中国科学院地质与地球物理研究所孙继敏等在研究晚渐新世西藏中部南亚季风的构造和轨道作用力上取得新突破
研究人员展示了从27.32至23.24个百万年(Ma)前-晚渐新世期间，Nima盆地岁差尺度旋回的地层沉积剖面，基于环境磁性代理的周期性干湿波动的指示，研究表明南亚季风(SAM)至少在27.3Ma 之前就已经推进到青藏高原中部 (32°N)了。岩性和天文轨道周期的变化、替代测量的放大幅度以及约25.8Ma 的水文气候转变表明，在大约 25.8Ma 时南亚季风增强，青藏高原达到了增强隆升高原和南亚季风之间耦合的古海拔阈值。
轨道短偏心率步调的降水变率被认为主要是由轨道偏心率调节的低纬度夏季日射量，而不是冰川-间冰期南极冰盖的波动驱动的。来自青藏高原内部的季风数据提供了关键证据，将25.8Ma 热带南亚季风的大幅度增强与青藏高原隆升而非全球气候变化联系起来，并表明南亚季风向北扩展到北亚热带是由晚渐新世多时间尺度的构造和天文作用力共同控制的。
据介绍，人们普遍认为亚洲季风的现代模式形成于渐新世或中新世过渡时期，通常将其归因于喜马拉雅-青藏高原(H-TP)隆起。然而，由于缺乏来自青藏高原内部的高分辨率地质记录，人们对古亚洲季风在青藏高原上的时间、其对天文作用力和青藏高原隆升的响应仍然知之甚少。
附：英文原文
Title: Tectonic and orbital forcing of the South Asian monsoon in central Tibet during the late Oligocene
Author: Jin, Chun-Sheng, Xu, Deke, Li, Mingsong, Hu, Pengxiang, Jiang, Zhaoxia, Liu, Jianxing, Miao, Yunfa, Wu, Fuli, Liang, Wentian, Zhang, Qiang, Su, Bai, Liu, Qingsong, Zhang, Ran, Sun, Jimin
Issue&Volume: 2023-4-3
Abstract: The modern pattern of the Asian monsoon is thought to have formed around the Oligocene/Miocene transition and is generally attributed to Himalaya–Tibetan Plateau (H–TP) uplift. However, the timing of the ancient Asian monsoon over the TP and its response to astronomical forcing and TP uplift remains poorly known because of the paucity of well-dated high-resolution geological records from the TP interior. Here, we present a precession-scale cyclostratigraphic sedimentary section of 27.32 to 23.24 million years ago (Ma) during the late Oligocene epoch from the Nima Basin to show that the South Asian monsoon (SAM) had already advanced to the central TP (32°N) at least by 27.3 Ma, which is indicated by cyclic arid–humid fluctuations based on environmental magnetism proxies. A shift of lithology and astronomically orbital periods and amplified amplitude of proxy measurements as well as a hydroclimate transition around 25.8 Ma suggest that the SAM intensified at ~25.8 Ma and that the TP reached a paleoelevation threshold for enhancing the coupling between the uplifted plateau and the SAM. Orbital short eccentricity-paced precipitation variability is argued to be mainly driven by orbital eccentricity-modulated low-latitude summer insolation rather than glacial-interglacial Antarctic ice sheet fluctuations. The monsoon data from the TP interior provide key evidence to link the greatly enhanced tropical SAM at 25.8 Ma with TP uplift rather than global climate change and suggest that SAM’s northward expansion to the boreal subtropics was dominated by a combination of tectonic and astronomical forcing at multiple timescales in the late Oligocene epoch.
DOI: 10.1073/pnas.2214558120
Source: https://www.pnas.org/doi/10.1073/pnas.2214558120