Geomagnetic palaeointensity just prior to the Cretaceous normal superchron

Details Geomagnetic palaeointensity just prior to the Cretaceous normal superchron Geomagnetic palaeointensity just prior to the Cretaceous normal superchron

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001pepi..128..207z&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 128, Issue 1-4, p. 207-222.

Physics

22

Scientific paper

A combined geochronologic (K-Ar) and palaeomagnetic study has been conducted on a basalt lava sequence at Zhuanchengzi in Liaoning province, northeastern China. The new K-Ar age obtained from these lava flows is /120.93+/-0.88Ma (marine anomaly M0). Detailed investigations were conducted on two samples from each lava flow to determine their rock-magnetic properties. The temperature dependences of the saturation magnetization (J-T) and the initial susceptibility (κ-T) show evidence of low-titanium magnetite and a Curie temperature of 560-585°C with generally good reversibility of heating and cooling curves. Hysteretic properties, ratios of Mrs/Ms and Hcr/Hc, indicate that pseudo-single-domain (PSD) grains of magnetite are dominant in these lavas. Stepwise thermal demagnetization isolated well-defined characteristic magnetization (ChRM) in all the 20 lava flows with a mean direction of /D/I=174.9/-60.1° with α95=2.3°. The modified version of the Thellier and Thellier palaeointensity method () with systematic partial thermoremanent magnetization (pTRM) checks was used. Forty-two of 71 samples (59%) yielded reliable palaeointensity results. Virtual dipole moment (VDM) values range from 1.71×1022 to 5.27×1022Am2 with an average of (3.96+/-0.07)×1022Am2. This low dipole-field intensity value is approximately half the present day VDM, consistent with older results obtained from the Caribbean submarine basalt glasses for the period of /125+/-1Ma (). This suggested that a weak geomagnetic field probably occurred just prior to the Cretaceous normal superchron (CNS).

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