ABSTRACT To address persistent challenges in lithological classification and diagenetic characterization of mixed sedimentary rocks in the Lower Youshashan Formation (Neogene) of the Fengxi area, Dafengshan structural belt, northwestern Qaidam Basin, an integrated methodology incorporating core observation, thin‐section petrography, and X‐ray diffraction analysis was employed. This study proposes a refined classification scheme for fine‐grained mixed sediments, enabling more accurate lithofacies delineation and reservoir evaluation. The lacustrine Diamictite in the Fengxi N 2 1 interval can be categorized into six lithotypes, among which algal (calcitic)dolomite and micritic dolomite are identified as the most favorable reservoir lithologies, followed by micritic limestone. Dominant diagenetic processes include Dolomization, dissolution, authigenic mineral precipitation, and fracturing. Based on a systematic diagenetic assessment, the N 2 1 reservoir is classified into five distinct diagenetic reservoir facies, reflecting divergent diagenetic pathways and variations in reservoir quality. Constructive diagenesis locally alleviates porosity reduction and promotes the development of high‐quality algal (calc‐)dolomite and micritic dolomite reservoirs, indicating significant exploration and development potential within medium‐to‐deep tight mixed sedimentary sequences. This study provides robust guidance for the identification of Neogene mixed sedimentary rocks in northwestern Qaidam Basin and the investigation of their favorable “sweet‐spot” diagenetic facies.
Xie et al. (Sat,) studied this question.