Search

Search Results

• 41. [Article] Hydrologic Response to Extreme Warm and Cold Summers in the McMurdo Dry Valleys, East Antarctica

  The meteorological characteristics and hydrological response of an extreme warm, and cold summer in the McMurdo Dry Valleys are compared. The driver behind the warmer summer conditions was the occurrence ...

  Citation × Citation Citation Abstract Copy Title: Hydrologic Response to Extreme Warm and Cold Summers in the McMurdo Dry Valleys, East Antarctica Author: Doran, Peter T., McKay, Christopher P., Fountain, Andrew G., Nylen, Thomas H., McKnight, Diane M., Jaros, Chris, Barrett, John E. Year: 2008 The meteorological characteristics and hydrological response of an extreme warm, and cold summer in the McMurdo Dry Valleys are compared. The driver behind the warmer summer conditions was the occurrence of down-valley winds, which were not present during the colder summer. Occurrence of the summer down-valley winds coincided with lower than typical mean sea level pressure in the Ross Sea region. There was no significant difference in the amount of solar radiation received during the two summers. Compared to the cold summer, glaciological and hydrological response to the warm summer in Taylor Valley included significant glacier mass loss, and 3- to nearly 6000-fold increase in annual streamflow. Lake levels decreased slightly during the cold summer, and increased between 0.54 and 1.01 m during the warm summer, effectively erasing the prior 14 years of lake level lowering in a period of three months. Lake level rise during the warm summer was shown to be strongly associated with and increase in degree days above freezing at higher elevations. We suggest that strong summer down-valley winds may have been responsible for the generation of large glacial lakes during the Last Glacial Maximum when ice core records recorded annual temperatures significantly colder than present. Title: Hydrologic Response to Extreme Warm and Cold Summers in the McMurdo Dry Valleys, East Antarctica Author: Doran, Peter T., McKay, Christopher P., Fountain, Andrew G., Nylen, Thomas H., McKnight, Diane M., Jaros, Chris, Barrett, John E. Year: 2008 The meteorological characteristics and hydrological response of an extreme warm, and cold summer in the McMurdo Dry Valleys are compared. The driver behind the warmer summer conditions was the occurrence of down-valley winds, which were not present during the colder summer. Occurrence of the summer down-valley winds coincided with lower than typical mean sea level pressure in the Ross Sea region. There was no significant difference in the amount of solar radiation received during the two summers. Compared to the cold summer, glaciological and hydrological response to the warm summer in Taylor Valley included significant glacier mass loss, and 3- to nearly 6000-fold increase in annual streamflow. Lake levels decreased slightly during the cold summer, and increased between 0.54 and 1.01 m during the warm summer, effectively erasing the prior 14 years of lake level lowering in a period of three months. Lake level rise during the warm summer was shown to be strongly associated with and increase in degree days above freezing at higher elevations. We suggest that strong summer down-valley winds may have been responsible for the generation of large glacial lakes during the Last Glacial Maximum when ice core records recorded annual temperatures significantly colder than present. Close

• 42. [Article] Cenozoic biogenic silica sedimentation in the Antarctic Ocean, based on two deep sea drilling project sites

  The Antarctic Ocean during the Cenozoic experienced four periods of increased surface productivity: the Middle Eocene; the beginning of the Miocene; the Middle Miocene; and near the Miocene-Pliocene boundary. ...

  Citation × Citation Citation Abstract Copy Title: Cenozoic biogenic silica sedimentation in the Antarctic Ocean, based on two deep sea drilling project sites Author: Brewster, Nancy Ann The Antarctic Ocean during the Cenozoic experienced four periods of increased surface productivity: the Middle Eocene; the beginning of the Miocene; the Middle Miocene; and near the Miocene-Pliocene boundary. The fourth increase in productivity began five million years ago and has since progressively increased to the present level of intense surface productivity. The major control of Antarctic surface productivity is climate. Opal production in the Neogene increased during glacial times, due to the intensification of upwelling south of the Polar Front, caused from accelerated atmospheric circulation and an increased volume production of Antarctic Bottom Water. Cenozoic variations in surface productivity are also related to the tectonic changes in the Antarctic Ocean basin, which altered the patterns of surface and thermohaline circulation. Antarctic Surface Waters became more conducive to biological productivity with the progressive latitudinal and thermal isolation of Antarctica, The efficiency of surface productivity has progressed to such an extent that much of the global silica supply has been transferred to the Antarctic at the expense of other productive oceanic regions such as the Central Equatorial Pacific. In the Neogene, the preservation or dissolution of calcium carbonate is influenced by the rate of upwelling south of the Polar Front. During glacial times, the upwelling of COB_rich Circumpolar Deep Water accelerates and effectively raises the calcite compensation depth. Title: Cenozoic biogenic silica sedimentation in the Antarctic Ocean, based on two deep sea drilling project sites Author: Brewster, Nancy Ann The Antarctic Ocean during the Cenozoic experienced four periods of increased surface productivity: the Middle Eocene; the beginning of the Miocene; the Middle Miocene; and near the Miocene-Pliocene boundary. The fourth increase in productivity began five million years ago and has since progressively increased to the present level of intense surface productivity. The major control of Antarctic surface productivity is climate. Opal production in the Neogene increased during glacial times, due to the intensification of upwelling south of the Polar Front, caused from accelerated atmospheric circulation and an increased volume production of Antarctic Bottom Water. Cenozoic variations in surface productivity are also related to the tectonic changes in the Antarctic Ocean basin, which altered the patterns of surface and thermohaline circulation. Antarctic Surface Waters became more conducive to biological productivity with the progressive latitudinal and thermal isolation of Antarctica, The efficiency of surface productivity has progressed to such an extent that much of the global silica supply has been transferred to the Antarctic at the expense of other productive oceanic regions such as the Central Equatorial Pacific. In the Neogene, the preservation or dissolution of calcium carbonate is influenced by the rate of upwelling south of the Polar Front. During glacial times, the upwelling of COB_rich Circumpolar Deep Water accelerates and effectively raises the calcite compensation depth. Close

• 43. [Article] Origin of the Tucannon phase in Lower Snake River prehistory

  Approximately 5,500 years ago a discreet period of wetter and cooler environmental conditions prevailed across the southern Columbia Plateau. This period was marked by the first prominent episodes of erosion ...

  Citation × Citation Citation Abstract Copy Title: Origin of the Tucannon phase in Lower Snake River prehistory Author: Lucas, Steven W. Approximately 5,500 years ago a discreet period of wetter and cooler environmental conditions prevailed across the southern Columbia Plateau. This period was marked by the first prominent episodes of erosion to occur along the lower Snake River following the height of the Altithermal and eruption of Mt. Mazama during the mid post-glacial. In addition to the reactivation of small stream courses choked with debris and sediment, large stream channels began downcutting and scouring older terrace faces incorporated with large accumulations of Mazama ash. The resulting degradation of aquatic habitats forced concurrent changes within human economies adapted to the local riverine-environments. These adjustments reported for the Tucannon phase time period along the lower Snake River are notable and demonstrate the degree to which Cascade phase culture was unsuccessful in coping with environmental instability at the end of the Altithermal time period. This successionary event has demonstratively become the most significant post-glacial, qualitative change to occur in the lifeways of lower Snake River people prior to Euro-American influence. Title: Origin of the Tucannon phase in Lower Snake River prehistory Author: Lucas, Steven W. Approximately 5,500 years ago a discreet period of wetter and cooler environmental conditions prevailed across the southern Columbia Plateau. This period was marked by the first prominent episodes of erosion to occur along the lower Snake River following the height of the Altithermal and eruption of Mt. Mazama during the mid post-glacial. In addition to the reactivation of small stream courses choked with debris and sediment, large stream channels began downcutting and scouring older terrace faces incorporated with large accumulations of Mazama ash. The resulting degradation of aquatic habitats forced concurrent changes within human economies adapted to the local riverine-environments. These adjustments reported for the Tucannon phase time period along the lower Snake River are notable and demonstrate the degree to which Cascade phase culture was unsuccessful in coping with environmental instability at the end of the Altithermal time period. This successionary event has demonstratively become the most significant post-glacial, qualitative change to occur in the lifeways of lower Snake River people prior to Euro-American influence. Close

• 44. [Article] The changing glaciers of Mt. Hood, Oregon and Mt. Rainier, Washington : implications for periglacial debris flows

  Mountain glaciers are receding worldwide with numerous consequences including changing hydrology and geomorphology. This study focuses on changes in glacier area on Mt. Hood, Oregon and Mt. Rainier, Washington ...

