晚奥陶世—早志留世高精度天文年代标尺及其对奥陶纪末生物大灭绝的时间约束OA

[Objective]The Late Ordovician to Early Silurian represents a critical transition in Earth's history,char-acterized by the Hirnantian glaciation and the end-Ordovician mass extinction event.However,significant uncertain-ties persist in the chronostratigraphic framework for this interval,limiting our understanding of the mechanisms driv-ing biotic extinction and climatic evolution.This study aims to establish a high-resolution absolute astronomical time scale for the Late Ordovician-Early Silurian through the integration of cyclostratigraphy and isotopic geochronology,providing robust temporal constraints for major geological events.[Methods]Three sections(Shuanghe in Chang-ning,Sichuan;Anwen in Qijiang,Chongqing;and Wangjiawan in Yichang,Hubei)were selected as study sites.High-resolution elemental data(Si,Fe,Ca,Al,Rb/Sr,etc.)were analyzed using AnalySeries and Acycle software to identify Milankovitch cycle signals.Sedimentation rates were estimated using the COCO/eCOCO and TimeOpt methods to construct floating astronomical time scales.CA-ID-TIMS zircon U-Pb dating was conducted on volcanic ash beds to obtain absolute age anchors,enabling precise conversion from the depth domain to the time domain.[Results](1)Stable sedimentary cycles corresponding to 405-kyr and～100-kyr long and short eccentricity cycles were identified in the XRF elemental series.Floating astronomical time scales of 12.2 Myr,10.3 Myr,and 2.75 Myr were established for the Shuanghe section,Anwen section,and Wangjiawan section,respectively.(2)Given the most complete geological record preserved in the Shuanghe section,the ages of the Ordovician/Silurian(O/S)bound-ary and the base of the Hirnantian stage,calibrated to 442.34±0.22 Ma and 443.78±0.22 Ma respectively through cyclostratigraphic analysis combined with U-Pb dating of volcanic ash beds(Shuanghe section:438.47±0.17 Ma),can serve as a candidate for future international chronostratigraphic standards.(3)The duration of the Hirnantian stage is 1.44 Myr at the Shuanghe section,but only～0.41 Myr at the Wangjiawan section,suggesting that a sedimen-tary hiatus may exist in the Wangjiawan section.(4)Paleoclimatic proxies and sea-level changes exhibited long-peri-od fluctuations of 1.2 Myr and 2.4 Myr.[Conclusions]The high-precision astronomical time scale established in this study significantly improves the accuracy of the chronostratigraphic framework for the Late Ordovician-Early Silurian,revealing the rapid onset of the end-Ordovician mass extinction.Astronomical cycles played a significant role in driv-ing climate-environmental evolution during this interval,providing key temporal constraints for understanding the triggering mechanisms of the end-Ordovician mass extinction.