Abstract:

Based on field geological investigations and microscopic analysis of samples, this paper analyzed the characteristics of the
Neogene gypsum veins in Wusu area in detail. Also, the forming process of gypsum veins is analyzed by examining the ancient
sedimentary environment, diagenesis, weathering, and saline solution injection. The gypsum veins of this area were very special
because they were mainly composed of various secondary gypsum veins that were derived from two vertical and two horizontal linear master gypsum veins, displaying a turtle-shell-like geometry. The study shows that the forming process includes 4 stages. Ancient warm deposition environment is needed for depositing abundant gypsoide. Diagenesis is necessary for the gypsum formation. Furthermore, the strong weathering and multi stages of injected saline solution precipitation lead to the formation of the turtle-shell-like geometry of gypsum veins. The findings of this gypsum may provide clues for predicting that the central part of the northern sedimentary area where naturally fracture-affected reservoir may exist. It may also be used to indicate arid sedimentary environment of the Neogene strata in the northwestern region.

Key words: Wusu area, Neogene, turtle-shell-like structure, gypsum vein