  Citation × Citation Citation Abstract Copy Title: The changing glaciers of Mt. Hood, Oregon and Mt. Rainier, Washington : implications for periglacial debris flows Author: Ellinger, Jonathan R. Mountain glaciers are receding worldwide with numerous consequences including changing hydrology and geomorphology. This study focuses on changes in glacier area on Mt. Hood, Oregon and Mt. Rainier, Washington where damaging debris flows have occurred in glaciated basins. Landsat imagery is used to map debris-free ice on a decadal time scale from 1987 to 2005. Debris-free glacier ice is clearly delineated using a ratio of Landsat spectral bands in the near-infrared part of the spectrum (bands 4 & 5). Landsat scenes were chosen during the months of September and October to minimize snow cover left over from the accumulation season and maximize exposure of debris-free glacial ice. SNOTEL data were also used to find the lowest snow year for each decade to minimize the potential of misclassifying remnant snow as glacial ice. Changes in debris-free ice are mapped to produce the most up-to-date rates of glacier retreat. Average glacial slopes, derived from airborne LiDAR data are used to compute slope corrected debris-free ice areas for all glaciers. A threshold value for the Landsat NDGI scenes was selected based on threshold testing on the Eliot and Reid glaciers on Mt. Hood. Contradicting earlier studies that say the glaciers on Mt. Hood are receding faster than the glaciers on Mt. Rainier, results show that from 1987 to 2005 Mt. Rainier and Mt. Hood lost similar amounts of debris-free ice extent at 14.0% and 13.9%, respectively. For both Mt. Hood and Mt. Rainier the change in slope corrected debris-free ice area was greater than that of the projected area change due to the steep slopes of both mountains. For Mt. Rainier an increase in recession rate was shown from 1992-2005 compared to 1987-1992 while on Mt. Hood the opposite is seen. On Mt. Rainier it was found that highly fragmented glaciers at lower elevations such as the Inter, Pyramid, and the Van Trump Glaciers lost the highest percent of their original 1987 ice extent and were also shown to be associated with new debris flows in 2006. On Mt. Hood none of the 2006 debris flows initiated within zones of recent glacial recession, however, all debris flows from 2006 originated from streams with a direct connection to glaciers. The Newton Clark Glacier, having lost the most coverage of debris-free ice from 1987 to 2005, is also associated with the highest number of debris-flows in its drainage since 1980. Precipitation data for both mountains show no trend but there was a statistically significant increase in summer air temperature at Mt. Hood over the period 1984-2009. This study suggests that glaciers may play a role in the location of initiation sites, of debris flows, but there is not enough evidence to argue that glacier recession is responsible for producing debris flows. Title: The changing glaciers of Mt. Hood, Oregon and Mt. Rainier, Washington : implications for periglacial debris flows Author: Ellinger, Jonathan R. Mountain glaciers are receding worldwide with numerous consequences including changing hydrology and geomorphology. This study focuses on changes in glacier area on Mt. Hood, Oregon and Mt. Rainier, Washington where damaging debris flows have occurred in glaciated basins. Landsat imagery is used to map debris-free ice on a decadal time scale from 1987 to 2005. Debris-free glacier ice is clearly delineated using a ratio of Landsat spectral bands in the near-infrared part of the spectrum (bands 4 & 5). Landsat scenes were chosen during the months of September and October to minimize snow cover left over from the accumulation season and maximize exposure of debris-free glacial ice. SNOTEL data were also used to find the lowest snow year for each decade to minimize the potential of misclassifying remnant snow as glacial ice. Changes in debris-free ice are mapped to produce the most up-to-date rates of glacier retreat. Average glacial slopes, derived from airborne LiDAR data are used to compute slope corrected debris-free ice areas for all glaciers. A threshold value for the Landsat NDGI scenes was selected based on threshold testing on the Eliot and Reid glaciers on Mt. Hood. Contradicting earlier studies that say the glaciers on Mt. Hood are receding faster than the glaciers on Mt. Rainier, results show that from 1987 to 2005 Mt. Rainier and Mt. Hood lost similar amounts of debris-free ice extent at 14.0% and 13.9%, respectively. For both Mt. Hood and Mt. Rainier the change in slope corrected debris-free ice area was greater than that of the projected area change due to the steep slopes of both mountains. For Mt. Rainier an increase in recession rate was shown from 1992-2005 compared to 1987-1992 while on Mt. Hood the opposite is seen. On Mt. Rainier it was found that highly fragmented glaciers at lower elevations such as the Inter, Pyramid, and the Van Trump Glaciers lost the highest percent of their original 1987 ice extent and were also shown to be associated with new debris flows in 2006. On Mt. Hood none of the 2006 debris flows initiated within zones of recent glacial recession, however, all debris flows from 2006 originated from streams with a direct connection to glaciers. The Newton Clark Glacier, having lost the most coverage of debris-free ice from 1987 to 2005, is also associated with the highest number of debris-flows in its drainage since 1980. Precipitation data for both mountains show no trend but there was a statistically significant increase in summer air temperature at Mt. Hood over the period 1984-2009. This study suggests that glaciers may play a role in the location of initiation sites, of debris flows, but there is not enough evidence to argue that glacier recession is responsible for producing debris flows. Close

• 45. [Article] Late Quaternary paleoceanography in the Eastern Equatorial Pacific Ocean from Planktonic Foraminifiers : a high-resolution record from Site 846

  High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time ...

