New Paleointensities From the Skinner Cove Formation, Newfoundland, Suggest a Changing State of the Geomagnetic Field at the Ediacaran‐Cambrian Transition. Issue 9 (12th September 2021)

• Record Type: Journal Article
• Authors: Thallner, Daniele; Biggin, Andrew J.; McCausland, Phil J. A.; Fu, Roger R.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-12
• Subjects: paleointensity -- Ediacaran‐Cambrian transition -- Laurentia -- Newfoundland; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022292
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: The geomagnetic field in the Ediacaran period appears to be characterized by anomalous directions, high reversal frequencies, and ultra‐low field strength. At the Ediacaran‐Cambrian transition, apparent polar wander paths become less controversial, but hyper‐reversing fields with reversal frequencies similar to earlier in the Ediacaran have been reported until the mid‐Cambrian. To understand the long‐term behavior of the magnetic field during this transitional interval, information about the field strength is vital but currently lacking. To improve the intensity record at that time, samples of volcanic rocks from the 550 Ma Skinner Cove Formation, western Newfoundland, have been used for paleointensity determination. This multi‐method paleointensity study, utilizing thermal and microwave Thellier as well as double‐heating Shaw and pseudo‐Thellier experiments produces paleointensity estimates of 2.6–10.3 μT, corresponding to virtual dipole moments of 0.65–2.25 × 10 22 Am 2 . Analyses using scanning electron microscopy and rock magnetic measurements, as well as a positive intraformational conglomerate test, suggest that the remanence is primary. These intensity estimates are higher than earlier Ediacaran intensities and could point to the geomagnetic field entering into a stronger, more dipole‐dominated state at the Ediacaran‐Cambrian boundary. Plain Language Summary: The geomagnetic field in the Ediacaran period (635–538 million years ago) is extremely weak and shows many polarity reversals, in addition to other strange behavior. At the end of the Ediacaran, less strange behavior is reported, but the frequency of polarity reversals may remain high until the mid‐Cambrian (∼500 Ma). In this transitional interval vital information to understand the long‐term behavior of Earth's magnetic field is currently lacking due to a scarcity of data. This study provides new estimates on the strength of Earth's magnetic field at the end of the Ediacaran, based on volcanic rocks from the 550 million years old Skinner Cove Formation in western Newfoundland. To increase the reliability of the results, we used four different methods. Our data show that the field is still very weak in the transitional period, but stronger than in the earlier Ediacaran, which means that the magnetic field is likely increasing in strength in the transitional period. Key Points: New paleointensity results from 7 units of the Skinner Cove Formation in Newfoundland Measured field strengths around 550 Ma are up to two times higher than earlier in the Ediacaran Results suggest that the geomagnetic field behavior may change substantially at the Ediacaran‐Cambrian transition