【摘要】 尖扎盆地地处青藏高原的东北缘,位于青藏高原寒旱区、西北内陆干旱区和东部季风区的交汇地带,同时又处在东亚季风和西风环流的汇聚地带,属于气候极度敏感区域,盆地内部沉积了巨厚且连续的新生代沉积物。青海省尖扎县城西面的加让剖面主要以风成红粘土沉积为主体,但发生过多次沉积微相变化,夹杂有短暂的湖相及河流相沉积。红粘土中主要的碳酸盐矿物由方解石和白云石组成,通过对红粘土中方解石和白云石含量的实验测定,将方解石含量变化曲线和磁化率变化曲线进行对比分析,可将厚度为361 m的加让剖面经历了11.8-5.8 Ma沉积序列划分为以下4个气候阶段:11.8～9.8Ma气候干冷期;9.80～8.57 Ma气候温暖湿润期;8.57～6.15 Ma气候温暖湿润期及6.15～5.80 Ma气候干冷期。在约8.57 Ma沉积物方解石含量和磁化率急剧变化,由于青藏高原的隆升,夏季风明显加强,约7.2 Ma之后,夏季风的变化受高原隆升、全球变冷和北极冰盖扩张综合影响。白云石含量在10～8 Ma变化显著增加,可能是由于这一时期青藏高原快速隆升,盆地周缘山脉风化剥蚀加快,近源物质增多所致。更多还原

【Abstract】 Jianzha Basin is located in the northeastern Tibetan Plateau and situated in a climatically sensitive area-at the transition zone between the monsoon region to the east and the arid region to the west; its location, together with its thick, continuous sequence of Cenozoic sediments, makes it well be suited to monitoring changes in Late Cenozoic climate. Jiarang section is located in the left bank of the Jiarang river, near the Jiarang village of Jianzha County,Qinghai Province, and its geographical coordinates are 35°57′43. 1″N, 101°58′24.1″E, 2200 m a.s.l. Based on the field observation and the study of sedimentary facies, the 361-m-thick sediments sequences of the Jiarang section mainly consist of clastic material of fluviolacustrine and eolian origin, with loess-like silt or clay comprising about two-thirds of the entire section. The samples of this experiment was sampled at 20 cm intervals, and a total of1781 samples were collected. The magnetostratigraphic results show that the sediments have recorded a continuous geomagnetic polarity sequence from C5 r.3 r to C3 r, spanning the interval from 11. 8～5. 8 Ma in the Late Miocene.By the experiments analysis of the carbonate minerals in sedimentary section, the content of calcite and the low frequency magnetic susceptibility change were analyzed to reveal the paleoclimatic information from the deposits during 11. 8～5. 8 Ma, which the paleoclimate change can be divided into four stages. Stage Ⅰ : 11. 8 ～ 9. 8 Ma,dry and cold climate; Stage Ⅱ :9. 80～8. 57 Ma,warm and humid climate; Stage Ⅲ:8. 57～6. 15 Ma,warm and humid climate and Stage Ⅳ : 6. 15～5. 80 Ma, dry and cold climate. The content of calcite and the magnetic susceptibility change dramatically before ca. 8. 57 Ma reflect intensified precipitation which resulted from the growth of the NETP. From ca. 8. 57 Ma to ca. 7. 2 Ma, the East Asian summer monsoon was impacted by global cooling and ice build-up in the Northern Hemisphere in addition to the uplift of the Tibetan Plateau in the Late Miocene.From ca.10 Ma to ca. 8 Ma, the content of dolomite increases significantly, which probably caused by the rapid uplifting and deforming of the Tibetan Plateau in this stage.更多还原