  Citation × Citation Citation Abstract Copy Title: Late Quaternary paleoceanography in the Eastern Equatorial Pacific Ocean from Planktonic Foraminifiers : a high-resolution record from Site 846 Author: Shackleton, N.J., Le, J., Mix, Alan C. High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time scale was constructed by correlating the benthic δ¹⁸0 record to the SPECMAP and ODP Site 677 δ¹⁸0 time scales using the mapping function technique of Martinson et al. (1981). Our observations show that variations in the foraminiferal assemblages, although influenced by dissolution, are interpretable in terms of changing characteristics of upper ocean waters. Carbonate dissolution as indicated by fragmentation of planktonic foraminifers shows concentrated variance that is coherent with δ¹⁸0 at the 100 and 41 k.y. orbital periods. At these periods, maximum dissolution occurs during interglacial extremes. This finding differs from previous studies that have indicated that in this region percent carbonate minimum lags global ice volume minimum. N. dutertrei and dextral N. pachyderma dominate the assemblages, but do not show consistent relationships relative to glacial-interglacial cycles. However, less abundant species G. ruber, G. menardii, G. glutinata and G. sacculifer show positive and G. bulloides negative correlation with the δ¹⁸0 record. Q-mode factor analysis of the Site 846 assemblages and comparison with modern assemblages suggest the following. Prior to and during interglacials, the area was considerably warmer and more subtropical than at present; during glacials, the area was colder than at present with greater upwelling and advection off the eastern boundary, and possibly a stronger Peru Current; the equatorial “cool tongue” was also possibly stronger. Title: Late Quaternary paleoceanography in the Eastern Equatorial Pacific Ocean from Planktonic Foraminifiers : a high-resolution record from Site 846 Author: Shackleton, N.J., Le, J., Mix, Alan C. High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time scale was constructed by correlating the benthic δ¹⁸0 record to the SPECMAP and ODP Site 677 δ¹⁸0 time scales using the mapping function technique of Martinson et al. (1981). Our observations show that variations in the foraminiferal assemblages, although influenced by dissolution, are interpretable in terms of changing characteristics of upper ocean waters. Carbonate dissolution as indicated by fragmentation of planktonic foraminifers shows concentrated variance that is coherent with δ¹⁸0 at the 100 and 41 k.y. orbital periods. At these periods, maximum dissolution occurs during interglacial extremes. This finding differs from previous studies that have indicated that in this region percent carbonate minimum lags global ice volume minimum. N. dutertrei and dextral N. pachyderma dominate the assemblages, but do not show consistent relationships relative to glacial-interglacial cycles. However, less abundant species G. ruber, G. menardii, G. glutinata and G. sacculifer show positive and G. bulloides negative correlation with the δ¹⁸0 record. Q-mode factor analysis of the Site 846 assemblages and comparison with modern assemblages suggest the following. Prior to and during interglacials, the area was considerably warmer and more subtropical than at present; during glacials, the area was colder than at present with greater upwelling and advection off the eastern boundary, and possibly a stronger Peru Current; the equatorial “cool tongue” was also possibly stronger. Close

• 46. [Article] Increased dissolved terrestrial input to the coastal ocean during the last deglaciation

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Increased dissolved terrestrial input to the coastal ocean during the last deglaciation Author: Haley, B. A., Klinkhammer, Gary P., Mix, Alan C. Copyrighted by American Geophysical Union. Title: Increased dissolved terrestrial input to the coastal ocean during the last deglaciation Author: Haley, B. A., Klinkhammer, Gary P., Mix, Alan C. Copyrighted by American Geophysical Union. Close

• 47. [Article] Sediment storage and delivery on Holocene glacial timescales, Granite Creek, southern Alaska

  Sediment storage in and release from the Granite Creek catchment over Holocene timescales is modulated by the fluctuations of Tana Glacier, which periodically blocks the outlet of Granite Creek. Little ...

  Citation × Citation Citation Abstract Copy Title: Sediment storage and delivery on Holocene glacial timescales, Granite Creek, southern Alaska Author: Blair, Mehgan O'Hearn Sediment storage in and release from the Granite Creek catchment over Holocene timescales is modulated by the fluctuations of Tana Glacier, which periodically blocks the outlet of Granite Creek. Little Ice Age expansion from 1500-1900 AD is suggested by lichenometric ages of alpine glacial moraines within Granite Creek valley. Trimlines above the Tana Glacier terminus indicate that, during this period, ice was at least 120 m thicker in the Tana Valley. According to the elevation of shorelines within the valley, the resultant ice-dammed lake occupied 50 km2 in the lower -10 km of Granite Creek valley, contained 5.9 km3 of water, and was at least 90 m deep at its maximum. Removal of the ice dam occurred during twentieth century thinning of Tana Glacier and caused a 100-m drop in the base level of Granite Creek, driving evacuation of lacustrine valley fill. The reestablishment of the fluvial system was characterized by lateral migration of Granite Creek and formation of a series of paired terraces, indicating a on-catastrophic and possibly seasonal drainage of the lake. Roughly 1.3 x 10" ms of stored sediment has been removed from the basin since drainage of the lake. Radiocarbon ages within the valley fill reveal an unconformity between overlying sediment deposited during the Little Ice Age and underlying, older sediment dating to --900 yrs B.P. Two episodes of impoundment and lacustrine deposition in the basin occurred during the mid-late Holocene and may have been separated by a period of incomplete evacuation of the valley fill. These observations reveal that sediment production within, and sediment delivery gut of this catchment are out of phase, which is characteristic of paraglacial landscape response following deglaciation. In southern Alaska, paraglacial landscape adjustment may explain the discrepancy between erosion rates estimated from short-term sediment yields and those from long-term exhumation rates. It is clear that the interpretation of sediment yields requires consideration of all sources of eroded sediment, including stored material, on a variety of timescales. Title: Sediment storage and delivery on Holocene glacial timescales, Granite Creek, southern Alaska Author: Blair, Mehgan O'Hearn Sediment storage in and release from the Granite Creek catchment over Holocene timescales is modulated by the fluctuations of Tana Glacier, which periodically blocks the outlet of Granite Creek. Little Ice Age expansion from 1500-1900 AD is suggested by lichenometric ages of alpine glacial moraines within Granite Creek valley. Trimlines above the Tana Glacier terminus indicate that, during this period, ice was at least 120 m thicker in the Tana Valley. According to the elevation of shorelines within the valley, the resultant ice-dammed lake occupied 50 km2 in the lower -10 km of Granite Creek valley, contained 5.9 km3 of water, and was at least 90 m deep at its maximum. Removal of the ice dam occurred during twentieth century thinning of Tana Glacier and caused a 100-m drop in the base level of Granite Creek, driving evacuation of lacustrine valley fill. The reestablishment of the fluvial system was characterized by lateral migration of Granite Creek and formation of a series of paired terraces, indicating a on-catastrophic and possibly seasonal drainage of the lake. Roughly 1.3 x 10" ms of stored sediment has been removed from the basin since drainage of the lake. Radiocarbon ages within the valley fill reveal an unconformity between overlying sediment deposited during the Little Ice Age and underlying, older sediment dating to --900 yrs B.P. Two episodes of impoundment and lacustrine deposition in the basin occurred during the mid-late Holocene and may have been separated by a period of incomplete evacuation of the valley fill. These observations reveal that sediment production within, and sediment delivery gut of this catchment are out of phase, which is characteristic of paraglacial landscape response following deglaciation. In southern Alaska, paraglacial landscape adjustment may explain the discrepancy between erosion rates estimated from short-term sediment yields and those from long-term exhumation rates. It is clear that the interpretation of sediment yields requires consideration of all sources of eroded sediment, including stored material, on a variety of timescales. Close

• 48. [Article] The Holocene History of Nares Strait: Transition from Glacial Bay to Arctic-Atlantic Throughflow

  This is the publisher's version of record. The original submission is copyrighted by Oceanography Society and can be found here: http://www.tos.org/

  Citation × Citation Citation Abstract Copy Title: The Holocene History of Nares Strait: Transition from Glacial Bay to Arctic-Atlantic Throughflow Author: Francus, Pierre, Sheldon, Christina, Andrews, John, Stoner, Joseph, Cronin, Thomas M., Jennings, Anne E. This is the publisher's version of record. The original submission is copyrighted by Oceanography Society and can be found here: http://www.tos.org/ Title: The Holocene History of Nares Strait: Transition from Glacial Bay to Arctic-Atlantic Throughflow Author: Francus, Pierre, Sheldon, Christina, Andrews, John, Stoner, Joseph, Cronin, Thomas M., Jennings, Anne E. This is the publisher's version of record. The original submission is copyrighted by Oceanography Society and can be found here: http://www.tos.org/ Close

• 49. [Article] Thorium-230 normalized particle flux and sediment focusing in the Panama Basin region during the last 30,000 years

  Copyright 2007 by the American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Thorium-230 normalized particle flux and sediment focusing in the Panama Basin region during the last 30,000 years Author: Francois, R., Kienast, M., Calvert, S. E., Kienast, S. S., Mix, Alan C. Copyright 2007 by the American Geophysical Union Title: Thorium-230 normalized particle flux and sediment focusing in the Panama Basin region during the last 30,000 years Author: Francois, R., Kienast, M., Calvert, S. E., Kienast, S. S., Mix, Alan C. Copyright 2007 by the American Geophysical Union Close

• 50. [Article] Eastern Pacific Warm Pool paleosalinity and climate variability: 0–30 kyr

  Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, ...

