摘要
白垩纪中期大洋缺氧事件2(OAE 2)是地史时期一次全球性重大古海洋和古气候事件,记录了地球温室期全球碳循环扰动和地球系统反馈过程的重要信息。由于全球不同剖面OAE 2年代学约束仍存在争议,制约了对这一全球性事件成因机制的认识。针对上述问题,本研究选取了全球不同纬度带的8个剖面,通过对碳同位素和硬等温剩余磁化率数据进行旋回地层分析,开展了OAE 2天文年代学研究。结果显示,研究剖面的OAE 2发生时间被约束在94.55~93.98 Ma,结束时间被约束在93.80~93.17 Ma,持续时间为430~910 ka,不同剖面的OAE 2起止时间和持续时间存在差异。火山活动为海洋环境提供了营养物质,暂时性的全球海洋连通性影响了火山喷发物质搬运,季风强弱影响了陆源物质风化速率和火山喷发物、陆源剥蚀物的搬运,故剖面地理位置及其与火山活动区域的距离、海洋连通性和季风活动共同影响OAE 2的起止时间和持续时间。OAE 2的发生阶段大致与短偏心率调制周期极大值时期(即约2.4 Ma超长偏心率周期)或从较大值向极大值过渡时期对应,且天文理论曲线La2010d中约2.4 Ma超长偏心率周期也为极大值时期或从较大值向极大值过渡时期。在此天文轨道配置下,气候季节对比性明显增加,增强的季风降水导致陆地向海洋输送的营养物质增加,海洋初级生产力提高,造成海水缺氧,随后大量有机质的分解进一步导致了O2消耗,这些因素的共同作用可能促进了大洋缺氧事件的形成。相反,OAE 2的结束阶段与超长偏心率周期较小值时期对应,此时气候以低季节性对比为特征,季风降水减弱,水柱混合良好,从而提高海洋中间和底部水域O2浓度,这些因素的共同作用可能导致大洋缺氧事件的结束。在OAE 2期间,天文轨道周期驱动的季风强度的变化,通过影响陆源物质的剥蚀以及陆源和火山喷发物质的搬运、海洋水体分层状况等,在OAE 2演化中扮演着重要角色。
The mid-Cretaceous Oceanic Anoxic Event 2(OAE 2)is a globally significant paleo-oceanic and paleoclimatic event in geohistory that recorded important information on global carbon cycle perturbations and Earth system feedback processes during the Earth's greenhouse period.The chronological constraints of OAE 2 in different profiles around the world are still controversial,which limits the understanding of the causal mechanism of this global event.To address the above issues,eight profiles were selected in this study,including Carthage,SH#1 core and Portlan#1 core located in the United States of America,about 34°~38°N latitude and 105°~112°W longitude,Wunstorf and Vocontian located in Western Europe,about 30°~53°N latitude and 10°~12°E longitude,and Tappu located in Japan(44°N,142°E),Gongzha is located on the South Indian plate margin(37°S,57°E),and Sawpit Gully is located in northeastern New Zealand(70°S,172°E).Astrochronology research on OAE 2 was carried through carbon isotope and magnetic susceptibility data from these profiles.The results show that the onset of OAE 2 in the studied profiles is constrained to 94.55~93.98 Ma,the end time is constrained to 93.81~93.17 Ma,with a duration of 430~910 ka.The onset and duration of OAE 2 vary heterogeneously among different profiles.Volcanic activity provides nutrients to the marine environment,ocean connectivity affects eruptive material transport,and monsoon strength affects the weathering rate of land-source material and the transport of eruptive and land-source denudation material.Therefore,the address and distance of the profile from the region of volcanic activity,ocean connectivity,and monsoon activity jointly affect the onset and duration of OAE 2.The initial phase of OAE 2 roughly corresponds to the maximum periods of short eccentricity modulation cycles(ca.2.4 Ma,the super-long eccentricity cycles)or the period of transition from larger to maximum,and the ca.2.4 Ma eccentricity cycles in the astronomical solution La2010d is also a period of maxima or a period of transition from larger to maximum.Under this astronomical orbital configuration,the seasonal contrast of climate increases significantly,and the enhanced monsoon precipitation leads to an increase in nutrient delivery from the land to the ocean and an increase in the primary productivity of the ocean,resulting in the hypoxia of seawater,the subsequent decomposition of large amounts of organic matter further contributed to O2 depletion,the combined effect of these factors may have contributed to the formation of the oceanic anoxic event.Conversely,the end phase of OAE 2 corresponds to the period of smaller values of the ultra-long eccentricity cycle,when the climate is characterized by low seasonal contrasts,weakened monsoon precipitation,and good mixing of the water column,which enhances the concentration of O2 in the middle and bottom waters,the combination of these factors may have facilitated the end of the Oceanic Anoxic Event.Changes in monsoon intensity driven by the astronomical orbital cycle during OAE 2 play an important role in OAE 2 evolution by influencing the denudation of terrigenous material as well as the transport of terrigenous and volcanically erupted material,and the stratification conditions of the oceanic water column.
作者
李雪霜
张坦
马超
LI Xueshuang;ZHANG Tan;MA Chao(State Key Laboratory of Oil&Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,Sichuan;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,Sichuan;Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications of Ministry of Natural Resources,Chengdu University of Technology,Chengdu 610059,Sichuan;College of Computer Science and Cyber Security,Chengdu University of Technology,Chengdu 610059,Sichuan)
出处
《第四纪研究》
CAS
CSCD
北大核心
2023年第6期1597-1613,共17页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:41888101、42172137和42302129)
四川省天然气成藏物质基础青年科技创新团队基金项目(批准号:2022JDTD0004)
国际地球科学计划(IGCP)739项目
深时数字地球国际大科学计划项目共同资助。
关键词
旋回地层学
地球轨道周期
天文调谐
火山活动
cyclostratigraphy
Earth orbital period
astronomical tuning
volcanic activity
