Abstract
To clarify geomagnetic field behavior in the Late Cretaceous, paleointensity and rock-magnetic studies were carried out on basalts with K-Ar ages of 78.6 ± 2.5 and 73.1 ± 1.6 Ma in northwest South Korea. A total of 314 samples (262 from six lava flows and 52 from massive basalts) were subjected to Thellier-type IZZI paleointensity experiments. Through the application of seven paleointensity selection criteria that mainly verify the thermal alteration of magnetic minerals and the stability of remanence direction, fifteen paleointensity data were obtained from five of the lava flows. Based on rock-magnetic experiments and microscopic observations, it is revealed that the measured paleointensity is carried by single-domain (titano)magnetite. The site-mean paleointensities ranged 13.1−21.3 μT, which corresponds to a virtual axial dipole moment of 2.3−3.8 × 1022 Am2. The combination of this result with selected data from the IAGA paleointensity database establishes the existence of different dipole moments according to rock type. In particular, the geomagnetic field strength recorded in Late Cretaceous crystalline volcanic rock was relatively low and stable, with a mean dipole moment of 4.0 ± 1.9 × 1022 Am2 regardless of geomagnetic field reversals.
Highlights
The Earth’s magnetic field is generated by electrical currents flowing in the liquid outer core and is sustained permanently by a self-exciting geodynamo (e.g., Glatzmaier et al, 1999)
We focused on basalts in the Yeoncheon area of South Korea (Fig. 1), which formed during the Late Cretaceous after the Cretaceous Normal Superchron (CNS)
In this study, absolute paleointensity values for Korean basalts dating from the Late Cretaceous—after the Cretaceous Normal Superchron (CNS)—are obtained
Summary
The Earth’s magnetic field is generated by electrical currents flowing in the liquid outer core and is sustained permanently by a self-exciting geodynamo (e.g., Glatzmaier et al, 1999). That the time interval of 83–72 Ma has been suggested to correspond with a stationary regime for the geodynamo and a low geomagnetic reversal rate (Gallet and Hulot, 1997), high dipole moments are plausible, as suggested by numerical simulation (e.g., Olson and Hagee, 1990) Such a discrepancy between the dipole moments of various studies could be explained by the materials used for the experiments, given that the magnetic minerals in SBG are sometimes chemically altered during paleointensity experiments (Heller et al, 2002; Smirnov and Tarduno, 2003).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
