Results of geochemical analyses in the Urakawa area. Typical pyrograms of Rock-Eval pyrolysis (a) and histograms of vitrinite reflectance (b) for the Cretaceous sedimentary rocks in the Urakawa area (geologic map and columnar section are shown in parts (c) and (d) of the figure). Darkened bars in histograms represent data adopted for mean calculations. Sample numbers (CH-series) are identical with the paleomagnetic sampling sites of Tamaki et al. (2008).