Studies on sedimentary events in Mariana Trough and characteristics of geomagnetic field change

The analysis on the magnetic fabric of profile of the sedimentary core taken in five stations in the small spreading ridge area in Mariana Trough shows that the effect of indicating its depositional fabric, sedimentary rhythm, sedimentary events, sedimentary interfaces and sediment composition as well as sedimentary dynamic environment by magnetic parameters is clearer than that by traditional method of analysis. The indication of sedimentary events show its high resolution. The study on the Late Quaternary sedimentary events in this area shows that this area underwent four big events of sudden change in the Holocene epoch, based on the sudden change of underflow direction and the position relationship between ash beds and erosion sediment layers. The sudden change of underflow direction is a believable evidence for judgement and study of sudden event within this area. The direction changes of its geomagnetic field show three morphotypes i.e. relatively stable type and non-stable type of oscillatory amplitude of magnetic inclination (Inc) which existed during the relatively stable period of amplitude of magnetic declination (Inc).Another type is characterized by big amplitude of both inclination and declination.The space-time series of the three types mentioned above is a new way for forming a high-resolution stratigraphical timetable.