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• 41. [Article] Late Pleistocene and Holocene glacier and climate change

  This dissertation presents results from three studies that address major scientific questions in glacial geology and paleoclimatology for the late Pleistocene and Holocene using relatively new geochemical ...

  Citation × Citation Citation Abstract Copy Title: Late Pleistocene and Holocene glacier and climate change Author: Marcott, Shaun Andrew This dissertation presents results from three studies that address major scientific questions in glacial geology and paleoclimatology for the late Pleistocene and Holocene using relatively new geochemical and statistical techniques. Each of the studies attempts to answer a longstanding question in the respective field using geochemical or statistical methods that have not been applied to the problem thus far. A longstanding question in glaciology is the nature and mechanism of the so- called "Heinrich events" of the last ~60 ka. These massive iceberg discharge events into the North Atlantic from the partial breakup of the Laurentide Ice Sheet are identified from distinct ice rafted debris and detrital carbonate layers in marine sediment cores. The mechanism associated with the initiation of these events is commonly thought to be related to internal ice sheet instabilities. However, Heinrich events consistently occur following a long cooling trend that culminates in an extreme cold event, thus suggesting a possible triggering mechanism by climate. Recent modeling work has proposed an oceanic mechanism associated with ocean warming, but no physical evidence has been made available to date. To test this ocean-warming hypothesis, we measured temperature sensitive trace metals and stable isotopes in benthic foraminifera from a sediment core collected in the western North Atlantic that spans the last six Heinrich events and compared our results to climate model simulations using CCSM3. Our results show subsurface warming occurred prior to or coeval with nearly all of the Heinrich events of the last ~60 ka, thus implicating subsurface ocean warming as the main trigger of these rapid breakups of the Laurentide Ice Sheet. In the field of glacial geology a longstanding question has been the timing of alpine glacial advances during the Holocene. A number of studies have interpreted several Holocene glacial advances in western North America, but age control is based largely on relative dating techniques, which have been shown to be in error by up to 10,000 yrs in some cases. Based on 124 ¹⁰Be surface exposure ages from twenty cirque moraines in ten mountain ranges across western North America, glacier were retreating from moraine positions during the latest Pleistocene or earliest Holocene and not throughout the Holocene epoch as previously assumed, thus requiring a refined interpretation of Holocene glacial activity in western North America and the associated climate forcing. In the field of paleoclimatology a question regarding how global temperature varied over the entirety of the Holocene epoch has remained to be answered for some time. While many temperature reconstructions exist for the last 2000 years, a full Holocene temperature stack does not exist, despite its potential utility of putting modern climate change into a full interglacial perspective. Based on a global composite of 73 proxy based temperature record, a Holocene temperature stack was constructed and used to demonstrate that a general cooling of ~1°C has occurred from the early to mid Holocene and that centennial and millennial scale variability is modest. We account for both temperature calibration and chronologic uncertainties using a Monte Carlo based approach. Our results are consistent with prior reconstructions of the last 2000 years and now allow for a full Holocene temperature perspective for evaluation with present and future climate change. Title: Late Pleistocene and Holocene glacier and climate change Author: Marcott, Shaun Andrew This dissertation presents results from three studies that address major scientific questions in glacial geology and paleoclimatology for the late Pleistocene and Holocene using relatively new geochemical and statistical techniques. Each of the studies attempts to answer a longstanding question in the respective field using geochemical or statistical methods that have not been applied to the problem thus far. A longstanding question in glaciology is the nature and mechanism of the so- called "Heinrich events" of the last ~60 ka. These massive iceberg discharge events into the North Atlantic from the partial breakup of the Laurentide Ice Sheet are identified from distinct ice rafted debris and detrital carbonate layers in marine sediment cores. The mechanism associated with the initiation of these events is commonly thought to be related to internal ice sheet instabilities. However, Heinrich events consistently occur following a long cooling trend that culminates in an extreme cold event, thus suggesting a possible triggering mechanism by climate. Recent modeling work has proposed an oceanic mechanism associated with ocean warming, but no physical evidence has been made available to date. To test this ocean-warming hypothesis, we measured temperature sensitive trace metals and stable isotopes in benthic foraminifera from a sediment core collected in the western North Atlantic that spans the last six Heinrich events and compared our results to climate model simulations using CCSM3. Our results show subsurface warming occurred prior to or coeval with nearly all of the Heinrich events of the last ~60 ka, thus implicating subsurface ocean warming as the main trigger of these rapid breakups of the Laurentide Ice Sheet. In the field of glacial geology a longstanding question has been the timing of alpine glacial advances during the Holocene. A number of studies have interpreted several Holocene glacial advances in western North America, but age control is based largely on relative dating techniques, which have been shown to be in error by up to 10,000 yrs in some cases. Based on 124 ¹⁰Be surface exposure ages from twenty cirque moraines in ten mountain ranges across western North America, glacier were retreating from moraine positions during the latest Pleistocene or earliest Holocene and not throughout the Holocene epoch as previously assumed, thus requiring a refined interpretation of Holocene glacial activity in western North America and the associated climate forcing. In the field of paleoclimatology a question regarding how global temperature varied over the entirety of the Holocene epoch has remained to be answered for some time. While many temperature reconstructions exist for the last 2000 years, a full Holocene temperature stack does not exist, despite its potential utility of putting modern climate change into a full interglacial perspective. Based on a global composite of 73 proxy based temperature record, a Holocene temperature stack was constructed and used to demonstrate that a general cooling of ~1°C has occurred from the early to mid Holocene and that centennial and millennial scale variability is modest. We account for both temperature calibration and chronologic uncertainties using a Monte Carlo based approach. Our results are consistent with prior reconstructions of the last 2000 years and now allow for a full Holocene temperature perspective for evaluation with present and future climate change. Close

