Characteristics and diagenesis of lacustrine mixed sedimentary rocks of the Neogene Lower Youshashan Formation in Dafengshan structural belt, Qaidam Basin

doi:10.3969/j.issn.1006-6535.2026.01.002

Abstract

Abstract: To clarify the lithological classification,diagenetic types,and genetic mechanism of the tight mixed sedimentary rocks of the Neogene Lower Youshashan Formation in Fengxi Area of the Dafengshan structural belt,northwestern Qaidam Basin,an integrated analysis was made using core observation,thin-section identification,X-ray diffraction,and other techniques.A new classification scheme for fine-grained mixed sedimentary rocks was proposed,which specified the rock types of the Lower Youshashan Formation mixed rocks in Fengxi Area and further guided the division of mixed-rock facies and analysis of the main development controlling factors.The results show that algal dolomite and micritic dolomite are the most favorable rock types in the study area,followed by algal limestone and micritic limestone.Diagenetic processes include dolomitization,dissolution,authigenic mineral filling,and fracturing.Based on the diagenetic analysis,the Lower Youshashan Formation reservoir is subdivided into five diagenetic facies.The genesis of the lacustrine mixed sedimentary rock reservoir in the Dafengshan area is controlled by multiple factors;with increasing burial depth,various diagenetic processes lead to further reservoir densification,but constructive diagenesis still enables the formation of high-quality reservoirs.This study provides valuable guidance for the identification of mixed sedimentary rocks and for research on favorable“sweet-spot”diagenetic facies in the Dafengshan structural belt of northwestern Qaidam Basin.

Key words: mixed sedimentary rocks, diagenesis, Dafengshan structural belt, Fengxi Area, Lower Youshashan Formation, Qaidam Basin

CLC Number:

TE122.3

HE Hui, XIE Lin, LI Xianming, HE Jianhong, LI Shiyuan, HOU Mingqiu, MA Pengshan. Characteristics and diagenesis of lacustrine mixed sedimentary rocks of the Neogene Lower Youshashan Formation in Dafengshan structural belt, Qaidam Basin[J]. Special Oil & Gas Reservoirs, 2026, 33(1): 11-21.

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