time of fundamental change for the eastern equatorial Pacific, and perhaps for most of the ocean basins. Unlike many of the carbonate variations that precede and postdate it, this "crash" represents a major dissolution event whose effects can be traced seismically in the central and western Pacific. The changes in bottom water chemistry associated with this event (or series of events) appear to be related to the early phases of the closing of the Panama Gateway. The role of NADW initiation and intensification for controlling carbonate accumulation in the eastern equatorial Pacific is still not resolved; however, ocean modeling demonstrates that the closing of the Panama Gateway may also have a direct influence on NADW production. Therefore, the effects of changes in the Panama Gateway sill depth and the production of NADW may be manifested in the history of eastern equatorial Pacific sedimentation. The "carbonate crash" was followed by a recovery of the carbonate system (except in the Guatemala and Peru basins, which never recovered) that led up to the late Miocene/ early Pliocene sedimentation rate maxima, during which equatorial sedimentation rates are as much as five times greater than those of the late Pliocene or Pleistocene. Examination of modern productivity/ preser vation relationships implies that the sedimentation rate maximum was the result of enhanced productivity. The distribution of eolian sediments and isotopic gradients, along with an analysis of the modes of variance in carbonate deposition over the last 6 m.y., suggest a more northerly position of the Intertropical Convergence Zone (ITCZ), a stronger north south gradient across the equator, and a more zonal circulation focused along the equator during the time of maximum sedimentation. The mechanisms suggested for these changes in circulation patterns include the response of the eastern equatorial Pacific to the closing of the Isthmus of Panama, as well as a global increase in the flux of Ca and Si into the oceans, a possible response to evolution of the Himalayas and the Tibetan Plateau. In an effort to understand the response of the climate system to external (orbital) forcing, 6-m.y.-long, continuous records of carbonate (derived from GRAPE), δ¹⁸O and insolation were analyzed and compared. Evolutionary spectral calculations of the variance and coherence among these records indicate that the insolation record is dominated by precessional frequencies, but that the relative importance of the two precessional frequencies has changed significantly over the last 6 m.y. In general, precessional forcing is not found in the carbonate or isotopic records. In the tilt band, however, a linear response is present between solar forcing and the carbonate and isotope records over some intervals. The carbonate record appears to be tightly coupled to the tilt component of insolation before about 1.9 Ma; however, the isotope record does not begin to show sensitivity to orbital tilt until about 4.5 Ma, the time of significant changes in sedimentation patterns in the eastern equatorial Pacific. Only during the last 500,000 yr do all frequencies respond in a similar manner; we also see a marked increase in the response of the isotopic record to orbital forcing (including 100,000- and 400,000-yr periods). Close

• 209. [Article] Chemical element profiles by instrumental neutron activation analysis : in, part 1, two species of wheat bunt spores, Tilletia caries (DC) Tul. and Tilletia controversa Kühn; part 2, representative sediment and basalt samples taken from a DSDP 678 m core, site 525A, Leg 74, Walvis Ridge

  Part 1 The concentration of seventeen elements in two species of fungus which cause wheat bunt disease, Tilletia caries (DC.)Tul. (TS) and Tilletia controversa Kiihn (DS), were determined by instrumental ...