  Citation × Citation Citation Abstract Copy Title: Eastern Pacific Warm Pool paleosalinity and climate variability: 0–30 kyr Author: Haley, Brian A., Benway, Heather M., Mix, Alan C., Klinkhammer, Gary P. Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 kyr. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ~4 practical salinity units occur with a dominant period of ~3–5 ky during the glacial/deglacial interval and ~1.0–1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively. Title: Eastern Pacific Warm Pool paleosalinity and climate variability: 0–30 kyr Author: Haley, Brian A., Benway, Heather M., Mix, Alan C., Klinkhammer, Gary P. Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 kyr. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ~4 practical salinity units occur with a dominant period of ~3–5 ky during the glacial/deglacial interval and ~1.0–1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively. Close

• 51. [Article] Geology of the Whetstone anticline area, Teton County Wyoming

  Over 10,000 feet of marine and nonmarine Late Cretaceous sedimentary rocks are exposed within a 110 square mile area in northeastern Teton County, Wyoming. An additional 1400 feet of nonmarine Paleocene ...

  Citation × Citation Citation Abstract Copy Title: Geology of the Whetstone anticline area, Teton County Wyoming Author: Hill, David Ray Over 10,000 feet of marine and nonmarine Late Cretaceous sedimentary rocks are exposed within a 110 square mile area in northeastern Teton County, Wyoming. An additional 1400 feet of nonmarine Paleocene and Miocene rocks overlie these. Landslide deposits and Pleistocene glacial moraine cover over one-half of the area. The Late Cretaceous Cody Shale and Bacon Ridge Sandstone, which are the oldest rocks exposed, represent the last marine invasion of the region. The overlying Late Cretaceous nonmarine rocks consist of the Coaly Sequence, Lenticular Sandstone and Shale Sequence, Mesaverde Formation, and Harebell Formation. These formations are composed largely of poorly sorted quartz arenites with intercalated mudstones, claystones, shales, and coals. A few quartzite conglomerate lenses are present near the top of the sequence. These rocks, which contain numerous quartz, chert, and metaquartzite grains, were derived from Precambrian metamorphic and Paleozoic sedimentary rocks exposed to the west and northwest. The sediments were carried into the area by streams and were deposited on a broad coastal plain similar to the modern Texas Gulf Coast. Many of the fine-grained sediments were deposited in swamps and small freshwater lakes. Near the end of Cretaceous time, a large area of Precambrian Beltian quartzite was exposed in central Montana. Powerful streams carried large volumes of coarse sediments into the area mapped forming the Paleocene Pinyon Conglomerate. Basalt and andesite were extruded locally during the Miocene. Morainal deposits from two Pleistocene glacial stages are recognized. Two periods of Laramide deformation are represented by broad asymmetric folds. The Spread Creek anticline, a large doubly plunging fold, was formed near the end of Cretaceous time. Three adjacent folds to the northeast are post-Paleocene in age. Several high-angle faults are present. Structural and stratigraphic conditions appear to be favorable for the formation and accumulation of oil and gas. However, five dry oil and gas test holes have been drilled. The possibilities of finding commercial production are not encouraging. The area has also been prospected for coal and alluvial gold. Title: Geology of the Whetstone anticline area, Teton County Wyoming Author: Hill, David Ray Over 10,000 feet of marine and nonmarine Late Cretaceous sedimentary rocks are exposed within a 110 square mile area in northeastern Teton County, Wyoming. An additional 1400 feet of nonmarine Paleocene and Miocene rocks overlie these. Landslide deposits and Pleistocene glacial moraine cover over one-half of the area. The Late Cretaceous Cody Shale and Bacon Ridge Sandstone, which are the oldest rocks exposed, represent the last marine invasion of the region. The overlying Late Cretaceous nonmarine rocks consist of the Coaly Sequence, Lenticular Sandstone and Shale Sequence, Mesaverde Formation, and Harebell Formation. These formations are composed largely of poorly sorted quartz arenites with intercalated mudstones, claystones, shales, and coals. A few quartzite conglomerate lenses are present near the top of the sequence. These rocks, which contain numerous quartz, chert, and metaquartzite grains, were derived from Precambrian metamorphic and Paleozoic sedimentary rocks exposed to the west and northwest. The sediments were carried into the area by streams and were deposited on a broad coastal plain similar to the modern Texas Gulf Coast. Many of the fine-grained sediments were deposited in swamps and small freshwater lakes. Near the end of Cretaceous time, a large area of Precambrian Beltian quartzite was exposed in central Montana. Powerful streams carried large volumes of coarse sediments into the area mapped forming the Paleocene Pinyon Conglomerate. Basalt and andesite were extruded locally during the Miocene. Morainal deposits from two Pleistocene glacial stages are recognized. Two periods of Laramide deformation are represented by broad asymmetric folds. The Spread Creek anticline, a large doubly plunging fold, was formed near the end of Cretaceous time. Three adjacent folds to the northeast are post-Paleocene in age. Several high-angle faults are present. Structural and stratigraphic conditions appear to be favorable for the formation and accumulation of oil and gas. However, five dry oil and gas test holes have been drilled. The possibilities of finding commercial production are not encouraging. The area has also been prospected for coal and alluvial gold. Close

• 52. [Article] Palynological Perspectives on Younger Dryas to Early Holocene Human Ecology at Paisley Caves, Oregon

  The Younger Dryas climatic event is a global phenomenon associated with a 1,000 year return to glacial conditions during the late Pleistocene period between 12,800 and 11,500 cal BP. Because of its significant ...

