青藏高原东南缘的云南区域是研究晚新生代以来气候和环境演化的重要区域之一。虽然针对云南区域已经开展了大量古气候和古环境演化的研究,但是晚中新世到上新世云南区域湿度变化的记录仅为碳同位素和孢粉记录,且分辨率较低。因此,该区域缺乏晚中新世到上新世连续的高分辨率古湿度变化记录。本研究主要基于云南省东北部昭通盆地内晚中新世到上新世的沉积物岩心,通过对沉积物粒度的测试分析,综合沉积序列、岩性特征和沉积构造,表明:昭通盆地在8.8~6.2 Ma以沼泽亚相沉积环境为主;在6.2~2.8 Ma以浅湖亚相沉积环境为主;在2.8~2.6 Ma以湖滨亚相沉积环境为主。昭通盆地沉积物粒度参数记录的晚中新世到上新世云南区域呈现干旱化的趋势。结合前期该钻孔黏土矿物和化学风化的相关成果,认为晚中新世到上新世南亚季风呈现逐渐减弱的趋势,并主要受控于全球变冷和全球CO₂浓度降低的影响。

Situated at the southeast margin of the Tibetan Plateau, the Yunnan region is pivotal for investigating Late Cenozoic climatic changes. While considerable research has focused on the paleoclimate and paleoenvironmental evolution of Yunnan, the understanding of climate change from the Late Miocene to Pliocene primarily relies on carbon isotope and pollen records. Consequently, there is a dearth of high-resolution, continuous paleoclimatic records documenting humidity changes during this period. This study utilizes sediment cores from the Late Miocene to Pliocene in the Zhaotong Basin, northeastern Yunnan Province. Through sediment grain size analysis, the sedimentary sequence, lithological characteristics, and sedimentary structures indicate that the Zhaotong Basin was predominantly characterized by swamp-subfacies sedimentary environments during 8.8-6.2 Ma, transitioning to shallow lake subfacies during 6.2-2.8 Ma, and lakeside subfacies during 2.8-2.6 Ma. Grain size parameters of sediments in the Zhaotong Basin exhibit a drying trend of the South Asian monsoon during the Late Miocene to Pliocene. Combined with clay mineral and chemical weathering results from borehole data in the early period, it is inferred that the South Asian monsoon gradually weakened from the Late Miocene to Pliocene, primarily influenced by global cooling and decreasing global CO₂ concentrations.