Estimation of the depositional time by comparison of foreset lamina cross-stratification angles and ocean current fluctuations: The Pleistocene Ichijiku Formation, Kazusa Group

The formation time of cross-beds was estimated by comparing fluctuations of foreset angle of cross-stratification of paleo-Kuroshio current deposits within the Pleistocene Ichijiku Formation Japan with variations in flow velocity in the present-day Kuroshio current.Foreset lamina angles were measured from a continuous 14 m long bed, and angles of cross-stratification were determined using Fourier analysis. The periodicities of Kuroshio current velocity fluctuations were also subjected to the same Fourier analysis. Comparison between the periodicities of foreset lamina angle and Kuroshio velocity revealed that the two are related with interval ratios of the peaks in periodicity of 1:1.8:3.2:4.2 and 1:1.9:3.2:4.4, respectively. These two ratios are almost identical. It is calculated that 4.0, 7.3, 12.8 and 17.0 foreset lamina were formed in 12.4, 24.0, 39.4, 55.9 h.