柴达木盆地上新世狮子沟期古气候演化与层序地层

Palaeoclimate evolution and sequence stratigraphy during Pliocene Shizigou stage, Qaidam Basin

李清山 郭少斌 侯泽生 王波

LI Qingshan GUO Shaobin HOU Zesheng WANG Bo

中国地质大学(北京) 能源学院, 北京 100083 中国石油 青海油田 勘探开发研究院, 甘肃 敦煌 736202

School of Energy Resources, China University of Geosciences(Beijing), Beijing 100083, China Exploration and Development Research Institute of Qinghai Oilfield, PetroChina, Dunhuang, Gansu 736202, China

柴达木盆地是中国西部青藏高原内部的一个大型中、新生代压扭性沉积盆地，印支运动以来一直处于沉降发展阶段，期间形成了总量达30 000×108 m3的天然气资源。上新世狮子沟组沉积时期古气候演化过程不仅控制了盆地内部层序地层的发育和演化过程，也是世界最大生物气资源形成的重要控制因素之一。以柴达木盆地全井取心最长的气钾1井为重点，利用地球化学方法进行氯离子含量、微量元素、总有机碳含量测定，综合岩心、测井及古生物资料，结合层序地层特征，对盆地狮子沟组沉积时期古气候演化过程进行重建。气钾1井Sr/Ba、Sr/Ca比值与氯离子含量呈正相关，Sr/Ba、Sr/Ca比值随盐度增加而增大，在干旱环境中呈高值；Rb/Sr比值、总有机碳含量与氯离子含量呈负相关，Rb/Sr比值、总有机碳含量随盐度增加而减少，在干旱环境中呈低值，为柴达木盆地古气候演化精细研究提供了依据。柴达木盆地上新世狮子沟组沉积期古气候整体经历了干旱-湿润-干旱的演化过程，湖盆水体呈微咸水，结合层序地层特征，内部首次划分出5个次级气候旋回。古气候演化过程中呈现的旋回性与层序地层演化基本一致，表明前者对后者具有明显的控制作用。

The Qaidam Basin is a large transpressional Mesozoic to Cenozoic basin in the Tibet Plateau, West China. Since the Indosinian Movement, it has been in the subsidence stage and more than 3 trillion cubic meters of natural gas accumulated at the same time. The palaeoclimate evolution during the Pliocene Shizigou stage not only controlled sequence stratigraphy development and evolution, but also worked as a key restraining factor for the largest biogas resource in the world. A case study was made in the well Qijia 1, which is the longest cored well in the Qaidam Basin. The palaeoclimate evolution during the Shizigou stage was reconstructed by using geochemistry methods, including the contents of chloride ion, trace elements and TOC, combined with core data, well logging, paleontology data and sequence stratigraphy. The contents of Sr/Ba and Sr/Ca have a positive correlation with chloride ion, which means that the values of Sr/Ba and Sr/Ca are high in an arid environment. But the contents of Rb/Sr and TOC have a negative correlation with chloride ion, which means that the values of Rb/Sr and TOC are low in an arid environment. The palaeoclimate during the Shizigou stage came through an arid-humid-arid evolution and the water body is brackish water. Based on sequence stratigraphy, five sub-palaeoclimate cycles were recognized for the first time. The palaeoclimate evolution and sequence evolution have the same cyclicity, which shows the controlling function of palaeoclimate.

国家科技重大专项"大型油气田及煤层气开发" 2011ZX05003-006

https://doi.org/10.11781/sysydz202001028