**Author details**

**5. Summary**

wabata Formation

Rock-magnetic investigation of sedimentary rocks provides insights into the basin's formation and sedimentation processes on an active margin. Cretaceous (Yezo Supergroup) ~ Eocene (Ishikari Group) strata and middle Miocene (Kawabata Formation) turbidites in central Hokkaido represent forearc and foreland settings, respectively. Progressive demagnetization successfully isolated characteristic remanent magnetization (ChRM) of the Kawabata Forma‐ tion. Mean declination of the formation's ChRM exhibited significant westerly deflection, suggesting counterclockwise rotation of the study area since the middle Miocene. This differs from previous reports that indicated clockwise rotation. We attribute the difference to complicated deformation around the terminations of faults that form the N-S elongate Kawabata sedimentary basin. Anisotropy of magnetic susceptibility (AMS) principal axes were clearly determined for both the Cretaceous/Paleogene samples and Neogene samples, and regarded as a proxy of sediment influx directions. Paleocurrent directions inferred from the Eocene AMS data tend to align in N-S azimuth (Figure 14), and accord with the results of sedimentological paleoenvironment reconstruction, which suggest a northward downstream trend in fluvial to tidal estuarine systems [4]. As for the Cretaceous, further acquisition of AMS data is necessary to assess the effect of intensive syn-depositional deformation of the forearc [20]. After correcting for the tectonic rotation, most of the paleocurrent markers in the Kawa‐

**Figure 17.** Magnitudes of magnetic fabrics in natural samples and re-deposited non-magnetic fine particles of the Ka‐

250 Mechanism of Sedimentary Basin Formation - Multidisciplinary Approach on Active Plate Margins

Yasuto Itoh1\*, Machiko Tamaki2 and Osamu Takano3

