宁夏固原寺口子剖面色度记录的29 Ma以来气候演化

Climate evolution since 29 Ma recorded by sediment color on Sikouzi Section, Guyuan, Ningxia

宁夏自治区南部固原寺口子剖面位于青藏高原东北缘,记录了青藏高原隆升、扩展与区域气候变化之间的相互作用过程,重建该地区气候演化历史对于揭示高原隆升与全球气候变冷对亚洲大陆腹地干旱化的影响具有重要意义。通过对寺口子剖面晚渐新世—第四纪地层沉积物色度(a~*、b~*、L~*)的系统测量,建立了29～0.5 Ma颜色指标变化序列,结合研究区内已发表的磁化率、孢粉和总无机碳数据,揭示出该区域气候经历了四个阶段:29～24.8 Ma为最湿热阶段、23.8～18 Ma为较湿热阶段、18～5 Ma为逐渐变冷阶段、5～0.5 Ma为快速变冷阶段。剖面记录了25～24 Ma、18 Ma、5 Ma两次显著的气候变冷事件和3 Ma气候变暖事件。结合青藏高原东北缘新生代盆地气候代用指标,发现这些气候变冷事件和3 Ma气候变暖事件具有区域性。通过对比深海氧同位素记录、北太平洋粉尘通量记录、青藏高原构造隆升事件和研究区气候演化特征,我们认为青藏高原隆升和全球气候变化共同控制了区域气候演化,但在不同时期所起作用有所差异。

Objectives: The Sikouzi Section,Guyuan,Ningxia,locates in the convergence zone of East Asian monsoon region and Central Asian drought region. The climate evolution history of the Sikouzi Section during the Cenozoic time is crucial for understanding the continental climate respondence under the background of global cooling and revealing whether global cooling or the uplift of Tibetan plateau is the first-order driver for aridification of Central Asia.Methods: Sediment color is a sensitive and useful index to record paleoclimate change. We adopted this index for the Sikouzi Section.Results: By measuring the fluvial-lacustrine sediment color proxies( a*,L*,b*) of the Sikouzi Section,we establish high-resolution color sequence from late Oligocene to Quaternary( 29 ~ 0.5 Ma). Integrating published susceptibility( SUS),pollen and total inorganic carbon( TIC) data,we reconstruct regional climatic evolution history since 29 Ma. The multiple proxies unravel four climate events: 25 ~ 24 Ma,18 Ma,5 Ma cooling events and 3 Ma warming events.Conclusion: Comparing climate proxies of other Cenozoic basin in northeastern Tibetan Plateau,these climate events are regional events,but climatic changes has regional discordance during 12 ~ 5 Ma. By sorting out the records of the deep sea oxygen isotopes,the dust fluxes in the northern Pacific Ocean,the tectonics of Tibetan Plateau and the climate evolution of study area,we speculate that regional climate evolution is controlled by the tectonics of Tibetan Plateau and global climate change. However,tectonics and climate factors play different roles in certain periods.