  Citation × Citation Citation Abstract Copy Title: Chemical element profiles by instrumental neutron activation analysis : in, part 1, two species of wheat bunt spores, Tilletia caries (DC) Tul. and Tilletia controversa Kühn; part 2, representative sediment and basalt samples taken from a DSDP 678 m core, site 525A, Leg 74, Walvis Ridge Author: Liu, Yun-gang Part 1 The concentration of seventeen elements in two species of fungus which cause wheat bunt disease, Tilletia caries (DC.)Tul. (TS) and Tilletia controversa Kiihn (DS), were determined by instrumental neutron activation analysis in 37 TS spore samples, and 31 DS spore samples. Aluminum was chosen as a soil contamination indicator to correct for soil contamination. The plot of the concentrations of the ith element [X[subscript i]] versus Al, yielded the biological concentrations of [X.[subscript i]]. The results show that the biological concentrations of Sc, V, La, and Sm are insignificantly small and that their contents in the spores are essentially all derived from soil dust contamination. For Na and Fe, considerable fractions, 0.15 and 0.60, respectively, of their total concentrations are derived from soil contamination. For other elements, the soil contamination contributions are relatively small compared to their biological concentrations. The "student" t-test was used for comparisons of the geometric means of the element concentrations between the TS and DS spore series. The differences between the mean values of Cl, K, Ca, Mn, Zn, and Br for the TS and CS series are not totally due to random errors within the 95% confidence level. The differences for K and Cl between the TS and DS series are large and outside the ±10- limits; therefore, the concentrations of these two elements can be used as reliable criteria for distinguishing these two species. Also, Br may be useful as a diagnostic trace element due to the significant difference between the Br geometric means of the TS and DS spores. Part 2 Forty sediment and four basement basalt samples, taken from a 678 m core drilled by the DSDP (Deep Sea Drilling Project) at Site 525A, Leg 74 (June 10-15, 1980), as well as sixteen selected basalt samples around the south Atlantic Ocean were subjected to instrumental neutron activation analysis. Thirty-two major, minor, and trace elements were determined. The core from the Wavlis Ridge site (2467 m) consisted of 574.6 m of sediment and 103.5 m of basalt. The downcore element concentration profiles and regression analyses show that the rare earth elements (REE) are present in significant amounts in both the carbonate and non-carbonate phases in sediments; Sr is concentrated in the carbonate phase; most of the other elements determined exist mainly in the non-carbonate (mostly clay) phase. The calculated partition coefficients of the REEs between the carbonate phase and the free REE ion concentrations in sea water were high and increased with decreasing REE ionic radii or increasing atomic number from 3.9x10⁶ for La to 15x10⁶ for Lu. Using the partition coefficients of the REEs in the carbonate and non-carbonate (clay) phases, the REE concentrations in Atlantic sea water were calculated, and the results indicate that the lanthanide concentrations have not been changed significantly in south Atlantic sea water over the past 70 m.y.. The Ce anomaly observed in >95% carbonate sediments is related to the Ce⁺³ concentration in sea water; therefore, the Ce anomaly is a redox (reducing-oxidizing) indicator of sea water. (Essentially, >99.99% of soluble Ce in sea water is present as Ce⁺³.) The REE patterns show no Ce depletion in mollusc shell segments from the late Campanian, and a slight Ce depletion in carbonate phases from the late Paleocene sediments. From early Eocene on, the REE patterns in the carbonate phase show a marked Ce depletion, the same as is observed in carbonates from the late Pleistocene to early Holocene (about 0.3 m.y. ago). The abrupt and striking change in the Ce depletion indicates that sea water was anoxic over the Walvis Ridge during the late Campanian. As the gap between northeast South America (northeast Brazil) and west central Africa (near the southwest corner of the upper half of Africa, e.g., near Liberia) widened and the Walvis Ridge subsided between the late Campanian and late Paleocene, sea water flow between the north Atlantic and south Atlantic oceans increased steadily, and gradually flushed out the anoxic water layer over the Walvis Ridge, thereby achieving oxidation conditions at about 54 m.y. ago, that are similar to present day sea water redox conditions: in the world oceans. The chemical compositions of the basement rocks of the core corresponds to alkalic basalts, not MA-Crean Ridge basalts (MORBs). Only a few basement rocks had been recovered from other Walvis Ridge sites. The results add more evidence which supports the hypothesis that the Wavlis Ridge was formed by a series of volcanoes moving over a "hot spot" near the Mid-Atlantic Ridge. These volcanoes migrated eastward as the South American and African continents drifted away. Most of the basalt samples taken from the southeast Brazilian continental margin also are not similar to MORE. From the bulk chemical composition and the REE pattern, one 112 m.y. old basalt has been identified as an early-stage MORB. To date, this is the oldest oceanic tholeiite recovered from the south Atlantic. This direct evidence indicates that the continental split between South America and Africa commenced ≥112 m.y. ago, and is consistent with the suggestion that the rift between the two continents began about 125 m.y. ago. Title: Chemical element profiles by instrumental neutron activation analysis : in, part 1, two species of wheat bunt spores, Tilletia caries (DC) Tul. and Tilletia controversa Kühn; part 2, representative sediment and basalt samples taken from a DSDP 678 m core, site 525A, Leg 74, Walvis Ridge Author: Liu, Yun-gang Part 1 The concentration of seventeen elements in two species of fungus which cause wheat bunt disease, Tilletia caries (DC.)Tul. (TS) and Tilletia controversa Kiihn (DS), were determined by instrumental neutron activation analysis in 37 TS spore samples, and 31 DS spore samples. Aluminum was chosen as a soil contamination indicator to correct for soil contamination. The plot of the concentrations of the ith element [X[subscript i]] versus Al, yielded the biological concentrations of [X.