William Sager | University of Houston (original) (raw)
Papers by William Sager
Journal of Geophysical Research, 1999
Oceanic plateaus are major ocean features, yet their origins and development are poorly understoo... more Oceanic plateaus are major ocean features, yet their origins and development are poorly understood. Many are huge piles of basalt, and it is widely accepted that mantle plumes are their source, perhaps from eruptions of the voluminous head of an emerging plume. Shatsky Rise is a basaltic plateau that formed during a period of geomagnetic reversals, unlike many mid-Cretaceous plateaus, so magnetic data can help us understand its tectonic history. In this study, we analyzed magnetic anomaly data from 131 cruises over and around Shatsky Rise and constructed a magnetic lineation chart for tectonic interpretation. A significant finding is that magnetic lineations are traceable through low parts of the rise between volcanic massifs, indicating nearly normal lithosphere, and between large volcanic edifices.
Geology, 1992
... Station, Texas 77843 Carlos A. Mortera-Gutierrez Department of Geophysics, Texas A&am... more ... Station, Texas 77843 Carlos A. Mortera-Gutierrez Department of Geophysics, Texas A&M University, College Station, Texas 77843 Jaime Urrutia-Fucugauchi ... 6.8°, Butler and Taylor, 1978; Mogollon-Datil Volcanics, -2.6° ±5.1°, Diehl et al., 1988; -7.1° ±4.8°, Mcintosh, 1991) are ...
Journal of Geophysical Research, 1988
JB_description.
Science, 1995
Paleomagnetic data from the Mid-Cretaceous Mountains suggest that Pacific plate motion during the... more Paleomagnetic data from the Mid-Cretaceous Mountains suggest that Pacific plate motion during the Early to mid-Cretaceous was slow, less than 0.3 degree per year, resembling the polar standstill observed in coeval rocks of Eurasia and North America. There is little evidence for a change in plate motion that could have precipitated the major volcanic episode of the early Aptian that is marked by the formation of the Ontong Java Plateau. During the volcanism, oceanic plates bordering the Pacific plate moved rapidly. Large-scale northward motion of the Pacific plate began after volcanism ceased. This pattern suggests that mantle plume volcanism exerted control on plate tectonics in the Cretaceous Pacific basin.
Marine Geology, 1999
High-frequency seismic reflection profiles showing near-surface sediments of the Mississippi-Alab... more High-frequency seismic reflection profiles showing near-surface sediments of the Mississippi-Alabama outer shelf define two shelf-margin deltas and three unconformities. The deepest unconformity lies below the westernmost delta, the middle unconformity separates the two deltas, and the shallowest unconformity is atop the easternmost delta. The deeper two unconformities are extensive and erosional to the shelf edge, implying Type-1 sequence boundaries. The shallowest is restricted in its depth range and extent, suggesting a Type-2 boundary. Both delta wedges contain sigmoid reflectors, representing foreset beds, and have apparent transgressive layers at their bases. Thus, these two sediment wedges and their bounding unconformities represent parts of three sea level cycles. Although we lack good age constraints, the middle unconformity appears to represent the last glacial maximum, so the western delta must have been deposited before and the eastern delta, afterwards. Internal reflector geometries suggest the eastern delta was deposited during an episode of falling sea level, implying a relative sea level regression within the overall deglacial transgression. q 1999 Elsevier Science B.V. All rights reserved. Such sediment bodies commonly display a cycle of deposition, lowstand truncation and incision, and subsequent burial by later deltas Ž . e.g., . Because their formation is thought to be closely tied to sea level, deltas have been widely studied for evidence of sea level variations as well as for testing sequence strati-0025-3227r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
Journal of Geophysical Research, 2008
