Astronomical cycles of Middle Permian Maokou Formation in South China and their implications for sequence stratigraphy and paleoclimate

Abstract

High-resolution (930 samples) magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) analyses were conducted on the ~49m thick Middle Permian Maokou Formation at Dukou, South China. Spectral analysis of covariant MS and ARM series reveal Milankovitch cycles with eccentricity, obliquity, and precession. A 5.7myr floating 405kyr eccentricity cycle-calibrated astronomical time scale was constructed and used as a geochronometer for estimating the durations of the conodont zones. The results indicate that the durations of the Jinogondolella postserrata, J. altudaensis, J. prexuanhanensis, and J. xuanhanensis conodont zones were 490kyr, 560kyr, 820kyr, and 750kyr, respectively. The 405kyr-calibrated MS and ARM series also show prominent ~1myr cyclicity, which may correspond to the secular frequencies of Earth and Mars, s4–s3, in the Middle Permian. The early Capitanian time interval was synchronous with the Kamura cooling event, and the accentuated obliquity cycling may signal ice-sheet expansion. The modulations of the obliquity have a close relationship with third-order eustatic sequences of the Wordian and Capitanian stages, suggesting a glacioeustatic origin during the Middle Permian.