RATES OF MAGNETIC FIELD REVERSALS FROM THE EDIACARAN-PRESENT DAY: REVIEW AND NEW DATA

Reversals of the Earth’s magnetic field have been documented back to Archean times. The rates at which the magnetic field reverses polarity are highly variable. In particular, there are at least two lengthy intervals of geologic time during which the field underwent no reversals. These are known as the Kiaman Reverse Superchron (262-318 Ma) and the Cretaceous Normal Superchron (83-121 Ma). There are also intervals of geologic time where the field has undergone rapid reversal rates (>10 reversals/Ma--most notably during the Jurassic). Attempts to explain the relationships between field reversal frequency and field strength are contentious. Magnetic field models suggest that a non-reversing state is associated with an elevated dipole intensity whereas a rapidly-reversing dynamo is associated with a decreased dipole intensity. In addition, arguments have been forwarded linking superchrons to changes in heat flux across the Core-Mantle boundary. Paleointensity measurements provide no clear answer as to whether or not the field models resemble the Earth’s dynamo.

In this presentation, we review the overall reversal history of the Earth’s magnetic field from Late Ediacaran (~550 Ma) time to the present-day along with a summary of field models and ground-truth. At least one new interesting feature of the Earth's magnetic field is obtained from sedimentary rocks in the Urals. The Late Ediacaran-aged sediments (~550 Ma) document an anomalously high reversal rate (<20/Ma). We speculate that the rapid reversal frequency observed in the Late Ediacaran rocks may have influenced evolutionary changes across the Ediacaran/Cambrian boundary as field reversal frequency remained high into the Middle Cambrian (~8/Ma). Reversal frequency appears to drop during the Ordovician and the presence of a third Phanerozoic superchron has been posited for this time.