[subscript i]]. The results show that the biological concentrations of Sc, V, La, and Sm are insignificantly small and that their contents in the spores are essentially all derived from soil dust contamination. For Na and Fe, considerable fractions, 0.15 and 0.60, respectively, of their total concentrations are derived from soil contamination. For other elements, the soil contamination contributions are relatively small compared to their biological concentrations. The "student" t-test was used for comparisons of the geometric means of the element concentrations between the TS and DS spore series. The differences between the mean values of Cl, K, Ca, Mn, Zn, and Br for the TS and CS series are not totally due to random errors within the 95% confidence level. The differences for K and Cl between the TS and DS series are large and outside the ±10- limits; therefore, the concentrations of these two elements can be used as reliable criteria for distinguishing these two species. Also, Br may be useful as a diagnostic trace element due to the significant difference between the Br geometric means of the TS and DS spores. Part 2 Forty sediment and four basement basalt samples, taken from a 678 m core drilled by the DSDP (Deep Sea Drilling Project) at Site 525A, Leg 74 (June 10-15, 1980), as well as sixteen selected basalt samples around the south Atlantic Ocean were subjected to instrumental neutron activation analysis. Thirty-two major, minor, and trace elements were determined. The core from the Wavlis Ridge site (2467 m) consisted of 574.6 m of sediment and 103.5 m of basalt. The downcore element concentration profiles and regression analyses show that the rare earth elements (REE) are present in significant amounts in both the carbonate and non-carbonate phases in sediments; Sr is concentrated in the carbonate phase; most of the other elements determined exist mainly in the non-carbonate (mostly clay) phase. The calculated partition coefficients of the REEs between the carbonate phase and the free REE ion concentrations in sea water were high and increased with decreasing REE ionic radii or increasing atomic number from 3.9x10⁶ for La to 15x10⁶ for Lu. Using the partition coefficients of the REEs in the carbonate and non-carbonate (clay) phases, the REE concentrations in Atlantic sea water were calculated, and the results indicate that the lanthanide concentrations have not been changed significantly in south Atlantic sea water over the past 70 m.y.. The Ce anomaly observed in >95% carbonate sediments is related to the Ce⁺³ concentration in sea water; therefore, the Ce anomaly is a redox (reducing-oxidizing) indicator of sea water. (Essentially, >99.99% of soluble Ce in sea water is present as Ce⁺³.) The REE patterns show no Ce depletion in mollusc shell segments from the late Campanian, and a slight Ce depletion in carbonate phases from the late Paleocene sediments. From early Eocene on, the REE patterns in the carbonate phase show a marked Ce depletion, the same as is observed in carbonates from the late Pleistocene to early Holocene (about 0.3 m.y. ago). The abrupt and striking change in the Ce depletion indicates that sea water was anoxic over the Walvis Ridge during the late Campanian. As the gap between northeast South America (northeast Brazil) and west central Africa (near the southwest corner of the upper half of Africa, e.g., near Liberia) widened and the Walvis Ridge subsided between the late Campanian and late Paleocene, sea water flow between the north Atlantic and south Atlantic oceans increased steadily, and gradually flushed out the anoxic water layer over the Walvis Ridge, thereby achieving oxidation conditions at about 54 m.y. ago, that are similar to present day sea water redox conditions: in the world oceans. The chemical compositions of the basement rocks of the core corresponds to alkalic basalts, not MA-Crean Ridge basalts (MORBs). Only a few basement rocks had been recovered from other Walvis Ridge sites. The results add more evidence which supports the hypothesis that the Wavlis Ridge was formed by a series of volcanoes moving over a "hot spot" near the Mid-Atlantic Ridge. These volcanoes migrated eastward as the South American and African continents drifted away. Most of the basalt samples taken from the southeast Brazilian continental margin also are not similar to MORE. From the bulk chemical composition and the REE pattern, one 112 m.y. old basalt has been identified as an early-stage MORB. To date, this is the oldest oceanic tholeiite recovered from the south Atlantic. This direct evidence indicates that the continental split between South America and Africa commenced ≥112 m.y. ago, and is consistent with the suggestion that the rift between the two continents began about 125 m.y. ago. Close

• 210. [Article] Coastal sand dunes of Oregon and Washington

  In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature ...