  Citation × Citation Citation Abstract Copy Title: Palynological Perspectives on Younger Dryas to Early Holocene Human Ecology at Paisley Caves, Oregon Author: Saban, Chantel V. The Younger Dryas climatic event is a global phenomenon associated with a 1,000 year return to glacial conditions during the late Pleistocene period between 12,800 and 11,500 cal BP. Because of its significant effects on paleoenvironmental conditions in some parts of the world, archaeologists commonly seek to assess whether the Younger Dryas climatic event had any measureable influence on prehistoric human societies. The early, well preserved archaeological and paleoenvironmental records held in the Paisley Caves site of Oregon's Northern Great Basin provide an opportunity to examine questions human-environmental interaction at the end of the Pleistocene Epoch. Based on a study of pollen records and artifact frequency in the site's Cave 2 deposits, this thesis reports a positive relationship between artifact deposition and marsh expansion in the Summer Lake sub-basin during the Younger Dryas chronozone. While not indicative of a major change in early forager cultural patterns in the Northern Great Basin, these results provide an important perspective on early settlement patterns and human ecology in the far western region of North America. Title: Palynological Perspectives on Younger Dryas to Early Holocene Human Ecology at Paisley Caves, Oregon Author: Saban, Chantel V. The Younger Dryas climatic event is a global phenomenon associated with a 1,000 year return to glacial conditions during the late Pleistocene period between 12,800 and 11,500 cal BP. Because of its significant effects on paleoenvironmental conditions in some parts of the world, archaeologists commonly seek to assess whether the Younger Dryas climatic event had any measureable influence on prehistoric human societies. The early, well preserved archaeological and paleoenvironmental records held in the Paisley Caves site of Oregon's Northern Great Basin provide an opportunity to examine questions human-environmental interaction at the end of the Pleistocene Epoch. Based on a study of pollen records and artifact frequency in the site's Cave 2 deposits, this thesis reports a positive relationship between artifact deposition and marsh expansion in the Summer Lake sub-basin during the Younger Dryas chronozone. While not indicative of a major change in early forager cultural patterns in the Northern Great Basin, these results provide an important perspective on early settlement patterns and human ecology in the far western region of North America. Close

• 53. [Article] Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho

  The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been ...

  Citation × Citation Citation Abstract Copy Title: Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho Author: Moran, John Lee The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been divided into 23 mapped units. Pre-Belt metamorphic basement rocks are overlain unconformably by 3,433 feet of Paleozoic strata included in eleven formations. These formations represent all of the periods of the Paleozoic except the Ordovician and Silurian. Nine formations represent all the periods of the Mesozoic and total approximately 3,127 feet in thickness. Cenozoic units present in the area are basalts and rhyolites, landslide debris, glacial deposits, and alluvium. The major structure of the thesis area is a fault block that is the result of uplifting and tilting of the east-west trending Centennial Range during the downwarp of the Snake River Plain in late Pliocene and Pleistocene time. No stratigraphic or structural conditions in the thesis area are favorable for the accumulation and entrapment of oil and gas. Phosphorite has been mined from the Phosphoria Formation in the area. Title: Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho Author: Moran, John Lee The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been divided into 23 mapped units. Pre-Belt metamorphic basement rocks are overlain unconformably by 3,433 feet of Paleozoic strata included in eleven formations. These formations represent all of the periods of the Paleozoic except the Ordovician and Silurian. Nine formations represent all the periods of the Mesozoic and total approximately 3,127 feet in thickness. Cenozoic units present in the area are basalts and rhyolites, landslide debris, glacial deposits, and alluvium. The major structure of the thesis area is a fault block that is the result of uplifting and tilting of the east-west trending Centennial Range during the downwarp of the Snake River Plain in late Pliocene and Pleistocene time. No stratigraphic or structural conditions in the thesis area are favorable for the accumulation and entrapment of oil and gas. Phosphorite has been mined from the Phosphoria Formation in the area. Close

• 54. [Article] Late Quaternary sedimentation and geologic history of the North Willamette Valley, Oregon

  Late Quaternary sediments in the Willamette Valley, Oregon, include a unit of chiefly silt and fine sand, the Willamette Silt Formation. Previous workers have (1) Assigned the Willamette Silt different ...

  Citation × Citation Citation Abstract Copy Title: Late Quaternary sedimentation and geologic history of the North Willamette Valley, Oregon Author: Glenn, Jerry L. Late Quaternary sediments in the Willamette Valley, Oregon, include a unit of chiefly silt and fine sand, the Willamette Silt Formation. Previous workers have (1) Assigned the Willamette Silt different ages which range from Sangamon interglacial to late Wisconsin glacial, (2) Proposed that the Willamette Silt was deposited in a ponded body of water which was produced by (a) a tectonic rise in sea level, (b) icejam dams, (c) a eustatic rise in sea level, or (d) a "hydraulic dam", (3) Attributed the Willamette Silt to (a) one catastrophic flood- -the Spokane Flood- -in the Columbia River Valley, (b) "normal" Columbia River floods supplemented by locally derived sediments, or (c) multiple large Columbia River floods. The petrography and stratigraphy of the Willamette Silt and the geomorphology of the Willamette Silt surface have been investigated in the north Willamette Valley. The results of these investigations and the results of a radiocarbon dating program provide data for a new interpretation of the nature and sequence of late Quaternary geologic events in the Willamette and Columbia Valleys. Petrography establishes: (1) that the Willamette Silt was not derived from the local Willamette Valley provenance, (2) that sediments mineralogically similar to the Willamette Silt are present in the Columbia Valley and in the Yakima and Walla Walla Valleys of southeastern Washington, and (3) that the Willamette Silt contains no more locally derived heavy minerals than Columbia River sediment contains. Stratigraphy indicates: (1) that the Willamette Silt unconformably overlies weathered Tertiary bedrock and older Quaternary glacial outwash on the valley margins, (2) that the silt conformably overlies locally derived fluvial-lacustrine sediments in deep central parts of the valley and conformably overlies young glacio-fluvial fan gravels, (3) that deposition of the silt was accomplished during at least 40 large Columbia River floods into the Willamette Valley, (4) that these floods carried heavy loads of chiefly silt and fine sand, (5) that the silt, at least at lower altitudes, was emplaced in a continuously ponded water during a geologically short time span, and (6) that ponded water was not stable at any altitude for long periods of time and that it drained rapidly from the Willamette Valley. Geomorphology of the Willamette Silt surface shows:(1) that deposition of the Willamette Silt was followed by rapid stream entrenchment, (2) that a climactic Columbia River flood, larger than previous floods, entered the Willamette Valley after subaerial weathering and erosion of the Willamette Silt. Stratigraphy, geomorphology, and radiocarbon dates show: (1) that the last Cascade Mountains glaciation that resulted in a significant aggradation by Willamette River tributaries began more than 34,410 ± 3,450 years before present (B.P.), (2) that the last climactic flood occurred about 19,000 years (B. P.), and (3) that the age of the Willamette Silt is between 19,000 years (B.P.) and 34, 410 ± 3,450 years (B.P.). The writer proposes: (1) that flooding was caused by repeated failures of the Lake Missoula glacial ice darn northeast of the channeled scablands, (2) that floods, which sequentially eroded scabland tracts, scoured the Palouse Formation sediments from the scabland tracts, and redeposited part of the sediments in the Columbia River Valley and in major tributary valleys, and (3) that ponded water was maintained in the Willamette Valley by more rapid aggradation in the Columbia Valley than in the Willamette Valley. Title: Late Quaternary sedimentation and geologic history of the North Willamette Valley, Oregon Author: Glenn, Jerry L. Late Quaternary sediments in the Willamette Valley, Oregon, include a unit of chiefly silt and fine sand, the Willamette Silt Formation. Previous workers have (1) Assigned the Willamette Silt different ages which range from Sangamon interglacial to late Wisconsin glacial, (2) Proposed that the Willamette Silt was deposited in a ponded body of water which was produced by (a) a tectonic rise in sea level, (b) icejam dams, (c) a eustatic rise in sea level, or (d) a "hydraulic dam", (3) Attributed the Willamette Silt to (a) one catastrophic flood- -the Spokane Flood- -in the Columbia River Valley, (b) "normal" Columbia River floods supplemented by locally derived sediments, or (c) multiple large Columbia River floods. The petrography and stratigraphy of the Willamette Silt and the geomorphology of the Willamette Silt surface have been investigated in the north Willamette Valley. The results of these investigations and the results of a radiocarbon dating program provide data for a new interpretation of the nature and sequence of late Quaternary geologic events in the Willamette and Columbia Valleys. Petrography establishes: (1) that the Willamette Silt was not derived from the local Willamette Valley provenance, (2) that sediments mineralogically similar to the Willamette Silt are present in the Columbia Valley and in the Yakima and Walla Walla Valleys of southeastern Washington, and (3) that the Willamette Silt contains no more locally derived heavy minerals than Columbia River sediment contains. Stratigraphy indicates: (1) that the Willamette Silt unconformably overlies weathered Tertiary bedrock and older Quaternary glacial outwash on the valley margins, (2) that the silt conformably overlies locally derived fluvial-lacustrine sediments in deep central parts of the valley and conformably overlies young glacio-fluvial fan gravels, (3) that deposition of the silt was accomplished during at least 40 large Columbia River floods into the Willamette Valley, (4) that these floods carried heavy loads of chiefly silt and fine sand, (5) that the silt, at least at lower altitudes, was emplaced in a continuously ponded water during a geologically short time span, and (6) that ponded water was not stable at any altitude for long periods of time and that it drained rapidly from the Willamette Valley. Geomorphology of the Willamette Silt surface shows:(1) that deposition of the Willamette Silt was followed by rapid stream entrenchment, (2) that a climactic Columbia River flood, larger than previous floods, entered the Willamette Valley after subaerial weathering and erosion of the Willamette Silt. Stratigraphy, geomorphology, and radiocarbon dates show: (1) that the last Cascade Mountains glaciation that resulted in a significant aggradation by Willamette River tributaries began more than 34,410 ± 3,450 years before present (B.P.), (2) that the last climactic flood occurred about 19,000 years (B. P.), and (3) that the age of the Willamette Silt is between 19,000 years (B.P.) and 34, 410 ± 3,450 years (B.P.). The writer proposes: (1) that flooding was caused by repeated failures of the Lake Missoula glacial ice darn northeast of the channeled scablands, (2) that floods, which sequentially eroded scabland tracts, scoured the Palouse Formation sediments from the scabland tracts, and redeposited part of the sediments in the Columbia River Valley and in major tributary valleys, and (3) that ponded water was maintained in the Willamette Valley by more rapid aggradation in the Columbia Valley than in the Willamette Valley. Close

