【作者】 周勇；

【导师】 李祥辉；

【作者基本信息】 成都理工大学 ， 地质学， 2011， 硕士

【摘要】 白垩纪是地质历史中的特殊时期,是“温室气候”的典型代表。对其气候的研究有助于人类预测未来气候变化。中国大陆广泛分布有陆相白垩系地层,这为进行相关时期的气候研究提供了物质基础。西北地区的酒泉盆地和六盘山盆地的白垩系以河湖相为特征,生物和年代地层工作基础较好,剖面出露良好,有利于古气候分析。在古气候研究中有多种方法和技术手段。在沉积学领域,除了常见的特殊沉积外,碎屑组分、粘土矿物相对含量和碳酸盐的碳氧同位素也是相关研究的方法。这是因为,它们在时空上与古气候都有紧密的联系。碎屑组分方法通常是利用气候F/Q和构造L/Q两种指数来反映古气候的干燥程度及其构造活动强度;粘土矿物相对含量则是根据蒙脱石、伊利石、绿泥石和高岭石的相对含量变化以及结晶指数来分析气候的干湿、冷热情况;湖相碳酸盐的碳氧同位素系根据分馏原理来说明气候和环境变化。对西北地区两个盆地的白垩系气候指数(F/Q)与构造指数(L/Q)结果显示,盆地沉积在早白垩世早期构造活动起一定作用,其后早白垩世大部分时期受控于气候;粘土矿物相对含量和结晶度结果指示:贝利阿斯期-凡兰吟期为干湿气候,欧特里夫期-巴雷姆期为干旱气候,阿普特期为干冷-温湿-干热气候,阿尔布期为干热、干冷气候的交替变化为主;湖相碳酸盐岩碳、氧同位素比值结果显示,六盘山盆地古湖泊早白垩世(阿普特-阿尔布期)早期为开放性淡水湖泊,后期由于河流控制减弱,降雨量下降,水体咸化,湖泊具有一定的封闭性。阿普特期δ(13)~C强烈正偏,正偏幅度为2.79‰,与120 Ma时的OAE1a (Selli层)缺氧事件可以对比。更多还原

【Abstract】 As a special period in geological history, the Cretaceous is a typical representative of extreme“greenhouse climate”pahse. Researching paleoclimate of the Cretaceous can help human beings predict that in future. The continental Cretaceous is widespread in mainland China, which provides material basis for study of the coeval climate. It is characterized by fluvial and lake lithofacies in Jiuquan Basin and Liupanshan Basin northwestern China, and its biostratigraphic and chronostratigraphic works are relatively well done. These features plus good outcrops enable us to analyze the Cretaceous climate over thereA variety of methods and techniques have been used for paleoclimate study. Besides of some special sediment for the purpose in sedimentology, clastic composition, relative content of individual clay mineral, and carbon-oxygen isotope are also alternatives, which contain much paleoclimate information. Parameters of F/Q and L/Q are used to indicate the dryness and tectonic activity; relative contents of clay minerals, such as smectite, illite, chlorite and kaolinite are indicatives of wet and dry, hot and cold conditions; carbon-isotope fractionation regimes can be analyzed for interpretation of climatic and environmental changes.Results of F/Q and L/Q ratios from the two basins indicate that tectonic activities had been influencing the deposition to a certain degree in the early Early Cretaceous, but the paleoclimate had mostly controlled the basin sediments thereafter. Clay mineral relative contents and crystallinity show that it was wet and dry climate in the Valanginian-Berriasian; arid climate in the Barremian–Hauterivian, dry-cold, warm-humidity, and dry-hot climate in the Aptian, and alternation of dry-hot and dry-cold climate in the Albian . The carbon-oxygen isotopic values of lake carbonates suggest that the lakes were of open freshwater in the Aptian-Albian, and became relatively closed by weakened fluvial effects, decreased rainfall and water salinization in the late Aptian and Albian. The positive excursion ofδ(13)~C (2.79‰) can be compared to the OAE1a (Selli) at 120 Ma in the early Aptian.更多还原