• 42. [Article] Sedimentation, Climate Change and Tectonics: Dynamic Stratigraphy of the Pliocene-Pleistocene Fish Creek-Vallecito Basin, California

  In order to better understand the interactions between climate change, landscape erosion and sedimentation, a detailed study was conducted on Plio-Pleistocene non-marine deposits of the Palm Spring Group ...

  Citation × Citation Citation Abstract Copy Title: Sedimentation, Climate Change and Tectonics: Dynamic Stratigraphy of the Pliocene-Pleistocene Fish Creek-Vallecito Basin, California Author: Peryam, Thomas Year: 2012 In order to better understand the interactions between climate change, landscape erosion and sedimentation, a detailed study was conducted on Plio-Pleistocene non-marine deposits of the Palm Spring Group in the Fish Creek-Vallecito basin, California, USA. Three inter-related studies focused on (1) local response to global climate change in late Pliocene-early Pleistocene time, (2) large-scale evolution of lithofacies architecture, and (3) climate modulation of late Pliocene sediment flux on Milankovitch time scales. Stable isotopes and paleosol classification reveal that between ~4.0 and 0.75 Ma, aridity increased in the study area concurrent with a shift towards a less intense and more winter-dominated precipitation regime. These changes are interpreted to reflect the long-term waning of summer monsoon precipitation in southern California. A dramatic and enigmatic reorganization of basin strata occurred at 2.9 Ma. Detailed basin analysis shows that locally-derived sediment was supplied by the predecessors of two modern drainages, Vallecito and Carrizo creeks. Initial progradation of alluvial deposits from these two sources across the Colorado River delta plain began between 4.0-3.4 Ma. At 2.9 Ma, rapid progradation of these two deposystems was coeval with emplacement of a megabreccia and transgression of Borrego Lake. My data indicate that tectonic realignments at both local and regional scales drove this reorganization. Time series analysis of rock magnetic data from a densely-sampled stratigraphic section of the lacustrine Tapiado Formation reveals that between 2.9 and ~2.75 Ma landscape denudation in the Carrizo Creek catchment was partly modulated by orbital obliquity. Peaks in landscape denudation implied by my data correspond to obliquity highs. More frequent high intensity precipitation events (i.e. monsoons and tropical storms) probably drove increased erosion during these time periods relative to obliquity lows. The breakdown of this relationship at around 2.75 Ma corresponds to a dramatic increase in northern hemisphere glaciation and may reveal a reduction in monsoonal influence in southern California. A geologic map of the Fish Creek-Vallecito basin is included as a supplemental file to this dissertation. This dissertation contains previously published and unpublished coauthored material. Title: Sedimentation, Climate Change and Tectonics: Dynamic Stratigraphy of the Pliocene-Pleistocene Fish Creek-Vallecito Basin, California Author: Peryam, Thomas Year: 2012 In order to better understand the interactions between climate change, landscape erosion and sedimentation, a detailed study was conducted on Plio-Pleistocene non-marine deposits of the Palm Spring Group in the Fish Creek-Vallecito basin, California, USA. Three inter-related studies focused on (1) local response to global climate change in late Pliocene-early Pleistocene time, (2) large-scale evolution of lithofacies architecture, and (3) climate modulation of late Pliocene sediment flux on Milankovitch time scales. Stable isotopes and paleosol classification reveal that between ~4.0 and 0.75 Ma, aridity increased in the study area concurrent with a shift towards a less intense and more winter-dominated precipitation regime. These changes are interpreted to reflect the long-term waning of summer monsoon precipitation in southern California. A dramatic and enigmatic reorganization of basin strata occurred at 2.9 Ma. Detailed basin analysis shows that locally-derived sediment was supplied by the predecessors of two modern drainages, Vallecito and Carrizo creeks. Initial progradation of alluvial deposits from these two sources across the Colorado River delta plain began between 4.0-3.4 Ma. At 2.9 Ma, rapid progradation of these two deposystems was coeval with emplacement of a megabreccia and transgression of Borrego Lake. My data indicate that tectonic realignments at both local and regional scales drove this reorganization. Time series analysis of rock magnetic data from a densely-sampled stratigraphic section of the lacustrine Tapiado Formation reveals that between 2.9 and ~2.75 Ma landscape denudation in the Carrizo Creek catchment was partly modulated by orbital obliquity. Peaks in landscape denudation implied by my data correspond to obliquity highs. More frequent high intensity precipitation events (i.e. monsoons and tropical storms) probably drove increased erosion during these time periods relative to obliquity lows. The breakdown of this relationship at around 2.75 Ma corresponds to a dramatic increase in northern hemisphere glaciation and may reveal a reduction in monsoonal influence in southern California. A geologic map of the Fish Creek-Vallecito basin is included as a supplemental file to this dissertation. This dissertation contains previously published and unpublished coauthored material. Close

• 43. [Article] The Ore bin ; Vol. 28 No. 11 (November 1966)

  Introduction -- Stratigraphy -- Pre-Tertiary rocks -- Umpqua Formation -- Tyee Formation -- Pre-Coaledo - Post-Tyee beds -- Coaledo Formation -- Bastendorff Formation -- Tunnel Point Formation -- Miocene ...

  Citation × Citation Citation Abstract Copy Title: The Ore bin ; Vol. 28 No. 11 (November 1966) Author: Oregon. Dept. of Geology and Mineral Industries, Baldwin, Ewart Merlin, 1915- Introduction -- Stratigraphy -- Pre-Tertiary rocks -- Umpqua Formation -- Tyee Formation -- Pre-Coaledo - Post-Tyee beds -- Coaledo Formation -- Bastendorff Formation -- Tunnel Point Formation -- Miocene beds -- Empire Formation -- Coquille Formation -- Pleistocene terraces -- Structural geology -- Faulting -- Folding and warping -- Bibliography. Title: The Ore bin ; Vol. 28 No. 11 (November 1966) Author: Oregon. Dept. of Geology and Mineral Industries, Baldwin, Ewart Merlin, 1915- Introduction -- Stratigraphy -- Pre-Tertiary rocks -- Umpqua Formation -- Tyee Formation -- Pre-Coaledo - Post-Tyee beds -- Coaledo Formation -- Bastendorff Formation -- Tunnel Point Formation -- Miocene beds -- Empire Formation -- Coquille Formation -- Pleistocene terraces -- Structural geology -- Faulting -- Folding and warping -- Bibliography. Close

• 44. [Article] Surface and subsurface geology of the Santa Barbara-Goleta metropolitan area, Santa Barbara County, California

  The Santa Barbara-Montecito and Goleta basins are structurally continuous fault-controlled Pleistocene basins containing up to 3000 feet (925 m) of marine Pleistocene Santa Barbara Formation which were ...