• 55. [Article] Lacustrine micro-fossil assemblage in core NP04-KH3, a Kullenberg piston core from the Moba-Kalya Horst region of Lake Tanganyika, East Africa, as a biogeochemical proxy for Late Pleistocene and Early Holocene climate and lake level changes

  The objective of this research is to determine the correlation of lacustrine micro-fossils in Lake Tanganyika to changes in climate and lake levels during the Late Pleistocene and Early Holocene. Lake ...

  Citation × Citation Citation Abstract Copy Title: Lacustrine micro-fossil assemblage in core NP04-KH3, a Kullenberg piston core from the Moba-Kalya Horst region of Lake Tanganyika, East Africa, as a biogeochemical proxy for Late Pleistocene and Early Holocene climate and lake level changes Author: Steinkamp, Matthew J. The objective of this research is to determine the correlation of lacustrine micro-fossils in Lake Tanganyika to changes in climate and lake levels during the Late Pleistocene and Early Holocene. Lake Tanganyika is the second deepest and one of the oldest lakes in the world. The horst and graben geometry of the lake has created subaqueous structural platforms that accumulate pelagic sediments that contain and archive changes in micro-fossil assemblages controlled by changes in climate and lake levels. One such structural platform is the Moba-Kalya Horst. Micro-fossil analysis of lacustrine sediments from a single Kullenberg piston core from the Moba-Kalya Horst indicate dramatic Late Pleistocene and Early Holocene climate and lake level changes that appear to be synchronized with regional, as well as hemispherical climate shifts. During the Late Pleistocene at the Last Glacial Maximum which ended approximately 15 ky B.P., Lake Tanganyika experienced low-lake stands of 250-350 meters or more below the present lake level. From 17,537 to 15,000 calendar years BP, periphytic diatoms such as Rhopalodia gibberula and Surirella fuellebornii were abundant, as were grass phytoliths and sponge spicules, indicative of a dry climate regime. The dominant planktonic diatom was Stephanodiscus astraea, which thrived in low Si:P supply ratio, stratified lake environments in Na-HCO3 rich waters, indicative of a cool, arid climate regime. Periphytic diatoms were also abundant in Lake Malawi to the south and significantly negative δ180 values were recorded in Greenland ice cores for this period. Following the low-lake stands of the Late Glacial Maximum, lake levels generally rose as East Africa experienced the AHP (African Humid Period) (14.4-5.5 cal ky BP). An increase in planktonic diatoms and decrease in periphytic diatoms were recorded in the lacustrine sediments at this time which indicate a positive water balance and rising lake levels. The accumulation of dark-bundled, laminated sediments indicate that the climate was wet and the coring site was below the annual thermocline. A decrease in S. astraea and increase in Cyclostephanos damasii signal conditions of increased moisture to the lake, and decreased evaporation. Around 13 ky B.P. conditions at Lake Tanganyika reverted to Late Glacial Maximum conditions which lasted until approximately 11.5 ky B.P.. Periphytic diatoms once again became abundant, and sponge spicule and grass phytolith counts rose. S.astraea dominance again rose as lake conditions were calm and stratified and the climate was cool and arid. Periphytic diatoms became abundant in Lake Malawi during this period, and increased negative δ180 values were recorded in the Greenland ice cores correlating with increased periphytic diatoms in both Lake Tanganyika and Lake Malawi. Following the Late Pleistocene cold period, lake levels once again began rising as the climate became wetter and windier. Fluctuations from wet and windy to wet and calm occurred at the terminus of the Late Pleistocene as diatom dominance alternated from Aulacoseira granulata, which indicates wet and windy with increase upwelling, to C.damasii, which indicate wet and stratified. Around 9800 B.P. lake conditions stabilized and remained wet and windy with increase turbulence and upwelling which optimized conditions for the dominance of A.granulata. These conditions prevailed through the Early Holocene to at least 6500 B.P. From the Middle Holocene to the present, the general climate of East Africa was and is more arid than the early Holocene, with dry windy conditions and continued upwelling. Title: Lacustrine micro-fossil assemblage in core NP04-KH3, a Kullenberg piston core from the Moba-Kalya Horst region of Lake Tanganyika, East Africa, as a biogeochemical proxy for Late Pleistocene and Early Holocene climate and lake level changes Author: Steinkamp, Matthew J. The objective of this research is to determine the correlation of lacustrine micro-fossils in Lake Tanganyika to changes in climate and lake levels during the Late Pleistocene and Early Holocene. Lake Tanganyika is the second deepest and one of the oldest lakes in the world. The horst and graben geometry of the lake has created subaqueous structural platforms that accumulate pelagic sediments that contain and archive changes in micro-fossil assemblages controlled by changes in climate and lake levels. One such structural platform is the Moba-Kalya Horst. Micro-fossil analysis of lacustrine sediments from a single Kullenberg piston core from the Moba-Kalya Horst indicate dramatic Late Pleistocene and Early Holocene climate and lake level changes that appear to be synchronized with regional, as well as hemispherical climate shifts. During the Late Pleistocene at the Last Glacial Maximum which ended approximately 15 ky B.P., Lake Tanganyika experienced low-lake stands of 250-350 meters or more below the present lake level. From 17,537 to 15,000 calendar years BP, periphytic diatoms such as Rhopalodia gibberula and Surirella fuellebornii were abundant, as were grass phytoliths and sponge spicules, indicative of a dry climate regime. The dominant planktonic diatom was Stephanodiscus astraea, which thrived in low Si:P supply ratio, stratified lake environments in Na-HCO3 rich waters, indicative of a cool, arid climate regime. Periphytic diatoms were also abundant in Lake Malawi to the south and significantly negative δ180 values were recorded in Greenland ice cores for this period. Following the low-lake stands of the Late Glacial Maximum, lake levels generally rose as East Africa experienced the AHP (African Humid Period) (14.4-5.5 cal ky BP). An increase in planktonic diatoms and decrease in periphytic diatoms were recorded in the lacustrine sediments at this time which indicate a positive water balance and rising lake levels. The accumulation of dark-bundled, laminated sediments indicate that the climate was wet and the coring site was below the annual thermocline. A decrease in S. astraea and increase in Cyclostephanos damasii signal conditions of increased moisture to the lake, and decreased evaporation. Around 13 ky B.P. conditions at Lake Tanganyika reverted to Late Glacial Maximum conditions which lasted until approximately 11.5 ky B.P.. Periphytic diatoms once again became abundant, and sponge spicule and grass phytolith counts rose. S.astraea dominance again rose as lake conditions were calm and stratified and the climate was cool and arid. Periphytic diatoms became abundant in Lake Malawi during this period, and increased negative δ180 values were recorded in the Greenland ice cores correlating with increased periphytic diatoms in both Lake Tanganyika and Lake Malawi. Following the Late Pleistocene cold period, lake levels once again began rising as the climate became wetter and windier. Fluctuations from wet and windy to wet and calm occurred at the terminus of the Late Pleistocene as diatom dominance alternated from Aulacoseira granulata, which indicates wet and windy with increase upwelling, to C.damasii, which indicate wet and stratified. Around 9800 B.P. lake conditions stabilized and remained wet and windy with increase turbulence and upwelling which optimized conditions for the dominance of A.granulata. These conditions prevailed through the Early Holocene to at least 6500 B.P. From the Middle Holocene to the present, the general climate of East Africa was and is more arid than the early Holocene, with dry windy conditions and continued upwelling. Close

