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- Title
A New Middle to Late Jurassic Geomagnetic Polarity Time Scale (GPTS) From a Multiscale Marine Magnetic Anomaly Survey of the Pacific Jurassic Quiet Zone.
- Authors
Tominaga, Masako; Tivey, Maurice A.; Sager, William W.
- Abstract
The Geomagnetic Polarity Time Scale (GPTS) provides a basis for the geological timescale, quantifies geomagnetic field behavior, and gives a time framework for geologic studies. We build a revised Middle to Late Jurassic GPTS by using a new multiscale magnetic profile, combining sea surface, midwater, and autonomous underwater vehicle near‐bottom magnetic anomaly data from the Hawaiian lineation set in the Pacific Jurassic Quiet Zone (JQZ). We correlate the new profile with a previously published contemporaneous magnetic sequence from the Japanese lineation set. We then establish geomagnetic polarity block models as a basis for our interpretation of the origin and nature of JQZ magnetic anomalies and a GPTS. A significant level of coherency between short‐wavelength anomalies for both the Japanese and Hawaiian lineation magnetic anomaly sequences suggests the existence of a regionally coherent field during this period of rapid geomagnetic reversals. Our study implies the rapid onset of the Mesozoic Dipole Low from M42 through M39 and then a subsequent gradual recovery in field strength into the Cenozoic. The new GPTS, together with the Japanese sequence, extends the magnetic reversal history from M29 back in time to M44. We identify a zone of varying, difficult‐to‐correlate anomalies termed the Hawaiian Disturbed Zone, which is similar to the zone of low amplitude, difficult‐to‐correlate anomalies in the Japanese sequence termed the Low Amplitude Zone (LAZ). We suggest that the LAZ, bounded by M39–M41 isochrons, may in fact represent the core of what is more commonly known as the JQZ crust. Plain Language Summary: The western Pacific Ocean has by far the largest extent of Jurassic (145 to 180 Myr) ocean crust remaining in the world forming an important repository of the oldest oceanic crustal recording of geomagnetic field history. We use this magnetic record to establish a Geomagnetic Polarity Time Scale that forms the basis for the Geological Time Scale that quantifies Earth's geological evolution. Jurassic magnetism has been difficult to quantify because of its weak signal in the Pacific leading to its characterization as the Jurassic Quiet Zone with limited polarity reversals. In this study, we use a new approach by measuring magnetism in the Pacific Hawaiian magnetic sequence at multiple scales using sensors at the sea surface, on a deep towed sled and on a near‐bottom autonomous underwater vehicle. We find a sequence of rapid magnetic reversals that can be correlated with a previous record obtained from the Pacific Japanese anomaly sequence. Superimposed on this reversal history is a longer wavelength variation in magnetic anomaly amplitude that suggests the Mid Jurassic indeed had a weak field intensity. Thus, the Jurassic magnetic field was weak and reversing polarity at much greater rates than any time since. Key Points: This study confirmed global geomagnetic field behavior during Mid to Late JurassicOur new, multiscale marine magnetic anomaly data revealed the crustal age of the oldest Pacific is ∼Chron M42Newly discovered the Jurassic Disturbed Zone, bounded by M39–M41 isochrons represents the core of widely known the Jurassic Quiet Zone
- Subjects
PACIFIC Ocean; GEOMAGNETISM; MAGNETIC anomalies; CENOZOIC Era; OCEANIC crust
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 3, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2020JB021136