Measurement of remanent magnetization of borehole samples and its significance in geological interpretation

Magnetic properties of core samples in stratigraphic test wells are presented in an attempt to apply to comprehensive geological interpretation. Stability parameter of magnetization of igneous basement cores in MITI “Kesennuma-Oki” and “Goto-nada” indicates that rock magnetic property is essential for reliable interpretation of geomagnetic anomaly in sedimentary basins. Sedimentary core samples from MITI “Kesennuma-Oki”, “Soma-Oki”, “Joban-Oki” are described to obtain information on core-orientation. Magnetic cleaning for them shows that drilling-induced secondary magnetization is common in deep borehole samples. After careful rock magnetic cleaning, a site-mean direction of primary remanent magnetization for the Cretaceous sample in MITI “Soma-Oki” has large westerly declination. Together with other paleomagnetic data, the present result suggests a differential tectonic movement and reorganization of sedimentary basins in northeast Japan since the Cretaceous. Thus rock magnetic study of borehole samples contributes to understand the origin of basement, tectonic history, and regional basin evolution.