• 56. [Article] Late-quaternary stratigraphy, pedology and paleoclimatic reconstruction of the Cremer Site (24SW264), south-central Montana : a geographical case study

  This study utilizes a multidisciplinary research approach integrating the sciences of archaeology, geology, pedology and paleoclimatology. Deeply stratified and radiocarbon dated sedimentary sequences ...

  Citation × Citation Citation Abstract Copy Title: Late-quaternary stratigraphy, pedology and paleoclimatic reconstruction of the Cremer Site (24SW264), south-central Montana : a geographical case study Author: White, Dustin This study utilizes a multidisciplinary research approach integrating the sciences of archaeology, geology, pedology and paleoclimatology. Deeply stratified and radiocarbon dated sedimentary sequences spanning the last 10,000 yr B.P. are reported for the Cremer site (24SW264), south-central Montana. Previous investigations at the site revealed an archaeological assemblage with Early Plains Archaic through Late Prehistoric period affiliations. Expanded testing of the site integrates the existing cultural record with new data pertaining to Holocene environmental changes at this northwestern Great Plains locality. Detailed pedological descriptions were made along three trenches excavated at the site. The combined soil-stratigraphic record indicates that distinct intervals of relative landscape stability and soil development occurred at the site at ca. 10,000 yr B.P., 7,500 yr B.P. and intermittently throughout the last ca. 6,000 yr B.P. Periods of significant landscape instability (upland erosion and valley deposition) occurred immediately following each of the early Holocene soil forming intervals identified above, and episodically throughout the middle to late Holocene. The impetus for early Holocene environmental instability is attributed to generally increased aridity on the northwestern Great Plains. Comparative analyses of site data with both regional environmental proxy records and numerical models of past climates (General Circulation and Archaeoclimatic models) are made to test the findings from the Cremer site. The collective paleoenvironmental evidence indicates that the period of maximum post-glacial warming and aridity occurred at the Cremer site during the early Holocene period (prior to ca. 6,000 yr B.P.). These data also indicate that the existing archaeological assemblage from the site is younger than ca. 6,000 yr B.P., although future excavations may reveal cultural sequences associated with the earliest dated soils at the site. This geoarchaeological study of the Cremer site should contribute to a much needed research base in this sparsely studied region. Title: Late-quaternary stratigraphy, pedology and paleoclimatic reconstruction of the Cremer Site (24SW264), south-central Montana : a geographical case study Author: White, Dustin This study utilizes a multidisciplinary research approach integrating the sciences of archaeology, geology, pedology and paleoclimatology. Deeply stratified and radiocarbon dated sedimentary sequences spanning the last 10,000 yr B.P. are reported for the Cremer site (24SW264), south-central Montana. Previous investigations at the site revealed an archaeological assemblage with Early Plains Archaic through Late Prehistoric period affiliations. Expanded testing of the site integrates the existing cultural record with new data pertaining to Holocene environmental changes at this northwestern Great Plains locality. Detailed pedological descriptions were made along three trenches excavated at the site. The combined soil-stratigraphic record indicates that distinct intervals of relative landscape stability and soil development occurred at the site at ca. 10,000 yr B.P., 7,500 yr B.P. and intermittently throughout the last ca. 6,000 yr B.P. Periods of significant landscape instability (upland erosion and valley deposition) occurred immediately following each of the early Holocene soil forming intervals identified above, and episodically throughout the middle to late Holocene. The impetus for early Holocene environmental instability is attributed to generally increased aridity on the northwestern Great Plains. Comparative analyses of site data with both regional environmental proxy records and numerical models of past climates (General Circulation and Archaeoclimatic models) are made to test the findings from the Cremer site. The collective paleoenvironmental evidence indicates that the period of maximum post-glacial warming and aridity occurred at the Cremer site during the early Holocene period (prior to ca. 6,000 yr B.P.). These data also indicate that the existing archaeological assemblage from the site is younger than ca. 6,000 yr B.P., although future excavations may reveal cultural sequences associated with the earliest dated soils at the site. This geoarchaeological study of the Cremer site should contribute to a much needed research base in this sparsely studied region. Close

• 57. [Article] Geology of the Whetstone Ridge area, Meagher County, Montana

  The thesis area consists of 65 square miles located in the southeastern part of Meagher County, Montana. Ranging in age from Precambrian to Quaternary, the strata exposed in the area have a total thickness ...