  Citation × Citation Citation Abstract Copy Title: Surface and subsurface geology of the Santa Barbara-Goleta metropolitan area, Santa Barbara County, California Author: Olson, Daniel J. The Santa Barbara-Montecito and Goleta basins are structurally continuous fault-controlled Pleistocene basins containing up to 3000 feet (925 m) of marine Pleistocene Santa Barbara Formation which were deposited on previously deformed Sisquoc and older strata. Structures subcropping against the unconformity at the base of the Santa Barbara Formation show that pre-basin deformation was mainly by folding. In addition, high-angle reverse faulting occurred along the Cameros, Goleta, and Modoc faults prior to Santa Barbara deposition in the Goleta basin. These are the oldest faults in the study area. Deposition of the Santa Barbara Formation began less than 1.2 Ma ago. Post-Santa Barbara (post-basin) deformation includes disharmonic folding of incompetent Miocene strata above broad folds in competent Oligocene strata, as displayed in the Elwood oil field and La Goleta gas field, and reverse faulting along several south-dipping faults of large displacement. The More Ranch fault, which juxtaposes Sisquoc and older strata against the Santa Barbara and Pico(?) Formations, displaces a 40,000 year old marine terrace, forms a north-facing eroded fault scarp, and marks the southern edge of the Goleta basin. The fault dips more than 80° south and displays up to a maximum of 2000 feet (610 m) vertical separation. The fault in the area with the largest amount of vertical separation, is the Coal Oil Point fault of post-Sisquoc age. This fault fails to reach the surface even though vertical separation of the Oligocene Vaqueros Formation is as great as 5400 feet (1650 m). Comparison with other faults in the area suggests that this fault belongs to the set of south-dipping, east-trending, Quaternary reverse faults that are characteristic of the coastal basins adjacent to the central Santa Ynez Mountains. All post-basin faults disrupt late Pleistocene strata and are potentially active. Other post-basin faults include the Mesa fault, which may link the More Ranch and Rincon Creek faults, the Lavigia fault which cuts older alluvium, and the San Jose fault which forms a north-facing scarp in late-Pleistocene fanglomerate. Distribution of aftershocks and focal mechanism solutions of the 1978 Santa Barbara earthquake suggest a gently north-dipping fault plane which would be unrelated to any of the faults exposed at the surface in the study area. However, the linear pattern of aftershock epicenters is parallel to the Mesa and Mission Ridge- Arroyo Parida faults; if the alternate south-dipping nodal plane is the correct solution then the earthquake could have originated on a member of the south-dipping fault set. Title: Surface and subsurface geology of the Santa Barbara-Goleta metropolitan area, Santa Barbara County, California Author: Olson, Daniel J. The Santa Barbara-Montecito and Goleta basins are structurally continuous fault-controlled Pleistocene basins containing up to 3000 feet (925 m) of marine Pleistocene Santa Barbara Formation which were deposited on previously deformed Sisquoc and older strata. Structures subcropping against the unconformity at the base of the Santa Barbara Formation show that pre-basin deformation was mainly by folding. In addition, high-angle reverse faulting occurred along the Cameros, Goleta, and Modoc faults prior to Santa Barbara deposition in the Goleta basin. These are the oldest faults in the study area. Deposition of the Santa Barbara Formation began less than 1.2 Ma ago. Post-Santa Barbara (post-basin) deformation includes disharmonic folding of incompetent Miocene strata above broad folds in competent Oligocene strata, as displayed in the Elwood oil field and La Goleta gas field, and reverse faulting along several south-dipping faults of large displacement. The More Ranch fault, which juxtaposes Sisquoc and older strata against the Santa Barbara and Pico(?) Formations, displaces a 40,000 year old marine terrace, forms a north-facing eroded fault scarp, and marks the southern edge of the Goleta basin. The fault dips more than 80° south and displays up to a maximum of 2000 feet (610 m) vertical separation. The fault in the area with the largest amount of vertical separation, is the Coal Oil Point fault of post-Sisquoc age. This fault fails to reach the surface even though vertical separation of the Oligocene Vaqueros Formation is as great as 5400 feet (1650 m). Comparison with other faults in the area suggests that this fault belongs to the set of south-dipping, east-trending, Quaternary reverse faults that are characteristic of the coastal basins adjacent to the central Santa Ynez Mountains. All post-basin faults disrupt late Pleistocene strata and are potentially active. Other post-basin faults include the Mesa fault, which may link the More Ranch and Rincon Creek faults, the Lavigia fault which cuts older alluvium, and the San Jose fault which forms a north-facing scarp in late-Pleistocene fanglomerate. Distribution of aftershocks and focal mechanism solutions of the 1978 Santa Barbara earthquake suggest a gently north-dipping fault plane which would be unrelated to any of the faults exposed at the surface in the study area. However, the linear pattern of aftershock epicenters is parallel to the Mesa and Mission Ridge- Arroyo Parida faults; if the alternate south-dipping nodal plane is the correct solution then the earthquake could have originated on a member of the south-dipping fault set. Close

