摘要
High-resolution (930 samples)magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) analyseswere conducted on the ~49 m thick Middle Permian Maokou Formation at Dukou,South China. Spectral analysis of covariant MS and ARM series revealMilankovitch cycles with eccentricity, obliquity, and precession. A5.7 myrfloating 405 kyr eccentricity cycle-calibrated astronomical time scale wasconstructed and used as a geochronometer for estimating the durations of theconodont zones. The results indicate that the durations of the Jinogondolellapostserrata, J. altudaensis, J. prexuanhanensis, and J. xuanhanensis conodontzones were 490 kyr, 560 kyr, 820 kyr, and 750 kyr, respectively. The 405kyr-calibrated MS and ARM series also show prominent ~1 myr cyclicity, whichmay correspond to the secular frequencies of Earth and Mars, s4–s3, in theMiddle Permian. The early Capitanian time interval was synchronous with theKamura cooling event, and the accentuated obliquity cycling may signalice-sheet expansion. The modulations of the obliquity have a close relationship.
with third-order eustatic sequences of the Wordianand Capitanian stages, suggesting a glacioeustatic origin during the MiddlePermian.
关键词:Milankovitchcycles; Third-order eustatic sequences; Long-period astronomical cycles;Cooling event; South China