MAGNETOSTRATIGRAPHY OF BOREHOLE CH500 ON WESTERN COAST OF BOHAI BAY

Magnetostratigraphic studies have been conducted for the 377 samples taking from the borehole of CH500 (503.22 m) on the western coast of the Bohai Bay. Based on the alternating demagnetization results of the specimens and compared them to the geomagnetic polarity timescale, we calculated the characteristic directions of remanent magnetization and clarified the polarity of each samples. A stratigraphic classification was then established and the tectonic significance of the borehole discussed. The Brunhes/Matuyama boundary was found at the core depth of 119.5 m, and the Matuyama/Gauss boundary at the core depth of 359.1 m. The age of the hole bottom is supposed to be less than 3.33 Ma. Comparing with other boreholes in the west and north coasts of the Bohai Bay, it is found that the depths of both the B/M and M/G boundary change from place to place are dependent upon the stratigraphic thickness of the deposits in different tectonic units. The results have not only provided a reliable chronological framework for the borehole CH500, but also facilitated a Quaternary stratigraphic framework for the western coast of the Bohai Bay.