• 45. [Image] Boston Bay, looking north from Weymouth, Massachusetts

  	Drumlins, left when the great ice-sheet melted, are seen rising above the waters of the bay. In the Pleistocene epoch (the last geologic epoch before the present time) most of the northern and eastern ...
  	Citation × Citation Citation Abstract Copy Title: Boston Bay, looking north from Weymouth, Massachusetts Drumlins, left when the great ice-sheet melted, are seen rising above the waters of the bay. In the Pleistocene epoch (the last geologic epoch before the present time) most of the northern and eastern North America was covered by a great glacier, similar to the one which now covers Greenland. Title: Boston Bay, looking north from Weymouth, Massachusetts Drumlins, left when the great ice-sheet melted, are seen rising above the waters of the bay. In the Pleistocene epoch (the last geologic epoch before the present time) most of the northern and eastern North America was covered by a great glacier, similar to the one which now covers Greenland. Close

• 46. [Article] Tectonic controls for transverse drainage and timing of the Xin-Ding paleolake breach in the upper reach of the Hutuo River, North China

  This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/geomorphology/.

  Citation × Citation Citation Abstract Copy Title: Tectonic controls for transverse drainage and timing of the Xin-Ding paleolake breach in the upper reach of the Hutuo River, North China Author: Zhang, Shimin, Yeats, Robert S., Ren, Junjie, Meigs, Andrew J., Shen, Xiaoming, Ding, Rui This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/geomorphology/. Title: Tectonic controls for transverse drainage and timing of the Xin-Ding paleolake breach in the upper reach of the Hutuo River, North China Author: Zhang, Shimin, Yeats, Robert S., Ren, Junjie, Meigs, Andrew J., Shen, Xiaoming, Ding, Rui This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/geomorphology/. Close

• 47. [Article] Biogenic and terrigenous sedimetations at Ceara rise, western tropical Altantic, supports Pliocene - Pleistocene deep - water linkage between hemispheres

  Calcium carbonate percentages at five Ceara Rise sites were estimated at 1- to 2-k.y. intervals over the past 5 m.y., using reflectance spectroscopy and magnetic susceptibility proxies. From these estimates ...

