Inheritance and filling of precursor-derived pores in dolomites during penecontemporaneous to shallow-burial dolomitization: Insights from U-Pb geochronology, clumped-isotope (Δ47) thermometry, and Mg isotopes

The role of dolomitization in controlling pore evolution within dolomite reservoirs remains a longstanding geological enigma. We systematically investigated and reconstructed the inheritance and modification of pores during dolomitization, from penecontemporaneous to shallow-burial environments, in the lower Paleozoic dolomite reservoirs of the Jiyang Subbasin, Bohai Bay Basin, eastern China. Petrographic observations and geochemical techniques were employed to achieve these objectives. The Δ47/U-Pb thermochronometry, together with Mg isotope, δ18O, δ13C, 87Sr/86Sr, and trace element signatures, indicates penecontemporaneous dolomitization in a relatively open system, followed by shallow-burial dolomitization. Dolomites in the study area primarily formed through three dolomitization mechanisms: evaporative pumping associated with the upward migration of seawater, top-down seepage-reflux dolomitization, and dolomitization driven by the lateral migration of dolomitizing fluids. The close temporal and geochemical relationship between relict dolomite grains and Cd1—the earliest-formed dolomite cement adjacent to the grains—indicates that Cd1 precipitated from dolomitizing fluids following the complete dolomitization of pre-existing limestones. This suggests the pore systems in dolomite reservoirs were largely inherited from precursor limestones during penecontemporaneous dolomitization. Following the full dolomitization of precursor limestones, continued exposure to dolomitizing fluids in an open system led to partial to complete occlusion by Cd1, with the extent of pore destruction proportional to the duration of the fluid supply. Here, we elucidate the mechanisms underlying primary porosity destruction in granular limestones and the inheritance and preservation of pore spaces in dolomite reservoirs during high-frequency sea-level fluctuations. These findings provide new insights into the critical role of dolomitization in controlling reservoir quality in dolomite systems.