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

Abstract

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.

Keywords

• geochemistry
• palaeoclimate evolution
• sequence stratigraphy
• shizigou formation
• pliocene
• qaidam basin