  Citation × Citation Citation Abstract Copy Title: Biogenic and terrigenous sedimetations at Ceara rise, western tropical Altantic, supports Pliocene - Pleistocene deep - water linkage between hemispheres Author: Harris, Sara E., King, Terri, Mix, Alan C. Calcium carbonate percentages at five Ceara Rise sites were estimated at 1- to 2-k.y. intervals over the past 5 m.y., using reflectance spectroscopy and magnetic susceptibility proxies. From these estimates and detailed correlations between sites, gradients of calcite and terrigenous sediment accumulation rates in a depth transect of sites reveal variations in local climate and calcite dissolution related to deep-water masses. Relative to shallow sites on the southern Ceara Rise, accumulation rates of terrigenous sediments at deeper sites near the Amazon Fan were higher during glacial periods. Analogous variations in terrigenous sedimentation before the expansion of Northern Hemisphere ice sheets ~3 m.y. ago suggests that tropical climate cycles occurred independently of polar glaciation. Decreasing accumulation rates of calcite with increasing water depth reveal patterns of carbonate dissolution, which varied on orbital time-scales (10- 100 k.y. periods) throughout the Pliocene-Pleistocene. Maximum dissolution at deep relative to shallow sites occurred in the transition from interglacial to glacial conditions, and maximum preservation occurred during global warming, at all orbital periods. If the local dissolution gradient is linked to relative contributions of North Atlantic Deep Water and Antarctic Bottom Water, this phasing of events confirms a key prediction of SPECMAP that deep-water adjustments may translate climate changes between hemispheres. Dissolution and preservation events, however, may also reflect a transient response to a net flux of organic matter between the continents and the oceans during ice-age climate transitions. Title: Biogenic and terrigenous sedimetations at Ceara rise, western tropical Altantic, supports Pliocene - Pleistocene deep - water linkage between hemispheres Author: Harris, Sara E., King, Terri, Mix, Alan C. Calcium carbonate percentages at five Ceara Rise sites were estimated at 1- to 2-k.y. intervals over the past 5 m.y., using reflectance spectroscopy and magnetic susceptibility proxies. From these estimates and detailed correlations between sites, gradients of calcite and terrigenous sediment accumulation rates in a depth transect of sites reveal variations in local climate and calcite dissolution related to deep-water masses. Relative to shallow sites on the southern Ceara Rise, accumulation rates of terrigenous sediments at deeper sites near the Amazon Fan were higher during glacial periods. Analogous variations in terrigenous sedimentation before the expansion of Northern Hemisphere ice sheets ~3 m.y. ago suggests that tropical climate cycles occurred independently of polar glaciation. Decreasing accumulation rates of calcite with increasing water depth reveal patterns of carbonate dissolution, which varied on orbital time-scales (10- 100 k.y. periods) throughout the Pliocene-Pleistocene. Maximum dissolution at deep relative to shallow sites occurred in the transition from interglacial to glacial conditions, and maximum preservation occurred during global warming, at all orbital periods. If the local dissolution gradient is linked to relative contributions of North Atlantic Deep Water and Antarctic Bottom Water, this phasing of events confirms a key prediction of SPECMAP that deep-water adjustments may translate climate changes between hemispheres. Dissolution and preservation events, however, may also reflect a transient response to a net flux of organic matter between the continents and the oceans during ice-age climate transitions. Close

• 48. [Article] Oblique strike-slip faulting of the central Cascadia submarine forearc

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Oblique strike-slip faulting of the central Cascadia submarine forearc Author: Yeats, Robert S., Goldfinger, Chris, Hummon, Cheryl, McNeill, Lisa, Kulm, LaVerne D. Copyrighted by American Geophysical Union. Title: Oblique strike-slip faulting of the central Cascadia submarine forearc Author: Yeats, Robert S., Goldfinger, Chris, Hummon, Cheryl, McNeill, Lisa, Kulm, LaVerne D. Copyrighted by American Geophysical Union. Close

• 49. [Article] Garwood Valley, Antarctica: A new record of Last Glacial Maximum to Holocene glaciofluvial processes in the McMurdo Dry Valleys

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Geological ...

  Citation × Citation Citation Abstract Copy Title: Garwood Valley, Antarctica: A new record of Last Glacial Maximum to Holocene glaciofluvial processes in the McMurdo Dry Valleys Author: Fountain, Andrew G., Welch, Kathy A., Lyons, W. Berry, O'Connor, Jim E., Levy, Joseph S. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Geological Society of America and can be found at: http://gsabulletin.gsapubs.org/. Title: Garwood Valley, Antarctica: A new record of Last Glacial Maximum to Holocene glaciofluvial processes in the McMurdo Dry Valleys Author: Fountain, Andrew G., Welch, Kathy A., Lyons, W. Berry, O'Connor, Jim E., Levy, Joseph S. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Geological Society of America and can be found at: http://gsabulletin.gsapubs.org/. Close

• 50. [Article] Paleomagnetic inclination shallowing in deep-sea sediments

  In this thesis anomalous downcore shallowing of paleomagnetic inclinations is interpreted to be caused by sediment compaction. Thus, compaction-induced inclination shallowing may influence tectonic reconstructions ...