1] The Jurassic Quiet Zone (JQZ) is a region of low-amplitude magnetic anomalies whose distinctiv... more 1] The Jurassic Quiet Zone (JQZ) is a region of low-amplitude magnetic anomalies whose distinctive character may be related to geomagnetic field behavior. We collected deep-tow magnetic profiles in Pigafetta Basin (western Pacific) where previous deep-tow data partially covered the JQZ sequence. Our goals were to extend the survey through the JQZ, examine anomaly correlations, and refine a preliminary geomagnetic polarity timescale (GPTS) model. We collected a series of closely spaced profiles over anomaly M34 and Ocean Drilling Program Hole 801C to examine anomaly correlation in detail, one profile in between previous profiles, and two long profiles extending the survey deeper into the JQZ. Anomaly features can be readily correlated except in a region of lowamplitude, short-wavelength anomalies in the middle of the survey area (''low-amplitude zone'' or LAZ). The small multiprofile surveys demonstrate anomaly linearity, implying that surrounding anomalies are also linear and likely result from crustal recording of geomagnetic field changes. We constructed a GPTS model assuming that most anomalies result from polarity reversals. The polarity timescale is similar to the polarity sequences from previous studies, but its global significance is uncertain because of problems correlating anomalies in the LAZ and the ambiguous nature of the small JQZ anomalies. Overall anomaly amplitude decreases with age into the LAZ and then increases again, implying low geomagnetic field strength, perhaps related to a rapidly reversing field. Other factors that may contribute to the LAZ are interference of anomalies over narrow, crustal polarity zones and poorly understood local tectonic complexities. Citation: Tominaga, M., W. W. Sager, M. A. Tivey, and S.-M. Lee (2008), Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications for the geomagnetic polarity reversal timescale and geomagnetic field behavior,
Journal of Geophysical Research, 1997
The paleomagnetism of 10 seamounts from the Joban Seamount Chain (northwestern Pacific) were stud... more The paleomagnetism of 10 seamounts from the Joban Seamount Chain (northwestern Pacific) were studied using a method that calculates mean magnetization parameters by an inversion of magnetic anomaly and edifice bathymetry. Of the 10 seamounts, eight gave results consistent with other paleomagnetic studies of Pacific seamounts. Joban seamounts appear to have formed at two different mean paleolatitudes, contrary to what would be expected for a single hotspot origin. Furthermore, six of the consistent poles plot along the 129 to 82 Ma portion of the Pacific plate apparent polar wander path (APWP), implying the seamounts formed mainly during the mid-to Late Cretaceous. Two other poles, from Iwaki and Hitachi seamounts, are located northwest of the older end of the established Pacific APWP, possibly indicating Early Cretaceous ages. Because Iwaki and Hitachi seamounts are located in the middle of the chain, age does not progress along the chain, arguing against a single-hotspot origin.
Earth and Planetary Science Letters, 1983
Seamount magnetic anomaly inversions as well as DSDP paleomagnetic and equatorial sediment facies... more Seamount magnetic anomaly inversions as well as DSDP paleomagnetic and equatorial sediment facies data constrain a paleomagnetic pole for the Pacific plate of Late Eocene age. The location of the pole at 77.5°N, 2h2°E implies 12.5 -I-1.6 ° of apparent polar wander for the Pacific plate during the last 41 + 5 m.y. The Late Eocene pole is significantly different from the Pacific Maastrichtian pole at the 95% confidence level and indicates 7.2 ° of apparent polar motion of the Pacific between 69 and 41 m.y.B.P. The data source locations for the Late Eocene pole are scattered over a large area of the North Pacific and thus the consistency of the data supports the hypothesis that the north central Pacific plate has been rigid since the Eocene. The agreement of the Late Eocene pole with the motion predicted for the Pacific from hotspot models suggests that relative motion between the spin axis and hotspots has been small since that time. Additionally, this finding dictates that the significant amounts of hotspot versus spin axis motion inferred by other authors to have occurred since the Cretaceous must have instead occurred at a faster rate and concluded before the Eocene. 0012-821X/83/$03.00
Marine Geology, 2003
ABSTRACT
Journal of Geophysical Research, 1999
Oceanic plateaus are major ocean features, yet their origins and development are poorly understoo... more Oceanic plateaus are major ocean features, yet their origins and development are poorly understood. Many are huge piles of basalt, and it is widely accepted that mantle plumes are their source, perhaps from eruptions of the voluminous head of an emerging plume. Shatsky Rise is a basaltic plateau that formed during a period of geomagnetic reversals, unlike many mid-Cretaceous plateaus, so magnetic data can help us understand its tectonic history. In this study, we analyzed magnetic anomaly data from 131 cruises over and around Shatsky Rise and constructed a magnetic lineation chart for tectonic interpretation. A significant finding is that magnetic lineations are traceable through low parts of the rise between volcanic massifs, indicating nearly normal lithosphere, and between large volcanic edifices.
