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
- 收稿日期:
2026-01-26
- 网络出版日期:
2026-04-27
摘要: 晚奥陶世-早志留世是地球演化史上的关键转折期，以赫南特冰期和奥陶纪末生物大灭绝事件为核心标志，但该时期地质年代框架的精度仍存在较大争议，制约了对生物灭绝机制与气候演化过程的深入理解。本研究旨在通过旋回地层学与同位素测年的交叉融合，建立晚奥陶世-早志留世的高分辨率绝对天文年代标尺，为重大地质事件的精细时间约束提供科学依据。【方法】以四川长宁双河、重庆綦江安稳和湖北宜昌王家湾三个剖面为研究对象，对采集的高分辨率元素数据（Si、Fe、Ca、Al、Rb/Sr等），利用AnalySeries和Acycle软件进行旋回分析，识别米兰科维奇旋回信号；通过COCO/eCOCO和Timeopt方法估算沉积速率，建立浮动天文年代标尺；同时对剖面火山灰层进行CA-ID-TIMS锆石U-Pb测年，获取绝对年龄锚点，实现深度域到时间域的精确转换。【结果】① 在XRF元素序列中识别出稳定的对应于405 kyr和~100 kyr长短偏心率周期的沉积旋回，双河、安稳和王家湾剖面分别建立了长度为12.2 Myr、10.3 Myr和2.75 Myr的浮动天文年代标尺；② 结合火山灰层U-Pb年龄（双河剖面：438.47±0.17 Ma；安稳剖面：439.32±0.13 Ma），将奥陶纪-志留纪界线年龄标定为442.34~442.65 Ma，较GTS2020方案年轻约0.42~0.73 Myr；③ 王家湾剖面的赫南特阶持续时间约为411 kyr，奥陶纪末生物大灭绝两幕的持续时间分别为379 kyr和89.5 kyr；④ 古气候指标与海平面变化均显示出1.2 Myr和2.4 Myr的长周期波动。【结论】本研究建立的晚奥陶世-早志留世高精度天文年代标尺，显著提升了该时期地质年代框架的精度，揭示了奥陶纪末生物大灭绝事件的快速发生过程。天文周期对该时期气候-环境演化具有显著的驱动作用，为深入理解奥陶纪末生物大灭绝的触发机制提供了关键时间约束。
High-Precision Astronomical Time Scale for the Late Ordovician-Early Silurian and Its Temporal Constraints on the End-Ordovician Mass Extinction
- Received Date:
2026-01-26
- Available Online:
2026-04-27
Abstract: [Objective] The Late Ordovician to Early Silurian represents a critical transition in Earth's history, characterized by the Hirnantian glaciation and the end-Ordovician mass extinction event. However, significant uncertainties persist in the chronostratigraphic framework for this interval, limiting our understanding of the mechanisms driving 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 Changning, 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, Anwen, and Wangjiawan sections, respectively. ② Combined with U-Pb ages of volcanic ash beds (Shuanghe: 438.47±0.17 Ma, Anwen: 439.32±0.13 Ma), the Ordovician-Silurian boundary was recalibrated to 442.34-442.65 Ma, approximately 0.42-0.73 Myr younger than the GTS2020. ③ The duration of the Hirnantian Stage at the Wangjiawan Section was estimated at ~411 kyr, with the two pulses of the end-Ordovician mass extinction lasting 379 kyr and 89.5 kyr, respectively. ④ Paleoclimatic proxies and sea-level changes exhibited long-period 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 driving climate-environmental evolution during this interval, providing key temporal constraints for understanding the triggering mechanisms of the end-Ordovician mass extinction.
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