白垩纪大洋缺氧事件2(OAE 2)期间的百年到千年周期

Centennial to millennial cycles during the Cretaceous Oceanic Anoxic EventⅡ(OAE 2)

太阳周期是地球气候系统的重要调节因素之一。深时地质时期由于时间跨度长以及高分辨率数据的缺乏,导致太阳周期的研究还存在欠缺。本研究以北美西部内陆海白垩纪Iona-1钻孔岩芯Eagle Ford组(42~153.41 m)为对象,以泥灰岩中明暗纹层的高分辨率(230μm)灰度数据为载体,开展了详细的旋回地层学分析。结果表明,白垩纪大洋缺氧事件2(OAE 2)期间存在781~1150 a、188~242 a、79~126 a、38~50 a的周期信号。通过与过去9400年以来重建的太阳总辐照度(TSI)对比,这些周期被解释为太阳周期中的Eddy周期(约1000 a)、de Vries-Suess周期(200~250 a)、Gleissberg周期(88~120 a),其中38~50 a的周期虽然在全新世太阳活动记录中未发现,但地质时期存在类似的周期,认为可能是Bruckner周期(30~50 a)。Bruckner周期仅在OAE 2期间存在,这可能是由于不同的沉积环境导致不同时间段对该周期的差异性响应。结合深时中已发现的一些太阳周期记录,本研究认为太阳活动在过去几十亿年中有效地影响了气候变化,从而影响沉积过程。太阳活动对陆地气候和大气-海洋过程产生影响,进而导致了海洋有机物含量、氧化还原条件和生物群落的差异。这些因素共同促成了北美西部内陆海白垩纪沉积物中毫米级明暗纹层的形成。上述研究成果可为深入了解OAE 2气候效应以及现今温室效应下的极端气候变化提供一定借鉴。

The solar cycle is one of the important regulating factors of the Earth's climate system.However,research on deep-time solar cycles remains limited,owing to a lack of suitable high-resolution,deep-time archives.Here we present well-preserved,millimeter-scale laminated marlstone from the Shell Iona-1 research borehole(29.23°N,100.74°W),which was deposited in the Western Interior Seaway(North America)during the mid-Cretaceous(Eagle Ford Formation(42~153.41 m),ca.94 Ma:Cenomanian-Turonian).The grayscale data obtained from scanning the light-dark laminae can reflect the sedimentological,geochemical,and micropaleontological characteristics of the sediment.A comprehensive cyclostratigraphic analysis conducted using high-resolution(230μm;Δt=ca.23 a)grayscale data from the main studied interval M1(124.41~124.56 m;95.553~95.562 Ma),M2(106.97~107.14 m;94.542~94.552 Ma),M3(99.86~100.14 m;94.305~94.314 Ma),M4(95.39~95.60 m;94.135~94.144 Ma)and M5(81.80~81.93 m;93.284~93.293 Ma)of the Eagle Ford Group reveals variations with 781~1150 a,188~242 a,79~126 a and 38~50 a periodicities during the Cretaceous'greenhouse'period.We observed a strong correlation between these cycles and the reconstructed Total Solar Irradiance(TSI)time series over the last 9400 a,these cycles are attributed to the Eddy cycle(ca.1000 a),de Vries-Suess cycle(200~250 a),Gleissberg cycle(88~120 a),and Bruckner cycle(30~50 a).Although the 38~50 a cycle isn't observed in the Holocene solar activity record,similar cycles exist in geological periods.The Bruckner cycle is only observed during the OAE 2 period shows that different sedimentary environments lead to distinct responses to this cycle in different time intervals.Combined with several deep-time solar cycle records,the results indicate that solar activity has significantly influenced climate change over billions of years,altering sedimentation processes.Solar activity affects the terrestrial climate,atmosphere-ocean processes,which then vary marine organic content,redox conditions,and biomes.These factors collectively contribute to the formation of millimeter-scale light-dark laminae in the Cretaceous sediments of the Western Interior Seaway(North America).These research findings can provide valuable insights into understanding the climate effects of OAE 2 and extreme climate change in today's greenhouse effect.