塔里木盆地白垩系—古近系砂岩岩石学及地球化学

PETROLOGY AND GEOCHEMISTRY OF SEDIMENTS FROM CRETACEOUS-TERTIARY IN THE TARIM BASIN

针对塔里木盆地典型的白垩系—古近系的3个露头剖面(库车河剖面、卡普沙良河剖面阿瓦特河剖面及3个钻井剖面(YM32井,DH12井,YD2井)中48个样品的岩石学和沉积序列研究,以及微量元素组合、稀土总量,轻重稀土分异及铕异常等特征值的对比与研究,研究区砂泥岩的地球化学特征尽管也受气候、成岩作用等的影响,但主要还是受物源区岩性、构造运动背景的控制为主。研究也表明白垩纪与古近纪在构造背景等方面有明显的区别。综合分析认为,证明白垩系构造相对稳定,而古近系的岩石中碎屑成份较多,且不稳定,暗示阿瓦特河的古近系沉积稳定性较差;并认为,白垩系沉积中心靠近东部,而在古近系,刚西移。研究表明,研究区进入白垩纪后,成分成熟度开始降低,古近系的成分成熟度最低,显示了新一轮不断增强的陆内构造活动。碎屑演化主要受控于物源区一(古)天山的构造活动与造山作用,尽管第三纪,特别是上新世,气候变化因素的影响不可忽视。

The Tarim basin experienced tectonic change and environmental alteration from Creta- ceous to Tertiary. Many researchers have done important research on the tectonics, petrology, sed- imentary facies and sequence and achieved many result, but few people done any research about geochemistry of sandstone and mudstone from Cretaceous to Tertiary, especially the geochemis- try background at the boundary between Cretaceous and Tertiary. After observation of rocks from three typical cross sections and drilling wells of Cretaceous and Tertiary in the Tarim basin, this paper studied the sedimentary source, tectonic background and paleogeography based on the data of main elements, trace elements and rare earth elements from 48 selected samples. After the analysis of petrology and sedimentary sequence, the source of sediments and tectonic background and geography were discussed. According the oxide of the important elements and the ratios, efflo- rescent index and stabilization index, combined with the characters of trace elements,rare earth el- ements and Eu abnormality,it was found that the mudstone and sand from Cretaceous and Tertia- ry may be affected by weather and diagenesis, still controlled by tectonic background.