  Citation × Citation Citation Abstract Copy Title: Geology of the Whetstone Ridge area, Meagher County, Montana Author: Glasheen, Richard Michael The thesis area consists of 65 square miles located in the southeastern part of Meagher County, Montana. Ranging in age from Precambrian to Quaternary, the strata exposed in the area have a total thickness of about 11,100 feet. Low grade metamorphic rocks, mainly slates, and limestones represent the estimated 2,000 foot thick Precambrian unit. Paleozoic rocks, about 2,600 feet in thickness, consist mainly of carbonates but include marine sandstones, some of which were metamorphosed into quartzites. Ordovician, Silurian, and Permian strata are absent. The Mesozoic rocks are dominantly marine, continental, and lacustrjne sandstones, siltstones, and shales. Rocks of Triassic age are not present in this 6, 500 foot thick sequence of sedimentary rocks. Intrusive and extrusive igneous rocks, glacial deposits, and unconsolidated alluvium represent the Cenozoic Period. The major structures in the thesis area are the result of the Lararnide Revolution and date from Late Cretaceous to Early Tertiary. Title: Geology of the Whetstone Ridge area, Meagher County, Montana Author: Glasheen, Richard Michael The thesis area consists of 65 square miles located in the southeastern part of Meagher County, Montana. Ranging in age from Precambrian to Quaternary, the strata exposed in the area have a total thickness of about 11,100 feet. Low grade metamorphic rocks, mainly slates, and limestones represent the estimated 2,000 foot thick Precambrian unit. Paleozoic rocks, about 2,600 feet in thickness, consist mainly of carbonates but include marine sandstones, some of which were metamorphosed into quartzites. Ordovician, Silurian, and Permian strata are absent. The Mesozoic rocks are dominantly marine, continental, and lacustrjne sandstones, siltstones, and shales. Rocks of Triassic age are not present in this 6, 500 foot thick sequence of sedimentary rocks. Intrusive and extrusive igneous rocks, glacial deposits, and unconsolidated alluvium represent the Cenozoic Period. The major structures in the thesis area are the result of the Lararnide Revolution and date from Late Cretaceous to Early Tertiary. Close

• 58. [Article] Stratigraphy and structure of part of the southern Madison Range, Madison and Gallatin Counties, Montana

  The thesis area consists of 42 square miles located in Madison and Gallatin counties, Montana, in the southern part of the Madison Range. The strata exposed in the area range in age from Precambrian to ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy and structure of part of the southern Madison Range, Madison and Gallatin Counties, Montana Author: Rosé, Robert Rowland The thesis area consists of 42 square miles located in Madison and Gallatin counties, Montana, in the southern part of the Madison Range. The strata exposed in the area range in age from Precambrian to Quaternary and have an aggregate thickness of more than 7,600 feet. The Paleozoic rocks, about 3,900 feet thick, are mainly carbonates but include sandstones, shales, and cherts of marine origin. Ordovician and Silurian formations are absent. The Mesozoic rocks consist mainly of sandstones, shales, calcareous claystones, and argillaceous limestones of marine and continental origin. All Mesozoic periods are represented in this 3700 foot thick sequence of sedimentary rocks. The Cenozoic rocks and sediments include welded tuff, glacial deposits, and alluvium. Quaternary landslides cover about one-quarter of the thesis area. The structures are Late Cretaceous to Early Tertiary (Laramide) and Late Cenozoic in age. The Laramide structures are northwest- trending, asymmetrical (steeper to the northeast) folds and high angle reverse faults. The Late Cenozoic structures are normal faults that displace Upper Cretaceous strata. Title: Stratigraphy and structure of part of the southern Madison Range, Madison and Gallatin Counties, Montana Author: Rosé, Robert Rowland The thesis area consists of 42 square miles located in Madison and Gallatin counties, Montana, in the southern part of the Madison Range. The strata exposed in the area range in age from Precambrian to Quaternary and have an aggregate thickness of more than 7,600 feet. The Paleozoic rocks, about 3,900 feet thick, are mainly carbonates but include sandstones, shales, and cherts of marine origin. Ordovician and Silurian formations are absent. The Mesozoic rocks consist mainly of sandstones, shales, calcareous claystones, and argillaceous limestones of marine and continental origin. All Mesozoic periods are represented in this 3700 foot thick sequence of sedimentary rocks. The Cenozoic rocks and sediments include welded tuff, glacial deposits, and alluvium. Quaternary landslides cover about one-quarter of the thesis area. The structures are Late Cretaceous to Early Tertiary (Laramide) and Late Cenozoic in age. The Laramide structures are northwest- trending, asymmetrical (steeper to the northeast) folds and high angle reverse faults. The Late Cenozoic structures are normal faults that displace Upper Cretaceous strata. Close

• 59. [Article] Calcium carbonate, organic carbon, and quartz in hemipelagic sediments off Oregon : a preliminary investigation

  An analysis of the amounts of calcium carbonate, organic carbon, quartz, and the rates of sediment accumulation in hemipelagic sediments off Oregon has revealed that the accumulation rates of the total sediment, ...

  Citation × Citation Citation Abstract Copy Title: Calcium carbonate, organic carbon, and quartz in hemipelagic sediments off Oregon : a preliminary investigation Author: Peterson, Robert E. An analysis of the amounts of calcium carbonate, organic carbon, quartz, and the rates of sediment accumulation in hemipelagic sediments off Oregon has revealed that the accumulation rates of the total sediment, organic carbon, and quartz were at least twice as high in the late Pleistocene as they were during the Holocene. The accumulation rate of calcium carbonate was at least 8 times as high. There may have been a short transition period at the end of the last glacial stage from about 14,000 to 12,500 years B.P. when the sedimentation rate was very high up to 75 cm/l000 years. There is evidence that the amount of organic carbon in deep-sea sediments is a function of terrigenous influx, of preservation, and possibly of depth of burial in the sediment. Turbidite sequences in the deep-sea environment off Oregon contain much higher amounts of organic carbon in the upper fine-grained portion of the sequence than in the coarser basal sediment of the sequence, indicating that organic carbon is concentrated in the finer and slower settling parts of the flow. In lower continental slope sediments, the greatest amounts of organic carbon are found in the <4 micron size fraction. Title: Calcium carbonate, organic carbon, and quartz in hemipelagic sediments off Oregon : a preliminary investigation Author: Peterson, Robert E. An analysis of the amounts of calcium carbonate, organic carbon, quartz, and the rates of sediment accumulation in hemipelagic sediments off Oregon has revealed that the accumulation rates of the total sediment, organic carbon, and quartz were at least twice as high in the late Pleistocene as they were during the Holocene. The accumulation rate of calcium carbonate was at least 8 times as high. There may have been a short transition period at the end of the last glacial stage from about 14,000 to 12,500 years B.P. when the sedimentation rate was very high up to 75 cm/l000 years. There is evidence that the amount of organic carbon in deep-sea sediments is a function of terrigenous influx, of preservation, and possibly of depth of burial in the sediment. Turbidite sequences in the deep-sea environment off Oregon contain much higher amounts of organic carbon in the upper fine-grained portion of the sequence than in the coarser basal sediment of the sequence, indicating that organic carbon is concentrated in the finer and slower settling parts of the flow. In lower continental slope sediments, the greatest amounts of organic carbon are found in the <4 micron size fraction. Close

• 60. [Article] Variable relationship between accumulation and temperature in West Antarctica for the past 31,000 years

  Access to this item has been restricted by repository administrators at the request of the publisher until October 28, 2016.

  Citation × Citation Citation Abstract Copy Title: Variable relationship between accumulation and temperature in West Antarctica for the past 31,000 years Author: Steig, Eric J., Fudge, T. J., Buizert, Christo, Markle, Bradley R., Taylor, Kendrick C., Cuffey, Kurt M., Waddington, Edwin D., Koutnik, Michelle, Conway, Howard Access to this item has been restricted by repository administrators at the request of the publisher until October 28, 2016. Title: Variable relationship between accumulation and temperature in West Antarctica for the past 31,000 years Author: Steig, Eric J., Fudge, T. J., Buizert, Christo, Markle, Bradley R., Taylor, Kendrick C., Cuffey, Kurt M., Waddington, Edwin D., Koutnik, Michelle, Conway, Howard Access to this item has been restricted by repository administrators at the request of the publisher until October 28, 2016. Close