渤海湾北岸平原钻孔岩心的古地磁研究

PALAEOMAGNETIC STUDY ON DRILL CORE FROM NORTHERN BOHAI COASTAL PLAIN

Palaeomagnetie measurement on 254.samples. from the 600 m-long drill core Bo-3(118°30'E， 39°15'N) clearly reveals the epoches of Gauss normal polarity, Matuyama reversed polarity and Brunhes normal polarity and several important polarity events,such as Kaena. olduvai and Jaramillo et.al since 300my ago.On the basis of polnrity,boundary ages and the corresponding thickness an average sedimentation rate is estimated to be 19.5cm per 1000years which is in agreement with data in other areas in the North China Plain.Micro-palaeobiologic fossils indicate three marine beds to a depth of 80m that can be compared with the western coast of Bohai Bay,suggesting three raphic divission of the drill core has also been discussed.The base of Holocene is at a depth of 15m(0.01-0.012my B.P.),Late Pleistocene at 46m(0.11-0.13my B.P.0Middle Pleistocene 171m(0.73my B.P.)and the Quarternary bottom can be defined prcliminarily at 490m(2.48my B.P.)or 587m(about 3my B.P.).

Palaeomagnetic measurement on 254 samples from the 600 m-long drill core Bo-3(118°30′E, 39°15′N) clearly reveals the epoches of Gauss normal polarity, Matuyamareversed polarity and Brunhes normal polarity and several important polarity events,such as Kaena, Olduvai and Jaramillo et al. since 300 my ago. On the basis of polarityboundary ages and the corresponding thickness an average sedimentation rate is esti-mated to be 19.5 cm per 1000 years which is in agreement with data in other areas inthe North China Plain. Micro-palaeobiologic fossils indicate three marine beds to a depthof 80m that can be compared with the western coast of Bohai Bay, suggesting threetranspressions since the middle-late period of Middle Pleistocene. Quarternary stratig-raphic divission of the drill core has also been discussed. The base of Holocene is ata depth of 15m (0.01-0.012 my B. P.), Late Pleistocene at 46 m (0.11-0.13 my B.P.), Middle Pleistocene 171 m (0.73 my B. P.) and the Quarternary bottom can be definedpreliminarily at 490 m (2.48 my B. P.) or 587 m (about 3 my B. P.).