Jurassic Magnetism - Near-bottom magnetic record
Jurassic-aged ocean crust represents the oldest surviving ocean crust in the
world today and consequently only resides in a few places, such as along the
continental margins of the Atlantic Ocean and in the western Pacific Ocean.
This Jurassic crust is marked by the disappearance of correlatable magnetic
anomaly stripes in both the Atlantic and Pacific oceans, thus leading to name of
the "Jurassic Quiet Zone" or JQZ [Larson and Chase, 1972; Larson and Hilde,
1975; Cande et al, 1978; Vogt and Einwich, 1979]. The precise origin of the
JQZ is unclear. It could be period of constant polarity similar to the more
well-known the Cretaceous Quiet Zone. It could be that the crust has suffered
sufficient aging that the signal has been totally degraded. The equatorial
latitude of the Pacific JQZ and deep water depths has meant that sea surface
magnetic profiles are contaminated by noise from the strong diurnal and magnetic
effects of the equatorial electrojet, so even measuring the magnetic field in
these areas is difficult.
I was Co-Principal Investigator with Paul Johnson (U Washington) and Will Sager (TAMU) on a 1992 deeptowed-magnetic survey of the JQZ in the western Pacific. This survey found correlatable magnetic lineations within the Jurassic Quiet Zone proving that the field was reversing quite fast (8-10 revs/million years) during this period. A paper was been published in Journal of Geophysical Research, 1998 on the results of this study.
I was Co-Chief Scientist on RV Thompson (TN152) with Will Sager again in 2002/2003 when we revisited the area using the deeptow-towed DSL-120 sidescan sonar and magnetometer to extend the high-resolution survey south to ODP Hole 801C and also complete a detailed survey around the hole. Several papers
have been published on those results (Tivey et al., 2006; Tominaga et al., 2008); see links to them below.
In 2011, I was a Co-Principal Investigator again, this time with Masako Tominaga (Mich. State Univ) on a deeptow and autonomous underwater vehicle (Sentry) survey of the Pacific Hawaiian magnetic record. As part of this RV Thompson (TN272) marine survey we had a significant outreach component with Prof. Adrienne Oakley of Kutztown University who brought undergraduates out on the research vessel with an innovative outreach program.
Most recently I completed a 2014/2015 cruise onboard the newly launched icebreaker RV Sikuliaq where we took the ship to the tropical Pacific to complete the transect we started in 2011 on the Hawaiian lineations. This cruise with CoPIs Masako Tominaga (TAMU) and Will Sager (Houston) successfully completed seven long AUV Sentry dives along the transect corridor along with deeptow and sea surface towed magnetic profiles.
Historical JQZ cruise data from 1992 (and soon 2002/2003 cruise) will be available from the
IEDA-MGDS database. This was part of a small data rescue project to Maurice Tivey made possible by IEDA.
Links to published papers
- Sager, Weiss, Tivey, and Johnson, 1998:
Geomagnetic polarity reversal model
of deep-tow profiles from the Pacific Jurassic Quiet Zone.
J. Geophys. Res.
- Tivey, Larson, Schouten and Pockalny, 2005:
Downhole magnetic measurements of
ODP Hole 801C: Implications for Pacific oceanic crust and magnetic field behavior
in the Middle Jurassic. Geochem. Geophys. Geosys.
- Tivey, Sager, Lee and Tominaga, 2006:
Origin of the Pacific Jurassic Quiet Zone.
- Tominaga, Sager, Tivey and 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.
J. Geophys. Res.
- Tominaga and Sager, 2010: Revised Pacific M-anomaly geomagnetic polarity Time scale Geophys. J. Int.
- Tominaga, Tivey, and Sager, 2015: Nature of the Jurassic Magnetic Quiet Zone. Geophys. Res. Lett.
Click here to go to the results from the 1992 survey.
Link to the 2002/2003 survey that extended the survey south and over Hole 801C
Link to the 2011 page documenting the survey of the Jurassic Pacific Hawaiian lineations
Link to the 2014 page documenting the AUV survey of the Jurassic Pacific Hawaiian lineations
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