青藏高原东北缘宁南盆地晚古近纪气候变化及其驱动机制

宁南盆地咸化湖相清水营组沉积记录,是研究青藏高原东北缘地区晚古近纪气候变化及其驱动机制的绝佳选择。以宁南盆地古近系清水营组为研究对象,通过野外地质调查、样品采集、石膏主量元素和锶同位素的测试,分析沉积地层记录的化学风化和古气候的变化;并通过与全球气候变化和青藏高原隆升过程的对比分析,研究青藏高原东北缘宁南盆地气候变化的驱动机制。结果表明:宁南盆地清水营组石膏中Al₂O₃/SiO₂、Al₂O₃/Ti₂O、K₂O/Na₂O和87Sr/86Sr等指标可以很好地反映晚古近纪气候变化,在38~36 Ma、34.5~33 Ma、32~31 Ma、30~27 Ma、26~23 Ma这5个时期,化学风化减弱,气候干旱化;在36~34.5 Ma、33~32 Ma、31~30 Ma、27~26 Ma这4个时期,化学风化增强,气候湿润化。晚古近纪38~26 Ma,青藏高原东北缘宁南盆地古气候变化主要受到全球气候变化的驱动;但在26~23 Ma之间,宁南盆地古气候变化受到了青藏高原隆升的重要影响。

Late Paleogene Climate Change and Its Driving Mechanism in the Ningnan Basin,Northeastern Tibetan Plateau

The sedimentary record of the saline lacustrine Qingshuiying Formation is the perfect object for the study of the Late Paleogene climate change and its driving mechanism in the Ningnan Basin, northeastern Tibetan Plateau and is taken as the research target in this study. Through field geological investigation, sample collection, and the tests of the major elements and strontium isotopes in gypsum, the chemical weathering and paleoclimate changes recorded in sedimentary strata are analyzed. Based on the comparison with the global climate change and the uplifting process of the Tibetan Plateau, the driven mechanism of the Late Paleogene climate change in the Ningnan Basin, northeastern Tibetan Plateau is studied. The results show that the indices of Al₂O₃/SiO₂, Al₂O₃/Ti₂O, K₂O/Na₂O, and 87Sr/86Sr well reflect the Late Paleogene climate change. During the 5 periods of 38-36 Ma, 34.5-33 Ma, 32-31 Ma, 30-27 Ma, and 26-23 Ma, the chemical weathering decreased, and the climate was arid, while during the 4 periods of 36-34.5 Ma, 33-32 Ma, 31-30 Ma, and 27-26 Ma, the chemical weathering increased, and the climate was humid. During the Late Paleogene 38-26 Ma, the climate change in the study area was mainly driven by the global climate change. While during 26-23 Ma, the climate change in the basin was affected by the Tibetan Plateau uplift.