  Citation × Citation Citation Abstract Copy Title: Paleomagnetic inclination shallowing in deep-sea sediments Author: Arason, Pórdur In this thesis anomalous downcore shallowing of paleomagnetic inclinations is interpreted to be caused by sediment compaction. Thus, compaction-induced inclination shallowing may influence tectonic reconstructions that are based on inclinations from deep-sea sediment cores. Progressive downcore shallowing of the remanent inclination was observed in a 120-m section of Plio- Pleistocene sediments at Deep Sea Drilling Project (DSDP) site 578 in the northwest Pacific. Near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53° but shallows downcore by about 6° to 8°. In sediments spanning the same time interval of neighboring site 576, no inclination shallowing was observed. This second site has considerably lower sedimentation rates, and the Plio- Pleistocene is represented by a 26-m sedimentary section. The inclination shallowing at site 578 was correlated to a downhole decrease in porosity, and these results are interpreted to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 were caused by sediment compaction. Microscopic models demonstrate that sediment compaction may lead to inclination shallowing of the magnetic remanence. Furthermore, it is shown that inherent initial within-sample dispersion of the magnetic moments will transform any form of microscopic mechanism to an equation of a standardized form: tan (I-ΔI) = (1-a ΔV) tan I, where I is the inclination of the ambient field, ΔI is the inclination shallowing, a is a constant and ΔV the compaction. Paleomagnetic inclinations of Cretaceous DSDP sediments from the Pacific plate are known to be systematically shallower than predicted from paleolatitudes of hot spot reconstructions. Published paleomagnetic data were reexamined and the shallow Cretaceous inclinations explained as a result of sediment compaction. The Cretaceous data are used to estimate the parameter a. The resulting a values are comparable to those of previous studies of compaction-induced inclination shallowing, both from laboratory experiments and the considerably younger deep-sea sediments at site 578. Values of the parameter a suggest that it might be controlled by sediment lithology with greater shallowing for clayey than calcareous sediments. Title: Paleomagnetic inclination shallowing in deep-sea sediments Author: Arason, Pórdur In this thesis anomalous downcore shallowing of paleomagnetic inclinations is interpreted to be caused by sediment compaction. Thus, compaction-induced inclination shallowing may influence tectonic reconstructions that are based on inclinations from deep-sea sediment cores. Progressive downcore shallowing of the remanent inclination was observed in a 120-m section of Plio- Pleistocene sediments at Deep Sea Drilling Project (DSDP) site 578 in the northwest Pacific. Near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53° but shallows downcore by about 6° to 8°. In sediments spanning the same time interval of neighboring site 576, no inclination shallowing was observed. This second site has considerably lower sedimentation rates, and the Plio- Pleistocene is represented by a 26-m sedimentary section. The inclination shallowing at site 578 was correlated to a downhole decrease in porosity, and these results are interpreted to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 were caused by sediment compaction. Microscopic models demonstrate that sediment compaction may lead to inclination shallowing of the magnetic remanence. Furthermore, it is shown that inherent initial within-sample dispersion of the magnetic moments will transform any form of microscopic mechanism to an equation of a standardized form: tan (I-ΔI) = (1-a ΔV) tan I, where I is the inclination of the ambient field, ΔI is the inclination shallowing, a is a constant and ΔV the compaction. Paleomagnetic inclinations of Cretaceous DSDP sediments from the Pacific plate are known to be systematically shallower than predicted from paleolatitudes of hot spot reconstructions. Published paleomagnetic data were reexamined and the shallow Cretaceous inclinations explained as a result of sediment compaction. The Cretaceous data are used to estimate the parameter a. The resulting a values are comparable to those of previous studies of compaction-induced inclination shallowing, both from laboratory experiments and the considerably younger deep-sea sediments at site 578. Values of the parameter a suggest that it might be controlled by sediment lithology with greater shallowing for clayey than calcareous sediments. Close