  Citation × Citation Citation Abstract Copy Title: Coastal sand dunes of Oregon and Washington Author: Cooper, William Skinner, 1884- In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature is relatively low in summer and rarely reaches the freezing point in winter. Winter precipitation is heavy, and there is almost no snow; there is a pronounced deficiency in precipitation in summer. The summer wind is a very constant afternoon sea breeze from north to northwest; winter winds are variable but include frequent southwest gales. Longshore currents are governed by the seasonal winds, moving southward in summer and northward in winter. The regional vegetation is dense, tall conifer forest. The influence of man has been comparatively slight: in prehistoric times the starting of forest fires; in historic time moderate disturbance due to grazing and recent efforts to control the movement of the sand. Part II deals with forms and processes. The simplest combination of elements comprises sand, wind, and water. Interaction of these produces two patterns. In the transverse-ridge pattern the individual unit is a ridge essentially normal to the summer wind and moving with it; it is asymmetric in profile with gentle windward slope and steep leeward slope (slipface). Origin and maintenance of this profile are explained in accordance with principles developed in the field of aerodynamics, and conclusions arrived at deductively are confirmed by slow-motion photography of smoke streams on the dunes. The oblique-ridge pattern occurs only where there is full exposure to both seasonal winds, plenty of space, and plenty of sand. These conditions are met only in Region III (Coos Bay dune sheet). The units are much more massive than the transverse ridges and are essentially stationary. Their trend lies between the means of summer and winter winds. A theoretical explanation of their origin and maintenance is presented, and the oblique ridges and the "longitudinal dunes" of certain desert regions are compared. Neither transverse nor oblique ridge is found in stabilized condition. The factor vegetation added to the other three-sand, wind, and water-promotes stabilization. On a prograding shore, successive beach ridges are quickly captured and fixed, and retain their initial form indefinitely. On a retrograding shore the processes are exceedingly complex and involve repeated stabilization and rejuvenation. Two cases are presented: flat shore, with and without abundant sand supply; stabilized dune masses undergoing erosion. In the latter case, the commoner, development involves the following phases: trough blowout, merging of troughs, reduction to deflation base, and precipitation ridge, which may in time become completely stabilized while still retaining its characteristic form. In places sheltered from one or the other of the seasonal winds, usually the summer wind, giant parabola dunes, which may likewise become fixed by vegetation, develop. Part III is a description of the dune localities of the Oregon-Washington coast and an account of their history. Forty per cent of this coast bears dunes of greater or lesser magnitude. Thirty dune localities are grouped in four regions. Region I includes four localities north of Tillamook Head, Oregon, making a continuous strip 53 km long, that bears the parallel beach-dune-ridge pattern associated with progradation. The forms in Regions II, III, and IV, heterogeneous and complex, are those characteristic of retrograding shores. The two principal stabilized forms are the precipitation ridge and the parabola dune. In Regions II, III, and IV the existing features came into being mainly during the last grand period of sea-level rise, and the seaward portions of massive parabola complexes have been sliced away in varying degree by the advancing sea. The beach-ridge dunes of Region I were formed during the period of comparatively stable sea level, with a probable small net lowering, which followed the maximum of sea advance and has extended to the present. Progradation here during this period, in contrast with almost none south of Tillamook Head, has been possible because of the ample bed load carried to the coast by the Columbia River. South of Tillamook Head there is, in a number of well-distributed localities, evidence of three episodes of advance. The first is represented by the strip of thoroughly stabilized dunes that nearly everywhere forms the inner marginal part of the dune complexes. This episode reached its culmination before the sea had attained its maximum of advance-attested by the slicing away of portions of completely stabilized masses. The second advance for the most part fell short of the first, though in a few places it overpassed the limits of the latter; present condition ranges from complete stabilization to vigorous activity. The third episode is represented by active dunes with open access to the shore. In certain localities there are only an inner strip of stabilized dunes and an outer zone of active dunes. It is assumed that in these the visible effects of the second and third episodes have merged. An earlier cycle of dune development, similar to the modern one in character and extent, is proved by eolian sediments containing altered podzolic soils, which make a minor part of the mantle of unconsolidated materials that lies upon the rock platform of the 30-m terrace. The dunes of which these masses are remnants were formed during the next-to-the-last grand period of submergence. Development of the dunes of Regions II, III, and IV, associated with the grand period of submergence, is assigned to the period of deglaciation that followed the Wisconsin maximum, and mainly to the period of rapid deglaciation that began after the Valders-Mankato advance. The beach-ridge dunes of Region I, on the other hand, have developed in their entirety in the time since sea-level rise was succeeded by stability. By analogy, the earlier cycle of dune development was associated with the waning phase of Illinoian glaciation, and it may be assumed that similar dune cycles were associated with the earlier glaciations