The Middle–Lower Ordovician Yingshan Formation is an important reservoir unit in the Tazhong oil field (Tarim Basin, northwestern China). This oil field is deeply buried (>5500 m [>18,045 ft]) and has endured a complex diagenetic history. To understand the mechanisms of reservoir formation, we conduct a broad portfolio of geochemical analyses on the calcite cements that fill the pores and fractures in samples retrieved from wells penetrating the Yingshan Formation. Our results identify six diagenetic episodes, each associated with the emplacement of different cements, varying from marine conditions (C1), near-surface to shallow burial (C2), intermediate-to-deep burial (C3 and C4), and infiltration of the formation with mixing of the underlying basinal brines with meteoric waters and hydrothermal fluids (C5 and C6) along northeast-trending strike-slip faults. The productive wells display evidence of a strong burial diagenetic overprint linked to exotic fluids (C5 and C6) along fractures. We conclude that eogenetic meteoric waters were vital in producing early diagenetic porosity within the Tazhong reservoir, which was subsequently refined by late burial (hypogenic) diagenetic processes. We anticipate our findings hold lessons for the evolution of other geodynamically active cratonic basins.