Geology, 1992
... Station, Texas 77843 Carlos A. Mortera-Gutierrez Department of Geophysics, Texas A&am... more ... Station, Texas 77843 Carlos A. Mortera-Gutierrez Department of Geophysics, Texas A&M University, College Station, Texas 77843 Jaime Urrutia-Fucugauchi ... 6.8°, Butler and Taylor, 1978; Mogollon-Datil Volcanics, -2.6° ±5.1°, Diehl et al., 1988; -7.1° ±4.8°, Mcintosh, 1991) are ...
Journal of Geophysical Research, 1988
JB_description.
Science, 1995
Paleomagnetic data from the Mid-Cretaceous Mountains suggest that Pacific plate motion during the... more Paleomagnetic data from the Mid-Cretaceous Mountains suggest that Pacific plate motion during the Early to mid-Cretaceous was slow, less than 0.3 degree per year, resembling the polar standstill observed in coeval rocks of Eurasia and North America. There is little evidence for a change in plate motion that could have precipitated the major volcanic episode of the early Aptian that is marked by the formation of the Ontong Java Plateau. During the volcanism, oceanic plates bordering the Pacific plate moved rapidly. Large-scale northward motion of the Pacific plate began after volcanism ceased. This pattern suggests that mantle plume volcanism exerted control on plate tectonics in the Cretaceous Pacific basin.
Marine Geology, 1999
High-frequency seismic reflection profiles showing near-surface sediments of the Mississippi-Alab... more High-frequency seismic reflection profiles showing near-surface sediments of the Mississippi-Alabama outer shelf define two shelf-margin deltas and three unconformities. The deepest unconformity lies below the westernmost delta, the middle unconformity separates the two deltas, and the shallowest unconformity is atop the easternmost delta. The deeper two unconformities are extensive and erosional to the shelf edge, implying Type-1 sequence boundaries. The shallowest is restricted in its depth range and extent, suggesting a Type-2 boundary. Both delta wedges contain sigmoid reflectors, representing foreset beds, and have apparent transgressive layers at their bases. Thus, these two sediment wedges and their bounding unconformities represent parts of three sea level cycles. Although we lack good age constraints, the middle unconformity appears to represent the last glacial maximum, so the western delta must have been deposited before and the eastern delta, afterwards. Internal reflector geometries suggest the eastern delta was deposited during an episode of falling sea level, implying a relative sea level regression within the overall deglacial transgression. q 1999 Elsevier Science B.V. All rights reserved. Such sediment bodies commonly display a cycle of deposition, lowstand truncation and incision, and subsequent burial by later deltas Ž . e.g., . Because their formation is thought to be closely tied to sea level, deltas have been widely studied for evidence of sea level variations as well as for testing sequence strati-0025-3227r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
Journal of Geophysical Research, 2008
1] The Jurassic Quiet Zone (JQZ) is a region of low-amplitude magnetic anomalies whose distinctiv... more 1] The Jurassic Quiet Zone (JQZ) is a region of low-amplitude magnetic anomalies whose distinctive character may be related to geomagnetic field behavior. We collected deep-tow magnetic profiles in Pigafetta Basin (western Pacific) where previous deep-tow data partially covered the JQZ sequence. Our goals were to extend the survey through the JQZ, examine anomaly correlations, and refine a preliminary geomagnetic polarity timescale (GPTS) model. We collected a series of closely spaced profiles over anomaly M34 and Ocean Drilling Program Hole 801C to examine anomaly correlation in detail, one profile in between previous profiles, and