of the Pleistocene. Title: Coastal sand dunes of Oregon and Washington Author: Cooper, William Skinner, 1884- In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature is relatively low in summer and rarely reaches the freezing point in winter. Winter precipitation is heavy, and there is almost no snow; there is a pronounced deficiency in precipitation in summer. The summer wind is a very constant afternoon sea breeze from north to northwest; winter winds are variable but include frequent southwest gales. Longshore currents are governed by the seasonal winds, moving southward in summer and northward in winter. The regional vegetation is dense, tall conifer forest. The influence of man has been comparatively slight: in prehistoric times the starting of forest fires; in historic time moderate disturbance due to grazing and recent efforts to control the movement of the sand. Part II deals with forms and processes. The simplest combination of elements comprises sand, wind, and water. Interaction of these produces two patterns. In the transverse-ridge pattern the individual unit is a ridge essentially normal to the summer wind and moving with it; it is asymmetric in profile with gentle windward slope and steep leeward slope (slipface). Origin and maintenance of this profile are explained in accordance with principles developed in the field of aerodynamics, and conclusions arrived at deductively are confirmed by slow-motion photography of smoke streams on the dunes. The oblique-ridge pattern occurs only where there is full exposure to both seasonal winds, plenty of space, and plenty of sand. These conditions are met only in Region III (Coos Bay dune sheet). The units are much more massive than the transverse ridges and are essentially stationary. Their trend lies between the means of summer and winter winds. A theoretical explanation of their origin and maintenance is presented, and the oblique ridges and the "longitudinal dunes" of certain desert regions are compared. Neither transverse nor oblique ridge is found in stabilized condition. The factor vegetation added to the other three-sand, wind, and water-promotes stabilization. On a prograding shore, successive beach ridges are quickly captured and fixed, and retain their initial form indefinitely. On a retrograding shore the processes are exceedingly complex and involve repeated stabilization and rejuvenation. Two cases are presented: flat shore, with and without abundant sand supply; stabilized dune masses undergoing erosion. In the latter case, the commoner, development involves the following phases: trough blowout, merging of troughs, reduction to deflation base, and precipitation ridge, which may in time become completely stabilized while still retaining its characteristic form. In places sheltered from one or the other of the seasonal winds, usually the summer wind, giant parabola dunes, which may likewise become fixed by vegetation, develop. Part III is a description of the dune localities of the Oregon-Washington coast and an account of their history. Forty per cent of this coast bears dunes of greater or lesser magnitude. Thirty dune localities are grouped in four regions. Region I includes four localities north of Tillamook Head, Oregon, making a continuous strip 53 km long, that bears the parallel beach-dune-ridge pattern associated with progradation. The forms in Regions II, III, and IV, heterogeneous and complex, are those characteristic of retrograding shores. The two principal stabilized forms are the precipitation ridge and the parabola dune. In Regions II, III, and IV the existing features came into being mainly during the last grand period of sea-level rise, and the seaward portions of massive parabola complexes have been sliced away in varying degree by the advancing sea. The beach-ridge dunes of Region I were formed during the period of comparatively stable sea level, with a probable small net lowering, which followed the maximum of sea advance and has extended to the present. Progradation here during this period, in contrast with almost none south of Tillamook Head, has been possible because of the ample bed load carried to the coast by the Columbia River. South of Tillamook Head there is, in a number of well-distributed localities, evidence of three episodes of advance. The first is represented by the strip of thoroughly stabilized dunes that nearly everywhere forms the inner marginal part of the dune complexes. This episode reached its culmination before the sea had attained its maximum of advance-attested by the slicing away of portions of completely stabilized masses. The second advance for the most part fell short of the first, though in a few places it overpassed the limits of the latter; present condition ranges from complete stabilization to vigorous activity. The third episode is represented by active dunes with open access to the shore. In certain localities there are only an inner strip of stabilized dunes and an outer zone of active dunes. It is assumed that in these the visible effects of the second and third episodes have merged. An earlier cycle of dune development, similar to the modern one in character and extent, is proved by eolian sediments containing altered podzolic soils, which make a minor part of the mantle of unconsolidated materials that lies upon the rock platform of the 30-m terrace. The dunes of which these masses are remnants were formed during the next-to-the-last grand period of submergence. Development of the dunes of Regions II, III, and IV, associated with the grand period of submergence, is assigned to the period of deglaciation that followed the Wisconsin maximum, and mainly to the period of rapid deglaciation that began after the Valders-Mankato advance. The beach-ridge dunes of Region I, on the other hand, have developed in their entirety in the time since sea-level rise was succeeded by stability. By analogy, the earlier cycle of dune development was associated with the waning phase of Illinoian glaciation, and it may be assumed that similar dune cycles were associated with the earlier glaciations of the Pleistocene. Close