Genesis and Distribution of Laumontite in Yanchang Formation of Upper Triassic in Ordos Basin

Laumontite cement is widely distributed in the sandstone of Yanchang Formation of Upper Triassic of Ordos basin.Secondary pores dissolved from the laumontite aremajor storage space for oil-gas. By thin-section observation, fluid inclusion analysis, SFNI and energy spectrum analysis, X-diffraction and electron microprobe analysis for clay mineral, we hold that the laumontite of the Yanchang formation is distributed in the delta whose sediments come from the ancient hill in the north-easternOrdos basin.The formation of laumontite is related to sediments formed by volcanic activities and volcanic tuff rock from Yinshan Fold belt. Laumontite shows a pore-filling pattern or being replaced feldspar, whose formation has a multi-stage feature.