河北衡水地区钻孔岩芯的古地磁研究

PALEOMAGNETIC INVESTIGATION ON DRILLING CORES IN THE HENGSHUI AREA, NORTH CHINA PLAIN

Paleomagnetic measurements were carried out on 134 vertically oriented spccimens taken from a Cenozoic drilling core in the Hengshui area, North China Plain.An alternating magnetic field with a peak value of 160 Oe, was adopted for oppositedirection-magnetic cleaning to eliminate secondary viscous and rotated remanent magnetization. The results proved greatly successful. It is evident from the paleomagnetic studies that geomagnetic polarity epochs and events were recorded in this set of loose sediments during the last 3 m.y. with the boundary between the Brunhes normal epoch and the Matuyama reversed epoch (ca. 0.7m.y.) at a depth of 140m and the Matuyama-Gauss boundary (ca. 2.43m.y.) at 489 m depth with respect to the drilling cores. At present, it is acceptable that the beginning of the Quarternary should be dated back at 1.8--2 m.y., rightly corresponding to the basal limit of the Olduvia event at the depth of 360m. The area is characterized by a high and constant rate of sedimentation (ca. 200mm per 1,000 years).

Paleomagnetic measurements were carried out on 134 vertically oriented specimens taken from a Cenozoic drilling core in the Hengshui area, North China Plain. An alternating magnetic field with a peak value of 160 Oe. was adopted for opposite' direction-magnetic cleaning to eliminate secondary viscous and rotated remanent magnetization. The results proved greatly successful. It is evident from the paleo-magnetie studies that geomagnetic polarity epochs and events were recorded in this set of loose sediments during the last 3 m.y. with the boundary between the Brunhes normal epoch and the Matuyama reversed epoch (ca. 0.7 m.y.) at a depth of 140m and the Matuyama-Gauss boundary (ca. 2.43 m.y.) at 489m depth with respect to the drilling cores. At present, it is acceptable that the beginning of the Quarternary should be dated back at 1.8-2 m.y., rightly corresponding to the basal limit of the Olduvia event at the depth of 360m. The area is characterized by a high and constant rate of sedimentation (ca. 200mm per 1,000 years).