Genetic mechanism of albite cements in Bashijiqike Formation reservoirs of Kelasu Structural Belt,Kuqa Depression
This paper systematically investigates the microscopic characteristics,spatial distribution,and genetic mechanisms of albite cements using optical microscopy,electron microscopy,thin section analysis,laser Raman,and laser ablation-in-ductively coupled plasma-mass spectrometry(LA-ICP-MS)microanalysis.Under an optical microscope,albite cements ap-pear very clean,typically forming as overgrowths or elongated single crystals.Under cross-polarized light,polycrystals are common.Horizontally,albite cements are primarily distributed in the southern Keshen section,the western and southern parts of the Dabei section,and the eastern and northern parts of the Bozi section.However,albite cements are almost absent in the northern parts of the Dabei and Kela 3 section.Vertically,albite cements are more abundant near unconformities.These cements exhibit high purity,and Raman spectroscopy confirms that they are low-temperature albite,with trace element characteristics similar to those of dissolved feldspar particles.The source material for the albite cements is dissolved feldspar,and the associated fluid is atmospheric freshwater.At the end of Cretaceous,during the tectonic uplift,atmospheric freshwa-ter leached large amounts of feldspar,becoming enriched in H4SiO4,Na+,Ca2+,and other ions.Atmospheric freshwater played a stronger role closer to the surface,leading to the deposition of more albite cements near current unconformities.Higher activity ratios of Na+,H+,and H4SiO4 in low-lying areas promoted albite precipitation,resulting in the enrichment of albite cements in areas with lower paleotopography.Conversely,regions near unconformitiesor higher ancient terrains,with low content of albite cements,are the favorable areas for high-quality reservoir development.
albite cementsgenetic mechanismBashijiqike FormationKelasu structural belt
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