Geomagnetic palaeointensity just prior to the Cretaceous normal superchron

摘要: Abstract 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 flows is 120.93±0.88 Ma (marine anomaly M0). Detailed investigations were two samples each flow to determine their rock-magnetic properties. temperature dependences of the saturation magnetization (J–T) initial susceptibility (κ–T) show evidence low-titanium magnetite Curie 560–585°C with generally good reversibility heating cooling curves. Hysteretic properties, ratios Mrs/Ms Hcr/Hc, indicate that pseudo-single-domain (PSD) grains are dominant lavas. Stepwise thermal demagnetization isolated well-defined characteristic (ChRM) all 20 mean direction D/I=174.9/−60.1° α95=2.3°. modified version Thellier palaeointensity method ( Coe, 1967a ) systematic partial thermoremanent (pTRM) checks was used. Forty-two 71 (59%) yielded reliable results. Virtual dipole moment (VDM) values range 1.71×1022 5.27×1022 A m2 an average (3.96±0.07)×1022 A m2. This low dipole-field intensity value approximately half present day VDM, consistent older results Caribbean submarine glasses for period 125±1 Ma Pick Tauxe, 1993 ). suggested weak geomagnetic field probably occurred just prior Cretaceous normal superchron (CNS).