Fig. 6

Cyclostratigraphy and floating astronomical time scale (ATS) of the Waidani section. a Silica rank and frequency–amplitude modulations of the Upper Permian (Changhsingian) bedded chert sequence. The average sedimentation rate for the Changhsingian bedded chert is ~ 0.3 cm kyr⁻¹, so the extracted 6 cm cycle was converted to a long precession cycle (~ 20 kyr) for orbital tuning (Yao et al. 2015). b Variations in sedimentation rate for each bed, calculated from the Changhsingian ATS and frequency–amplitude modulations of orbital-tuned silica rank. Red, orange, and blue lines in the REDFIT spectra delineate 99%, 95%, and 90% confidence levels (CL) against red-noise background from a first-order autoregressive process, respectively (Schulz and Mudelsee 2002). P and SP at the spectral peaks represent precession and semi-precession (Berger et al. 2006; Soda et al. 2015), respectively. Black contours and shaded regions in the wavelet spectra indicate 95% CL against the red noise and cone of influence due to zero padding, respectively (Torrence and Compo 1998)