two long profiles extending the survey deeper into the JQZ. Anomaly features can be readily correlated except in a region of lowamplitude, short-wavelength anomalies in the middle of the survey area (''low-amplitude zone'' or LAZ). The small multiprofile surveys demonstrate anomaly linearity, implying that surrounding anomalies are also linear and likely result from crustal recording of geomagnetic field changes. We constructed a GPTS model assuming that most anomalies result from polarity reversals. The polarity timescale is similar to the polarity sequences from previous studies, but its global significance is uncertain because of problems correlating anomalies in the LAZ and the ambiguous nature of the small JQZ anomalies. Overall anomaly amplitude decreases with age into the LAZ and then increases again, implying low geomagnetic field strength, perhaps related to a rapidly reversing field. Other factors that may contribute to the LAZ are interference of anomalies over narrow, crustal polarity zones and poorly understood local tectonic complexities. Citation: Tominaga, M., W. W. Sager, M. A. Tivey, and S.-M. Lee (2008), Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications for the geomagnetic polarity reversal timescale and geomagnetic field behavior,
Journal of Geophysical Research, 1997
The paleomagnetism of 10 seamounts from the Joban Seamount Chain (northwestern Pacific) were stud... more The paleomagnetism of 10 seamounts from the Joban Seamount Chain (northwestern Pacific) were studied using a method that calculates mean magnetization parameters by an inversion of magnetic anomaly and edifice bathymetry. Of the 10 seamounts, eight gave results consistent with other paleomagnetic studies of Pacific seamounts. Joban seamounts appear to have formed at two different mean paleolatitudes, contrary to what would be expected for a single hotspot origin. Furthermore, six of the consistent poles plot along the 129 to 82 Ma portion of the Pacific plate apparent polar wander path (APWP), implying the seamounts formed mainly during the mid-to Late Cretaceous. Two other poles, from Iwaki and Hitachi seamounts, are located northwest of the older end of the established Pacific APWP, possibly indicating Early Cretaceous ages. Because Iwaki and Hitachi seamounts are located in the middle of the chain, age does not progress along the chain, arguing against a single-hotspot origin.
Earth and Planetary Science Letters, 1983
Seamount magnetic anomaly inversions as well as DSDP paleomagnetic and equatorial sediment facies... more Seamount magnetic anomaly inversions as well as DSDP paleomagnetic and equatorial sediment facies data constrain a paleomagnetic pole for the Pacific plate of Late Eocene age. The location of the pole at 77.5°N, 2h2°E implies 12.5 -I-1.6 ° of apparent polar wander for the Pacific plate during the last 41 + 5 m.y. The Late Eocene pole is significantly different from the Pacific Maastrichtian pole at the 95% confidence level and indicates 7.2 ° of apparent polar motion of the Pacific between 69 and 41 m.y.B.P. The data source locations for the Late Eocene pole are scattered over a large area of the North Pacific and thus the consistency of the data supports the hypothesis that the north central Pacific plate has been rigid since the Eocene. The agreement of the Late Eocene pole with the motion predicted for the Pacific from hotspot models suggests that relative motion between the spin axis and hotspots has been small since that time. Additionally, this finding dictates that the significant amounts of hotspot versus spin axis motion inferred by other authors to have occurred since the Cretaceous must have instead occurred at a faster rate and concluded before the Eocene. 0012-821X/83/$03.00
Marine Geology, 2003
ABSTRACT