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Laumontite cement's genesis and impacts on reservoir quality in sedimentary basins have long been studied in sedimentology and petroleum geology. This study aims to analyze the petrological and geochemical properties of laumontite in the Shaximiao Formation, Sichuan Basin, China, and to determine the evolutionary process behind the formation of laumontite. Approximately 175 million years ago, huge volume of volcanic materials filled the Sichuan Basin. During the burial diagenesis phase, the hydrolysis of volcanic particles and alteration of plagioclase provided the necessary ions—Ca2+, Al3+, Si4+, Fe3+—facilitating the formation of laumontite. Simultaneously, the hydrolysis of volcanic substances released ions like Ca2+, Mg2+, and Na+, elevating the PH of pore fluids, and fostering the requisite alkaline conditions for laumontite. Additionally, the dehydration of smectite to illite in nearby mudstones generated Ca2+-rich fluids, migrating into sandstones. The hydrolysis of volcanic particles combined with the Ca2+-rich fluids migrating into sandstones led to the abundant formation of laumontite within temperatures ranging from 60 to 100 °C. During this phase, the formation of laumontite accelerates the densification of the reservoir, leading to a reduction in porosity. In the meso-diagenetic period, organic acids from the underlying formations penetrate the sandstones through fractures, creating secondary pores and dissolution-related grain-edge fractures, significantly enhancing reservoir permeability. • The volcanic activity provided the material basis for the formation of laumontite. • Summarizes the evolution process of laumontite and its impact on reservoir quality. • The dissolution of laumontite increase the reservoir permeability. [ABSTRACT FROM AUTHOR]

Quartz cement is an essential authigenic mineral in the tight sandstones of the Shaximiao Formation in the Sichuan Basin, China. Accurately identifying its sources and investigating its impact on reservoir quality is important for understanding diagenetic fluid evolution and pore development in these reservoirs. To address this, we conducted a systematic analysis of the silicon sources in quartz cement employing mineralogical, fluid inclusion, and geochemical data. Quartz cement is characterized by two phases of quartz overgrowth and pore-filling authigenic quartz. Homogenization temperatures of fluid inclusions range from 60 to 150 °C, indicating that quartz cementation occurred from the early diagenetic phase (B stage) to the late mesodiagenetic phase. During the early diagenetic stage, volcanic material was dissolved by meteoric water, resulting in the formation of the earliest quartz cement and smectite. At temperatures of approximately 70–100 °C, smectite illitization, accompanied by K-feldspar consumption and SiO 2 precipitation. In the mesodiagenetic stage (temperature approximately 100–130 °C), organic acids led to the dissolution of minerals like feldspar and laumontite, releasing SiO 2. In the deep burial stage, clastic quartz grains experienced dissolution due to high stress, providing a limited source of SiO 2. Smectite alteration and the dissolution of aluminosilicate minerals represent the primary sources of silicon for quartz cementation, while contributions from volcanic material hydrolysis and pressure solution are relatively minor. The presence of chlorite films inhibits the development of quartz overgrowths, and the limited precipitation of authigenic quartz within the primary porosity has a minimal impact on reservoir quality. Consequently, sandstones rich in chlorite films represent a favorable lithology for the development of high-quality reservoirs. • The precipitation of quartz cement was a prolonged and complex diagenetic process. • The illitization of smectite and dissolution of aluminosilicate minerals provide a significant supply for quartz cementation. • The hydrolysis of volcanic materials and pressure dissolution provide limited sources for the formation of quartz cement. • Chlorite films inhibit quartz overgrowths, and authigenic quartz has little effect on reservoir quality. [ABSTRACT FROM AUTHOR]