中三叠世早中期华南古海洋磷富集演化及其对天文驱动力的响应

海洋的初级生产力是全球磷循环的重要环节, 响应并且影响着全球气候变化。通过探讨地质历史时期的古海洋生产力的变化及其驱动机制, 为预测未来全球气候变化提供重要启示。中生代古海洋生产力变化及其对轨道尺度的气候变化的响应和驱动机制仍不清楚, 有待于进一步研究。本研究以贵州关岭永宁镇剖面中三叠世关岭组地层(约2.467亿至2.425亿年前)为对象, 通过旋回地层手段分析沉积物中磷(P)含量的变化及其周期, 揭示古海洋生产力在轨道尺度上的驱动机制。研究发现, 中三叠统沉积物中P/Al比值的变化对长、短偏心率天文周期的响应较为稳定和显著, 并与反映大陆风化和夏季风强弱的Fe/Al比值在10万年以上尺度上, 特别是在40.5万年长偏心率周期上呈现出显著的反相位关系, 进一步印证P是对冬季风的响应而Fe是对夏季风的响应这一假说。该时期古海洋生产力的大幅提升和海平面上升及生物辐射相一致, 但滞后于古气候的变化, 体现了古海洋生产力控制因素的复杂性。

Evolution of phosphorus enrichment in the early to middle Middle Triassic Epoch in Southern China's ancient oceans and its response to astronomical forcing

The primary productivity of the ocean is an important component of the global phosphorus cycles, and it responds to and influences global climate change. By exploring the variations in ancient ocean productivity and its driving mechanisms during geological history, valuable insights can be gained for predicting future global climate change. The changes in Mesozoic ocean productivity and its response to and driving mechanisms for orbital-scale climate changes are still unclear and require further investigation. In this study, the Middle Triassic(spanning ca. 246.7~242.5 Ma)Guanling Formation with 520.8 m thickness in Yongning section(from 25°53'55.15″N, 105°28'18.33″E to 25°53'28.18″N, 105°27'52.78″E), Guanling County, Guizhou Province, is taken as the research target. A cyclostratigraphic study is conducted to analyze the variations and periods in phosphorus(P)content in sediments, the driving mechanisms of ancient ocean productivity at orbital scales are revealed. The study finds that the variations in the P/ Al ratio in the Middle Triassic sediments show stable and significant responses to long and short eccentricity astronomical cycles. Moreover, they exhibit a significant out-of-phase relationship with the Fe/ Al ratio, which reflects the intensity of continental weathering, on a timescale greater than one hundred thousand years, especially at the 405 ka eccentricity cycle. This further proving the hypothesis that P is a response to winter monsoon whereas Fe is a response to summer monsoon. The enhancement of ancient ocean productivity during this period is consistent with the biotic radiation, but it lags the changes in paleoclimate to some extent, highlighting the complexity of controlling factors for ancient ocean productivity.