title: Time-calibrated Milankovitch cycles for the late Permian.
abstract: An important innovation in the geosciences is the astronomical time scale. The astronomical time scale is based on the Milankovitch-forced stratigraphy that has been calibrated to astronomical models of paleoclimate forcing; it is defined for much of Cenozoic-Mesozoic. For the Palaeozoic era, however, astronomical forcing has not been widely explored because of lack of high-precision geochronology or astronomical modelling. Here we report Milankovitch cycles from late Permian (Lopingian) strata at Meishan and Shangsi, South China, time calibrated by recent high-precision U-Pb dating. The evidence extends empirical knowledge of Earth's astronomical parameters before 250 million years ago. Observed obliquity and precession terms support a 22-h length-of-day. The reconstructed astronomical time scale indicates a 7.793-million year duration for the Lopingian epoch, when strong 405-kyr cycles constrain astronomical modelling. This is the first significant advance in defining the Palaeozoic astronomical time scale, anchored to absolute time, bridging the Palaeozoic-Mesozoic transition.
authors.affiliation: 1] State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China [2] School of Ocean Sciences, China University of Geosciences, Beijing 100083, China.
authors.forename: Huaichun
authors.initials: H
authors.lastname: Wu
authors.forename: Shihong
authors.initials: S
authors.lastname: Zhang
authors.forename: Linda A
authors.initials: LA
authors.lastname: Hinnov
authors.forename: Ganqing
authors.initials: G
authors.lastname: Jiang
authors.forename: Qinglai
authors.initials: Q
authors.lastname: Feng
authors.forename: Haiyan
authors.initials: H
authors.lastname: Li
authors.forename: Tianshui
authors.initials: T
authors.lastname: Yang
mesh_terms: D002138:Calibration; D002681:China; D019015:Geologic Sediments; D055593:Geological Phenomena; D060328:Magnetic Phenomena; D013997:Time Factors
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