青藏高原东北缘尖扎盆地晚中新世地层绝对天文年代标尺的建立  

Establishment of Absolute Astronomical Time Scale of Late Miocene Strata in Jianzha Basin, the Northeastern Margin of Tibetan Plateau, China

作　　者：杨彦峰 符超峰[1,2] 徐新文[3] 王凤 孟媛媛 强小科[2] YANG Yan-feng;FU Chao-feng;XU Xin-wen;WANG Feng;MENG Yuan-yuan;QIANG Xiao-ke(School of Earth Science and Resources,Chang an University,Xi'an 710054,Shaanxi,China;State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710061,Shaanxi,China;College of Urban and Environmental Sciences,Northwest University,Xi'an 710127,Shaanxi,China;Department of Geology,Northwest University,Xi'an 710069,Shaanxi,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,陕西西安710061 [3]西北大学城市与环境学院,陕西西安710127 [4]西北大学地质学系,陕西西安710069

出　　处：《地球科学与环境学报》2021年第4期710-723,共14页Journal of Earth Sciences and Environment

基　　金：第二次青藏高原综合科学考察研究专题(2019QZKK0704);国家自然科学基金项目(41772167,41140028);黄土与第四纪地质国家重点实验室基金项目(SKLLQG1905)。

摘　　要：位于青藏高原东北缘的尖扎盆地沉积了巨厚的新生代风成沉积物,夹杂有河湖相沉积层段,已进行了高分辨率磁性地层学和环境磁学研究,是旋回地层学研究的良好剖面。以尖扎盆地加让剖面3~361 m晚中新世沉积地层为研究对象,通过系统的旋回地层学研究,旨在建立加让剖面的绝对天文年代标尺,提取尖扎盆地中蕴含影响古气候演化的地球轨道参数的主导周期,为进一步进行海陆对比和深入研究古气候环境演化提供基础数据。加让剖面古气候替代性指标频率磁化率(χ fd)数据序列深度域频谱分析表明:3~361 m层段存在稳定的代表长偏心率周期的26 m沉积旋回,代表其他地球轨道参数周期的沉积旋回也有所体现,但并不稳定。基于识别出的沉积旋回,利用稳定的405 ka长偏心率周期对3~361 m深度域频率磁化率数据序列进行天文调谐,结合加让剖面磁性地层年代框架,建立了11.758~5.890 Ma的绝对天文年代标尺。经过天文调谐的频率磁化率数据序列时间域与古地磁年代结果吻合较好,表明建立的天文年代标尺是可靠的。加让剖面频率磁化率与深海氧同位素记录频谱分析显示,在约7.2 Ma存在明显的周期转变。这一记录表明,东亚夏季风在7.2 Ma之前由41 ka的斜率周期主导,在7.2 Ma之后受控于100 ka的短偏心率周期。The Jianzha Basin is located in the northeastern margin of Tibetan Plateau, and contains a thick sequence of Cenozoic sediments, which is composed of the sequence of eolian red clay with a bit part fluviolacustrine deposits. The Jiarang section in Jianzha Basin is an ideal section for cyclostratigraphy, because of its high resolution on magnetostratigraphy and environmental magnetism. Based on the systematic cyclostratigraphy of 3-361 m sedimentary strata of Late Miocene in Jiarang section, the absolute astronomical time scale of Jiarang section was established, and the dominant period of earth orbital parameters affecting the paleoclimate evolution in Jianzha Basin was extracted, in order to provide basic data for the further comparison between land and sea, and the paleoclimatic and environmental evolution. The result of spectrum analyses of frequency-dependent magnetic susceptibility(χ fd) in depth domain shows that there is a stable 26 m sedimentary cycle representing long eccentricity period in the 3-361 m interval, and the sedimentary cycles representing other astronomical orbital periods are also present, but not stable. Based on the identified sedimentary cycles, the long eccentricity period was used to tune frequency-dependent magnetic susceptibility data series in depth domain of 3-361 m. Combined with the magnetostratigraphic chronological framework of Jiarang section, the absolute astronomical time scale of 11.758-5.890 Ma was established. The astronomical tuning for frequency-dependent magnetic susceptibility data series in time domain is consistent with the paleomagnetic age, which indicates that the astronomical time scale is reliable. The spectrum analyses for frequency-dependent magnetic susceptibility and marine oxygen isotope records show that there are obvious periodic shifts in about 7.2 Ma. This record reveals that the East Asian summer monsoon(EASM) is dominated by 41 ka obliquity period before 7.2 Ma, and controlled by 100 ka short eccentricity period after 7.2 Ma.

关 键 词：旋回地层学 天文年代标尺 天文调谐 频谱分析 地球轨道参数 沉积旋回 青藏高原 

分 类 号：P539[天文地球—古生物学与地层学] P534.621[天文地球—地质学]