【作者】 孔立；

【导师】 戴霜；

【作者基本信息】 兰州大学 ， 第四纪地质学， 2010， 硕士

【摘要】 白垩纪是全球构造-环境演变的重要转折时期,是距今最近的典型“温室地球”时期,作为地史时期“温室气候”阶段的一面镜子,研究该时期气候环境演变及其动力学机制对于认识过去气候变化和现今全球变暖的原因以及预测未来气候变化趋势具有重要的指示意义。六盘山盆地位于我国大陆中心部位,盆地内部连续出露的六盘山群沉积物较好地记录了早白垩世古气候信息。通过对盆地北部有高精度磁性地层年代控制的火石寨剖面下白垩统六盘山群中部沉积物的高密度采样和色度、化学元素、全岩矿物及粘土矿物定量分析,首次获得了128.11-112.97Ma时段高分辨率的颜色变化序列,和125-112.97 Ma时段粘土矿物组合特征。发现在地表冲积扇-辫状河沉积环境亮度值低并呈升高趋势、红度黄度值高且逐渐降低,在滨浅湖环境色度值趋势性不明显,波动幅度不大；亮度值与岩石胶结物有关而红度值与赤铁矿含量有关。六盘山群粘土矿物的组合特征为伊利石、高岭石、绿泥石和伊/蒙脱石混层；其中伊利石含量普遍较高,结晶度值为0.15-0.37，化学指数为0.22-0.46。综合分析色度、粘土矿物组合及与岩性、沉积环境关系表明,沉积物记录的气候条件总体相对温暖偏干,以125Ma为界分为两个变化阶段,其中第Ⅰ段(128.11-125Ma)岩性为三桥组上段冲积扇相和和尚铺组辫状河-扇三角洲相紫红色调为主的砂岩,以沉积物色度指标低亮度、高红度和黄度为特征,总体反映一种相对湿热的气候状态；第Ⅱ段(125-112.97Ma)岩性为李洼峡-马东山组下部滨浅湖-半深湖相杂色-绿色泥岩、灰岩、泥灰岩,总体为相对温暖偏干的气候状态。此阶段沉积物色度值变化不大(在115.4Ma之后略有增大)；由下至上粘土矿物中伊利石含量表现为降低-稳定-升高的变化趋势,高岭石含量变化与之相反；岩石主要矿物中白云石、方解石的含量呈现出多-少-多的变化形式。通过沉积物中白云石、伊利石含量的变化,结合元素(K2O+Na2O+CaO)/Al2O3比值共同揭示了124-122.8Ma、114.8-113.8Ma期间发生了两次干旱事件。色度指标结合全球白垩纪气候变化趋势,发现在125Ma左右六盘山群记录的气候发生转型,与全球海平面温度在123.3Ma温度由高逐渐降低可能为同一事件,但时间上相对于海洋系统提前约1.7 Ma,同时在113.7Ma左右温度由降温趋势转变为升温趋势,疑似与白垩纪海洋沉积物中发现的112.2Ma左右温度转折(由降温趋势转变为升温趋势)相对应,可能指示陆相沉积物对全球气候变化的响应更敏感。更多还原

【Abstract】 The Cretaceous is a significant transition of global tectonic and environmental system, which is the nearest typical greenhouse Earth state. As a mirror of "greenhouse climate" phase in earth history, it has important implications to recognize the causes of the past climate change and current global warming and to predict the future climate trends through studying the evolution of climate and environment in this period.The Cretaceous nonmarine sediments of the Liupanshan Group in Liupanshan basin, located in the central of China, have well documented the information of early Cretaceous climate. Based on the high-density sampling and measurement of the color, chemical elements and minerals and clay minerals of the sediments of the Liupanshan Gr. which has been already strictly constrained by high-density magnetostratigraphy, high-resolution color sequence ranging 128.11-112.97Ma, and clay mineral assemblages.ranging 125-112.97Ma were obtained for the first time. It is found that the brightness values (L*) of alluvial and fluvial sediments in the lower portion of the Liupanshan Gr. was low and gradually increased, the red (a*) and yellow value (b*) were high and decreased gradually, there was no conspicuous variation of color values in the sediment of a shallow lake environment. The L* fluctuations is related to the cement of the rock, and a* to the hematite content within the rocks. The rocks are characterized by a clay assemblage of illite, kaolinite, chlorite and illite/smectite mixed layer, Which is a mass amount of illite with the crystallinity of 0.15-0.37 and Chemical index of 0.22-0.46. Comprehensive analysis of color, clay mineral assemblages and the relationship with lithology and sedimentary environment, it is indicated that climate recorded by sediment were overall relatively warm, and was divided into two stages by the boundary at 125Ma. The early stage (128.11-125Ma) with the low L*, high a* and b*.The Lithology is the purplish red, visual color of sandstone in the upper Sanqiao Formation through Heshangpu Formation, indicative of a relatively humid and hot climate. The second stage (125-112.97Ma) with the shallow lake and semi-deep lake facies in Liwaxia Formation through Madongshan Formation, indicative of a relatively dry and warm climate. The characteristics of low L*, high a* and b* has a little change. The variation of illite content was decline-level-rise, but Kaolinite is reversely varied. The dolomite and calcite content was more-less-more. Combination of elements (K2O＋Na2O＋CaO)/Al2O3 ratio, Dolomite and Illite content reveals the two drought events during 124-122.8Ma and 114.8-113.8Ma.Analysis of color together with global climate trend in Cretaceous, it is founded that the early Cretaceous climate transition at 125Ma revealed by the record of the sediments of the Liupanshan Gr., which is approximately equivalent to the transition of global sea-surface temperature at 123.3 Ma, but it was about 1.7 Ma in advance. Meanwhile the temperature trend at 113.7Ma changed from decreasing to increasing, corresponding to the temperature transition(temperature trend change from decreasing to increasing) at about 112.2Ma founded in Cretaceous marine sediments, indicative of the land systems were more sensitive to global change than marine systems.更多还原