Analysis of Binary Series to Evaluate Astronomical Forcing of a Middle Permian Chert Sequence in South China

Abstract:

We describe a Middle Permian radiolarian chert sequence in South China (Chaohu area), with sequence of chert and mudstone layers formulated into binary series.Two interpolation approaches were tested: linear interpolation resulting in a “triangle” series, and staircase interpolation resulting in a “boxcar” series. Spectral analysis of the triangle series reveals decimeter chert-mudstone cycles which represent theoretical Middle Permian 32 kyr obliquity cycling. Tuning these cycles to a 32-kyr periodicity reveals that other cm-scale cycles are in the precession index band and have a strong ~400 kyr amplitude modulation. Additional tuning tests further support a hypothesis of astronomical forcing of the chert sequence. Analysis of the boxcar series reveals additional “eccentricity” terms transmitted by the boxcar representation of the modulating precession-scale cycles. An astronomical time scale reconstructed from these results assumes a Roadian/Wordian boundary age of 268.8 Ma for the onset of the first chert layer at the base of the sequence and ends at 264.1 Ma, for a total duration of 4.7 Myrs. We propose that monsoon-controlled upwelling contributed to the development of the chert-mudstone cycles. A seasonal monsoon controlled by astronomical forcing influenced the intensity of upwelling, modulating radiolarian productivity and silica deposition.